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RST Engineering has installed a Hurco VMX30U five-axis machining centre to reduce large-batch aircraft component production costs.

The company installed a Hurco Hawk 30 CNC mill in 1998 and in 2007 traded in the hawk for a three-axis Hurco VM2 vertical machining centre, taking advantage of automatic tool change to fulfil contracts more economically for increasingly complex aerospace, medical and motorsport components.

In 2009, the company progressed to five-axis machining on a Hurco VMX30U machining centre, with positive results.

The machining centre was bought initially to reduce production costs when the manufacture of prototype housings for aircraft on the VM2 moved to large batch runs.

The circuit board housings are 200mm2 and have to be machined from aluminium billets on six sides to dimensional tolerances within 15 microns.

In the process, over 90 per cent of the material is removed.

When the part was milled on the three-axis machine, five sides were completed in eight to 10 hours, including repeated manual re-fixturing.

The part is now machined in around three hours on the five-axis Hurco.

As only one additional set-up is needed for machining the sixth face, the component is produced in two milling operations followed by sparking.

Jason Taylor, owner of RST Engineering, said: ‘A useful feature of the five-axis VMX is that the aircraft housing and similar, relatively simple cube-type parts can be programmed at the machine in Hurco’s twin-screen Ultimax control.

‘This takes a fraction of the time that would be needed on our Vero Visi 3D CAD/CAM system, which is freed for more complex programming.

‘A further benefit is that the setter-operator does not have to walk back to the office to edit a program to adjust a tool, for example – it can be easily done on the shop floor using the control’s Winmax software,’ he added.

Taylor is said to be particularly impressed with the NC-Merge feature within Winmax, which allows complex parts of a program to be generated off-line using a CAD/CAM system and imported into the Ultimax control for the remainder to be completed.

There are occasions when this strategy allows a more efficient program to be written than would be possible using off-line CAD/CAM alone.

One recent example was a 3D part that needed holes drilled in it after rotation.

They would have had to be drilled straight to depth, whereas pecking cycles were easily added in Winmax.

Other five-axis jobs machined on the VMX30U include plastic clock parts and a wrist support plate in titanium, both of which required fully interpolative five-axis machining.

Taylor said that while this is useful, allowing RST to take on extra work that it could not have tackled before, the main benefit of five-axis is to reduce set-ups when machining components on five or six sides.

He said: ‘Every time you want to mill a sharp corner in a pocket to replace a radius, or drill a hole at a compound angle, it would involve another set-up.

‘This not only adds production cost and risks introducing accumulative errors, but is monotonous for operators if there are, say, 50- or 100-off to produce.

‘Automatic five-axis positioning in-cycle avoids the potential problem of an operator’s attention wandering and the consequent risk of scrapped parts,’ Taylor added.

An example of a contract where five-axis benefits are considerable is the production of components for high-voltage electrical switchgear.

They were previously produced in three operations but are now machined in one hit on the VMX30U.

In August 2010, 25-off of each of 10 varieties were produced and the customer wants a further 175-off.

That will be 4,000 set-ups saved, according to Hurco.

In RST’s case, with its EDM specialism, the five-axis Hurco machine is assisting in the production of copper electrodes, which are also becoming more complex.

Accuracy of +/-6 micron is easily held on the VMX30U, which Taylor describes as rigid, reliable and repeatable.

He said that it took only two days’ training to become conversant with programming five-sided milling and drilling routines on the Ultimax control.

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