Liquid Silicone Rubber Moulding

Liquid silicone rubber (LSR) moulding is a thermoset process that mixes a two-component compound together which is then heat cured in the mould with a platinum catalyst to produce a final part. LSR parts are formed through an injection-moulding process similar to that of conventional plastic injection moulding with one major difference — the material delivery system is cooled and the mould is heated. Liquid silicone rubber possesses thermal chemical and electrical resistance plus biocompatibility. LSR parts can withstand sterilisation while maintaining physical properties at extreme temperatures.

Proto Labs brings a practical and cost effective way to get real liquid silicone rubber parts really fast. We use our injection moulding technology to analyse part geometry, provide design and manufacturability feedback and produce the tools. At Proto Labs the LSR process is suitable for producing low volumes of liquid silicone rubber parts — typically between 25 to 5,000+ pieces but up to 25,000 in some cases — in about three weeks from order to delivery of samples. Depending on part complexity it is possible to get parts faster. Standard expedite offerings and rates apply on eligible parts. The equipment and processes that we use are directly in alignment with industry standards so a transition to high volume is seamless.
Get 25 to 5,000+ parts
in less than 15 days

Process

The LSR moulding process starts with proper part design. Anyone familiar with designing parts for injection moulding should find designing an LSR part to be similar. However, the shrink rate on LSR is fairly high, and the material also tends to flash very easily during moulding. Protomold helps mitigate challenges related to high shrink rates by planning appropriate tolerances and incorporating additional features into the mould design to help reduce flash. LSR typically fills thin wall sections with minimal challenges and is accommodating to variations in wall sections as sink is almost nonexistent.

Mould production

When an order is placed Proto Labs will then design the LSR moulding tool. Due to the flexible nature of LSR, parts are manually removed from the mould and thus ejector pins are not built into the mould design. Like a standard Protomold aluminium tool, an LSR moulding tool is fabricated using a combination of CNC milling and CNC electrical-discharge machining (EDM) to create a high-temperature aluminum tool built to withstand the LSR moulding process. After milling the tool is polished by hand to customer specifications which allows four standard surface finish options: F0, F1, C1 or A2. Others may be available by request.
Mould production

Part production

The finished tool is loaded into an advanced LSR-specific injection-moulding press that is precision geared for accurate control of shot size to produce the most consistent liquid silicone rubber parts. LSR moulding shares many similarities with conventional injection moulding but there are a few notable differences. Unlike thermoplastic resin which is melted before injection LSR is a two-part thermoset compound that is chilled before being injected into a heated mould and ultimately cured into a final part. Note that Protomold uses an automated meter mixing pump to assure the exact combination of the two-part compound; nothing is hand-mixed. Since LSR is a thermosetting polymer its moulded state is permanent — once it is set it can’t be melted again like a thermoplastic.
Part production
LSR part production
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