The 3D ‘additive manufacturing’ process. Instead of standard ‘subtractive manufacturing’ – where material is cut away from a single piece – additive manufacturing involves building up a part from a series of layers, each one printed on top of the other. It is the difference from digging out a bunker to building a house. The process starts with a computer-aided design (CAD) model, which is then sliced horizontally apart to plan its layer-based physical construction. Anything suitable for the printing process can be designed by computer then printed as an actual item, typically by melting powder or wire materials, in plastic or metal.