不同電極形狀對加工特性之影響與放電加工參數之決策

Abstract

在機械製造產業中，模具為工業製造中不可或缺的部分。模具製造除了使用傳統切削方式，還常與放電加工做配合去完成模具製作，因放電加工具有加工複雜細微特徵、高精度加工、加工高硬度材料以及模具修整等優勢。目前業界放電加工應用於模具的技術與、對品質控管的能力相當成熟。但在放電間隙的設置，至今仍必須依賴操作者的加工經驗去設定，缺乏系統化的策略規劃，是目前放電加工的CAD/CAM仍有進步空間的部分。本研究進行不同加工參數條件的探討，不同幾何形狀的放電間隙變化趨勢為何，探討的加工參數為：電流、電壓、脈衝時間、工作因子與幾何尺寸，先利用田口方法規劃實驗與分析，瞭解各參數的改變對放電間隙的走勢，據此發展出多目標的放電加工決策系統。

研究中利用田口方法直交表L27進行，依田口方法的分析瞭解各設計參數的改變會怎麼影響放電間隙變化的趨勢，放電間隙之計算不考慮電極消耗。探討之加工特性為：加工時間、表面粗糙度、放電間隙，發現加工時間不受形狀影響，受加工面積影響；表面粗糙度不受形狀影響，受電氣參數影響。而放電間隙會受不同形狀影響，正方形與長方形的間隙大小幾乎相同，三角形的放電間隙則平均小於正方形與長方形的放電間隙。

最後依變異數分析發現電流、脈衝時間對加工時間、表面粗糙度、放電間隙的貢獻度皆大於75%，表示控制電流及脈衝時間即可大致掌握加工特性，因此放電參數的決策系統以訂定電流、脈衝時間為首要步驟，後續再依需求用電壓、工作因子進行微調以達到要求之品質。

In the mechanical manufacturing industry, molds are an indispensable part of industrial production. In addition to using traditional cutting methods, mold manufacturing often combine with electrical discharge machining (EDM) to achieve complex and intricate features, high-precision processing, machining of high-hardness materials, and mold finishing. Currently, the application of EDM in mold manufacturing has reached a mature level in terms of technology and quality control capabilities. However, the setup of EDM gap still heavily relies on the operator's experience, lacking a systematic strategy, which has room for improvement in the CAD/CAM of EDM. This research explores different processing parameter conditions and the variation trends of EDM gap for different geometric shapes. The processing parameters include current, voltage, pulse-on time, duty factor, and geometric dimensions. The Taguchi method is used to plan and analyze experiments, understanding the effects of various parameters on EDM clearances and developing a multi-objective EDM decision-making system.

The research uses the Taguchi method with an orthogonal table L27 for analysis to understand how changes in each design parameter will affect the variation trend of EDM gap. The investigated machining characteristics are processing time, surface roughness, and EDM gap. It is found that the processing time is not affected by the shape but influenced by the machining area, and the surface roughness is not influenced by the shape but affected by the electrical parameters. However, the EDM gap is influenced by different shapes, with the gap of squares and rectangles being nearly the same, while the gap of triangles is on average smaller by approximately 0.03 mm compared to squares and rectangles.

Finally, the analysis of variance reveals that the current and pulse on time contribute over 75% to the variations in processing time, surface roughness, and EDM gap. This indicates that by controlling the current and pulse-on time, the machining characteristics can be roughly managed. Therefore, the decision-making system for EDM parameters should give priority to setting the current and pulse-on time, and then adjust the voltage and duty factor as needed to achieve the required quality.