A model of the object is created on a computer. Software analyses this model, taking a series of cross-sections and working out the distribution of space and solid matter within each layer.
The 3D printer builds up the object, one layer at a tme, using one of several methods. A bed of powder may be laid down and then solidified in certain places by squirting a liquid binder onto it; lasers may be used to fuse together powdered ceramic, metal or glass in selected areas; plastic may be squirted out of a nozzle to build up material in the approproate parts of each layer; or light may be used to harden selected regions of a photosensitive gel. Some devices can use more than one material for each layer, or apply inks to produce multicoloured objects.
Once each layer is complete, the build tray is lowered by a fraction of a millimetre and the construction of the next layer begins. When all the layers have been completed, any excess material is cleaned away to reveal the finished object.