In-process monitoring of track geometry as a control approach for laser metal deposition

Abstract

Laser metal deposition (LMD) is an additive manufacturing process, which is used to generate large parts or for reconditioning machine components. During the process the welding tracks are affected by complex dynamic temperature-time curves that results in geometric deviations, which limits the build-up process. Therefore, complex structures are more difficult to manufacture with constant parameters. The present work describes an in-process monitoring system and first approaches of a control concept for LMD processes. It is set up using a newly developed laser triangulation sensor from Falldorf Sensor GmbH, which is trailing mounted. Due to the resistance to diffused radiation, e.g. from process light, it is possible to place the sensor close to the process zone which offers the possibility of a height control system. For the experiments, single tracks were welded from 316L powder by using a diode laser. The results show that the track width and height increase with rising laser power. Depending on the process parameter the height changes up to 29% and the width up to 58% if only the laser power is modified by 1800 W. The monitoring system forms a good basis for a later control concept, which can be used to make the process more stable in the case of complex structures.