The effect of operating parameters and tool materials on cutter wear/life and hole quality when drilling Al/SiC metal matrix composite (MMC)

Experimental data is presented relating to tool wear/life, hole accuracy (diameter, out of roundness, cylindricity, edge quality), chip morphology and workpiece surface integrity when drilling an aluminium based metal matrix composite (MMC) reinforced with 15 vol% SiC particulate. The performance of 6.35mm diameter uncoated and TiAlN +TiN coated tungsten carbide (WC) drills as well as brazed polycrystalline diamond (PCD) tools was evaluated, with high pressure cutting fluid at 70 bar employed in all tests. When operating at 160m/min with a feed rate of 0.1mm/rev, flank wear progression of the PCD drill was gradual, with a maximum scar length of only ~60µm after 300 holes. In contrast, the tool life of both the uncoated and coated carbide drills did not exceed 10 holes (based on a flank wear criterion of 0.3mm), despite operating at a lower cutting speed of 80m/min. Corresponding SEM micrographs of the worn drills indicated abrasion was the dominant wear mechanism. Uniform burrs (without caps) were prevalent at both hole entry and exit when employing WC tools, while no sign of burring was evident in any of the holes machined using the PCD drills. Chip morphology was also markedly different, with the WC drills producing fan-shaped chips while needle-like swarf was typically observed when utilising PCD tools. Assessment of hole surfaces revealed the presence of flaws including cavities/voids, grooves, workpiece smearing and flaking/removal of the matrix material when using carbide drills.