Vision-based weld pool boundary extraction and width measurement during keyhole fiber laser welding

• A coaxial monitoring system has been developed to in-process monitor weld pool dynamics in keyhole laser welding.
• Weld pool boundaries are successfully extracted by a new edge detection algorithm.
• Extracted weld pool boundaries are validated by experiments and a numerical model.
• The proposed edge detection algorithm can be implemented on various welding processes.

In keyhole fiber laser welding processes, the weld pool behavior is essential to determining welding quality. To better observe and control the welding process, the accurate extraction of the weld pool boundary as well as the width is required. This work presents a weld pool edge detection technique based on an off axial green illumination laser and a coaxial image capturing system that consists of a CMOS camera and optic filters. According to the difference of image quality, a complete developed edge detection algorithm is proposed based on the local maximum gradient of greyness searching approach and linear interpolation. The extracted weld pool geometry and the width are validated by the actual welding width measurement and predictions by a numerical multi-phase model.