Gap and force adjustment during laser beam welding by means of a closed-loop control utilizing fixture-integrated sensors and actuators

The development of adaptive and intelligent clamping devices allows for the reduction of rejects and defects based on weld discontinuities in laser-beam welding. The utilization of fixture-integrated sensors and actuators is a new approach, realizing adaptive clamping devices that enable in-process data acquisition and a time-dependent adjustment of process conditions and workpiece position by means of a closed-loop control. The present work focused on sensor and actuator integration for an adaptive clamping device utilized for laser-beam welding in a butt-joint configuration, in which the position and acting forces of the sheets to be welded can be adjusted during the process (studied welding speeds: 1 m/min, 5 m/min). Therefore, a novel clamping system was designed allowing for the integration of inductive probes and force cells for obtaining time-dependent data of the joint gap and resulting forces during welding due to the displacement of the sheets. A novel automation engineering concept allowed the communication between different sensors, actuators and the laser-beam welding setup based on an EtherCAT bus. The subsequent development of a position control and a force control and their combination was operated with a real time PC as master in the bus system and proved the feasibility of the approach based on proportional controllers. Finally, the scalability regarding higher welding speeds was demonstrated.