Over Molding, Insert Over Molding Process and Applications
Overmolding is a process whereby one material is molded over a second material. The initial “substrate” is commonly the harder plastic of the 2 resins. Once the “substrate” is molded, it is then placed into another mold cavity and the “over mold” resin is injected to specific surface areas of the substrate to achieve the intended design and usage.
This “overmolded” resin is typically a thermoplastic elastomer (softer feel), although there are other resin grades that also provide a softer feel. There are many applications where these types of products are chosen to be overmolded with a softer resin to aid comfort, ergonomics, cushioning, shock absorption, and functionality.
Material Selection
When overmolding plastic resins, proper material selection is critical – the two resins must be compatible. Resin suppliers provide guidance on which thermoplastic elastomers (the softer plastic) or other resin grades will bond to particular substrates dependent on which grade of resin is used to mold substrate. There are also different hardness criteria that is determined by the functionality or feel needed for an application. The range of durometers can be from 15 Shore A (very soft) up to 90 Shore A (hard but still offers some softness dependent on wall thickness).
If the proper materials have been chosen, the two materials bond together chemically and/or mechanically. This process yields a strong finished piece with a long life. In many cases, this process can be less expensive than post-molding processes.
Using Over Molding for Design Enhancement
Meridian also overmolds metal components for added design enhancement, such as brass inserts or other metal components. Dependent on part design, this may be feasible where post molding operations such as ultrasonic welding is not viable.
Overmolding processes lend itself to multiple industries and applications , such as:
- Toys
- Petroleum industry components
- Therapeutic tools
- Musical instrument aids
- Consumer filtering
- Toothbrushes
- Handheld tools
- Lawn equipment
- Electronic cases
- Computer mice