sawing & tubeforming
After half a century the late Colin Chapman’s iconic lightweight sports car is still instantly
recognisable, but its manufacture has been adapted to exploit modern laser techniques
New lease of life for the ‘Seven’
THE Caterham Seven’s original design has over the years been refined and enhanced, but the car remains
much the same in terms of appearance and construction. While the traditional tubular chassis is instantly
recognisable, the method of manufacture has changed. One of the most significant productivity
improvements in recent years has resulted from a switch to tube laser machining of the numerous
individual components needed for the variations of the ten-plus chassis produced every week by subsidiary
company Steel Fabrications. Incidentally, this investment in new production techniques has contributed to
a 12% greater torsional stiffness that has further improved the car’s legendary roadholding capability.
Steel Fabrications uses a BLM Adige LT120 LaserTube with a capacity from 12 to 120mm OD tube or box section to cut and profile steel chassis components
prior to welding. The LT120 takes up to four tons of 6.5 metre-long tube in its bundle loader and nests finished parts cut to an accuracy of 0.1mm at the other
end. As well as cutting and notching tubes for chassis, wishbones and A-frames, the LaserTube’s diffusion cooled CO2 laser source pre-cuts rivet holes in the
chassis components, thereby reducing significantly the time taken to attach body panels.
Chassis components are stored in racks ready for making up a kit of parts, a key element in a production process that Gideon Wigger, Caterham Cars’
operations director, says has to deliver each chassis complete with body panels to the Dartford, Kent, assembly facility on schedule, within budget and to the
agreed specification. ‘We are, in effect, both the customer and the supplier,’ he says, ‘and it is essential that the two roles are managed in such a way that the
quality of the completed car is not compromised in any way.’
The latest parametric software is used to design the definitive chassis and to model its component parts, and this CAD data provides the basis for
programming the Siemens Sinumerik 840D CNC of the LT120 tube laser cutting system. Joints between tubes that would have been impossible or too expensive
to produce by traditional machining methods take just a few minutes programming for the tube laser, with prototypes and re-designs again requiring just a few
minutes to program. And the inherent accuracy and repeatability of laser cut parts ensure they always fit the welding jigs without further dressing.
Chassis components are designed for ease of fabrication, with tabs and profiles combining to minimise the time needed to assemble them in a welding jig
prior to robot welding. Once the chassis is complete it is washed in a series of phosphate baths to remove all traces of dirt and grease before being powder
coated and the body panels attached. At this point its destination is final assembly at the Dartford factory, from where more than half of Caterham's annual
output is exported, much of it to Japan, France and Germany. www.blmgroup.com
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