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How to 3D print a part for your car

Struggling to find a rare or difficult component? The answer may lie in the rapidly developing science of 3D printing

You need a bit of car, some small but vital piece of plastic trim. No new bits available, secondhand ones as broken or crumbly as yours… Then you read about this brilliant new idea: you scan the part (preferably an intact one, borrowed) and print a new one in layers of plastic. Job done.
The technology has been around for a good three decades, and has diversified into different processes, collectively known as ‘additive manufacturing’. This alludes to the fact that the pieces are built up from nothing, rather than machined out of a block of pre-existing material from which the excess is ‘subtracted’. The principle of the processes is, however, the same: thin layers (typically around five thousandths of an inch thick) of plastic or metal are slowly and accurately built up on top of previous layers to create a complete part replicating a 3D, computer-scanned, virtual image. 
Stereolithography was an early type of 3D printing, the one that first stunned the world with its scanned hands and hip-joints. It uses thin layers of liquid resin, hardened with an ultra-violet laser beam, but the resultant object tends to be brittle and unsuitable for use as a real part. A better method is laser sintering, which uses a laser beam to melt powder and fuse it into the solid micro-layers. The powder can be plastic or, rather thrillingly, metal – steel, aluminium or titanium, for example.
Another variation is a 3D version of an inkjet printer, which sprays photopolymer liquids in layers and hardens them with light as they go. With this method you can have several different materials in one part, by using a separate jet for each material.
Most useful to us, though, is fused deposition modelling (FDM), which uses thin layers of thermoplastic melted onto the layer beneath. This process produces the strongest and most usable plastic parts – stereolithography is limited to prototype parts and the making of moulds. It’s even possible to combine the plastic with carbonfibre filaments for strength.
The usefulness of all this to our world is obvious. Jay Leno had his garage make an airbox for his 1966 Ford Galaxie, while racing driver Martin Stretton had the engine cover recreated for his Alfa Romeo 33/3 race car by 3D specialist KW Special Projects. KW has also made a 3D printed pattern for an Amilcar C6 gearbox extension. 
This is game-changing stuff – and we’re just at the beginning. 
Words: John Simister

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