M-scan cross-sectional imaging of resistance spot welds during welding

This paper presents a method for monitoring cross-sections of resistance spot welds in real-time during the welding process. The existing in-line system uses a single element transducer that acquires A-scans in time through the axial center of the weld to form an M-scan image of the welding process. The system being presented uses a 10 MHz 24 element linear phased array transducer specifically designed to be used in spot welding. This is used to perform cross-sectional imaging of the heat affected zone via beam-steering. The linear phased array was driven by the Ultrasound Advanced Open Platform (ULA-OP), which provides the high speed electronics needed to capture the welding process that occurs in less than 300ms. This setup provides a method to measure the nugget diameter along the imaged cross-section improving the real-time non-destructive evaluation of resistance spot welds.