What is the working principle of overmolding

A overmolding is a mold in which two plastic materials are injected on the same injection molding machine, and the product is molded twice, but the product is only ejected once. So what is the working principle of overmolding?


Overmolding usually have two sets of molds, half of which is mounted on the fixed mold plate of the overmolding injection molding machine, that is, the side with the injection gate, and the other half is mounted on the movable mold rotary plate, that is, the side where the mold is ejected. The movable molds of the two sets of molds are generally the same, but the primary fixed mold and the second fixed mold are different. After the injection of the first material is completed, the fixed and movable molds are opened under the pulling force of the injection molding machine, and the movable mold is rotated 180 degree with the product at one time. At this time, the movable mold is not ejected, and then the mold is closed for the second material. After heat preservation and cooling, the fixed and movable molds are opened, and the products on the movable mold side are ejected. In each forming cycle, there will be one-mould primary products and one-mould secondary products.

1. The two shapes of the front die are different, forming 1 product respectively, while the two shapes of the back mold are exactly the same.

2. The front and back molds are rotated 180 degrees around the center, while the front and back mold must be inosculated when rotating. This check must be done during work, because this point has higher requirements for the positioning and processing of the mold base. The total thickness of the front die panel plus A plate cannot be less than 170mm. This should carefully check the model of the injection molding machine and other reference data.

3. When designing the master mold for the second injection, in order to avoid the secondary master mold from scratching the structure of the product that has been formed for the first time, a part of the avoidance can be designed. However, the strength of each sealing position must be carefully considered, that is, whether the plastic will be deformed due to the large injection pressure during injection molding, which may lead to the possibility of cracking in the second injection.

4. During injection molding, the size of the first injection molded product can be slightly larger, because it can be pressed tighter with another male mold during the second molding to achieve the effect of sealing. And pay attention to whether the flow of the plastic impulses the product that has been formed the first time and deforms the structure during the second injection? If this is possible, we must find ways to improve it.