A Traub TNC 42DG seven-axis mill-turning centre, supplied by Traub Heckert UK of Brackley, has allowed the Woodley plant of Dura Automotive, based near Reading, to adopt a 'one-hit' turning philosophy for producing power steering racks up to 790mm long in 1.5 minutes. Previously, a pair of single spindle autos sited 'back-to-back' and linked by automatic transfer, turned the parts in two operations, which took up valuable floor space and extended lead times. Dura Automotive is one of the fastest growing groups in the world, its turnover having increased from GBP350 million to the GBP2.7 billion over the past two and half years.
It operates from 88 sites worldwide, specialising in systems for driver control, engine control and body and glass.
The Woodley plant of Dura Automotive near Reading supplies power steering systems to some of the world's most prestigious vehicle manufacturers, including Rolls Royce and Land Rover.
Meeting their requirements calls for systems of advanced design and investment in the most modern manufacturing methods.
The parts produced at the Woodley plant fall within the company's 'Engineered Products', and it is the only group site producing power steering systems for which it has over 50 years experience in design, manufacture and application.
Innovation is the company's hallmark and it claims the development of the world's first power-assisted rack-and-pinion steering unit in the early sixties.
Today, accredited to ISO 9001 and QS 9000, it offers rack-and-pinion system such as Pow-a-Rak(r) for passenger cars and 'Serv-a-Rak(r)' for commercial and military all-terrain vehicles and buses.
Dura also produces Var-a-Matic(r), a worm-and-roller power steering box for 4x4s, which are fitted to Land Rover Discovery, Defender, LTI Carbodies and Metrocab UK Taxis.
The latest innovation from Woodley is Elektr-a-Steer(tm) that applies DC motor technology rather than hydraulic power to steering, which gives significant savings in weight, packaging and fuel consumption and improved control functionality.
These are not off-the-shelf products but are of a modular concept that allows Woodley, unlike other power steering manufacturers, to design each system to meet the users exact requirements.
Thus, physical size, turn ratios and interface connections are dedicated to the user's specification, which means production is geared to small to medium-sized batches and not high volume.
Steering components are also safety critical, precision engineered items which puts a high demand on the machine tools and processes.
The initial justification for the Traub TNC 42DG was to improve rack machining productivity up to 790mm long for Pow-a-Rak(r) and Serv-a-Rak(r) systems.
Apart from length, a rack is not a complex component but involves drilling, counter-boring and tapping each end, milling a radial groove as well as turning each end.
However, to switch to a twin spindle lathe so as to complete the operation in a single 'hit' did present a problem due the need to hold the rack on two different diameters during the cycle.
It was the application ability of Traub Heckert UK to solve this, that finally clinched the order.
Nick Davies, production engineer, says: 'We had narrowed our choice down to two manufacturer's twin spindle machines that met our specification but only Traub Heckert were prepared to spend time in application engineering to achieve an acceptable process.
They came up with a solution allowing the rack to be held throughout the operation in the same size collet.' As a result, the racks are now completed in far shorter cutting cycles.
Also admired by Nick Davies is the rigidity and versatility of the Traub with its twin-spindle, twin-turret configuration.
It is equally proficient at machining Dura's rotary valve sleeves, as it is the long racks.
Although shorter, sleeves are more complex with a propensity of machined features, including formed outside diameters, radial grooves, internal bores and grooves, and radial and axial slots.
These bring into play the TNC 42's C-axis controls on each spindle combined with driven tools in the two turrets.
Nick Davies comments: 'The sleeves used in the speed sensitive steering systems supplied to Rolls Royce have four off-centre axial milled slots in three different sizes.
We could not find another twin- spindle lathe that could accommodate so many sizes,' he maintains.
He continues: 'We would be the first to admit that the Traub machine is not low cost but it is very versatile and gives us an ideal machining solution.
Also, the support provided by Traub Heckert from Brackley has been superb with the application engineering being particularly good.
Even our setter and setter-operator, who can be quite opinionated on suppliers, are complimentary about the help and training that they received by the people from Brackley.'