Electropolishing -Tool for post-processing of metallic additive manufacturing parts

Since the early 2000s, additive manufacturing (AM) has been booming thanks to the potential it offers for the rapid production of metal parts with complex shapes or sophisticated internal structures. In the early days, it was mainly used for rapid prototyping. Today, all industrial sectors have adopted the technique, which has become more profitable and enables the innovative shaping of almost all alloys, from the noblest (precious metals, copper alloys) for the watchmaking industry to the most demanding (titanium alloys, Inconel®, stainless steel, light alloys...) for aerospace and biomedical applications. Among the various existing processes, powder bed technology is probably the most widespread. Based on a 3D digital model, a part is constructed using successive layers of material and a localized input of energy to fuse the powder. A laser beam (LBM) or an electron beam (EBM) is used to fuse each successive section of the part and ensure material cohesion.

While technological progress has enabled us to produce additive manufacturing components with core mechanical and structural properties equivalent to those of forged parts, there remains a major obstacle to extending the process, and that is the extremely degraded surface condition of the parts produced. Indeed, the surface of the prototypes obtained is characterized by high roughness (Ra of up to 40 µm), a strong texture (linked to the process and manufacturing parameters) and the presence of potentially detachable infound particles. These defects are generally incompatible with the intended applications (hollow parts for fluid flow), and lead to a degradation of the material's functional properties such as increased sensitivity to fatigue and corrosion. The use of a finishing step to improve the overall surface finish, including in occluded areas such as channels and orifices, is therefore an imperative for the deployment of AF in industry. It is also a significant cost item, and a key component in the value chain.

Among the subtractive finishing techniques available (mechanical, physical or chemical), electrolytic polishing, also known as electropolishing, is a prime candidate due to its efficiency, wide industrial distribution and ease of implementation. It is an electrolytic dissolution process in which the part to be treated is anodically polarized, and therefore works in the opposite way to electroplating, as used in the electroplating industry. This article presents this technology and its recent developments, in particular for the surface finishing of metal parts produced by additive manufacturing.