| Summary: | 碩士 === 國立高雄應用科技大學 === 模具系碩士在職專班 === 105 === In order to overcome the mold material which is difficult to machine, the Electrical Discharge Machining (EDM) is a very popular candidate for the mold industries. However, due to the very long working time, the production capacity will be reduced by EDM process. Copper electrode, copper-tungsten electrode and graphite electrode are generally adopted as electrode in the EDM processes of tungsten steel. Therefore, the purpose of this research is to study the processing efficiency, surface morphology and surface roughness by a new compound electrode with red copper and a small amount of graphite powder. This thesis is aimed at shortening the EDM time during the roughing stage and improves the EDM process by applying compound copper with graphite of #200 mesh grains (75μm) to tungsten steel, which was made by Mitsubishi Heavy Industries, Ltd. The main research methods are to investigate the physical properties and mechanical strength of the newly developed electrode in the first step. Then, the EDM material removal rate (MRR), surface roughness (SR), and relative electrode wear rate (TWR) by different composite proportions from 5% to 25% of graphite are investigated. It is also to break through the habitual thought that only red copper or copper tungsten are proper options in the EDM efficiency of supper hard alloy mold.
Secondly, according to the Taguchi Methods and ANOVA analysis, the operation conditions of IL 20A, TON 200 μs, TOFF 75 μs, Spindle revolution 1,500 RPM, and with ultrasonic assistance by Cu90%+Gr10% electrode can obtain the highest MRR. Confirming with verification experimental, it is recommended to optimize the operating parameters as, IL 20A, TON 200 μs, TOFF 75 μs, revolution 1,200 RPM, 220Hz, and with ultrasonic assistance contributes to highest MRR of 20.28mg/min. Based on one hour machining time, the results show that the MRR of Cu90%+Gr10% electrode is 15% higher than copper electrode and 41% higher than copper tungsten electrode. But the tool wear rate is also extremely high. The reason of high MRR and consumption TWR by the compound electrode is because of no chemical bonding and other adhesives. Due to the fact that a large number of debris will be released quickly into the dielectric fluid, graphite powder and copper powder are exposed into kerosene with discharge phenomenon during EDM. The electrode will be reduced dramatically (including the tool-tip and side all) and caused secondary discharge with high concentration of debris. As a result, the tungsten steel was removed very efficiently by such an EDM and both the MRR and TWR are drastically increased.
|
|---|
