Rubber Overmolding is a manufacturing approach that overmolding silicone rubber/liquid silicone onto thermoplastics, glass, electronics, metal, stainless steel, aluminum, and brass, which also called as silicone overmolding, LSR overmolding, rubber insert molding, two-shot molding. Rubber to metal bonding and rubber overmolding on plastic are most common, widely used in the automotive, electrical and medical industries.
Rubber Overmolding Parts
Rubber overmolding parts find a wide range of application like overmolded rubber seal, overmolded cable/tubing in multiple industries, including electrical components, automotive parts, brackets and handles, medical devices etc. LSR overmolding & liquid silicone overmolding usually applied to medical field and daily supplies. Here are some rubber overmolded parts:
Overmolded Rubber Gasket(Rubber+Metal)
Overmolded Rubber Grips(Silicone+Strew/Thread)
Silicone Baby Toothbrush(Liquid Silicone+Plsatic)
Medical Silicone Overmolding Mask(LSR+PVC)
Anti-vibration Isolator Mount(Rubber+Hardware)
P+R Keypad(Liquid Silicone Rubber+Plastic)
Rubber Overmolding Material
Rubber insert overmolding should take material, substrate and adhesive agent selection into consideration.
Before overmolding, there are limitations and compatibility issues to consider between different materials. Overmold Material Compatibility Chart is critical to be taken as a good reference to select overmolding material and substrate.
Silicone Rubber Materials: Silicone, LSR(Liquid Silicone Rubber), Nitrile (NBR), FKM (Viton), EPDM, Chloroprene Rubber (Neoprene), Natural Rubber
Substrate Materials: The substrate could really be anything, a metal part, glass, PBC circuit board, electrical connectors, an existing product like threaded inserts, screws, or thermoplastics like Polycarbonate (PC), PP, PA, PBT, PBSU
Adhesive Agent: The overmolding agents help in forming a stronger bonding between the rubber and the surface of the substrate being used. The selection of the overmolding agents depends on the overmolded part design, the rubber and substrate material. Without primer, the substrates and the rubber part may be easy to be separated. Plasma surface treatment is preferred to overmolding parts for medical devices when necessary, because the process will not introduce new substances.
Rubber Overmolding Ways
Liquid Silicone Rubber (LSR) Injection molding（LIM）
Rubber Overmolding Process
Material Preparation: Preparing substrate and silicone rubber material and keeping the surface of the substrate clean and dry
Substrates Surface Treatment: Applying overmolding agent to the surface of substrates
Overmolding Production: Locating substrates in mold and putting silicone material in the cavities to mold
To reduce the LSR overmolding steps and improve production efficiency, an addition type liquid silicone rubber, self adhesive LSR is helpful. It will form a strong bond to thermoplastics like polycarbonate without need for pretreatment.
Overmolding Self Bonding LSR Advantage
Saving the time and the cost of applying primer so to save the production cost and improve the production efficiency to 5-10 times
Reducing the failure rate of finished parts
The temperature required to cure the silicone and the substrates heat deflection temperature, especially using plastic as substrate, must be considered prior to developing a rubber insert molding. Liquid silicone molding temperature is 120-150℃. For HCR, high temperature cured silicone needs 170-180℃, and low temperature cured rubber needs 135℃. Generally, some plastic will add with moderate GF(Glass Fiber) to improve temperature resistance.
Rubber Overmolding Common Problems and Solutions
Unreasonable overmolding seal design between rubber and substrate--Take the problems may occur in actual production into consideration when designing
Having many burrs and flashing in parting line--Using precision molds, controlling production process strictly, including the amount of raw material placed in cavities, the pressure setting of molds, and the ways of applying glue on substrates and designing proper location for substrates
Silicone rubber flows to substrates surface in rubber overmolding process--Adding additional sleeve to prevent the silicone material flowing to the inserts
Substrates Location Design Cases
The metal insert for silicone membrane has two holes to be fixed in mold in insert molding process
Silicone caps are designed to help the plastic buckles for silicone bracelet locate in the mold
Adding 0.5-0.1mm step to firmly fix the strew insert for rubber mount in the mold and prevent it from rotating
As rubber overmolding manufacturers/silicone overmolding companies, we have the experience guide you the entire process from design to manufacturing. Once the material and design are confirmed, we will take over and produce products that meet your need.
Why Rubber Overmolding?
Silicone overmolding supports different materials or material in different color/hardness combination for achieving product’ design flexibility and multi-function. LSR overmolding supports more types of thermoplastic to be overmolded with silicone rubber for the lower curing temperature needed.
There is no secondary operation after silicone rubber overmolding manufacturing process so that the assembly time and labor costs will be saved.
Liquid silicone overmolding builds stronger bonding between rubber and substrates than gluing rubber to metal/plastic, which improves products physical and mechanical performance.
Rubber overmolding, LSR overmolding especially, offers products with high tolerance and enhance the fitting and sealing between products components.
Rubber insert overmolding combines different materials properties to increase product longevity, like reducing shock and vibration, providing electrical insulation, or improving chemical/UV resistance.