Micro-electrical discharge machining

Micro-electrical discharge machining (ESR 3). State-of-the-art
Micro Electrical Discharge Machining (micro-EDM) milling is one of the variants of the EDM process for generating accurate μ-features on advanced engineering materials (e.g. conductive ceramics, cermet, hardmetals, tool steels. Usually a cylindrical tool of diameter down to a few tens of μm is sued to remove/mill the material layer by layer.

Since material is also removed from the tool electrode, tool wear need to be effectively compensated in EDM processes. In a layer-bylayer strategy (micro-EDM milling), the linear anticipated tool wear compensation method is the most often used. Due to complex non-linearities in the sparking process, it is still a challenge to achieve high accuracy in micro-EDM milling process, and to compensate by post-process metrology the tool wear.

Real-time tool wear compensation by discharge counting has been demonstrated. Recent research at KU Leuven has observed that RC pulses in the finishing regime of micro-EDM often display a negative part of current flow at the end of the positive part. The negative pulse parts have been reported as leading to excessive electrode wear. It is still unknown how and why it influences the material removal mechanism in the μ-EDM process.

Fingerprint concept implementation
The focus of the research of ESR3 will be in the finishing regime of the micro-EDM process and the reasons are twofold: the finishing process determines the results and quality of part; the parameter settings in the finishing regime result in more stable and predictable sparking phenomena. With indepth and systematic DoE (Deign of Experiment) analysis of the micro-EDM settings, ESR3 will build up the
relationship between the sparking phenomenon and the local material removal through in-process sparking analysis and on-machine metrology. With the material removal information at each position in the micro-EDM milling operation, the manufacturing fingerprint of the process is identified at the same time. On-machine metrology will support and verify the identified manufacturing fingerprint for in-process parameter optimization to realize zerodefect manufacturing.

Expected progress beyond current state-of-the-art
Through systematic investigation into the sparking process in micro-EDM, the influence of various parameter settings and on-machine metrology based on the current state-of-the-arts at both KU Leuven and Sarix will result in two significant progresses and further benefit industrial users with the implementation of manufacturing fingerprint concept. Immediately after the micro-EDM operation the deviation of geometrical and dimensional tolerance will be available to the users without post-process metrology. Post-metrology is necessary only at locations if there is uncertainty in the identification of manufacturing
fingerprint. Zero-defect micro-EDM milling will be enabled and smart process decision will be possible (e.g. the manufacturing process will stop once over-tolerance occurs to avoid useless further machining). Much userfriendly operation for micro-EDM machine operator through on-machine parameter auto-tuning.

http://www.microman.mek.dtu.dk/PhD-positions/Micro-electrical-discharge-machining
23 SEPTEMBER 2017