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指導教授： 戴子堯 教授 ( Prof. T. Y. Tai)

報告者：陳嘉文 (J.W Chen)

南臺科技大學 機械工程系Department of Mechanical Engineering,

Southern Taiwan University of Science and Technology

Date ： 2015 / 06/ 08

Paper Survey

Evaluation of the effectiveness of low frequency workpiece vibration in deep-hole micro-EDM drilling of tungsten carbide

Journal of Manufacturing Processes 14 (2012) 343–359

M.P. Jahana, , Y.S. Wongb, M. Rahmanb∗a Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR 72701, USAb Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore

Technical paper

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Abstract

Experiment Setup Design and development of low-frequency vibration device

Micro-EDM arrangement

Methodology

Evaluate the effectiveness of low-frequency workpiece vibration

Experimental results and discussion

Conclusions

Outline

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Abstract

The application of micro-electrical discharge machining (micro-EDM) in deep-hole drilling is still limited due to the difficulty in flushing of debris and unstable machining. Present study introduces a simplistic analytical model to evaluate the effectiveness of low frequency workpiece vibration during the micro- EDM drilling of deep micro-holes. In addition, experimental investigation has been conducted to validate the model by studying the effects of workpiece vibration on machining performance, surface quality and dimensional accuracy of the micro-holes. The effect of vibration frequency and amplitude for three different

settings of aspect ratios has been studied experimentally.

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Experiment SetupDesign and development of low-frequency vibration device

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Experiment SetupMicro-EDM arrangement

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Experiment SetupMicro-EDM arrangement

(a) Schematic diagram of the setup and (b) magnified view of the micro-EDM arrangement with vibration unit

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Experiment SetupMethodology

The machining performance of the micro-EDM drilling process was evaluated by the material removal rate (MRR) and electrode wear ratio (EWR). The accuracy of the micro-holes was evaluated by overcut, taper angle and the circularity of the fabricated microholes.

Measurement of (a) overcut, (b) taper angle(c) circularity.

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Assumptions:

Low frequency workpiece vibration follows a simple harmonic motionThe workpiece is completely horizontal and the vibration direction is fully perpendicular to the workpiece.The debris particles will have the same frequency, velocity and acceleration of the vibrating plate, as the force due to sparking and electrical field was not consideredThe maximum acceleration of the workpiece will be experienced at the two extreme positions of the vibration plate

Evaluate the effectiveness oflow-frequency workpiece vibration

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Evaluate the effectiveness oflow-frequency workpiece vibration

(a) Schematic diagram showing the mechanism of the workpiece vibration assisted micro-EDM drilling used in this study.(b) Displacement–time relationship for the workpiece vibration at different position of vibrating plate.

vv

vv

v vv

v

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Experimental results and discussion

Comparison of EWR for micro-holes of (a) aspect ratio 5, (b) aspect ratio 7.5 using without vibration (Kv = 0), with vibration (f = 500 Hz, a = 0.5 m, Kv < 1) and with vibration (f = 750 Hz, a = 1.5 m, Kv > 1) [electrical parameters: voltage: 80–140 V, capacitance: 10 nF]

v v v v v v v v

Comparison of taper angles of micro-holes of (a) aspect ratio 5, (b) aspect ratio 7.5 using without vibration (Kv = 0), with vibration (f = 500 Hz, a = 0.5 m, Kv < 1) and with vibration (f = 750 Hz, a = 1.5 m, Kv > 1) [electrical parameters: voltage: 80–140 V, capacitance: 10 nF].

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Experimental results and discussion

Comparison of (a) MRR (b) EWR and (c) machining time for without vibration(Kv = 0) and with vibration (Kv > 1) for micro-holes with aspect ratios 5 and 7.5[electrical parameters: capacitance: 1000–10,000 pF, voltage: 100 V].

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Experimental results and discussion

Comparison of overcut of micro-holes of (a) aspect ratio 5, (b) aspect ratio 7.5 using without vibration (Kv = 0), with vibration (f = 500 Hz, a = 0.5 m, Kv < 1) and with vibration (f = 750 Hz, a = 1.5 m, Kv > 1) [electrical parameters: voltage: 80–140 V, capacitance: 10 nF].

Comparison of (a) taper angle, (b) overcut and (c) circularity of micro-holesfor without vibration (Kv = 0) and with vibration (Kv > 1) for aspect ratios 5 and 7.5[electrical parameters: capacitance: 1000–10,000 pF, voltage: 100 V].

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Experimental results and discussion

Comparison of the entrance side of 100 m hole for machining without vibration (Kv = 0) and with vibration (Kv > 1) during micro-EDM [SEM images taken at 0◦ tiltangle].

(a) Micro-hole [O 200 m, aspect ratio 5] without vibration (Kv = 0), (b) micro-hole [O 200 m, aspect ratio 7.5] with vibration (Kv > 1),(c) micro-hole [O 200 m,aspect ratio 10] with vibration (Kv > 1) [SEM images taken at 30◦ tilt angle].

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Conclusions 加工性能提高的MRR增加和應用工件振動（ Kv 值 >1）在微細電火花加工後 EWR顯著下降。在施加振動後的性能的提高是在較低的放電能量設置更為明顯。

在微孔的邊緣和尺寸精度，表面質量由於顯著減少電弧和短路的提高。沉積碎屑周圍的微孔邊緣的數額在微細電火花加工鑽施加振動（ Kv 值 >1）後顯著減少。

為的 Kv>1的設定，在加工性能和微孔質量隨振動頻率提高和振幅達到一定的最佳值。然而，非常高的頻率和振幅被發現是從微孔表面質量和精度的角度不合適。

用於加工高縱橫比和更小的微孔， Kv的值必須大於 1 並且微電極應在機器製造。 的主要原因在低頻工件振動輔助微細電火花改進的性能被認為是增加的有效排放比率，減少短路和電弧和整體改善的電介質潮紅。改進的加工穩定性和提高加工效率在一起有助於加工性能的改善過程中的振動輔助微細電火花加工

低頻振動輔助微放電加工的性能取決於參數的 Kv（在重力方向重力加速度 'G'振動工件的最大加速度的比）的數值。 Kv的值是從振動頻率，振動工件的幅度和相位角的選擇限定

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