| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 103 === This thesis proposes an innovative elector-polishing process and research schemes aiming at surface polishing of micro mold’s cavity. Generally, fabricating micro mold inserts adopts micro electrical discharge machining (micro-EDM) in the industries. However, after discharging, works surface remains the recast layer and discharge crater, which results in severe impact on the quality of surface integrity. It needs other procedures and more time to mend the defect. Therefore, this research proposes a novel electrolysis polishing (Electro-Polishing, EP) with pure deionized water on micro-EDM machine and fabrication of the cavity profile simultaneously. The processes adopt tungsten carbide as tool electrode, and M333 tool steel from Austria is adopted as work-piece material. The advantages of electrolysis are that it will not produce discharge crater, nor tool electrode consumption, but better surface roughness than EDM. Pure deionized water is an environmentally friendly electrolyte and it is very liable to get. Moreover, the transistor type switching power supply of micro-EDM can cut down the cost of conventional electrochemical machining (ECM) for micro-cavity.
First of all, the experiment employed a wire electrical discharge grinding (WEDG) mechanism to produce a ball-nose tool electrode with 0.35 mm diameter, then, carried on electrolysis in a new designed electrolyte circulation tank. The experiments were conducted by electrolysis with pure deionized water, and electrolysis with Al_2 O_3 mixed water, respectively, and comparison on micro-cavity profile and surface roughness were investigated. For electrolysis with 〖Al〗_2 O_3 powder, mixing alumina powder with deionized water, the alumina particles will be deposited onto the micro-tool and be used as fixed abrasive for grinding at the same time during electrolysis. By employing the 30 μm/min feed-rate with 50mA current and 0.2μs pulse-width in pure deionized-water electrolysis, it results in the best profile and surface roughness in variable operation conditions. As compared with conventional micro-EDM in kerosene, the work’s surface roughness by pure water electro-polishing is superior to about 60% of Ra roughness. From electrolysis polishing with mixed alumina powder, the highest alumina deposition is achieved with 15g/l of concentration and 500 rpm of spindle speed. In addition, by combining hybrid electrolysis machining with composite alumina powder and grinding with alumina abrasives, with the conditions employing 500 rpm, associated with 30μm/min feed-rate, 50mA current and 0.4μs pulse-width results in better profile and surface roughness of Ra 0.4 μm. Furthermore, hybrid electro-polishing with ECM milling by using deionized water achieves micro square insert 0.2 x 0.2 mm with depth of 0.01 mm with integrated surface. A slot with 0.2 x 0.1 with depth of 0.1 mm could also be achieved by ten layers of such a hybrid micro-ECM milling and electro-polishing scheme simultaneously, and the typical roughness of the finished bottom is Ra 0.227 μm.
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