Same but different

Chas A Blatchford & Sons'Index G200 mill-turn centre has put in sterling service for the medical parts maker since the mid-1990s, when it decided it was the best machine for manufacturing metal components used in prosthetics for lower limbs. Now, following a recent reappraisal of machines on the market, the company has, once again, opted for the same model 15 years on. In May 2010, the company bought another G200, again through UK agent Geo Kingsbury Machine Tools (023 9258 0371), to replace its ageing machine that has been running 24 hours a day since it was installed. Indeed, it is of identical construction, with two turrets and twin opposed C-axis spindles, but, of course, has undergone significant improvements since the original was introduced. According to Ian Keeley, the company's senior manufacturing engineer, the uprated-specification machine has resulted in a typical reduction in cycle time of 10% across all of the components. And this is a direct result of the faster machine movements and more powerful control, since exactly the same programs are being used on this latest machine as were used on the older machine. Among the improvements to the G200 have been a more powerful control, the INDEX 200-4D based on the Siemens 840D Powerline, which has sufficient memory to drip-feed entire programs for machining even the most complex of Blatchford's components. Image: An uprated-specification machine has resulted in a typical reduction in cycle time of 10% across many components, at Chas A Blatchford & Sons Furthermore, processing power has doubled, enabling more accurate contour control and allowing enhanced look-ahead for producing a better surface finish. The required 0.8 microns Ra finish is now easily achieved. Dimensional tolerance of ± 10 microns is routinely held on the G200, incidently. Other upgrades to the second-generation G200 are a doubling of linear acceleration of the turrets to rapid traverse rates that are 50 per cent faster at 45 m/min and 22.5 m/min in X and Z, respectively. The lower, X/Z turret accommodates 14 live or static tools, while the upper turret also has a 120 mm Y-axis and a 360-degree B-axis. Both turrets can work simultaneously at either the main or the counter spindle or, alternatively, machining can be carried out at both spindles by deploying one turret at each. Instead of the former VDI toolholder clamping system, the latest turrets have W-form clamping that allows equally fast changeover of preset tools, but affords greater positional accuracy of 5 microns. It means that clocking tools into position is largely a thing of the past. There are about 40 part numbers for ankle products machined from bar up to 65 mm diameter on the G200, a majority being aluminium, with some stainless steel and titanium. All parts need some prismatic machining and, in certain instances, turning accounts for less than 50 per cent of the cycle. The proven programs are being transferred seamlessly to the latest machine, with the assistance of new post-processor software provided through Geo Kingsbury. BETTER THAN THE AVERAGE While a 10 per cent average saving is quoted, the savings are even greater on six particular components, as they were previously produced in three operations: turning on a 3-axis lathe, so they could be fixtured on a machining centre before being transferred to the G200. The latest mill-turn centre is able to produce the same parts in one hit, taking 10 minutes out of a total cycle time of 35 minutes, for example – a saving of over 28 per cent. The reduction in floor-to-floor time is even greater, as there is now no inter-machine handling or work in progress. Moving on to heavier workpieces and lower volumes, and at Frome Tool & Gauge, the machining of a large S99 high carbon aircraft steel forging is just the sort of one-off/small batch challenge that the company relishes and one that highlights why the 35-employee company continues to invest in machine tools from Burlescombe, Devon-based XYZ Machine Tools (01823 674200). The 2½ per cent nickel-chromium-molybdenum steel forging originally weighed in at 820 kg, prior to machining on an XYZ ProTURN SLX 555 CNC/manual gap-bed lathe, with the finished component, which has a 650 mm maximum OD and is more than 1 m long and weighing 355 kg. Image: Forgings are just the sort of one-off component Frome Tool & Gauge tackles With 17 XYZ machine tools installed to date, Frome Tool & Gauge is one of XYZ Machine Tools' largest customers in the south-west of England. Its 11 kW/30-1800 rpm XYZ ProTURN SLX 555 is a 1.75 m between-centres distance CNC/manual lathe having an 800 mm swing in the 153 mm gap to accommodate larger workpieces. It features Constant Surface Speed as standard and is equipped with the latest-generation ProtoTRAK control. In the past, any component with a large radius would, perhaps, have been machined on a hydraulic copy lathe, requiring a template to be made. However, as Tony Hazel, manufacturing director, points out: "This would be much more time consuming than simply entering the co-ordinates into the ProtoTRAK control and with CNC you can, of course, fully check the profile before actually machining it." Says Michael West, Frome Tool & Gauge's managing director: "It is the combination of being easy to set up and the efficiency with which the machines function that has convinced me that XYZ has a range of milling and turning machines ideally suited to our type of work. This often involves building a single item of precision equipment that is being made for the first time, which demands an enormous amount of skilled input and the ability to solve difficult problems. Right-first-time is a fairly recent objective in volume production, whereas we have always to get it right first time, as there are no second chances." With a customer base split equally between aerospace and automotive, the company is subject to cost-down pressure and has to "constantly seek new ways to improve our productivity and competitiveness", says Mr West. "We are always pressed on delivery times and this is why we have to be flexible and why it is always a changing picture here," Mr Hazel adds. "The fact that our XYZ turning and milling machines are so easy to use allows programming to be done on the machine, rather than off-line. And while the one-off nature of the majority of our work means we still use purely manual machines for some processes such as finish grinding, machining operations such as screwcutting are very much easier, and faster, on a combination CNC machine." First published in Machinery, December, 2010