Simultaneous imaging and measurement of pool surface and metal transfer

Laser lines reflected from the specular weld pool surface have been used to determine the weld pool surface geometry in gas tungsten arc welding (GTAW). In gas metal arc welding (GMAW), the weld pool surface is highly dynamic and fluctuating, but laser lines reflected from the deformed weld pool surface can also be imaged. In addition, the reflected laser lines are intercepted by the droplet. While this interception adds complexity to laser lines clustering, it also provides sources to simultaneously detect the droplet. This paper focuses on extracting the droplet while still analyzing laser line deformation for a simultaneous measurement. To this end, the interception points are extracted, and the droplet is modeled by combining four separately fitted local models. To improve the reliability and accuracy, local thresholding and Gaussian filtering are proposed as preprocessing before edge detection and a polar coordinate model with closure constraint is proposed to describe the contour of the droplet. In addition, the effect of missing segments on laser lines is overcome through modeling, and the modeled laser lines are used to analyze the deformation caused by the reflecting weld pool surface. Experimental results verified the effectiveness of the proposed image processing algorithms and modeling methods. Because the droplet contour and laser lines deformed by the reflecting weld pool surface can both be extracted from the same image, a method has been established to simultaneously image and measure the weld pool surface and metal transfer process.