Roger Ashton (right) and Oliver Clayton with the Brother M140X2 5-axis mill-turn centre at Jointmedica’s R&D facility in Hallow, Worcestershire. As no photographs of plastic components were allowed for reasons of confidentiality, an aluminium billet for a fixture is shown on the table.

Close-up of the aluminium fixture about to be produced. The machine’s working envelope is 200 x 440 x 305 mm and the A-axis trunnion is tilted from +120 to -30 degrees by a backlash-free roller drive.

The Brother high-speed C-00 control system is convenient for editing programs, many of which may be stored in the large memory.

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The Brother TC-32BN QT has a top spindle speed of 16,000 rpm and 1.5 g acceleration to rapids of 70 m/min in X,Y and Z. These figures are much higher than the 8,000 rpm and 30 m/min on the subcontractor’s other VMCs recently purchased from another supplier. Mr Pepper said, “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 a year later, 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. 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 16,000 rpm in 0.46 sec, 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 16,000 rpm, ready to cut immediately with the correct tool.

Not a moment is wasted. Installed in March 2010, the TC-32BN QT is operated flat-out by Greenway Pepper all of the time. High-pressure coolant at 90 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 8,000 rpm. 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 360 degrees to provide a 4th 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 20 microns. Flatness on the back of the component must be within 25 microns, which can only be achieved using a relatively small, 4 mm diameter milling cutter, as a larger tool would introduce stresses.

The maximum 70 m/min cutting feed rate and 16,000 rpm 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 0.8 mm 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, 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 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, 7.00 am to 10.00 pm. The approximately 250 mm by 100 mm side plate for the DNA equipment is machined from 10 mm thick, 6082 T6 aluminium plate.

As before, it is essential to keep machining stresses low, so an 8 mm diameter cutter reduces the thickness to 7 mm, 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 continued, “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 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.”

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However, the Brother’s ability to take so much time out of the cycle was also down to minimising non-cutting time. 70 m/min rapid traverse in all linear axes contribute significantly in this respect, and so too does the fast automatic tool change (ATC) time, which at 900 milliseconds tool- to-tool including spindle acceleration and deceleration, is described by Adaero’s managing director, Andy Dickinson, as amazingly fast.

Since it was installed to raise production capacity for servicing new and existing customers, the TC-22B-O has been retrofitted by Brother’s UK agent, Whitehouse Machine Tools, with a 2-axis Nikken table. It sits at one end of the machine table while a conventional workholding arrangement is positioned at the other end. Converting the machining centre into a 5-axis facility was planned at the outset and was a key reason for Adaero choosing the equipment.

Mr Dickinson continued, “It is useful to us that the Brother control is Fanuc-based with a proprietary front end. It means we can run programs from our other Fanuc-controlled machining centres with very little modification.”

Adaero’s migration of jobs from older technology, 3- and 4-axis machines onto the 5-axis TC-22B-O stems from a desire to reduce the number of set-ups for each job by at least one. Single hit machining is the goal. The results are shorter floor-to-floor times and reduced work-in-progress. Accuracy is also improved, as it is easier to control tolerances and there is less risk of operator error. So far, over two dozen components have been moved over to the 5-axis machine. All jobs so far have used the extra two axes to position the parts for 3-axis machining, rather than involving fully interpolative cycles.

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Tim Whitehouse, managing director of UK sales and service agent, Whitehouse Machine Tools, commented, “Normally one would expect high-torque spindle motors on 40- and 50-taper machines, but Brother has broken the mould by bringing heavy machining capability within reach of manufacturers using these lighter duty machines.

“At the low end of the speed range, for example, it is now possible to drill a 32 mm diameter hole and tap to M27 in 150 HB carbon steel, up from 25 mm and M16 for the standard 10,000 rpm spindle motor. In aluminium, similar increases take the figures to 40 mm and M39.

“At higher speeds, a 16 mm diameter end mill can take a 15 mm wide by 8 mm deep side cut in carbon steel, while a 125 mm diameter face mill will remove 1,700 cc/min from an aluminium billet.”

Higher torque is provided by the brushless interior magnet motor at the mid to high speed range as well as at the low end, where it is 2.7 times higher at 92 Nm between zero to 2,200 rpm. Maximum power output is also raised from 18.4 to 26.2 kW.

Owing to the increased torque at higher speeds, an extra advantage is that the spindle can be decelerated faster from top speed to zero, ie in 0.15 instead of 0.2 of a second, and accelerated similarly quickly. The servomotor-driven turret’s ATC (automatic tool change) time is therefore shortened from 1.6 to 1.5 seconds. Just over six per cent reduction may not sound much, but it can make a considerable difference when producing batches of thousands of components whose cutting cycles involve frequent tool changes.

Brother has used regenerative power technology on the high torque motor to utilize braking power and improve energy efficiency. Power consumption has been reduced by between 20 and 30 per cent, says the manufacturer. There is the option of face-and-taper contact tooling for all spindles, including the standard 10,000 rpm type and the high-speed, 16,000 rpm version.

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Whereas the company used only to machine its own zinc and aluminium high-pressure die castings, during the second half of 2009 it started a subcontract milling and turning service, producing components in a variety of materials for a much wider spread of industry sectors.

Since the mid 90s, six Brother machining centres have been supplied by Whitehouse Machine Tools to R D Castings’ Mildenhall factory. They systematically took over from manual milling, drilling and tapping, which was labour intensive and subject to quality variation due to human involvement. All of the Brothers are fitted with twin APC (automatic pallet change) and some are equipped with a Nikken rotary indexer to provide a fourth CNC axis.

According to R D Castings’ Sales and Marketing Director, Anthony Pateman, the production centres are ideally designed for machining castings. In particular he cites fast feeds rates and tapping speeds as well as sub-second tool change time as central to the ability of these high-speed machines to generate profit. Floor-to-floor times, he says, are twice as fast when machining centres without APC are used.

Latest to be installed at Mildenhall was a Brother TC-32BN QT 4-axis machining centre with 16,000 rpm spindle, 40-station BT30 tool magazine, 8,000 rpm rigid tapping, 70 m/min rapids, 20 m/min cutting feed rate and acceleration up to 1.5g. Such a specification makes it one of the quickest machines on the market and underlines why R D Castings has continued to invest in this Japanese manufacturer’s equipment.

Cycle time can be as short as 20 seconds, although at the other end of the scale, a complex gearbox casting recently took 10 minutes to machine on all six faces. It required the use of 26 tools to produce a complex sequence of milled features including numerous undercuts and circlip grooves. Very tight tolerances were held in respect of squareness, concentricity and roundness.

When machining its aluminium and zinc high-pressure and gravity die castings, minimum run is typically 1,000-off but when providing subcontract services, batch runs on the APC machining centres are often as low as 200-off. General tolerances are ± 0.10 mm, reducing to ± 0.01 mm for some bore diameters and flatness features.

Continued Mr Pateman, “The Brother machines have pushed the boundaries regarding the cutting tool technology we use; no longer is carbide tooling sufficient.

“We are now fully committed to the use of polycrystalline diamond (PCD) inserts, which are clamped in dynamically balanced tool holders to achieve speeds and feeds that are not possible by conventional machining.

“Coupled with the benefit of high-pressure, through-tool coolant fitted to the Brother machines, the new tooling allows a level of productivity that a few years ago was beyond our imagination.”

In 1995, when researching the market for its first machining centre, R D Castings’ directors were looking for a fast, compact machine with APC and programming software that was intuitive and easy to use. Mr Pateman says that the Brother TC-32 met all of these requirements and was much faster than anything else on the market for general production applications.

He added that a competitive price, ready availability of spares and good service back-up were also important. In the latter respect, he described Whitehouse Machine Tools’ support as “first class”.

Machine reliability is also crucial to an operation like R D Castings’ and Mr Pateman commented, “I can count on one hand the breakdowns across all our Brother machines over the last 16 years.

“Their reliability and speed combined with the high level of support from Whitehouse has been an unbeatable package for us.”

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