Insert molding is a plastic injection molding process in which an insert, such as an object or component, is placed into the mold cavity and then injected with molten plastic that is thus molded around the insert. Insert molding is a more effective alternative to the assembly of discrete parts by means of soldering, adhesives, or fasteners.
Quick links to Insert Molding Information
Applications of Insert Molding
Insert molding serves many industries, such as:
- Food Processing
Typical insert injection molding applications include:
- Cable Embedded Electronics
- Medical Devices
- Aerosol Nozzles
- Electrical Plugs
- Needle Hubs
- Threaded Fasteners
Materials Commonly Used in Insert Molding
Materials used during the insert molding process includes polystyrene, polyvinyl chloride, polyethylene, polypropylene, thermoplastic elastomers, and many more engineering plastics.
Process of Insert Molding
Insert molding is done through an injection molding machine. On the top of the machine is a hopper, through which the plastic granules enter the barrel of the machine. In the barrel, the plastic granules are heated until they become molten plastic. A reciprocating screw inside of the barrel carries the plastic granules into the mold cavity by way of a nozzle. The nozzle leads directly into the mold cavity. The mold is attached to a moveable platen so that it can push into and pull back from the mold cavity. An insert, which can be metal or plastic, is placed into the mold cavity just before molding. The molten plastic is then injected into the cavity through the nozzle and molds around the insert piece. Once the plastic has cooled, the mold is opened and the newly joined components are removed.
Two types of bonding occur during insert molding: mechanical and molecular. Molecular bonding takes place by either shrinking the encapsulating plastic resin around the insert as it cools or surrounding the irregularities on the insert’s surface by the plastic resin. Mechanical bonding, however, only takes place when the insert’s material is the same as or very similar to the plastic resin.
Here are the three types of insert molding:
- Low Volume
- 100-1000 parts that the operator inserts all at once.
- Medium Volume
- 1000-10,000 parts that the operator loads in multiples and is aided by a loading device.
- High Volume
- 100,000 parts or more that are loaded automatically.
Benefits of Insert Molding
Some benefits of plastic insert molding include:
- Low Costs
- Since multiple tasks are being done at once both labor and assembly time is saved.
- Greater Durability
- As the plastic resins mold to the insert more securely than other joining methods.
- Lighter Components
- Since plastic resin weighs less than metal connectors.