High-speed milling of titanium and gamma-titanium aluminide: An experimental investigation

Objectives. This thesis explores the potential for high-speed milling (HSM) of difficult-to-machine materials by seeking to understand the root causes of tool failure.; The objective was to achieve an order of magnitude increase in tool life when machining at high speed, simply by controlling or avoiding the failure mechanism.; Experimental results. The experimental work yielded the following results:; High-speed rough milling of Ti6Al4V (high a e), is feasible at speeds of 152--229 m/min (500--750 sfm) using directed through-spindle coolant (TSC) with uncoated carbide and PCD tooling. Later testing showed the ability of PCD to function from 229--610 m/min (750--2000 sfm) using directed high-pressure (600 psi) TSC under fine peripheral finishing (low ae) conditions. Chip loads were constrained to 0.025--0.038 mm.; High-speed finish milling of Ti6Al4V (152--305 m/min or 500--1000 sfm) with carbide tooling under pressurized air coolant is more effective than flood (which in turn is better than TSC) for finishing cuts, but wet machining may perform better under lower speed or high immersion conditions.; Ultra-high-speed finish milling of Ti6Al4V (457--1,372 m/min or 1500--4500 sfm) using PCD tooling under TSA50 is feasible if immersions (<0.5 mm or 0.020&inches;) and chip thickness (<0.038 mm or 0.0015&inches;) are maintained below critical levels. Cutting speeds >915m/min (3000 sfm) are possible but may pose a fire risk if precautions are not taken. The tool life versus cutting speed behaviour for PCD on Ti6Al4V is not straightforward and is highly dependent on the PCD grade. Using high TRS (low grain size) PCD grades (DA2200, CTB002, and FG (a developmental grade from Element6)) 216--252m (8,500--9,900&inches;) of tool life may be achieved at 457m/min (I500sfm). Alternatively, at 457m/min (1500 sfm) the FG grade at hx = 0.038 mm (0.0015&inches;) will yield the same tool life as a conventional PCD grade E30 at hx = 0.025 mm (0.001&inches;), approximately 71 m (2800&inches;). Below 305 m/min (1000 sfm), cutting forces may become excessive for PCD, resulting in edge chipping.; HSM finish milling of gamma-titanium aluminide at cutting speeds below 500 m/min produces cutting temperatures in excess of that for Ti6Al4V. Under finish milling conditions (h x = 0.038 mm (0.0015&inches;), ae = 0.25 mm (0.010&inches;), TSA50) a cutting speed threshold of 76 m/min (250sfm) is exhibited for carbide tooling. Above this threshold, coolant performs better than pressurized air, but the resulting tool life is very low. For radial immersions of 0.50 mm (0.020&inches;) and larger, FLOOD coolant is also recommended under light chip loads. (Abstract shortened by UMI.)...