The effect of cutting speed and tool material on hole quality when reaming C355 aluminium alloy

A reaming operation is typically performed when the requirements for hole accuracy (form and size) and surface finish cannot be achieved solely by drilling. Experimental work was carried out to evaluate the influence of tool material/coating (uncoated carbide, CVD-diamond coated carbide and PCD) and cutting speed (32 and 96 m/min) on tool wear, cutting forces/torque and hole quality/integrity, when reaming pre-drilled (4.8 mm diameter) blind holes in cast, heat treated C355 aluminium alloy (~ 4.7% Si content). All of the reamers were 5.08 mm in diameter with trials undertaken at a constant feed rate of 0.12 mm/rev. Flank wear up to ~ 40 µm was observed after ~1680 holes when employing the uncoated tungsten carbide (WC) reamers whereas no discernible signs of wear were seen on either the CVD-diamond coated or PCD tools at test cessation. Thrust forces were found to be ~50% higher when utilising the diamond coated reamers compared to the uncoated WC tools. Workpiece surface finish generally improved at the higher cutting speed with PCD tools producing roughness levels down to ~0.05 µm Ra. Average hole out of roundness was below 5 µm in all trials while corresponding cylindricity did not exceed 14 µm. Material microhardness variation over the test duration was negligible and cross sectional micrographs showed no significant workpiece damage or deformation regardless of operating conditions.