Investigation of micro-EDM material removal characteristics using single RC-pulse discharges Class ：碩研機械一甲 Student ID ： MA Student ：陳肇文 Professor ：戴子堯 教授 Date ： 2015/5/25 Journal of Materials Processing Technology 140 (2003) 303–307 使用 RC 單脈衝放電於微細放電加工之材料移除特性研究 Y.S. Wong a, ∗, M. Rahmana, H.S. Lima, H. Hanb, N. Ravib a Mechanical Engineering Department, 10 Kent Ridge Crescent, National University of Singapore, Singapore , Singapore b Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore , Singapore

outline Abstract Introduction Experimental Results and discussion Conclusions

Abstract In micro-EDM, intense heat is generated between the work piece and tool electrode by the discharge through a dielectric medium to result in the formation of a micro crater that is much smaller in size. It is found that at lower-energy (<50 μ J) discharges, the energy required to remove the unit volume of material, defined as the specific energy, is found to be much less than that at higher-energy discharges. indicating greater consistency in shape and size when the discharge occurs at lower energy.

Introduction The power supply of discharge energy and the resolution of the X-, Y- and Z-axes movement. At low energies (10–20 mJ), the net metal removal efficiency has been found to be near 1.0 and at higher energies (50–700 mJ), the efficiency is found to fall of rapidly until The work presented in this paper aims to study the mechanism of material removal by investigating the formation of micro crater and its characteristics using very low single RC- pulse discharge which is approximately 1000 times lower than those in EDM, to shed a new light on this subject.

Experimental Fig. 1. Micro craters at 2μm spark gap.

Fig. 2. Single-discharge RC circuit of micro-EDM.

Results and discussion A micro crater resembling that of a quarter moon shaped structure in cross-section is produced using the single RC- pulse generator. Fig. 1(a)–(f) show some examples of micro craters produced using the single discharge on the sample. The critical problem in the single-discharge machining is the unevenness in the size of the micro craters produced. Hence, five micro craters are produced at each machining condition to determine the expected size.

Effects on the volume of micro crater Fig. 3. Discharge energy vs. cavity volume of micro crater.

Fig 4. Discharge energy vs. average ratio of standard deviation (S.D.) to Micro crater size.

Fig 5. Discharge energy vs. specific energy.

Conclusions The volume and size of the micro craters are found to be more consistent at lower-energy discharges than at higher-energy discharges. The specific energy required to remove the material is found to be significantly less at lower energies (<50.J) when compared with that at higher energies. Using a simple theoretical model, the estimated erosion efficiency of material removal at low-energy discharges is found to be seven to eight times higher than that at higher-energy discharges. The aforementioned strongly indicate that lower-energy discharges produce more consistent size of micro crater at higher efficiency.

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