電流波形對於放電加工特性之影響

Abstract

放電加工(Electrical discharge machining)過程實際上是電能轉移熱量的結果，電流波形在放電加工製程中代表著能量傳遞函數，關係著單位時間能量的分佈情形，所以電流波形在放電加工中代表一個供給能量的重要因素。本實驗將探討電流波形對於加工特性的影響，電流波形的特徵包含電流初始值(I0)、電流斜率(mcr)、電流上升時間(Tcr)和電流上升形式，其中電流上升形式可將電流波形的形狀分為方形波、梯形波、三角波和一階波。 由材料移除率與電極消耗比的加工結果顯示，使用方波電流波形具有最大的材料移除率與電極消耗比。當工件材料為模具鋼(SKD11)，使用梯形電流波形， 初始電流為峯值電流一半且電流上升斜率0.3，其材料移除率雖然比方波少了14%，但電極消耗比改善了60%。當工件材料為碳化鎢(Tungsten Carbide)材料時，使用一階電流波形，電流上升時間為20μs，其材料移除率可維持與方波接近相同，但消耗改善了30%。

Electrical discharge machining (EDM) is a machining process transforming electric energy into thermal energy to remove materials. The current impulse stands for the energy function. Therefore, current impulse is a very important factor for providing type of energy. A series of experiments were performed to investigate the influence of current impulse on machining characteristics. The features of current impulse have initial current (I0), current rising slope and impulse pattern. The used patterns of current impulse included rectangular current impulse and trapezoid current impulse and 1st order current impulse. The machining characteristics are associated with wear ratio, material removal rate. Experimental results show the rectangular current impulse has the most MRR and wear ratio. The wear ratio can be improved about 60%, although the MRR decreased 14% for SKD11 when trapezoid current impulse with initial current of 13A and current rising slope of 0.3. Experimental results show the wear ratio can be improved about 30% than rectangular current impulse for tungsten carbide while keeping the same MRR when 1st order current impulse with current rising time of 20μs.