At Goldwin, we specialize in high-precision mold making and plastic injection services with over 23 years of industry experience. Among our advanced molding capabilities, overmolding stands out as a powerful solution for enhancing product performance, durability, and user comfort across various industries.

What Is Overmolding?

Overmolding is a multi-material injection molding process where a rubber-like plastic—often TPE (Thermoplastic Elastomer)—is molded over a pre-formed substrate. The substrate is commonly another plastic part but may also be made from metal or other materials. This technique is ideal for creating parts with improved grip, sealing, or vibration resistance.

Applications of Overmolding

• Grip: Enhances safety and comfort, especially for handheld tools or devices, by providing a non-slip surface—even in wet conditions.
• Vibration Dampening: Protects delicate components like electronics from mechanical vibrations.
• Ergonomics & Comfort: TPE can be molded into ergonomic shapes to improve user experience.
• Sealing: Creates water-resistant seals for devices such as outdoor electronics or enclosures.
• Sound Absorption: Reduces unwanted noise and mechanical rattling.

Designing for Overmolding

Successful overmolding begins with a clear understanding of part functionality and environmental exposure. Whether your goal is to create a soft-touch grip or a watertight enclosure, material selection and geometry must be carefully considered.

Key Design Considerations:

• Wall Thickness: Maintain uniform wall thickness to ensure consistent flow and prevent defects like voids or warping.
• Gate Location: Impacts material flow and surface aesthetics—particularly important for visible surfaces.
• Sealing Features: Necessary for water or dust resistance, requiring precision fit between substrate and overmold.
• Shrinkage: Anticipate material shrinkage to avoid detachment or distortion after cooling.

Material Selection

Choosing the right materials is crucial. TPEs vary in hardness, flexibility, bonding ability, and environmental resistance. The compatibility between the overmold and substrate material (e.g., polypropylene, ABS, PC) must be validated for proper adhesion or mechanical interlock.

Key Properties to Consider:

• Bonding: Determine whether chemical adhesion is needed or if mechanical interlocks will suffice.
• Temperature Resistance: Ensure the substrate can withstand the molding temperature without deformation.
• Hardness & Flexibility: Tailor these to meet ergonomic or protective needs.
• Compression & Tensile Strength: Important for durability under repeated use or stress.
• Friction Coefficient: Affects grip and surface interaction.
• Wall Thickness: Thicker layers improve cushioning but increase cycle time and cost.

Overmolding Operations

Overmolding can be performed through two main methods depending on production volume, budget, and part complexity:

Manual Overmolding

Ideal for low to medium production volumes. Substrates are molded separately and manually loaded into a secondary mold for overmolding. It’s simple and cost-effective but labor-intensive and less consistent.

Two-Shot Molding

Best for high-volume runs. This automated process uses a dual-barrel machine to mold the substrate and overmold in a single cycle. Though more complex and costly to set up, it offers greater efficiency, consistency, and reduced labor.

Overmolding vs. Insert Molding

While both techniques involve molding plastic over another component, overmolding is generally used for molding TPE over plastic, whereas insert molding surrounds metal or non-plastic inserts like screws or magnets with thermoplastic material.

Why Choose Goldwin for Overmolding?

With extensive expertise in mold design, material selection, and high-precision plastic injection molding, Goldwin is your trusted partner for developing custom overmolded parts. Whether you’re prototyping or scaling to mass production, our team is ready to guide you every step of the way.

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📞 Contact us today to start your overmolding journey with a free quote and expert advice.