Modelling Electrochemical Polishing of Additive Manufactured Parts. Limits of Secondary Distribution Model in Circulating Flow

Additive manufacturing allows to design and to realize parts with complex geometries, which were difficult, even impossible, to obtain by conventional means. Nevertheless, the final surface finish obtained at the end of the 3D printing process do not fit with technological specifications especially due to high roughness levels. Thus, an additional finishing step must be implemented in order to get the expected surface finish. Electrochemical polishing is of great interest because it allows, as main advantage comparatively to tribological ones, to be able to deal with small parts exhibiting high complex shapes and/or material hard to be polished [1]. Electropolishing is an electrolytic process based on the anodic dissolution of the workpiece under constant current or potential [2]. As it is done for electroplating systems, it is nonetheless necessary to uniformize the current distribution lines in the treatment cell, in order to optimize the effect of the finishing on the whole surface of the parts. The ability to provide a relevant simulation of the processing by the help of an accurate modelling is a major issue to ensure its industrial deployment through the development of specific tools and the selection of relevant operating parameters [3]. These processes can be considered as a succession of unitary steps, in order to get the expected degree of surface state; and the simulation may be of great help in the design of the full treatment line-up. In this objective, the use of a secondary current distribution model is a useful first step and gives interesting results if special care is paid to the specificity of electropolishing processes. However, this approach faces limitations because of the agitation into the treatment cell which is not accounted for by the model. A correction is possible by integrating the influence of an average level of agitation on the polarization curves (current vs potential) used in the simulation. The present work describes this model based on secondary current distribution upgraded by considering a global agitation and presents comparison between experimental results and simulations. Eventually, even if the enhanced model improve the prediction ability of the model in term of dissolution rates and roughness reduction, some discrepancies confirms the need to reach a more accurate model, and the conclusion is that the local agitation knowledge at the surface vicinity of the surface to be polished is crucial. [1] C. Rotty, A. Mandroyan, M-L Doche, J-Y Hihn, Surface & Coatings Technology 307, 125–135 (2016) [2] P. A. Jacquet, Nature 135,1076 (1935) [3] V. Urlea, V. Brailovski, Int. J. Adv. Manuf. Technol. 92, 4487–4499 (2017) Figure 1