For Materialise, it all started in 1990 with the RP technology stereolithography. Stereolithography is now one of the most widely used rapid prototyping techniques for plastic models and still the core process at the Materialise rapid prototyping shop.
Starting from a 3D image, a part is built slice by slice from bottom to top in a vessel of liquid polymer that hardens when struck by a laser beam.
Starting from your STL file, the required supports for overhangs and cavities are automatically generated in the model under construction. The support and model files are then "cut" into thin horizontal slices and programmed into the stereolithography 3-D Printing machine.
This machine then uses a computer-controlled laser to draw the bottom cross section onto the surface of a liquid polymer that hardens where struck by the laser. The part is then lowered to a depth corresponding to the section's thickness and the next cross section is then drawn directly on top of the previous one. This is repeated until the part is finished. The supports are removed manually after the product is taken from the stereolithography machine.