At Greenway Pepper Precision Engineering, a subcontractor in Newcastle-under-Lyme, aluminium components are reportedly being machined much faster following the installation of a Brother high speed, 4-axis, vertical machining centre from Whitehouse Machine Tools. Solutions investigates.

Greenway Pepper employs 20 people and is firmly committed to developing its own engineering staff. Finding potential employees of the right calibre is a challenging task so the company prefers to nurture from within. For example, it is currently putting 17 year old Jake Hall through the company apprenticeship scheme and is supporting Grant Barnes, 21, to combine his role as production controller with completing his degree course.

The installation of the Brother machine has streamlined the company’s manufacturing processes. For example, a medical component that used to be produced in one hour and 10 minutes on a standard, one year-old VMC 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.

Moreover, 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 further.

Impressive output

Joint owner and managing director Greg Pepper is justifiably impressed with his new purchase. The Brother TC-32BN QT has a top spindle speed of 16,000rpm and 1.5g acceleration to rapids of 70m/minute in X, Y and Z. These figures are much higher than the 8,000rpm and 30m/minute on the subcontractor’s other VMCs recently purchased from another supplier.

Mr Pepper says: “It was the relative slowness of our other machines and a sudden upturn in medical business that prompted us to buy the Brother machine. I had seen the TC-32BN at MACH 2008 and visited the Whitehouse technical centre in Kenilworth last year, where I was impressed with the 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, pushing our company turnover past £1 million.”

Trials were carried out by a number of potential machine suppliers, including Whitehouse and according to Mr Pepper, 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 while the machine is in-cut, and part is due to short idle times. Promoting the latter is acceleration of the BT30 spindle from 0 to 16,000rpm in 0.46 seconds, enabling a chip to chip time of 2.1 seconds.

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 16,000rpm, ready to cut immediately with the correct tool. 

In detail

Installed in March this year, 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 8,000rpm. 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 whilst the other pallet supports a Nikken trunnion and tailstock indexer that rotates a MicroLoc plate through 360° to provide a fourth CNC axis.

Looking in a little more detail at a couple of the applications put on the Brother so far – one 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 20µm. Flatness on the back of the component must be within 25µm, which can only be achieved using a relatively small, 4mm diameter milling cutter, as a larger tool would introduce stresses.

The maximum 70m/minute cutting feed rate and 16,000rpm spindle speed of the Brother are ideal for removing material quickly from both faces without distorting the plate. Total cycle time is 40 minutes, which Mr Pepper describes as ‘incredible’, 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.

Shifting up

Another medical component, referred to earlier, 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 global launch in July 2010, the US-designed equipment has an aluminium casing comprising a family 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 looking forward to reaping the benefits of the claimed 63% 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.

Mr Pepper continues: “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.

“The back-up provided by Whitehouse was excellent 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 shopfloor.”

Whitehouse Machine Tools
www.wmtcnc.com