Overmolding is an injection molding process where two materials are molded together. Types of overmolding include two shot sequential overmolding, multi-shot injection molding or insert overmolding.
- Multi-shot injection molding injects multiple materials into the cavity during the same molding cycle.
- Insert overmolding uses a pre-molded insert placed into the mold before injecting the second material.
- Two shot sequential overmolding is where the molding machine injects the first material into a closed cavity, and then moves the mold or cores to create a second cavity, using the first component as an insert for the second shot using a different material.
Overmolding analyses consist of a two step process, where a
Fill+Pack analysis is performed on the first cavity (first component stage), and then a
Fill+Pack analysis or a
Fill+Pack+Warp analysis is performed on the overmolding cavity (overmolding stage). The overmolding stage on the second cavity uses a different material from the first component stage. As the temperature of the insert, injected in the first component stage, is not uniform, mold and melt temperatures used in the overmolding stage are initialized by the temperatures recorded at the end of the first component stage.
Note: It is assumed that the material injected in the first component stage does not melt and flow when the second material is injected in the overmolding stage, even though the temperature does rise.
Materials are usually chosen specifically to bond together, using the heat from the injection of the second material to form that bond. This avoids the use of adhesives or assembly of the completed part. It can result in a robust multi-material part with a high quality finish. When designing an overmolded part, wall thicknesses of both the insert and the overmolded component should be as uniform as possible to ensure an even and robust bond. Avoid ribs and sharp corners to reduce flow problems.
Tip: You may find it easier to model your part in two separate studies, one for the first component stage and one for the overmolding stage. You can then add these two stages together in one model.
Overmolded parts take longer to cool than single shot injection molded part, and cooling systems are less effective. The insert acts as an insulator and heat is less efficiently extracted from the part. However, optimising the cooling system can help reduce the cycle time.
Note: Warp analyses on overmolded components on 3D models which contain part inserts, take into account the influence of contact between the part inserts and the overmolded component.