Investigation of liquid metal embrittlement of dual phase steel joints by electro-thermomechanical spot-welding simulation

A 3D electro-thermomechanical model is established in order to investigate liquid metal embrittlement. After calibration to a dual phase steel of the 1000 MPa tensile strength class, it is used to analyse the thermo-mechanical system of an experimental procedure to enforce liquid metal embrittlement during resistance spot welding. In this procedure, a tensile stress level is applied to zinc coated advanced high strength steel samples during welding. Thereby, liquid metal embrittlement formation is enforced, depending on the applied stress level and the selected material. The model is suitable to determine and visualise the corresponding underlying stresses and strains responsible for the occurrence of liquid metal embrittlement. Simulated local stresses and strains show good conformity with experimentally observed surface crack locations

Service life estimation of self-piercing riveted joints by linear damage accumulation

Tests under variable amplitude loading on self-piercing riveted components with semi-tubular rivets result in longer service lives than those calculated by linear damage accumulation. An overview of the literature shows that damage sums greater than one are found for other types of riveted joints either, while an explanation for this unusual behavior is still missing. Therefore, this behavior is examined in more detail. A correlation is shown between the damage sum and the hardness of the load spectrum. Considering this correlation, the accuracy of the service life estimation can be improved significantly

Numerical analyses of the influence of a counter punch during deep drawing

In the automotive sector, the demand for high crash safety and lightweight construction has led to an increased use of steels with higher strengths. However, the rising number of varying materials with different strengths and ductilities lead to an increasing complexity in productionmaking it more challenging to ensure robust processes. Therefore, the focus of current researches still lays on the further development and extension of forming processes to enable high productivity and reliable production. A powerful tool for an efficient optimisation and extension of forming processes is the Finite Element Method (FEM), which offers time-and cost saving potentials in the design phase. In deep drawing, the use of a counter punch offers the possibility oextending the process limits. By superimposing compressive stresses on the workpiece, the initiation of cracks can be delayed, thus higher drawing ratios can be achieved. The aim of this research is therefore the numerical investigation of a deep drawing process with a counter punch to analyse the influence on the crack initiation and identify optimisation potentials for the processFor this cause, the applied force as well as the position and geometry of the counter punch are varied and the influence on fracture initiation is evaluated. It is found that the applied force on the counter punch is the major influencing factor for crack initiation. Furthermore, it was concluded that the contact between the counter punch and the workpiece should be applied as soon as the bottom of the cup is shaped. A further improvement can be achieved if the counter punch is geometrically adapted to the bottom of the workpiece

Avoidance of liquid metal embrittlement during resistance spot welding by heat input dependent hold time adaption

Liquid metal embrittlement (LME) cracking can occur during resistance spot welding (RSW) in zinc-coated advanced high-strength steels (AHSS) for automotive production. In this study, a methodological variation of hold time is performed to investigate the process-related crack influence factors. A combination of numerical and experimental investigations confirms, that the extent of heat dissipation and re-heating of the sheet surface can be influenced and thus the degree of crack formation can be controlled in a targeted manner by the parameterisation of the hold time. The temperature and stress history of crack-free and crack-afflicted spot welds are analysed and a conclusion on the borders defining the LME active region is derived

On Welding of High-Strength Steels Using Laser Beam Welding and Resistance Spot Weld Bonding with Emphasis on Seam Leak Tightness

The design of most electric vehicles provides for the positioning of the heavy energy storage units in the underbody of the cars. In addition to crash safety, the battery housing has to meet high requirements for gas tightness. In order to test the use of high-strength steels for this sub-assembly, this paper examines welded joints utilizing resistance spot weld bonding and laser remote welding, with special regard to the gas tightness of the welds. For this purpose, the pressure difference test and helium sniffer leak detection are presented and applied. The combination of both leak test methods has proven ideal in experimental investigations. For laser remote welding, gas-tight seams can be achieved with an inter-sheet gap of 0.1 mm, even if occasionally leaking samples cannot be prevented. Resistance spot welding suits gas-tight joining with both one- and two-component adhesives. Against the background of leak tightness, process fluctuations that lead to weld spatter and defects in the adhesive layer must be prevented with high priority

Leichtbau in der Fahrzeugtechnik (2. Auflage)

Werkstoffe und vor allem die Werkstofftechnik bleiben Schlüsseltechnologien im Automobilbau. Denn nichts, das an einem Fahrzeug dargestellt wären ist nicht auch aus Werkstoffen realisiert. So auch im Leichtbau, der als "Königsdisziplin" der Fahrzeugtechnik gesehen werden kann