What is Silicone Overmolding?
Silicone Overmolding, also named Rubber Overmolding, Liquid Silicone Rubber(LSR) Overmolding, is a multi-step injection molding process where two or more components are molded over top of one another. Overmolding is sometimes referred to as two-shot molding because it is a two-step process.
The common secondary molding material concludes PC, PPSU, PA + GF, PBT, etc., All are thermoplastic materials with high-temperature resistance. While common overruled material is silicone (high-temperature vulcanization silicone or low-temperature vulcanization silicone) or liquid silicone rubber (LSR). Compared with the assembly or bonding parts, the silicone overmolding parts have better quality.
How is Silicone Overmolding Done?
Silicone Overmolding is a multi-step injection molding process where two or more components are molded over top of one another. Overmolding is sometimes referred to as two-shot molding because it is a two-step process.
(1) First, a base component (otherwise known as a substrate) is molded and allowed to cure. Overmolded substrates are often made of plastic.
(2) Then the second layer is molded directly on top of the first to create a single solid piece.
Overmolding is commonly used to manufacture plastic parts that feature a rubber handle. The two-shot process of overmolding a toothbrush, for example, consists of forming a base layer for the plastic handle and a top layer of rubber (to make the toothbrush less slippery to hold).
LSR Overmolding is widely used in health care, high-precision seals& gaskets, and automotive parts.
Two Options for Materials in Silicone Overmolding
1) Self-adhesive silicone rubber. This material requires that the product structure is conducive to sealing, if there is glue overflow in the production process, it is difficult to clean up.
2) Liquid silicone rubber. Brushing the primer on the substrate material before the overmolding of liquid silicone rubber. There will be adhesion where the substrate is brushed, and there is no adhesion where the substrate is not brushed. Therefore, It is better to clean up the overflow glue than the self-adhesive silicone rubber.
Liquid silicone rubber overmolding generally uses a needle, valve-type cold runner. Theoretically, the mold cavity can achieve a complete vacuum for glue sealing. This advantage can avoid the poor appearance of parts& products for the reason that the gas in the mold cavity cannot discharge. Most liquid silicone rubber products have a greater risk of glue overflow during the process of silicone overmolding, so the mold cavity should keep a vacuum and use a needle valve runner.
The Benefits of Silicone Overmolding
Silicone Overmolding offers many benefits. One of the benefits of liquid silicone over-molded components is that the manufacturing process allows for using the non-plastic substrate. Aside from thermoplastic materials and liquid silicone rubber, it is the only way to incorporate the material into the injection molding.
You can manufacture products with various material and customized the color. Overmolding is labor and cost saving compared to other manufacturing methods where a part would need to be transferred to a completely different mold or machine.
• Compatible with more plastic materials, such as medical cryogenic PC, PA, PPS, or other high-temperature resistant plastic
• The curing time is short
• The injection molded parts without burrs
• The size control of LSR plastic parts with strict tolerance
• Better quality control
Multi-shot Overmolding & Insert Molding
There are two methods to achieve silicone overmolding: Multiple-shot molding or Insert molding. In double-shot molding, the first material is a substrate, the second one is the mold. The pressure from multiple barrels to press shooting two different resins into the same injection molding tool. The entire operation uses one machine in the whole process, instead, double-shot molding is more suitable for large volumes because the mold and machine are more expensive.
Insert Molding usually place the substrate, like metal, or plastic into the mold, then oversold the partial parts or the whole parts. For better adhesive strength, the insert part will be preheated, and the insert parts will be coated with a coating. Insert molding is more sufficient for low volume, however, insert molding needs a substrate and a cavity mold for overmolded material.
Applications of Silicone Overmolding
Manufacturers use overmolding and insert molding to produce products for a wide range of industries. Here are some examples of products that are commonly made through one or a combination of these processes:
Consumer Goods
Look around your home, and you’re likely to spot more than a few plastic objects that are one solid piece made up of multiple colors. You can bet that many of those products were manufactured using overmolding. This popular manufacturing process is used to make everything from bowling pins and children’s game pieces to storage bins and plastic containers.
Toothbrushes, cell phone cases, and thumb drives are commonly produced using overmolding and/or insert molding. Overmolding is used to make a variety of two-tone plastic furniture, such as step stools or patio chairs. Plastic housing for GPS units and navigational devices are often manufactured using overmolding and insert molding, as well.
Electrical sensors, gears, fasteners, and other automotive parts that consist of a combination of metal and plastic or rubber material are commonly manufactured using insert molding. Overmolding is used to create solid two-tone interior components, such as door and dash panels, handles, knobs, and various controls. Certain motors and batteries also go through a process of insert molding.
The medical industry relies heavily on insert molded and overmolded parts because plastics are easier to sterilize than electrical and computer components. Defibrillators, medical cables, and wiring are often encased in plastic using insert molding both to protect the fragile interior components and make the finished device easier to clean for use.
Medical devices, such as pacemakers, designed to be implanted inside the body are commonly manufactured using insert molding. Manufacturing facilities also use insert molding to produce a variety of camera equipment used for internal imaging, such as those employed to conduct endoscopies and colonoscopies.
Electrical wires are made safer and, in certain cases, weatherproof by insert molding a rubber exterior. Manufacturers often coat wiring components in rubber to make products, like cellphone and computer chargers, safer for consumers. Sometimes, multiple wires are encased in one layer of rubber, and other times, wires are separated out and differentiated using contrasting colors, like blue and red.
Beauty Industry
Overmolding and insert molding are routinely used to make cosmetics packaging more attractive. They enable designers to create custom packaging with unique surface textures and multiple colors. Products such as compacts, makeup brushes, and perfume bottles can all be manufactured using overmolding and/or insert molding.
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We are a Silicone Manufacturer who has rich skills and experience in Liquid Silicone Rubber Over-Molding technologies and silicone over-molded cases. We acquire LSR overmolding prototyping, tooling, and process. We had made many silicone over-molded parts for specific programs. Under a strict quality control system and standard, we guarantee our well-performed LSR parts and exact manufacturing process. From prototype and design to manufacturing and assembly, we can be your first solution for complex LSR parts. Message us today to tee us your requirements!
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Liquid silicone rubber Overmolding parts have used in nearly every aspect of daily life.
- Mechanical uses
- Electrical applications
- Automotive applications
- Extreme temperature resistance
- Sterilization capability
- Many more applications!
Contact us today for your free quote if you’re ready to discuss your liquid silicone rubber manufacturing project.
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