A New Approach to Empirical Optimization of Laser Powder Bed Fusion Process for Ti6Al4V Parts

Abstract

Optimization of all the process parameters for laser powder bed fusion (L-PBF), considering the effects of individual parameters on Ti6Al4V fabricated parts, can be complex and challenging. Therefore, for the first time, the effects of three main variable process parameters (laser power, scan speed, and hatch spacing) on three outcomes parameters (surface roughness, bulk porosity, and production rate of parts) were studied in this work. Then, the combination of above-mentioned process parameters in the form of volumetric energy density (VED) was investigated in order to establish a practical method for optimization of process parameters for making Ti6Al4V parts with the desired quality targets, i.e., the smoothest surface, the lowest bulk porosity and a higher production rate. It was revealed that although VED is a reliable metric for the optimization of process parameters, some thresholds and ranges should be considered for all three parameters of laser power, scan speed, and hatch spacing. It was demonstrated that by employing an optimum laser power of 180 W or 270 W and changing the scan speed and hatch spacing to keep VED in the range of 50-100 J/mm3, fabrication of samples with micro-roughness Ra < 10 µm and bulk porosity less than 0.15% is achievable. In addition, the surface of the L-PBF fabricated parts may appear in two categories of surface morphology; wavy surface classified “meso-roughness topography” and non-wavy surface termed “micro-roughness”. Since there was not any correlation between the value of roughness of samples with meso-rough surface and their bulk porosity, and besides, their process parameters were far from optimized parameters, the samples with meso-rough surface were not included in the final results. However, it was realized in the samples with micro-rough surfaces, the value of their micro-roughness could accurately indicate the porosity content of Ti6Al4V samples.