Journal Articles and Conference Papers

Abstract

This book presents, in sixteen papers, recent developments and some of the main topics seen in academic Medieval Archaeology studies in Spain. The papers explore some of the emergent and consolidated topics of the discipline, such as landscapes, cities, rural spaces, bio-archaeological records, archaeology of architectures, agrarian archaeology, post-Roman archaeology, colonial archaeology in the Canary Islands and the archaeology of religious minorities, opening new lines of enquiries and providing new theoretical and methodological approaches. An overview of Medieval Archaeology studies in Spain is offered, proposing a wide range of topics for discussion. Finally, the book explores the connections between Spanish Medieval Archaeology and other European traditions, specifically, English, Italian and Portuguese Medieval Archaeology.

Abstract

Emerging process limits in sheet metal forming of tailored blanks are determined by the mechanical propertiesMechanical properties of semi-finished sheet materials to be joined and the type of weld seam. The weld seam properties in turn depend on the welding tool material and the utilized process parameters. In this study, tailored blanks were produced made of aluminumAluminum AA6016 (2 mm) and the steel grade DX54 (1 mm) as well as from AA6016 (2 mm) and HX380 (1 mm) using different welding tool materials such as steel and ceramics. The joint between both blanks was performed as a butt joint or combined lap-/butt-joint. The formabilityFormability of the tailored blanks produced in this way was investigated using a three-point bendingThree-point bending device. The tests carried out were evaluated with regard to the maximum bending force. Best results were obtained for tailored blanks produced with ceramic welding tools producing a combined lap-/butt-joint.

Abstract

Due to the ongoing endeavors to reduce CO2 emissions in the energy sector, particularly through advancements in electric mobility, the demand for thin metallic components is currently increasing. This demand is notably apparent for bipolar plates, which are used in fuel cells. The production of these bipolar plates requires high-precision hollow embossing of thin metallic foils with thicknesses below 100 µm. Even minor variations in this process can result in forming defects and undesirable springback in produced parts. A robust design of manufacturing processes for bipolar plates therefore necessitates the implementation of accurate finite element analysis (FEA), since this is crucial for predicting material behavior during and after the forming process. However, the precision of such simulations is heavily dependent on the material models employed. For this reason, the study presented in this paper specifically focused on the numerical modeling of high-precision hollow embossing of bipolar half-plates. For this purpose, a comprehensive material characterization of a 1.4404 stainless-steel foil with a thickness of 0.1 mm was conducted first. Moreover, an experimental laboratory geometry and a corresponding laboratory tool for the hollow embossing of miniaturized bipolar half-plates was developed in order to enable a comprehensive evaluation of the simulation results. The validation and assessment of widely used material models for metal forming in LS-Dyna, exemplified by MAT_036 Barlat ’89 and MAT_133 Barlat 2000, were effectively demonstrated through experimental forming tests. These tests confirmed distinct performance differences between the two material models concerning springback and thinning. Importantly, it was confirmed that the simpler MAT_036 model exhibits high accuracy in predicting both springback and thinning, emphasizing its effectiveness in capturing relevant deformation properties during the hollow embossing process.

Abstract

The International Journal of Advanced Manufacturing Technology, https://doi.org/10.1007/s00170-023-12880-2

Abstract

Embossings on sheet metal surfaces allow a targeted enhancement of local part strength and affect thinning in deep drawing. However, conventional manufacturing of tailor embossed blanks on press machines with simultaneous intrusion of embossing punches results in high force demands and tool wear. Incremental forming of each indentation reduces the embossing forces required but increases cycle time. Embossing by rolling provides limited flexibility in embossing patterns. Therefore, presented paper deals with the development of a new approach for an efficient and flexible embossing of sheet metals -- the Plate Roll Embossing Process (PRE Process). Here, a modular design of an upper and lower tool is used, into which various embossing, counter punch or blank positioning inserts can be integrated. The sheet metal is placed between the tools and the setup is moved through a defined roll gap of a mill stand. The line contact between rolls and tool defines a relatively small forming zone, which is moved translationally through the workpiece by the rotation of the rolls. Numerical and experimental investigations were performed with aluminium AA6014 and steel DC01, showing homogenous embossing results with reduced loads compared to conventional embossing. Furthermore, the paper demonstrates that the high flexibility of the tool and process design enables embossing of flat workpieces as well as the simultaneous embossing and forming of curved parts. Finally, tensile tests performed with embossed specimens show that the PRE Process represents a fast and efficient sheet metal forming method for the targeted modification of component properties.

Abstract

Fuel cellsFuel cell offer a sustainable solution for providing electric drive energy in the course of advancing e-mobility. Essential components of the fuel cellFuel cell represent the bipolar platesBipolar plate, which are being produced in ever higher quantities from thinner and thinner materialsMaterials. Consequently, this leadsLead to high requirements on the precision and robustness of corresponding production processesProcess as well as associated tool designs for such bipolar platesBipolar plate. In order to ensure these requirements at an early stage of forming processProcess planning, especially with regard to the tool design, the use of prototype tools has become inevitable. However, there is currently no cost- and time-efficient way of producing prototype tools for bipolar platesBipolar plate that may be considered as rapid prototypingRapid prototyping. In general, prototype tools made from steelSteel alloys are used here, which are manufactured by costly high-precision milling processesProcess. Hence, this paper pursues the approach of producing low-cost prototype tools from synthetic materialsMaterials by means of additive manufacturingAdditive manufacturing (AM). As a proof of concept, experimental investigations were carried out comparing dimensional accuracy of downscaled bipolar platesBipolar plate made of 1.4404 stainless-steelSteel produced by using a printed plastic tool on the one hand and a milled steelSteel tool on the other.

Abstract

Abstract. When forming high-strength steel sheet material, premature failure can occur at shear-cut component edges because formability of the base material is reduced due to work hardening caused by the previous punching process. Here, the digitization of production processes provides new possibilities for quality monitoring of such forming and stamping processes. In this context, the present paper deals with a novel machine learning (ML) based method for determining the residual formability of sheet metal materials from measured punching force curves. The specific objective of the study carried out was to develop an efficient and accurate method for predicting the residual formability of shear-cut edges. The methodology proposed for this purpose involves collecting a comprehensive dataset comprising experimental measurements of material properties, cutting conditions and punching-force curves measured during blanking. To determine the residual formability of the sheet metal materials investigated, hole tensile tests were performed and the maximum major and minor principal strain at initiation of cracking were measured. This dataset was then used to train and validate different AI prediction models, which employ machine learning algorithms to establish complex relationships between input parameters and residual formability.

Abstract

By near-surface embossing, work hardening can be introduced into sheet metal blanks, thus increasing the material´s yield strength. Hence, this property-modifying process can be used to improve the lightweight potential of a component on the one hand and its crash performance on the other. For the early design of such embossing or forming processes and to predict the modification of the material properties, FE modelling is currently used. Here, the embossing of the near-surface structures is usually simulated first, followed by the forming process. However, existing simulation methods are time-consuming and computationally intensive, due to the simulation of the whole embossing process. For this purpose, this paper presents two approaches for improving the simulation time of embossing and forming processes. Compared to the conventional holistic embossing and forming simulation, these approaches are based on a new mapping strategy and experimental data. In the mapping variant, solid elements’ stress and strain distribution is mapped to shell elements, thus including the embossing history for the forming simulation. For the experimental-based variant, the yield curves of embossed tensile tests are determined and used to approximate the property changes in the simulation. Both concepts are compared with each other and the conventional simulation method in terms of accuracy and calculation time. This paper finally shows that simulation can be performed faster with the new approaches than with the current sequential modelled workflow.

Abstract

Das Scherschneiden zählt zu den wirtschaftlich bedeutenden Fertigungsverfahren in der blechbearbeitenden Industrie. Grund dafür ist, dass nahezu jedes Blechbauteil im Laufe seiner Fertigungskette beschnitten und/oder gelocht wird. Im Zuge der stetig ansteigenden Anforderungen an die Qualität von Blechbauteilen müssen die beim Scherschneiden entstehenden Bauteilkanten heute vermehrt Qualitätsanforderungen wie denjenigen von Bauteilfunktionsflächen entsprechen. In der industriellen Praxis sind derartig hohe Qualitäten von Schnittkanten bzw. –flächen durch einen geringen Kanteneinzug, einen hohen Glattschnittanteil sowie geringe Bruchflächen- und Grathö- hen gekennzeichnet. Darüber hinaus ist neben der möglichst hohen Schnittflächenqualität bei der Herstellung von schergeschnittenen Bauteilen auch die Produktivität des verwendeten Verfahrens von entscheidender Bedeutung. Diese Produktivität ist insbesondere durch hohe Ausbringungsmengen, geringe Werkzeugkosten und niedrige Werkzeuginstandhaltungskosten gekennzeichnet. In diesem Zusammenhang zählt das konventionelle Scherschneiden bzw. das Lochen mit einfachwirkenden Pressen zu den produktivsten Schneidverfahren. Nachteilig ist dabei jedoch, dass mit dem konventionellen Scherschneiden nur Schnittkanten mit vergleichsweise groben Toleranzen und maximalen Glattschnittanteilen von bis zu 50 % der Blechdicke erzielt werden können. Sind höhere Bauteilkantenqualitäten erforderlich, so werden bislang Präzisionsschneidverfahren wie Feinschneiden, Genauschneiden oder Nachschneiden eingesetzt. Verglichen mit dem Normalschneiden führt die höhere Werkzeug- und Prozesskomplexität der genannten Präzisionsschneidverfahren jedoch zu deutlich geringeren Ausbringungsmengen und damit zu höheren Bauteilkosten. Vor dem Hintergrund dieser Problemstellungen wurde das Verfahrensprinzip des Hohlschneidens in den vergangenen Jahren am Institut für Umformtechnik (IFU) entwickelt. Das Hohlschneiden stellt ein Sonderschneidverfahren dar, welches sich infolge geometrisch angepasster Lochstempelgeometrien signifikant von Normalschneidprozessen unterscheidet. In Abgrenzung zu konventionell plan geschliffenen Lochstempeln wird die Stempelgeometrie beim Hohlschneiden durch eine stirnseitig angebrachte „Stegbreite“ entlang der Schneidkante des Stempels sowie durch einen sogenannten „Stegwinkel“ definiert. Diese geometrische Anpassung von Lochstempeln bewirkt eine Druckspannungsinduktion in der Scherzone, wodurch die Rissentstehung innerhalb der Scherzone unterdrückt und schließlich eine Glattschnittsteigerung gegenüber dem Normalschneiden erzielt werden kann. Die Motivation des Hohlschneidens besteht demnach darin, Schnittflächen von hoher Qualität zu erzeugen, ohne dass hierfür technologisch aufwendige Werkzeugkonstruktionen wie bei den Sonderschneidverfahren des Fein-, oder Nachschneidens benötigt werden. Das theoretisch hohe wirtschaftliche Anwendungspotential dieses Verfahrens lässt sich dadurch begründen, dass die Steigerung von Schnittflächenqualitäten in bereits bestehenden konventionellen Scherschneidwerkzeugen allein durch den Austausch von Normalschneidstempeln durch Hohlschneidstempel erreicht werden kann. Die der Arbeit zugrundeliegende wissenschaftliche Problemstellung hinsichtlich des Verfahrensprinzips des Hohlschneidens besteht darin, dass Wissensdefizite bezüglich des Zusammenhangs zwischen einzelnen Werkzeugparametern (Stegbreite, Stegwinkel, Schnittlinienführung, Schneidspalt, etc.) sowie Qualitätskenngrößen an den gescherten Blechbauteilrändern vorlagen. Aufgrund mangelnder veröffentlichter Untersuchungsergebnisse existierten bis heute keine mit dem Normalschneiden vergleichbaren Normen, Richtlinien oder Datensätze, die eine entsprechende Werkzeug- bzw. Verfahrensauslegung unterstützen. Als problematisch erwies sich hierbei, dass neben den Parametern des Normalschneidens weitere werkzeugseitige Einflussfaktoren hinsichtlich des Schnittergebnisses zu berücksichtigen sind. Für den Fall solch multidimensionaler Problemstellungen haben sich in den vergangenen Jahren vermehrt datengetriebene Modellierungsansätze des maschinellen Lernens (ML) durchgesetzt. Die Eignung maschineller Lernverfahren für den technologischen Anwendungsbereich des Scherschneidens wurde bislang allerdings nur für spezifische Teilproblemstellungen des Normal- und Feinschneidens nachgewiesen. Diesbezüglich wurden in der Vergangenheit insbesondere Verschleißproblematiken, seltener jedoch qualitätsbezogene Auslegungskriterien für Scherschneidwerkzeuge betrachtet. Die Zielsetzung der vorliegenden Arbeit adressiert die Entwicklung solch datenbasierter Auslegungsmodelle für das Verfahrensprinzip des Hohlschneidens. Eine ausschließlich experimentelle Erprobung unter Praxisbedingungen erschien aufgrund des dafür benötigten Versuchsumfangs als unrealistisch. Die Methode der Surrogat-Modellierung konnte vor diesem Hintergrund als geeigneter Lösungsansatz identifiziert werden. Der grundsätzliche Gedanke hinter der Entwicklung von Surrogat-Modellen besteht darin, auf Basis von Simulationsergebnissen interpolierende bzw. approximierende Ausgleichsfunktionen zur Vorhersage von Zielkenngrößen für einen vorabdefinierten Bereich statistisch verteilter Eingabemerkmale zu ermitteln. Die Ausführungen der vorliegenden Arbeit zeigen, dass höherdimensionale Wirkzusammenhänge zwischen Halbzeug-, Werkzeug- und Schnittflächenparametern des Hohlschneidens von maschinellen Lernalgorithmen auf Grundlage numerischer Daten erlernt und quantifiziert werden können. Unter Verwendung so angelernter ML-Modelle, Methoden der erklärbaren Künstlichen Intelligenz sowie einer differenzierten Betrachtung des in der Scherzone vorherrschenden Spannungszustandes konnte neues explizites und experimentell validierbares Prozesswissen für das Verfahrensprinzip des Hohlschneidens generiert werden. Unter Berücksichtigung dieses so hergeleiteten Prozesswissens ist eine signifikante Verbesserung von Schnittflächenqualitätskenngrößen gegenüber dem Referenzzustand des Normalschneidens gelungen. Die vorliegende Arbeit präsentiert somit eine neuartige systematische Vorgehensweise für die Auslegung und Optimierung einhubiger Scherschneidprozesse.

Abstract

The progressing digitization in the manufacturing industry and the enhancements in the field of machine learning (ML) offer new approaches for monitoring manufacturing processes. In this context, the image classification using ML methods represents a well-solved task that can be leveraged for evaluating processes and products. From this perspective, this paper presents an application of ML methods in order to classify defective deep drawn parts. It proposes a methodical approach which includes not only the data acquisition using a low-cost equipment, but also the data pre-processing as well as the setup and training of the ML model. The described method is applied on an academic part of rectangular shape. After collecting a dataset of nearly 1000 images, a convolutional neural network was trained to identify three different quality classes. The trained model was then evaluated on a test dataset containing 30\% of the samples and shows an accuracy of 96,77\%.

Abstract

Der stetige technologische Fortschritt und die fertigungstechnologischen Innovationen in der Produktion spielen eine Schlüsselrolle, die Effizienz etablierter Technologien in Hochlohnländern radikal zu steigern, um mit Unternehmungen einen Vorteil im agilen globalen Wettbewerb zu erlangen 1. Umformtechnische Fabrikationsmethoden bieten hierzu eine etablierte, kosteneffiziente und ressourcenschonende Produktionstechnologie, um performante Komponenten in hoher Stückzahl herzustellen 2,3. Gegenwärtig stellt die begrenzte Gestaltungsmöglichkeit der herzustellenden Geometrie einen bedeutenden und stark limitierenden Faktor für den Einsatz umformtechnischer Produktionsmethoden dar. Exemplarisch können Stirnpassverzahnungen nach aktuellem Stand der Technik umformtechnisch nicht vollständig ausgeformt werden, wodurch eine zerspanende Bearbeitung für eine Vielzahl von Komponenten bislang unumgänglich ist. Das Ziel der vorliegenden wissenschaftlichen Arbeit besteht darin, die bekannten Verfahrensgrenzen der umformtechnischen Herstellung von schwierig auszuformenden Formelementen bedeutend zu erweitern, um die technologischen, wirtschaftlichen und verfahrensspezifischen Vorteile für ein breites Bauteilspektrum zu erschließen. Stirnpassverzahnungen werden zumeist als Kupplungselemente zur Kraft- und Drehmomentübertragung verwendet, wobei die Leistungsfähigkeit dieser Maschinenelemente direkt von der Bauart des Kupplungssystems und der Fertigungsqualität der ineinandergreifenden Kupplungskomponenten abhängt. Aufgrund stetig steigender Anforderungen an die Leistungsfähigkeit von Kupplungselementen wird es in Zukunft nur mit erheblichem Fertigungsaufwand möglich sein, die geforderten Verzahnungsgeometrien mit den bekannten Methoden herzustellen. Damit die wirtschaftliche umformtechnische Herstellung auch zukünftig für Hochleistungskupplungselemente verwendet werden kann, müssen neue Methoden und Verfahren erforscht werden, um die Formfüllung von Verzahnungsgeometrien maßgeblich zu verbessern. Nach aktuellem Stand der Technik werden Stirnpassverzahnungen überwiegend mit einem Prägeverfahren umformtechnisch hergestellt. Charakteristisches Merkmal von Prägeprozessen ist die große Kontaktzone zwischen Werkstück und Werkzeug am Ende des Umformprozesses. Der Werkstoff wird im Prägeprozess von solchen Pressteilen ausschließlich im Bereich der Formelemente plastisch umgeformt. Dabei entstehen große Kontaktzonen ohne Werkstoffrelativbewegung, welche hohe Prozesskräfte und Werkzeugbelastungen am Ende des Prägeprozesses verursachen. Aufgrund der hohen Werkzeugbelastungen am Ende des Prägeprozesses werden die Verzahnungsspitzen in der Praxis nicht vollständig ausgeformt. Um die Formgebung in Prägeprozessen zu verbessern, wurden jedoch bereits diverse Untersuchungen zur Erweiterung der Verfahrensgrenzen von Prägeprozessen durchgeführt. Zumeist wird hierzu eine Vorform zur gezielten Materialvorverteilung vor der Prägestufe in das Werkstück eingeformt. Die aus dem Stand der Technik bekannten Vorformen für Prägeprozesse werden ohne Berücksichtigung der herzustellenden Verzahnung oder Prägegeometrie gestaltet, wobei eine umlaufende Fase am Rohteil die meist genutzte Vorform darstellt. Eine Vorform dieser Bauart bewirkt eine Reduktion des überproportionalen Kraftanstieg am Prozessende, wodurch der Füllgrad der Verzahnungen nur geringfügig gesteigert werden kann. Für die Entwicklungen einer kraftreduzierenden Werkstoffvorverteilung für Prägeprozesse wird aktuell die herzustellende Geometrie für die Konstruktion der Vorform nicht berücksichtigt. Somit kann der Werkstofffluss nicht gezielt in die herzustellende Geometrie geleitet werden, wodurch das volle Potenzial der Werkstück-Werkzeugkontaktreduktion derzeit nicht ausgeschöpft wird. Eine an die Formelemente angepasste Materialvorverteilung bietet das Potenzial, die WerkstückWerkzeugkontaktreduktion bedeutend zu verbessern und damit die Prozesskräfte signifikant zu reduzieren. Diese allgemeine Forschungshypothese wird in der vorliegenden Arbeit dazu verwendet, eine Stirnverzahnungsgeometrie herzustellen, wobei untersucht wird, wie die Materialvorverteilung an die zu fertigende Verzahnung angepasst werden kann, um den Werkstofffluss in der nachfolgenden Prä- gestufe zu begünstigen. Hierzu wird eine konkretisierte Forschungshypothese aufgestellt: Wird der Werkstück-Stempelkontakt in schwierig auszuformenden Zonen (Zahnspitze) vor dem Kontakt in einfach auszuformenden Zonen (Zahnfuß) erzeugt, kann eine hohe Formfüllung mit geringen Prozesskräften erreicht werden. Basierend auf dieser konkretisierten Forschungshypothese werden in dieser Arbeit zwei Verfahren zur Materialvorverteilung entwickelt: das Free-Divided-Flow- (FDF) und das Pin-to-Gear- (PtG) Verfahren. Im FDF-Verfahren wird das Material einseitig neben der Verzahnung vorverteilt. Hierdurch wird zunächst der Bereich, in welchem das Material vorverteilt wurde, nachfolgend die Verzahnung und abschließend der zweite Bereich neben der Verzahnung ausgeformt. Im PtG-Verfahren wird das Material im Bereich der Verzahnung in einer simplifizierten Geometrie vorverteilt, wodurch zunächst die Verzahnung ausgeformt wird und erst darauffolgend alle angrenzenden Bereiche. Mit beiden Verfahren können die auftretenden Prozesskräfte, im Verhältnis zur konventionellen Formgebung, signifikant reduziert werden. Unter Berücksichtigung einer umformtechnischen Vorformherstellung können die Einsatzgebiete beider vorgestellten Verfahren dargestellt werden: Das FDF-Verfahren eignet sich für die Herstellung von Werkstücken mit großen Abständen zwischen den Einzelzähnen während sich das PtG-Verfahren zur Formgebung von Verzahnungsgeometrien mit hohem Aspektverhältnis eignet. Zur Validierung der Forschungshypothese und zur Analyse der entworfenen Verfahren wird zunächst ein Materialmodell erstellt, um darauf basierend die mehrstufigen FEM-Simulationen der numerischen Verfahrensuntersuchung aufzubauen. Ziel der numerischen Untersuchung ist die Entwicklung einer parametrisierten Vorformgeometrie für beide Verfahren, welche in Abhängigkeit der herzustellenden Verzahnung und ohne weiterführende numerische Simulationen definiert werden kann. Hierzu werden statistische Versuchspläne, Sensitivitätsanalysen, Optimierungsfunktionen und Methoden der Data Analytics angewendet. Zur experimentellen Validierung wird ein Versuchswerkzeug für fünf unterschiedliche Verzahnungen konstruiert und gefertigt (vier Sperrverzahnungen und eine Hirth-Verzahnung). Schwerpunkte der experimentellen Untersuchung stellen die Formfüllungsanalyse, die Maßabweichungsanalyse, die Presskraftanalyse, die Oberflächenrauheitsanalyse, die metallurgische Gefügeanalyse sowie die Analyse der Härteverteilung der Verzahnungsgeometrien dar. In der experimentellen Untersuchung wird im hinteren Teil der Arbeit gezeigt, dass alle Verzahnungsgeometrien beider Verfahren vollständig und ohne Umformfehler ausgeformt werden können. Dabei werden die Verzahnungen sowohl aus dem Einsatzstahl 16MnCrS5 als auch aus dem unlegierten Baustahl C4C mit unterschiedlichen Schmierstoffsystemen im identischen Umformwerkzeug umgeformt. Zur zukünftigen und vereinfachten Verfahrensanwendung werden Konstruktionsrichtlinien verfasst sowie die ermittelten Verfahrensgrenzen des FDF- und des PtG-Verfahrens erläutert. Im Rahmen dieser wissenschaftlichen Arbeit wird mittels unterschiedlicher Verzahnungsgeometrien dargestellt, dass die Prozesskräfte deutlich reduziert und der Formfüllungsgrad bedeutend gesteigert werden können, wenn der Werkstück-Stempelkontakt in der Zahnspitze vor dem Kontakt mit dem Zahnfuß erfolgt. Somit kann die aufgestellte Forschungshypothese am Ende dieser Arbeit mittels numerischer und experimenteller Verfahrensuntersuchungen vollumfänglich validiert werden. Die entwickelten Verfahren erweitern die Verfahrensgrenzen von konventionellen Prägeprozessen signifikant, wodurch zukünftig eine Vielfalt bislang zerspanend hergestellter Verzahnungsgeometrien umformtechnisch und in hoher Qualität gefertigt werden können. Die daraus resultierenden Steigerungen der Produktgestaltungsmöglichkeiten haben überdies eine direkte Auswirkung auf unterschiedliche Fertigungsbereiche entlang der gesamten Prozesskette. Hierdurch werden sowohl die lokal umformenden Fertigungsbetriebe im internationalen Wettbewerb gestärkt als auch ein gesamtwirtschaftlicher Nutzen zur Standortsicherung erwirtschaftet.

Abstract

The development of components with tailored properties is one of the ways to increase efficiency in areas such as the automotive sector. Hybrid components, in particular plastic-metal composites, meet this requirement by combining different material properties. In this context, this paper presents preliminary investigations regarding the use of fibre-reinforced plastics as an active medium for forming metallic materials. Several challenges arise for such a processing method, such as, the compressive strength of the plastics depending on the fibre fraction, -length and -orientation. Furthermore, the dissimilar elastic behavior of the two materials has a decisive influence on the composite- and bond strength. Therefore, in a first step, a material selection was performed, followed by material characterization. In addition, this paper presents a preliminary numerical analysis showing the feasibility of manufacturing a hybrid component using as example a spur gear with a polymer core made of glass fibre reinforced polypropylene and an outer geometry made of aluminum alloy AA6082.

Abstract

We propose a novel method to simulate digital holograms for multiwavelength holography using height maps generated from arbitrary 3D CAD models. The simulated holograms can be numerically reconstructed and analyzed for error compensation methods.

Abstract

In former papers methods to join different aluminium or different steel plates having same thicknesses are presented. These blanks are often joined by friction stir welding using flat tools. In order to increase the lightweight potential, the Materials Testing Institute of the University of Stuttgart developed a modified friction stir welding process to join aluminium and steel plates of different thicknesses. The process differs from the conventional method in stir welding tool used, which consists of a stepped welding pin and enables combined lap-and-butt joints to be produced. In this paper, a suitable material model is presented to describe this weld seam, allowing the forming behavior of hybrid sheet metal compounds to be realistically simulated.

Abstract

The availability of effective and eco-friendly powertrain systems for electrification of passenger and commercial traffic is a crucial requirement for achieving current climate targets. With increasingly limited energy resources, fuel cell technology is gaining interest as an alternative to conventional electrical drives. Especially for heavy-duty and long-distance vehicles, where the required payload and range would require enormously heavy batteries, fuel-cell-technology offers a promising solution. Critical components of such modern fuel cells are metallic bipolar plates (MBPP) manufactured by high-precision embossing of thin metallic foils. The critical point is that even slightest fluctuations within the manufacturing process can lead to forming defects and result in unacceptable springback of metallic bipolar plates. Combined with the dimensional accuracy required for MBPP, extensive quality assurance and thus relatively low cycle times are inevitable in today´s production of these components. In this context, this paper deals with an approach to actively control the manufacturing process of MBPP based on numerical data sets. For this purpose material characterization of 0.1 mm stainless-steel foil (1.4404) was performed, allowing for comprehensive modelling of the embossing process and the springback behavior. In order to maintain a robust forming process aimed at increasing productivity, a numerical analysis was then conducted under variation of different geometric parameters using AutoForm R10. It was found that variation of selected geometric parameters such as channel width, channel height, draft angle and tool radii can remarkably reduce thinning and springback in MBPP production in compliance with tight tolerance specifications. Furthermore, the investigations show that active control of the lubrication conditions offers an additional possibility for subtle adjustments of the dimensional accuracy of produced components.

Abstract

Ramp-up phases right at the beginning of batch processing in cold-forging of high volumes are accountable for a significant amount of scrap due to transient process conditions. To understand the emerging impacts of transient effects during ramp-up phases on the final dimensional product properties more deeply, process conditions like forming load, part temperature and part geometry were monitored exemplarily in this study

Abstract

Fuel cell technology offers a sustainable power supply solution for heavy-duty vehicles, aviation and shipping as well as stationary application. Manufacturing of metallic bipolar plates (MBPP) as a key component of fuel cells is nowadays one of the main topics in production-based research and processing industry. One reason for this is that although stamping of thin stainless-steel foils enables an economic large-scale production of metallic bipolar plates, tooling and press technologies required for embossing and shear cut operations are highly demanding and thus continuously being developed. Particular challenges are posed by the embossing of the complex flow field structure, which can cause forming defects and pronounced springback phenomena. Moreover, multiple embossing operations and high press forces are needed to plastify the metal foils as homogeneously as possible and thus form the desired channel geometry. Accordingly, future demand for large metallic bipolar plates is likely to exceed the limits of current press technologies in terms of force capacity and stiffness. Similarly, rolling is also not suitable for forming such large plates due to severe wrinkling and springback. Therefore, this paper proposes the so-called TIP-Form as a new forming process with a tilting forming kinematic of one or both tool halves as well as a crowning of the active surface. In this regard, a numerical study is presented, in which the new forming approach to decrease the force demand and improve the formability when embossing bipolar plates was investigated. Explicit forming simulations of a flow field section were performed using LS-DYNA and forming forces as well as formability were evaluated. Compared to conventional embossing, the controlled tipping and crowning of the punch could reduce the simultaneous acting contact zone between tool and foil and therefore maximum forming forces have been reduced. In addition, thinning of formed channels decreased, as the tipping forming kinematics enabled a beneficial material flow. The promising numerical results motivate for further research work and emphasis the development of a new press technology with tipping ram or table for the manufacturing of large metallic bipolar plates.

Abstract

Abstract. Cold forging processes, such as cold extrusion and in particular the Samanta process, provide a considerable potential for improvement in gears production. The method behind the Samanta process is based on the principle of cold extrusion in stacks. After partial forming of a workpiece, another workpiece is inserted into the die in order to eject a completely formed gear in the direction of the punch movement. Although this operating principle offers great potential for high-volume production, the industrial relevance of this process is limited by disadvantages such as high tool loads, limited gear accuracy and deformations on both face ends of the gear wheel. In order to overcome the technological challenges associated with the Samanta process, the die geometry was adapted. In this case the die operating surface was modified in terms of an extended forming zone length combined with an undercut in the tooth cavities of the die. In this paper the numerical results for this novel process regarding the correlations between geometric die parameters and resulting process data, such as punch force, contact pressure and die filling, are presented. The spline-based tool was methodically varied between one linear and two square (concave, convex) designs and was numerically evaluated using Deform 3D™ software.

Abstract

Data acquisition and data analysis to gain a better process understanding are one of the most promising trends in manufacturing technology. Especially in cold forging processes, data acquisition close to the deformation zone seems challenging due to the high surface pressure. Thus far, process parameters such as die temperature are mainly measured with state-of-the-art sensors, including standard thermocouples, which are integrated into the tooling system. The application of thin-film sensors has been tested in hot forging processes for local die temperature measurement. However, the process conditions regarding tribology and tool load in cold forging are even more difficult. In this contribution, the use of thin-film sensors, applied on a cold forging punch for cup backward extrusion, is subjected. The aim is to investigate the applicability of such thin-film sensors in cold forging with special emphasis on temperature measurement in cyclic forming processes. The thin-film sensor system and its manufacturing procedure by vacuum coating technology combined with microstructuring are described. With these thin-film sensors the cup backward cold extrusion of steel billets was investigated experimentally. Cyclic tool heating simulations with thermal parameter variations were performed as a reference to experimental results.

Abstract

Die Qualität der durch Umform- und Schneidprozesse hergestellten Bauteile wird durch schwankende mechanische Eigenschaften des verwendeten Blechmaterials beeinflusst. In dieser wissenschaftlichen Veröffentlichung wird eine neuartige, auf maschinellem Lernen basierende Methode zur Inline-Bestimmung von Werkstoffkennwerten vorgestellt. Diese soll es erlauben, die mechanischen Kennwerte direkt aus den im offenen Schnitt gemessenen Schneidkraftverläufen zu ermitteln. The quality of components produced by forming and stamping processes is affected by fluctuating mechanical properties of the sheet metal material. This scientific publication presents a novel method based on machine learning for the inline determination of material properties. It enables the determination of mechanical properties directly from the punching force curves measured when shearing with an open cutting line.

Abstract

The part quality that can be achieved in forming and stamping processes strongly depends on the properties of the sheet metal material to be processed. However, since these material properties may fluctuate considerably and thus lead to the production of scrap, it is important to monitor such material fluctuations during part production. For this, the ongoing digitization of production processes provides new possibilities for part or quality monitoring. In this context, a novel AI-based method for the direct determination of material parameters from punching forcePunching force curves measured in production was presented in a past study by the authors. This paper deals with the investigation of three further methods for extracting features from these recorded measuring data. In addition to domain knowledge-based feature engineering, statistical feature extraction (PCAPrincipal component analysis (PCA)) as well as a derivative-based method are analyzed and compared with each other and with the previously used AI (ANN) regarding their prediction accuracy of sheet metal properties.

Abstract

Der Beitrag beschreibt die Entwicklung eines Umformwerkzeugs zur Herstellung von Faltstrukturen aus Stahlblechen, welche für Sandwich-Anwendungen eingesetzt werden können. Ausgehend von einer Analyse des Standes der Technik hinsichtlich der Faltkinematik von Faltstrukturen und unterschiedlichen Werkzeugkonzepten wurde ein Werkzeug entwickelt, welches die Herstellung von Faltstrukturen aus Feinblech ermöglicht. Dieser Beitrag verdeutlicht, dass die Herstellung von Faltstrukturen durch das gezielte Biegen von Blechen mit nicht vernachlässigbaren Dicken nur durch die Verwendung eines geeigneten Faltwerkzeugs möglich ist.

Abstract

Die Bemühungen zur Emissionsreduktion in den Bereichen Energie und Mobilität führen zu einer steigenden Nachfrage nach geformten Bauteilen aus dünnen Metallfolien. Die Herstellung und Auslegung solcher Komponenten gestalten sich als äußerst anspruchsvoll. Herkömmliche Charakterisierungsversuche für die digitale Auslegung dieser Bauteile stoßen an ihre Grenzen. Daher wird in diesem Kontext ein innovativer Versuchsaufbau für den zyklischen Scherversuch vorgestellt, der die strukturelle Stabilität der Probe erhöht und eine Modellierung des Verfestigungsverhaltens ermöglicht. Efforts to reduce emissions in the fields of energy and mobility lead to an increasing demand for shaped components made from thin metal foils. Manufacturing and designing such components is highly challenging. Conventional characterization tests for designing these components digitally are reaching their limits. In this context, an innovative setup for cyclic shear testing is introduced, enhancing the structural stability of the specimen and enabling modeling of the material`s strengthening behavior.

Abstract

In the field of additive manufacturing (AM) technologies, the development of metal-based extrusion processes constitutes a significant industrial trend in the recent years. Respective processes are differentiated into powder bed, powder-fed and wire-fed depending on the used feedstock. Among those, powder-fed AM represents the most widely used approach, despite its physical limitations leading to intense thermal gradients and an uncontrollable defective microstructure of produced parts. In this context, extrusion-based AM using a wire semi-finished product in the semi-solid state offers a novel alternative for the direct processing of metallic alloys, avoiding the limitations mentioned. For this reason, a new method for consecutive extrusion of semi-solid AlSiMg aluminum wires has been developed at the Institute for Metal Forming (IFU, Stuttgart, Germany), particularly investigating the influence of the material´s microstructure on the process result. By modifying microstructure via heat treatment, a specific modification of the rheological material behavior can be achieved in terms of a pronounced shear-thinning characteristic, thus systematically affecting extrusion and deposition. First, an experimental setup for continuously extruding semi-sold aluminum wires was realized. Subsequently, experimental investigations were carried out on the extrusion of aluminum wires prepared via the strain induced melt activated (SIMA) process as well as untreated aluminum wires, using a conductively heated printhead concept. The objective was to determine process parameters necessary for successful extrusion and deposition of the modified aluminum material as well as the final proof of concept regarding a specific transformation of the material´s microstructure during the extrusion process.

Abstract

Dry processes represent promising approaches in forming technology to improve environmental aspects and human health by avoiding harmful substances and additives of conventional lubricants. Among many different approaches for dry forming investigated within the priority program SPP 1676, this paper addresses the use of volatile media as lubricants such as CO2 or N2. These volatile media are introduced directly into the interstice between sheet metal and tool surface via microinjectors. Indeed, this does not contradict the principle dry forming approach, as dry forming is defined as a process in which no residues are left on the surfaces 1. This is ensured by the complete evaporation of the volatile media. The general feasibility of this novel tribological system has already been demonstrated in previous research work. However, despite good tribological results, the manufacturing costs of the required tool inserts and the media consumption per component are not yet economically competitive with conventional tribological systems. Therefore, this paper focuses on new designs of dry deep-drawing tools utilising volatile lubricants, considering the economics of different manufacturing processes.

Abstract

In order to reduce the use of classic lubricants such as synthetic or mineral oils, emulsions or waxes in the deep drawing process, a new tribological system based on volatile lubricants was investigated. In this system, a volatile medium is injected under high pressure through laser drilled micro holes directly into the contact zone between the tool and the sheet metal and serves as a temporary lubricant. In order to investigate this tribological system under realistic conditions, strip drawing experiments with different volatile lubricants (air, nitrogen, carbon dioxide and argon) were performed on galvanized sheets. Therefore, a new generation of strip drawing tools was designed and numerically calculated for low elastic deformations to ensure a uniform contact pressure distribution over the entire friction contact area. To obtain a homogeneous distribution of the volatile lubricants, a number of micro holes with a depth of several millimeters were drilled into the hardened strip drawing jaws using ultrashort pulsed laser radiation. Taking into account the capabilities of this laser drilling technique in terms of size and shape of the micro holes, computational fluid dynamics simulations were performed to predict the flow behavior of the lubricant within the micro hole as well as the contact zone and were compared with observable effects in outflow tests. The chemical composition of the acting tribological layers was characterized by means of X-ray photoelectron spectroscopy and their changes during the deep drawing process were correlated with the lubricants used as well as the measured wear and friction values.

Abstract

Punching represents one of the most frequently used manufacturing processes in the sheet metal processing industry. As an important quality criterion for shear cutting processes, the geometric shape of the cutting surface is considered. In this regard, the edge draw-in height, the clean cut proportion, the fracture surface height, and the burr are relevant parameters for monitoring the production quality in punching processes. These parameters can easily be measured in shear cutting processes with an open cutting line (e.g. using laser triangulation). For processes with a closed cutting line, however, such a measurement is often not possible due to the limited accessibility. The present paper therefore proposes a machine learningMachine learning approach, which enables a data-driven prediction of cutting surface parameters based on measurable process data. The new approach presented in this paper is to pre-train a neural network on numerically determined cutting force curves. As an output, the neural network predicts the mentioned quality parameters of punched sheet metal component edges. The output of the numerically pre-trained neural network is evaluated for numerically and experimentally determined process data and cutting surface parameters.

Abstract

Punching is one of the most commonly used production processes in sheet metal working industry. Here, major criterion for the quality of cutting surfaces is a high clean cut proportion. However, the disadvantage of conventional punching processes is that they can only produce clean cut proportions up to 20--50\% of the sheet thickness. Until today, more complex processes such as fine blanking are therefore required for a higher cutting surface quality. The content of this paper is a numerical and experimental investigation for a new tool design called ``concave punch nose design''. The idea of the concave punch nose design is to optimize the cutting edge geometry of conventional punches in order to enlarge clean-cut proportion along the cutting surface despite a process sequence similar to conventional shear cutting. The numerical and experimental investigations presented in this contribution show, that the concave punch nose design increases compressive stresses in the shear-affected zone and therefore significantly raises the cutting surface quality. Compared to conventional punching, concave punch nose design increases clean cut proportions by more than 100\%.

Abstract

Punching represents one of the most frequently used manufacturing processes in the sheet metal processing industry. Thereby, one of the most important quality criteria for such punching processes constitutes the geometric shape of the cutting surface. High cutting surface qualities are usually characterized by the lowest possible edge draw in, a high clean cut, as well as a small fracture surface and a low burr height. In this respect, conventional punching processes can only produce clean cut proportions (CCP) up to 20-50% of the sheet thickness. By means of the so called "concave punch nose design" developed at the Institute for Metal Forming Technology, the geometry of conventional punches could be optimized in such a way that the clean-cut proportion along the cutting surface is significantly increased. The findings reported about in this paper show that the quality parameters of the sheared component edges thereby show highly nonlinear relationships to the tooling and sheet metal material parameters used. In order to quantify these effects, the data from several numerical punching simulations is used to pretrain an artificial neural network (ANN). Input data for the neural network included features of the punch geometry, the size of the clearance, the sheet thickness and the material data of the semi-finished product. The output of the neural network is precise predictions of the achievable cutting surface quality parameters. The experimentally validated findings presented in this paper show that the process design for novel punching processes such as cutting with concave punch nose design is possible, when using a modern machine learning approach.

Abstract

Klappentext Das hier entwickelte Verfahren des Hohlschneidens ermöglicht schergeschnittene Kanten mit relativ geringem Kanteneinzug, einem vergleichsweise hohen Glattschnittanteil und einer zur Blechoberseite nahezu rechtwinkligen Schnittfläche. Es entspricht einer Qualitätsgüte, die annähernd mit der des Feinschneidens vergleichbar ist. Die Werkzeug- und Prozesskomplexität ist dabei mit dem Normalschneiden vergleichbar, da der Unterschied zwischen dem konventionellen Scherschneiden und dem Hohlschneiden lediglich in der Stirnflächengeometrie der verwendeten Schneidstempel besteht.

Abstract

Die Anforderungen an die Qualität von schergeschnittenen Bauteilkanten haben in den letzten Jahren erheblich zugenommen. Insbesondere in der Elektronikindustrie werden Schnittkanten mit einem möglichst großen Glattschnittanteil gefordert, wobei sie zugleich gratfrei sein und ein hohes verbleibendes Formänderungsvermögen aufweisen sollen. Dieser Trend resultiert aus dem verstärkten Einsatz gestanzter metallischer Produkte in elektronischen Komponenten, wie beispielsweise Kantsteckern oder Leiterplattenhalteklipps, die zur Befestigung von Platinen in Steuergeräten dienen. In diesen Anwendungen sind Bauteilkanten mit Schnittgraten inakzeptabel, da sie während des Produktlebenszyklus, zum Beispiel aufgrund von Vibrationen im Betrieb eines Kraftfahrzeugs, zu Einrissen und Brüchen des Bauteils oder aber auch zu Ablösungen führen können. Dies könnte zu einem Kurzschluss und somit zu einem Ausfall des Produkts führen. Daher ist es insbesondere im Bereich des Stanzens von Elektronikprodukten von entscheidender Bedeutung, dass die Schnittkanten gratfrei sind und hohe Anforderungen an die Schnittflächenqualität erfüllen. Die steigenden Qualitätsanforderungen an schergeschnittene Bauteilkanten in der Elektronikindustrie stehen im Einklang mit dem Bestreben nach immer präziseren und zuverlässigeren Komponenten. Durch die Realisierung von gratfreien Schnittkanten und einer hohen Schnittflächenqualität wird die Funktionalität und Langlebigkeit elektronischer Produkte verbessert. Dies ist von großer Bedeutung, insbesondere in sicherheitskritischen Anwendungen wie der Automobilindustrie, in der Ausfälle aufgrund von fehlerhaften Bauteilen große Rückrufaktionen zu Folge haben können. Um den gestiegenen Qualitätsanforderungen gerecht zu werden, sind Forschungs- und Entwicklungsanstrengungen erforderlich, um neue Schneidverfahren und Werkzeugkonzepte zu entwickeln. Die Vergrößerung des Glattschnittanteils, die Realisierung von gratfreien Schnittkanten und das Beibehalten eines möglichst hohen Formänderungsvermögens bilden dabei entscheidende technologische Aspekte. Durch innovative Technologien und Prozesse können schergeschnittene Bauteilkanten hergestellt werden, die den hohen Qualitätsstandards der Elektronikindustrie gerecht werden und gleichzeitig eine effiziente und zuverlässige Produktion ermöglichen. Diese Arbeit greift das Problem auf und zielt darauf ab, die Schnittflächenqualität von schergeschnittenen Bauteilkanten durch die Induzierung lokaler Druckspannungen zu verbessern. Dies wird durch eine geometrische Modifikation bzw. Neugestaltung der Stempelschneidkanten erreicht. Im ersten Teil der Arbeit wird eine solche Modifikation an einem klassischen Schneidstempel durchgeführt. Dabei wird die Stirnfläche des Stempels stark konkav ausgeformt und nur mit einer relativ kleinen ringförmigen Auflagefläche auf den auszutrennenden Butzen versehen. Durch die Reduzierung der Kontaktfläche werden lokale Druckspannungen in der Scherzone erzeugt, so dass sich während des Schervorgangs ein hinreichend großer Gradient dieser Schubspannungen mit der Bewegungsrichtung des Stempels mitbewegen. Dadurch erfolgt die Rissinitiierung deutlich verzögert, was zu einem höheren Glattschnittanteil und geringerem Kanteneinzug führt. Allerdings ist mit diesem Verfahren keine Gratfreiheit und kein ausreichendes Formänderungsvermögen der Schnittkante erreichbar. Aus diesem Grund wird im zweiten Teil der Arbeit ein zweistufiges Schneidverfahren weiterentwickelt. Dabei erfolgt eine Modifikation der Stempelschneidkante in der Anschneidestufe beim Konterschneiden. Dies ermöglicht die Kombination der Vorteile zweier Verfahren: des Konterschneidens und des Nachschneidens. Beide Verfahren werden in zwei Stufen durchgeführt. Das Konterschneiden ermöglicht gratfreie Bauteile, während das Nachschneiden hohe Glattschnitte mit einem hohen verbleibenden Formänderungsvermögen der Schnittkante ermöglicht. Durch die geometrische Modifikation der Anschneidestufe, beispielsweise durch das Einbringen einer abgesetzten Schneidkante in Kombination mit negativen Schneidspalten beim Anschneiden wird es möglich, beide Verfahren zu kombinieren und ebenfalls senkrechte Druckspannungen in Blechdickenrichtung beim Anschneiden zu erzeugen. Dadurch wird eine Schnittkante erreicht, die gratfrei ist, eine sehr hohe Schnittflächenqualität aufweist und gleichzeitig ein hohes verbleibendes Formänderungsvermögen für nachfolgende Umformvorgänge ermöglicht. Durch die entwickelten Verfahren und deren kombinierter Einsatz wird angestrebt, die Herausforderungen in Bezug auf die Schnittflächenqualität bei schergeschnittenen Bauteilkanten in der Elektronikindustrie zu bewältigen. Durch die Optimierung der Schneidverfahren wird eine präzise Herstellung von Bauteilkanten mit hohen Qualitätsanforderungen ermöglicht, was insbesondere in sicherheitskritischen Anwendungen von großer Bedeutung ist.

Abstract

Aluminium-matrix composites (AMC) are produced in order to improve specific properties (e.g. mechanical, thermal or tribological) of the matrix alloy using discontinuous reinforcements like fibres or particles. If functional requirements of application specific components such as brake discs have to be met, reinforcement contents of more than 35 % may be required. Therefore, a new manufacturing route is currently being investigated at the Institute for Metal Forming Technology (IFU) of the University of Stuttgart, combining powder pressing with subsequent semi-solid forming to obtain near-net-shape components. A key challenge of this process route includes compacting the green bodies. In this contribution, therefore, powder pressing of AlSi7Mg0.6 and SiCp powders with up to 50 vol.% SiCp are investigated in order to gain a deeper understanding of the compacting behaviour of powder with particularly high reinforcement contents. During the investigations, homogenously mixed powders were consolidated to a cylindrical green body by uniaxial powder pressing in order to determine the compressibility of different AMC powder mixtures. At first, the influence of the consolidation pressure onto the reached density was analysed, resulting in compressibility curves as well as process limits for different amounts of reinforcement particles. Subsequently, the influence of particle size onto the achieved density as well as consolidation behaviour could be identified. Furthermore, the high tool wear due to the abrasive behaviour of the reinforcement is quantified in this paper.

Abstract

Aluminium matrix composites (AMC) do combine a high lightweight potential with a wide range of specific mechanical or thermal properties, depending on their material composition or the content of reinforcement particles, respectively. Currently, the three main production technologies for manufacturing such AMC are powder metallurgy, semi-solid processes and casting. Here, the AMC´s reinforcement proportion that can be processed depends on the chosen manufacturing strategy and is therefore often limited to a maximum value of 30 vol. \%, due to agglomeration and porosity problems. In this context, the main objective is to understand the fundamental mixing behaviour of powder mixtures for AMC green body production having reinforcement contents of up to 50 vol.\% SiC p . For this purpose, powder mixtures of monomodal AlSi7Mg0.6 and different SiC p fractions were prepared with different mixing times and speeds to investigate the influence of these mixing parameters on the homogeneity of the particle distribution. Afterwards, the influence of powder size on the mixing process was investigated. The results showed that a slower mixing speed resulted in faster homogenisation as well as a larger particle size can be faster mixed. Furthermore, a regression model was developed using mixing time, speed and particle loading, to determine sufficient mixing parameters.

Abstract

Aluminium matrix composites (AMCs) offer improved mechanical and tribological properties compared to monolithic materials and therefore provide great potential for various applications. This particularly applies to particle-reinforced AMCs revealing comparatively high contents of reinforcement particles. However, these types of composites are difficult to manufacture due to their abrasive characteristics as well as their complex rheological material behaviour. An approach to produce such AMCs is semi-solid powder processing, combining powder pressing and sintering in one step in order to produce fully dense composites with currently only cylindrical shapes. Therefore, the tools as well as the powder mixture are first heated into the semi-solid temperature range of the aluminium powder and subsequently formed using low pressures under 200 MPa. Due to the shear thinning behaviour of the semi-solid aluminium matrix the porous structure of the pressed powder is filled during compaction, resulting in homogenous particle distributions in the component. However, this process results in high process times as well as energy costs, due to the heating inside of the die. In contrast to the semi-solid powder processing in one step, in this paper, a novel process route combining cold uniaxial compaction of particle reinforced aluminium powders having up to 50 vol.% SiC with subsequent semi-solid forming is presented. Here, a particle reinforced and cylindrically shaped green body is utilized as raw material, in order to produce complex components through semi-solid forming. The parts produced in this way are featuring varying wall thicknesses and are used in order to determine the process limits for manufacturing particle reinforced components having up to 50 vol.% SiC. Thereby, the influence of reinforcement particle size as well as particle loading on the homogeneity of the resulting particle distribution of an academic component is investigated. Future main objective of the process route is the manufacturing of complex parts with homogenously distributed particles.

Abstract

Trimming processes are frequently used for the manufacturing of fastener heads and similar parts with high precision requirements for specific regions of the part. Compared to conventional cold forging processes, the desired geometry can be achieved with significantly lower forces. However, trimming of sharp-edged geometries often leads to a highly inhomogeneous material flow and stress state in the workpiece, resulting in crack formation at such edges. To address this shortcoming, superposition of compressive stresses can be used to reduce the damage in the trimming process significantly. In this paper, the beneficial effect of stress superposition on damage reduction in a trimming process of a splined part is presented. By means of a numerical investigation using the FE-software DEFORM 3D, the impact of compressive stress superposition on the damage respectively crack formation at the edges of a splined part was investigated. Afterwards, trimming dies were manufactured and experimental investigations with three different trimming die geometries and different preform geometries were conducted to manufacture the splined parts. The edges of the splined parts were then characterized with a digital microscope and compared to the numerical results.

Abstract

In der blechverarbeitenden Industrie nehmen Bedeutung und Einsatz von belastungsgerechten Leichtbaustrukturen mit einem geringen CO2-Fußabdruck stetig zu. Diesbezüglich ermöglicht die Technologie des Rührreibschweißens, Blechverbunde aus Aluminium- und Stahllegierungen in unterschiedlichen Dicken zu fügen. Mit Blick auf eine möglichst intelligente Auslegung des Umformprozesses solcher Blechverbunde wird in diesem Beitrag ein Modellierungsansatz für einen Hybridblechverbund aus DX54 und AL6016 mit besonderer Berücksichtigung der Schweißnaht vorgestellt. In the sheet metal processing industry, relevance and application of load-oriented lightweight structures requiring a low carbon footprint are steadily increasing. In this respect, friction stir welding allows joining of tailor welded blanks made of aluminum and steel sheets of different thicknesses. Focusing on an intelligent engineering of the forming process of such tailor welded blanks, this paper presents a modelling approach for a hybrid sheet metal compound made of DX54 and AL6016 with particular consideration of the weld seam.

Abstract

By applying the rules of technical origami, flat raw materials can be folded into cellular structures. This also includes semi-finished sheet metal materials. Such folded sheet metal structures can be used as multifunctional core materials for sandwich-structured composites, offering outstanding strength and stiffness properties at comparatively low component weights. Applications of this type of sandwich-structured composites comprise, for example, optically appealing claddings, heat exchangers and, in particular, lightweight constructions.

Abstract

Kraftgebundene Umformmaschinen erlauben eine freie Gestaltung der Stößelbewegung. Diese Eigenschaft wird genutzt, um die Produktivität zu erhöhen. Das Potenzial solcher Stößelantriebe wird aber im produktiven Betrieb nicht ausgeschöpft, da nur etablierte Stößelbewegungsprofile genutzt werden. Daher wird in diesem Beitrag der Einfluss nicht konventioneller Stößelbewegungsprofile auf das Tiefziehergebnis untersucht. Hierfür wurden experimentelle Untersuchungen durchgeführt, um den Einfluss solcher angepassten Stößelbewegungsprofile auf das Umformergebnis bewerten zu können. Force-controlled forming machines allow for freely programming the ram movement. This feature is only used for increasing productivity. The potential of such ram motion is not exploited in production environments, since only established ram motion profiles are used. Therefore this paper investigates how non-conventional slide motion profiles influence the deep-drawing result. It undertakes experimental investigations to be able to evaluate the influence of such adapted slide motion profiles on the forming result.

Abstract

Abstract Optical measuring systems allow to observe the sheet metal instability more precisely. The section method was first standardised and made available in commercial measurement systems in order to evaluate the forming limit curves almost automatically. The insignificant contribution of the necking area to the evaluated critical strains compared to the neighbouring volume of material led to alternative approaches such as the time-based evaluation criteria. The majority of these criteria take into account the strain evolution at the material necking location and are also suitable for evaluating other types of limits such as edge-crack sensitivity. Some advanced high-strength steels typically exhibit very short deformation after the onset of instability, which complicates the application of time-based approaches because they require sufficient amount of deformation after necking. The proposed approach is an attempt to reduce the dependence of the time-based approaches on the amount of deformation after necking by taking into account the local characteristics of the measurement curves. The approach is applied to some advanced high-strength steels to evaluate the forming instability and edge-crack sensitivity. The superiority of this identification approach is demonstrated in this paper by comparison with classical time-based approaches.

Abstract

In deep drawing processes, the use of lubricants is mandatory in order to prevent wear on tools and surface damage to the formed sheet metal components. Here, frequently used lubricants are synthetic and mineral oils, emulsions, and waxes. However, these conventional lubricants have to be applied to the sheet material prior to the forming operation and removed afterwards by cleaning processes. Additionally, the lubricants often contain substances that are harmful to the environment and to human health. To counteract these economic and ecological disadvantages, research is currently being conducted on a novel tribological system. For this, volatile media such as liquid carbon dioxide and gaseous nitrogen are being used, and are introduced directly into the friction zones between the tool and the sheet metal material during deep drawing under high pressure through special laser-drilled micro-holes. This paper covers the latest investigations and findings regarding the design of flow-optimized micro-holes, the laser drilling process, the friction characterization on tool radii, and the tool wear to be expected when using the lubrication medium CO2.

Abstract

Commonly used lubricants in sheet metal forming usually base on mineral or synthetic oils, water based emulsions, drawing films or hotmelts (waxes). However, these conventional lubricants often contain harmful substances to human health and the environment. For this reason, a novel tribological system for dry metal forming has been developed. Basic principle of this new tribological system comprises the use of volatile media such as CO2 (liquid) and N2 (gaseous), which are injected into the contact interface under high pressure via injectors integrated into the tool. The volatile media used, lead to a significant reduction in friction and ensure robust friction behavior in deep-drawing processes. The investigations reported about in this contribution particularly focus on the friction behavior occurring in this tribological system at highly loaded radii. The friction investigations were carried out by using a modified stretch-bending-test and showed the effects of the main process-influencing parameters. In the present paper, these results are compared to already published results of the friction behavior investigated by means of flat strip drawing investigations. The findings obtained in this way allow a better understanding and prediction of the tribological system´s properties, thus making it usable for sheet metal forming applications.

Abstract

The ongoing digitization of production processes provides new possibilities and potentials for process monitoring of forming and stamping processes. The component quality achievable by these processes is strongly dependent on the properties of the sheet metal material, so that a permanent digital recording of material data offers high potential for monitoring each component produced. In this context, presented paper deals with a novel AI-based method for the direct determination of ma-terial parameters from measured punching force curves. Using software systems Python and Tensor-Flow, an artificial neural network was first set up to determine mechanical material parameters (out-put data) from punching force curves (input data). As data basis for the adopted neural network, force curves were measured during punching of various sheet metal materials using a punching tool equipped with a direct force measurement device. Punching force curves were experimentally deter-mined for the sheet metal materials DP1200, DP1000, DP800, DP600, HX380LA, DC03 and DX54. Additionally, tensile tests were performed for these sheet metal materials to determine ultimate tensile strengths (Rm), yield strengths (Rp0.2, Re), uniform strains (Ag), elongations at break (At) and strain hardening exponents (n). The presented paper reveals that neural networks can accurately quantify the relationship between characteristic parameters of punching force curves and the mentioned me-chanical material properties.

Abstract

Interpenetrating Phase Composites (IPC) belong to a special category of composite materials, offering great potential in terms of material properties due to the continuous volume structure of both composite components. While manufacturing of metal-ceramic IPC via existing casting and infiltration processes leads to structural deficits, semi-solid forming represents a promising technology for producing IPC components without such defects. Thereby, a solid open pore body made of ceramic is infiltrated with a metallic material in the semi-solid state. Good structural characteristics of the microstructure as the integrity of the open-pore bodies after infiltration and an almost none residual porosity within the composites have already been proven for this manufacturing route within a certain process window. On this basis, the following paper focuses on the mechanical properties such as bending strength of metal-ceramic IPC produced by using semi-solid forming technology. Thereby, the impact of the significant process parameters on these properties is analysed within a suitable process window. Furthermore, a fractographic analysis is carried out by observing and interpreting the fracture behaviour during these tests and the fracture surface thereafter.

Abstract

Today, aluminium matrix composites (AMC) are widely used for the manufacturing of lightweight, yet highly stressed components in automotive, aeronautic and electrical engineering. In order to achieve particle distributions as homogeneous as possible within these component's volumes and thus ensure optimum component properties, efforts are being made to simulate the manufacturing process prior to production. In this paper, AMC with extremely high particle fractions of more than 25 vol.\% are considered in particular, as their processing still poses significant technological challenges. To model the particle motion in a computational fluid dynamics (CFD) simulation of the semi-solid forming process of this type of materials, a Lagrangian multiphase approach combining CFD and discrete element method (DEM) was used. Here, the DEM allowed all particle-particle interactions to be considered. Thus, different parameters influencing particle agglomeration, particle distribution as well as particle interaction with the cavity can be investigated during a numerical study. More specifically, the influence particle parameters such as cohesion forces and the influence of the forming speed onto the particle distribution in the final component ́s volume was analysed. The simulations were performed for a symmetric disc geometry. A forming tool was already available for this geometry, with which components could be manufactured to validate the simulation results. In the end, the study shows that by using four-way CFD-DEM coupling, simulation predictability for the semi-solid forming process of AMC could be significantly improved.

Abstract

Hybrid material structures allow different material properties to be combined in one single component and thus to meet high functional requirements. When manufacturing such hybrid components, particular attention must be paid to the transition zones between metallic composite partners. These transition zones need to show largely homogeneous and materially bonded structures in order to ensure ideal transmission of the material properties and to prevent component failure due to material defects. In this respect, this paper focuses on a newly developed process in which a powder metallurgical route is combined with semi-solid forming technology. Here, porous copper green bodies are inserted into a forming die and subsequently forged together with a semi-solid aluminium alloy. In this way, it was tried to combine both metal materials into a material locking or at least into a form locking manner in order to achieve ideal material properties in the final hybrid component. The aim of this paper is to find suitable process parameters to infiltrate the porous copper inlay with the semi-solid aluminium alloy during thixoforming. Therefore, different process parameters such as varying liquid fraction of the aluminium alloy and different densities of the green bodies were examined during the production of simply shaped hybrid Al-Cu-components. Afterwards the infiltration depth and produced microstructure of the components was analysed. In the future, this process allows for producing aluminium-copper hybrid heat sinks with improved heat transfer properties compared to conventional produced heat sinks.

Abstract

Manufacturing of hollow components with local functional internal surfaces often requires complex process routes with several individual operations. By using a special hollow cold forging process with an adjustable deformation zone it is possible to manufacture hollow shafts with varying wall thickness over its axial length parts just within a single stroke of the press. Combining this principle with a splined mandrel allows manufacturing of tailored hollow shafts with local internal splines. However, the impact of geometry of mandrel and other process parameters on the shape of the cold forged internal splines have not been investigated yet. Furthermore, an underfilling phenomenon can occur on the outer surface of shaft during specific process states. In this contribution, several mandrel geometries and their impact on the part shape and filling / underfilling phenomenon in the mentioned process are investigated. To determine those effects, a numerical investigation has been conducted. Besides the geometry of the splined mandrel, also other parameters such as die geometry and tool kinematics were considered. The numerically calculated workpiece geometries are compared to the ideal geometries using a deviation analysis.

Abstract

The use of ultra-high-strength steels (UHSS) enables a lightweight and resistant design of sheet metal parts in modern car body structures. In terms of manufacturing such dedicated materials, intense springback phenomena reduce the process stability and dimensional quality. In this context, new developments in springback compensation show promising results when superimposing stresses. Therefore, this paper deals with a new approach, which modifies conventional deep drawing of open profiles by substituting the blankholder by L-shaped sliders. This allows an additional application of horizontally acting forces along the edge of the flange and leads to advantageous free buckling and rolling of the material onto lateral punch surfaces. A numerical feasibility study of this new forming method was performed in this work, showing that compressive stresses and alternate bending through buckling in fact does reduce the amount of springback remarkably compared to conventional deep drawing.

Abstract

The subjective perception of the quality of sheet metal components mainly depends on geometric characteristics and surface structures. In this context, particular attention must be paid to avoiding surface defects such as skid lines during the sheet metal forming process for components with high surface quality requirements (e.g. outer skin passenger car panels). In principal, FEM simulation can provide an effective tool for predicting such surface defects. However, the numerical modelling approaches available today do not yet allow an adequate basis for assessing their quality relevance in production, which especially applies to skid lines. In a previously published study, new skid line criteria were developed in this regard, considering unbending strain, thinning and major strain. Using a simple steel sheet part (DC06) as reference, the study showed that these criteria allow the quality relevance of skid lines to be predicted relatively accurately. This paper focuses on the validation of the proposed skid line criteria and their applicability to the materials DC06 and AA6016. Furthermore, the numerical studies presented show that one of the novel skid line criteria, which considers unbending strain and thinning, is able to accurately locate and predict the quality relevance of skid lines even for complex shaped parts.

Abstract

In series production of sheet metal components, fluctuating sheet metal properties can lead to time-consuming start-up phases and increased scrap rates. One approach for overcoming these challenges is to change the blank position before the forming process. Against this background, this paper investigates the quality influence of the blank position on the deep-drawing result. Experimental and numerical investigations were carried out to evaluate the influence of the blank position on the forming result.

Abstract

Cold forging tools become increasingly complex and require enhanced functionality, especially in the context of digitisation. Conventional subtractive manufacturing processes often reach their limits when the geometric complexity of the workpiece increases, hence additive manufacturing processes have become increasingly important in the last decades. Additive manufacturing processes have already been used in many fields of manufacturing technology to produce tool components with promising results, but the potentials of additive manufacturing processes have not yet been applied to cold forging tools. Therefore, the Institute for Metal Forming Technology (IFU) of the University of Stuttgart has developed an additive manufactured cold extrusion tool with integrated functional features. As functional features in the additive manufactured extrusion tool, a close contour glass fiber sensor for temperature measurement, a cooling system and a lubrication system for the controlled injection of minimal lubricant amounts during the forming process were integrated. Due to the integrated functional features, structural degradation appears in the tool, therefore the structural-mechanical tool properties were analyzed numerically with the FE-Software DEFORM 3D™ in this report as well. Furthermore, the additive manufactured cold extrusion tool was experimentally evaluated in sequentially executed extrusion operations. Thereby the integrated functional features were used and gathered data were recorded. As a result of the experimental forming tests, near-contour temperature measurements in the extrusion tool with and without the use of the integrated cooling system as well as the modification of the maximum punch forces by an inline lubricant application were obtained. In addition, the experimentally determined temperature fields in the extrusion die are validated with numerically calculated results.

Abstract

Shortened product development processes in automotive industry combined with the upcoming lack of experts do challenge sheet metal part production fundamentally. Tryout time and manufacturing costs of large forming dies today are significantly influenced by their digitally supported engineering. The forming process by such tools is beside other influences is affected by elastic deformations of forming dies and press structure as well as contact areas between die and sheet metal part. In deep drawing such contact areas are influenced by the blank properties and the flange behavior in terms of thickening and thinning. Recent developments in sheet metal forming simulation do consider advanced friction models and structural modeling of die and press components improving simulation accuracy. Nevertheless thinning or thickening of sheet metal results into localized surface pressure distribution during deep drawing. For this reason, it is not sufficient to use the currently common practice of homogeneous surface pressure distribution in sheet metal forming simulation. In this respect, this paper presents a numerical approach for consideration of straining effects in the sheet metal part during forming operation. For this purpose, a systematic process improvement was developed in this paper to identify contact areas via a numeric simulation parameter. Validating the numerical investigation, a rectangle cup die is used, considering major strain. The main results of this contribution for that reason show how simulated contact areas can be estimated by reverse engineering of real forming parts. Hereby straining based contact areas lead to a novel contact area design in process planning, resulting in efficient die tryout.

Abstract

Ä new process is presented in which semi-finished products (AA6060) with tubular internal reinforcements of higher strength (AA7075) are produced by composite hot extrusion. Flange-shaped parts are manufactured from the extrudate by subsequent lateral extrusion and upsetting. The aim is to develop a robust process route for flange-shaped components by composite hot extrusion and subsequent cold forging. For this purpose, numerical investigations were carried out. The process can be conducted without errors if certain limits are observed, which can be shown numerically. The probability of solid state bonding can be increased by choosing the proper tube geometry, so that subsequent lateral extrusion can be carried out. The knowledge generated is to be used to expand the spectrum of components in the future to include higher strength tubular reinforcements.

Abstract

Large sheet metal parts with low drawing depths usually reveal only low work hardening levels in the central area of the components. As a result, such parts often do not meet specified property requirements. Short-cycle stretch technology (SCS) represents a novel forming process for combined stretching and deep drawing, which allows high-quality production of such large sheet metal parts with improved mechanical properties. Due to a consistently simple tool design with changeable die inserts, SCS technology additionally offers a cost-effective and relatively flexible alternative to currently known processes for combined stretch forming and deep drawing. This paper defines the basic principle and presents close-to-production tool concepts of the newly developed SCS process. Furthermore, the high energy saving potential of the novel forming technology is illustrated in comparison to conventional deep drawing.

Abstract

Residual stress development in deep drawing processes is investigated based on cylindrical cups made of duplex stainless steel sheet. Using a two-scale approach combining finite element modelling with a mean field homogenization scheme the macro residual stresses as well as the phase-specific micro residual stresses regarding the phases ferrite and austenite are calculated for steel X2CrNiN23‑4 for various drawing depths. The simulation approach allows for the numerical efficient prediction of the macro and phase-specific micro residual stress in every integration point of the entire component. The simulation results are validated by means of X‑ray diffraction residual stress analysis applied to a deep-drawn cup manufactured using corresponding process parameters. The results clearly indicate that the fast simulation approach is well suited for the numerical prediction of residual stresses induced by deep drawing for the two-phase duplex steel; the numerical results are in good agreement with the experimental data. Regarding the investigated process, a significant influence of the drawing depth, in particular on the evolution of the residual stress distribution in drawing direction, is observed. Considering the appropriate phase-specific strain hardening, the two-scale approach is also well suited for the prediction of phase specific residual stresses on the component level.

Abstract

The research subjects of current investigations at the Institute for Metal Forming Technology (IFU) Stuttgart include the manufacture of face gearings. Usually, gearings are produced by means of a coining process, which causes high process forces that considerably restrict the geometry of the teeth in terms of the height-to-width ratio. In order to avoid these problems, a new forming process has been developed. This technology offers significant advantages, such as the reduction of process forces and the ability to manufacture the required tall and acuminate tooth elements through a cold-forming process. This paper describes the design and functionality of the novel pin-to-gear forming process. In this paper, the operating principle of the method is presented first of all. The new pin-to-gear process is then compared to conventional coining and the free-divided-flow (FDF) process developed at IFU Stuttgart in 2018. This examination takes the form of a numerical simulation using DEFORM-2D software. To investigate the influence of preform parameters on the form filling of the tooth cavities, parameter studies in design and geometry are conducted. Process limits regarding geometric constraints are presented alongside possibilities for increasing process reliability. Through this investigation, the potential and opportunities of the innovative pin-to-gear forming process will be illustrated.

Abstract

Series production of sheet metal components in press shops is permanently subjected to an increasing pressure in time, cost and quality. Varying sheet metal properties due to batch fluctuations and changing process conditions lead to an increase of try out time phase and scrap rate, resulting in a demand for adaptive control strategies for deep drawing. Today, these chal-lenges are met by integrating sensors and actuators into tool structure which measure and control part quality, mainly through blank draw-in. However, such tool-based control systems require a complex and cost-intensive modification of the existing die or press technology. Against this background, the active adjustment of blank position prior the deep drawing process realized with an intelligent transfer and positioning system as a promising approach towards economic and technical aspects. This paper deals with blank positioning and its sensitivity to quality-related failures of deep drawn sheet metal components like splits and wrinkles. Therefore, a numerical study was conducted on a deep drawing process of an exemplary structural part geometry, wherein a typical fluctuation of material parameters and variation of local friction conditions was simulated. Subsequently, correlations between process disturbance and blank draw-in were elaborated, thus using local draw-in values as controlled variables for a closed loop system. Sim-ulation results showed that the manipulating parameter, i.e. the blank position prior deep draw-ing, reveals a significant influence on the draw-in and therefore on the component s quality. An essential finding of this study is the numerical proof of concept for this new deep drawing control strategy, demonstrated for different process conditions. Finally, disturbances in the deep drawing process considered could be successfully controlled by adapting the blank position.

Abstract

Bei der Serienproduktion von Blechbauteilen können schwankende Blecheigenschaften zu zeitintensiven Anlaufphasen und erhöhten Ausschussraten führen. Diesen Herausforderungen wird heute mit werkzeugbasierten Regelungssystemen begegnet, welche aber eine komplexe und kostenintensive Modifikation der bestehenden Werkzeuge beziehungsweise Pressen erfordern. Vor diesem Hintergrund befasst sich der Beitrag mit einem relativ einfachen und kostengünstigen Regelungsansatz auf Basis einer adaptiven Platinenpositionierung.

Abstract

Die für die FEM (Finite-Elemente-Methode)-Simulation von Blechumformprozessen benötigten validierten Materialparameter können heutzutage durch eine vollflächige optische Messung der Verformung eines Prüfkörpers in Kombination mit einem simulationsbasierten inversen Ansatz ermittelt werden. Dieser inverse Ansatz erfordert jedoch Fachwissen in der FEM-Analyse, Optimierung sowie Programmierung und kann zudem recht zeitaufwendig sein. Vor diesem Hintergrund wird in diesem Beitrag eine auf maschinellem Lernen basierende Methode zur Bestimmung von validierten Materialparametern vorgestellt. Today, validated material parameters required for FE simulation of sheet metal forming processes can be identified via full-field optical measurement of test specimen`s deformation combined with a simulation-based inverse approach. This inverse approach normally requires deep expertise in FE analysis, optimization, and programming and can be very time-consuming. This paper proposes a novel machine-learning approach for determining such validated material parameters.

Abstract

A novel tribological system has been developed, in which volatile lubricants (carbon dioxide - CO2 or nitrogen- N2) are used as a substitute for mineral oil-based lubricants in deep drawing processes. This process enables the introduction of an intermediate medium under high pressure through flow-optimized, laser-drilled micro holes into the contact surfaces. This eliminates the need for subsequent, cost-intensive cleaning processes, as the volatile lubricants evaporate without leaving any residue during expansion to ambient pressure. The design of initial micro hole geometries was based on simulations of the flow behaviour of the lubricants passing through, which in turn were validated using pressure reactor tests. In addition, the wetting behaviour of CO2 on relevant surfaces (tool surface and sheet material surface) was investigated experimentally using the captive-bubble-method. Thus, the optimal design of the micro holes (diameter, hole geometry and number of micro holes) could be determined using flat strip drawing tests. The optimal micro hole geometry determined in this way is suited for the use of both CO2 and N2 as volatile lubricant. Furthermore, extensive investigations for the production of the required micro hole geometry by laser drilling were carried out. The fundamentals for drilling micro holes in steel with high aspect ratios could be developed using an ultrashort pulsed research laser with very high pulse energy. Further experiments were conducted using an ultrashort pulsed prototype laser of the kW-class specially developed to increase productivity when drilling a multitude of micro holes with higher average laser power. The novel tribological system has been characterised by means of strip draw- ing tests and stretch bending tests. For both, CO2 (liquid) and N2 (gaseous), relatively low friction values could be achieved compared to conventional lubricants. It could be shown that deep drawing with both CO2 and N2 as dry lubricants is possible. Here, usage of the volatile lubricants not only allows the replacement of mineral oil based lubricants, but even improves the tribological system with regard to frictional forces in sheet metal forming. The feasibility of the new tribological system has been proven by performing deep drawing tests of rectangular cups. These tests showed a significantly enlarged process window of the forming process, which emphasise the tremendous potential of this new tribological system. Keywords:

Abstract

Die beim Lochen von Bauteilen aus Blech mit Blechlagewinkel erzielbaren Schnittflächenkenngrößen können nach aktuellem Stand der Technik nicht ausreichend präzise prognostiziert werden. Daher werden in der Praxis maximal realisierbare Blechlagewinkel meist zu konservativ abgeschätzt. Mit den in diesem Beitrag vorgestellten Schnittflächen-Regressionsmodellen kann der benötigte Einsatz von kosten- und wartungsintensiven Keilschiebern genauer bewertet und somit eine flexiblere, kostenoptimierte Gestaltung von Schneidwerkzeugen ermöglicht werden. Today, cutting surfaces achievable by punching sheet metal components with a slant angle cannot be predicted sufficiently precise. In industrial practicet, maximum slant angles applicable for shear cutting are therefore usually estimated rather conservatively. According to the regression model-based determination of cutting surfaces presented in this paper, demand for cost and maintenance-intensive cams can be evaluated more accurately, thus enabling a more flexible, cost-optimized design of cutting tools.

Abstract

The International Conference “New Developments in Sheet Metal Forming” held in Stuttgart / Germany is organised every second year alternatingly with the International Conference “New Developments in Forging Technology”. Main goal of both conferences is to gather engineers and experts from the industry as well as scientists from universities to discuss the current state of the art, and future tendencies and targets in research and development of new sheet metal and/or bulk metal forming technologies. Annually, the Institute for Metal Forming Technology (IFU / Stuttgart / Germany) organises this event in collaboration with the Forschungsgesellschaft Umformtechnik mbH (FGU Stuttgart / Germany). For many years, the concept of the conference was to focus on effectively transferring scientific results into value added chains of companies operating in the field of sheet metal forming and other sheet metal forming related market segments. Therefore, the topics of the papers selected to be presented at conference should have reference to current worldwide research activities in sheet metal forming, modern production technologies, tool design in general and new developments in the field of sheet metal material. During this two-days conference, experts from both universities and industrial companies will present their papers and discuss their newly achieved results with experts from all over the world. Conference topics include investigations performed at several European metal forming institutes, at companies from industry, and at the Institute for Metal Forming Technology (IFU) of the University of Stuttgart. Thus, a balanced mix of practical and theoretical contributions will be presented. In 2018, special attention is paid to present and to publish modern practical solutions in cold forming of sheet metal materials, modern concepts of material compositions, as well as modern sheet metal forming simulation technologies and new approaches in order to integrate modern sensors into the tool structure to control process development during serial production. Furthermore, the technological potential of new material developments e.g. new sheet metal alloys will be disclosed to make attendees able to respond easily to occurring questions of today when running their day to day business in the sheet metal forming industry. Therefore, the opening presentations in particular pay attention to recent questions in metal forming technologies around car body manufacturing and other business as well as future manufacturing strategies! Also a panel discussion will be held during late afternoon of first conference day. International experts in the field of establishing new startup companies encouraged by academia or business will discuss on chances, opportunities and threats of young entrepreneurs in Israel and Germany. VI Company visits offered on Monday, May 14th, 2018 and contributions from numerous international acting market players and different technological research institutions in Germany are objecting and presenting an deep insight into the current developments and research work in the field of sheet metal manufacturing. During the conference, the visitors and speakers are given the opportunity of contributing professionally, analysing and observing trends, exchanging ideas, and cultivating personal networks. Therefore, the conference programme includes visits to industrial companies and a welcoming evening at IFU on the day before conference, the gala dinner on the 1st conference day, and exhibitions of more than 20 companies throughout the entire conference. I appreciate to thank all authors in advance for contributing and feeling inspired on this conference! I am sure, this book comprising papers presented on May 15th – 16th, 2018 in Fellbach (near Stuttgart) Germany will be dispatched widely and will be available to all international experts involved.

Abstract

Cold forging of toothed components by extrusion is associated with high punching forces and tool loads, which requires the use of expensive and high-strength tool steels. High process forces result into a substantial tool deflection, which significantly reduces the precision of the toothed components. Thus, the development of alternative processes in order to reduce acting process forces in cold forging is of high interest. A potential process enhancement approach is to use a preform operation where the resulting preform can be formed partwise either in the same or in a subsequent die. Preforms allow to systematically control the material flow in subsequent forming operations. For this reason, the Institute for Metal Forming Technology in Stuttgart has developed a new cold extrusion process for manufacturing toothed components based on the conventional Samanta process. The newly developed die design of the Guided Material Flow---Samanta (GMF---Samanta) process enables efficient cold forging of gears. By means of numerical simulations and forging experiments it was successfully demonstrated that the new Guided Material Flow---Samanta process results into a significant reduction of punch force and normal pressure while simultaneously improving the die filling.

Abstract

Die Fertigung von Hohlwellen mit komplexer Innengeometrie bedingte bisher meist aufwendige Prozessrouten. Ein am Institut für Umformtechnik der Universität Stuttgart entwickeltes Kaltfließpressverfahren soll nun die wirtschaftliche und flexible Fertigung von Hohlwellen mit Wanddickenvariation ermöglichen. In diesem Beitrag werden das Verfahren beschrieben und die Ergebnisse der numerischen Untersuchung des Einflusses der Werkzeugkinematik auf die erzielbare Pressteilgeometrie dargelegt. Usually, the production of hollow shafts with complex internal geometry by cold forging requires extensive process routes. A novel cold forging process developed at the Institute for Metal Forming Technology at the University of Stuttgart allows for an economical and flexible production of hollow shafts. This article describes the manufacturing process and presents the results of a numerical investigation for determining the influence of tool kinematics on the achievable part geometry.

Abstract

Cold forging of toothed components presents a challenge for forming technology due to high punch forces and tremendous tool loads. This leads to development of alternative methods and processes to reduce the disadvantageous process characteristics during forming. A possible method for process improvement is using a preforming operation, where the achieved preform can be formed further either in the same die-set or in a different die-set of the following operation. Preforming can be used to systematically control the path of material flow and influences inherentlythe frictional contact of the workpiece with the tool and the die filling, etc. For this reason, the Institute for Metal Forming Technology in Stuttgart has developed various new processes for forming different types of gearing. For this purpose, a two-stage coining process and a two-stage transverse extrusion process were developed, by means of which an enhanced die filling in the second forming process.The developed type of material flow throughout the complete process chain is called the Free Divided Flow (FDF) -method. The FDF-method enables a more efficient die filling while simultaneously reducing the tool load. Applying this idea to the Samanta process lead to a modified version with enhanced process characteristics. This process includes a newly designed die which leads to a successive forming of the toothing. The process, which was developed as a packaged extrusion process, uses the advantages preforming leading to a completely different material flow path to achieve the required tooth geometry.

Abstract

Der aktuell starke Umbruch im Mobilitätsbereich führt nicht nur bei den Endkunden zur Frage nach der Wahl des Fahrzeugkonzepts bzw. Verkehrsmittels, auch bei den Fahrzeugherstel- lern sind viele neue Rahmenbedingungen für und Anforderungen an Fahrzeugkomponenten entstanden. So ist beispielsweise mit dem Einzug schwerer Batterien in Kraftfahrzeugen das Thema Leichtbau nicht minder relevant als in den vergangenen Jahrzehnten. Hierbei ist ne- ben dem Werkstoffleichtbau insbesondere der konstruktive Leichtbau von besonderer Be- deutung. Oftmals können hochbeanspruche Komponenten aufgrund der erforderlichen Fes- tigkeit nicht aus alternativen Werkstoffen mit geringerer Dichte ausgeführt werden. In diesen Fällen bietet es sich an, hohle Strukturen zu verwenden, um Gewicht einsparen zu können. Bei der Fertigung derartiger Komponenten sind insbesondere umformtechnische Verfahren gefragt. Diese bieten vor allem aus fertigungstechnischer Sicht entscheidende Vorteile, wie einen ununterbrochenen Faserverlauf, eine hohe Oberflächengüte und Materialausnutzung sowie die während der Umformung entstehende Kaltverfestigung des Materials. Nachfolgend sollen in diesem Zusammenhang am Beispiel einer exemplarischen Welle zu- nächst Festigkeitsaspekte beleuchtet werden, bevor anschließend mit dem derzeitigen Stand der Technik eine Übersicht von etablierten Fertigungsverfahren zur Herstellung von Hohlwel- len gegeben wird. Weiterführend werden neue technologische Ansätze aufgezeigt, welche zu einer effizienten Fertigung von hohlen Bauteilen beitragen können. Abstract

Abstract

Thixoforging allows one-step forming processes of near-net shape components having excellent mechanical properties. However, the high sensitivity of thixoforging regarding process conditions requires precise modelling and determination of process related parameters. At the same time, simple numerical design proves challenging because of the inaccuracy of existing one-phase material models regarding the shear thinning flow behaviour of semi solid metals. Consequently, this paper deals with the development of a new one-phase material model providing a more precise simulation of materials' shear rate dependency. By using this model, simulations could be performed, which allowed the prediction of solidification and flow-related component defects.

Abstract

Der Beitrag präsentiert ein Verfahrens- und Werkzeugkonzept zur Kaltumformung eines Kolbenbolzens mit einem strukturmechanisch optimierten helixförmigen Innenprofil. In der Untersuchung wurde der Umform- und Auswurfprozess numerisch modelliert und anhand der numerischen Ergebnisse ein Versuchswerkzeug entwickelt und aufgebaut. Damit wird der Auswurfprozess beim Einsatz unterschiedlicher Schmierstoffsysteme und Variation der Prozessgeschwindigkeit detailliert untersucht. Die Bewertung der Versuche erfolgt durch die Auswertung der Stempel- sowie Auswurfkräfte, die Analyse der Unterfüllung der Innengeometrie und der Härteverteilung im Bauteil. This paper presents a process and tool system for the cold forging of a piston pin with a helical inner profile optimized in terms of structure and mechanics. First in this investigation, the forming and ejection process was modelled numerically. Based on the numerical results, a test tool was developed and built. Bassed on this tool, the ejection process was examined in detail using different lubricant systems and varying the process velocity. The tests are verified by evaluating the punch and ejection forces and by analysing the underfilling of the internal geometry and the hardness distribution in the workpiece.

Abstract

Understanding and controlling tribological systems and thus the friction conditions during deep drawing processes represent two important challenges for stable and economical forming processes. In order to optimise the friction conditions in sheet metal forming processes, mineral oils with additives and oil-water based emulsions are usually used. When using such conventional lubricants two major disadvantages may emerge on the one hand, environmental aspects due to the partly environmentally hazardous additives have to be considered and on the other hand, cleaning steps after forming processes to enable further production steps such as welding, gluing and painting are not avoidable. To solve these problems, the Institute for Metal Forming Technology (University of Stuttgart) is currently investigating the use of volatile media as lubricant substitutes. Thereby, media are used which volatilise into the gaseous state without any residue after forming. In the present work, friction conditions at tool radii are particularly considered, since highest surface pressures between workpiece and tool usually occur at these areas. In this context, the work deals with experimental investigations on the tribological friction conditions at tool radii while using volatile lubricants, such as CO2 and N2. To keep the multitude of possible influences on the tribological system as low as possible, the investigations were carried out on a deflected strip-drawing testing rig. The aim of the investigations was the characterization of the tribological system and the friction conditions at tool radii under varying boundary conditions such as surface pressure and injection angle of the lubricant.

Abstract

Sustainability in production and avoidance of harmful substances are widespread drivers for further developments of production processes. In con- ventional deep drawing, for example, mineral lubricants are usually used to reduce friction or wear and to avoid surface damage to sheet metal components. These lubricants often contain harmful additives such as chlorinated paraffins. Furthermore, the lubricants must be applied to the sheet metal before the forming process and removed again, as they have a negative influence on subsequent processes such as bonding, welding and painting. In order to counter these disadvantages a new tribological system for deep drawing processes was developed using volatile media (nitrogen or carbon dioxide) as lubricants. The advantages are avoidance of harmful substances and reduction of necessary process steps, since these media are introduced directly into the tools during forming and evaporate without residue after the process. In this context, the paper gives an overview on gained results concerning basic friction investigations using a flat strip drawing testing rig and very first results of a new strip drawing testing rig with a simple deflection. With this testing rig friction conditions and friction coefficients at tool radii can be investigated using volatile lubricants. Also the results of first real deep drawn parts, using this new tribological system is presented, including tool and process set up and the investigations on the remarkably increased process window of this new dry forming process.

Abstract

Sustainability in production and avoidance of harmful substances are widespread drivers for further developments of production processes. In conventional deep drawingDeep Drawing, for example, mineral lubricants are usually used to reduce friction or wearWearand to avoid surface damage to components. These lubricants often contain harmful additives such as chlorinated paraffins. Furthermore, the lubricants must be applied to the sheet metal before the forming process and removed again, as they have a negative influence on subsequent processes such as bonding, welding and painting. In order to counter these disadvantages a new tribological system for deep drawingDeep Drawingprocesses was developed using volatile media (nitrogen or carbon dioxide) as lubricant. The advantages are avoidance of harmful substances and reduction of necessary process steps, since these media are introduced directly into the tools during forming and evaporate without residue after the process. In this context, the present work deals with experimental investigations on the tribological friction conditions at tool radii using volatile lubricants, such as CO2. In order to keep the multitude of possible influences on the tribological system as low as possible, the investigations were carried out on a strip drawing testing rig with simple deflection. The aim of the investigations was the characterizationCharacterizationof the tribological system and the friction conditions at tool radii under varying boundary conditionsBoundary conditionssuch as retention force and injection angle of the lubricant.

Abstract

Sustainability in production and avoidance of harmful substances are widespread drivers for further developments of production processes. In con- ventional deep drawing, for example, mineral lubricants are usually used to reduce friction or wear and to avoid surface damage to sheet metal components. These lubricants often contain harmful additives such as chlorinated paraffins. Furthermore, the lubricants must be applied to the sheet metal before the forming process and removed again, as they have a negative influence on subsequent processes such as bonding, welding and painting. In order to counter these disadvantages a new tribological system for deep drawing processes was developed using volatile media (nitrogen or carbon dioxide) as lubricants. The advantages are avoidance of harmful substances and reduction of necessary process steps, since these media are introduced directly into the tools during forming and evaporate without residue after the process. In this context, the paper gives an overview on gained results concerning basic friction investigations using a flat strip drawing testing rig and very first results of a new strip drawing testing rig with a simple deflection. With this testing rig friction conditions and friction coefficients at tool radii can be investigated using volatile lubricants. Also the results of first real deep drawn parts, using this new tribological system is presented, including tool and process set up and the investigations on the remarkably increased process window of this new dry forming process.

Abstract

Dieser Beitrag enthält wichtige Erkenntnisse zum Lochen mit Blechlagewinkel, die aus umfangreichen experimentellen Untersuchungen im Rahmen des EFB-Projektes 17/213 gewonnen wurden. Hierbei wurde die horizontale Stempelauslenkung messtechnisch über einen im Niederhalter eines Schneidwerkzeuges integrierten Wirbelstromsensor erfasst. Anhand der durchgeführten Untersuchungen konnte in Abhängigkeit der untersuchten Schneidparameter eine Auflistung maximal möglicher Blechlagewinkel erarbeitet werden, welche nach bestehendem Stand der Technik noch nicht vorlag. Durch eine Sensitivitätsanalyse der gemessenen (maximalen) horizontalen Stempelauslenkungen konnte außerdem gezeigt werden, dass der Zusammenhang zwischen der Größe des Blechlagewinkels und der maximalen Stempelauslenkung in guter Näherung durch eine Geradengleichung beschrieben werden kann. Neben den umfangreichen experimentellen Untersuchungen mit ISO8020 Schneidstempeln mit einem Stempeldurchmesser von d=10mm wurden auch Stichversuche mit einem kleineren Stempeldurchmesser (d=5mm) vorgestellt. Der Blechlagewinkel wurde in diesen Stichversuchen schrittweise bis zu $\beta$=17,5° untersucht. Ein Vergleich der gemessenen Stempelauslenkungen hat gezeigt, dass die Schneidstempel mit d=5mm trotz geringerer Biegesteifigkeit eine kleinere Auslenkung erfahren als die Schneidstempel mit d=10mm. Dies ist auf die geringeren Prozesskräfte, die bei einem kleineren Stempeldurchmesser wirken, zurückzuführen. Bei der Auslegung eines Schneidwerkzeuges nach bestehendem Stand der Technik hätten bei einem Stempeldurchmesser von d=5mm bereits ab einem Blechlagewinkel von $\beta$=5,0° bis $\beta$=7,5° Schieber im Werkzeug verwendet werden müssen. Die durchgeführten Stichversuche beweisen demgegenüber, dass die horizontale Stempelauslenkung die Prozessgrenze (Schneidspalt) selbst bei einem Blechlagewinkel von $\beta$=17,5° nicht überschreitet. Im vorliegenden Beitrag wird weiterhin verdeutlicht, dass eine Möglichkeit zur Erweiterung der Prozessgrenzen beim Lochen mit Blechlagewinkel in der Verwendung von Stempelanschliffen besteht. Die diesbezüglich vorgestellten Untersuchungen haben gezeigt, dass die Verwendung eines einseitigen (positiven) Stempelanschliffs zu einer Halbierung der gemessenen Stempelauslenkung führt und dass sich somit ein Stempelanschliff mit entgegengesetzter Neigungsrichtung zum Blechlagewinkel für das betrachtete Schneidverfahren empfiehlt.

Abstract

Nowadays, a major criterion for the quality of shear cut workpieces is characterised by a smooth final cutting surface. Normally, this surface only can be manufactured by using fine cutting or trimming technology. Major disadvantage of these processes is the complex tooling design caused by a double-acting press and corresponding tool layout. Content of this study is to investigate the impact of a new sheet metal cutting tool design, also called concave nosed punch design, to increase the clean-cut portion in conventional shear cutting. The investigation focuses on sheet metal materials DP600, DC03 and HC420LA with a thickness of 1mm. Using FEA-Software DEFORM 2D, the models of conventional cutting and cutting with new tool design were mapped by comparing cutting surface results and stress distribution in the shearing zone. The main criterion of the optimization of tool design focuses on an enlarged clean-cut area along the cutting surface compared to conventional shear cutting. New tool design shows in numerical investigation a significant increase of clear-cut surface up to 73% compared to conventional cutting surfaces disclosing 35% when using tools according to standard design rules. With the result of the punch optimization in the numerical investigation, two cutting punches with different web widths were manufactured and experimentally investigated. The focus of the experimental investigation was the comparison of the cutting characteristics of smooth cut portion and cutting burr. The influence of the cutting clearance between 5% and 15% on the clean cut portion and the burr was investigated. Metallurgical micrographs show a significant increase in the percentage of smooth cut portion when punching with the new cutting method presented here. For DC03, these concave nose punch design was able to achieve smooth cut percentages of up to 95%. However, using this new punch design, it is possible to sheet metal materials revealing a noticeably performed shearing surface quality.

Abstract

A recently developed joining method using lateral extrusion enables the clear- ance-free manufacturing of cylindrical and non-circular shaft-hub connections. While the method is highly efficient, joining by plastic deformation usually results into an uneven distribution of contact stress or even gaps in the inter- stice. In order to provide a more suitable contact stress distribution in axial direction, e. g. for minimized stress in the hub or fretting fatigue, shape modifi- cation of the contact surface is necessary. Since the contact stress is mutually dependent on both the hub und the shaft when performing joining by forming, an iterative approach is required. In this paper, an iterative method for adapting the axial contact stress distribution of plastically stressed shaft-hub connections with a predefined target contact stress is presented. For this purpose, the inner contour of the hub is updated iteratively. A single iteration of the design optimization process includes the following steps: 1) update of FE model 2) elastic-plastic FE simulation of the joining by forming process 3) characterisation of contact stress distribution by polynomial fit 4) geometrical modification of inner hub contour The automated contact stress adaptation is implemented in Python strongly linked with FE Simulations being performed with Ansys Workbench. In order to demonstrate the application of the new method, an exemplary circular shaft- hub connection is used to simulate the joining process by lateral extrusion. The inner contour of the hub is updated iteratively in order to create a uniform axial contact stress distribution. Additionally, the effects of different optimization settings on the adaptation of contact stress distribution and computation time are shown.

Abstract

In order to fully realize the strength potential of cold-formed parts, strain hardening and residu- al stress from the cold-forming process must be considered in structural FEA simulations of the loaded condi- tion. However, only topological data have previously been transferred when using separate forming and struc- tural-simulation tools. This paper presents a new method for transferring local residual stress and strain data from the forming simulation tool Deform3DTM to the structural analysis tool Ansys Workbench. The aim of the method is to increase the accuracy of structural-simulation results for cold-formed parts under load using sep- arate simulation tools for the cold-forming and structural behaviour of manufactured components. The appli- cation of the method is demonstrated using the example of a full-forward-extruded shaft under torsional load. Validation of the data transfer and comparison of simulated deformation behaviour of the shaft, both includ- ing and discarding residual stress and strain, are carried out.

Abstract

In terms of lightweight design of future powertrain components, hollow shafts are of decisive importance. Conventional manufacturing processes for such components often require a considerable consumption of energy and time, especially if there are complex internal contours. In this context, an innovative cold forging process for the manufacturing of hollow shafts with variable wall thickness has been developed. The process is based on a hollow-forward extrusion process with an internal mandrel with at least two different diameters. Using a multi-axis tool, the deformation zone can be specifically adjusted during the process by means of a controllable internal mandrel. Thus, the wall thickness of the hollow shaft can be varied. As a result, the newly developed cold forging process also offers the potential for manufacturing hollow shafts with internal undercuts within one stroke. In this paper, a numerical investigation of the process and fundamental correlations will be presented.

Abstract

Most metal forming processes use lubricants based on mineral oils as an intermediate medium to reduce friction and wear. Toavoid the well-known drawbacks of oil lubrication, a novel and environment friendly lubrication system for deep-drawing processes was demonstrated at the University of Stuttgart. Liquid carbon dioxide and gaseous nitrogen are being used as volatile lubrication during the deep-drawing process, locally injected at high pressure through laser-drilled microholes. This new tribological system provides a significantly enlarged working range and at least 15% larger drawing depths compared to conventional oil lubrication.

Abstract

Technical, economic and legal requirements lead to increasing demands on lubricants in sheet metal forming. Moreover, the effects of lubricant application on the environment become more and more relevant. The long-term goal in sheet metal forming is to reduce the amount of lubricant used in order to conduct sheet metal processing without lubricants in future. Based on the efforts of dry forming, a new procedure for the lubrication of deep drawing processes with volatile media as lubricant substitution is being developed at the University of Stuttgart. This method enables the insertion of an intermediate medium under high pressure through laser-drilled microholes into the tribological system without subsequent, cost-intensive cleaning processes as the volatile media evaporate without residue when the pressure is reduced to ambient pressure. During the first and second funding period of this research project, a general applicability of volatile media as lubricant substitutes was demonstrated by means of strip drawing experiments and a simple academic test component of an Ushaped profile. For this purpose, several problems in the area of fluid supply to the tool were solved. In this report, new findings from investigations of the pressure state of volatile media in the tool contact zone, depending on number, nozzle type and arrangement of laser-drilled microholes, are presented. In addition, results of the optimized laser drilling process are included. These investigations serve as a base for the new, more realistic implementation of the new approach of dry forming in a deep drawing tool. The design of this tool for the deep drawing of a rectangular cup is presented here in detail. Initial investigations of the deep drawing process have also shown that volatile lubricants can be used to realize a significantly enlarged process window compared to conventional lubricants. This promising result shows the wide range of applications for the new tribological system in deep drawing processes.

Abstract

In order to satisfy continuously increasing regulations, further improvement of crash performance proves to be one of the major technological challenges of modern automotive engineering. It is crucial to have detailed specifications of material properties available that allow strategic material selection for various applications in future car body design. Within the scope of this work, local ductility of three 6xxx-aluminium sheet alloys is investigated based on evaluation of the localised necking behaviour in post-uniform phases of tensile tests (e.g. true fracture strain). The considered ductility criteria are gained by optical, analytical and fracture surface measurement methods. In addition to that, fracture propagation investigations are carried out to refine the ductility characterisation. The potential of local ductility characterisation methods is validated with results of the Edge-Compression Test (ECT) which allows quantification of material ductility at load conditions that occur in actual crash events.

Abstract

A reduction in material usage of cold forged components while maintaining the functional requirements can be achieved using hollow or tubular preforms. These preforms are used to meet lightweight requirements and to decrease production costs of cold formed components. To increase production efficiency in common multi-stage cold forming processes, manufacturing of hollow preforms by combining the processes backward cup extrusion and piercing was established and will be discussed in this paper. Corresponding investigations and experimental studies are reported in this article. The objectives of the experimental investigations have been the detection of significant process parameters, determination of process limits for the combined processes and validation of the numerical investigations. In addition, the general influence concerning surface quality and diameter tolerance of hollow performs are discussed in this paper. The final goal is to summarize a guideline for industrial application, moreover, to trans...

Abstract

Adiabatic softening has an important impact on material behavior under dynamic loading. Temperature rise depends on the amount of plastic work converted into heat, as well as on the quantity of heat dissipation influenced by several parameters. In order to avoid complex thermomechanical coupling in simulation, a pseudo thermomechanical model based on an analytical approach of Dixon and Parry 1 was applied in in the past 2, 3, 4, 5 considering the influence of strain rate on temperature rise. In this work the additional influence of the stress state and the size of the localized zone on temperature rise is investigated for advanced high-strength steels (AHSS). Therefore high speed tests were performed for different multiaxial stress states at loading rates ranging from isothermal to adiabatic conditions. Local strain fields were measured by high-speed video recording, and evaluated by digital image correlation (DIC), and temperature fields were recorded by high-speed infrared (IR) measurement. For shear loading, the results show a significantly larger amount of local plastic work dissipated by heat transfer until failure emergence compared to tensile loading at comparable strain rates. Hence, an extended model “adiabatic tension-shear model (ATS)” is proposed considering adiabatic softening under shear-dominated loading conditions in simulations.

Abstract

Tracking each workpiece provides two major advantages in forging technology. First, the matching of physical workpiece with the monitored process information facilitates root-cause analysis for product quality. Second, the following process steps can be adapted according to the incoming workpiece properties to improve the robustness of hot forging process chain. The paper presents a general tracking methodology and tagging experiments on aluminium and steel forgings for harsh drop-forging technology. Furthermore, a framework for streaming and processing large amounts of real-time data as well as a multidimensional approach to model and analyse the workpiece information for individual and batch-tracking are presented.

Abstract

Mit dem zunehmenden Einzug der Elektromobilität steigt in einigen Marktsegmenten der Massivumformung das Planungsrisiko zukünftiger Marktbedarfe. Immer stärker stellt sich die Frage, wie sich die Antriebstechno-logien von Fahrzeugen zukünftig verändern und welche Konzepte sich am Ende durchsetzen werden. In dieser Hinsicht gibt es seitens der Fertigungstechnik viele offene Fragen, wie einzelne Fertigungsverfahren in Zukunft weiterhin eingesetzt werden könnten. Insbesondere die Kaltmassivumformung zählt heute zu den wichtigen Technologien für die Herstellung konventioneller, an den Verbrennungsmotor angepassten Antriebsstränge. In dieser wissenschaftlichen Arbeit sollen einerseits aktuelle Entwicklungen und Trends im Bereich der Elektromobilität objektiv dargestellt werden und andererseits die daraus resultierenden potentiel-len Auswirkungen auf die Kaltmassivumformung aufgezeigt werden. Scenario volume studies of cold formed components between combustion engine and electric mobility The increasing trend towards electric mobility leads to a great uncertainty concerning the transition of drive train systems in the future. There are many unanswered questions with respect to future manufacturing technologies and importance of individual production processes for drive train components. In particular, cold forging is one of the most important technologies in the manufacturing of conventional internal combustion engine drive trains today. In this scientific work, current developments and trends in the field of electric mobility are presented. Furthermore, possible impacts on future cold forming production volumes were elaborated in this paper as well as potential opportunities to produce new components.

Abstract

Reduction in use of conventional oil-lubricates in drawing processes has been important working aims of many investigations in sheet metal forming from past until today. A completely new approach is developed at the University of Stuttgart, using volatile media like N2 or CO2 as lubrication for sheet metal deep drawing pro- cesses. Doing so, remarkable results were obtained regarding friction behaviour of this new tribological sys- tem. Sustainability, environmental protection and economic efficiency are the most outstanding advantages of this new process compared to conventional oil based lubrication. The paper includes perspective results from testing and validating the applicability of the new process in a deep drawing tool. Tracking of workpieces provides two advantages in forging technology. First, the matching of workpiece with the monitored process information makes the root-cause analysis for product quality possible. Second, the process steps can be adapted based on the incoming workpiece properties to improve the robustness of hot forging process chain. For that purpose, a general tracking methodology was developed and labelling experi- ments on steel and aluminium parts appropriate for harsh drop-forging environments has been conducted. Furthermore, a multidimensional approach to model and to analyse the workpiece information for individual and batch-tracking as well as a framework for streaming and processing of large amounts of real-time data are presented in this contribution.

Abstract

A combination of several manufacturing process steps in a simultaneous manner allows to save energy costs, reduce investment and economic logistical efforts. This paper provides the contribution reports on particular research work performed by the Institute for Metal Forming Technology, which deals with gearwheel bodies manufactured by lateral extrusion (forging). The scope of this paper focuses on the joining process and achievement of desired properties for forged wheel bodies. At the beginning of the forming process, a blank is placed in a ring having an axial and tangential profile. Due to a force application on the face surface, the material flows into the ring radially and in the following, the joint provides both a form and press fit. Since the forming and joining process is conducted in one step, the lubricant for the forming process must fulfil two requirements. First, low friction for the manufacturing process is advised. On the contrary, the joint gearwheel needs to transmit the applied load during use. In order to determine the influences of two different lubricants onto both the manufacturing processes and static torque application, experimental investigations were performed

Abstract

Since the commercial usage of compact combustion engines, eccentric shafts have been used to transform translational into rotational motion. Over the years, several processes to manufacture these eccentric shafts or crankshafts have been developed. Especially for single-cylinder engines manufactured in small quantities, built crankshafts disclose advantages regarding tooling costs and performance. Those manufacturing processes do have one thing in common: They are all executed at elevated temperatures to enable the material to be formed to high forming degree. In this paper, a newly developed cold forging process is presented, which combines lateral extrusion and shifting for manufacturing a crank in one forming operation at room temperature. In comparison to the established upsetting and shifting methods to manufacture such components, the tool cavity or crank web thickness remains constant. Therefore, the developed new process presented in this paper consists of a combination of shifting and extrusion of the billet, which allows pushing material into the forming zone during shifting. In order to reduce the tensile stresses induced by the shifting process, compressive stresses are superimposed. It is expected that the process limits will be expanded regarding the horizontal displacement and form filling. In the following report, the simulation and design of the tooling concept are presented. Experiments were conducted and compared with corresponding simulation results afterwards.

Abstract

In umfangreichen Versuchen werden die Schneidparameter „Schneidspalt“ und „Stempellänge“ mit den Werkstoffen HC340LA, DP600 und DP1000 bis zu einem maximalen Blechlagewinkel getestet. Es zeigt sich, dass hochfeste Werkstoffe bis zu einem Winkel von 17,5° prozesssicher ohne kostenintensive Schieber gelocht werden können. Daraus werden Konstruktionsrichtlinien für Werkzeuge abgeleitet.

Abstract

Nowadays, a major criterion for the quality of shear cut workpieces is characterised by a smooth final cutting surface. Normally, this surface only can be manufactured by using fine cutting or trimming technology. Major disadvantage of these processes is the complex tooling design caused by a double-acting press and corresponding tool layout. Content of this numerical study is to investigate the impact of a new sheet metal cutting tool design to increase the clean-cut portion in conventional shear cutting of high strength steel (DP600). Using FEA-Software DEFORM 2D, the models of fine cutting, conventional cutting and cutting with new tool design were mapped by comparing cutting surface results and stress distribution in the shearing zone. The main criterion of the optimization of tool design focuses on an enlarged clean-cut area along the cutting surface compared to conventional shear cutting. This study is based on the design of experiments (DOE) using Latin-Hypercube-Variation of the factors cutting clearance, die radius, punch radius, punch velocity, part holder force and special geometry designs to identify and to optimise new tool geometry. New tool design shows a significant increase of clear-cut surface up to 73% compared to conventional cutting surfaces disclosing 35% when using tools according to standard design rules. Using this new punch design, it is possible to shear high strength steels revealing a noticeably performed shearing surface quality.

Abstract

Deep drawn parts often have complex designs and must therefore be trimmed or punched in a subsequent stage. Due to the complex part geometry, most punching areas have a critical slant angle (angle between part surface and ram movement direction) which differs from the vertical direction. Such piercing within the critical range of the slant angle may lead to severe damage of the cutting tool due to bending effects on the cutting punch. Consequently, expensive cam units are required to transform the ram movement direction in order to perform the piercing process perpendicularly to the local part surface. However, the critical angle of attack described above has not yet been sufficiently investigated for modern sheet metal materials. The purpose of this study is to investigate the influencing factors and their effect on lateral punch deflection during piercing of high strength steel DP600 with slant angles using the FEM Software DEFORM 3D and to create a simulation model that enables a previously sophisticated simulation of the shearing process at different cutting angles. The aim of the study was to measure the lateral deviation of the punch when cutting with a slant angle. The calculated results show that the horizontal deviation is mainly influenced by the slant angle of the workpiece surface, the cutting line and the length of the punch.

Abstract

Current research activities at the Institute for Metal Forming Technology of the University of Stuttgart are focusing on the manufacturing of hybrid components using semi-solid forming strategies. One process investigated is the joining of different materials in the semi-solid state and is so called “thixojoining”. In this process, metallic inlays are inserted into the semi-solid forming die before the actual forming process and are then joined with a material which was heated up to its semi-solid state. Earlier investigations have shown that using this process a very well-shaped form closure can be produced. Furthermore, it was found that sometimes intermetallic phases are built between the different materials, which decisively influence the part properties of such hybrid components for its future application. Within the framework presented in this paper, inlays made of aluminum, brass and steel were joined with aluminum in the semi-solid state. The aim of the investigations was to create an intermetalli...

Abstract

Technical, economic and legal requirements lead to increasing demands on lubricants in sheet metal forming. Moreover, the effects of lubricant application on the environment become more and more relevant. The long-term goal in sheet metal forming is to reduce the amount of lubricant used in order to conduct sheet metal processing without lubricants in future. Based on the efforts of dry forming, a new procedure for the lubrication of deep drawing processes with volatile media as lubricant substitution is being developed at the University of Stuttgart. This method enables the insertion of an inter- mediate medium under high pressure through laser-drilled microholes into the tribological system without subsequent, cost-intensive cleaning processes as the volatile media evaporate without residue when the pressure is reduced to ambient pressure. During the first and second funding period of this research project, a general applicability of volatile media as lubricant substitutes was demonstrated by means of strip drawing experiments and a simple academic test component of an U- shaped profile. For this purpose, several problems in the area of fluid supply to the tool were solved. In this report, new findings from investigations of the pressure state of volatile media in the tool contact zone, depending on number, nozzle type and arrangement of laser-drilled microholes, are presented. In addition, results of the optimized laser drilling process are included. These investigations serve as a base for the new, more realistic implementation of the new approach of dry forming in a deep drawing tool. The design of this tool for the deep drawing of a rectangular cup is presented here in detail. Initial investigations of the deep drawing process have also shown that volatile lubricants can be used to realize a significantly enlarged process window compared to conventional lubricants. This promising result shows the wide range of

Abstract

Most metal forming processes use lubricants based on mineral oils as an intermediate medium to reduce friction and wear. To avoid the well-known drawbacks of oil lubrication, a novel and environment friendly lubrication system for deep-drawing processes was demonstrated at the University of Stuttgart. Liquid carbon dioxide and gaseous nitrogen are being used as volatile lubrication during the deep-drawing process, locally injected at high pressure through laser-drilled microholes. This new tribological system provides a significantly enlarged working range and at least 15\% larger drawing depths compared to conventional oil lubrication.

Abstract

Forming limit strain curves of conventional aluminium alloy AA6014 sheets after loading with non-linear strain paths are presented and compared with D-Bressan macroscopic model of sheet metal rupture by critical shear stress criterion. AA6014 exhibits good formability at room temperature and, thus, is mainly employed in car body external parts by manufacturing at room temperature. According to Weber et al., experimental bi-linear strain paths were carried out in specimens with 1mm thickness by pre-stretching in uniaxial and biaxial directions up to 5%, 10% and 20% strain levels before performing Nakajima testing experiments to obtain the forming limit strain curves, FLCs. In addition, FLCs of AA6014 were predicted by employing D-Bressan critical shear stress criterion for bi-linear strain path and comparisons with the experimental FLCs were analyzed and discussed. In order to obtain the material coefficients of plastic anisotropy, strain and strain rate hardening behavior and calibrate the D-Bressan model...

Abstract

The aim of this study is to obtain higher plastic strains in the central gauge zone of the cruciform specimen under biaxial loading without compromising the simplicity of the specimen geometry and its manufacturing. The proposed novel geometry can be produced easily by a single machining operation performed on a cruciform geometry without requiring slits or any other operation on legs. Geometry of the specimen is determined through finite element analysis. It is observed that there are three characteristic regions with continuous transition in between, in the gauge of the specimen where material deforms under biaxial, plane-strain and uniaxial tensile conditions at the same time. Achieved biaxial strains are recorded to be as high as ever reported in the literature. Success of the geometry is demonstrated through experiments.

Abstract

Das Short Cycle Stretchforming (SCS) ist ein neuartiges Verfahren des kombinierten Tief- und Streckziehens, das ursprünglich für die Herstellung von Außenhautteilen von Kraftfahrzeugen entwickelt wurde. Im Rahmen einer Weiterentwicklung wurde diese Technologie erfolgreich in den Herstellungsprozess von Dosen und Behältern aus Blech integriert und dadurch Materialeinsparungen von 3 Prozent realisiert.

Abstract

Academic and industrial interest in flexible forming has grown rapidly over the last two decades, leading to a large volume of research in this area. However, despite this interest, numerical modelling of the process is still challenging and the mechanics of the process is not yet fully understood. This paper presents fast numerical models for Incremental Sheet Forming. The models are shown to reduce computational time by up to 24 times, with a maximum shape error of 8\%. The results suggest that the approach could be used to model process within acceptable time, and could be potentially used to explore the process in more detail using solid (brick) elements.

Abstract

Folding is a process of forming cellular structures out of a flat raw material. Through this technology it is possible to create sharp-edged structures with high depths and multiple bending axes and for this reason it is part of the technical origami. Current research work at the IFU focuses on applying this technique to sheet metals with thicknesses between 0.5 – 2mm. These kinds of structures can be used for optically appealing claddings, heat exchangers or sandwich panel core materials. In previous projects, it was shown that it is necessary to pre-crease the bending axis on the flat raw material to achieve a defined folding process. For sheet metals, in particular the embossing of grooves is a promising approach. The general challenges for folding sheet metals are the forming of radii, the hardening effects emerging in the bending axis, and well-ordered design of appropriate tool concept. Also appropriate FEA models are necessary for a sufficient development of this process. The embossing of grooves itself is a bulk metal forming process and, therefore requires volume elements. Folding itself, however, is a forming process of large blanks, which is why simulations based on tetrahedral elements are extremely time-consuming. For this reason, two different models are necessary. The first model, which has integrated volume elements, simulates the folding of single folding cells targeting to detect the interaction of the embossing and the subsequent bending process. In the second model, shell elements are used, with a focus on the effect of the grooves' run rather than the effects of the embossing itself. In this paper, a FEA model for the folding of a mono cell is presented, which shows that a defined folding with small radii for sheet metals with blank thicknesses larger than 0.5 mm is possible as well.

Abstract

In this work, the experimental and numerical analysis using nonlinear strain path forming limits were studied. Forming Limit Curves (FLC) of standard and pre stretched Advanced High Strength (AHS) steel grade DP600 were obtained. These FLCs were conducted in a standard Nakajima testing device at the Institute for Metal Forming Technology (IFU). Subsequently, the experimental forming limit stress curves (FLSCs) were calculated. Additionally, the anisotropic yield criterion Barlat2000 (Yld2000-2d) was applied for describing plastic flow behaviour of the investigated steel. The Swift strain hardening law was taken into account. In order to determine material properties for different states of stress and loading direc-tions, uniaxial tensile test, balanced biaxial bulge test and disk compression test were performed for obtain-ing anisotropy parameters for Yld2000-2d. To verify applicability of IFU-FLC-Criterion to determine local-ised necking in case of nonlinear strain path, an industrial part Mini-Tunnel was pressed and simulated. The applied yield criterion showed significant influences on the calculated FLSC and the simulated strain and stress results for the Mini-Tunnel. It was shown that the nonlinear strain path IFU-FLC could describe the formability behaviour under nonlinear strain paths more precisely.

Abstract

Der vorliegende Fachartikel stellt die wichtigsten zerstörungsfreien Prüfmethoden zur Qualitätssicherung von dünnen Strukturklebungen vor. Auf diese Weise wird ersichtlich, welche Methoden neben der zerstörenden Prüfung von dünnen Strukturklebungen eingesetzt werden können, um einen Haftfestigkeitsverlust zu detektieren. Steigende Leichtbau- und Dämpfungsanforderungen an großflächige Blechbauteile sorgen trotz erhöhter Kosten für einen zunehmenden Einsatz von modernen hybriden Schichtverbundwerkstoffen in zahlreichen Konstruktionsanwendungen. In der Luft- und Raumfahrtindustrie gehören solche Werkstoffe seit geraumer Zeit zum aktuellen Stand der Technik, wohingegen diese Werkstoffkonzepte in der mobilen Großserie derzeit nur selten zum Einsatz kommen. Neben dem Materialversagen der einzelnen Schichten von Schichtverbundwerkstoffen spielt das interlaminare Versagen der Schichten untereinander eine entscheidende Rolle. In der Umformtechnik ist es möglich, dass die polymere Zwischenschicht und das Deckblech nach der Umformung noch in Kontakt stehen, obwohl die Scherfestigkeit bereits überschritten wurde. Dieser Kraftschluss der beiden Fügepartner resultiert aus den schwachen Van-der-Waals-Kräften, die eine eindeutige Detektion mit Hilfe von zerstörungsfreier Prüfung erschweren. Die vorliegende Publikation soll die Eignung diverser zerstörungsfreier Prüfverfahren auf die Detektion von sogenannten „kissing bonds“ (schwaches Anhaften der Schichten nach Versagen der Verbindung) überprüfen.

Abstract

Multicomponent processes for production of high performance gearwheels combines both high power density and high lightweight potential. In this paper, the focus is on manufacturing an assembled gearwheel using cold forging and simultaneously joining the gearwheel body and a gear ring. In this study, FEA results regarding the joining process of two different materials for assembled gearwheels are presented. The aim of the numerical investigation is to achieve a robust forging process and define appropriate tool parameters.

Abstract

In dem durch die Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF) und das Bundesministerium für Wirtschaft und Energie (BMWi) geförderten Verbund- Forschungsvorhaben „massiverLEICHTBAU“ werden verschiedene Ansätze zur In- tegration von Leichtbaukonzepten der Massivumformung verfolgt. Im Teilprojekt „In- telligenter Leichtbau durch Mehrkomponentenverfahren“ (IGF-Vorhaben: 18189N/4) werden verschiedene Konzepte zur Substitution eines Zahnradkörpers untersucht. Eine hohe Leistungsdichte bei geringerem Bauteilgewicht soll mittels „gebauter“ Zahnräder erreicht werden. Dazu wird ein hochfester Stahl für einen Zahnkranz mit hochbelastbarer Verzahnung mit einem Radkörper in Leichtbauweise kombiniert. In diesem Beitrag wird auf die erzeugten Bauteileigenschaften infolge der Fertigung von umformgefügten Zahnrädern eingegangen. Dazu wird das Verfahrenskonzept zur umformtechnischen Herstellung von solchen Zahnrädern mittels Quer-Fließpressen im Mehrkomponentenverfahren dargestellt. Dieses Verfahren erlaubt das gleichzeiti- ge form- und/oder reibschlüssige Fügen von Zahnkranz, Radkörper und Welle und ermöglicht so eine kompakte, gewichtsoptimierte Bauweise gebauter Zahnräder. Die Verwendung komplexer und hinterschnittiger Zahnkranzinnenprofilgeometrien führt zu einer form- und reibschlüssigen Verbindung. In Abhängigkeit des Zahnkranz- innenprofils wird der Einfluss auf die Unrundheit in Folge des Umformfügens ermit- telt. Dazu wird die Auswirkung der variablen Vorspannung zur Vermeidung unzuläs- siger Deformationen des Zahnkranzteilkreises infolge tangentialer Zugspannungen und im Umfang nicht konstant wirkender Radialspannungen gezeigt. Die Untersu- chung gibt Aufschlüsse über die Wechselwirkung zwischen der Zahnkranzvorspan- nung und der Zahnkranzinnenprofilexzentrizität und –kavität.

Abstract

Short Cycle Stretch Forming (SCS) is an innovative stretch forming technology developed at the Institute for Metal Forming Technology (IFU) at the University of Stuttgart. The SCS technology combines plane pre-stretching of blank and subsequent deep drawing operations within the same stroke of press ram. The sheet metal thickness is reduced while denting resistance and yield stress increases due to hardening effects.Current research work focuses on applying SCS-technology to rotational-symmetrical bodies. A process simulation for SCS-Cupping process was performed for food cans. Based on these results a tool was manufactured and commissioned. The results showed that the thickness of cup bottoms of two-piece drawn and ironed (D&I) steel cans can be reduced. Therefore, it is possible to save material costs in serial production based on a reduced blank diameter.In this paper the different effects leading to the thinning of steel can bottom and failure types, such as, wrinkling and cracking are observed in a number of experimental series. Based on these results, the tool geometry was optimized and an advanced tool was manufactured. The results of this paper show that SCS-Cupping offers promising potential to save material, as well as outlining the main effects for this technology.

Abstract

The following paper deals with the production of Interpenetrating Phase Composites (IPC) using semi-solid forming technology. Therefore, adequate ceramic foams were selected and infiltrated by processing the aluminium alloy A356 in the semi-solid state. In the studies presented in this paper, the infiltrations of two ceramic materials (Al2O3 and SiC) with three different pore sizes (10, 20 and 30 ppi) were investigated. During the forming process the liquid phase fraction of the aluminium was varied to analyze infiltration effects in relation to the raw material´s liquid phase fraction. Afterwards, microsections of the produced specimens were analyzed in order to characterize their microstructure and the quality of infiltration. The results showed that completely filled composite components with good mechanical properties can be produced by infiltrating ceramic preforms with a semi-solid aluminium alloy.

Abstract

Wrinkling is one of the primary failure modes in deep drawing of sheet metal parts. Previous studies showed that the second principle stress can be a measure for the initiation and growth of wrinkles. The wrinkling analysis is usually made with using conical cup geometries. Recent experiments and numerical simulation results at the Institute for Metal Forming Technology (IFU) showed that the wrinkling analysis using simple conical cup geometries is not suitable for description of complex wrinkling conditions for real deep drawing processes. In the presented experimental results, fender shaped geometry was chosen as an example. During deep drawing of this geometry, different wrinkling formulation mechanisms were observed. Regarding these wrinkling mechanisms, a new wrinkling limit curve can be determined. By use of this new wrinkling limit curve, it is possible to detect the occurrence of wrinkles in each area of the formed sheet metal part until the wrinkle is finally formed.

Abstract

Lubricants in sheet metal forming have to meet increasing demands resulting from political aims and ecological requirements. For that reason, industry aspires the reduction of lubrication with the long term goal of replacing conventional mineral oil based lubricants entirely. Dry metal forming to a certain limit can be achieved by using liquid CO 2 during the forming process. This lubricant vaporizes after deep drawing process and leaves a clean work piece that can be used in coating or joining processes without any subsequent cleaning. In this contribution, further development and resulting effects of numerous process parameters are evaluated and presented. Investigations of restraining forces in strip draw tests when lubricated with liquid CO 2 include different tool parameters like drilling diameters (120 and 140 µm), different numbers of drillings (25 and 49) as well as different process parameters like surface pressure (2,5 and 6,5 MPa) or drawing speed (50 and 100 mm/s). Amount of restraining forces in this paper also are compared to two different conventional mineral oil based lubricants (Wisura AK 3080 and Wisura ZO 3368). The results presented in this contribution may provide a better understanding of tribological mechanisms emerging within this new lubrication system.

Abstract

Light weight engineering in structural design and use of lighter materials are becoming increasingly important in bulk metal forming. Results gained by a DGF funded project which will be introduced in the following, concerning novel advancements of hollow lateral extrusion. Paper exhibits further development of this process, so cold forged components having undercuts without using a lateral tool plane easily can be manufactured. Thereby, the focus of attention is on the tool design as well as on the analysis of the unmodified forming process. Therefore, experimentally investigations have been carried out, failures on components are analyzed and process limitations of an experimental setup for cold forging of hollow billets at room temperature are illustrated.

Abstract

The superplastic forming process is used to form light weight components with complex features in one manufacturing step. However, the non-uniformity of the produced part thickness and the possibility of severe thinning are among its major disadvantages. The goal of this parametric study was to investigate feasible geometries for triangular channels to be manufactured by superplastic forming. The channels considered had sharp radii and served as secondary features extending along a circular path at the base of a shallow cup. An axisymmetric finite element model in ABAQUS™ was used to simulate the forming process. Effects of the aspect ratios of both the cup and the triangular channel on the thickness distribution and the pressure profiles were investigated. An experimental setup was used for validating the simulation results for AA5083 at 500 °C.

Abstract

The present paper analyses a multi-stage cold forging process focussing the final upsetting stage regarding to annular fold formation during upsetting. Recent numerical and experimental investigations showed that annular folding is not only affected by geometrical instability of tubular parts or buckling respectively but also by high local strain hardening effects interacting with forging temperature, specific material flow and surface quality of inner lateral surface of the tubular part. Depending on mentioned influencing factors three different mechanisms or kind of folds respectively have been determined and analyzed. It has been shown, that annular folding occurs at related free upsetting heights (hs/ØDo) hitherto known as uncritical if strain hardening of semi-finished tubular part is considered. A newly developed semi-empirical fold criterion for prediction of fold of 2nd-order has been implemented into commercial code DEFORM ™ and assessed using experimental data.

Abstract

Intermediate annealing is a widely used process to recover formability in multi-stage deep drawing of austenitic stainless steel sheets. A special ability of metastable austenitic stainless steel is the so called strain-induced martensite formation, which causes the TRIP-effect (TRansformation Induced Plasticity). Major issues of intermediate annealing in serial production processes are long annealing times and high costs for annealing equipment and consumed heating energy. One suggestion for optimization of this process made in this paper is to anneal austenitic material only in regions of the part where it is required and to use suitable annealing parameters. This annealing parameters need to be optimized to requirements of follow-up forming processes. Therefor, basic intermediate annealing experiments were accomplished for austenitic grade EN 1.4301 within temperature range of 100-1100°C. Measurements of mechanical properties by uniaxial tensile tests, martensite contents measured by Feritscope and micrographs are showing the development of martensite reversion as well as reconstitution of austenitic phase. Especially 400°C, 600°C and 1000°C were identified as most interesting annealing temperature levels due to formation of carbides and recrystallization. This knowledge can be used as base for further local heat treatment concepts and may enhance, simplify and save costs of intermediate annealing process of deep draw components made of stainless steel.

Abstract

Short Cycle Stretch Forming (SCS) is a new stretching process patented by the Institute for Metal Forming (IFU) of the University of Stuttgart in 2006 . It was mainly developed for outer car panels like doors and roofs with the aim of:

Abstract

Increasing demands on vehicle safety and weight reduction in the automotive industry lead to an increased use of “advanced high strength steels” for car body manufacturing purposes. Mentioned material grades are having high levels of tensile strength and are often used in conventional sheet metal forming processes. One of the most significant factors on quality of stamped components as well as its manufacturing process robustness is the friction between tool and sheet material. During the deep drawing process, superposition of tensile stresses is causing enlargement of the sheet surface by a few percent. This effect can damage the zinc layer. Due to that fact, lubricant has to keep tool and work piece separated in order to prevent adhesion and abrasion. For that very reason, sufficient amount of lubricant has to be applied onto the surface texture reservoirs. Furthermore, the viscosity of lubricant is mainly influencing its ability of wetting the surface. The aim of this study is to define the relationship between friction coefficient, surface enlargement and lubrication having different viscosities. In this investigation the same amount of lubricant with viscosity of ϑ=65 mm 2 /s, ϑ=200 mm 2 /s and ϑ=400 mm 2 /s was applied on strips made out of DP1000 and DC04 steel. Then, the strips were stretched uniaxially, and restraining forces were measured by strip draw test considering constant surface pressure and drawing speed. In this paper, the correlation between friction coefficient, viscosity and surface enlargement for two different sheet material grades is shown.

Abstract

Im automobilen Karosserierohbau werden zum Fügen von Einzelteilen zu einer fertigen Baugruppe, wie Türen oder Heckklappen, umformende Verfahren eingesetzt. Mit Hilfe eines modularen Versuchswerkzeugs konnten die Prozesskräfte und die benötigte Energiemenge während des Falzens experimentell ermittelt werden. Auf Basis dieser Erkenntnisse wurde eine Parameterstudie zur Untersuchung einzelner Parameter eines repräsentativen Falzprozesses im Hinblick auf Energiebedarfsszenarien für den Gesamtprozesse des Falzens durchgeführt. Die für den Energieeinsatz signifikanten Prozessgrößen wurden identifiziert und Möglichkeiten zur Prozessoptimierung quantifiziert.

Abstract

In recent years the process simulation of entire manufacturing chains in sheet metal forming has gained more ground on its way to be established in the validation of feasibility and the meeting of quality targets. Nowadays, especially the simulation of manufacturing automotive sheet metal components such as doors, hoods roofs etc., using the finite element analysis, belongs to state of the art in the development process of sheet metal components. The different joining technologies in the bodyshell work, such as riveting, welding etc., can be simulated by numerical methods. Rarely are any of these methods linked to the forming simulations of the previous process step. Further developments in this field should deal with new strategies, linking both the forming simulation and the joining simulation. Regarding the process chain press line forming and bodyshell work, the prediction of springback of closure assemblies is of special interest, and thereby new strategies for springback compensation have to be developed in an early stage of product development. Until now, only few experiences have been gained concerning application of method to calculate springback of an assembly, so far a reliable comparison between simulation and reality is required. For this reason in this paper a closer examination of an automotive hood assembly was carried out to develop and to validate a corresponding simulation model. Based on close-to-production experiments and optical surface measurements of outer skin components (doors, bonnets, trunk lids etc.) and their assembly prior start of series production, a new simulation strategy was developed for a consistent process chain for the press plant and bodyshell work. The assembly in this example was comprised of an inner and outer panel. For forming objectives of both parts, finite element simulations were conducted, including secondary forming operations, as for instance trimming and flanging including individual unloading sequences. In a following simulation step both parts were joined together by roller hemming. Finally, a springback analysis of the assembly was also conducted. The simulation method illustrates the possibility of predicting springback of assemblies. Furthermore, the experiments and simulations show, that the springback of the assembly leads to different final shapes than those obtained from individual components. With this method it is possible to predict the final shape and the influence of the individual components on shape and dimensional accuracy, aiding the optimization of the assembly process.

Abstract

The shape of cutting edge and cutting geometry changes in tool life due to wear. These geometrical changes of the tool are leading to non acceptable deviations from the demanded target geometry and a loss of cutting surface quality. Consequently the tool has to be inspected at regular intervals and be replaced or grinded if necessary. Prediction of such inspection intervals emerge as one of the challenges for an effective production. The inspection interval is dependent on tool life, which can be determined by cost intensive and elaborate experiments. Determination of a database containing tool life data for different production conditions actually lead to excessive waste of material and energy. Due to this fact, this paper presents a new procedure to predict the wear behavior of shear cutting tools based on a modified Archard wear model linked with finite element analysis (FEA). The Archard equation requires an empirical adjustment factor K. The intention of this paper is to highlight a potential approach to determine this coefficient without conducting long lasting tool life tests. A design method oriented approach in this paper is leading to a procedure to be able to determine wear coefficient using a chip cutting process. Though this adjustment can be accomplished within a few hours (time required for tool life test normally needs 14 days or more) with a material usage of only 0.5 % of the required sheet metal material compared to corresponding shear cutting tests. In future practitioners might look for accurate prognosis of amount of tool wear in order to reduce machine downtime and discarded parts significantly what finally saves energy, time and material.

Abstract

Materials with good mechanical properties and low density are characteristic for lightweight constructions in automotive and aerospace application as well as in the building industry. For this reason, the manufacturing of composite and hybrid materials is in focus of academic and industrial research. Because of the complex and expensive manufacturing process, the application of composite and hybrid materials in many cases is confined to niche and custom-made products. Therefore, the Institute for Metal Forming Technology (IFU) is concerned with the development of new processes for the manufacturing of metal matrix composites and hybrid components by semi-solid forming. Fibre reinforced AlSi-alloys are produced by the application of laminates made of alternating metal matrix layers and carbon fibre fabrics. Hybrid components are manufactured by the integration of higher-strength materials in the semi-solid forming process of aluminium alloys. Here, the main challenge is the integration of the reinforcing components without damaging due to high thermal and mechanical loads that are affecting during the process. These research activities are not only interesting for the mechanical engineering, but also for the civil engineering as this paper will reveal.

Abstract

Challenging automotive design in the interaction of modern lightweight strategies to reduce car body weight as well as legislative regulations, impose higher requirements for future car body development. This trend leads to thinner sheet metal blanks and indicates higher requirements for narrow process windows in the entire manufacturing process to ensure the surface quality of outer shell panels. Especially, thermal loads within the coating process might cause local shape deviation in the startup phase of a new product. Further developments in multi-material-design for car body components induce material configurations with a complex deformation behavior due to different thermal expansion characteristics of the materials involved. For these reasons, there is a need to improve the prediction of the surface quality in the early car development process using numerical simulation methods. The influence of process parameters affecting the surface quality is shown and integrated into the process simulation.

Abstract

For various reasons, manufacturers of cold-forged steel parts are becoming increasingly interested in forming at elevated temperatures below 500 °C. The objective of this study, published by the Institute for Metal Forming Technology (IFU) of the University of Stuttgart, is to evaluate the capability of various phosphate coatings in combination with MoS 2 lubrication for extrusion processes of steel parts at elevated temperatures; it emphasizes the temperature range between 250 °C and 500 °C. Temperature resistance and the lubricating effect of the tested lubrication systems were examined using the double-cup-extrusion-test. Additionally, friction factors were calculated by comparing the test results with finite-element analysis.