Performing an Indirect Coupled Numerical Simulation for Capacitor Discharge Welding of Aluminium Components

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.

WELDING OF NITINOL BY SELECTED TECHNOLOGIES

Nitinol is a perspective alloy that is difficult to weld because of its high sensitivity to heat, atmospheric gases and the NiTi phase instability. We evaluated several welding techniques with regard to their applicability to weld fine pseudoelastic NiTi wires. Namely, we tested the microplasma arc, laser, electron beam, resistance and capacitor discharge welding. In conclusion, the behaviour of the weld for any of the implemented welding techniques is similar; it leads to a loss of mechanical properties in the welded joint caused by a recrystallization and an increased amount of brittle intermetallic phases. Yet, under perfect shielding and with a minimum heat input, the welds could, as a whole, retain the majority of their properties, and, as such, have the desired properties close to the base metal.