Thermal analysis of parts produced by L-PBF and correlation with dimensional accuracy

Abstract

Laser-Power Bed Fusion (L-PBF) is continuing to grow in use among the industrial field. This process allows the manufacturing of parts with complex geometry, good dimensional accuracy, and few post-processing steps. However, deviations can still be observed on the final parts. It is known in the literature that all of these deviations can be imputed to some extent to thermal phenomena such as overheating or thermal gradient through residual stress relaxation. The objective of this study is to reach a better understanding of the influence of the thermal properties on the dimensional accuracy of parts produced by L-PBF. To do so, an infrared camera has been instrumented inside the machine, allowing the determination of the temperature of parts during the process. Thin walls with different process parameters (laser power, scanning speed…) and nominal dimensions were manufactured and measured afterwards with a coordinate measuring machine (CMM). Thermal acquisitions were performed at different moments during the fabrication and give access to the cooling rate of the observed parts. Least square fitting has been used to approximate the cooling rate function and returns characteristic times that are used to compare the different manufacturing configurations. In the end, a correlation has been established between the process parameters, the thermal parameters, and the dimensional accuracy of the parts. Form deviations, possibly due to residual stress, have only been observed on the thinnest wall, which is also the part with the highest measured thermal gradients. Other form deviations were due to roughness.