Introduction
Silicone compression molding is a versatile manufacturing process used to create high-precision, durable silicone parts for industries ranging from automotive and medical to consumer goods. Proper design is critical to ensuring product quality, minimizing defects, and optimizing production efficiency. This guide outlines key considerations for successful silicone compression molding.
1. Material Selection
- Silicone Type: Choose between liquid silicone rubber (LSR) or high-consistency rubber (HCR) based on application requirements (e.g., flexibility, temperature resistance, chemical stability).
- Hardness (Shore A): Typically 10–80 Shore A. Softer materials require tighter mold tolerances to prevent flash, while harder grades may need reinforced tooling.
- Cure System: Platinum-cured silicones offer better thermal stability and biocompatibility, ideal for medical devices. Peroxide-cured grades are cost-effective for general applications.
2. Mold Design Fundamentals
a. Part Geometry
- Wall Thickness: Maintain uniform thickness (1–5 mm) to avoid uneven curing and warpage. Sharp corners should be radiused (minimum 0.5 mm) to reduce stress concentration.
- Draft Angles: Incorporate 1–3° draft on vertical walls to facilitate easy ejection.
- Undercuts: Use sliding cores or lifters for undercuts, as silicone’s high elasticity allows limited undercuts (≤10°).
b. Mold Construction
- Material: Tool steel (e.g., H13) is standard for durability. Coatings like chromium or nitride enhance resistance to abrasion and corrosion.
- Parting Lines: Position parting lines to minimize flash and ensure aesthetic appeal. Avoid parting lines in critical sealing areas.
- Ventilation: Design vents (0.01–0.03 mm depth) at mold cavities to release trapped air and gases, preventing voids.
c. Cavity Layout
- Balance multi-cavity molds symmetrically to ensure uniform pressure distribution.
- Calculate projected area to determine clamping force requirements (typically 1–3 tons/in²).
3. Process Parameters
- Temperature: Cure temperatures range from 120–200°C, depending on material and part thickness. Higher temperatures reduce cycle time but may increase thermal stress.
- Pressure: Apply 100–300 bar during compression to ensure material flow and minimize porosity. Adjust based on part complexity.
- Cure Time: Typically 10–60 seconds for LSR and 1–5 minutes for HCR. Longer cure times improve cross-linking but reduce throughput.
4. Common Defects and Solutions
| Defect | Cause | Remedy |
|---|---|---|
| Flash | Excess material or worn mold edges | Adjust material volume; refurbish mold edges |
| Voids/Bubbles | Poor venting or trapped air | Optimize venting channels |
| Short Shots | Insufficient material or low pressure | Increase shot size or clamping force |
| Warpage | Uneven cooling or thermal stress | Balance cooling channels; adjust cure time |
5. Post-Processing Tips
- Deflashing: Use cryogenic deflashing or tumbling for clean edges.
- Surface Treatment: Plasma or chemical treatments can enhance adhesion for bonding or printing.
- Inspection: Implement dimensional checks (e.g., CMM) and visual inspections for critical features.
Conclusion
A well-executed silicone compression molding design requires a balance between material selection, mold engineering, and process optimization. By following this guide, manufacturers can achieve high-quality parts with minimal waste and reduced production costs. For complex applications, collaboration between designers, material suppliers, and moldmakers is key to success.
How SHENGHUI Can Help
SHENGHUI is one of North America’s top injection molding companies, and we work exclusively with LSR. We have a long history of offering our customers excellent quality control and unsurpassed manufacturing capabilities.
Contact our skilled team of experienced injection molding professionals for a free consultation. We offer unparalleled customer service and manufacturing skills to produce high-quality, custom-made LSR and LSR multi-shot components that will meet all of your needs and specifications.