First-tier automotive supplier has, since 1998, installed 21 UK-built lathes for hard- and soft-turning of transmission components and a further three machines are ready.
Almost every day there are gloomy reports of a declining manufacturing base in Britain, but there is still some good news, even in large volume production which is supposedly being lost to low-wage countries. For example, first-tier automotive supplier, GKN Driveline, Birmingham, has since 1998 installed 21 UK-built lathes from the MHP division of Geo Kingsbury Machine Tools for hard- and soft-turning of transmission components. A further three machines are ready for pass-off at Geo Kingsbury's Gosport factory.

In addition, a robotically loaded MHP50 CNC lathe is currently in build, due for installation at GKN Driveline in October 2005, for hard turning critical features on the constant velocity joint, or bell, that forms part of front-wheel and four-wheel driveshafts.

There are already five robot-fed MHP machines on the Birmingham site being used for similar work, each teamed with other machinery including hardening, spline rolling, washing plant to form automated manufacturing cells for outer race constant velocity bells.

Production rate is 1,400 components per cell per shift with five operators.

Each automated MHP lathe is fitted with its ABB robot at Geo Kingsbury's Gosport factory and is supplied, after pass-off, to GKN Driveline as a turnkey package, complete with programs.

The other MHP lathes are in manually loaded cells for soft turning operations on bells and tulips, the latter forming part of the plunging joint in a driveshaft nearer to the gearbox.

Mike Poyner, the engineer responsible for project managing the new production cells at the Birmingham factory, said, 'It is our policy to replace as many grinders as possible with hard turning'.

'Each time a lathe is installed it replaces pairs of external, angle-approach grinders'.

'By doing this, there is a six-fold saving in capital investment, amounting to several hundred thousand pounds''.

''Additionally, it takes two hours to change over an external grinder for a new batch compared to 10 minutes for a lathe, so production downtime is less by a factor of 12.' Driving the original change from grinding to hard turning were difficulties with grinding the hub support diameter of the bell and more particularly a shoulder called the back location face, both of which are pre-hardened to 58-62HRC.

The main problem used to be cracking of the location face during grinding, caused by overheating owing to difficulty in projecting sufficient coolant between the grinding wheel and the vertical face.

The earlier grinding operation and the dry hard-turning sequence that has replaced it includes in-cycle machining of a third OD in an unhardened state of 45-48HRC, namely a seating diameter for an ABS pulse ring.

As all turned features need to be concentric with six internal ball tracks, drawing tolerances are tight: +/-0.013mm for the hub support diameter and +/-0.015mm for the ABS diameter, surface finish for both being 1.6 micron.

As regards the back face, 0.15mm of material is machined away to leave a 0.8 micron surface finish.

The Ra figures achieved in practice are significantly lower than these.

Process capability achieved is Cpk 3.66 for the hub support diameter and Cpk 2.65 for the ABS diameter - significantly better than the required Cpk of 1.67 (5 Sigma).

More recently, GKN Driveline has been working in conjunction with Geo Kingsbury to identify inserts for soft turning that would last longer and reduce cycle times.

When machining a bell in its soft state, the incumbent supplier's insert used to result in a 65s turning cycle and it lasted for 70 components.

After research and subsequent trials, a Kennametal insert reduced the cycle to 55s and was found to machine nearly three times as many parts before it needed replacing.