Computer-aided manufacturing
IN MY previous column, I discussed how computeraided design (CAD) was part of the digital creation of components. This one will be about the digital production of those parts, what’s referred to as CAM, or computer-aided manufacturing.
When we started developing the XJ41 project in the early Eighties, it was created in the old-fashioned manual way with sketches and eventually a clay model. But halfway through the project, we changed to CAD/CAM that resulted in a perfectly machined 3D model.
As I mentioned last month, Jaguar was ahead of the game with this and so we in the design studio plus all of our manufacturers and contractors needed to acquire new equipment and skills to achieve what was needed.
We still designed the car manually in clay but the process now moved to a process that digitally captured the car’s surfaces that resulted in a digital database. This was achieved with quite expensive measuring equipment that originally started with touch sensitive probes with tens of thousands of points across the surface but later non-contact lasers were used and eventually photographic data capture.
Whether for an engineering component or a full body, once those points had been compiled, the next step was to join them together into a surface creating a 3D digital model.
The only way of turning this into a physical one was to use an extremely expensive computer numerically controlled (or CNC) milling machine which was like a drill that had spinning tools that moved, cutting away the material’s surface underneath.
Milling a 3D model needs all three axes and so the CNC had lateral, longitudinal and vertical components. But because car bodies also have undercuts, the machining head also needed to rotate in two planes so it could machine underneath too, a so-called five axis milling machine.
BECAUSE IT WAS MACHINED FROM A DIGITAL MODEL, IT WAS SYMMETRICALLY PERFECT AND ACCURATE TO A MILLIMETRE
But in 1987 when we were looking at this for the XJ41 prototype, there wasn’t a five-axis
