NDE system for the quality control of spot welding in the automotive industry

Resistance spot welding is the main joining technique used for the fabrication of body-in-white structures in the automotive industry with a typical passenger car requiring approximately 4000 welds. Good welds are characterized by the diameter of the solidified weld nugget but this dimension not only depends upon the current and pressure applied which can be controlled, but also on the profile of the spot welding electrode cap which changes as the cap is worn. The increased use of zinc coated steel has exacerbated this problem as the zinc alloys with the electrode caps which increases the rate of wear. Quality control currently requires a complete tear down of a car body once every 10 days using the chisel or peel testing method on each individual weld during which production is halted. In addition to destructive testing, offline non destructive evaluation (NDE) is carried out on approximately 25 welds of every 10th car body and if a poorly formed weld is detected, then all ten cars are removed from production. This paper presents a novel online real time ultrasonic NDE system for resistance spot welding which evaluates every weld as it is formed. Results are also presented for SEM and X-Ray analysis and SORPAS© simulations.