bluuebunny/crossref_metadata_2025_split huggingface dataset:
Implementation of Real Contact Areas into Sheet metal Forming Simulations using Digital Spotting Images
Authors: Essig P. , Liewald M. , Hol J. 
Published: June 2021

AbstractIncreasing demands on quality of outer car panels and shortened product development processes fundamentally challenge automotive manufacturers. Development times are significantly influenced by the manufacturing process of dies, which are introduced by the time-consuming manual grinding operations carried out during die try-out. Blue color paste is often used to visualize contact areas between die surfaces and blank to provide a spotting image. The spotting image can be used to evaluate and optimize the pressure distribution. A homogeneous pressure distribution positively influences the forming process in terms of flange draw-in and surface quality. This paper presents an approach for implementing real contact areas into forming simulations based on digital spotting images of active surfaces. Spotting images were produced for different drawing depths and subsequently extracted by image processing. The simulation model presented in this study includes different spotting levels in conjunction with theTriboFormfriction model to describe tribological conditions during forming more accurately.
A new machine learning based method for sampling virtual experiments and its effect on the parameter identification for anisotropic yield models
Authors: Wessel A , Morand L , Butz A , Helm D , Volk W 
Published: June 2021

Abstract
A new method for sampling virtual experiments on the initial yield surface is introduced for the plane stress state. The method is based on a machine learning technique called active learning, which can be used to adaptively sample a parameter space with respect to a certain criterion. For the evaluation of this new method, it is compared against a random sampling approach taken from literature and the effect of both methods on three different anisotropic yield models, namely Yld89, Yld2000-2d and Yld2004-18p (in-plane), is analysed. The results demonstrate that the active learning based sampling approach has advantages over the random sampling approach in terms of reliability and sample efficiency. Moreover, it is found that the effect of the sampling method on the resulting yield surface depends on the anisotropic yield model considered.
Virtual die spotting: Advanced setup for coupling of forming and structure simulation
Authors: Zgoll F , Götze T , Volk W 
Published: June 2021

Abstract
Shorter product life cycles and increasing product variety in the automotive industry are leading to increasing pressure on manufacturing of stamping dies for car body parts. A high amount of manual rework is needed to meet product quality, which is one of the main drivers for long production time and high cost. The long-term goal is to meet quality requirements directly after machining of the active tool surfaces to reduce the manual rework needed to a bare minimum. This can only be achieved by taking elastic deformations of tools and press into account during the virtual die making process.
To predict the deflection at the active surfaces during the forming process, a conventional forming simulation with rigid tools is coupled with a structure simulation using elastic tools and press. For the accurate representation of the deflection behaviour of the real press, substitute models of moving bolster and ram are used, which are based on press measurement data.
In this paper, different press deformation characteristics are presented, and the viability of the universal FE substitute model is evaluated. Further, advanced settings for the coupled FE simulation are discussed and the simulation results are validated with experimentally determined data.
Towards forming simulations by means of reduced integration-based solid-shell elements considering gradient-extended damage
Authors: Barfusz O. , van der Velden T. , Brepols T. , Reese S. 
Published: June 2021

Abstract
The present contribution is concerned with the non-local damage analysis of geometrically non-linear shells. To this end, a low-order displacement-based solid-shell finite element formulation is combined with a gradient-extended damage-plasticity model. Due to a tailored combination of reduced integration with hourglass stabilization, the enhanced assumed strain (EAS) method and the assumed natural strain (ANS) method, the most dominant locking phenomena are eliminated. A polynomial approximation of the strain-like as well as the stress-like quantities within the weak forms enables the definition of a suitable and efficient hourglass stabilization. In this way, the internal element force vectors as well as the element stiffness contributions coming from the hourglass stabilization can be determined analytically. A numerical example of a circumferentially notched cylinder considering plasticity coupled with damage reveals the potential of the proposed methodology. Besides the ability to deliver mesh independent results within the softening regime, the framework is especially suitable for thin-walled structures, in which conventional low-order continuum elements suffer from well-known locking phenomena.
Development of a springback prediction for a hybrid laminate with sensor functionality
Authors: Graf A. , Kräusel V. , Rodio A. , Lanzotti A. 
Published: June 2021

Abstract
Developing the idea of lightweight construction even further, we have considered the integration of additional functionalities directly into the semi-finished product. Enormous weight savings can be achieved through integration into a large-scale production process. However, these new material composites in the form of hybrid laminates are accompanied by new challenges in terms of forming properties. In particular, there is a need to investigate how the plastic layer with sensor functionality in a hybrid laminate impacts its springback properties. To this end we designed tests using the design of experiments (DOE) technique and identified the significant factors using analyses of variance (ANOVA). Due to the material combination we had to include additional factors such as temperature and punch holding time. Our research showed an adequate distinction between springback and spring-forward behaviour. Utilising FEM, the results were simulated and compared. Our biggest challenge lay in the exact description of the interface between metal and plastic in the FEM.
A Numerical Study on Chain-Die Forming of the aluminium profiles with variable cross-section
Authors: Lu K , Liang Z , Liu Y , Zou T , Li D , Ding S 
Published: June 2021

Abstract
Roll forming is a widely used forming process of profile with constant cross-section because of its high quality, high efficiency, and low cost. However, variable cross-section profiles are becoming more common with the development of the vehicle industry while the demand can’t be met by the traditional roll forming technique. Chain-die forming is a newly introduced technique to deal with the problem. Chain-die forming extends the deformation zone by enlarging the rotation radii of the moulds. The study focused on the finite element simulations of chain-die forming aluminium profiles with variable cross-section and the comparation with high strength steels. The results showed the influence of materials such as anisotropy on wrinkling and scratch in chain-die forming and verify the finite element simulation in predicting the chain-die forming results.
Study on the influence of the strain rate sensitivity on the springback of the AA5086 alloy under warm forming conditions
Authors: Neto D M , Oliveira M C , Alves J L , Menezes L F 
Published: June 2021

Abstract
Warm forming processes have been successfully applied to overcome some important drawbacks of the aluminium alloys, such as poor formability and large springback. The virtual try-out of this type of processes requires the accurate prediction of springback. The process conditions considered in this work are the ones established for the benchmark 3 – Springback of an Al-Mg alloy in warm forming conditions, proposed under the Numisheet 2016 international conference. The material under analysis is the AA5086-H111 aluminium alloy. Its mechanical behaviour is described by a Hockett-Sherby hardening law and an orthotropic yield function. The numerical analysis of the warm forming process is performed considering different yield criteria, using a strain rate-dependent flow rule. Although the material presents a positive strain rate sensitivity at 240°C, the influence of the punch velocity on the punch force evolution is negligible due to the impact of the punch velocity on the temperature distribution in the cup. Since the hoop stress distribution on the ring (before splitting) is only slightly influenced by the punch velocity, the impact of the punch velocity on the springback is also negligible.
Effect of various shearing shape conditions for the scrap-used coining method on tensile residual stress on sheared edge
Authors: Honda Y , Yasutomi T , Yamagata M 
Published: June 2021

Abstract
Application of high strength steel for automobiles is required to achieve fulfilment of the CO2 emission regulation and improvement of collision safety. Nevertheless, high strength steel has the problem that hydrogen embrittlement and fatigue cracks are likely to occur especially on sheared edge. The previously proposed scrap-used coining method could reduce tensile residual stress on sheared edge using the scrap generated by shearing as the coining tool with a counter punch. However, the conditions this method could reduce tensile residual stress effectively were not clarified. In this report, the effects of the following shearing shape factors on residual stress on sheared edge were investigated, the size of shearing line curvature using punches with a diameter of 10 and 20 mm, positive and negative sign of curvature by testing both of the product and scrap part, and the flat and dome shape of counter punch head. Residual stress on sheared edge could be reduced in the 10 and 20 mm of punch diameter regardless of the product or scrap part. FEM analyses showed that the change of stress distribution in processing area during the scrap-used coining is caused by the shearing hole expansion and reduction and the sheared edge compression by contact of the product and scrap and these mechanisms are common to both of the parts. The dome shaped counter punch is able to reduce the coining load in addition to almost the same amount of residual stress as the flat shaped one. Thus, the tool cost decreases because the cushion pin required to get the reaction force for coining could be reduced.
A new Device for Determination of Forming-Limit-Curves under Hot-Forming Conditions
Authors: Triebus M , Gierse J , Marten T , Trôster T 
Published: June 2021

Abstract
Forming-Limit-Curves (FLCs) are widely used to characterize the forming behaviour of materials. Nevertheless, the determination of FLCs for hot forming processes is a challenging and time-consuming procedure. At the Chair of Automotive Lightweight Design, a new device for the determination of FLCs under hot forming conditions was developed. In a sealed isothermal oven atmosphere, blank holder, die and punch are used for the FLC determination relying on the DIN EN ISO 12004-2. External hydraulic forces actuate the punch and blank holder. To ensure insulation from the thermal load set inside the hot oven atmosphere an innovative cooling system with extensive use of additively manufactured components with integrated cooling channels is used. For the feed of the different deep drawing tests geometries an airlock is installed, which allows keeping the temperatures constant during the testing procedure. Afterward the forming limits for the different geometries are evaluated with optical measurement systems. The developed test rig proved the ability to determine FLCs for isothermal temperatures up to 800° C.
Local formability assessment of AHSS steels with shear cut tensile tests
Authors: Larour P , Freudenthaler J , Pauli H , Kerschbaum M , Wagner L , Felbinger A , Sonnleitner F. , Angeli J 
Published: June 2021

Abstract
As an alternative to the ISO16630 hole expansion test, the punched tensile test is increasingly popular for edge crack characterization of AHSS advanced high strength steels. In this investigation the reduction of area as well as thickness reduction at fracture in the vicinity of left/right sample edge fracture sides has been determined by means of light optical microscopy according to the Hance local formability test methodology for 10% to 40% cutting clearance in (both sided) sheared cut vs. spark eroded or milled edge conditions. An edge crack index has been defined based on the tensile sample fracture shape. Local formability tensile properties based on area reduction or average thickness reduction are more sensitive to edge condition than Axx fracture elongation values. The determination of the reduction of area at fracture is however challenging due to projection issues. The % thickness reduction at minimum thickness as well as at left/right thickness in cut edge vicinity may offer some additional information about edge crack initiation and final fracture. The shear punch edge quality (punch and die tool wear, target vs. actual clearance) should be closely monitored for accurate reproducible testing results.
Comparison of different testing approaches to describe the fracture behaviour of AHSS sheets using experimental and numerical investigations
Authors: Behrens B-A , Rosenbusch D , Wester H , Dykiert M 
Published: June 2021

Abstract
The damage behaviour of Advanced High Strength Steel (AHSS) differs from conventional deep-drawing steels due to their microstructure. For example, shear fracture can occur unexpectedly without prior necking, leading to inaccuracies using Forming Limit Diagram (FLD). An improvement of failure prediction can be obtained by the use of stress state dependent damage models, which have to be parametrised by tests at different stress states for which a wide range of methods exists. Research is still needed regarding the choice of specimen, evaluation methodology and model accuracy. For that purpose, in this study two different experimental approaches are compared to analyse the fracture behaviour depending on the stress state of the complex phase steel CP800. Therefore, tensile specimens of various geometries are used on the one hand and butterfly tests in different orientations on the other. Subsequently, the modified Mohr-Coulomb (MMC) damage model is parametrised with the determined characteristic fracture values of the respective experimental methods. For additional comparison, also an FLD is determined. The different approaches are finally compared regarding their suitability for the parameterisation of stress state dependent damage models.
A new specimen for investigating shear fracture strain
Authors: Gál V , Lukács Zs 
Published: June 2021

Abstract
In the automotive industry, the edge formability of a sheet metal part is usually defined by the Forming Limit Diagram despite its shortcomings. The success of the FLD can be explained by its easy applicability for dedicated FEM codes and physical measurements. However, the diagram covers a large range of strain paths of sheet metal parts, it does not fully specify the edge formability in the negative minor strain field, which is important for drawing operation with a small radius. This explains the great attention paid in the recent decade to the development of the shear test. Manufacturing the latest shear specimens (such as Butterfly or Smiley) is a significant cost and time-consuming process. In this paper, the applicability of a new flat shear specimen geometry was investigated, using finite element methods and physical measurements. Since the cracking can initiate on the boundary section of the flat specimen, first the effect of three different manufacturing methods (Wire EDM, laser cutting and drilling) were investigated. Based on the results a new flat specimen was created and optimized by finite element methods. The shear fracture strain of the new specimen was measured by an optical measurement system and the results were compared with the fracture strain of the smiley specimen.
Validation of Part Holder Models of Car Body Upper Line Dies for Return Stroke Loads
Authors: Burkart M , Liewald M , Wied J , Kaminsky C 
Published: June 2021

Abstract
In modern press shops, the latest press technology is used to meet today’s efficiency requirements of sheet metal body part production. Thus, for example, servomechanical press ram drives enable optimized process control through configurable motion profiles of the ram, resulting in increased stroke rates and output of the press line. However, the acceleration of moving masses arising during post-forming operations of line dies can lead to critical loads for the upper die and press ram drive. Especially the part holder of line dies causes dynamic loads when being accelerated during the return stroke. In this regard, this paper deals with the validation of dynamic part holder models on the basis of experimental data obtained by a prototype tool. Finally, design specifications could be defined using the validated dynamic models, enabling the process windows of line dies to be extended in future for robust high-speed production processes in modern press shops.
Data-driven analysis of cold-formed pin structure characteristics in the context of versatile joining processes
Authors: Romisch D , Zirngibl C , Schleich B , Wartzack S , Merklein M 
Published: June 2021

Abstract
Due to increasingly strict emission targets and regulatory requirements, especially for companies in the transport industry, the demand for multi-material-systems is continuously rising in order to lower energy consumption. In this context, mechanical joining processes offer an environmentally friendly and flexible alternative to established joining methods, especially in the field of lightweight design. For example, cold-formed cylindrical pin structures show high potentials in joining multi-material-systems without auxiliary elements. The pin structures are joined either by pressing them directly into the joining partner or by caulking with a pre-punched part. However, to evaluate the strength of the joint and to ensure the joining reliability for versatile processes, such as changing joining partners or batch variations, engineering designers currently have only limited design principles available compared to thermal joining processes. Consequently, the design of an optimal pin joint requires cost- and time-intensive experimental investigations and adjustments to design or process parameters. As a solution, data-driven methods offer procedures for structuring data and identifying dependencies between varying process parameters and resulting pin structure characteristics. Motivated by this, the paper presents an approach for the data-driven analysis of cold-formed pin structures and offers a deeper understanding of how versatile processes affect the pin characteristics. Therefore, the application of an intelligent design of experiment in combination with several machine learning methods enable the setup of a best-fitting meta-model. Resulting, the determination of a mathematical model provides the opportunity to accurately estimate the pin height considering only relevant geometrical and process parameters with a prediction quality of 95 %.
Parametric Shape Optimization of Stretch Webs in a Progressive Die Process using a Neural Network Surrogate Model
Authors: Athreya S , Weinschenk A , Steinlehner F , Budnick D , Worswick M , Volk W. , Huhn S. 
Published: June 2021

AbstractProgressive die stamping provides a solution for producing sheet metal parts in large quantities. These parts are connected to carriers by stretch webs. As the part undergoes bending and forming operations, the stretch webs are exposed to translational and rotational deformation. A suitable design of these entities is crucial to avoid failure caused by splits or excessive thinning. A common way to evaluate such designs is to use finite element (FEM) simulation. Since it is not efficient to run FEM based optimization studies for the design optimization and to enable further automation of the stretch web design, this paper is proposing the use of machine learning (ML) technologies. A surrogate model based on an artificial neural network is used as a predictor in the presented study. This neural network is used to optimize the geometric parameters of the stretch web to obtain a quality result. The model is trained using FEM results and the study shows that it was possible to obtain an accurate model with a prediction error of 5%. The trained surrogate model can be used for the optimization study. This approach is computationally inexpensive and can provide very good results.
Temperature-controlled tools for multi-stage sheet metal forming of high-strength aluminium alloys
Authors: Günzel J , Hauβ J , Groche P 
Published: June 2021

Abstract
The high-strength aluminium alloys EN AW-6082 and -7075 possess great light-weight construction potential due to their high specific strength. However, their range of applications is limited by the low cold formability and high springback in the ultra-high-strength T6 state. To extend formability, either preconditioned semi-finished products, requiring a subsequent heat treatment or temperature-supported process routes such as warm forming or hot forming die quenching (HFQ) are used. If the forming degrees achievable with these methods are not sufficient, multi-stage forming is required. The forming degrees are limited by strain hardening in case of a cold forming operation of preconditioned semi-finished products and by heat transfer between the component and the tool parts in case of temperature-supported process routes. In order to reduce or even eliminate the cooling of the component in the subsequent forming stages, a four-stage forming tool with temperature-controlled active parts was developed and its influences investigated in more detail. The paper will demonstrate how precise temperature control of the tool components contributes to an extension of the formability. In addition, reproducible and robust process conditions can be guaranteed throughout the entire process chain.
On thermal compensation of Hot-Form-Quench stamping die
Authors: Szegda D , Mohamed M , Ziane M 
Published: June 2021

Abstract
Today, most premium and EV vehicle body in white structures rely heavily on lightweight materials and lightweighting technologies to offset vehicle mass. Increased utilisation of lightweight metals is also being observed in mainstream vehicles. Press hardened steels have gained significant use, however high and ultra-high strength aluminium alloys are starting to follow as their usability is enhanced and exploited. Both material groups require hot forming technologies to be used in manufacture of vehicles components. Thermal expansion of aluminium alloys is approximately twice those of steel, and hence leads to significant material contraction during in-die quenching. This is especially pronounced for large area or long components. Therefore, stamping dies employed in the Hot-Form-Quench (HFQ) process used to manufacture lightweight components from aluminium alloys are required to be compensated for thermal expansion/contraction. This paper presents simulation methodology developed in PAM-STAMP and used to verify the level of die compensation required and the effect of the compensation on the part dimensional conformance after HFQ forming.