Effect of powder particle size distribution and contouring on build quality in electron beam powder bed fusion of a medium-C hot-work tool steel

Abstract

An electron beam powder bed fusion (EPBF) printability study of a medium-C hot-work tool steel with focus on part density and surface roughness was performed using three different powder particle size distributions (PSDs) of 45–105 $$\mathrm{\mu mmm}$$ μ mmm (typical for EPBF), 20–60 $$\mathrm{\mu mmm}$$ μ mmm (typical for laser beam powder bed fusion), and a 50–50 wt.% mixture of these two powders. First, acceptable process parameter windows were generated based on as-printed density for each PSD. Full density parts (at least 99.5% dense according to NIST) were produced using the 20–60 $$\mathrm{\mu mmm}$$ μ mmm PSD and the mix PSD. Fifteen different contouring strategies were also tested for potential improvement of the as-printed side surface roughnesses, which ranged from 23.3 to 25.7 $$\mathrm{\mu mmm}$$ μ mmm among the three PSDs. Side surface roughness as low as 13.8 $$\mathrm{\mu mmm}$$ μ mmm was attained by using contouring strategies employing two contouring lines, which were typically observed to be more effective than one-line strategies. Overall, the 20–60 $$\mathrm{\mu mmm}$$ μ mmm PSD was determined to convey a better as-printed build quality over a wider range of parameters without sacrificing process productivity.