RP is basically a visual aid that allows the moldmaker to evaluate the design and know it is correct before the process moves to the hard tooling stage.

From the model he can accurately determine where parting lines in the mold can and should be set up. If minor modifications need to be made, it can be done to the original SLA master. If they are major modifications, a new master will have to be produced. In either case, it is faster and less costly than modifying hard tools.

To start the rapid prototyping process, .STL files (the file extension that stands for stereolithography), the industry standard for rapid prototyping, are sent to the rapid prototyping source. Most CAD packages (SolidWorks, ProEngineer or Unigraphics) will allow the user to export to the .STL file format. Some CAD packages will let the user preview the .STL file to ensure the output quality.

If the moldmaker does not have a current CAD package that allows .STL files to be exported, then a 3-D CAD drawing can easily be made from blueprints and then converted to the needed .STL file for input to the RP machine. With .STL files in hand, either SLA or SLS prototyping processes can be used—depending on the desired requirements for the final model. For example, if the SLA process is to be used the .STL files will need to be scaled to compensate for mold shrinkage before a master is produced.

Moldmakers find it both cost-effective and comforting to spend only 20 percent of the final mold cost to prove out the fit and function of the design with an RTV molded part, instead of machining a final aluminum mold that may have to be fixed later. Rapid prototyping allows RP service suppliers to be involved in the whole plastic process, and because some are not design responsible, they give the moldmaker options when they become involved—which is typically after the production part approval process (PPAP).

Some service suppliers provide 1-100 RTV silicone molded prototypes if needed, keeping in mind that these types of silicone molds have a wear life because the material breaks down with time. But, that also depends on the complexity of the part geometry. Or, the service supplier can produce one piece if that validates that the mold will work. Typical turnaround for a rapid prototype is three to five days for either SLA or SLS, but that is dependent upon the geometry and size of the part.