FORMING PROCESS SIMULATION OF BIMETALLIC BILLET BY EXTRUSION FOR REW METHOD

The bimetallic joining elements were designed for lap joints of thin metallic (Fe-Fe, Fe-Al) as well as metallic – nonmetallic (Fe-PMMA, Al-PMMA) sheets by Resistance Element Welding (REW). The Cu tubes with an outer diameter of 4 mm, wall thickness of 0.5 mm, and a length of 11 mm filled with a solder Sn60Pb40 were used for the bimetallic joining elements producing. The required shape of joining elements is obtained by cold forming. Simulation by ANSYS software was chosen for the optimization of the forming process and geometry of functional parts of the forming tool allowing to use only one extrusion forming operation. The simulation results are stresses, strains, and modification of cross-section geometry of elements for the three proposed forming modes. The geometry of functional parts of the forming tool was compared with the results of cross-section macroanalysis of joining elements.

Joining of ultra-high-strength steels using resistance element welding on conventional resistance spot welding guns

Single-step joining of dissimilar material combinations between ultra-high-strength steels and high-strength aluminium alloys with sufficient mechanical joint properties by using conventional resistance spot welding equipment has not been reported yet. In this research paper, a novel single-step joining technology, so-called self-penetrating resistance element welding, is introduced. First, the motivation for this novel joining technology, the state of the art in joining, and the process characteristics are presented. In the results section, the welding rivet geometry is first determined using forming simulations and validated by head tensile tests. Followed by the description of the welding process and its characteristics, the mechanical joint properties are reported. The results show that a numerically optimised welding rivet geometry can guarantee sufficient joint strength. By this welding rivet geometry, a thermally assisted penetration of aluminium and therefore welding to steel is possible with and without adhesive. Furthermore, it is shown that the welding process can be designed by means of simulations. Finally, the shear tensile tests prove that an overall sufficient joint strength is ensured.

Preventing Nugget Shifting in Joining of Dissimilar Steels via Resistance Element Welding: A Numerical Simulation.

Joining the advanced high strength steels and the conventional steels is a critical issue for the manufacturing of lightweight vehicles. Resistance element welding (REW) is an emerging joining method for dissimilar metals and alloys by applying an auxiliary rivet-like resistance element in resistance spot welding (RSW). In this study, an electrical-thermal-mechanical coupled REW model for high-strength dual-phase (DP) steel and Q235 steel was developed by considering contact resistances as functions of temperature and surface contacting area. The results show that the welding element in REW serves to concentrate the current flow and thus Joule heat generation at the faying interface between the element and workpiece. For welding DP600 and Q235 workpieces with a small thickness ratio (≤0.4) or a high electrical resistivity ratio (≥3), REW could effectively mitigate nugget shifting between workpieces and reducing the thermal excursion to electrode as compared to RSW. Adding well-designed insulation layers in REW could further concentrate the current within the welding element, and enables a large-sized nugget at a lower current. This study is significant because it provides a better understanding to the electrical-thermal-mechanical behaviors with interfacial contacts in REW and contributes to its further advance.