Insert Molding of Plastic Mold

Insert molding refers to the molding method in which the mold is filled with pre-prepared inserts of different materials, then injected with resin, and the molten material is bonded and solidified with the inserts to form an integrated product. Typically, insert molding or overmolding involves accurately placing a part made of metal or other suitable material (called an insert) into a mold, closing the mold, and then injecting plastic into or around the insert. Typical applications are electrical connectors that incorporate machined metal pins or sockets into molded plastic housings. Most insert molding utilize metal parts including handles, threaded inserts or electrical contacts.

1. Manufacturing process of insert molding

Insert molding is the process of molding thermoplastic material around preformed components (inserts) to create multi-material parts. Inserts are usually metal parts used to enhance the mechanical properties of plastic parts. The insert is placed in a plastic mold, and thermoplastic is injected into the mold to form the part. Using molded-in inserts eliminates the need for secondary mounting of the inserts, reducing costs compared to installing the inserts into the plastic part during post-molding.

2. Advantages of insert molding over traditional injection molding

A typical application of insert molding is to include one or more threaded metal inserts in a plastic part when it is intended to mate with another part in an assembly. Plastic alone may not have sufficient mechanical properties to withstand the forces required to hold two parts together. For example, threads in plastic parts can wear down with repeated use, causing damage to the part. Metal inserts help reinforce the plastic and ensure reliable fastening when parts are reused. This combination of plastic and metal can take advantage of the lightweight of plastic and the strength of metal.

3. The main design criteria to be followed when designing insert molding parts

As with any molded part, typical design guidelines for formability apply to insert molded parts, such as increasing the draft to help the part release from the plastic mold and maintain a consistent wall thickness. Additionally, there are some unique considerations when designing parts for insert molding. For example, the design of undercut features can help improve the retention strength of the Insert within the molded part. Since the Insert must be placed into the plastic mold, it is also important to ensure that the Insert is in an accessible area of the plastic mold. Ensuring that the Insert is not too deep within the part and securing it in the plastic mold during the molding process will also help ensure a successful result.