Experimental and numerical exploration of defocusing in Laser Powder Bed Fusion (LPBF) as an effective processing parameter

Abstract

Laser powder bed fusion is a commonly used metal additive manufacturing method, which is widely used in multiple industries, including aerospace and medical orthopedics. The defocusing distance is one of the main parameters to influence the melt pool dimensions as well as the microstructure of the final parts. In this study, single-track scanning experiments of Ti-6Al-4 V at different laser focus distances were carried out and studied. The melt pool shape and dimensions of different defocusing distances were measured and analysed. With a Gaussian ray-tracing laser heat source introduced, the mesoscale CFD simulations were built to reveal the influence of defocusing on the laser absorptivity and thermal profile. Special attention to the influence of the defocusing position (above or below the focus plane) was paid. The research demonstrates the feasibility of defocusing as an important parameter to control the melt pool dimensions and the cooling rates during solidification, with quantitative guidance provided based on the numerical models.