Selection of Optimal Process Parameters to Obtain Defect-Free Builds in IN718 Made by Laser Powder Bed Fusion

This study investigates the effect of four major process variables viz. laser power, scanning speed, hatch distance and powder bed thickness on the densification behavior of Inconel 718 (IN718), with a view to obtain defect free builds during laser powder bed fusion (L-PBF) process. In order to determine the causes of defect generation, samples with different process variables were printed and examined microstructurally. Samples printed as per Taguchi’s L9 orthogonal array have exhibited different types of microscopic defects such as porosity, lack of fusion (LOF) and cracks. Based on detailed study, the optimized process parameters for obtaining defect free IN718 builds were found to be with a laser power of 320 W at a scanning speed of 850 mm/s and a hatch distance of 0.11 mm. LOF and un-melted tracks have formed at low volume energy density (VED) while porosity was found at high VED values. Cracks are most evident in XZ plane, and the formation of such cracks is high at high laser power and scanning speed. Although VED represents the energy input to the process, it should no longer be considered a process parameter, as multiple combinations of input process variables with different performance characteristics can result in the same value. This aspect has been demonstrated in this paper with experimental data. A Modified Taguchi’s approach has been followed in this study to develop empirical relationships to the performance characteristics (density), in terms of process variables and demonstrated their validity through comparison of test data. The method suggests few tests as per the orthogonal array and provides complete information for all combinations of levels and process variables. This method also provides the estimated range of output responses so that the scatter in the repeated tests can be assessed prior to the tests.