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How the Liquid Silicone Injection Molding Process Works

The materials commonly used in the liquid injection molding (LIM) process are . The LIM process requires the use of a spring-loaded pin nozzle to help prevent the machine hardware from becoming clogged with materials. The spring-loaded mechanism permits the injection pressure to be higher than the pressure of the injection barrel, which keeps the channel unblocked.

Utilizing a pump, the liquid injection molding (LIM) method brings together an apportioned mixing and dispensing of a two-part, platinum cured liquid silicone rubber. One plunger holds the base forming polymer (Part A), the other plunger contains the catalyst (Part B). Each will be pumped into a static mixer, which triggers the mixing reaction know as vulcanization. If color parts are being produced, a third plunger of color pigment is added.

The liquid mixture is then injected into a sealed mold where the cavities are heated. The material starts out as a fluid and is then heated within the mold to initiate curing. Once it hardens, the molding machine ejects the nearly finished part.

Thermoplastics operate in reverse. The materials are heated in the injection barrel to their melting point and then cooled in the mold.

Many manufacturers use computer-aided design (CAD) tools to optimize designs and check integrated components. Simulation software helps determine the most efficient and effective processing regimen to ensure the LIM process is fully optimized and pitfalls avoided. Thermal imaging technology can also help pinpoint potential production issues and help prevent molding defects and design irregularities.

Liquid Injection Molding Machines

Liquid silicone rubber injection molding machines are specifically designed for injection molding LSR materials. Liquid silicone rubber elastomers consist of two components — “A” and “B” and are received and remain in two separate drums until combined during the molding process. The following are the key elements of a liquid injection molding machine:

Supply drums: The liquid silicone supply containers, or plungers, connect to the pumping system. A third container is added with liquid color pigment for molding color parts.

Metering units: The metering device pumps the two liquid material components in predetermined ratios, which ensures a concurrent release at a steady ratio.

Mixers: The individual A & B liquid material components are pumped into the mixer upon passing through the metering unit for exact proportioning. The blended material is pressurized and injected into the mold.

Injectors: This device pushes the LSR material into the pumping mechanism under pressurized force. The pressure and injection rate can be adjusted if needed to fine tune the process according to the project specifications.

Nozzles: The liquid compound flows into the mold through a nozzle that has an automatic shut-off valve. This valve prevents the mixture from leaking or the mold from overfilling.

In an ideal production environment, the liquid injection molding machine and parts handling equipment are automated for maximum accuracy, consistency, and productivity. The process parameters are optimized and digitally established for a stable process. Any ancillary equipment used for parts handling or inline secondary processes are contained within the molding cell.