2020 Volume 38 Issue 1 Pages 11-18
Laser ultrasonic technique (LUT) is applicable for measurement under high temperature condition because of the non-contact and remoteness. In this study, LUT was applied to detection the welding defect such as solidification crack and/or lack of penetration at single bevel groove during Gas Metal Arc (GMA) welding process. Nanosecond pulse laser (1064nm, 60mJ/pulse 100Hz) was used to generate ultrasonic, and was scanned using a galvanometer mirror. Nd:YAG laser interferometer (532nm, 1W) was used for detection the surface micro vibration caused by arrival of ultrasonic wave. After acquiring the B-scope, which is composed of multi transmit- and receive-points, the synthetic aperture focusing technique (SAFT) is applied. SAFT image obtained by in-process measurement was evaluated to confirm the presence or absence of welding defect indication. As a result, it was possible to indicate the solidification crack and the lack of penetration in the joint even during the welding process. Furthermore, it was able to indicate the penetration depth change (2mm difference) due to the welding condition change during process. These results suggest that in-process measurement using LUT is very effective technique for detecting weld defects.