Cast nylon process makes quick work of medical prototypes

February 16, 2010

A cast nylon process already seeing use in production of very low-volume parts products and prototyping is being further developed to handle higher volumes, with a goal of being competitive with injection and blowmolding for small volume series of up to 5000 parts. The company's work is used to serve the medical, automotive, consumer goods and other markets.  

man inspects precision on cast nylon part from German processor rpm
The goal is to develop a process for higher volumes that still can compete with injection molding's tolerances.

Developed by German plastic specialist rpm ("rapid production manufacturing"; Helmstadt, with U.S. subsidiary in Rochester Hills, MI), the NylonMoldprocess relies on polyamide 6 (PA6). "We are supporting the work of the engineers with proposals for solutions to optimize the construction, without losing track of the costs," explains Klaus Kreutzburg, business managing director of rpm.

Parts take shape following a thermally activated polymerization of a monomeric mixture. This mixture is enriched with additives and catalytic components. Processing involves injection of the mixture at almost no pressure into molds made of silicon. These 'Soft Tools' are obtained by recasting the master form. The molds are heated to the monomer's reaction temperature in a kiln.

Components made via the process show a high crystallinity and are free of internal stress. "Signature to the cast polyamides is the high ductility with high density, the high abrasive resistance and the damping capacity", says Jörg Gerken, technical managing director of the company. If for example heat stabilizers and 30% glass fiber are added, then parts reach a tensile modulus of elasticity of 7500 MPa and Charpy impact strength of 26.2kJ/m2. Even neat, parts can handle temperatures between -40°C and 180°C and are chemically resistant to gasoline, hydrocarbon, and solvents, as well as conditionally permanent against acids and bases.

The company's officials claim that parts can be ready for shipping within a few days of an order, with the silicone molds helpful in reducing time-to-market and cost. "The high costs per unit will be more than recouped through time reduction until first delivery, the flexibility of the method and the low tool costs", says Sebastian Krüger, a management consultant who also works as a member of rpm's advisory board.

Compared to injection molding or blowmolding, the company says costs savings of 50% can be realized for, for example, a 1000-part order. Now the goal at rpm is to raise the bar so that higher-volume projects up to 5000 parts can be realized at similar savings levels. The company says interest for such volumes is especially strong in the medical device market. 

The economical limitations of the NylonMold method are currently set by the limited tool life of the silicon molds, which is between 15-35 parts depending on their complexity. The research project QbridMoldNylon, which was inaugurated last fall at the company, is striving to develop a flexible, partly automated process useful for small volume series of up to 5000 parts. The parts are to be comparable to injection molded parts regarding tolerance and surface appearance. "Our main focus is on short-term allocation times with comparatively low costs. This will maintain the competitiveness with injection molding," says Krüger. The project group is currently building molds using alternative materials and combinations of different materials. Matt Defosse




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