Silicone rubber compression molding is a manufacturing process widely adopted across various industries because it efficiently produces high-quality, durable silicone components.

By examining the process in detail, including raw material requirements, tooling specifics, and part production capabilities, we aim to equip engineers with the knowledge necessary to effectively leverage this molding technique’s benefits.

Understanding Silicone Compression Molding

The Molding Process

Silicone rubber compression molding is a manufacturing technique that uses compression and heat to cure the part in the compression machine itself:

The process is:

• A pre-determined amount of silicone rubber is placed into a heated mold cavity.
• The mold is closed under pressure, compressing the silicone rubber to fill the cavity.
• Heat and pressure are applied and maintained for a specific curing time.
• The cured silicone part is ejected from the mold.
• The part undergoes post-processing steps as required (e.g., trimming, finishing).

The precise curing conditions, including temperature and pressure, are critical to achieving the desired properties in the final product. These parameters are determined based on the specific silicone rubber compound used and the part requirements.

Raw Material Requirements

The raw silicone for compression molding is high-consistency rubber (HCR). HCR offers the necessary viscosity and curing properties for this process.

Key factors to consider when selecting a silicone rubber include:

• Hardness: Determines the final part’s stiffness and flexibility.
• Temperature resistance: Ensures the material can withstand operating conditions.
• Chemical resistance: Protects against degradation from exposure to various substances.
• Tear strength: Influences the part’s durability and resistance to damage.

Silicone’s unique properties

Silicone has an impressively wide range of useful properties that make it quite unique among production materials:

• Heat and cold resistance of between around -55°C to 300°C (-67°F to 572°F) before suffering any degradation.
• Flecible and elastic.
• Chemically inert, meaning that it won’t react with most chemicals such as acids or solvents.
• Electrical insulation even at high temperatures.
• Non-stick, so often used in cookware (which also benefits from heat resistance).
• Water, moisture, ozone, and UV resistant (so good for outdoor uses).
• Transparent by default and so can take on colors to suit most needs (we explain the process of adding color to silicone here: How to Color Silicone for Compression Molding: A Complete Guide).
• Hypoallergenic and so preferred for many medical devices.
• Great for adhesive and sealing applications.

Tooling for silicone rubber compression molding: Focusing on Steel Molds

Steel is the most common material for compression molding tools due to its strength, durability, and heat resistance. The choice of steel grade significantly impacts the mold’s lifespan and performance.

Steel Grades for Compression Molds

Several steel grades are commonly used for compression molds, each with its own set of properties and expected lifespan:

• P20 Tool Steel: A widely used general-purpose steel known for its good balance of hardness, toughness, and machinability. It offers a reasonable lifespan for moderate production volumes.
• H13 Tool Steel: Provides higher hardness and wear resistance than P20, making it suitable for more demanding applications and longer production runs.
• 420 Stainless Steel: Offers corrosion resistance, making it suitable for applications involving abrasive or corrosive materials. However, its hardness and wear resistance are lower than P20 and H13.
• Hot Work Tool Steels: For extremely high-temperature applications, hot work tool steels like H13 and D2 can be used, but they require specialized heat treatment and are generally more expensive.

Mold Life Expectancy

The lifespan of a steel mold depends on various factors, including:

• Steel grade: Higher-grade steels generally have longer lifespans.
• Mold design: Proper design and venting can extend mold life.
• Production volume: Higher production volumes lead to faster wear.
• Material properties: Abrasive or corrosive materials can accelerate wear.
• Maintenance: Regular cleaning and inspection can prolong mold life.

Typically, P20 molds might last hundreds of thousands of cycles, while H13 molds can handle millions of cycles under optimal conditions. However, these are estimates, and the actual lifespan can vary significantly based on the factors mentioned above.

Silicone Rubber Compression Molding Capabilities and Limitations

Process Capabilities

Silicone compression molding excels in producing parts with consistent quality and high volumes. The process is particularly well-suited for:

• Large-sized components: Due to the nature of the process, producing large silicone parts is often more efficient compared to other molding methods.
• Thick-walled parts: Compression molding can effectively create parts with substantial wall thicknesses.
• Simple to moderately complex geometries: While undercuts and complex shapes can be challenging, the process handles many designs effectively.

Process Limitations

While this type of compression molding of silicone offers several advantages, it also has limitations:

• Undercuts and complex geometries: Parts with intricate features or undercuts are difficult to produce without additional tooling or post-processing.
• Material distribution: Achieving uniform material distribution within complex shapes can be challenging.
• Flash: Excess material can form flash around the part edges, requiring trimming or secondary operations.
• Tolerances: While acceptable for many applications, tolerances in compression molding may be less precise compared to other molding processes.

Applications and Industries for Silicone Rubber Compression Molding

Typical parts using silicone

Silicone compression molding is ideal for producing a wide range of items that benefit from silicone’s unique properties (mentioned above), such as:

• Gaskets and seals: The process excels at creating components with precise dimensions and sealing capabilities.
• O-rings: Compression molding can produce O-rings with consistent cross-sections and excellent sealing performance.
• Diaphragms and membranes: The process is well-suited for creating flexible components with varying thicknesses.
• Automotive components: Silicone parts like engine mounts, hoses, and weatherstripping are commonly produced through compression molding.
• Medical devices: The process is used to manufacture components for various medical applications, including tubing, implants, and seals.
• Industrial components: Silicone parts for machinery, equipment, and electronics often benefit from compression molding.

Industries benefiting from molded silicone parts

Several industries can significantly benefit from silicone compression molding:

• Automotive: The process offers cost-effective production of durable and heat-resistant components.
• Medical: Silicone’s biocompatibility and the process’s ability to produce precise parts make it suitable for medical device manufacturing.
• Aerospace: The process can produce components that withstand extreme temperatures and harsh environments.
• Electrical and electronics: Silicone’s insulating properties and the process’s ability to create complex shapes make it valuable for this industry.
• Consumer goods: Silicone components in kitchenware, personal care products, and other consumer goods can be efficiently produced through compression molding.

Conclusion

Silicone compression molding is a versatile and efficient process for producing a wide range of silicone components. Its ability to handle large parts, thick walls, and consistent quality makes it a compelling choice for various industries. By understanding the process, raw material requirements, tooling considerations, and part capabilities, engineers can effectively leverage compression molding to meet their product development needs.

While the process excels in many areas, limitations such as difficulties with undercuts and complex geometries should be considered during part design. Careful material selection and mold design are crucial for achieving optimal results.

By carefully evaluating the specific requirements of a project, engineers can determine if silicone compression molding is the ideal manufacturing method. If your application demands large, durable silicone components with consistent quality, this process is worth exploring further.

To learn more about silicone compression molding or to discuss a specific project, contact us here.

Learn more about our injection molding capabilities

Agilian Plastic Molds specializes in silicone compression molding and offers comprehensive solutions for your project needs. Our team of experts can assist you with material selection, mold design, and production to ensure your project’s success. Speak with us to discuss your specific requirements.