LSR Tooling & Molding

• Precision (viscosity of LSR)
• Temperature (~420 degrees Fahrenheit / 215 degrees Celsius)
• Wear (abrasiveness of LSR)

In the silicone rubber molding process, the production tooling can be the lengthiest step and requires the largest capital investment. However, LSR’s ability to flow into very thin cross-sections, tight radii, and thick/thin features make the mold design a simpler task.

In addition, compared to injection molds for plastics, the surface of molds built for LSR injection molding do not require a highly polished finish, and draft angles are not required to help remove the finished component from the mold. Once the curing or vulcanization and solidification phase is completed, the LSR molded part is removed from the mold without concern for distortion or damage.

Liquid Silicone Rubber Part Production

The Liquid injection molding (LIM) manufacturing process is used to mold silicone rubber into a broad array of parts and products. While the traditional reaction injection molding (RIM) process focuses on a pressurized impingement mixing process, liquid injection molding uses a mechanical mixing method that blends a two-component platinum-cured LSR material compound together that flows into a mold.

A primary difference between LSR  LIM (liquid injection molding) and thermoplastic injection molding relates to the material delivery. The LSR injection tool is housed in an LSR-specific injection molding press, which is designed for precise control of the shot size and enables the consistent production of liquid silicone rubber components.

Here are the primary steps involved in the liquid silicone rubber Injection Molding process:

1. The uncured liquid silicone is contained in two containers, Compound A and Compound B, which connect to the pumping system. container A holds the base-forming material, and container B contains a catalyst. A metering unit automatically releases the two substances at a constant one-to-one ratio, as well as an additional color pigment for color parts.
2. The molder programs and customizes the automated injection-molding machine to control the injection settings for delivery of the appropriate shot size for each job. The platens and pistons align and close the mold and have settings for the temperature, pressure, injection rate, and cycle time adjusted to meet the customer part designs.
3. After the completion of the setup, the molding machine heats the mold’s cavities to the appropriate temperature and applies the appropriate clamping force. The mold closes in coordination with the machine’s injector, pump, and supply. The injection mechanism then pushes the material into the mold cavities.
4. A combination of heat and pressure applied to the liquid silicone rubber cures the material until it solidifies. Upon completion of the cycle, the mold opens for the demolding of the parts. The parts are removed and separated with an automated robotic parts removal system. In less sophisticated manual molding operations with smaller production runs, a worker removes the parts.
5. After the demolding and parts removal process, if post-molding secondary operations are required, these processes are performed after the molding is complete. Secondary operations could include slitting, printing, marking, assembly, or post-curing. Some advanced molders automate these steps and perform the value-added secondary processes immediately upon the parts removal from the mold. The molded parts are robotically removed from the molding machines and delivered to a designated station for completion of the secondary process, within the same manufacturing cell.

The molding of LSR components requires advanced technology, a robust quality system, and creative problem-solving. Your manufacturer must have the expertise to meet this challenge, as it is critical for your production process and the quality and performance of your end-product.