Investigation of tool wear suppression in ultraprecision diamond machining of die steel

Rapid tool wear in diamond machining of steel can cause catastrophic failures. Despite several approaches to reducing tool wear, diamond machining of steel for industrial applications remains limited. We investigated two solutions, namely plasma nitriding treatment for workpiece surface modification and elliptical vibration cutting for cutting process modification, to determine their effect on reducing tool wear in diamond machining of AISI 4140 die steel. Furthermore, a new approach by combining the two solutions was also explored. Experimental results showed that diamond tool wear could be reduced by several orders of magnitude and mirror-quality surface can be obtained by using either the plasma nitriding treatment or the elliptical vibration cutting. However, in contrast to our expectations, combining the two solutions did not yield further improvement of either the surface finish or the reduction of tool wear compared with that of elliptical vibration cutting alone due to microchipping. Care has been taken to investigate the mechanism responsible for microchipping, and it was found that microchipping is highly dependent on the crystal orientation of the diamond. A diamond tool with the (1 1 0) plane as the rake face and the (1 0 0) plane as the flank face was more resistant to damage, and the microchipping induced in the combined cutting process was almost completely suppressed.