Furthermore, rapid prototyping is very limited with respect to materials that can be used and often creates prototypes too fragile for rigorous physical testing. Rapid injection molding can utilize a wide range of production-grade resins to manufacture fully functional parts, allowing the design engineer to consider both mechanical properties (e.g.strength, temperature resistance, etc.) and cost when ordering the prototypes.

Rapid injection molding can be utilized from the earliest stages of product development through bridge tooling and ongoing production. After rapid injection molding is used to create prototypes, it can support the manufacture of 1,000, or even 10,000 parts for pilot production or market testing at no additional tooling cost. If high production volumes do justify production steel tooling, rapid injection molding can be used as bridge tooling, to produce fully functional production parts until the steel tool is available. And when production volumes are moderate, rapid injection molding can be a complete, cost-effective production solution.

Rapid injection molding is a unique, highly automated method of producing injection molded parts from a 3D CAD part model. The core technology is proprietary software that automatically converts the part model into toolpaths for CNC milling machines. These, in turn, produce the mold components that, when assembled and mounted on an injection molding press, produce the desired part. Although a vast array of geometries can be produced, some limitations in part size and complexity exist due to the highly automated nature of the mold making process. For example, CNC milling results in rounded external part corners. Some high-aspect ratio features, e.g.thin ribs, may not be machinable. And the ability to produce "under- cut" part geometry features is limited.

The software provides a rapid injection molding compatibility review, often suggesting changes that will improve moldability or reduce tooling cost. This automatic analysis highlights undercuts, wall thicknesses that could cause fill or sink problems,and areas where draft is required. The system also provides color-coded indications of radii resulting from the mold-milling process and areas where a minimum thickness might be required. The software automatically generates the mold design,including core and cavity geometries, shutoff surface generation, gate-design layout, and ejector-pin placement,and outputs toolpaths to CNC machine cells to manufacture the required mold components.

Before rapid injection molding,design engineers faced a large gap between the capabilities of rapid prototyping and conventional injection molding. Rapid prototyping parts were fast and relatively cheap, but weren 't "real" Injection molded prototypes were real parts, but neither cheap nor fast. With rapid injection molding it is now possible to get real parts, real fast, and at a real savings.

Rapid injection molding enables companies to experiment and perform functional tests with real parts without worrying about prohibitive cost overruns or skyrocketing design costs. Unshackled from the restraints of long lead times and high production costs, design engineers can instead focus their valuable time, efforts, and expertise on creating innovative, high- quality products.

This article was written by Brad Cleveland,president and CEO of The Protomold Company, Maple Plain, MN. Contact The Protomold Company at Tel: 763-479-3680, or visit www.protomold.com.