Penetration monitoring and control of CO 2 laser welding with coaxial visual sensing system

Abstract

This article designs a system for coaxially monitoring and penetration control in CO₂ laser welding with a visual sensor. The key techniques for imaging the keyhole and eliminating the plasma-induced severe interference have been developed. The two-dimensional image of the keyhole has been obtained clearly in real time. It shows that once the penetration status changes from “partial penetration” or “weld pool penetration” (keyhole not penetrates workpiece) to “moderate full penetration” (keyhole penetrates workpiece), a lower grayscale spot appears in the center of the keyhole image and the grayscale curve presents a concavity in the center. This criterion of penetration recognition is suitable for most welding conditions. An image processing method that compares the average grayscale of a central image window at the keyhole center (vector <i>Fc</i>) and the average grayscale of an annular window surrounding the keyhole center (vector <i>F_R</i>) has been proposed to quickly recognize “moderate full penetration”, based on which, the closed-loop control of penetration can be carried out and the weld bead can be kept at “moderate full penetration” during welding.