| Summary: | 碩士 === 中州技術學院 === 工程技術研究所 === 92 === Abstract
Electrical discharge machining (EDM) that is one of the non-conventional processes is extensively applied in mold industries. During EDM process, the tool electrode and the workpiece are separated with a small gap (5-100 m). The gap distance between workpiece and electrode is extremely small, so the machining debris resulted from EDM process is difficult to remove out of the machining gap. Thus, the isolated condition does not recover completely within the gap, so the situations of abnormal electrical discharge and short circuit will result in the machining zone during EDM process. The stability of EDM gap condition significantly affects the machining characteristics. The machining performance improves when the debris is expelled from the machining gap fast and easily. Therefore, when assistant magnetic poles were attached to EDM machine, the machining zone generates a magnetic force to drive the suspending debris expelling from the machining gap. The debris stacked on the machining zone can be reduced, so the machining condition becomes more stable to improve the machining performance. In this investigation, the magnetic poles were attached on EDM to explore the effects of assistant magnetic force on EDM machining characteristics. The main machining parameters of EDM such as machining polarity (P), peak current (IP), pulse duration (P), high-voltage auxiliary current(IH), no load voltage(V) and servo reference voltage(SV) were chosen to determine the effects on the material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR). Moreover, this work adopted L18 orthogonal array based on Taguchi method to coduct a series of experiments and using analysis of variance (ANOVA) to evaluate the experimental data. For determining optimization combination levels of machining parameters associated with each machining characteristic each an MRR, EWR and SR. More over the optimization of the EDM process with multiple performance characteristics was studied by grey relational analysis. The benefits of assistant magnetic force were confirmed from the analysis of electrical discharge waveforms. From the experimental results shown, using EDM with assistant magnetic force could obtain higher MRR and smother surface roughness than conventional EDM. Moreover, the variation of EWR between two processes is very small. The effects of assistant magnetic force on EDM machining characteristics were determined, and the significant machining parameters and the optimal combination levels of machining parameters associated with each experimental observed value also drew. Moreover, the contribution for expelling the machining debris through this experimental setup could also prove to attain a high efficiency, high precision and high quality combined process of EDM.
Keywords：EDM, material removal rate, electrode wear rate, surface roughness, debris
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