Robot-assisted non-destructive testing of automotive resistance spot welds

A commercially available matrix phased array (MPA) ultrasonic imaging system was successfully integrated into a robot-assisted automated non-destructive testing (NDT) method for resistance spot weld applications. The NDT system utilizes a dual-time gate feature, where optimized time gate positions and widths were determined for near-normal incidence inspections of spot welds in thin materials. The effects of probe contact pressure and ultrasonic beam incident angle were also studied using the robot arm. Based on the current robot-assisted automated NDT results, an optimized contact pressure of 0.5 lb, and an incidence angle of +/- 0.5(o)relative to the normal direction were determined. Under these optimum probe contact conditions, it was found that a measurement uncertainty of less than 5% can be achieved when the gate position is set to be between one-half and two-third positions of the total part thickness, along with a gate width equals to one-third of the total stack thickness.