Electrodes for resistance spot welding inevitably wear out. In order to extend their service life, the tip-dressing process restores their original geometry. So far, however, the point in time for tip-dressing is mainly based on experience and not on process data. Therefore, this study aims to evaluate the in-situ or inline wear during the welding process without using additional sensors, and to base the timing for tip-dressing on continuous process monitoring, extending electrode life even further. Under laboratory conditions, electrode wear is analyzed by topographical measurements deepening the knowledge of the known main wear modes of resistance-spot-welding electrodes, mushrooming and plateau forming, and characterizing an electrode length delta over the number of spot welds. In general, electrode wear results in deformation of the electrode contact area, which influences process parameters and thereby weld quality. The conducted tests show correlation between this deformed contact area and the electrode length delta. The study shows that this electrode length delta is visible in actual process data, and can therefore be used as a criterion to characterize the wear of electrodes. Furthermore, this study gives reason to question commonly used spot-welding quality criteria and suggests different approaches, such as basing spot-welding quality on the possibility of nondestructive testing.

Capacitor discharge welding (CDW) for projection welding provides very high current pulses in extremely short welding times. This requires a quick follow up behaviour of the electrodes during the softening of the projection. The possibilities of experimental process investigations are strongly limited because of the covered contact zone and short process times. The Finite Element Method (FEM) allows highly resoluted analyses in time and space and is therefore a suitable tool for process characterization and optimization. To utilize this mean of optimization, an indirect multiphysical numerical model has been developed in Ansys Mechanical APDL. This model couples the physical environments of thermal–electric with structural analysis. It can master the complexity of large deformations, short current rise times and high temperature gradients. A typical ring projection has been chosen as the joining task. The selected aluminium alloys are EN-AW-6082 (ring projection) and EN-AW-5083 (sheet metal). This paper presents the investigated material data, the model design and the methodology for an indirect coupling of the thermal–electric with the structural physic. The electrical contact resistance is adapted to the measured voltage in the experiment. The limits of the model in Ansys Mechanical APDL are due to large mesh deformation and decreasing element stiffness. Further modelling possibilities, which can handle the limits, are described.

The amount of aluminium sheets in future body-in-white concepts is still on the rise. There is a need for optimizing the joining techniques, caused by the different characteristics compared to the established steel components. Especially the electrode life for resistance spot welding as a reliable and established process needs to be improved. One reason for the short electrode life when welding aluminium is the insulating effect of the aluminium oxide layer. One possibility to reduce the electrode wear is the mechanical destruction of the oxide layer before the welding. This paper describes the influence of a translational and rotational electrode movement on the electrode wear. The oxide layer destruction is detected by resistance measurement. It could be shown that the destruction of the oxide layer already occurs at low movements. However, a homogeneous, large-area destruction is necessary for a wear reduction.