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At Greenway Pepper Precision Engineering, aluminium components are being machined much faster following the installation of a Brother high-speed four-axis VMC from Whitehouse Machine Tools.

For example, a medical component that used to be produced in 70 minutes on a standard, one-year-old VMC (vertical machining centre) now takes just 26 minutes to machine on the Brother.

Overall, cycle times were more than halved for producing this and five other components transferred in the first month.

As the Brother machine is equipped with a twin pallet changer, Greenway Pepper’s first parts are presented more quickly to the spindle so floor-to-floor times are reduced.

The Brother TC-32BN QT has a top spindle speed of 16,000rev/min and 1.5G acceleration to rapids of 70m/min in X,Y and Z.

These figures are much higher than the 8,000rev/min and 30m/min on the subcontractor’s other VMCs recently purchased from another supplier.

‘It was the relative slowness of our other machines and a sudden upturn in medical business that prompted us to buy the Brother machine,’ said Greg Pepper, joint owner and managing director.

‘I had seen the TC-32BN at Mach 2008 and visited the Whitehouse technical centre in Kenilworth last year, where I was able to see demonstrations.

‘It was like having the output of two machines in the footprint of one.

‘However, the opportunity to invest did not materialise until work for an Aids blood sampler and a DNA testing machine arrived in quick succession,’ he added.

Trials were carried out by a number of potential machine suppliers, including Whitehouse.

The TC-32BN QT was at least a third quicker than the other shortlisted VMCs and 2.6 times faster than a twin-pallet model offered by a recent supplier to the Newcastle-under-Lyme factory.

Part of the productivity advantage on the Brother is down to high speeds and feeds when the machine is in-cut, and the machine also has short idle times.

Promoting the latter is acceleration of the BT30 spindle from 0 to 16,000rev/min in 0.46s, enabling a chip-to-chip time of 2.1s.

While a tool is being exchanged from the 40-station magazine, the workpiece can be repositioned ready for the next feature to be machined, or else the twin pallet table can start its rotation.

By the time the part is in position, the spindle is hovering over it at 16,000rev/min, ready to cut immediately with the correct tool.

Installed in March 2010, the TC-32BN QT is operated flat out by Greenway Pepper all of the time.

High-pressure coolant at 70 bar through the spindle and tool dispels the large amounts of swarf generated.

Coolant of a relatively thick consistency prevents tap breakage, which is important as a large amount of synchronous tapping is carried out at 8,000rev/min.

This feature, a Brother first, involves true linear interpolation in Z with spindle rotation, resulting in higher speed, better control over thread quality and depth, and longer tool life than with conventional rigid tapping.

Workpiece clamping is configured differently on the two pallets, allowing Greenway Pepper a high degree of versatility.

On one pallet there is a Microloc baseplate with clamping elements for workholding.

The other pallet supports a Nikken trunnion-and-tailstock indexer that rotates a Microloc plate through 360deg to provide a fourth CNC axis.

One of the applications on this Brother VMC involves machining solid aluminium billet to produce a well plate for storing blood samples.

The component has a 12 x 8 array of tapered cones that have a drawing tolerance of half a degree and a fine internal surface finish.

Positional tolerance of the individual wells is within 20 micron.

Flatness on the back of the component must be within 25 micron, which can only be achieved using a relatively small, 4mm diameter milling cutter, as a larger tool would introduce stresses.

The maximum 70m/min cutting feed rate and 16,000rev/min spindle speed of the Brother are suitable for removing material quickly from both faces without distorting the plate.

Total cycle time is 40 minutes, which Pepper is said to be impressed with considering the amount of aluminium milled away by such small cutters.

The cycle time quoted includes the exacting routine of drilling 0.8mm diameter blind holes in the top face of the component, drilling similar holes in the side to meet the first holes.

This creates a vacuum-less hole for thermometer insertion.

Another medical component, whose cycle time has dropped from 70 to 26 minutes, is the side plate for a new instrument that will allow on-the-spot DNA profiling by medical staff and police forces.

Due for launch in July 2010, the equipment has an aluminium casing comprising a range of parts, prototypes for which Greenway Pepper produced at the end of 2009 in batches of 50-off on its slower machining centres.

The subcontractor is expecting a 63 per cent saving in production time on the Brother machine once volume manufacture starts.

To extract more benefit from investment in the twin-pallet machine, Greenway Pepper has moved from single- to double-shift operation, 7am to 10pm.

The approximately 250mm by 100mm side plate for the DNA equipment is machined from 10mm-thick 6082 T6 aluminium plate.

As before, it is essential to keep machining stresses low, so an 8mm-diameter cutter reduces the thickness to 7mm, rather than a much larger cutter that would normally be used.

High-speed drilling and tapping are again important, as the component incorporates many M2, M3 and M4 holes, all of which need to be tapped.

‘Securing the DNA machine contract took three months and underlines our evolution from a jobbing shop into a value-added machining facility, offering production of small to large batches and a fully integrated design, development and assembly function,’ said Pepper.

‘The support provided by Whitehouse was very good in transferring this and other work to the Brother machine.

‘It included writing early programs and comprehensive operator training both at Kenilworth and on our shop floor,’ he added.

Whitehouse Machine Tools

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