A method to fabricate plastic parts by utilizing a mold or cavity with a shape and size identical to the part being produced. Molten polymer is injected into the cavity and yields the desired part upon solidification. The mass production capability of injection molding offers low production cost.

Professional Prototype Tooling Services

Injection molds are typically made from steel alloys and can take several months to develop. Lower cost and shorter development time, therefore, has been an important focus in the prototype tooling services community. Stereolithography. with its capability to produce tools quickly and economically, offers a potential means to resolve this issue.

The stereolithography (SL) process starts with a CAD file of the desired object. The CAD model is sliced into layers of thickness typically ranging from 0.002" to 0.008"0 (50 to 200 [mu]m). The slice file then is input into the SL machine, which essentially consists of a laser source and a part platform. Each layer of the model is created as the laser cures the resin according to the slice pattern. After one layer is completed, the platform is lowered into the resin a distance equal to the layer thickness, and the curing is repeated to create the next layer. The cycle repeats until the whole model is built.

Tooling for injection-molding applications has been a promising area for deploying the SL technique. SL molds allow complex geometry to be built with ease and with considerable reduction in cost and tool-development time. SL molds can be built in hours instead of days or months as for conventional steel molds. The savings can be significant considering the size of the prototype tooling services industry. The SL process already has been used successfully in the production of short run injection molds. Current research in industry and academe has shown that SL molds can produce from 50 up to 500 parts before breakage.

Previous work on SL molds has shown that their life is highly dependent on the stress applied to the mold during the prototype tooling services cycle. During injection, the polymer flow creates a bending stress on small features, and can either permanently deform the mold or break it. During ejection, stresses are applied at the surface of the mold due to the plastic part shrinkage on the core coupled with inherent interlocking between SLA molds and the part.