Design and construction of a loading system for resistance welding and its dynamic properties: Optimisation of the loading system in high current density spot welding with a short energising time (1st Report)

Summary

High current density spot welding develops a large electromagnetic force between the electrodes. This electromagnetic force causes fluctuation of the load, which in turn adversely affects the weldability. The load fluctuation varies depending on the loading system stiffness, friction, or response. This paper describes the design of a loading system able to control the electrode movement together with an investigation of its dynamic properties at energising. The load is affected by the electromagnetic force and thermal expansion. The electromagnetic force increases proportionally to the square of the peak current in the opposite direction of loading, which consequently reduces the actual loading of the work. The electrode movement is controlled by a stopper and spring assembled in the loading system. In a rigid loading system with a large spring constant, the electrode movement due to the electromagnetic force is restrained, so that the load is increased by the thermal expansion. On the other hand, in a loading system with a small spring constant, the load is decreased, because the electrode movement due to the electromagnetic force is greater than the thermal expansion.