October 2013 was when the new, limited edition Jaguar XKR-S GT hit the streets, but it may be difficult to spot, as JLR has allocated only 10 for sale in the UK. Coventry subcontract machinists, Philip James, produced the front steering knuckles for the £135,000, five-litre, V8 coupe on a line of six Hurco 3-axis machining centres.
More usually, the subcontractor machines prototype suspension, chassis and steering components for practically every current and future make of Jaguar, Range Rover and Land Rover, including the new L550, nicknamed Baby Discovery. Ones and twos up to 50-off are normally produced.
Knuckles in particular require intensive milling. They start as a solid round aluminium billet that is typically reduced from 94 kg to less than 6 kg when the part is fully machined. For subsequent volume production, the components are produced from aluminium forgings – unless it is for a small run of cars like the XKR-S GT.
Philip Whitehouse, Managing Director of Philip James, stated, 'One of the front knuckles for JLR was proving problematic to machine.
'While most of the milling and drilling could be carried out on one of our 3-axis Hurcos, the component then had to be transferred to a CNC jig borer for five holes to be interpolated at three different angles – and therefore in three set-ups.
'We decided to buy a Hurco VMX42SR 5-axis machining centre to interpolate all the holes to within ± 10 microns in one automatic, 20-minute cycle, much faster than the two and a half hours it used to take on the jig borer.'
Apart from decreasing the cycle time, the new 5-axis process eliminates the need to use a tooling hole for component alignment prior to boring. One-hit machining on the Hurco also allows Philip James to swap between producing the two hands more quickly. This is important, as JLR often cannot wait for a full batch of, say, 20 left-hand and the same number of right-hand knuckles to be delivered in one consignment. Faster changeovers increase productivity by minimising spindle idle time.
The Hurco VMX42SR is the first 5-axis machining centre at Philip James. Mr Whitehouse asked the manufacturer to modify the machine so that the B-axis head can be tilted past horizontal to allow cutter access for all JLR knuckle bores to be interpolated in one hit.
The required negative angle was -8 degrees. Hurco engineers removed the limit switch on the head, allowing it to tilt up to -20 degrees. So other features like undercut faces can also be machined without repositioning the part on an angle plate, again saving time and improving accuracy.
The modification means that the head guarding comes close to the table and especially near to a laser tool measuring device. To avoid any chance of collision, the subcontractor used Work NC computer aided manufacturing (CAM) software from Sescoi to program the machining cycle and check for interference.
Although the knuckle application requires 3+2 axis machining, the VMX42SR is capable of full 5-axis cycles. Mr Whitehouse is hopeful that it will attract additional work from the aerospace and motorsport sectors and also pointed out that it will reduce the need to use expensive form cutters.
Shop floor programming suits small batch machining
Founded by Philip Whitehouse and James Parry in 1978, the firm started out as a manufacturer of special purpose machinery used for production in diverse industries, from business machinery to cars. It gradually moved into subcontract supply of prototype and low volume parts to a range of sectors, one important customer being machine tool manufacturer, Cincinnati, until the closure of its Birmingham factory in 2007.
In view of the relationship, it is unsurprising that Philip James became a user of Cincinnati machining centres. The Acramatic control fitted to the machines was popular with the subcontractor's operators, due to its clear and intuitive navigation which made it easy for less experienced users to master a complex mix of control functions.
At around the time of the Cincinnati factory's demise and as significant contracts from elsewhere started to come in, Mr Whitehouse looked around for another make of machine that would be easy to program on the shop floor, without recourse to G-codes. Hurco's Ultimax, now WinMax, conversational control software was deemed to be superior to others on the market. It was the deciding factor when placing orders for a Hurco VM1 vertical machining centre and a TM8 lathe.
It was helpful that one of Philip James' operators, from previous employment, had experience of operating machines from this supplier. The transition was therefore smooth and the other shop floor staff were quick to familiarise themselves with the software.
Mr Whitehouse continued, 'The last thing you want when producing just a few components is to spend hours programming the job at the control.
'In our environment, we find that WinMax software on the machining centres and lathes allows fast generation of programs and the same is true of the 5-axis Hurco as well for 3+2 axis cycles.'
Availability of the first two Hurcos brought in enquiries for more work, but the machines themselves were tied up, and largely still are, making stainless steel parts for the oil and gas industry. Investment in further machining centres and lathes from the same supplier followed in 2008 and 2010, prior to the 5-axis machine installation in October 2012.
Much of the increase in work derives from JLR, although contracts tend to peak during the development phase of a new model. The subcontractor relies on work from the petrochemical industry and also from aerospace to fill the gaps. For these contracts, a range of tough metals from 316 stainless steel to Duplex and Inconel for aerospace parts are machined on the Hurcos, sometimes to tolerances as tight as ± 5 microns.