Relationship between loading properties and resistance weldability, and an optimum loading system for weldability: Optimisation of the loading system in high current density spot welding with a short energising time (2nd Report)

Summary

The load is an important factor in spot welding. In high current density spot welding with a short energising time, the electromagnetic force increases proportionally to the square of the peak current in the opposite direction to the load direction, which consequently reduces the actual loading of the work. This paper describes an investigation of the effect of the loading properties on the weldability and the design of an optimum loading system for high current density spot welding with a short energising time. In a loading system with a small spring constant, the nugget forms under low current conditions, but defects readily form at the interface, and the load decreases because the electrodes move in response to the electromagnetic force. In a loading system with a large spring constant, it is difficult to produce welded joints because the electrode movement is restrained, and the load is increased by the thermal expansion. This feature more strongly affects a material with a high thermal conductivity, such as Al alloy. In high current density spot welding with a short energising time, it is important to design the loading system with regard for equivalence between the thermal expansion and the electrode displacement due to the electromagnetic force.