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Photopolymer saves cash and time for prototypers

Edited by the Engineeringtalk editorial team Sep 20, 2002

A register assembly prototype application has been used a basis for comparing turnaround times and costs of traditional RTV/polyurethane modelling versus a new generation stereolithography resin.

General Pattern, a service bureau providing rapid product development solutions for all engineering applications, has used a register assembly prototype application as a basis for comparing turnaround times and costs of traditional RTV/polyurethane modelling versus a new generation stereolithography (SL) resin.

The results suggest that parts manufactured using additive manufacturing processes such as SL are often the most economical solution for a project's goals - and that material advancements have expanded the application and range of additive manufacturing technologies.

General Pattern's SL material of choice was Somos Raven 7620, a clear, amber liquid photopolymer.

The dark colour created through photoimaging creates a tinted or smoked appearance to SL parts.

In addition to its unique appearance, Somos 7620 also offers high humidity resistance as well as tough, general purpose properties.

General Pattern had yet another motivation for wanting to test Somos Raven.

According to General Pattern's 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 viewed this as a great opportunity to compare a new photopolymer material against RTV/polyurethane modelling".

Traditionally, the procedure for prototyping from a urethane casting requires several steps to obtain a master pattern.

First, it takes approximately 1.5h to gate and vent the part and build a pattern box.

Secondly, it takes an additional 24h for the silicone mould to cure.

Within an 8h workday it is possible to produce three to five castings with regular urethanes or 10-16 parts with quick setting urethanes.

The general rule of thumb is that an additional RTV tool should be built if quantities exceed 50 pieces.

With regard to General Pattern's specific register assembly application there were 13 individual components: a housing, damper arm, vane link, thumbwheel, damper door, thumbwheel busing, barrel bushing, barrel and five vanes.

In total, the cost of modelling and moulding enough pieces for ten complete register assemblies using the RTV/polyurethane method was $10,300 and required a turnaround time of ten days.

By way of processing comparison, Somos Raven 7620 photopolymer is used in the solid imaging process to build three-dimensional parts and is intended to be used with a variety of layer thicknesses.

After part formation via UV light exposure in a stereolithography machine - in this instance an SLA 5000 from 3D Systems - the excess resin was removed by rinsing with a solvent (propylene carbonate or tripropylene glycol monomethylethers are acceptable), followed by a rinse in isopropyl alcohol (IPA or isopropanol).

The part was then post-cured by UV fluorescent light.

In total, the cost of modelling and moulding enough pieces for ten complete register assemblies using Somos Raven 7620 was $5295 - nearly half the cost of RTV/polyurethane.

Of equal importance, the required parts were produced in only three days - more than three times quicker than RTV/polyurethane modelling and moulding.

"It is clear to us", says General Pattern's Denny Reiland, "that designers, engineers and OEMs all should be alert to the emergence of new materials that offer the potential of improving cost and turnaround versus traditional methods of modelling and prototyping.

We have no doubt but that such advancements in materials will continue to positively impact economic cycles of product development".