Non-Contact Determination of Nugget Size of Spot-Welding Using Focused Air-Coupled Ultrasound

Abstract

Since the size and shape of a nugget of a spot weld are closely related to the bonding strength of the weld, their quantitative evaluations are very important to improve the reliability of the welded structures. In this work, a focused air-coupled ultrasound technique has been used for non-contact measurements of spot welds of steel plates. One-dimensional scanning in transmission configuration using a pair of focused air-coupled ultrasonic transducers operating with tone burst waves at 0.3 MHz is performed to obtain the amplitude profile of the transmitted ultrasound through the nugget area of a spot weld. A simple method for determining the nugget size from the amplitude profile is proposed. The validity of the method is verified using a calibration sample which imitates a spot weld. The proposed method has then been applied to the evaluations of spot welds fabricated with different electric currents.