Experimental investigation of the effect of drill coatings on hole quality under dry and wet drilling conditions

The performance of three different coatings in dry and wet drilling conditions are investigated to identify and understand their effect on the surface texture of the hole produced, the maximum temperature rise in the workpiece, chip clogging at the drill flutes and the size and profile of the hole produced. A statistical analysis of these responses demonstrates that refractory coated HSS drills (TiAlN/TiN and TiAlN) perform best in terms of the dimensional accuracy of the hole. The MoS2-coated carbide drills produced holes larger than the ones obtained with refractory coated HSS drills. Drill coatings did not have a significant effect on the measured workpiece temperatures nor on the surface texture of the hole produced. The use of coatings led to flute clogging in wet conditions only, flute clogging was not observed in the absence of cutting fluids. The experiments conducted also demonstrate, within the experimental space investigated, increasing feed rates induce lower workpiece temperatures in the absence of cutting fluids.