Electropolishing of 316L stainless steel parts elaborated by selective laser melting: from laboratory to pilot scale

Abstract

Electropolishing is an effective technique for surface finishing of additively manufactured parts, compatible with complex geometries. It consists of an electrochemical dissolution in which the part to be treated is polarized anodically.The present study focuses on the development of an electrofinishing process dedicated to 316 L stainless steel elaborated by SLM. A study, performed at laboratory scale, allowed to characterize the electrochemical behavior of raw substrates (produced according to different laser scan strategies) and to define the bests operating conditions for the levelling (electrolyte composition, temperature, electrical parameters, duration…) with acceptable dissolution rates (around 5 µm/min). The transposition to a pilot unit able to process samples of several square centimeters (plates or tubes) requires a precise recalibration. Difficulties are essentially due to the high roughness of the SLM substrates (Ra ⋍30 µm, Rz ⋍ 200 µm), but also to issues related to the scale-up such as the current lines distribution that cause an inhomogeneous dissolution. To fit with the double objective of roughness decrease and geometrical integrity preservation, the use of pulsed potential shows an excellent efficiency. In such conditions, a 90% roughness decrease was measured while better preserving the shape integrity.