In-process ultrasound NDE of resistance spot welds

Abstract

With new developments in manufacturing, a greater variety of metals are now being used in automotive structural engineering. High-strength steels, Usi-bore, aluminium and even magnesium are replacing conventional mild steels. Still, resistance spot welding remains a major technique to join these metals together. Destructive quality inspection of such welds is no longer practical when considering the huge production volumes, testing costs and reliability of the results. Thus, a new non-destructive spot weld characterisation technique is employed that uses an ultrasound transducer installed in the welding electrode, allowing for real-time quality evaluation of resistance spot welds. During welding, a series of A-scans is acquired through the centre of the heat affected zone and the liquid metal area. Additional reflections from the liquid metal can be observed when the base metal melts. An M-scan representation of successive A-scans is formed, which carries information regarding the total developed heat as well as melting and solidification rates; welding properties that affect joint quality. Using partial gating, pulse identification and tracking techniques, the M-scan is segmented into components used by higher-level algorithms to determine the quality of the resulting spot weld. Quality characterisation is performed quickly after welding, allowing for simple integration into existing manufacturing environments for real-time non-destructive evaluation of resistance spot welds.