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overmolding process

What is Overmolding

Overmolding is a process of taking a substrate part and then using injection molding to add additional layers over it, like thermoplastic or silicone rubber material. Traditionally, the substrate parts are plastic or metal with a higher melting point, once that part is cooled, the layer is injection molded over it. So the cycle time is a bit longer. Usually overmolding is used to create a grip or roller.

Overmolding Process

Overmolding is a multi-step manufacturing technique used to create complex, multi-material components.

  1. Initial Substrate Molding: The base or substrate part is first created using standard injection molding techniques.
  2. Substrate Preparation: The molded substrate is prepared, which may include cleaning and conditioning, to ensure proper adhesion for the overmolding process.
  3. Overmolding: The substrate is placed into a second mold where the overmold material is injected over or around it, forming a bond with the substrate.
  4. Cooling and Ejection: The assembled part is allowed to cool and solidify before being ejected from the mold, completing the overmolding process.

Overmolding Material

Substrate material for overmolding

Overmolding is commonly used to encapsulate one material (usually a softer or elastomeric material) over another rigid substrate. The most common substrate material for overmolding is thermoplastic, these material provides a stable base of overmolded components, the most common substrate material include:

  • ABS
  • PC
  • Nylon
  • PP
  • ABS/PC

Bonding material for overmolding

The most common overmolded material is thermoplastic elastomer, known for its flexibility, resilience, and compatibility with various substrates. Some other common bonding materials include:

  • TPE
  • TPU
  • TPV
  • Silicone

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FAQs of Overmolding

What is the difference between overmolding and insert molding?
Overmolding involves injecting two shots of materials to form the substrated and the overmold. Insert molding only involves injecting one shot of molten plastic, though the metal insert needs to be purchased or created separately.

Two-shot molding usually only makes sense for larger production runs, whereas overmolding is better for low volume production runs.

Overmolded parts are made in two-step process. This increases part cycle time and is thus more expensive than molding a single part with no overmolding.

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