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Through-Tool Coolant Drilling of Aluminium/SiC Metal Matrix Composite


 Through-tool coolant has been applied to the drilling of a 2618 aluminium alloy reinforced with 18% silicon carbide (SiC) particles. Titanium nitride coated, K10, solid carbide drills were used to investigate the effect of the coolant application method on the performance of the drilling operation. Through holes were drilled in a 24 mm thick workpiece material without the application of any coolant, with the conventional application of coolant and with the coolant applied through-the tool. Cutting forces were measured during the drilling trials in addition to the wear on the drills, the extent of the entry and exit burrs produced on the workpiece and the quality of the holes produced. The results obtained provided strong evidence that the conventional application of coolant was having no beneficial effect on the cutting operation compared to dry drilling. However, there was very little evidence of an increase in drill wear which some workers suggest is associated with the formation of an abrasive slurry when using coolant with MMCs. Nevertheless, examination of the used drills in the scanning electron microscope confirmed abrasion as the primary wear mechanism. The results showed mat even at the low coolant pressures, through-tool cooling gave a significant improvement in tool wear, cutting forces, surface finish and the height of the burrs produced. Consequently, the recommendations from this work are that through-tool coolant can result in a marked improvement in performance when drilling MMCs and that conventional cooling has virtually no effect on the machinability of this material compared with dry drilling.