Liquid Silicone Rubber Molding

PolyJet technology for LSR molds

Because injection molds used to produce liquid silicone rubber (LSR) parts are typically too expensive for low-volume production, manufacturers often resort to labor-intensive manual casting methods that can result in molds that stick or deform. 3D printing with PolyJet technology is an attractive alternative. Reliable, low-volume molds can be ready for use in as little as one day.

Overview of the application

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Liquid silicone rubber (LSR) is a widely used material due to its versatility and unique properties. It is non-reactive and stable, as well as resistant to extreme environments and temperatures. LSR is used in industries that span automotive, defense, sporting goods, medical devices and consumer products.

Mass production of LSR parts uses specialized injection molding machines that meter, mix and inject LSR into a heated mold. Due to the time and expense of this process, low-volume production and prototyping is often done with manual casting methods that use molds made of modeling board, RTV rubber or soft metal.

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However, although they are easier, faster and cheaper to produce, prototype molds have their own challenges. Making LSR parts with RTV molds is a multi-stage process requiring time and labor to produce the patterns and molds. Care is also needed to ensure the soft rubber RTV mold does not deform or stick to LSR parts. Machined molds overcome these challenges, but they can be much more expensive, time-consuming and labor intensive than RTV molds. Additionally, machining may have limitations with respect to the complexity of a part’s design.

Value of using PolyJet

Software
PolyJet mold
LSR part from PolyJet mold

PolyJet technology provides an alternative method for producing molds for LSR parts with dramatic time and cost savings. This 3D printing process (additive manufacturing) builds objects layer by layer, using data from computer aided design (CAD) files. With an inkjet-like process, PolyJet technology delivers extremely high-resolution molds with smooth surfaces.

Using 3D printed molds, LSR parts can be produced in just one or two days. After designing the mold in CAD, it is printed, often overnight, without operator attendance or added time for complex designs. PolyJet molds preserve fine details and deliver smooth surface finishes. With only a few minutes of labor for cleaning and assembly, the mold is ready to make LSR parts.

Liquid silicone rubber is usually made from low-viscosity, two-component materials. After mixing the two components, the LSR is injected into a pre-heated PolyJet mold. The LSR part is removed from the mold after curing, and the process is repeated to create the required number of parts.

LSR parts created with PolyJet molds have all the characteristics of mass-production, molded parts. They exhibit subtle details, excellent accuracy and exceptional aesthetics, combined with the desirable mechanical and thermal properties of production-grade LSR material. This makes both functional testing and low-volume production a practical alternative to conventional LSR molding techniques.

If the mold needs to change, simply revise the design and print a new mold, which will be ready for testing within a day or two.

Benefits of PolyJet

Average lead time savings: 70% – 90%
Average cost savings: 30% – 85%
Molds: Overnight production
Smooth, mold-ready finish
High resolution for fine details
LSR parts: Production materials for exact characteristics
Complex, intricate designs
Revisions: Rapid response to design changes

*Typical time and cost savings derived from numerous end-user analysis, testimonials and feedback. Actual savings may vary based upon numerous factors, including traditional time/cost, part geometry and utilized technology.

PolyJet is a best fit

Size: 6 mm (0.25 in) to 300 mm (12 in)
Quantity: 5 to 100 castings
Design: Complex, intricate
Revisions likely
Application: Functional prototyping
Low-volume production
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