Silicone overmolding is changing the way we manufacture by enabling the creation of durable, ergonomic and high performance components across industries. This advanced process involves molding flexible silicone onto a rigid substrate such as plastic, metal or glass in one single step. The result is a seamless bond that combines structural strength with silicone’s flexibility, comfort and resistance to environmental factors.
Liquid silicone overmolding (LSR overmolding) is the preferred method for producing reliable, multifunctional parts, from automotive seals and medical grips to electronic connectors. This article will cover everything you need to know about silicone overmolding, from the basics and materials to the process, benefits and applications across industries.
What is Silicone Overmolding?
Silicone overmolding is a multi-step injection molding process where flexible silicone material is molded directly onto a rigid substrate to create a single integrated component. This technique is essentially a two-shot molding process where a base substrate, typically made of plastic or metal, is created first and then silicone is applied over it. The result is a durable high performance part that combines the strength of the substrate with silicone’s unique properties.
Unlike traditional single material molding, silicone overmolding creates composite components that offer enhanced functionality by combining different materials. This process enables manufacturers to encapsulate sensitive electronics, improve ergonomics and provide superior sealing protection. Additionally, silicone overmolding eliminates the need for manual assembly, reducing labor costs and strengthening overall product durability through direct material bonding.
How it differs from traditional molding
Traditional molding works with single materials whereas overmolding combines multiple materials with complementary properties. Overmolding also creates seamless transitions between hard and soft components without requiring additional assembly steps. This technique provides better grip, improved ergonomics and better environmental protection than traditional molding methods.
The Materials Used in Silicone Overmolding
Silicone overmolding depends primarily on the pairing of rigid substrates with flexible silicone materials. This process combines distinct material properties to create parts with enhanced functionality and durability.
The rigid substrate options include:
- Thermoplastics: ABS, PC, PA, PBT, PEEK, TPU provide structural integrity
- Metals: Stainless steel, aluminum, magnesium alloys, titanium offer superior strength
- Reinforced polymers: Glass-filled or carbon-fiber reinforced plastics add rigidity
For the flexible layer, manufacturers use two types of silicone:
- Liquid Silicone Rubber (LSR): Corn syrup-like consistency, requires platinum catalyst, excellent chemical resistance, tensile strength, compression set, heat resistance, extreme low-temperature flexibility
- High-Consistency Rubber (HCR): Greater mechanical strength for demanding applications
Material selection requires careful consideration of compatibility factors. The substrate’s glass transition temperature should be above 300°F to ensure proper LSR curing. The thickness of the overmold material should be less than or equal to the substrate. Some LSR grades, known as primerless or self-adhesive silicones, can bond directly to plastics without primers, simplifying the process.
Step-by-Step Process of Silicone Overmolding
Silicone overmolding requires precision at every stage to ensure proper adhesion and functional performance. Let’s go through each critical step in this process.
1. Preparing the rigid substrate
The foundation of overmolding starts with substrate selection. Thermoplastics must have softening temperatures above 170°C to withstand the silicone curing process. Materials like PBT, PPS and PEEK work well as base components. For insert overmolding, careful inspection prevents dimensional variations that can cause improper mold fit.
2. Surface cleaning and treatment
Contaminants like oils and mold release agents can prevent proper bonding. So thorough cleaning is essential before overmolding begins. For better adhesion manufacturers use several methods. They may design the part with small undercuts to help the silicone grip the surface better, apply a primer that takes 30 minutes to 2 hours to dry or use surface treatments like plasma, corona discharge or particle blasting to make the surface more suitable for bonding.
3. Mold setup and preheating
Molds must be designed to secure substrates against injection pressure without crushing them. Preheating plastic and metal inserts helps with bonding. However, materials with low melting points should not be preheated. Temperature control is critical throughout the process.
4. Silicone injection
Most silicone overmolding is a two-step process. The substrate is placed into a special mold cavity and the mold closes and LSR is injected directly onto the substrate. The two-part silicone components (A+B) mix 1:1 before injection. The material flows through cooled runners into heated cavities where vulcanization occurs.
5. Curing and cooling
During curing the silicone vulcanizes under specific temperature and pressure conditions. This chemical reaction requires proper thermal management, typically 170-220°C. Cooling is 70-80% of the molding cycle time.
6. Part removal and finishing
After curing the parts are removed from the mold. Since LSR is a thermoset polymer its molded state is permanent. Post-molding processes often include deflashing to remove excess material from parting lines. Quality inspection follows to verify adhesion, dimensions and surface finish.
Benefits of Silicone Overmolding
Manufacturers use silicone overmolding because it offers many advantages that traditional manufacturing can’t match. It improves product design, comfort and performance in industries like healthcare, electronics and automotive.
1) Better grip and comfort
Silicone’s soft, rubber-like texture provides excellent tactile quality, a non-slip surface that ensures firm handling even in wet or oily conditions. This natural ergonomic quality reduces user fatigue during prolonged use of devices like surgical instruments and handheld tools. Silicone cushioning strategically applied minimizes pressure points making products more comfortable to hold and use.
2) Durability and resistance
Products with silicone overmolding are extremely durable against harsh environments, temperature extremes -100°F to 450°F and chemical exposure. This durability maintains product integrity even after prolonged and repetitive use. Silicone’s resistance to UV radiation, oxidation and moisture means products look and function over time.
3) Design flexibility and aesthetics
Silicone overmolding offers design flexibility and aesthetics. The process allows for multiple colors and textures for brand differentiation, complex shapes and custom patterns and to combine rigid and flexible materials in one component. This versatility means visually appealing and functional products.
4) Cost effective production
Silicone overmolding saves time and cost by eliminating secondary post-molding assembly operations. This means products get to market faster and more economically. Manual assembly is reduced and overall product quality improves.
5. Waterproofing and insulation
Silicone creates waterproof, airtight barriers that protect sensitive electronics from moisture, dust and contaminants. Beyond physical protection silicone overmolding provides electrical insulation preventing short circuits and ensuring operational safety.
Applications Across Industries
Liquid silicone overmolding is used across many industries because it improves performance, comfort and longevity.
1. Medical and Healthcare Devices
LSR is ideal for medical use as it’s body safe, hypoallergenic and easy to sterilize. It’s used in surgical tools with soft grips, breathing devices, wearable health trackers and implantable parts. These products stay clean, comfortable and durable even after many sterilizations.
2. Automotive Components
Automotive engineers use silicone overmolded connectors, seals and gaskets to withstand extreme engine temperatures and vibration. Overmolding ensures waterproofing in headlight assemblies, battery housings and EV charging systems.
3. Consumer Electronics
Smartphones, earbuds and smartwatches use overmolding silicone for protective casings, button pads and ergonomic straps. It adds a premium tactile feel and impact resistance and weatherproofing.
4. Industrial and Electrical Equipment
In heavy duty environments liquid silicone rubber overmolding protects electrical connectors, control panels and sensor housings. The insulation properties prevent electrical leakage and corrosion in high humidity or high heat conditions.
5. Home and Kitchen Products
Silicone’s resistance to water and cleaning agents makes it ideal for everyday household tools like kitchen utensil grips, faucet handles and food-grade dispensing valves. Its flexibility and safety makes it a preferred choice in cookware and hygiene products.
6. Sports, Toys and Baby Products
Soft-touch, safe and durable overmolding silicone adds comfort and safety to children’s toys, baby bottle nipples and sports gear. Non-toxic and temperature stable silicone means these products are safe for daily use.
Design Considerations for Silicone Overmolding
Design engineers must consider the following:
- Thickness Ratio: The silicone layer should not be thicker than the substrate to maintain balance and prevent delamination.
- Draft Angles: Proper draft angles help in demolding and prevent silicone layer tearing.
- Temperature Compatibility: Ensure the substrate’s melting point is higher than silicone’s curing temperature.
- Surface Preparation: For metal and glass substrates, primers are required; for plastics, self-adhesive LSRs often suffice.
- Mechanical Interlocks: Where chemical bonding is weak, add mechanical locking features for added strength.
- Texturing: Substrate and overmold surface textures improve adhesion, grip and aesthetics.
Proper material selection, mold design and surface treatment is key to liquid silicone overmolding success.
Why Choose Fecision for Silicone Overmolding Solutions
With over 20 years of innovation and craftsmanship, Fecision is a trusted name in precision manufacturing and advanced material processing. Our expertise goes beyond wheel design to cutting-edge silicone overmolding solutions that meet global standards for performance, durability and aesthetics.
Here’s why clients worldwide choose Fecision:
Unparalleled Expertise: Our 20+ years of materials science and manufacturing experience delivers superior liquid silicone overmolding products.
Precision Engineering: Dual R&D capabilities in equipment and product design ensures unmatched accuracy and repeatability.
Customization Flexibility: Small batches or complex designs, Fengchi provides tailor-made overmolding solutions that meet client needs and artistic vision.
Quality Assurance: Every silicone overmolded connector and component is tested for adhesion, durability and finish quality.
Global Recognition: Trusted by top automotive, industrial and consumer brands worldwide, Fecision drives innovation in material technology.
At Fecision, every project is a partnership built on innovation, precision and mutual growth. Our mastery of liquid silicone rubber overmolding enables clients to deliver high-value products that perform exceptionally in the real world.
Conclusion
Liquid silicone overmolding has transformed manufacturing by combining the best of multiple materials. Its ability to add durability, comfort and functionality makes it essential across healthcare, automotive, electronics and consumer products.
Partner with Fecision for world-class liquid silicone rubber overmolding and overmolded connectors. Our focus on quality, innovation and precision engineering means your products will perform, be reliable and look great. Overmold your next project with precision engineered silicone solutions. Choose Fecision for excellence you can trust.
