DEVELOPMENTS IN CHARACTERIZATION OF RESISTANCE SPOT-WELDING OF ALUMINUM

Automotive industry interest in aluminum is growing rapidly in Europe and North America. Resistance spot welding and weldbonding will be key techniques in the volume production of aluminum vehicles. A monitorin g system has been developed to collect process data during single-phas e alternating current (AC) and medium-frequency direct current (MFDC) inverter resistance welding. Features extracted from the captured data are used to characterize spot welding and to identify a range of proc ess phenomena. Statistical analysis has been applied to investigate th e relationship between the extracted features and the conventional phy sical parameters, e.g., weld size and static tensile strength. Welding trials using both MFDC and AC welding equipment have been carried out using aluminum of different gauges and surface conditions. Results on the Al-Mg alloy AA-5754 have shown that the monitoring methods develo ped previously for steel do not appear to be generally applicable to a luminum. No single parameter can accurately quantify weld quality. Mul tiple regression methods can, however, provide good prediction of nugg et diameter and static strength. This has proved effective even when o nly electrical variables are logged, removing the need for measurement of other process signals, e.g., electrode displacement or force.