Medical Equipment Replaces Metal with Solid Reaction Injection Molding: Reduces Assembly, Parts, Wall Thickness

Replacing an aluminum sheet metal housing with solid polyurethane Reaction Injection Molding netted manufacturer Computed Anatomy some impressive numbers:

  • 60% reduction in parts
  • 60% reduction in assembly time
  • 50% reduction in wall thickness

The redesigned third-generation corneal topographic modeling system also picked up a bronze award in the Medical Instruments category of the Industrial Design Excellence Awards.

The new Computed Anatomy TMS-2 parts manufactured by Exothermic Molding use the PRISM® CM-200 solid polyurethane Reaction Injection Molding system from Bayer Corporation's Polymers Division. This two-component system meets stringent flammability ratings while also offering a high modulus chemical resistance and high impact properties. The PRISM® CM-200 system also is a fast-cycling Reaction Injection Molding system that offers demold times of 60 seconds.

"The redesign of this third generation really was for manufacturing reasons," said Roy Maus, Vice President of Computed Anatomy, a wholly owned subsidiary of Tomey Corporation. "We wanted to eliminate as many parts as possible and make it less expensive to produce. The switch from sheet metal to solid polyurethane Reaction Injection Molding made it possible."

Manufacturing by Design

The TMS-2 is used for measuring and evaluating the corneal surface of the eye. It is typically used by ophthalmologists to gather accurate corneal topographic data for use in radial and astigmatic keratotomy. Using an X-Y-Z-axes joystick and a small feedback monitor, the doctor aligns the imaging head with the center of the patient's cornea. Once positioned, a button on the joystick records the image onto a hard drive so the data can be translated into a three dimensional shape.

When redesigning the equipment, ION Design of New Jersey needed to meet Computed Anatomy's manufacturing goals while also improving the aesthetics to appeal to both patients and doctors.

The TMS-2's RIM components include the base housing, X-Y platform mounted on slides, the tower component that holds the imaging head, housing for the monitor, and a small bump under the joystick.

"We needed a Reaction Injection Molding material that would serve as a structural member since the X-Y platform, which supports the tower and the weight of the physician's hand, is only supported at three points," said Mario Turchi, principal at ION Design. "We also needed good surface quality, we found the PRISM® materials to fit the application better than other Reaction Injection Molding materials. It has less voids and is more flexible."

Turchi adds that the reduced wall thickness of a part molded with Exothermic's PRISM® CM-200 System helped in reducing cost as well as fitting in all of the equipment's components into a smaller space. The PRISM® system also gave the designer the ability to do compound curves, softening the equipment to make it approachable for the patients.

"Given the target quantities of production and the design we had, no other materials were well suited for this," said Turchi. "Injection molding, structural foam, and regular RIM would have been too expensive. The PRISM® CM-200 system was a very good fit."

Quick Startup

The eight Reaction Injection Molding parts are molded by Exothermic Molding. The molder uses three tools prepared with an in-mold coating: a single-cavity mold for the X-Y platform: a two-cavity family mold for the tower's two clam shell components; and a five-cavity family mold for the base's front and rear bezels, the joystick bump and the monitor's front and rear housing. All parts have threaded inserts, and cure times average two to three minutes with cycle times around six minutes.

"We started up and the PRISM® CM-200 material ran flawlessly," said Paul Steck. President of Exothermic Molding. "Within one day we were 100 percent. There were no startup adjustments for us, which is unusual when you're running a new material. This resin gives a high quality part right out of the mold that needs very few secondary operations. We feel it's a superior material, especially for customers and industrial designers who are looking for thinner walls."

 Reaction Injection Molding