| Abstract: | 於電化學加工過程中，時常因為加工間隙太過狹窄容易導致電解液更新不良，所產生之金屬氧化物、氣泡和反應熱堆積難以排除，進而影響到加工的精度和表面品質，尤其加工如矩槽圓柱等特殊結構，加工間隙之流場更不均勻，甚至可能導致工件和刀具電極之間直接碰撞，造成刀具電極和工件損壞。基於前述加工困難處，本論文使用脈衝電流複合超音波振動輔助側壁絕緣電極，並採用沉浸式對SUS304不鏽鋼圓塊工件進行電化學留心加工矩槽圓柱構造，並探討脈衝頻率、加工電流、超音波功率等級及占空比等不同加工參數對圓柱直徑、圓柱高度及圓柱錐度角等各種加工特性之影響。
研究結果顯示，實驗中採用側壁絕緣電極，進行遮罩式及沉浸式加工結果比較，相較於於遮罩式加工，沉浸式加工結果有較小之圓柱錐度角及較佳之外觀形貌。另採用脈衝電流複合超音波振動輔助進行沉浸式留心電化學加工時，可改善流場不均勻，以及超音波振動輔助施加於側壁絕緣電極上，造成加工區域中的電解液壓力快速產生變化，產生泵吸作用與空蝕作用，此二者會擾動電解液，加速加工間隙內電解液的循環更新，進而降低加工區域內之電阻值，得到更小之圓柱錐度角，以及矩槽底部流痕明顯減少。當採用實驗參數組合為脈衝頻率1000 Hz、加工電流18.5 A、超音波功率等級Level 6(Amplitude：1.117 μm )及占空比50 %時，可得到加工後最小圓柱錐度角1.697 °，相較於遮罩式加工後之圓柱錐度角2.114 °，下降了19.73%。;During electrochemical machining (ECM) processes, narrow processing inter-gap often lead to poor electrolyte renewal, inhibiting the removal of the metal oxides, bubbles, and heat generated during reactions. This can adversely affect the machining precision and surface quality of the workpiece, especially for complex structures such as rectangular groove with inner cylindrical structure. The flow field is uneven in the processing inter-gap of such structures, increasing the likelihood of direct collisions between the workpiece and the tool electrode and potentially causing damage to both the tool electrode and workpiece. To overcome these difficulties, this study proposes an approach entailing the combination of a pulse current with ultrasonic-vibration-assisted sidewall-insulated electrodes. The study then applied this approach to conduct electrochemical trepanning with tool sinking on SUS304 stainless steel round workpieces to create rectangular groove with cylindrical structure. The effects of various processing parameters, including the pulse frequency, machining current, power of ultrasonic vibration, and duty factor, on the workpiece quality, such as the diameter, height, and taper angle of the cylindrical structures, were measured through experiments.
The experimental results indicated that when the sidewall-insulated electrodes were used, ECM with tool sinking resulted in a smaller taper angle and better external appearance than did ECM with mask. For ECM with tool sinking, applying the combination of a pulse current with ultrasonic-vibration-assisted sidewall-insulated electrodes improved the uniformity of the flow field. Moreover, for the sidewall-insulated electrodes, ultrasonic vibration assistance caused rapid changes in the electrolyte pressure in the machining area. This resulted in pumping and cavitation effects, both of which disturbed the electrolyte, accelerating the circulation and renewal of the electrolyte within the inter-gap. This reduced the resistance within the machining area, thus significantly reducing both the taper angle and the flow marks at the bottom of the groove. The minimal taper angle 1.697° of the cylindrical structures was obtained with the following experimental parameter combination: Pulse frequency of 1000 Hz, machining current of 18.5 A, power of ultrasonic vibration of level 6, and duty factor of 50%. The taper angle of the cylindrical structures was 19.73% smaller than that obtained through ECM with mask. |
