高效能精微線切割放電加工電源開發

Abstract

一般「電阻-電容」放電電源雖能提供短脈衝及高峰值的放電電流，獲得 更小及更淺的放電坑，但因加工效能低，未被廣泛採用。本研究旨在開發一 種高效能的多重「電阻-電容」放電電源(Plural RC power source)，並應用於高 熔點高硬度金屬的精微線切割放電加工。多重「電阻-電容」放電迴路係由場 效可程式化邏輯閘陣列(Field Progra mmable Gate Array)、「電阻-電容」、電 晶體驅動電路與放電迴路所組成。透由邏輯閘控制每組「電阻-電容」的電晶 體開關時間，使每組電容器能在規劃的時間內，產生充放電波列。實驗規劃 分別選用1 組及3 組「電阻-電容」電源以及商用電晶體電源，對常用金屬(銅 合金及鋁合金)與高熔點高硬度金屬(碳化鎢、導電陶瓷及含硼聚晶鑽石)進行 線切割放電加工。由加工結果發現，多重「電阻-電容」電源的放電頻率與切 割進給率分別可達單「電阻-電容」電源的3 倍及2 倍以上，而加工時間可節 省40%以上；在火花腐蝕能力(Spark erosion ability)方面，單「電阻-電容」的 電源表現最好，多重「電阻-電容」的電源次之，電晶體電源又次之。為判斷 放電電源的工作效能，本研究提出「精微放電加工切割效能評估準則(Cutting performance assessment criterion)」，並發現多重「電阻-電容」電源，其切割 效能比商用電晶體電源好，且具較低的鈷析出量，證實本研究開發的多重「電 阻-電容」放電電源，具高頻放電性能，極間恢復絕緣時間快，材料熱影響區 少，且單位時間的金屬移除率多。期待此多重「電阻-電容」電源的研發，著 實能貢獻到精微製造產業。The resistance-capacitance (RC) circuit effortlessly provides a discharge current with a short pulse and a high peak which leads to a very shallow and narrow discharge cavity. However, it has not been widely employed due to low production efficiency. The primary objective of this thesis is to develop a high-efficiency power source with plural RC discharge circuit and use it in cutting the high melting point metal. The plural RC discharge circuit is consisted of a Field-Programmable Gate Array (FPGA) device, plural resistor-capacitor, transistors base driving circuit and a discharge circuit. Each transistor that switches the discharge time for the corresponding RC circuit is controlled by the designed FPGA to generate a charge/discharge pulse train in time. By applying the developed power sources of single- and plural- RC circuits, and the commercial transistor power, experiments are conducted in cutting the often used metal (copper and aluminum alloy) and high melting point metal (tungsten carbide, conductive ceramic and boron-doped polycrystalline composite diamond). The test results indicated that the discharge frequency and cutting feed-rate in plural RC power are approximately 3- and 2- times for the single RC power, respectively, In addition, the machining time can be reduced to 40% above. In Spark Erosion Ability (SEA), the single RC power is better than that of plural RC and the plural RC better than that of the transistor. To determine the working efficiency of the power source in micro wire electrical discharge machining (w-EDM), a ‘cutting performance assessment criterion’ is proposed in this study. Comparing with the commercial transistor power, the plural RC power is superior in cutting performance and has lower amounts of cobalt deposition. Experimental results verified that the developed plural RC power source owns the high-frequency discharge performance and fast insulation recovery time resulting in a smaller heat-affected zone and creating more Metal Removal Rate (MRR). It is expected that the developed plural RC power source can be contributed significantly to the micro fabrication industry.