Photopolymer prototyped parts

• halved prototype cost

• trebled prototype speed

General Pattern, which provides rapid product development services, was assigned to provide a register assembly prototype application. They used the opportunity to test Somos Raven 7620 SL resin, a clear, amber liquid photopolymer. The dark color created through photoimaging creates a tinted or smoked appearance to the SL parts. In addition to its unique appearance, the material offers high humidity resistance and tough, general purpose properties. General Pattern had another motivation for testing this resin; according to their North American general manager, Denny Reiland, “We operate stereolithography equipment that is truly on the cutting and bleeding edge of technical capabilities. We saw Raven as being a leap ahead in materials technology and very compatible with our processes. Beyond that, however, we were very pleased with the price point and views this as a great opportunity to compare a new photopolymer material against RTV/Polyurethane modeling.”

This particular register assembly application had thirteen individual components: a housing, damper arm, vane link, thumbwheel, damper door, thumbwheel busing, barrel bushing, barrel and five vanes. Traditionally the procedure for prototyping from a polyurethane casting requires the following to obtain a master pattern:

1. 1. Approximately 1.5 hours to gate and vent the part and build a pattern box
2. 2. An additional 24 hours for the silicone part to cure
3. 3. Within an 8-hour workday, it is possible to produce 3-5 castings with regular urethanes or 10-16 parts with quick-setting urethanes.
4. 4. As a general rule of thumb, an additional RTV tool should be built if quantities exceed 50 pieces.

By way of processing comparison, Raven photopolymer was used in the solid imaging process to build 3D parts, with intention for use with a variety of layer thicknesses. After part formation via UV light exposure in a stereolithography machine, the excess resin was removed by rinsing with a solvent (e.g. propylene carbonate or tripropylene glycal monomethylethers), followed by a rinse in isopropyl alcohol. The part was then post-cured by UV fluorescent light.

While the traditional method took 10 days and over $10,000 to process ten prototypes, the new photopolymer produced parts in 3 days for under $5,300. “It is clear to us,” says Reiland, “that designers, engineers and OEMs should all be alert to the emergence of new materials that offer the potential of improving cost and turnaround versus traditional methods of modeling and prototyping. We have no doubt that such advancements in materials will continue to positively impact economic cycles of product development.”