EFFECT OF DRILL WEAR ON CUTTING FORCES IN THE DRILLING OF METAL-MATRIX COMPOSITES

Holes were drilled in 6061 T-6 aluminum alloy as well as in a particle reinforced metal matrix composite (MMCp) consisting of 20 vol.% SiC p articles, 12 mu m in diameter, in a 6061 aluminum matrix (6061/SiC/20p , or Duralcan(R) F3S.20S). HSS (high speed steel) drills of 10 mm diam eter were used, and measurements were made of thrust (normal force), t orque and flank wear for several feed rates and drill speeds. It was f ound that when drilling Duralcan(R) with unworn drills, bath torque an d thrust varied with feed rate raised to the power 0.81, as for classi cal materials. When flank wear V-b became significant, torque varied l inearly with V-b and with f(0.8) but no empirical relation with physic ally meaningful parameters was found to fit the thrust data. Speed had no significant effect on wear or on drilling forces. Flank wear proce eded linearly with depth of material drilled, or with the total distan ce passed by the lip or cutting edge of the drill. A linear relation b etween both thrust and torque against flank wear was observed, so that either thrust or torque may be measured to give an indication of wear of the drill. The linear relation between torque and wear of the dril l implies a linear variation of specific cutting energy with flank wea r. Drilling forces are controlled by the matrix material and not by th e particles.