Two plastic tooling prototyping methods were introduced in the previous pages, stereo lithography and fused deposition modeling. Both plastic tooling prototyping are valuable tools to check form or fit of a part design. With continuous improvements in the technologies, parts created by either of these methods are showing an increase in strength and accuracy, some parts are even being used in actual testing.

plastic tooling prototyping article

However, there remains a gap between prototyping and manufacturing. It is difficult and expensive to produce many high quality RP parts for testing. Also, parts made with present RP techniques do not have the material properties required for rigorous function testing. Rapid tooling fills this gap. Using rapid prototyping technologies, molds are created in a number of different ways in a much shorter time period than traditional molds. These are then used to produce parts in high quantity. Plastic tooling prototyping methods Some rapid tooling methods create molds that yield only 1 - 2 parts per day, referred to as soft tools.

Epoxy tools produce higher quantity and share a very similar method as the soft tool. If resources are limited, or the high quantities produced by a final production tool is not required, there are bridge tools to help a company "bridge" the typical 12 - 14 week gap between final design confirmation and the beginning of actual part production with a hard tool. Above and beyond these technologies, there is a great deal of research trying to further speed the steps from design to production, discussed below. Direct Tooling - New Technology Beyond the quantity restrictions of soft and bridge tools is hard tooling. Hard tools for plastic tooling prototyping are built of tough materials, made to withstand the rigors of long term injection molding. Traditional hard tool design is both time consuming and costly. A large block of steel is typically CNC machined to create cores and cavity inserts. An experienced designer must machine the mold bearing in mind correct sprue placement, draft angles, vents, cooling lines, and ejection pin locations. Fine details require EDM.

Polishing and grinding is usually required to achieve a good surface finish. If a mistake is made, the entire steel block may have to be scrapped and the process begins again. It would be most convenient to be able to build something as complex as a hard mold with something as efficient as rapid prototyping. This plastic tooling prototyping is the concept behind "direct tooling".

This goal is not yet fully realized, but there are many interesting developments. One method called Three Dimensional Printing comes from MIT. This technology works much like an ink-jet printer, a thin layer of powder is spread over a platform. Directed by a computer file, similar to the .stl, binder material is selectively deposited to join particles of the powder and form into the shape of the first layer. The platform lowers so the next layer can be built. At completion, the mold is heat-treated to remove the binder, among other post-processing steps in order to make the part more robust. Types of metal that can be used with this process include stainless steel for plastic tooling prototyping.