RP machines process CAD data by slicing the computer model into layers, each layer being typically 0.1 - 0.25mm thick. The machine then uses this data to construct the model layer by layer, each layer being bonded to the previous until a solid object is formed. Due to this laminated method of construction a stepped surface is developed on curved faces, the removal of which is essential if maximum advantage of the process is to be realised

Schematic representation of the stepped construction which requires post processing

• Converts 3D CAD images into accurate physical models at a fraction of the cost of traditional methods
• Improves design communication and helps eliminate design mistakes
• Reduces 'Time to Market' for a new product
• Can be used as a powerful marketing tool since the prototype can be seen rather than the drawing

More recent developments have been prompted by problems caused by the expansion of the model where it is used as a disposable pattern (like the wax pattern in the Lost Wax Process). Where the resin model is produced to form solid walls, expansion during the "burning-out" stage weakens the ceramic shell, and can cause failure in the firing and/or casting stages.

The company, 3D Systems GmbH, who specialise in the SLA system, have developed a machine and software which together allow for the model to be constructed in the form of a honeycomb. The honey comb structure collapses in on itself during "burning-out" thus avoiding the problems of expansion. Each pocket of the honeycomb structure is connected to its neighbour by a small hole that allows for the uncured resin to be drained prior to use.