In-process closed-loop control for stabilising the melt pool temperature in selective laser melting

Additive manufacturing processes are gaining more importance in the industrial production of metal components, as they enable complex geometries to be produced with less effort. The process parameters used to manufacture a wide variety of components are currently kept constant and closed-loop controls are missing. However, due to the part geometry that causes varying heat flow to neighbouring powder and solidified sections or due to deviations in the atmosphere caused by fumes within the work area, there are changes in the melt pool temperature. These deviations are not considered by system control, so far. It is, therefore, advisable to measure the melt temperature with sensors and to regulate the process. This work presents an approach that enables fast process control of the melt pool temperature and combines a closed-loop control strategy with a feedforward approach. The control strategies are tested by proof-of-concept experiments on a bridge geometry and partly powder-filled steel plates. Furthermore, results of a finite element simulation are used to validate the experimental results. Combining closed-loop and feedforward control reduces the temperature deviation by up to 90%. This helps to prevent construction errors and increases the part quality.