多線式精微線切割放電加工技術開發

Abstract

本研究旨在針對高細長比微細結構，開發一種「多線式精微線切割放電加工技術(Micro multi-wire electric discharge machining)」，以獲致高效率精微線切割加工。為開發具高深寬線切割放電加工的方法，本研究提出以陣列微細線電極配合高頻振動輔助(High-frequency vibration) 及偏置切割法(Offset cutting)，對微細碳化鎢棒材，進行放電切割加工。研究之初，先行開發一組多線式精微線切割加工機構，並設計陣列式細線張力控制的方法。為避免多線電極於加工過程中，發生晃動行為，實驗設計微細線的陣列導槽(Micro guide array)，以固定多線電極彼此間距。系列實驗後，證實本研究所提多線式線切割放電加工，能以Ø50 µm的陣列細線，加工出8×8陣列微結構的碳化鎢探針(Micro probe array)，每支探針尺寸20×20×500 μm，細長比達25：1；而以1 kHz的高頻振動(High-frequency vibration)輔助，著實能幫助陣列微細銅線產生極小振動，放電殘渣(Discharge debris)得以順利排除，並減少二次放電(Secondary discharge)、異常放電( Abnormal discharge)，以及短路(Short circuit)發生的機會。實驗結果也顯示，以雙線電極配合振動輔助，進行探針加工，其所耗時間比單線電極在振動輔助模式下所耗時間，可減少約65-70 %，多線電極切割的工件表面粗糙度(Ra:0.86 μm)亦比單線電極(Ra:1.0 μm)切割的更好，證實多線電極的放電，具火花分散(Spark dispersing)效果，可避免過渡放電集中而造成表面粗糙度不佳的問題。本研究證實多線式精微線切割放電加工技術，除了能有效提升線切割放電加工的效能外，亦能提升工件表面粗糙度，此研究成果能貢獻於精微加工產業。

This study presents the development of micro multi-wire electric discharge machining for efficiently machining the high-aspect-ratio microstructure. To achieve high-performance of machining for microstructure, a multi-wire EDM mechanism that performs arrayed micro wire cutting with high-frequency vibration and an offset machining approach are proposed in this study. The tensions of the multi-wire electrodes with 50µm in diameter are controlled by magnetic repulsive force to steady the wires during machining. A vibrating absorber and a micro guide notch array which exactly guides the multi-wire electrodes in a constant pitch are designed to suppress wires vibration. Experimental results demonstrate that the proposed approaches can fabricate microstructure with 8×8 micro probe array and 20×20×1000µm squared pillars by using the micro wire array electrodes of 50μm diameter. The microstructure array of an aspect ratio more than 25 are satisfactorily and precisely fabricated. By applying the high-frequency assisted vibration of 1 KHz, discharge debris can be removed swiftly from the wire and reduce the frequencies of secondary discharge, abnormal discharge and short circuit. On the other hand, comparing with the single wire EDM with vibration mode, the machining time can save up to 65-70% when using twin-wire EDM with vibration mode. Moreover, the surface roughness of the machined pillars by using the multi-wire cutting is better than that of single wire cutting, indicates that an effect of spark dispersing can be achieved to avoid discharge crowding effect. It is confirmed that the proposed approach could really realize the high performance of machining besides improving the surface roughness. The developed micro multi-wire electric discharge machining is effective, and should be very useful in the manufacture of the high-aspect-ratio micro probe array.