Using LIM to create better, faster, cheaper prototypes

Vesta Inc., a Wisconsin-based medical molder, has developed a process that it thinks puts an end to lengthy, expensive prototype production of medical products. The method, called Quick Response, is based on Vesta's ability to mold medical-grade liquid silicone rubber (LSR) in low volumes.

Quick Response uses liquid injection molding (LIM) equipment with specially designed pumping systems to deliver the LSR from its container directly into the mold, usually made of heat-treated steel. The molds are then pulled from the presses and opened, and the prototypes are removed (Figure 1). Additionally, Vesta elevates the mold temperatures, thereby achieving rapid curing cycles, enabling it to produce up to 100 or more prototypes quickly and with a minimal setup cost.

Vesta declined to release the setup costs or savings associated with this prototyping process, except to say that they vary depending on the parts prototyped, materials used, and product design. Vesta vice president of engineering Chuck Heide adds, "Quick Response can reduce prototype times by as much as 70 percent, and associated costs by nearly as much."

How It Works

Components of the Quick Response process include CAD, proprietary custom tooling, and Ram optical systems. The Ram systems increase the accuracy, speed, and efficiency of prototyping by providing complete dimensional data in a visual format. They feature an optical measurement inspection system (OMIS) for live video images, and run AutoMap X-Y-Z software measurement programs to display graphic representations of the part.

Raw material testing with Instron's 4301 tensometer completes the cycle. Each lot of incoming material is tested for tensile strength, elongation, modulus, and tear resistance. Durometer is also measured with a Shore hydraulic instrument.

"Incorporating raw material testing into our standard testing procedures has enabled us to prevent molding problems and to perform early evaluations of material properties to optimize the material's use," says Heide. "It allows us to make more informed material recommendations to customers."

Vesta's prototyping capabilities range from parts that weigh less than 1g to those that weigh in excess of 525g. Applicable materials include medical-grade LSR, compounded for a variety of physical properties. Prototypes can have radio opacity, coloring, and product markings. Typical examples of prototypes include seals, strain reliefs, manifolds, connectors, breathing cannulas, and valves. Quick Response benefits, according to Heide, include quality components with complete performance characteristics, lower costs as compared to room-temperature vulcanizing (RTV) or use of production-size LIM tools, and shorter lead times.