本研究是利用異形工具電極對Inconel 718鎳基超合金進行放電加工。以線放電研削機構(WEDG)將工具電極修製單邊及雙邊缺口，針對Inconel 718材料進行3 mm深度的穿孔加工，實驗中探討電極設計及峰值電流、脈衝時間、間隙電壓、電極轉速等加工參數，對加工時間、電極消耗率與微孔加工精度的影響，並利用掃描式電子顯微鏡觀察微孔內壁表面形貌。
實驗主要可分為兩部分，首先以不同寬度的單邊及雙邊缺口碳化鎢工具電極進行微孔加工，藉由加工時間、電極消耗率、入口孔徑與出口孔徑評估較佳加工效率及精度之工具電極外形。第二部分則利用第一部分實驗選擇的缺口電極，同樣對Inconel 718材料進行加工探討不同加工參數對加工的影響。
研究結果顯示，相較於圓柱電極，缺口電極具有較大的排屑空間，可促進加工屑排除，使微孔放電過程更穩定，進而提高加工效率。而使用單邊缺口寬度100μm的工具電極，加工時間可縮短至329秒，且能維持良好的孔徑精度；在加工參數方面，隨著峰值電流由3A增加至7A時，加工時間可由549秒縮短至 327秒，但不論入口、出口孔徑或電極消耗率都有明顯增加，當脈衝時間由11μs延長至23μs時，電極消耗率由0.15mg/min減少至0.04mg/min，且間隙電壓由62V增加到64V時，電極消耗率會由0.12mg/min降低至0.06mg/min，脈衝時間或間隙電壓增加，可減少電極消耗率，並改善出口孔徑加工誤差，而在高電極轉速條件下，微孔加工尺寸與幾何精度較佳，但加工表面粗糙度差。

This study presents an experiment in electrical discharge machining (EDM) of Inconel 718 by using the special-shape tool electrode. The tool electrodes with single notch and double notch were manufactured by WEDG and used to drill through holes with depth of 3 mm on Inconel 718. The influence of designed electrodes and the EDM parameters that included peak current, pulse on time, gap voltage, rotational speed were evaluated with respect to response characteristics such as machining time, electrode wear ratio, micro-hole quality. Besides, SEM was used to observe the surface morphology of the inner wall of micro-hole.
The experiment is divided into two parts. First, the micro-hole was machined by the tungsten carbide tool electrodes with various widths of single notch and double notch. Machining time, electrode wear rate, inlet and outlet diameter were evaluated to get the tool geometries with a higher efficiency and quality. Second, the notch type of electrode acquired from part one was used to drill on Inconel 718 again and evaluated the effects of working parameters on micro-hole EDM process.
Experimental results reveal that the electrode with notch is conducive to the efficient removal of debris through the gap channel during the discharge process in comparison with the cylindrical electrode. Therefore, the micro-hole EDM is more stable, and the machining efficiency is improved. Applying the tool electrode with 100 μm wide single notch, machining time is down to 329 seconds and causes less hole enlargement. Machining time decreases from 549 seconds to 327 seconds, as peak current increases from 3A to 7A. Electrode wear rate decreases from 0.15mg/min to 0.04mg/min, as pulse on time increases from 11μs to 23μs. Electrode wear rate also decreases from 0.12mg/min to 0.06mg/min, when gap voltage increases from 62V to 64V. An increase in pulse on time or gap voltage leads to decrease in electrode wear rate. Thus the accuracy of outlet diameter is improved. High rotational speed results in a higher dimensional and geometrical precision of the micro-hole but the surface is coarser.

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