Effect of support structures and surface angles on near-surface porosity in laser powder bed fusion

Additive manufacturing (AM) provides tremendous design freedom, but also introduces many sources of defects. Use of AM in safety-critical parts requires an excellent understanding of these defects and their potential impacts. The most common defects studied in laser powder bed fusion (LPBF) are pores. However, most work examines average porosity in the sample bulk while failures commonly originate near the surface where stresses are often highest. This study measures the porosity in 316 SS samples manufactured by LPBF as a function of distance from the down facing surface using various scan parameters, support spacing values, and build angles. These results show that the surface porosity is often much higher than bulk porosity. While parts with small build angles (5 degrees) reach low porosity (<1 %) very quickly (<50-100 mu m), at larger build angles porosity commonly remain >1 % at depths >400 mu m. The effects of build angle are exacerbated by close support spacing values. These results show the importance of considering near surface porosity rather than just bulk values. These results provide valuable guidance in selecting build conditions and finishing requirements for PBF parts.

Automated summary

Additive manufacturing (AM) provides design freedom but also introduces defects. This study examines porosity in 316 SS samples manufactured with LPBF at different depths from the surface. Results show that surface porosity is often higher than bulk porosity, especially at larger build angles and close support spacing values. These findings highlight the importance of considering near surface porosity in selecting build conditions and finishing requirements for PBF parts.