April 1, 1997

5 Min Read
Rapid Prototyping

Medical Device & Diagnostic Industry Magazine | MDDI Article Index

An MD&DI April 1997 Feature

MEDICAL PLASTICS

Some major rapid prototyping companies share which plastics they use for model building.

Since its introduction to the medical device industry fewer than 10 years ago, rapid prototyping has revolutionized the way devices are designed. Manufacturers can now combine sophisticated 3-D software with model-building machines to quickly and cost-effectively produce resin parts. These soft models can then be used to make casts for metal or injection-molded prototypes. In fact, the time and cost savings of rapid prototyping are so dramatic that it has become a thriving industry in its own right, and one that is continually changing as faster and more accurate processes are developed.

Nearly all of the rapid prototyping processes available involve specialty plastics, designed to maximize not only the ease of processing, but also the durability of the soft prototype parts that are produced.

A sample of companies representing a variety of rapid prototyping methods offers a useful overview of the types of materials being used in this new industry.

BPM Technology, Inc. (Greenville, SC). BPM uses an ink-jet spray machine to deposit prototype materials in layers. The company has developed a polystyrene thermoplastic made of a resin styrene acrylic copolymer, a primary aromatic sulfanimide carrier, and an antioxidant that keeps the material white over time. The material was developed to ensure that it would have a high viscosity while maintaining accurate surface tension even at high temperatures. Its design also provides a short cooling time and the ability to rapidly build up surface area.

Cubital America (Troy, MI). With its solid-ground curing technique, Cubital America creates soft parts from a mixture of wax and layers of an acrylic photopolymer. In this process, a resin layer that is partially masked with a toner on a charged glass plate is exposed to ultraviolet light, and the unexposed resin is then removed from the exposed layer. The empty areas are then filled with a liquid wax, which hardens. When the layers are complete, the wax is dissolved with an acidic solution.

The resin used by Cubital was chosen for hardness and strength, but the company also plans to introduce a modeling epoxy next year in order to offer improved strength and flexibility as well as more secondary process options.

DTM Corp. (Austin, TX). In DTM's selective laser sintering process, a CO2 laser makes solid cross sections by sintering powdered plastic. One of the advantages of the process is the variety of materials that can be used to create the models; DTM uses as many as 11 different materials, including metals as well as plastics.

Among the new materials that the company offers is a flexible elastomer, DuPont Somos 201, that can be used for medical applications such as endoscopy or orthopedics. The material, which has rubberlike characteristics, enables manufacturers to develop functional prototypes of products such as gaskets, seals, and moldings, where flexibility is a key requirement.

Sanders Prototype (Wilton, NH). With a double ink-jet machine, Sanders Prototype deposits thermoplastic in layers from one ink jet while simultaneously depositing a surrounding wax support for the resin model that is being formed. The company uses a proprietary thermoplastic that has been optimized for useful heat and adhesion properties.

The thermoplastic has a high melting temperature, 95°C, while the wax that will surround the part melts at between 50° and 70°C, so it can be partially melted to ease its removal when the thermoplastic part is finished. The thermoplastic is also chemically engineered for only loose adhesion with the wax material. Easy removal of the wax is important to ensure that the part will not be marred.

Stratasys Corp. (Eden Prairie, MN). Fused-deposition modeling rapid prototyping, in which liquid thermoplastic is layered onto a fixed base, is the specialty of Stratasys Corp., and the firm has recently introduced a new modeling material for its process, one that is designed to meet medical specifications. Methylmethacrylate/acrylonitrile/butadiene/styrene, or MABS for short, which meets USP Class VI requirements, can be sterilized with gamma radiation, and offers resistance to chemicals that commonly come in contact with medical devices, such as saline, betadine, and fatty lipids.

A 3-D printer from Stratasys creates multiple iterations of concepts quickly at a designer's workstation.

3D Systems (Valencia, CA). 3D Systems is the developer of the stereolithography process in which liquid resin is cured in the shape of thin layers, or slices, of a 3-D computer design with an ultraviolet laser. In this process, the machine that performs the curing, a stereolithography apparatus, adds each layer to the previous layer until a 3-D part is formed. This master part can then be used to make molds for small-numbers of polyurethane parts, injection-molded plastics, or even volume protection metal prototypes.

A recent new offering from 3D Systems is the SLA SmartStart package, which is an all-in-one system with everything manufacturers would need to install stereolithography facilities at their premises. The system uses Cibatool SL 5170 epoxy resin, a low-viscosity, photocurable liquid. According to the company, the material provides high-level accuracy and strong, durable rapid prototyping parts. It can be used for form, fit, and function studies; for assembly verification; for photo stress analysis; for direct injection molding; and for preparing masters for secondary tooling applications.

Leslie Laine is a senior editor for MD&DI.

Copyright © 1997 Medical Device & Diagnostic Industry

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