Control of spatter due to liquid metal expulsion in additive manufacturing

Abstract

The undesired, unpreventable, liquid metallic spatters can significantly degrade the surface quality, dimension accuracy, and mechanical properties of the manufactured parts of the laser powder bed fusion (LPBF). However, the control and prediction for spatter formation are still challenging because additive manufacturing involves many simultaneously occurring physical processes. Among the various influencing factors, vapor recoil and surface tension forces are the primary contributors to metallic spatter formation. In this work, we present a novel spatter index that captures the synthetic influence of vapor recoil and surface tension forces on the periphery of the melt pool and the metallic spatter’s formation and behavior. An analytical model, considering the influence of various process conditions (such as shielding gas, powder bed, and alloy properties), is applied to calculate the temperature field of the LPBF process, and the computed results have been rigorously tested by three alloys under various process conditions. The calculated temperature field and the alloy’s chemical composition are applied to compute the surface tension force, vapor recoil force, and spatter index. This derived dimensionless spatter index reveals insights into the formation mechanism and shows a linear relationship with the spatter’s amount and initial ejection speed for various alloys. In addition, we generate a spatter index process map for AF9629 under different process conditions. The proposed easy-to-calculate and easy-to-apply spatter index and process map offer significant potential for optimizing process conditions, mitigating metallic spatter formation, and enhancing printed components' surface quality and mechanical properties.