By Brad Cleveland, Protomold

Related links: Plastic Prototyping | Fused Deposition Modeling (FDM) | Rapid Prototyping (RP) | Stereolithography | Additive Process

Comparative Speed

Long ago, before the Internet, there was a cartoon going around showing a character convulsed with laughter under the heading “You want it when?!” It was funny at the time, but anyone who still thinks it’s funny could end up with time to spare; lots of it, because today’s market waits for no one. If you can’t meet the deadline, there’s someone who will.

Because prototypes can be critical to the performance and market acceptance of a product, delays in prototyping, almost by definition, translate to delays in development. That’s why the introduction of “rapid prototyping,” the additive process for building up a prototype in layers, was such a milestone in the history of product development.

Before rapid prototyping, plastic prototypes were made either by slow, manual machining or slow, manual injection molding. Rapid prototyping automated the process, permitting service bureaus to quickly produce reasonable prototypes—using additive processes like stereolithography, fused deposition modeling, and others—in days, directly from CAD models. They weren’t a perfect match for production parts, and they could be expensive if more than a few were needed. But they were fast, and that was enough to make them a valuable addition to the designer’s arsenal.

But while the term “rapid prototyping” came to be applied specifically to those additive processes, other, non-additive methods were becoming rapid as well. By 1999, Protomold’s rapid injection molding was producing real, injection-molded parts in as few as five days. Like the additive processes, it was able to work directly from 3D CAD models and offered automated quoting with a free moldability analysis in just one day.

In 2006, First Cut Prototype entered the marketplace, producing CNC-machined plastic parts in as little as a day. Like Protomold’s rapid injection molded parts, these come in a variety of materials and are made directly from the customer’s 3D CAD model. Not to be outdone, Protomold soon announced one-day turnaround as well, giving users a three-way choice for one-day production of prototypes.

As of this writing, however, the additive process is leading the race by a nose, with one option neither of the other two can match: automated on-premise production from 3D CAD models. Users can now purchase relatively inexpensive 3D printing equipment that will produce a layered plastic-like prototype directly from a CAD model in just hours, eliminating the need to ship finished parts. Like all additive prototypes, they leave something to be desired in finish and material, but they are certainly fast.

The accompanying figure illustrates the relative parts-making speed of each of these processes.