モリブデンのクラックレス放電加工 (第2報)

Abstract

Molybdenum (Mo) is often machined by electrical discharge machining (EDM) because of its high hardness. The cracks did not occur by EDM with a silicon electrode in deionized water. The silicon electrode cannot be used for small-hole EDM because of its heavy wear. Mo was machined by EDM with a Ti electrode in deionized water, while many cracks occurred in the base material and recast layer in the case of the positive electrode polarity. The cracks might generate by crystal grain boundary embrittlement. Because an Mo rolled plate has crystal grain anisotropy, the machining direction has an effect on the crack direction or density. In this study, the effect of the crystal grain anisotropy on the crack generation was investigated. The crack direction and density in the EDMed surface and cross section is parallel to the crystal grain boundary of Mo on the positive electrode polarity. In the case of the machining in the rolling and transvers direction, the crack reached more deeply than that in the normal direction. In contrast, the EDMed surface and cross section indicated crack-less on the negative electrode polarity.