Plasma Polishing

ESR 6 – Plasma Polishing. State-of-the-art. 
Plasma-electrolytical polishing (PeP) is a technology to structure surfaces of metallic materials. In a typical setup, two electrodes (cathode/bath and anode/work piece), separated by an electrolyte, are connected to a DC voltage (>250V). 

PeP makes use of the establishment of a plasma film which is covering the anode surface. Electrolytical, plasma and hydrothermal processes take place, leading to a drastic reduction of roughness down to 0.01μm Ra, an increase of gloss and a change of surface properties (wear resistance, corrosion resistance). Compared to established processes (e.g. electropolishing), non-toxic electrolytes can be used and the temperature at the work piece surface does not exceed 100°C. Furthermore, the processing time and the achievable roughness are much smaller.

Plasma-electrolytical polishing is currently mostly used on parts of plain stainless steel. There are very few approaches to enhance the concept to other materials and complex geometries. Next to the development of specific electrolytes, the parameter sets need to be adapted with regard to the part’s composition, shape, active surface area pre-processing (initial roughness levels, existence of burrs).

Fingerprint concept implementation
In ESR6 project, the current limitations of PeP will be overcome through an in-depth understanding of the process characteristics that allows for an effective adaption to specific materials, geometrical shapes and roughness/ tolerance requirements of micro parts. To achieve this, ESR 6 will investigate, develop and implement in-line process monitoring systems and suitable micro geometries to establish a fingerprint feature within the PeP of complex micro parts in different materials, aiming at applications in the medical, AM, aerospace sectors (deburring, cleaning, smoothing) and micro forming tools (tribological optimised tool surfaces).

Expected progress beyond current state-of-the-art
The innovative approach of integrating:

1. In-line monitoring

2. Finger print features into the process allows for a reduction of measurement/QC effort which leads to an increase in efficiency in terms of both resources and setup/production time.

3. Knowledge-based electrolyte composition recipes enable an easy transfer to a wider range of materials.

Thus, the requirements for part/job preparation, parameter finding and adjusting as well as post-process measurement will be significantly reduced. Material-based part innovations are possible by PeP of very difficult to process metals such as Pt, Ir, Ta, Nb. The extensive knowledge gained in the project will contribute substantially to a zero-defect PeP manufacturing of micro parts with highest requirements to surface quality and accuracy such as non-invasive surgery μ-metal components.

Also relevant for ESR6: Mechanical Polishing