When we talk about injection molding, most people picture hard plastics. But there’s a whole other side to this process that deals with materials that are much softer, more flexible, and highly durable. Enter Liquid Silicone Rubber, or LSR. In this article, we’ll explore what LSR is, how it’s used in injection molding.
The Basics of LSR Injection Molding
The process of LSR injection molding is somewhat similar to traditional plastic injection molding, but with a few key differences that cater to the unique properties of silicone.
- Preparation: LSR comes in two parts—Part A and Part B—which are mixed together in a 1:1 ratio. Once combined, the mixture starts to cure, so timing is crucial.
- Molding Process: The mixed LSR is injected into a preheated mold at high pressure. Because LSR is a thermoset material, it cures as it heats up, solidifying into the desired shape.
- Curing and Cooling: Unlike thermoplastics that solidify when cooled, LSR cures when exposed to heat. Once the material has filled the mold and cured, the part is ejected from the mold, ready for any necessary post-processing.
What is Liquid Silicone Rubber (LSR)?
Liquid silicone rubber is a two-part, highly engineered polymer that, when mixed in precise ratios, cures into a solid, elastomeric material. It’s different from traditional solid silicone rubbers in that it starts as a low-viscosity liquid, making it ideal for injection molding processes that require precise control and the ability to fill complex mold cavities with ease.
Why Use LSR for Injection Molding?
The primary reason LSR is so valued in injection molding is its ability to flow easily into molds with intricate geometries and tight tolerances. This makes it ideal for creating parts that require high precision, such as gaskets, seals, membranes, and overmolded components.
- Temperature Resistance: LSR remains stable across a wide temperature range, from as low as -60°C to as high as 200°C or more.
- Chemical Inertness: It resists oils, chemicals, and water, which is why it’s often used in automotive and medical applications.
- Flexibility: Even after curing, the material retains its flexibility and elasticity, which is key for products like seals and gaskets that require movement without wear and tear.
- Biocompatibility: LSR is hypoallergenic and non-toxic, making it ideal for medical applications like catheters and baby products such as pacifiers.
- Design Freedom: With LSR, manufacturers can create complex geometries and thin-walled parts that would be challenging or impossible with other materials.
- Transparency and Colorability: LSR can be manufactured in various colors or left transparent, providing flexibility in product design.
Applications of LSR Injection Molding
LSR’s unique properties make it suitable for a wide range of applications across various industries. Here are a few examples:
- Seals and gaskets
- O-rings
- Keypads
- Valve components
- Baby bottle nipples
- Medical tubing
- Catheter balloons
- Hearing aid components
- Electrical connectors
- Overmolded parts
- Watch bands
- Cookware handles
- Automotive bellows
- Sensor housings
- Diaphragms
Advantages of LSR Injection Molding
Choosing LSR for injection molding offers several advantages:
- Perfect for intricate designs with tight tolerances.
- Automated process, fast curing time.
- Minimal waste due to precise metering.
- To temperature, chemicals, and wear.
- Recyclable material.
- Suitable for various sizes, shapes, and colors.
- Consistent quality in mass production.
- Energy-efficient.
- Minimal post-processing required.
- In large-scale production.
The disadvantages of LSR (Liquid Silicone Rubber) injection molding mainly include the following aspects:
- Precise, high-tolerance molds are expensive to produce.
- Demands intricate design and precise manufacturing.
- Can lead to bubbles or imperfections in the final product.
- LSR material costs can be higher than some other rubbers.
- Multiple steps require precise control.
- Demands experienced personnel for optimal results.
- Specialized equipment needs regular, professional maintenance.
How Does LSR Injection Molding Work?
LSR injection molding starts with CNC machining a high-temperature mold, polished by hand for a precise finish. Unlike thermoplastics, LSR parts are manually removed from the mold due to their flexibility, eliminating the need for ejector pins. The mold is then loaded into an advanced LSR-specific press that ensures accurate shot size and consistency. As a thermosetting polymer, LSR remains permanently set after molding, with parts carefully boxed and shipped once the run is complete.
What Should You Know About Designing for LSR Injection Molding?
When working with Liquid Silicone Rubber (LSR) injection molding, key design and manufacturing considerations are crucial for success. Here are some essential tips:
Part Design Rules:
- LSR allows for simpler designs compared to thermoplastics due to its flexibility, reducing the need for ejector pins and allowing looser draft angles.
- The material’s shear thinning property enables easy flow into all mold sections, making uniform wall thickness less critical and allowing thicker parts.
- LSR’s softness allows for protruding undercuts that can be easily demolded without requiring side actions.
- To prevent leaks at the separating line, ensure the tooling is properly sealed.
General Design Tips:
- Short parting lines minimize flash.
- For shallow parts, draft may not be needed; otherwise, use one degree per 2.5 cm.
- Gates should be positioned on the underside or hidden areas.
Other Considerations:
- Ensure the mold design supports proper bonding and accounts for potential dimensional variations due to curing and shrinkage.
- Proper draft angles and reduced undercuts ensure easy part ejection.
- Select appropriate textures based on functional and aesthetic requirements.
- Optimize mold design with correct gate placement, venting, and cooling channels for better part quality and reduced cycle times.
Choose BOYI for Expert LSR Injection Molding Services
Ready to bring your complex designs to life with precision and durability? BOYI’s advanced LSR injection molding services offer unparalleled quality and flexibility for a wide range of applications. With our expert team, state-of-the-art equipment, and commitment to excellence, we ensure your parts meet the highest standards. Whether you’re in the medical, automotive, or consumer goods industry, trust BOYI to deliver exceptional results. Contact us today to discuss your project and experience the BOYI difference!
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FAQ
Liquid Silicone Rubber (LSR) injection molding typically involves mold temperatures ranging from 150°C to 200°C (about 300°F to 390°F).
Liquid Silicone Rubber (LSR) is created by mixing a silicone base with a curing agent, usually in equal parts. The mixture undergoes a chemical reaction, triggered by heat, which cures the liquid into a flexible, durable rubber.
The best rubber for injection molding often depends on the specific application, but Liquid Silicone Rubber (LSR) is widely regarded as one of the top choices
Catalog: Injection Molding Guide
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
