In-Process Monitoring of Weld Pool Geometry during Laser Welding of Magnesium Alloys

In the laser keyhole welding process, the weld pool behavior is important to determining welding quality, especially with use of assisted gas. To better monitor and control the welding process, accurate extraction of the weld pool boundary is required.  This work presents a weld pool edge detection technique based on an off-axial green illumination laser and a coaxial visual monitoring system that utilizes a CCD camera as well as some necessary optical filters.  The proposed edge detection algorithm is derived from the maximum grey-value gradient searching approach according to the difference of illumination reflecting features in captured images, which efficiently reduces the effects of imaging noises.  Experiments and image processing are conducted under various welding conditions during laser welding of magnesium alloys with a fiber laser.  Extracted geometries of weld pool are validated by comparisons with a three-dimensional transient model developed and validated to investigate the dynamics of weld pool and keyhole.