Model assisted closed-loop control strategy for selective laser melting

Selective laser melting is a growing technology for the production of complex metal parts. However, the workpiece heat conduction differs for different points due to its geometry, which results in a varying melt pool temperature and a varying part quality. A desired closed-loop control of the melt pool temperature is currently missing, because the production machines have no suitable sensors or the slow measurement hinders the in-process control. For this reason, a novel control approach is presented and verified by a proof-of-concept experiment. The control consists of a model-based feedforward control using a finite element heat simulation in combination with a robust feedback control employing a pyroelectric sensor. Simulation and experimental results prove a reduction of the temperature deviation of up to 73 % compared to an open-loop approach for the tested demonstration geometry. The feedback control concept is further shown to be capable of achieving cycle durations <50 µs, which enables in-process control.