As a fundamental study of grinding mechanism, a single grit grinding test was performed, and the effects of heat treatment condition of steel on the metal removal mechanism and chip shape were investigated. The relation between the cutting speed or the shape of tool and the chip shape formed under different heat treatment conditions was also examined.
After the chip forming process in the single grit grinding had been frozen by a quick stop device, the chip shape and material behavior ahead of the rake face were observed on the cross section of the chip through optical and electron microscopes.
It was found from the detailed observations that, in the case of thin chip (about 30μm in thickness), slips cause by secondary shear occurred inside the chip and the temparature of the shear plane rose so high as to soften the steel. Next moment, a white hardened layer was formed on the slip plane as the result of rapid cooling. In quenched steel, as the chip was pushed out to the tool face, it became thin and long by the removal mechanism of workpiece. The chip shape developed into a flow type in the normalized steel, and a shear type in annealed steel under the condition of a cutting speed of 460m/min and an apex angle of 100°. As the cutting speed increased, the chip became smaller, and as the apex angle of cutting edge increased, the chip became longer and wider in all of the three conditions of heat treatment used in this test.
