Dry micro-electro-discharge machining of carbon-nanotube forests using sulphur-hexafluoride Saleh, Tanveer; Dahmardeh, Masoud; Nojeh, Alireza; Takahata, Kenichi
The effect of using sulphur hexafluoride (SF6), a high-dielectric-strength gas, for dry micro-electro-discharge machining (µEDM) of carbon-nanotube (CNT) forests is investigated. It is found that SF6 enables µEDM of CNTs without O2, which is known to be essential for CNT machining in N2. The process in the SF6 ambient is found to lead to a smaller discharge gap, i.e., tighter tolerance as well as higher machining quality at a discharge voltage level (25 V) compared with the case of N2 at the same voltage. N2 environment produces lower discharge gap when a voltage level of 10V is used. However, the quality of the machining (e.g. the inner post sidewall) seems to be somewhat poorer in this case, and rate of machining is somewhat lower. The mixture with 20% O2 in SF6 is revealed to be an optimum condition in terms of both machining tolerance and quality. CNT forests are used as the cathode in the SF6-based µEDM process, as opposed to conventional µEDM where the workpiece forms the anode. This reverse-polarity configuration in the SF6-O2 mixture is observed to generate higher discharge currents at low voltages, presumably due to effective field-emission by the CNTs, leading to finer and cleaner machining than the conventional normal-polarity case. Energy-dispersive X-ray analysis reveals that the optimal machining conditions result in less contamination by the electrode element on the processed forest surfaces.
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