October 2013 was when the new limited-edition Jaguar XKR-S GT hit the streets, but you will be lucky to see one, as Jaguar Land Rover has allocated only 10 for sale in the UK.
The Coventry-based sub-contract machinist Philip James produced the front steering knuckles for the £135,000 five-litre V8 coupé on a line of six Hurco three-axis machining centres. Indeed, the sub-contractor has machined prototype suspension, chassis and steering components for practically every current model of Jaguar, Range Rover and Land Rover; it has also machined parts for the new L550 (nicknamed Baby Discovery). Ones and twos are the norm, although batches of 50 are sometimes produced.
Knuckles in particular require intensive milling. They start as a solid round aluminium billet weighing some 94kg; this is reduced to less than 6kg when the part is fully machined. For subsequent ‘volume’ production, the components are produced from aluminium forgings — unless they are for a small run of cars like the XKR-S GT.
Philip Whitehouse, managing director of Philip James, says: “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 three-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 five-axis machining centre to interpolate all the holes to within ±10µm in one automatic 20min cycle, which is much shorter than the 21/2hr it used to take on the jig borer.”
Short lead times
As well as reducing the cycle time, the new five-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 left-hand and right-hand knuckles more quickly. This is important, as JLR often cannot wait for a full batch of, say of each hand to be delivered in one consignment.
The Hurco VMX42SR — from High Wycombe-based Hurco Europe Ltd
(www.hurco.co.uk) — is the first five-axis machining centre at Philip James. Furthermore, Mr Whitehouse asked the manufacturer to modify the machine so that the B-axis head can be tilted past horizontal, thereby allowing cutter access for all JLR knuckle bores to be interpolated in one hit. The required angle was -8deg; Hurco’s modification allows the head to tilt up to -20deg, which means that the head guard comes close to the table — and particularly close to a laser-based tool-measuring device. To avoid any chance of collision, the sub-contractor uses Work NC 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 five-axis cycles. Mr Whitehouse is hopeful that this machine will attract additional work from the aerospace and motor-sport sectors; he also highlights the fact that it reduces the need to use costly form cutters.
‘Specials’ background
Founded by Philip Whitehouse and James Parry in 1978, the firm started out as a manufacturer of special-purpose production machines used by a wide range of industries, from business machinery to cars. It gradually moved into the sub-contract supply of prototype and low-volume parts, one important customer being the machine tool manufacturer Cincinnati — until the closure of its Birmingham factory in 2007.
In view of this relationship, it is unsurprising that Philip James became a user of Cincinnati machining centres. The Acramatic control fitted to these machines was popular with the sub-contractor’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 closure — 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 shopfloor, without recourse to G-codes. Hurco’s Ultimax (now WinMax) conversational control software ‘fitted the bill’ and was the deciding factor when Philip James placed orders for a Hurco VM1 vertical machining centre and a TM8 lathe.
Mr Whitehouse says: “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 programs to be generated quickly; the same is true of the five-axis Hurco.”
Philip James’s first two Hurcos brought in enquiries for more work, but the machines were tied up (and 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 installation of the five-axis machine in October 2012.
Much of the increase in work derives from JLR, with contracts tending to peak during the development phase of a new model; the sub-contractor relies on work from the petrochemical and aerospace industries 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 ±5µm.