線電化學加工多孔隙銅金屬之特性分析

Abstract

線電化學加工(Wire Electrochemical Machining,WECM)在加工多孔隙銅的過程中，孔隙結構容易滯留電解液與反應產物，造成加工間隙內電場與質量傳輸條件不均勻，進而加劇雜散電流(stray current)影響與過切（overcut）現象，使加工切口寬度與切口輪廓一致性難以控制。 為了提升線電化學加工多孔隙銅之加工穩定性與切口輪廓精度，本研究採用直徑0.18 mm鉬線作為線電極、NaNO3水溶液為電解液，首先比較側向供應、軸向供應與浸沒式供應三種電解液供應方式，來選定後續實驗之電解液供應方式。接著以多孔隙銅與實心銅（厚度8mm）為實驗對象來進行切槽實驗，並以三因子三水準全因子設計系統性探討加工電壓（5/10/15V）、進給速度（0.06/0.18/0.3mm/min）與電解液濃度（5/10/15wt%）對加工結果之影響。加工品質以加工切口寬度及其沿加工深度方向的輪廓變化為主要評估指標，透過多點量測結果計算相鄰量測位置寬度之差值（例如D2−D1、D3−D2、D4−D3、D5−D4）， 並以此相鄰位置差值建立輪廓穩定性之量化指標，將加工結果分類為三類輪廓型態，以客觀描述不同條件下切口輪廓由入口至深部的變化趨勢。 實驗結果顯示，軸向電解液供應方式相較於側向供應與浸沒式供應能夠有效更新加工區域內之電解液並去除反應產物，整體加工穩定性最佳。在多孔隙銅加工中，進給速度對切口入口處寬度與切口輪廓穩定性影響最為顯著，輪廓分類結果顯示在低進給速度之下較容易落入輪廓變動劇烈之類型，因為低進給容易使反應時間過長而造成側向反應過度與切口入口處寬度過大;提高進給則有助於抑制過度反應並改善輪廓穩定性。相較之下，實心銅在相同的分類架構下多呈現較小的輪廓變動量，顯示其輪廓控制相對穩定，然而在部分參數組合下仍會出現由切口入口處至切口內部逐步收縮或不均勻變化的輪廓型態。在材料結構驗證方面，藉由光學顯微鏡觀察多孔隙銅經線電化學加工過後之孔隙結構，確認經線電化學加工過後孔隙結構仍可維持，顯示線電化學能在不破壞孔隙結構的前提下，具備加工多孔隙材料的可行性。

During the Wire Electrochemical Machining (WECM) of porous copper, the inherent pore structures tend to entrap electrolyte and reaction byproducts. This accumulation results in non-uniform electric field distribution and poor mass transfer within the machining gap, which exacerbates stray current effects and overcut phenomena, making it challenging to control slit width and profile consistency. To enhance machining stability and profile accuracy, this study employed a 0.18 mm diameter molybdenum wire as the tool electrode and a sodium nitrate (NaNO3) aqueous solution as the electrolyte. The research first compared three electrolyte delivery methods—lateral, axial, and immersion—to determine the optimal supply configuration. Subsequently, slotting experiments were conducted on both porous copper and solid copper workpieces (8 mm thickness). A three-factor, three-level full factorial design was utilized to systematically investigate the effects of machining voltage (5, 10, 15 V), feed rate (0.06, 0.18, 0.3 mm/min), and electrolyte concentration (5, 10, 15 wt%) on the machining outcomes. The primary evaluation metrics included slit width and its profile variation along the machining depth. A quantitative stability index was established by calculating the width differences between adjacent measurement points (e.g.,D2−D1 , D3−D2,…). Based on these indices, the results were categorized into three distinct profile types to objectively characterize the evolution of the slit profile from the entry to the depth under various conditions. Experimental results indicate that the axial electrolyte supply method outperforms lateral and immersion methods in terms of electrolyte renewal and byproduct removal, yielding the highest overall machining stability. In the machining of porous copper, the feed rate emerged as the most significant factor influencing entry width and profile stability. The classification results revealed that low feed rates frequently led to severe profile fluctuations; the prolonged reaction time at low feed rates caused excessive lateral dissolution, resulting in oversized entry widths. Conversely, increasing the feed rate helped suppress over-reaction and improved profile consistency. In comparison, solid copper exhibited smaller profile variations under the same analytical framework, indicating superior profile control, although tapering or non-uniform variations from the entry to the interior were still observed under specific parameter combinations. Regarding material integrity, optical microscopy (OM) confirmed that the pore structure of the porous copper remained intact after WECM. These findings demonstrate the feasibility of WECM for processing porous materials without compromising their structural characteristics.