What is Overmolding?
Overmolding is a process where two or more materials are molded together to form a single finished part. Typically, a rigid base (substrate) such as plastic or metal is molded first, followed by a second injection of a softer or functional material that covers part or all of the substrate. This creates a strong mechanical or chemical bond between the two materials.
Common Types of Overmolding
1. Soft-on-Hard Overmolding
First, a rigid plastic substrate (e.g., ABS, PC, PA) is molded.
Then, a soft elastomer (e.g., TPU, TPE) is overmolded.
Applications: Power tool grips, razor handles, seals, soft-touch buttons
2. Insert Molding
Metal components (nuts, terminals, pins) are placed in the mold.
Plastic is then injected to form a solid bond with the insert.
Applications: Threaded inserts, plugs, medical device components, connectors
3. Multi-Shot (2K/3K) Molding
Uses a specialized multi-shot injection molding machine.
Two or more materials are injected sequentially in the same mold for a seamless bond.
Applications: Dual-color buttons, transparent+soft parts, automotive trims
Advantages of Overmolding
Improved Ergonomics: Soft-touch handles offer better comfort.
Enhanced Sealing: Overmolded layers can act as watertight seals.
Stronger Assembly: Insert molding strengthens the mechanical bond.
Better Aesthetics: Enables multi-color or multi-material visual effects.
Reduced Assembly Cost: Eliminates secondary operations like gluing or heat staking.
Key Process Considerations
Mold Design: Avoid thin walls in the overmold, ensure proper flow and venting.
Injection Temperature: Ensure overmold material reaches bonding temperature.
Pre-treatment of Inserts: For metals, degreasing, roughening, or plasma treatment may be required.
Material Drying: Materials like TPU and PA are hygroscopic and require proper drying.
Clamping & Holding: Prevent shifting or floating of inserts during injection.
Application Industries
Consumer Electronics: Earbud housings, USB connectors, grips
Medical Devices: Overmolded syringes, instrument handles
Automotive: Gaskets, soft interior trims
Hand Tools: Screwdriver grips, tool handles
Yize Mould focuses on precision injection mold, medical injection molding, plastic injection molding, machining parts and PFA tube fittings
