Smooth surfaces are becoming increasingly important in many industries, such as medical, chemical or food. In some industrial areas, the mechanical treatment of surfaces (grinding and polishing) does not fulfil desired specifications. Non-abrasive methods (chemical and electrochemical) have the advantage that even complex geometries and free-form shapes can be polished. In the context of this paper, electrochemical surface treatment is considered in more detail. Both electro polishing, which is state of the art, and the novel electrolytic plasma polishing (EPP) process are presented. This paper focusses on the electrolytic plasma polishing because it has many advantages compared to the process of electro polishing. The theoretical operation of the electrolytic plasma polishing is shown. A prototype system for plasma polishing of internal surfaces of pipes was installed and a polishing head was developed. Several parameters are investigated, such as the width of the adjustable polishing head gap and different velocities v or different applied potential differences U, and first results of the average surface roughness Sa as function of the various parameters were evaluated. It can be seen that a stable polishing process can be achieved at the highest potential difference of 320 V and that the average surface roughness Sa reaches a range from 0.065 to 0.090 µm. At the same time, it has been shown that with increasing potential difference, the average surface roughness becomes independent of the width of the adjustable polishing head gap.

Electrolytic plasma polishing (EPP) is an emerging technology for polishing, cleaning, deburring and smoothing of free-formed metal surfaces. The electrolytic plasma polishing of outer metal surfaces is state-of-the-art, whereas the polishing of pipe inner surfaces has only recently been reported by the authors. A prototype system and first experimental results were presented. It was found in the previous study that the average surface roughness Sa reaches a range from 0.065 µm to 0.090 µm. The current study systematically investigates the influence of the velocity v as well as the number n of polishing passages on the average surface roughness Sa. The polishing of the pipe inner surface and weld seam are considered separately. The results show that the average roughness Sa is mainly dependent on the effective polishing time t ept of the polishing process. The average surface roughness Sa of the pipe inner surface can reach a range from 0.030 µm to 0.034 µm starting from an initial surface roughness Sa 0 of 0.719 µm, whereas the average surface roughness Sa of the weld seam can reach a range from 0.088 µm to 0.096 µm starting from an initial surface roughness Sa 0 of 0.282 µm. These ranges are achieved after an effective polishing time of approximately 25 s for both the inner pipe surface and the weld seam.