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Cross Manufacturing invests in second large Puma 480 lathe
Cross Manufacturing invests in second large Puma 480 lathe

Cross Manufacturing invests in second large Puma 480 lathe

Added to MTDCNC by Mills CNC Ltd on 07 June 2013

Leading precision manufacturing specialist - Cross Manufacturing Co (1938) Ltd - has recently invested in a second large Doosan Puma 480 lathe, supplied by Mills CNC.

The latest Puma lathe brings the total to five Mills supplied Doosan CNC lathes, further demonstrating Cross’s confidence in these machines capabilities. It has been installed at the company’s recently acquired and refurbished 50,000sq ft South Site facility in Devizes during spring 2013.

The Puma lathes are used to manufacture a range of different diameter high-performance and high-precision brush seals used extensively in the aerospace industry (specifically in aircraft gas turbines), and increasingly in the power generation sector (land-based turbines).

The box guide-way Puma 480 purchased by Cross Manufacturing is a heavy-duty, versatile machine equipped with a powerful 37/45kW 1500rpm gearbox-driven spindle, a 10-tool position turret and the Fanuc 32iT Control. The lathe is being used to machine to high-accuracy a range of thin walled components in tough, difficult-to-machine materials such as Inco® 718.

In addition to its standard specification the machine was delivered with a number of additional options that enhance its flexibility and productivity, and these included a tow-along type programmable tailstock, a specialist tooling package, a swarf conveyor and bin, and a Renishaw HPRA tool-setter.

Following delivery and installation by Mills the machine was further customised on-site by Cross Manufacturing’s engineers working in conjunction with work-holding specialists to equip the Puma 480 with a PML-PAL light-weight precision pneumatic chuck (replacing the machine’s standard OE fit hydraulic chuck), and the quick and flexible ‘Ball Lock’  fixturing system.

To understand why the Puma 480 was purchased and why the machine was retro-fitted with air chucks etc., it is necessary to understand more about brush seals and the manufacturing methods employed by Cross Manufacturing.

Brush seals

Brush seals are used to improve the performance and operational efficiency of gas turbines.

They consist of dense, finely-packed 0.05mm to 0.168mm.diameter wire bristles fused (welded) between side-plates (a front plate and a backing plate), and are designed to come in contact with a jet engine’s rotor to create a positive seal.

Importantly they also retain the ability to deflect during shaft excursions and through thermal expansion/contraction without losing their sealing efficiency.

The bristle material, usually a cobalt or nickel alloy, provides an optimal combination of low wear and oxidation resistance. The front- and back-plates are typically manufactured from stainless steel or nickel alloys (selected for their heat and corrosion resistance).

Brush seals produced by Cross Manufacturing are supplied as either single units or in multiple segments according to customer requirements and are manufactured to rigorous industry best-practice standards.

There are a number of different processes involved in the manufacture of brush seals. Typically these will include initial roughing out of side plates from (ring form) forgings; assembly and welding of side-plates and bristles; heat treatment; machining (turning and milling); wire EDM machining; inspection; marking and packaging etc. The new Puma 480 was added to increase capacity after successfully proving the bespoke tooling concept on their first Puma 480 purchased 12 months earlier.

Brush seals, which resemble large rings, are essentially thin-walled parts and are manufactured to exacting tolerances. Critical to achieving part accuracies and maintaining roundness are the work-holding and fixturing methods employed during the machining (turning) process and the balance achieved between optimal chucking force and part stability.

(A small chucking force cannot restrain the part during machining operations whereas an excessive chucking force results in part deformation and roundness errors).

Explains Daniel Holton, Cross Manufacturing’s Production Manager, Brush Seals and Aerospace Products:

'Brush seals are critical performance components and there is no room or margin for error in their manufacture.

'To ensure that roundness tolerances are achieved and maintained during machining we work closely (in collaboration) with our machine tool (Mills), tooling (Sandvik) and work-holding (MicroLoc and WDS) partners to arrive at the optimum solution.

'It was through such discussions that we determined that our needs would be best met by replacing the Puma’s hydraulic chuck and draw bar with a high precision, low pressure (PML-PAL) 350mm 3-jaw pneumatic chuck system. To ensure quicker set-ups and improved productivity a bespoke work holding system was developed using the flexible Jergens Ball-Lock fixturing system, these are used on the modular custom chuck jaws designed and manufactured in house by Cross.

The two Puma 480’s with their modifications and adaptations are being put to use manufacturing a range of new, redesigned brush seals with re-usable back-plates.

The new seal which is patented by Cross Manufacturing provides further evidence of the company’s innovation and expertise in designing, testing and manufacturing class-leading brush seal solutions to its customers.

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