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Silicone Compression Molding Complete Guide

This guide provides essential information on silicone compression molding.

  • Materials: Understand the types of silicone and their impact on the molding process.
  • Mold Design: Focus on key elements like draft angles, parting lines, and venting to optimize mold efficiency.
  • Process: Recognize how heat, pressure, and time influence the final product.
  • Troubleshooting: Identify common issues and their solutions to improve quality and consistency.
  • Preparation: Learn the correct methods for mixing, degassing silicone.
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At Dabojin Custom Silicone Product Manufacturer, we are a dedicated team of engineers and manufacturers who provide quality silicone products customized to meet the specific needs of various industries since 2005.

If you’re looking for silicone compression molding services, learn more about our offerings and get started on your project today.

Understanding the silicone compression molding

Compression molding is a manufacturing technique where silicone material is placed onto a mold cavity. The mold is CNC machined to perfectly match the product design, comprising two distinct components: a base plate and an elevated profile.

The product design is sliced into two separate components. Compression molding machines hold two molds, with the silicone material placed between them. When the mold on the machine is compressed using heat and pressure, the silicone shapes onto the product. This process results in visible flash lines on the surface of the molded product. While these lines may be smaller than 0.05 mm, they are a common characteristic of compression molding.

The flash line itself is often caused by incomplete filling of the mold or uneven pressure distribution within it. However, with proper design and execution, compression molding can also produce overmolded products. This method involves combining multiple layers of different materials into a single molding process.

A custom-designed aluminum bracket featuring a linear shape and silicone end caps for secure attachment to industrial machines or other components. Overmolded silicone product.
A compressed molded silicone cup, highlighting the result of compression molding as a common process in producing silicone parts.

The properties of silicone for compression molding: an overview

To get the quality assurance in silicone manufacturing you need to understand the silicone material. Silicone is a standout material, known for handling heat well. It keeps its shape and strength in both hot kitchens and flying planes. It lasts long, fighting off sun, rain, and wear.

Different types of silicone

You’ll find silicone in many forms. Some are soft or clear, used for things like bio-labs and cookware. Others are for cars and medical gear. High-clear silicone lights up LED and is used in medical and food areas. Platinum silicone is pure and sets quickly, perfect for healthcare and food. Some silicone are tough, bouncing back after stress, ideal for seals and cushions. Others resist flames or extreme heat, key in cars, planes, and electronics. Some even manage oil or static, solving specific problems in cars and electronics. The key point: With the right additives, silicone can be used on any application.

Factors Influencing Silicone Production

Different types of silicone require tailored manufacturing approaches. For instance, platinum-cured silicones set faster, affecting work speed and temperature. The material’s softness or stretchability influences mold-making and shaping, while additives for fire resistance or clarity can alter production methods. Understanding these variables ensures manufacturers and designers choose the right silicone for specific applications and achieve optimal results.

Know the Silicone Properties

For a deeper understanding of silicone’s properties and the tests it undergoes to ensure quality and compliance, please refer to:

  • Silicone Rubber Test Report: For insights into specific silicone’s compliance with standards like RoHS, EN 71-3, and Prop 65, visit Silicone Rubber Test Report.
  • 17 Types of Silicone: Applications, Features, and Tests: To explore the resilience, uses, and versatility of 17 different silicone types, along with their specific applications and the tests they undergo, visit 17 Silicone Types.

Silicone Compression Molding Process Parameters

Optimal Temperature Range

For silicone, the optimal molding temperature ranges between 160°C to 232°C . This range ensures proper flow and curing without degrading the material.

Too Low 160°C. If the temperature is below this range, the silicone may not flow into all parts of the mold. Incomplete filling can occur when curing is insufficient, resulting in poor mechanical properties. High adhesive materials can lead to shape and surface defects in the mold.

Image of a defective silicone product with uneven surface and gaps, caused by too low compression temperature, resembling a keyboard bubble.

Defective Silicone Product due to Insufficient Compression

Too High 232°C. If the temperature exceeds this range, the silicone can burn or discolor parts. Overheating can result in premature cross linking or vulcanization. This can lead to distorted shapes, weaker parts, or material degradation.
The specific temperature within this range can vary and it depends on:

  • The type of silicone,
  • The intended application,
  • And the desired properties for the final product.

Product Manufacturers often need to conduct tests. These tests help determine the optimal temperature for a new material or mold design.
In summary: Silicone molds well between 160°C and 232°C. Too cold, it won’t fill the mold; too hot, it burns. The right temperature varies with the silicone type, use, and desired product quality.

An image of an overheated silicone product showing visible burn marks and warping. The surface appears discolored and distorted, indicating thermal damage.

Overheated Silicone Product with Burn and Distortion Damage

Silicone Compression Molding Pressure Application

In our example case: Plasticity in the context of silicone materials refers to the material’s ability to deform under pressure.

Therefore when considering a silicone material with a plasticity of 160 for compression molding. The amount of pressure applied is critical. Ensuring that the material flows and the final product meets the specifications.

Key Considerations for Pressure Application

Material Flow Properties: With a plasticity of 160, the silicone is likely to have a certain stiffness and viscosity. To get the same flow in intricate mold areas, you need higher pressure than with softer silicone like 330.

Mold Design and Complexity

The specific design of the mold, including its complexity, size, and the fineness of details, will impact how much pressure is needed. It’s important to use enough pressure for stiffer materials to fill the mold without causing damage or excess material. Keep in mind: Molds can be prone to breaking, and excessive pressure can lead to costly repairs.

Part Thickness and Geometry

Thicker parts need extra pressure to fill before the silicone starts to harden. Yet, too much pressure on thinner or delicate parts can cause material distortion. The overall geometry of the part will guide the necessary adjustments in pressure.

Impact of Pressure Variation

Too Low Pressure

Silicone doesn’t fill the mold, leaving parts incomplete. Stiffer silicone worsens it, missing fine details and shaping wrong.

Image of an incomplete silicone keyboard product with missing details and sections, indicating insufficient pressure during the molding process.

Incomplete Silicone Keyboard due to Low Pressure in Molding

Too High Pressure

Silicone squeezes out, creating flash. Needs trimming, affects precision. Stresses the mold, causing wear or damage.
Image of a silicone product with excess material, known as flash, due to high pressure in the molding process, showing the need for trimming and potential mold damage.

Excess Flash on Silicone Product Due to High Pressure

Right pressure is key

It fills the mold, cures evenly, giving consistent parts. Wrong settings causes defects: incomplete filling, air, uneven surfaces. Balance is crucial for silicone to fill properly without problems.

In practice, finding the right settings needs testing and tweaking. Consider silicone’s plasticity, mold design, and the final product’s needs. Start with standard pressure for the silicone type, then adjust from trial results. Aim for consistent, quality output meeting all requirements.

Operating the compression molding process in 5 steps

Setting up the mold right is key for good production in compression molding. Here are the main steps to get the mold ready, aligned, and secure:

1. Clean the mold

Clean the mold well. Remove all old residue and dirt. This includes the mold surfaces, vents, and any hidden parts. Some molds might need special cleaners. Note: Leaving any scratch on mold will result scratches on product.

A contaminated compression mold with residual rubber and fingerprints

2. Apply Mold Release

Use the right mold release so the silicone doesn’t stick. The choice depends on the silicone and mold type. Be careful with release agents, as some may not work well with silicone. Ensure the agent chosen is compatible with silicone’s properties.

3. Check for Damage

Look over the mold for any damage or wear that might ruin the final product. Make sure everything fits tight and right.

4. Assemble the Mold

Put all parts of the mold together. This includes any slides, inserts, or cores.

5. Heat the Mold

Warm up the mold to the right temperature for the silicone. This helps cure faster and evenly.

Ensuring correct mold alignment and security in 5 steps

1. Alignment Checks

Check the mold halves align precisely. Wrong alignment can lead to defects like flash or poor filling.

2. Clamping and Securing

Clamp the mold tightly in the press. The force should be enough to keep it shut during compression but not damage it.

3. Double-checking Tightness and Positioning

Check bolts and clamps after setting up and during production.

4. Safety Measures

Keep all safety guards in place and follow safety standards to protect workers and equipment from the damage.

5. Test Run

Do a test run to find any issues before starting production. Adjust as needed for quality production.

Follow these steps and maintain the mold well to cut down on defects, boost safety, and make quality silicone parts. Each step is vital for good molding, especially with the precision silicone needs.

Guidelines for Silicone Material Placement and Mold Closure

Pre-forming the Material

Measure and cut the silicone precisely for less waste and complete filling. Shape it for easy placement and distribution in the mold.

Image of precisely measured silicone for mold placement.

Placing silicone on mold

Put the silicone evenly in the mold cavity. Make sure it’s centered for uniform filling. Lay it carefully to prevent air pockets.

Image of evenly placed silicone in the mold cavity.

Mold Closure

Shut the mold gently and securely. Check that everything lines up and that the silicone spreads evenly if there are multiple sections.

Heat and Pressure Application

  1. Understand Material Specifications: Check the datasheet for the silicone you’re using for temperature and pressure ranges. Understand its viscosity, curing, and reaction to heat and pressure.
  2. Consider Product Specifications: Factor in part design like size and complexity for the right settings. Different designs need different conditions.
  3. Start with Baseline Settings: Begin with manufacturer’s recommended settings. Adjust from these baselines based on your mold and material.
  4. Adjust Based on Experience and Testing: Refine settings after testing initial parts. Look for signs of improper curing or defects to guide adjustments. Keep track of changes.
  5. Check and Control Temperature and Pressure: Ensure the whole mold is uniformly at the right temperature.

Optimizing cooling and ejection in compression molding

  1. Cooling time varies with part thickness, shape, and silicone type. Ensure the part is solidified and safe to handle. A freshly made silicone product is always larger in size until it cools down.
  2. Cooling Method: Natural or active cooling. Uniform cooling prevents warping.
  3. Ejection Mechanism: Align and maintain ejection system for gentle part removal.
  4. Air Pressure Pistol: Use evenly distributed, gentle air pressure for ejection.
  5. Handling: Use proper tools or gloves. Ensure parts are cool and retain shape. Inspect Post-Ejection: Check for defects immediately. Adjust procedures if damage occurs.
  6. Prevent Sticking: Apply release agent to avoid part sticking to mold.
  7. Training: Train personnel for proper ejection and handling techniques.

Quick check problems and solutions in compression molding

  1. Low mold temperature.
  2. Insufficient vulcanization time.
  3. Poor exhaust.
  4. Material issues.
  5. Material discharge issues.
  6. Insufficient pressure.

1. Adjust temperature.
2. Extend vulcanization time.
3. Ensure vacuum requirements are met.
4. Confirm material requirements.
5. Improve material discharge position.
6. Adjust pressure.

1. Insufficient material weight.
2. Improper material discharge position.
3. Uneven distribution of rubber fabric.
4. Insufficient pressure.
5. Excessive temperature.
6. Expired or poor-flowing material.
7. Damage to mold padding.
8. Inappropriate material thickness.

1. Weigh materials properly.
2. Accurately discharge materials.
3. Distribute rubber evenly.
4. Increase pressure.
5. Lower temperature.
6. Return to compounding.
7. Replace mold padding.
8. For deeper keying, adjust material thickness.

  1. Excessive weight of material
  2. Improper material discharge position

How to countermeasure:

  1. Reduce and adjust material weight
  2. Adjust discharge position and method

1. Excessive temperature
2. Prolonged external operation time
3. Excessive exhaust frequency
4. Excessive curing agent usage

How to countermeasure:

1. Lower mold temperature
2. Shorten external operation time
3. Adjust exhaust methods
4. Reduce curing agent amount

  1. High temperature
  2. Improper use of demolding water
  3. Incorrect blowing method
  4. Mold issues
  5. Excessive material thickness or poor stretch resistance

How to countermeasure:

  1. Lower mold temperature
  2. Follow demolding guidelines, sandblast if necessary
  3. Improve blowing method
  4. Repair mold
  5. Careful with material handling

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