Non-contact in-process ultrasonic screening of thin fusion welded joints

Joining of metal structures, or welding, plays a critical role in our modern world, where safety welds thin sheet metals are used pipework, nuclear cannisters and aircraft ducting among others. A potential failure such could prove to be catastrophic, hence the need for thorough inspection testing. With ever-increasing automation welding operations, manually deployed Non-destructive Evaluation (NDE) has become major bottleneck supply chain. This paper introduces first time, non-contact gas-coupled ultrasonic sensors in-process during weld deposition, screening penetration directly at point manufacture. 3 mm thick mild steel plates were butt-welded together using Gas Tungsten Arc Welding (GTAW) while air-coupled transducers, generating surface guided Lamb waves, performed seam. Optimised Signal-to-Noise Ratio (SNR) was achieved through customised acoustic matching layer, low-noise amplifiers real-time signal processing. By performing multiple trials varying levels input power (0.59 kJ/mm 1.03 kJ/mm), it demonstrated that amplitude transmission A0 wave is correlated Weld Penetration Depth (WPD) can on-line quality screening. Advantages outlined method include higher production rates, reduced scrap regards welded components.