Electrochemical plasma electrolytic polishing (ECPeP) for the modification of bounda-ry layer properties of metallic surfaces

• Applicant: Professor Dr.-Ing. Andreas Schubert
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556741968

Plasma electrolytic polishing (PeP) enables the polishing and deburring of electrically conductive workpieces within a few minutes. Low-concentration, water-based electrolytes are used, which are characterized by good environmental compatibility. The positive properties are off-set by high energy consumption and relatively low removal rates compared to electrochemical polishing (EC). In addition, EC generally requires highly concentrated acid solutions to localize the material removal. In summary, the problem is that both PeP and EC have processrelated disadvantages that limit the potential of both processes for finishing initially rough surfaces, for example in additively manufactured components. The pulsed, voltage-controlled, electrochemical-plasma-electrolytic polishing (ECPeP) process considered in this research project represents one possible solution. In this process, a voltage curve is set which is characterized by a processing voltage of up to 50 V, which is typical for electrochemical polishing, between plasma-electrolytic pulse phases with a processing voltage of approx. 200 V to 400 V. The plasma-electrolytic pulse phase is characterized in particular by the formation of a local gas film on the workpiece surface. This makes it possible to combine the advantages of rapid roughness reduction with a high removal rate and to dispense with the use of highly concentrated acid solutions. The primary objective of the initial project phase is to gain expertise in the ECPeP process for the post-processing of initially rough metallic surfaces, a topic that has not yet been addressed in the existing literature. This requires an in-depth scientific understanding of the periodically evolving chemical and physical mechanisms of action throughout the transition from the electrochemical (EC) to the plasma-electrolytic partial period (PeP). For this purpose, a simulation method for the description of the transient gas film formation mechanism during ECPeP is developed and validated. The developed model will be used to determine suitable parameters for a stable ECPeP process. In addition, the evaluation of the anode-related mass transport contributes to the expansion of knowledge about the chemical and physical mechanisms during ECPeP. The optical metrological evaluation of the areas near the surface of the workpiece with the high-speed camera is used to analyze the gas film behavior and also to validate the simulation model. Another focus of the experiments is the characterization of the influence of the ECPeP process parameters (frequency f, duty cycle tp, voltage U) on the polishing process and the polishing result. At the end of the first project phase, the mechanism of gas film formation during ECPeP is understood and the influence of the periodically occur-ring gas film on mass transfer is described.

• DFG Programme: Research Grants