高頻等脈衝微放電電源開發應用於含硼聚晶鑽石陣列微結構線切割放電研究

Abstract

本研究旨在開發一種高效能「高頻等脈衝微放電電源」，並應用於含硼聚晶鑽石高深寬比微細結構陣列的精微線切割放電加工研究。透由「元件可程式邏輯閘陣列(FPGA)」精準控制雙極放電迴路中的電容充放電週期，以創造出高頻、高峰值及短脈衝的電流波列；研究並提出以「電磁式」控制超微細線極張力的技術及設計「微細線極放電切割機構」。電磁式線張力控制技術係非接觸式作用，無摩擦與磨耗，僅微調電流，便能精密且平穩地控制微細線極的張力及川流速度，線極偏擺量可抑制在0.2 μm內(線張力10 gf)。研究以線徑ψ13μm鎢線對含硼聚晶鑽石進行切割加工實驗，並對不同工作電容下所生成的單位時間電荷量、放電短路時間比、火花熔蝕能力及材料移除率等影響因素作評估。實驗證實，結合「高頻等脈衝微放電電源」及「電磁式線張力控制技術」，能成功實現包括平板、梯形板及梯形柱等微結構陣列的切割，深寬比達1:22。因放電電源所創造出的每發能量波形，均具等脈衝及等間距特性，故放電波列能高速、微量且定量地移除材料，即使面對高阻抗、高硬度及高熔點的含硼聚晶鑽石，也能加工出具高一致性且高深寬比的鑽石微細結構陣列。為提升鑽石微結構的切割效能，實驗也提出「多線式切割」及「開放式切割」兩方法，前者包含對放電短路時間比與放電短路機率作可行性評估。結果顯示聚晶鑽石因阻抗大，短路比高，顯示多線極切割效能並未能優於單線極；而後者實驗結果發現，相較於封閉式切割，開放式切割具較佳的切割品質及較高的切割效能。實驗也對聚晶鑽石微結構的加工面粗糙度、形狀精度與石墨化變質層等影響因素，以及應用於電子元件散熱場合的可行性作探討。實驗結果顯示本研究開發的技術成果具商業化價值。

This paper presents the development of a 'high-frequency iso-pulse micro-EDM power source' with high-performance for the study on microwire-cutting microstructure array made of Boron-doped Polycrystalline Composite Diamond (B-doped PCD). A FPGA (Field Programmable Gate Array)-controlled power source based on a Bipolar Resistance-Capacitance (Bi-RC) relaxation circuit that can create a current of high-frequency and high-peak with an iso-pulse train is proposed in this study. To eliminate friction and wear between the microwire and device, a small microwire-cutting mechanism in which the microwire tension is controlled by electromagnetic technique is designed. Swaying and wriggling of the microwire can be swiftly minimized within 0.2 μm through fine tuning the work current, ensuring the microwire tension and the running speed kept steady. Experiments of B-doped PCD cutting are conducted by a tungsten microwire of ϕ13 μm. An extensive examination of the quantitative and qualitative properties comprising the Electric Charges per unit Volume (ECV) under different work capacitance, Discharge Short Circuit Rate (DSCR), Spark Erosion Ability (SEA), and Material Removal Rate (MRR) has been undertaken. Experimental results demonstrate that by combining the developed 'high-frequency iso-pulse micro-EDM power source' with the 'electromagnetic microwire tension control' techniques can successfully machine the plate-shaped, trapezoidal plate-shaped, and trapezoidal pillar-shaped diamond microstructures array. The aspect-ratio of microstructures array is up to 1:22. The discharge current of high-frequency and high-peak with an iso-pulse train generating a high-temperature spark erosion energy facilitates diamond material removed by high-speed, quantitatively and minor, creating uniform and consistent microstructures array. To enhance machining efficiency during diamond microstructures cutting, the two 'multi-wire cutting' and 'opened-pathway cutting' approaches are also suggested. Experimental results show that the multi-wire cutting is not superior in DSCR compared with that of single-wire cutting because of a high electrical resistivity of B-doped PCD. In terms of the pathway, the resultant quality and performance of cutting are better in the case of opened-pathway cutting. The formed microstructures have also been evaluated with regard to the influential factors of surface roughness, geometrical accuracy and graphitized layer as well as the discussion of heat dissipation for semiconductor chips. This development is expected to contribute substantially to the commercial applications of precision micromanufacturing industries.