Published MPMN May 2004
Originally Published MPMN May 2004
Photopolymer Yields Functional Prototypes
Material offers strength and durability
|The optical housing built using the RenShape SL 7560 material consists of two sections. The opaque white color of the photopolymer facilitated painting and assembly to produce lighttight units.|
New optical equipment from Welch Allyn promises early detection and management of glaucoma. However, the company ran into some challenges in designing an internal
optical housing for the unit.
Steve Slawson, engineering specialist at Welch Allyn, says, "Designing the optical housing and building the prototypes was a complicated process because of the number of advanced functions featured on the new glaucoma detection equipment."
The housing holds the optical lenses for the unit and is the support base for light-meter and camera control circuit boards and infrared LEDs. The housing also incorporates small triangular details that help with the alignment of the patient before the test is administered. Slawson continues, "As the engineers refined the operating characteristics of the advanced equipment, they changed apertures and lens diameters, altering the shape, size, and placement of the various components that are part of the housing."
Because of this, eight different stereolithography (SL) designs for the internal optical housing were built before the product was finalized. RenShape Solutions Tooling Group of Huntsman Advanced Materials (East Lansing, MI; www.huntsman.com/renshape) supplied its RenShape SL 7560 photopolymer material for prototype iterations. The SL material produces extremely accurate complex parts with ABS-like durability, according to the company. It yields functional prototypes that can be assembled using self-tapping screws without cracking.
FineLine Prototyping (Raleigh, NC; www.finelineprototyping.com) built the SL housings. According to Rob Connelly, president of FineLine, "Welch Allyn approached us with the project, its performance requirements, and a deadline of three to four months. After building models and evaluating several SL materials, we chose RenShape SL 7560 because it offered us the strength and durability needed for the functional housing prototypes, along with the accuracy required to ensure complete matching of multiple mating surfaces."
The housing also had to be able to retain light to perform in sensitive optical tests. The opaque color of the SL material enabled FineLine to minimize the amount of paint used to coat the housing to eliminate light transmission. "Multiple layers of paint can contribute to reduced accuracy as parts are assembled," says Connelly.
Slawson adds, "With its combination of rigidity and durability, RenShape SL 7560 photopolymer effectively simulated production parts that are being injection molded from GE Plastics' Cycolac ABS thermoplastic."
Once awarded the project, FineLine used Welch Allyn's CAD data to produce a series of housing designs on one of its three Viper SL systems. Each set of six prototypes took about a day to complete. As each design iteration was built, Welch Allyn engineers worked with the prototypes to make further refinements. New data were then sent to FineLine for the production of the next set of housings. When engineers and sales and marketing staffs were satisfied with the design, the unit was put into production.
"With the multiple design iterations that were required, the processing speed and accuracy of the RenShape SL material were key to moving the project ahead in a timely manner," says Slawson.
"With its ABS-like performance, the SL 7560 photopolymer met Welch Allyn's need for a material that was durable and accurate enough to be used in functional prototypes that were packaged, shipped throughout the country, and withstood frequent handling without breaking," Connelly concludes.
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