The difference between two-color injection molding and overmolding

Medical Double-Color Plastic Injection Molding Companies and overmolding are two common injection molding processes. Although they both involve multiple molding of two plastic materials, there are differences in specific operation methods and mold design.

Two-color mold
Two-color mold refers to using the same injection molding machine to mold twice on the same set of molds, and the final product only needs to be ejected once. This process is usually called two-material injection molding and requires a dedicated two-color injection molding machine. When designing a two-color mold, special attention should be paid to the following points:

Cavity shape: The two cavity shapes are different and are used to mold the same product. The core shape is exactly the same.
Mold symmetry: The front and rear molds must match after rotating 180 degrees around the center to ensure symmetry.
Ejector hole position: The ejector hole position should be kept at least 210mm. For large molds, the number of ejector holes needs to be increased. In addition, the ejector needs to be extended to about 150mm below the bottom plate of the mold base.
Front mold panel thickness: The total thickness of the front mold panel plus the A plate shall not be less than 170mm. It is necessary to refer to the maximum mold thickness, minimum mold thickness, ejector hole distance and other parameters of the injection molding machine.
Three-plate mold gate design: The gate design should facilitate automatic demolding, especially the demolding action of the soft glue gate.
Gate depth limit: The depth of the front gate should not exceed 65mm, and the distance from the top of the upper gate to the center of the mold base should not be less than 150mm.
Avoid damage: When designing the second injection cavity, it is necessary to avoid damaging the first molded product, and at the same time ensure the strength of the sealing position to prevent deformation from causing batch fronts.
Size control: The size of the product for the first injection can be slightly larger than the second, so that the product can be better pressed during the second injection to achieve the sealing effect.
Prevent deformation: It is necessary to ensure that the plastic flow during the second injection will not impact the molded product and cause deformation.
Protect the product: Before the A and B plates are molded, it is necessary to prevent the front mold Slider or Lifter from resetting in advance to damage the product, which can be solved by adjusting the mold closing sequence.
Cooling system: The cooling system of Cavity and Core should be reasonably laid out and evenly distributed.
Injection order: Usually the hard plastic part is injected first, and then the soft plastic part is injected to prevent the soft plastic from deforming.
Overmolding mold
Overmolding mold refers to two plastic materials that are not necessarily injected on the same injection molding machine and are molded in two times. The product is taken out of one mold and then put into another mold for the second injection molding. Overmolding molds usually consist of two sets of molds, and no special two-color injection molding machine is required. When designing, special attention should be paid to the positioning of hard plastic parts to ensure reliable sealing and prevent deformation of plastic parts. The design focus of overmolding molds includes reliable positioning of hard plastic parts, strength of sealing positions, etc.

In summary, two-color molds and overmolding molds have their own characteristics. The choice of which process depends on product requirements, equipment conditions and cost budget.