Now more than ever, technological advancements drive the product design process.Increasingly powerful CAD programs allow more complex product designs, which in turn drive the demand for more complex prototypes. At the same time,fast-moving competitive markets require frequent design changes, shorter lead times, and tighter budgets. In short,prototyping must be faster, better, and less expensive.

While traditional rapid prototyping is still widely used, a growing number of design engineers are turning to rapid injection molding for prototype development. Rapid injection molding offers superior prototype quality while dramatically reducing the time and cost normally associated with conventional injection molding. As acceptance grows, rapid injection molding is changing the way designers think about prototyping in industries like aerospace, appliances, automobiles, electronics, and medical devices.

ImageWhile rapid prototyping and rapid injection molding both start with a 3D CAD part model, the actual processes and end results are very different. Rapid prototyping — which includes technologies like stereolithography, selective laser sintering,fused deposition modeling, laminated object manufacturing, and three-dimensional printing — creates a prototype layer-by-layer to form the end product.

Rapid injection molding, on the other hand, uses the familiar process of injecting heated thermoplastics into a metal mold, where the material cools into the desired shape. Unlike rapid prototyping, rapid injection molding produces a fully functional, injection-molded part. The resulting quality difference is so significant that many design engineers who test form and fit using rapid prototyping will still check the functionality of their prototypes using rapid injection molding. Also,while conventional mold-making is very labor-intensive, rapid injection molding fully automates this step, typically reducing tooling cost and lead time by two-thirds. Rapid prototyping may be an acceptable choice for creating small numbers of prototypes in very short lead times — typically fewer than 10 parts in one to five days. But rapid injection molding can economically deliver 25 to 1,000 production-quality prototypes in three to 15 days. When production-quality surface finishes are not required, rapid prototyping may be an acceptable choice, but the "stairstep" surface it leaves on parts is a significant disadvantage, as it keeps parts from fully reproducing the intended design. Rapid injection molding, on the other hand, uses a CNC-machined metal mold to create the part shape, so it can replicate the intended shape much more accurately, just as with conventional injection molded parts. This can greatly increase the value of the prototype to the design engineer.

NASA Tech Briefs Magazine

This article first appeared in the November, 2004 issue of NASA Tech Briefs Magazine.

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