Characterization of physical processes in the process zone during free jet-based plasma electrolytic polishing

• Applicant: Professor Dr.-Ing. Andreas Schubert
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536840529

Jet-based plasma electrolytic polishing (Jet-PeP) enables local polishing of part sur-faces made of electrically conductive materials without need for masking and with low consumption of environmentally friendly electrolytes. It based on plasma electro-lytic polishing in a bath, where chemical-physical processes stimulate the formation of a local vapor-plasma-zone (VPZ) on the workpiece surface. This occurs when a DC electrical voltage is applied, provided a suitable combination of workpiece mate-rial, electrolyte composition and electrolyte temperature is used. This VPZ is a basic requirement for the successful initiation and continuity of the process. However, in the context of Jet-PeP, the formation and continuity of this zone has been insuffi-ciently studied and is therefore poorly understood. A specific and reproducible ad-justment of the process conditions is hardly possible, especially in case of devia-tions from the few known parameter combinations. In the present research project, the influence of the electrical and thermal energy supply on the initiation and continuity of the VPZ in the Jet-PeP process will be in-vestigated. For this purpose, the free jet is divided into characteristic zones along the flow direction of the jet. The proportions of which are investigated at the working dis-tance between the nozzle and the workpiece surface at different energy inputs. By varying the applied DC voltage, the characteristic current-voltage curves of the pro-cess initialization and the polishing process will be derived for Jet-PeP. Further-more, the influence of the flow velocity of the electrolyte jet on the formation and continuity of the VPZ in connection with the electrolyte temperature will be investi-gated. For this purpose, the electrical and thermal measurement equipment of the existing Jet-PeP setup has to be adapted and expanded. The spatial expansion of the VPZ and the process-immanent gas formation will be analyzed with a high-speed camera and image evaluation. The charge efficiency based on the electric charge of anodic dissolution and the electrolysis as well as the heat transfer between electrolyte and workpiece based on the thermal energy supply will be derived from the recording of the temporal charac-teristic of electric current and voltage as well as the electrolyte and workpiece tem-perature. The measurement analysis of the machined workpiece surfaces is used to evaluate the local polishing process and enables a differentiation between EC and PeP removal processes. Based on the experimentally received findings on the in-fluencing variables and sub-processes, it is aimed to get a first physical model for the effect of the electrical and thermal energy input on the formation of the Jet-PeP process and the VPZ.

• DFG Programme: Research Grants