Robust Process-controller for Nd:yag Welding

A robust process-controller was developed which maintains a fully penetrated weld. This feedback-controller is robust for various process disturbances that may occur, like variations in sheet thickness, welding velocity, focal position, shielding gas variations, etc. The signals from an optical sensor are used to design a so-called “switching” controller, which enables fully penetrated welding at a minimum amount of laser power. It is shown that the working principle of the controller is applicable to different material types, more specific different steels and stainless steels. Experiments have been carried out to show the ability to cope with varying sheet thickness and welding velocity on FeP04 mild steel. Furthermore a method is described which can be used to easily find a good set of control parameters from a single identification experiment.