Modeling of Conduction Mode Laser Welding Process For Feedback Control

The response of conduction mode laser weld pool dimensions, specifically weld width, to a step change in power input has been modeled using two-dimensional heat flow analysis. The goal is to develop a simplified model suitable for feedback control. The weld pool geometry was approximated by a tear-drop shape. The workpiece thermal properties were assumed to be lumped and temperature-independent. The result was a first-order weld pool thermal model. A series of experiments was performed using different welding conditions (plate thickness, step power changes, and welding speeds) to validate the model. The weld pool image was recorded using a vision system and digitized. The process time constant as calculated by the model was of the order of $10−4$ seconds. The response of the laser machine, estimated by the least squares method, was found to be about $10−2$ seconds, which is much slower than that of the weld pool. Thus, within the constraints of the assumptions on which the model is based, the entire laser welding process is considered to be dominated by the laser machine dynamics. [S1087-1357(00)00502-5]