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JVM Castings, a UK aluminium die caster and a supplier to the automotive industry, uses machining centres supplied by Whitehouse Machine Tools for both large and small components.

To machine products at JVM’s Worcester factory from larger die casting machines rated up to 2,700 tonnes, two OKK HP400 horizontal machining centres with four-axis interpolation, 630 x 620 x 710mm working envelopes and twin pallet changers (2APCs) were selected in 2005.

They were followed in 2007-08 by an identical model and another with an additional rotary fifth axis for positioning.

A similar-sized, heavier-duty, four-axis HM400 was installed in August 2009, bringing the total to five.

Kevin Jones, engineering manager at JVM, said: ‘The HP400 accelerates in the linear axes at around 1G to 60m/min rapid traverse in all axes, which is fast for a machine of this size with ballscrew drives.

‘In addition, the Big Plus 40-taper spindle is powerful [22kW/12,000rev/min] and rigid for a machine of this size and speed,’ he added.

According to Jones, the machine cuts at up to 40m/min, exchanges tools in one second and completes a pallet change in five seconds.

Table rotation through 90 degrees in half a second is effected while automatic tool change is in progress.

In-cut productivity is, therefore, maximised and non-cutting time is minimised.

One of the OKK horizontal machining centres at Worcester is devoted to producing left- and right-hand body parts such as door-frame pillars and transmission tunnel elements.

The other four machines manufacture three varieties of sump for the five-litre V8 engine powering the Land Rover Discovery, the Range Rover Sport and the Jaguar XF saloon.

Each machine is equipped with automatic, hydraulically actuating, flexible fixturing to enable the production of any of the three sumps in two operations – one per pallet.

The production rate has doubled in the past five years to 100,000 per annum.

Despite the latest parts requiring additional operations, cycle times for machining the new, more complex sumps are eight, 10 and 12 minutes respectively.

For the previous, simpler models, however, the cycle time was 7.5 minutes, hence the investment in further OKK plant.

The HP400, equipped with the fifth positioning axis, has an additional duty: machining left- and right-hand cast aluminium shock towers for the Jaguar XF.

According to Graham Jolliffe, JVM’s manufacturing engineer, the sump length and the flatness of some milled faces have to be within 0.1mm – in other words, as tight as the tolerances on the engine block to which the sump will be bolted.

The OKK machines feature a coolant management system, which uses seven individual pumps and supports the production of high-accuracy components.

In addition to 20bar through-tool coolant, there are coolant jets around the spindle, a flume wash, a bed wash and a coolant curtain from the ceiling.

Media-free filtration with refrigeration avoids the temperature variation of the coolant, which is important when cutting aluminium owing to its high coefficient of thermal expansion.

Temperature sensors are fitted to monitor the ambient temperature and that of the machine bed.

Accuracy is further promoted by the use of core-chilled, double-anchored ballscrews, according to Whitehouse.

Following the award in 2008 of a contract to supply half a million machined aluminium brackets to Ford, JVM produced Part Submission Warrant (PSW) batch samples in October last year and will start full production in May 2010.

The cast components are a fuel pump bracket and a vacuum pump mounting bracket for the new Ford Sigma diesel engine.

The parts are much smaller than the structural vehicle components produced at Worcester, so they needed to be produced on a more compact machine.

High speed was again imperative to keep down the unit cost of manufacture.

In the smaller size range, there are more 2APC machines available that might have fitted the bill, including turret-type drill/tappers and light-duty machining centres.

However, after comparing axis speed and acceleration across a range of smaller plant, the most suitable machine was the TC-32BN QT from Brother, another Japanese machine tool builder represented in the UK by Whitehouse Machine Tools.

Jolliffe said: ‘Machine elements on the Brother are light so there is low inertia as the axes move, resulting in fast acceleration to 70m/min rapid feeds in all axes.

‘Pallet change is 3.4 seconds and it takes just 2.1 seconds chip to chip, which includes time for the spindle to decelerate from a top speed of 16,000rev/min to zero for automatic tool change and accelerate again to maximum revs.

‘Overall, idle times are considerably shorter than on other machines of similar capacity,’ he added.

The Brother is also quick when cutting thanks to the 16,000rev/min spindle and cutting feeds up to 20m/min.

The 70bar through-tool coolant increases drilling and tapping productivity, especially on deeper holes, and extends tool life.

The company can tap at 8,000rev/min.

According to Jolliffe, the Brother’s cutter breakage monitoring system within the chain-type magazine is important for 24/7 operation where one operator looks after several machines.

When the next tool is called up into the ATC position, a mechanical arm checks if the length of the tool matches the parameter in the control or if is present.

If not, the cycle stops automatically.

As the monitoring of the tool is carried out while the next cut is in progress, there is no loss of production.

Supplied as a turnkey package by Whitehouse Machine Tools, the four-axis Brother cell at Worcester was delivered with programs; hydraulic automatic fixtures complete with air sensing; and tooling.

Bespoke, trunnion-and-tailstock rotary indexing units are fitted on both pallets to accommodate the two component types.

Services are fed through a rotary joint through the centre of the pallet for maximum efficiency.

On one pallet, two sets of two fuel pump brackets are clamped for operations one and two to be carried out in a 70-second cycle.

After APC, operation-one castings are inverted manually into the operation-two positions and fresh castings are clamped for operation one.

The indexing table is needed purely for gaining access to the components when machining and also allows swarf to drop away.

On the other pallet, the indexing table presents two sets of three components to the spindle, each of the fixtures being offset by 90 degrees for operations one and two to be carried out sequentially.

The cycle time is 40 seconds.

High accuracy is needed on both components, as they mount to the cylinder head and fuel pump, with some flatness tolerances down to 18 microns in total.

Polycrystalline diamond tooling is used to achieve the required accuracy and speed.

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