LSR Injection Molding

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Overview of LSR Injection Molding

Liquid silicone rubber (LSR) injection molding, also called LSR molding or silicone injection molding, which have some types according to liquid silicone rubber materials feeding systems, silicone materials state, mould runner systems and silicone molded machines types etc.

LSR starts out as a 2-part liquid that cures into a solid form when mixed together. Mixing is performed by a metered mixer that precisely combines the two parts in a 1:1 ratio (mixing in additives if needed) right before pumping the fluid into the mold, which is heated to accelerate the vulcanization process.

The mixed LSR is pushed into the mold under pressure. LSR’s low viscosity results in a quick mold fill and pack time, while the elevated mold temperature ensures a short cure time. Since all curing takes place inside the mold, there is less wasted material. The use of “cold drop” or “cold runner” tooling reduces this waste even further by keeping the LSR cool inside the sprue and runners, which means vulcanization only occurs inside the hot part cavities, resulting in no LSR lost to the sprue and runner volume and no additional step of trimming these sections from the molded part.

Diverse Molding Capabilities

Single-shot Molding

In this process, a single LSR material is employed for the injection molding of parts.

Multi-shot Molding

LSR is combined with two or more polymers, or a polymer and substrate, in this advanced process suitable for crafting complex components.


Liquid silicone rubber is molded around a substrate or finished component, enhancing versatility and functionality.


This precision injection molding process specializes in producing tiny, intricate parts, typically with a shot weight of less than 1 gram.

Non-dust Hygienic Molding

LSR parts are manufactured in a meticulously controlled, hygienic environment, ranging from white rooms to more stringent ISO cleanrooms with varying classifications.

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How it Works

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Step 1: Create LSR Molding Tool

The process begins by fabricating a molding tool for liquid silicone rubber through CNC machining. This tool, designed to withstand the LSR injection molding process, must exhibit high-temperature resistance. Additionally, it can be polished to achieve various finish options. The completed molding tool is then placed into an LSR-specific injection molding press.
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Step 2: Prepare Material

Uncured liquid silicone rubber (LSR) is prepared in two containers connected to the pumping system. One container holds the base-forming material, while the other contains the catalyst, typically platinum-based. Both materials are pumped through a static mixer using a metering pump. Before entering the static mixer, color pigments and additives may be introduced. The two compounds are mixed in a 1 to 1 ratio.

Step 3: Inject the Material into Mold

The material is heated and injected into the mold cavity under high pressure through a nozzle. As the mold cavities are filled, the material takes the shape of the molds, determining the final form of the liquid silicone rubber products. High-pressure injection ensures the material fills intricate details and features.

Step 4: Curing Process

Following mold filling, the mold undergoes heating to initiate the curing process. This transforms the liquid silicone rubber substance into a solid silicone rubber part. The curing time is determined by the size and complexity of the parts or products.

Step 5: Cooling and Demolding

Uncured liquid silicone is prepared in two containers connected to the pumping system. One container holds the base-forming material, while the other contains the catalyst, typically platinum-based. Both materials are pumped through a static mixer using a metering pump. Before entering the static mixer, color pigments and additives may be introduced. The two compounds are mixed in a 1 to 1 ratio.

Step 6: Post-molding Secondary Operations

Post-molding secondary operations may be required after demolding and parts removal. Typically conducted after the molding process, these operations include tasks such as slitting, printing, marking, assembling, and post-curing. The need for secondary operations depends on specific product requirements and desired finishing touches.

Design and Manufacturing Guidelines for Successful LSR Injection Molding

To ensure a successful LSR injection molding process, it is crucial to consider specific design and manufacturing principles. Here are key considerations for designing and manufacturing parts using Liquid Silicone Rubber (LSR) injection molding

Part Design Rules

Flexibility and Removal: LSR’s flexibility allows for manual removal from molds, eliminating the need for strict ejector pin placement. Designers can employ looser draft angles.
Protruding Undercuts: LSR’s pliability enables the extraction of parts with protruding undercuts without necessitating side actions during the molding process.
Wall Thickness: Liquid silicone’s shear-thinning nature permits the freedom to vary wall thickness, allowing for thicker parts compared to thermoplastics.
Sealing: Due to LSR’s viscosity, proper sealing of tooling is essential to prevent leakage at the separating line.

Short parting lines minimize flash impact.

Shallow parts may not require draft angles; otherwise, one degree per 2.5 cm is recommended.
Gates should be strategically located, preferably on the underside or in less visible areas.

Metering and Mixing

LSR injection molding involves two materials, one being a platinum catalyst. These are consistently pumped and mixed in a predetermined ratio using a metering unit and a static or dynamic mixer.

Working Principle

Unlike thermoplastic injection molding, LSR is liquid at room temperature. The mold is heated to accelerate curing after injection. Cooling systems, like cooled runners and sprues, prevent premature curing before entering the mold.

Other Considerations

  • Substrate Bonding: Ensure the process and mold design support proper bonding between the substrate and the LSR material.
  • Dimensional Variations: Account for potential variations in dimensions due to curing and material shrinkage by consulting mold designers for accurate dimensions.
  • Draft Angles and Undercuts: Design parts with appropriate draft angles and reduce undercuts to facilitate easy ejection during the molding process.
  • Texture Selection: Choose a texture that aligns with both functional requirements and aesthetic preferences of the silicone rubber parts.
  • Mold Design: Optimal part quality and reduced cycle times depend on proper mold design, including gate placement, venting, and cooling channels.

By adhering to these guidelines, designers and manufacturers can enhance the efficiency and success of LSR injection molding processes while ensuring the production of high-quality parts.

Benefits of LSR Injection Molding

LSR injection molding stands out as an ideal method for crafting precise components, offering benefits such as exact dimensions, intricate designs, and superior surface finishes. Below, we highlight key advantages associated with LSR injection molding


LSR molded parts exhibit outstanding resistance to UV rays and ozone, coupled with superior electrical insulation properties. This makes LSR molding well-suited for applications ranging from gaskets to cushioning pads in portable communications and ruggedized electronic devices.

Reduced Flash

The low viscosity nature of liquid silicone rubber ensures complete filling of mold cavities, minimizing flash development. Consequently, the need for post-molding trimming or finishing operations is significantly diminished.

Consistent Quality

The uniform distribution of liquid silicone rubber within the mold leads to consistent quality and minimal variation between individual pieces.

Less Waste Production

Silicone molding is recognized as an environmentally friendly solution due to its minimal to zero waste production during manufacturing. Unlike metals that cannot be recycled, silicone can be recycled to create other items in the future.

High Precision Products

Liquid silicone molding facilitates the production of intricate parts with tight tolerances. The liquid silicone material flows seamlessly into complex mold cavities, ensuring the precise replication of features and dimensions.

Automated Processing

LSR molding can be seamlessly automated, minimizing external human intervention. The liquid silicone rubber material is easily handled and injected using machines, reducing the risk of human error.

High-volume Production

Advanced LSR materials enable cost-effective production of complex liquid silicone injection molded parts in high volumes, making it an efficient choice for mass manufacturing.

Enhanced Safety

The automation options in LSR molding eliminate the need for operators to enter the molding area. Parts can be safely removed and transported from the injection molding machine using robots, chutes, or conveyor belts, reducing the risk of handling-related injuries and enhancing overall safety.

Silicone overmolding is an essential and versatile technique in the electronics industry, providing protective layers, customization options, and functional improvements for a wide range of electronic components.

LSR Injection Molding Highlights