As if a host of Starrag developments and innovations in the machining of turbine blades, blisks and casings were not enough, then the keynote address by Rolls-Royce’s Doctor Gregor Kappmeyer certainly enthralled every visitor to Starrag’s recent Turbine Technology Days.
Showcasing a range of machines as well as complementary software and tooling for world-class turbine engine production, the event attracted customers and partners from as far afield as China and the USA to the company’s headquarters in Rorschacherberg, Switzerland. And to add to interest levels, the technology demonstrations were intermingled on Starrag’s working manufacturing floor where a high number of machines were at various stages of build.
Rolls-Royce Deutschland’s Manufacturing Manager of Engineering & Technology, however, certainly made delegates think when he spoke about ‘Modern aero-engine components – efficient machining is the key to success’.
Talking about the technical challenges in machining such components – and the lifecycle cost factors, such as fuel usage, that are driving the quest for higher efficiency engines - Dr Kappmeyer pinpointed a number of product and business challenges:
 Product challenges – including more complex designs, new materials (more high-temperature super alloys and composites) and tighter quality specifications;
 Business challenges – for example, aggressive cost targets, improved safety and improved delivery adherence.
“To remain competitive,” he said, “we must continue to adopt new materials and manufacturing technologies, modern equipment and methods, and improve our process understanding – embracing an increased attention to detail by the use of simulation, tool specification and quality control (with suppliers).”
There was, in fact, no shortage of developments in any of these areas at the Turbine Technology Days workstations with, for instance, the single set-up machining (milling and turning) of aero-engine compressor casings, 24 x 7 production of blades on a robot fed machining centre (alongside details of various Starrag-led flexible manufacturing systems) and the utilisation of Starrag’s new NB machine’s unique A/B axis configuration to vastly improve blisk machining times.
Single set-up milling-turning
The milling and turning in a single set-up of a 500 mm long by 660 mm diameter aero-engine compressor (typically Inconel or titanium) saw the workpiece mounted on a Starrag STC 800 MT, a 60 kW machine with a spindle speed of 15,000 revs/min and a torque rating of 174 Nm.
The full process, after Vericut simulation, is milling, turning, internal machining with angle head (Benz), back spot facing (with Heule Solo 2) and measuring (by Renishaw TC53-30 probe). Wall thicknesses down to 5 mm were characteristic.
Non-stop blade production
With robot handling, the Starrag LX 051 horizontal machining centre has X, Y and Z axis strokes of 650 mm by 650 mm by 680 mm, respectively (and traverse rates of 62 m/min), plus 360 deg in the 200 revs/min A axis and a 60 revs/min B axis of 360deg continuous.
The machine shown was capable of the automated loading and unloading of 40 blades of up to 400 mm long, extending unmanned operation time to up to ten hours. Any profiles within workpiece envelopes of 10 mm by 10 mm and up to 200 mm by 200 mm can be processed, and the use of modular fixturing means set-ups can be changed within minutes.
Starrag’s considerable expertise at developing flexible manufacturing solutions, and being the prime integrator of such, was also highlighted with a number of systems being illustrated, including:
 For precision forged compressor blades (40,000 blades/year) plus integrated inspection and marking, two tool grinding machine stations, as well as tool presetting and tool shrinkage stations; and
 For forged guide vanes (35,000 vanes/year) complete with polishing cells, integrated inspection and marking, plus tool presetters and tool shrinking stations).
Blisks machined with very small axis movements
With 56 titanium blades of 30 mm long, the 524 mm diameter turbine engine blisk mounted on a Starrag NB 251 demonstrated how the machine has been specifically developed for machining the blades via a tip-entry strategy.
With a B axis head that intersects with the spindle centreline, and pivots around that intersection by its tool length of 150 mm, the resulting minimal compensatory movement (reduced by 96 per cent) results in time reductions of up to 80 per cent. This equates to machining the blade edges five times faster than usual!
The NB 251 is capable of handling blisk diameters of up to 1,100 mm and with blades up to 200 mm long.
More to see
In addition, the Turbine Technology Days also highlighted the prowess of Heckert HEC machines – on titanium alloy hydraulic blocks (using a HEC 500 X5), on turbine casings (HEC 800), landing gears (HEC 1800) and structural parts (HEC 800 X5), in all cases demonstrating the cost-saving benefits of Starrag’s mission of providing machines that enable customers to ‘Engineer precisely what you value’.
Also, a Heckert HEC 630 was demonstrating in-cycle friction stir welding, and a Starrag LX 151 was shown producing unblemished surfaces on even the thinnest (1.94 mm on inner pockets) aluminium outlet guide vanes, producing the vane to profile form tolerances of +/- 0.102 mm and to a surface quality of Ra 1.6 in the direction of flow.
Other areas of note included TTL adaptive machining for blisk repair (rather than scrap – repairs usually equate to 60 per cent of the cost of buying new), Haimer tool shrinking and tool balancing, and the latest (version 7.4) of Starrag’s RCS software which has improved routines for snubber machining, trochoidal milling and reduced tool wear.