The first line, supplied in mid 2004, produces knuckle pairs for the new Land Rover Discovery and the Range Rover Sport, as well as for earlier Land Rover models. Four Okuma twin-pallet MA500 machining centres of nominal half-metre-cube capacity are served by two inverted, 6-axis robots travelling on an overhead gantry. Datum and inspection stations, conveyors, a washing machine and part programs were included in the package.

A second Okuma line comprising three machining centres has since been installed to machine knuckles for the new Land Rover Freelander, while a third line, with seven Okuma machining centres, is devoted to machining knuckles for the BMW Mini.

A team of six King Automotive engineers, including operations director, Roger Ball, asked five suppliers to tender for the first project. NCMT won the contract, as it offered the best overall solution in terms of production output, cost and footprint, as well as offering two technical features worthy of special mention.

First was the inclusion of D'Andrea heads to provide an additional CNC axis in the two Op 20 machining centres. This U-axis on the spindle is interpolated with the machine's X/Y/Z axes to drill and ream a 9-degree, reverse-taper hole with a 1.6 Ra surface finish in the upper ball joint of the knuckle. Other suppliers tendering for the project struggled with this challenging operation, as the obvious solution of providing a form tool could not meet the required accuracy.

A second technical feature devised by NCMT allows faster transfer of components from the two Op 10 machines to the Op 20 end of the line. NCMT configured two Fanuc robots to effect a handshake, passing the part-machined knuckle directly from one gripper to the other. This was in contrast to solutions offered by others, such as an intermediate buffer stand or conveyor to link the robots, which would have slowed component exchange and in the latter case, entailed unnecessary work-in-progress.

Line operation is as follows. Stillages of knuckle castings, either type 319 or 320, are placed in front of the line for machining. Automatic pallet change on one of the Op 10 machines triggers the host computer to direct the first robot to pick two raw castings, a left-hand and a right-hand 319 or 320, which are taken successively to a datum station. Here, each casting is verified and regripped accurately for presentation to the double hydraulic fixtures on the second pallet of either of the two Op 10 machines, prior to which a second gripper on the robot arm removes the previously machined part of the same hand from the fixture.

These parts are transferred one at a time directly to the Op 20 robot as previously described, there being no need for redatuming, as precise location is achieved using features machined during Op 10. The components are then loaded into an Op 20 machine and each time, the second gripper removes a completely machined knuckle, passing it to a conveyor feeding a Hafroy (Durr) washing and drying machine. The component is picked up from the output conveyor, checked again for type and hand, and placed in a stillage for delivery to the customer.

Op 10 involves machining brake calliper holes and an ABS hole, and tapping additional cast holes for subsequent fitting of a dust cover. Op 20 includes drilling and taper-reaming not only the upper ball joint using a D'Andrea head, but also the lower ball joint and steering arm, plus drilling of four bolt holes for bearings.

The two operations are well balanced, as although Op 10 is shorter than Op 20, additional time is needed for datuming prior to the first operation; and it has been arranged that the Op 10 robot does the work travelling to the Op 20 end of the line to meet the other robot, which in any case has a busier schedule.

Final inspection is carried out after Op 20. A check is made after every U-axis tool change, plus one knuckle per stillage undergoes full inspection, the robot automatically selecting parts in turn that have come off each of the pallets in all four machines. Checks are either made in an Op 20 machining area on an unclamped part using a Marposs air gauge to verify critical bores and tapers, or alternatively by transferring the part to a co-ordinate measuring machine. Both methods are able to capture data for SPC analysis and a process capability of Cpk 1.3 to 1.6 is routinely achieved.

Other partners on the project were BIG Daishowa which supplied 25.83-degree angle heads (also through NCMT) for combination drill-tapping of brake calliper holes, Bartling Designs which manufactured the fixtures, and Kennametal for most cutting tools except those used in the D'Andrea head, where Stellram was found to provide better consistency.