Selective Surface Feature Electropolishing of Additively Manufactured 316L Using Pulse Electrochemistry

Abstract

Electrochemical finishing of metallic surfaces is a scalable, relatively cost-effective technique that is also versatile. One of the main detractions is that the current distribution is uneven and unspecific, often leading to a lack of shape retention and, if it goes too far, inducing corrosion. Pulsing the electrical input creates an unsteady state during electropolishing, controlling the current distribution across the part. The pulse wave prevention of general non-uniform current distribution across the entire geometry instead produces local non-uniformities in the current distribution at given surface features. Many pulse electropolishing parameters can be varied to target individual surface features, including the electrolyte, pulse height, pulse width (equally and unequally distributed), time of polishing as well as the overall waveform.Additive manufacturing (AM) can produce unique, complex structures rapidly. The fast local melting of metal AM parts cool quickly due to the small area, causing unique microstructures, pores, and larger surface roughness compared to cast. AM microstructures change mechanical and chemical properties, such as strength and corrosion, compared to traditionally manufactured parts. Variations in build parameters and composition creates a complicated, feature dependent, corrosion response. By polishing the surface, some of the features, namely the corrosion resistance, wear, and aesthetics can be standardized and enhanced.In this work, we explore the underlying electrochemistry that governs pulse electropolishing. We show that controlling the electrolyte with environmentally benign chemicals ultimately influences the part dimensions that can be polished, the ability to polish, and the propensity to corrode. The pulse height, pulse width (Fig. 1), and total charge passed have an impact on different surface feature removal. We will demonstrate impact of the pulse parameters on the polishing of additively manufactured stainless steel. We go beyond simple planar geometry and apply our understanding to larger scale complex geometry parts, while maintaining near-net shape and minimizing mass loss. Figure 1