Influence of the CNC behaviour on the laser spot trajectory in LPBF process

The quality of the parts produced in additive manufacturing by laser powder bed fusion (LPBF) depends on the understanding of all the physics involved in the process. In LPBF, the effective path of the laser spot is rarely studied and existing works are mainly focused on the choice of the scanning strategy and its parameters. However, the programmed scanning path during the CAM stage is adapted by the numerical control (NC) unit of the manufacturing machine in order to generate admissible setpoints for the actuators (galvanometers). This modification locally generates deviations on the scanning path and significant decrease of the laser spot velocity. In order to identify the NC unit behaviour, a test bench that replicates an industrial machine has been developed. This test bench allows the acquisition of the setpoints sent to the actuators and their real positions at a frequency of 100 kHz, as well as the energy deposited by the laser spot in the work plane. An analysis of those data shows that the processing done by the NC is based on a filtering method which in some cases can generate a deviation of the scanning path of more than 100 µm for a programmed speed of 2 m/s. Finally, in order to correctly estimate the amount of energy brought by the laser on the powder, a dedicated model has been developed. This model takes into account the dynamics of the actuators, the behaviour of the NC unit and the optical chain of the system. Experimental tests have been conducted to validate the simulations produced by the proposed model.