Rapid Prototyping (RP) is a general name that encompasses numerous methods used to fabricate objects from CAD data. There are a number of different RP processes, and new developments are constantly being made.
RP most commonly is used with investment casting, sand casting and plaster molding to produce an actual cast part to test for form, fit and function, as well as to determine the approximate final properties of the cast parts.
Investment Casting—RP models for investment casting are created by converting a 3-D CAD model into an .STL file. The file then is printed three-dimensionally using either photopolymer, thermopolymer, polystyrene or other materials, depending on the RP method. The prototype models then can be attached to a gating system and processed through typical investment casting to produce cast prototype parts.
Sand Casting—In sand casting, RP-generated parts can be used as patterns for fabricating a sand mold. RP processes that use a material similar to wood are common. The molds are created in a fraction of the time and then affixed to the pattern board before sand is packed around to create half of a mold cavity.
To save even more time, RP processes can be used to directly fabricate molds and cores. These processes build the cores and molds layer by layer by fusing either polymer-bonded sand together or using a wide-area inkjet to bond the sand. The molds and cores also may be created by forming a block of sand and machining out the cavity.
Plaster Molding—RP often is used with plaster molding processes to circumvent or transition to the production of hard tooling. This is accomplished by creating a rubber mold from an RP-generated pattern (similar to sand casting). The rubber mold then is used to create plaster molds for casting production. Plaster casting often serves as a precursor to diecasting production while the hard tool is being made.
A final form of RP worth mentioning is the use of CNC machining to create individual parts, tooling or dies, or to take blocks of sand and machine them to create prototype sand molds.