Machining of titanium-based materials using the hybrid Mechano-Electrochemical Milling process

This research aims the investigation and development of a novel hybrid machining process, called “Mechano‑Electrochemical Milling” (MECM). The combination of milling and Electrochemical Machining (ECM) can extend the range of machinable materials and increase the performance of ECM. The considered materials in this research are titanium-based because of the typical interaction between ECM and titanium‑based materials. This interaction implies the formation of a passivating layer hindering the ECM process. The MECM process aims to remove the passivating layer mechanically in order to push ECM to its full potential.

To enable detailed investigation of the up‑to‑now non‑existing process in order to get an in-depth understanding of the material‑process interaction in MECM, a new machining platform was developed in this research. The developed platform consists of: a mechanical system which enables positioning and rotation of the tool and workpiece, an electrical system which provides the electric current high enough to enable (M)ECM, and an electrolyte system which conditions and provides the electrolyte to the process. The MECM tool combines the electrochemical and mechanical process components and allows adjustment of the relation between those components.

In the investigation, two simultaneous process mechanisms, mechanical and electrochemical, have been identified. An increase of the material removal rate up to 11 % has been observed for MECM compared to pure ECM on the same platform, and both the shape of the machined geometry and the removal rate were found to be more consistent for MECM compared to ECM. In contrast with the promising results on material removal rate and shape geometry, ECM and MECM with the MECM tool did result in high roughness values of 3 µm Ra or more.

Although the current implementation of MECM shows some potential drawbacks when looking purely at the process stability of the electrochemical component, overall, the process output seems to be rather positively impacted by MECM compared to ECM. The detection of some specific weaknesses during this investigation offers clear opportunities to improve the MECM behaviour and, potentially, to improve the MECM results as well. Therefore, setting the first (small) steps in the development and investigation of the MECM process, paving the road for further improvement of the process and more extensive research on the process-material interaction, is probably the largest achievement of the work described in this dissertation.