As the aerospace industry’s demand for titanium continues to climb – according to some sector observers, global usage could grow by 40 per cent this year – the Starrag Group continues to reinforce its world technology lead in the machining of a material that offers high tensile strength-to-density ratios and is highly resistant to corrosion and fatigue.
In an exclusive series of Ti Benchmark Days at its headquarters in Rorschach, Switzerland, Starrag enthralled visitors by presenting demonstrations on a variety of typical titanium aerospace workpieces using a range of Starrag machining centres:
Five- and six-axis horizontal machining centres STC 800 - 1800
Five-axis titanium profilers EcoForce Ti 9, 13, 24 and 30
BTP 5000/2 twin-spindle Profiler.
Each machine showed impressive chip removal capability as well as cost-effective production routines - unrivalled in their class in every case.
Taking centre stage, the BTP 5000/2 five-axis twin-spindle Profiler was shown simultaneously machining two airframe spar segments of Ti6Al-4V. Measuring about 3,300 mm by 700 mm by 80 mm, the workpieces start life as 317 kgs billets and are reduced to 15 kgs finished parts in 28.3 hours.
The 37 kW (52 kW optional), 8,000 revs/min machine, which boasts a torque of 940 Nm, cuts at depths of cut up to 100 mm achieving a massive maximum material removal rate of 750 cm3/min per spindle compared to the usual 200-300 cm3 for hard metal machines.
A number of innovative machine features contribute to such impressive performance figures – where the results are also consistently dictated by Starrag applications engineers’ expert balancing of cycle times with tool life/cost and workpiece quality.
Not the least of these are a geared spindle and steel-on-steel worm gears, as well as the clever use of a damping brake within the very rigid A axis swivel head, which operates in much the same way as a car clutch system. With this system, heavy roughing becomes a reality even in five-axis simultaneous operation.
In addition, high-pressure 100-bar, ambient temperature-controlled through-tool coolant allows for higher cutting speeds and tool life. It is complemented by the use of flood coolant to minimise the effects of the inherent excessive build-up of heat at the cutting face, which could lead to distortion of the workpiece/reduced tool life.
Importantly, too, Starrag engineers also adopt best-in-class tooling – the best from Ceratizit, Kennametal, Mitsubishi and Walter, combined with Starrag’s in-house tool production expertise – to achieve the most cost-efficient production solution to each unique scenario.
The BTP Profiler demonstration involved:
Initial roughing – using a 160 mm diameter face mill at a cutting speed of 70 m/min and a depth of cut of 8 mm; then
Contour roughing – using a 63 mm diameter porcupine cutter at speeds of 40 m/min and taking 65 mm depths of cut;
Pocket roughing – using a 25 mm end mill at 70 m/min and a 50 mm depth of cut; and finally
Finishing – using a 25 mm end mill at 40 m/min and a 30 mm depth of cut.
BTP machines are available with pallet lengths from 4,500 mm to 8,000 mm, and X, Y and Z axis travels of 5,000 mm to 8,000 mm, 1,300 mm to 1,850 mm and 1,200 mm, respectively. The A axis is +/- 100deg and C axis is 360deg continuous. Feed rate in X, Y and Z is 25 m/min, and 14 revs/min in A and C.
Starrag also offers a range of STC machines, extending from the 800/130 with axis strokes of 1,450 mm by 1,200 mm, up to the STC 1800/130 for components of 3,300 mm by 2,200 mm.
The STC’s articulated head is available with the same geared spindles as the BTP, ranging in speed from maximum 5,600 to 12,000 revs/min, in power from 37 to 52 kW and in continuous torque from 620 to 1,300 Nm.
Crucially, the use of the optional two-axis head (as used on the BTP machines) effectively transforms STC models into six-axis machines.