Cutting hard-to-machine aerospace mould tools

Citation

(2007), "Cutting hard-to-machine aerospace mould tools", Aircraft Engineering and Aerospace Technology, Vol. 79 No. 1. https://doi.org/10.1108/aeat.2007.12779aab.005

Cutting hard-to-machine aerospace mould tools

Cutting hard-to-machine aerospace mould tools

The combination of Walter's Tiger.tec inserts and Xtra.tec milling cutters is enabling Larkshill Engineering to meet extremely demanding machining requirements on a batch of networking press tools for aerospace engine components.

In fact, without the new tooling, the Birmingham-based specialist machinist would “definitely struggle to even machine the highly abrasive workpieces in a cost-effective manner, let alone meet the customer's exacting surface finish and delivery demands” says Managing Director Frank Murphy.

Walter's Xtra.tec/Tiger.tec duo - a 66mm diameter button cutter and a 25mm diameter ball nose cutter for finishing routines - is successfully producing the heat-resistant tool steel moulds (male and female) that include 25 per cent chrome and 20 per cent nickel constituents, making them very difficult to machine with conventional tooling.

The press tools are heated to around 900/1,0008C and, in a hot creep process (similar to super plastic forming) are used to form titanium alloy components. The tools range in size from 1 to 1.5m long by 0.8 to 1.2m wide and have a total top to bottom height of 0.5m.

Other tooling from different suppliers has been applied to the material, but none is said to have compare with the Walter products in terms of machining speeds and feeds and, crucially, tool life - which is at least three times more than previously achieved with alternative tooling.

Larkshill's 20-year reputation for high-class machining, special-purpose machine manufacture as well as jigs and fixtures has been borne from its roots in the armaments, automotive and aerospace industries. Today, the ISO 9001-accredited company today focuses much of its shopfloor capacity on meeting a rising order book from its blue chip aerospace customer base.

The workload is such that Frank Murphy's policy of investment to achieve continual improvements has in recent times seen almost £1 million spent on new machine tools, resulting in an impressive array of CMC lathes, milling machines, VTLs and machining centres, for example, adorning the 18,000ft 2 site in the heart of the city.

“But buying the best machine tools available is just one part of the equation,” comments Larkshill's CMC Manager Neil Harrison. “We know how to make the most of CMC machines in terms of speeds and feeds, and multi-loading, for example, but our all-round project management expertise - beginning with a sophisticated CAD/CAM department - also plays a key role.”

This, he says, even includes materials sourcing, as was the case with the aerospace mould tools.

“Equally, we are also dependent on tooling specialists like Walter GB to provide best-in-class tooling as part of our strategy of always considering every aspect of production for maximum effectiveness.”

“We have used Walter tooling for certain jobs across the machines for many years,” he continues. “We always choose the best tools for the job, and Walter products are critical to our ability to remain both cost-efficient and responsive.”

Another example of this, he says, is the fact that Walter's Tiger.tec is currently being trialled in a turning application of exotic materials.

He continues: “The order for the heat-resistant chrome/nickel tool steel moulds presented particular problems in terms of the abrasive nature of the workpieces. When it is recognised that each billet is worth five-figures even before machining starts, we simply can't afford to make any mistakes, particularly during the finishing blending passes prior to hand polishing to achieve the standard 0.1 Ra finish.”

Walter recommended its latest PVD Al Ox Tiger.tec inserts (WSM 35) in combination with the F2334 66mm diameter button cutter for initial machining, plus the F2139 25mm diameter ball nose cutter with P3204- D25 WXM 35 Tiger.tec inserts for finishing.

Tiger.tec inserts combine a mixture of aluminium oxide and titanium nitride coatings on a tungsten carbide substrate to offer unrivalled cutting performance - the inserts are claimed to regularly achieve up to 75 per cent more components per edge than competitor products, and in some cases double output is said to be achieved, due to their improved process reliability courtesy of a high resistance to flank wear, cratering and thermal cracking.

The inserts' black, aluminium oxide coating is said to be particularly effective against tribochemical wear and permits higher cutting speeds and feeds to be employed while also providing longer service life. The golden coating applied to the clearance surfaces simplifies wear detection and thus avoids the unnecessary waste of unused cutting edges.

Both tools are applied at 95m/min (“alternative products couldn't get anywhere near this,” adds Neil Harrison) and at 0.3rev/tooth and 0.2rev/min tooth for roughing and finishing, respectively.

The result is that the hard-to- machine material presents no problems at all and tool life “is at least three times that possible with alternative tooling”. Indeed, visible insert wear is negligible in the regular 27h non-stop machining routines!

With its continual improvement philosophy, Larkshill Engineering is clearly soaring ahead in supplying machined parts to what is undeniably a demanding industry sector. And because it is Frank Murphy's unwavering policy, the 28-employee company is successfully competing on a global basis in terms of cost, lead times and delivery - and that includes winning business back from Eastern Bloc competitors that were falling down on quality of both castings and machining - and is on course to a record £2.8 million turnover (Figures 5 and 6).

Figure 5 Walter's Xtra.tec/Tiger.tec tooling duo successfully produces heat-resistant tool steel moulds for aerospace engine components at Larkshill Engineering

Figure 6 Larkshill Engineering's MD Frank Murphy, right: “Without the Walter tooling, we would struggle to machine the highly abrasive workpieces cost-effectively.”

Details available from: Walter GB Limited, Tel: +44 (0)1527 60281, E-mail: gerry.ohagan@walter-ag.de Web site: www. walter-aq.de