| Summary: | 碩士 === 臺灣大學 === 機械工程學研究所 === 98 === In this research, we used air as dielectric fluid instead of traditional EDM oil, trying to decline toxic substances against environment during manufacturing processes.
To lead air into discharge gap, we set up a desktop EDM machine and designed the spindle by ourselves. When the spindle rotates, the discharge arcs will be eliminated rapidly. Besides, air with high pressure can take both ionizations and melting materials away from the gap, leading higher efficiency.
The Taguchi Methods was used in this research. The chosen factors are listed in the following: open voltage, peak current, pulse duration, duty factor, servo ratio, reference ratio of gap voltage, air pressure, spindle speed. We compared different machining effects resulted from various factors by analyzing machining characteristics such as material removal rate (MRR), relative electrode wear ratio (REWR) and surface roughness (Ra), hoping to develop the base of Dry EDM
The degrees of significant factors influenced MRR from large to small as follows: peak current, reference ratio of gap voltage, air pressure, open voltage, duty factor. The MRR can achieve to 23.64mm3/min under the optimum condition with open voltage of 400V, peak current of 30A, pulse duration of 100us, duty factor of 0.75, air pressure of 0.5MPa, spindle speed of 600rpm, servo ratio of 25%, reference ratio of gap voltage of 10%.
Besides, the degrees of significant factors influenced REWR from large to small as follows: reference ratio of gap voltage, duty factor, peak current, duty factor. The REWR can achieve to 0.13% under the optimum condition with open voltage of 400V, peak current of 20A, pulse duration of 50us, duty factor of 0.75, air pressure of 0.1MPa, spindle speed of 1400rpm, servo ratio of 75%, reference ratio of gap voltage of 30%.
The degrees of significant factors influenced surface roughness from large to small as follows: duty factor, air pressure, peak current, pulse duration. The Ra can achieve to 5.447 um under the optimum condition with open voltage of 400V, peak current of 10A, pulse duration of 50us, duty factor of 0.25, air pressure of 0.1MPa, spindle speed of 600rpm, servo ratio of 50%, reference ratio of gap voltage of 10%.
During Dry EDM, the reason of lower REWR is that the melting workpiece material stuck onto the electrode surface and thus produced a protection layer. The protection layer is formed from arc, and the area of protection layer increase with the arc discharge ratio.
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