Case Study - DT40 - Delta Turn
The Deltaturn Super Precision Lathe was designed and built to meet the specifications necessary to turn hard disc drive hubs for the computer industry. Cranfield Precision were contracted to manufacture and demonstrate capability on a range of customer components before delivering two machines to the US production facility in California.
The original workpieces, shown at the bottom of the collection of hard and soft turned samples, were made from either soft steel or brass. The outer surfaces and the bore were turned from the semi-finished blanks. A hydrodynamic, sinusoidal, bearing scroll had to be broached or grooved into the finished bore without leaving either swarf or a burr behind.
The required accuracy, repeatability and surface finish of the component exceeded
specifications normally seen on conventional chucking lathes. A new concept in machine
design was needed to ensure that the parts could be manufactured in volume production
and within tolerance.
Key precision machine design techniques were invoked, in particular, hydrostatic bearing
systems, high machining loop stiffness and direct drive control. The most notable aspect
of the design is the use of a two-axis plate grating scale to provide position control for the
principle orthogonal linear axes and to provide intrinsic correction for straightness,
squareness and cutting force errors.
The machine was built and successfully achieved the necessary productivity targets and
accuracy criteria. The DT40 machine platform was later redesigned to allow the
development of a high precision hard turning processes. The original aerostatic workhead
was replaced with a higher stiffness hydrostatic bearing design capable of reaching
cutting speeds of 220 m/min on small and medium sized hardened bearing parts. Trials
using CBN tools have demonstrated semi-finishing material removal rates at cut depths
up to 0.25mm in 60Rc bearing steels. High quality finish turned surfaces as fine as 20nm
Ra have also been produced in similar hardened bearing steels.
Cranfield Precision operates to ISO9001 quality standard and is accredited by Lloyds Quality Register.
A Division of Cinetic Landis Ltd.
Registered in England
Registration Number 05577045
Registered Office: Cross Hills, Keighley, West Yorkshire, BD20 7SD