bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental analysis of the influence of the embossing and upsetting process on joint strength in resistance element welding with upset auxiliary joining elements
Authors: Meinhardt M , Lechner M , Merklein M 
Published: June 2021

Abstract
The use of conventional resistance spot welding in the car body shop for joining an aluminium part to a steel part is possible with the process-invention of the resistance element welding (REW) with upset auxiliary joining elements. Within this process, the challenges arise from the novel approach of combining forming process steps in the insertion of the auxiliary joining elements. Thus, the process understanding is to be compiled to the combination of the individual process steps. For this reason, the study deals with the influence of the forming process steps on joint strength of REW with upset auxiliary joining elements. The focus is set to the improvement of the positive locking and force fit considering the results of previous strength analysis. As the key result, the initial relative position of the carrier sheet and the auxiliary joining element is highlighted as the most significant factor on joint strength. The material flow, illustrated in metallographic microsections, is used to explain this effect. Based on the elaborated cause-and-effect-chains, a geometrical model is derived and validated to produce high-quality joints with high joint strength.
Joining with Friction Spun Joint Connectors – Manufacturing and Analysis
Authors: Wischer C , Steinfelder C , Homberg W , Brosius A 
Published: June 2021

Abstract
Nowadays, the production of modern lightweight structures, like a body in white structure requires a wide variety of mechanical joining processes. To fulfill the various demands, mechanical joining processes and joining elements (JE) are used. Very often, they are adapted to the application, which leads in turn to a numerous of different variants, high costs, and loss of the process chain versatility. To overcome this drawback, an innovative approach is the usage of individually produced and task-adapted JE, the so-called friction spun joint connectors (FSJC). These connectors can be modified in shape as well as in material properties. This flexibility offers high potential for lightweight design but also increases the necessary analytical effort regarding the forming process as well as the manufactured joint’s properties. Therefore, a new analysis strategy based on the Finite-Element-Method (FEM) is proposed, which numerically determines the local load bearing capacity within a given joint in order to identify the critical regions for load transfer. The process of joining element manufacturing and the analysis strategy will be described in detail and optimization results of the joints are shown. Numerical results are discussed and possible recommendations for joint manufacturing are derived.
Effect of heat treatment conditions on the fatigue resistance of press hardened 22MnB5 steel evaluated through rapid testing technique
Authors: Parareda S. , Casellas D. , Frómeta D. , Garcia-Llamas E. , Lara A. , Pujante J. , Mateo A. 
Published: June 2021

Abstract
Fatigue strength is considered as a crucial parameter for automotive applications subjected to cyclic loads during their long service life, as chassis parts. The high yield stress of press hardened steels poses them as good candidates for lightweight solutions with improved fatigue resistance. However, their high strength leads to an increase in notch sensitivity which can ruin the whole part’s integrity. This behaviour was observed in previous works on press hardened steels, where their high fatigue strength was significantly affected by the surface conditions and by heat treatment conditions. Nevertheless, press hardening steels are still good candidates to manufacture complex geometry parts reaching high performance.
Aiming at increasing the existing knowledge on the fatigue behaviour of press hardened steels, this paper analyses the fatigue performance of boron steel (22MnB5) under different time austenitizing times. Fatigue resistance is evaluated using a novel rapid fatigue testing technique based on the stiffness evolution. The method permits a fast and reliable determination of the fatigue limit. Based on results obtained with this rapid testing method, the most suitable heat treatment to mitigate fatigue notch sensitivity and then achieving the best fatigue performance for chassis applications is discussed.
Effect of strain rate on formability of 22MnB5 steel during hot stamping process
Authors: Singh Amarjeet Kumar , Narasimhan K 
Published: June 2021

Abstract
Hot stamping is a high temperature and high strain rate deformation process, which is widely used in automotive industries because of the advantages associated with the process like higher formability, no spring back, higher specific strength to weight ratio etc. When strain rate increases, the formability of materials decreases but in some conditions reversal behavior was also observed, therefore in this work, the focus is to find the effect of strain rate on thickness distribution, thickness gradient evolution and formability of 22MnB5 Steel. To capture the effect of strain rate, a wide range of high-temperature tensile tests were conducted in the thermomechanical simulator (Gleeble-3800) for different strain rates (0.01, 0.1, 1/s) under uniaxial and plain strain conditions. It is found that formability of 22MnB5 steel increases with increase in strain rate in the drawing region.
New sheet metal forming process for springback reduction by continuous stress superposition
Authors: Briesenick D , Liewald M , Riedmueller K R 
Published: June 2021

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.
Dimensionally accurate parts made of high-strength steels - compressive stress superposition instead of tool compensation
Authors: Linnepe M , Sieczkarek P , Kibben M , Botz F 
Published: June 2021

Abstract
As a result of the increasing use of high-strength and ultra-high-strength steels as part of the automobile lightweight construction strategies, the issue of dimensional accuracy of component structures is increasingly becoming the focus of toolmakers, pressed part suppliers and automobile manufacturers. In particular, the modern dual-phase steels with strengths of over 800 MPa possess-depending on the respective component geometry and the forming process employed-a pronounced springback behaviour. The compensation measures commonly used so far are more and more reaching their limits, which in turn impairs the process ability of these grades in the cold forming process. The smartform® process developed by thyssenkrupp Steel Europe AG allows the cold forming of high-strength steels with high repeatable accuracy, which significantly expands their areas of application. In this process, the tensile stresses from the forming operation causing the springback of the part are eliminated by compressive stress-superposition, which leads to high dimensional stability. There is almost no need to adapt the tool surfaces to achieve a dimensionally accurate part. How close the formed component comes to the dimensional tolerances specified by the end user is usually determined within the framework of numerical method development. In this context, the result of a springback simulation depends on various parameters. The description of the material behaviour is of major importance. Moreover, the use of extended material models can have an influence on the predictive accuracy and reduce the deviations between simulation and real material behaviour. It remains to be identified to what extent the increase in accuracy is proportional to the modelling effort.
Springback and compensation in sheet metal forming reconsidered as an ill-posed problem
Authors: Hartmann Christoph , Maier Lorenz , Volk Wolfram 
Published: June 2021

Abstract
Springback is a fundamental challenge in sheet metal forming and a critical issue with respect to part quality and dimensional accuracy. To overcome the problem, different strategies for springback compensation have emerged in recent years. In this paper, we give a review on fundamental strategies of compensation for deviations in sheet metal forming and embed them, for the first time, in a general description framework rooted in the solution of ill-posed problems. On this basis, we conclude by briefly comparing different approaches and elaborate on future challenges and chances that naturally arise from the presented problem formulation.
Comparison of different forming methods on deep drawing and springback behavior of high-strength aluminum alloys
Authors: Rigas N , Schmid H , Merklein M 
Published: June 2021

Abstract
High-strength aluminum alloys of the 7XXX series have a high potential for safety and crash-relevant components due to their advantageous density-to-strength ratio. Currently, the use of these alloys is limited because of the low formability at room temperature. By using thermal supported forming strategies, failure-free deep drawing is possible for these materials. At present, several thermal-assisted forming processes exist, but so far there is no comparison between these forming operations. For this purpose, this study compares the deep drawing behavior of the alloy AA7075 by using different thermally-assisted forming operations. Aim of this work is to enhance the understanding and comparability between different thermally-assisted forming processes for high-strength aluminum alloys. First, a thermal simulator is used to investigate the mechanical material behavior according to different temperature-time curves by using uniaxial tensile tests. Subsequently, the formability and springback behavior is determined numerically and experimentally in a model test. Finally, for one thermally assisted forming method, the experiments are scaled up to a real size process with drawbeads to validate the transferability. This study can help to improve the scientific knowledge for the use of these materials in future.
Equivalence between Localization Criteria and Fracture Criteria as Forming Limit in Failure Evaluation for 7xxx Series Aluminum Alloy Sheets
Authors: Hong J-H , Kim D 
Published: June 2021

Abstract
The equivalence between the localization criteria and the fracture criteria was validated as a forming limit for the proper prediction of failure induced by severe strain localization in the two-step hybrid forming process of 7xxx series aluminum alloy sheets at the elevated temperature. In the previous researches, an extensive and systematic method combined with sophisticated material characterization had been revisited as the localization criterion to estimate the onset of the failure without any fracture criteria. As for the fracture criteria, a deformation path and effective strain-rate sensitive fracture criterion was utilized. In the event of failure occurrence with abrupt strain localization, which has been traditionally known as the localization criteria dominant case, the fracture criteria can replace the localization criteria as a forming limit.
Simplified measurement of the strain to fracture for plane strain tension: On the use of 2D DIC for dual hole plane strain tension mini Nakazima specimens with dihedral punch
Authors: Adlafi M. , Galpin B. , Mahéo L. , Roth C. C. , Mohr D. , Grolleau V. 
Published: June 2021

AbstractA plane-strain-tension stress state leads to a minimum in ductility in most micro-mechanical and phenomenological fracture models as well as Forming Limit Curves. Hence, this stress state plays a crucial role in many applications and a reliable measurement of the strain to fracture under plane strain tension is of particular importance when calibrating modern fracture initiation models. Recently, a new experimental technique has been proposed for measuring the strain to fracture for sheet metal after proportional loading under plane strain conditions. The basic configuration of the novel setup includes a dihedral punch applying out-of-plane loading onto a Nakazima-type disc-shaped specimen with two symmetric circular cut-outs. 3D Digital Image Correlation (DIC) is used to measure the surface strains of the specimen up to fracture. In contrast to the widely used V-Bending test, the maximum obtainable strain is not limited when using this set up, and fracture will always initiate after proportional loading in a plane strain tension stress state. In the present study, a major simplification of the testing methodology is proposed, reducing from 3D DIC to a simple 2D DIC method for measuring the fracture strain. Comparisons are presented on three metals, a 1.5 mm thick DP600 steel, a 0.8 mm thick DP450 steel and a 1.2 mm thick AA2024 aluminum alloy.
Performance Evaluation of Planar Anisotropy Yield Criteria for Aluminum Sheet Forming Analysis
Authors: Ghoo B , Ichijo N , Selig M , Manopulo N , Carleer B , Suzuki W , Takizawa H 
Published: June 2021

Abstract
The present work aims making a step by identifying a set of standardized accuracy measures based on laboratory experiments. Uniaxial tension, plane strain tension, hemispherical dome, and square cup tests were conducted for a 6000 series aluminum sheet used as automotive panels. Principal strain distribution, punch height at fracture, draw-in, and wrinkling were measured and compared with numerical simulation predictions. The performance of the five yield criteria, Barlat89, BBC2005, Hill48, Vegter2017, and YSD6 (Yoshida 6th order polynomial function) was measured and evaluated using the conventional accuracy index and the proposed accuracy indexes that represent manufacturing defects encountered in practice. It is found that state of the art material models such as BBC2005, Vegter2017 and YSD6 are fully able of representing standardized material test results, which is also well reflected in the predictive accuracy of simulated hemispherical dome and square cup tests. Because earlier models such as Hill48 and Barlat89 lack in capturing a high number of experimentally determined data points, they should be used with caution even Barlat89 shows good performance in the hemispherical dome tests.
Potential use of machine learning to determine yield locus parameters
Authors: Karadogan C , Cyron P , Liewald M 
Published: June 2021

Abstract
The determination and validation of material parameters required for the finite element simulation of sheet metal forming processes can be realized by a full-field optical measurement of the deformation of a test specimen in combination with a simulation-based inverse approach. Development of such an inverse approach can be quite time consuming and requires programming skills and also expertise in FEM analysis and optimization. Emerging machine learning techniques offer a practical alternative to optimization and inverse approaches provided that the ground truth is completely known and generalized by the machine learning model. To be more precise, a machine learning model can directly compute the material parameters from the experimental measurements if the hypothetical mapping function between material parameters and deformation behavior is learned as ground truth. This paper presents such a machine learning based approach for the determination of validated yield locus parameters.
Effects of initial microstructure before cold rolling on microstructure evolution and mechanical behaviour of CGLcompatible Q&P steel
Authors: Wang Yu , Xu Yunbo , Zhang Tianyu 
Published: June 2021

Abstract
Quenching and partitioning (Q&P) steels offer impressive combination of strength and ductility that can reduce the mass and improve the crash worthiness. In order to be able to meet consumer’s durability expectations, corrosion protection and galvanizability become crucial. In this paper, based on a cold-rolled high strength steel (0.225C-0.85Si-2.02Mn-0.91Al, in wt.%) and continuous galvanizing line (CGL) compatible Q&P treatment, the effects of the initial microstructure before cold-rolling were systematically investigated by means of SEM, EPMA, TEM, EBSD and XRD. It is shown that the resulting microstructure and mechanical properties after Q&P treatment are influenced by the initial microstructure. About 10.2-16.1vol.% RA are obtained, which is potential to gain the desired mechanical stability. Compared with “Q&P sample with initial microstructure prepared by quenching and austempering (i.e., Q&P(QAT))”, “Q&P sample with initial microstructure prepared by quenching and austempering followed by tempering (i.e., Q&P(QAT&T))” obtained a higher fraction of retained austenite (16.1%RA) and relatively low carbon content, thus resulted in an excellent ductility because of better mechanical stability and consequently more effective and sustained TRIP effect at high strain. With increasing the tempering time, the tempering degree of martensite increases markedly, while it does not have strong effects on the microstructures, leading to the similar fractions of RA and properties in “Q&P sample with initial microstructure prepared by quenching and tempering for 4min (i.e., Q&P(Q&T-1))” and “Q&P sample with initial microstructure prepared by quenching and tempering for 10min (i.e., Q&P(Q&T-2))”.
Virtual design of formability for Zircaloy-4 sheet through texture control
Authors: Liu H , Deng S , Chen S , Song H , Zhang S 
Published: June 2021

Abstract
Zircaloy-4 (Zr-4) sheet is commonly used in fuel assembly structural parts as spacer grids which are subjected to high temperature and stresses, corrosive and radiation environment. The knowledge regarding the properties and the formability with respect to initial texture of Zr-4 sheet is not enough. In this paper, finite element method was used to simulate the forming process of Zr-4 sheet, and effect of different initial hardening exponent (n value) on the formability of sheet is studied. The results show formability of sheet reveals better with larger n value. However, the hardening exponent (n value) is closely related to the features of initial texture of sheet. Thus, the well-established polycrystal plasticity method, visco plastic self-consistent (VPSC) model, was used to predict the effect of different initial textures on the hardening exponent of Zr-4 sheet, and plastic deformation mechanism of different initial textures in stamping process was analyzed. The results show that a larger the hardening exponent is obtained under a smaller normal Kearn factor (Fn) of the initial texture, and the activation of prismatic slip decreases with increasing the Fn.
A novel approach for characterising the cause of disc formation by the shear cutting process in a punching machine
Authors: Niessner S , Liewald M 
Published: June 2021

Abstract
The objective of this paper is to validate a method for identifying the cause of disc formation by numerical and experimental investigations for a single-stage shear cutting process in a tool-bound punching machine. To this end, first a 2D simulation model for the deep-drawing steel DC01 is developed, which enables the sophisticated requirement of tracking the material flow behaviour in the cutting process to be met by using the FEM Software DEFORM. Furthermore, the plastic flow behaviour is measured in an equivalent experiment with strain gauges near the cutting process. Then, the measurement results from the experimental investigation are contrasted with those from the simulation and compared for reliability at the measuring position of the strain gauges. The main contribution of this paper is a numerically and experimentally performed comparative study, in which the verified results of the first investigation near the shearing process are transferred into the cutting area and are validated subsequently.
Zero-error-production through inline-quality control of presshardened automotive parts by multi-camera systems
Authors: Pierer A , Wiener T , Gjakova L , Koziorek J 
Published: June 2021

Abstract
Visual inspection often represents a bottleneck in the production chain due to limited receptivity and human fatigue. Depending on the inspection task, human classification error decisions greater than 10% are not uncommon. In order to make the manufacturing process more robust and sustainable, this paper presents innovative automated inline monitoring to realize a zero-error strategy in the field of industrial manufacturing. The central idea is to detect surface defects in the running production process by data fusion of a multi-camera system. Due to the required data analysis in conjunction with the targeted high throughput rates in production, this generates large amounts of data to process. Massively parallel hardware structures are used to enable defect detection within the production cycle. The paper especially addresses how to tackle boundary conditions in productive press-lines like the software-based mitigation of placement tolerances of parts and real-time capabilities. As a result, benefits could be achieved in terms of minimum detectable failure sizes and inspection speed, enabling 100% inline inspection of produced parts. The feasibility of the presented approach is demonstrated on realistic press-hardened deep-drawn automotive parts.
New press deflection measuring methods for the creation of substitutive models for efficient die cambering
Authors: Pilthammar J. , Skâre T. , Galdos L. , Frojdh K. , Ottosson P. , Wiklund D. , Carlholmer J. , Sigvant M. , Ohlsson M. , Argandoña E. Sáenz de , Abbasi F. , Sarasua O. , Garro A. , Rutgersson W. 
Published: June 2021

Abstract
Cost and time for die tryout are significant within the car industry, and elastic deflections of dies and presses are most commonly not considered during the virtual die design and forming simulation phase. Because of this, active surfaces of stamping dies are only cambered based on previous experiences of tool types and presses. However, almost all stamping dies and presses are unique, and available experiences are not valid for new materials. Partners within the Eureka SMART Advanced Manufacturing research project CAMBER have developed advanced deflection measuring devices to quantify the elastic deformations of presses. Using these measurements, cambering methodologies can be utilized in sheet metal forming simulations. Important breakthroughs in recent years enabling the cambering methodology consists of efficient simulation strategies for full scale simulations with elastic dies and optimization techniques for creating substitutive press structures based on measurements. Furthermore, modern press deflection measurement methods are beneficial in applications such as Industry 4.0, predictive maintenance, product quality control, etc. through a more advanced understanding and live monitoring of the press system.