Product Code: ICAL05_2304

Monitoring of Nd:YAG Laser Spot Welding - Detection of Porosity Defect by Weld Sound
Authors:
Tadashi Misu, Chiba Institute of Technology; Chiba Japan
Shunro Yoshioka, Chiba Institute of Technology; Narashino Chiba Japan
T. Tokunaga, Chiba Institute of Technology; Narashino Chiba Japan
Toshiyuki Miyazaki, Chiba Institute of Technology; Narashino Chiba Japan
Yosuke Kitamura, Chiba Institute of Technology; Narashino Japan
Presented at ICALEO 2005

The generation of porosity defect is detected by analyzing the generated sound in Nd:YAG laser spot welding of stainless steel sheet (AISI304). The welding is done by a single pulse. The short-Time Fourier Transform (STFT) analysis is applied for obtaining the time dependence of the sound on the defect generation, which is classified into two frequency ranges, that is, 11 to 18 kHz (HFR) and 4 to 11 kHz (LFR). The causes of the dependence are discussed from observations of high speed photography and the molten cross sections. The HFR signal is caused by vapor generation and the LFR signal by plume generation. When the intensity of HFR signal is stronger than that of LFR at the last stage of laser irradiation, the defect is not generated, and vice versa. This can be utilized for monitoring the laser spot welding.