Full penetration of a weld is an important quality demand in many laser welding applications. Furthermore for economical reasons the highest possible production speed is preferred. To achieve both goals simultaneously, process settings close to partial penetration should be applied. Consequently the risk of losing full penetration increases due to external disturbances or gradual changes in process parameters.
In this work a feedback controller is described which is able to search for and operate at the highest possible welding speed given a certain maximum available laser power while at the same time full penetration is maintained. The signal from an optical detector which is placed inside the Nd:YAG laser source is used as a feedback signal. The ability of this detector to monitor the transition from a fully penetrated keyhole to a partially penetrated keyhole weld has been used to design a ‘switching’ controller. In a first feedback control loop the laser power is used as an actuator to operate near the edge of partial penetration. The fast response of this controller can cope with sudden disturbances. A second feedback loop maximizes the welding speed utilizing all available laser power.