Adding another layer of plastic to an existing element offers several advantages. These include improved material flexibility and a reduction in production costs by eliminating the need for adhesives.
The design of the substrate and cover material must be compatible to ensure a strong bond. This includes examining tensile-related properties such as elongation and flexural modulus.
Thermoplastics
Thermoplastics are plastic materials that melt into a soft, pliable form above a specific temperature. They are molded into shapes and cooled to produce solid parts that can be reused multiple times. These materials are used for overmolding to create products with a variety of features, including improved grip, chemical resistance and noise dampening.
Using overmolding can reduce the overall manufacturing time of a product because it eliminates assembly steps. This is a great way to reduce costs and get your products or devices to market faster.
Overmolding is typically used to add a soft grip surface above a hard substrate, but it can also be employed for flexibility, increased material durability or color variation. The choice of materials depends on the core function of the part and what environmental conditions it will be exposed to. A good place to start is by looking at the flexural modulus and material thickness. These properties help determine how well the overmolded material will adhere to the substrate.
Elastomers
Elastomers (or rubbers) are used for overmolding because they are flexible and resilient. They are also lightweight, making them easier to mold into tight spaces and lowering the cost of production. They are highly resistant to chemicals and extreme temperatures and can be molded into complex shapes with high accuracy.
These softer materials can be overmolded onto rigid plastics like polycarbonate, acrylonitrile butadiene styrene (ABS), or thermoplastic vulcanizates (TPVs), or even harder engineered resins such as PEEK and Ultem. This allows manufacturers to streamline the production process by eliminating the need for connectors and o-rings.
To ensure compatibility between the different materials used in overmolding, it is important to consider their flexural modulus and material thickness. These properties will determine how well the overmolding process works. It is also important to choose a manufacturing partner with the right experience. Fictiv vets each of our injection molding partners carefully so you can be confident that your plastic prototype will meet your exact specifications.
Flexural Modulus
Although similar, flexural modulus and tensile modulus are not the same. While tensile modulus measures the resistance of a material to compression, flexural modulus is an indicator of how well a sample will resist bending.
Ductile materials, such as steel and brass, have clearly defined flexural moduli. However, brittle materials like glass and concrete have no such ranking.
The flexural modulus of a sample is the slope of the stress-strain curve generated by a bending test. Like tensile modulus, the slope represents the ratio of the stress to the strain in an isotropic material under ideal elastic conditions.
When choosing a material for overmolding, producers should look at its flexural modulus and bond strength. The bonding process between the substrate and overmold is important for a durable, long lasting part. Bonding is influenced by several factors, such as: – Substrate thickness; – Overmold temperature and viscosity; – Overmold/Substrate surface textures; – Gate location; and – Resin flow characteristics.
Material Thickness
From textured grips on power tools to waterproof seals in cable connectors, overmolding uses multiple materials to make strong, durable products that function and look great. This process eliminates the need for adhesives, making it more reliable and cost-effective.
Overmolding composites can be made from a mixture of different materials, but both the substrate and overmold must be chemically compatible to form effective bonding during fabrication. Incompatible materials could deform during the molding process, so product teams should always consult an overmold material compatibility chart.
The overmolding process is used in a wide range of products, including toothbrush handles, car tail-lights, and housewares. Overmolded grips increase safety and comfort for users, while rubber bumpers protect electronic components from vibrations. Thermoplastic elastomers are especially well-suited for overmolding, as they are strong and can be molded to create a variety of textures. The thickness of the overmold is also important to consider, as thicker walls will absorb more vibrations while maintaining a soft feel.
