Cold working die steel, SKD11, is commonly used for the fabrication of metal molds owing to its superior wear and corrosion resistance properties. Carbides containing coarse grains in a melted layer can be completely decomposed into their elements by the laser irradiation of SKD11. Crystalline structures also change in the melted layer. In this study, the creation of a functionally graded material based on hardness was carried out experimentally, by controlling the crystalline structure and grain size on the basis of the change in feed speed. The crystalline structures in the melted layer become fine-grained, columnar and coarse-grained at a power density of 3.1x10⁵W/cm² and a feed speed of 300mm/min. The tensile residual stress on the laser-irradiated material can be removed by aging treatment for 5 minutes at 850°C. Under the above-mentioned conditions, the crystalline structures barely change before and after the aging treatment. Finally, the hardness changes linearly from 830HV at the surface to 680HV in the base metal. Thus, SKD11 with functionally graded structure was developed by combining laser irradiation and aging treatment.

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In this paper, we describe the results of our study of precision micro-Electro-Discharge Machining. Micro-EDM had been developed and mainly used for making holes in nozzle plates within the inkjet printer field. Smaller-diameter hole boring and burr minimization are required in the manufacture of aperture disks for electron beam equipment such as SEM and FIB. Specifically, this study focuses on the measurement of the floating stray capacitance of a relaxation pulse-type electro- discharge generator, the investigation of the effect of the waveform of pulse discharged current, and the resulting surface roughness of the machined area as they relate to each element of the discharge circuit including the pulse generator and equipment. Additionally, it is confirmed that the use of a low gap voltage achieves a smoother surface finish. This is the result of the diameter of each single crater generated on the surface by a single pulse discharge being smaller than 1.2μm, which is 50% smaller than that for conventional micro-EDM equipment.

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In this paper, we describe the development of an advanced micro-EDM device. A smaller micro-EDM process and more complex microshaping technology are required by various industries. To meet these requirements, an original advanced high-speed gap control technique and an independent process feed control function of two-axis contouring have been improved. We observed capability to shape a tungsten electrode minimum diameter of 2.4 μm using low gap voltage of 25 V with high-speed gap control. The capabilities of the advanced micro-EDM function and its application are reported.

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