104 空気超音波によるスポット溶接部の非接触評価に関する検討(構造部材や加工プロセスの信頼性を支える計測・評価技術)

Abstract

Spot-welding technique is widely used in the various fields of engineering and industries. Since the size and quality of the nugget which is melted and re-solidified part of a welding are closely related to the strength of the welded structure, it is important to estimate the diameter and mechanical property of the nugget quantitatively. In this work, an air-coupled ultrasound technique employing focused transducers has been used for non-contact measurements of a spot welding. Transmission C-scan measurements were performed using a pair of focused transducers operating with tone burst waves at 0.4 MHz. Signal processing techniques, an averaging, a band-pass filtering, and a matched filtering are used to improve the signal to noise ratio of the measured results. It has been found that the C-scan images using the matched filtering have a high signal to noise ratio even though a small number of data is used for averaging.