Investigation of processes occurring above laser exposed area during powder bed fusion by optical diagnostics

Abstract

Powder-bed fusion is accompanied by the occurrence of processes such as the formation of a vapor-gas jet, the outflow of powder particles and the movement of gas masses in the laser processing zone, which must be taken into account to improve the quality of the process. In this work, the methods of optical diagnostics of the space above the processing zone were used to identify and investigate the main occurring processes. Using the Schlieren-method, it was possible to fix the emission of powder particles from the laser exposure zone and evaluate their speed and expansion angle depending on the laser processing parameters, type of material, and particle size distribution. To study the emerging vapor-gas flows, the interferometry method was used, as a result of which a spatial change in the refractive index of the gas medium was recorded. Based on the data obtained, the velocity of the jet was calculated and the flow geometry was determined. It is also shown that metal vapor makes up the majority of the observed flows.