Montrose Molders

Custom Injection Molding

Over-Molding in Custom Injection Molding

Combining two different materials is often required for a custom injection molded part design. This process is called over-molding and consists of molding one material over another to create a single, integrated product. From enhancing product durability to providing ergonomic grips, over-molding offers many benefits. The blog below will examine its uses, suitable plastics, ideal scenarios, and key design considerations.

What is Over Molding?

Over molding, also known as two-shot molding or multi-shot molding, is a process where a second material is molded over a pre-formed part, typically made of a different material. This technique allows for the creation of complex, multi-material parts with various properties in a single production cycle. It enables manufacturers to combine different colors, textures, and functionalities into one seamless component, reducing assembly costs and improving product aesthetics.

Plastics to Use for Over Molding:

Selecting the right materials is crucial for successful over-molding. Common combinations include:

  1. Thermoplastic Elastomers (TPE): TPEs offer excellent flexibility and soft-touch properties, making them ideal for creating ergonomic grips and cushioning.  These materials are usually used for the second shot of the overmold.
  2. Polycarbonate (PC) or Acrylonitrile Butadiene Styrene (ABS): These rigid plastics serve as a durable substrate for over-molding, providing structural support and impact resistance.
  3. Polypropylene (PP) or Polyethylene (PE): These materials are also frequently used as the base for over-molding due to their low cost, chemical resistance, and ease of molding.

When to Use Over Molding:

Overmolding finds applications across various industries and product categories:

  1. Consumer Electronics: Overmolding adds durability and aesthetics to electronic devices, such as remote controls, headphones, and mobile phone cases.
  2. Automotive: Over-molded parts improve the comfort and functionality of automotive interiors, including steering wheels, gear shift knobs, and dashboard components.
  3. Medical Devices: Over molding is utilized in medical device manufacturing to create ergonomic grips, soft-touch surfaces, and seals for devices like surgical instruments and handles for diagnostic equipment.

Design Considerations for Over Molding:

Designing for overmolding requires careful consideration of several factors:

  1. Material Compatibility: Ensure compatibility between the base material and the over-molding material to prevent adhesion issues or material failure.
  2. Part Geometry: Design parts with appropriate draft angles, wall thicknesses, and undercuts to facilitate proper mold filling and ejection.
  3. Bonding Surface: Provide sufficient bonding surface between the base and over-molding materials to achieve a strong adhesion and prevent delamination.
  4. Gate Placement: Strategically place gates to minimize flow length and reduce the risk of material degradation or weld line visibility.
  5. Tolerance Control: Maintain tight tolerances to ensure precise fit and alignment between the over-molded layers, especially in applications requiring mating components.

Overmolding revolutionizes custom injection molding by offering unparalleled design flexibility, improved product performance, and cost-effective manufacturing solutions. By understanding the intricacies of material selection, application suitability, and design optimization, manufacturers can harness the full potential of over-molding to create innovative, high-quality products across diverse industries. Whether enhancing ergonomics, durability, or aesthetics, over-molding continues to shape the future of injection molding technology.

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