Recent technological developments have greatly widened the range of metals used in automotive structural engineering. High strength steels, Usi-bore, aluminum, 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 huge production volumes, testing costs and reliability of the results. Thus, a new non-destructive spot weld characterization 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 are acquired through the center 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: total developed heat, melting and solidification rates; all of which 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 characterization is performed quickly after welding, allowing for simple integration into existing manufacturing environments for real-time non-destructive evaluation of resistance spot welds.
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