Five-axis productivity raised by 25% on impellers

A 5-axis VMC has proven to be 25 per cent more productive than other 5-axis equipment as bigger diameter milling cutters that take double the depth of cut could be used.

One of the world's top independent 5-axis milling houses, Turbocam specialises in producing blades, blisks and impellers for aerospace applications and for turbomachinery such as air compressors, gas turbines and turbochargers for train and ship propulsion.

The group's European headquarters in Fareham, Hampshire, has increased the size of component that it can manufacture by nearly a quarter - now 800mm diameter - following the installation at the beginning of 2004 of a Hermle C 40 machining centre from Geo Kingsbury.

The latest purchase brings to eight the number of 5-axis machines at Turbocam Europe, although the group uses over 30 more at its factories in the USA, India and Taiwan.

Established in 1985, the Fareham company employs 18 people and currently operates two shifts, five days a week.

About 30 per cent of output is consumed within the UK and some components find their way overseas via British multinational customers, the remainder of the business being direct exports.

A particular focus for expansion is the manufacture of implants for the medical industry, which is another sector that demands high precision, 5-axis machining.

Rob Taylor, managing director and a shareholder of the UK-based subsidiary, commented, "Our parent company in Dover, New Hampshire, was the first to invest in a Hermle machine in 2002 and based on its reliability, we decided to go the same way.

"Compared with our other plant, we find that the C 40 produces a better, more consistent surface finish due to the machine's rigid construction and the use of a vibration-resistant mineral casting for the bed.

These are more important for true 5-axis interpolative profiling than for the more usual 3- or 4-axis cutting plus positioning.

Blade profile tolerance held on our larger parts is typically 50 microns total but reduces to 15 microns on some smaller components.

"The machine has also proved to be around 25 per cent more productive than our other 5-axis equipment, partly because we are able to use bigger diameter mills and take double the depth of cut.

With over 60 per cent of material removed from each turned billet - normally stainless steel but also titanium and aluminium - in cycles of up to 20 hours, the savings are considerable, especially when roughing." Higher productivity is also a result of the 18,000 rev/min top speed of the 15kW/40-taper spindle (there are options up to 40,000 rev/min) as well as linear slideways in X, Y and Z which allow 6m/s2 acceleration to 45m/min.

More particularly, rotation of the table and trunnion on the Hermle is faster thanks to the use of linear motor technology, which drives the C and A axes at 65 rev/min and 25 rev/min respectively.

This, according to Taylor, makes a big difference because rotary axis speed tends to be the limiting factor when machining blades, as a lot of manipulation is needed especially around the leading edges.

Another imperative in blade and impeller manufacture is to have a good controller able to handle the large amounts of data needed to define sculpted surfaces.

In this respect, the Hermle machine's powerful Heidenhain iTNC 530 contouring CNC system with path control optimisation performs well.

Programs are downloaded over a wireless network directly to the control's hard drive to avoid the potential errors of drip-feeding large amounts of data over a DNC link.

Turbocam's manufacturing disciplines are highly specialised.

Jobs come in as IGES solid models but more usually as CFD (computational fluid dynamics) data.

The company carries out detail work on leading edge definitions using SDRC and Camax Comand as its base CAD/CAM package.

Overlaying this is Turbocam's own Truepath software, which has been developed in-house to take the generated toolpaths and perform smoothing, editing, visualisation and post-processing.

The group has started selling this proprietary software to other 5-axis machining specialists around the world.

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