Study on in-air electro-contact discharge (ECD) truncating of coarse diamond grinding wheel for the dry smooth grinding of hardened steel

摘要

Dressing is used to protrude the micron-scale grains from wheel bond, but the grain protrusion height is not identical due to the irregular grain shape and distribution. In order to assure the grain uniformity with identical protrusion height, the electro-contact discharge (ECD) truncating is proposed after dressing. In the ECD truncating, an in-air impulse discharge thermal between wheel and electrode is transferred to cutting interface of diamond grain through the cutting chip. Accordingly, the outstanding thermal conductivity of diamond is utilized to perform a mechanical and thermochemical removal of grain edge layer without any damage to its hardness. The objective is to realize an efficient truncating of coarse diamond wheel for dry smooth grinding of hardened steel. First, a constant-voltage/constant-current transform was employed to suppress the short-circuiting current between wheel and electrode and to adjust the discharge thermal to diamond grain surface. Then the grain temperature distribution was modeled with reference to the transfer of impulse discharge thermal to cutting interface for diamond graphitization. Finally, the truncated diamond wheel was used to perform a grinding in contrast to general CBN wheel. It is shown that the spark-discharge thermal transferred from the rolled-up cutting chip to the grain cutting interface contributes to truncating. In in-air ECD truncating, the spark-discharge voltage ranges 19-23 V, which increases the grain truncating rate by 95% against the general arc-discharge. The truncating temperature may be maintained as about 626 degrees C to induce the layer graphitization of diamond grains with the mechanical and thermochemical removal up to about 6435 mu m(3)/min. In contrast to wet CBN grinding, the dry grinding greatly improves the ground surface with the truncated diamond wheel rather than the dressed one.