Surface finishing of additively manufactured stainless steel surgical instruments

Additive manufacturing (AM) has the potential to revolutionise the fabrication of complex surgical instruments. However, AM parts typically have a higher surface roughness compared to machined or fine cast parts. High surface roughness has important implications for surgical instruments, particularly in terms of cleanliness and aesthetic considerations. In this study, bulk surface finishing methods are described to produce end-use selective laser melting parts.

The aim was to achieve a surface finish as close as possible to machined parts (Ra = 0.9 µm, Wa = 0.2 µm, Pv = 7.3 µm). A sample coupon was designed to systematically evaluate different finishing techniques. Processes included bulk finishing, blasting and centrifugal finishing methods on individual parts, as well as heat treatment before and after surface finishing.

Abrasive blasting or centrifugal finishing alone was not adequate to achieve an end-use surface finish. White oxide vapour blasting at high water pressure was the most effective of the abrasive blasting processes. For centrifugal finishing, a 4 h runtime resulted in an acceptable reduction in surface roughness (Ra = 2.9 µm, Wa = 2.0 µm, Pv = 34.6 µm: inclined surface [30°]) while not significantly increasing part radii. The combination of finishing methods resulting in the smoothest surfaces was white oxide blasting followed by 4 h of centrifugal finishing and a final glass bead blast (Ra = 0.6 µm, Wa = 0.9 µm, Pv = 6.9 µm: inclined surface [30°]). The order of these methods was important because white oxide blasting was significantly less effective when applied after the centrifugal finishing.

Collectively, these results describe the development of a practical bulk finishing method for stainless steel surgical instruments produced by AM.