The process of overmolding includes molding one material on top or around another. A base layer is injection molded first, and then an additional plastic layer is molded over and around the base layer - resulting in a single, finished product.   Typically, overmolding combines two types of plastic materials to produce a single component or device. The injection molding of two different plastics creates a unified structure that is strong and rigid on the inside and flexible, colorful, and easy-to-hold on the outside. Leaving no gaps or spaces within a product and thus eliminates contamination.

Often the exterior layer is an elastomer giving the desired texture or physical property. For instance, pliability, enhancing the product's aesthetic and functional features. An example would be soft-touch handles in medical instruments to improve grip and minimize slipperiness.

Benefits of Overmolding Plastic Components

Durable Designs – Parts and devices can help to reduce vibration and other sources of wear and tear that can eventually break the materials apart. Parts that have been molded together withstand the stress of use and are a more durable product with an extended life. Make products resistant to water, dust, and vapor.  

Vibration Resistance – Products, when exposed to noise and vibration, can loosen the product’s shape and severely affect the accuracy and reliability of the product. Overmolding creates high-strength and high-touch parts by isolating materials that are vulnerable to vibrations.

Safety Mechanisms – The plastic injection molding technique allows manufacturers to mold different durometer materials onto sharp corners or edges to ensure safety for the user. And makes applications more resistant to shock.

Aesthetic Value – The craft of overmolding enables manufacturers to create unique designs by using materials of any texture or color that match the product specification and function. An unlimited choice of colors provides the ability to color-code products and explore bright colors for greater usability and ease-of-use.

Ergonomic Benefits – Overmolding offers practical benefits besides adding beauty and style to a product. It allows manufacturers to add handles of any shape or thickness to products without natural grips offering sleek materials or coarse surfaces for more comfortable and easier to grab.

Overmolding Design Considerations

The challenge of the overmolding process is to make sure the two pieces -rigid substrate and outer elastomer – fit together without any gaps, slack, or slippage.   So, it's a matter of making molds that create a perfect fit, which in turn heavily relies on a stable injection molding process that boasts extreme precision. The matching of two molded parts requires a great deal of skill and experience. And that requires a strong injection molding engineering team that has intimate knowledge of the overmolding process and simulation software to anticipate possible issues before fabrication of the mold or production begins.

Overmolding Applications

  • Medical devices and instruments
  • Parts with grip handles,
  • Knobs for controls and assemblies
  • Encapsulated electronic devices and electronic components
  • Communication and navigation devices

Overmolding for plastic injection molded components is used for products in the medical, pharmaceutical, dental, defense, safety, and industrial markets.   To learn more on how plastic injection molding process monitoring ensures quality components, understanding the plastic injection molding costs by evaluating total cost of ownership, and more - go to the Complete Guide to Plastic Injection Molding.

Topics: plastic injection molding