Notes on the design of two-shot mold and overmold

mold design

1、 Two shot mold

A mold in which two plastic materials are injected on the same injection molding machine and molded twice, but the product is only molded once. Generally, this molding process is also called double material injection molding, which is usually completed by a set of molds and requires a special two-shot injection molding machine.

2、 Overmold (secondary molding)

The two plastic materials are not necessarily injected on the same injection molding machine, and are molded in two times; After the product is removed from one set of molds, it is put into another set of molds for the second injection molding. Therefore, the general molding process is usually completed by 2 sets of molds, without the need for a special two-shot injection molding machine.

3、 Two shot mold and overmold

During the design of the overmold, attention shall be paid to the positioning of the hard rubber parts. Reliable sealing of the rubber parts shall be achieved and the rubber parts shall be provided with anti inclined holes to prevent the deformation of the rubber drawing. The two-shot mold is increasingly popular in the market at present, because this process can make the appearance of the product more beautiful, and it is easy to change shots without spraying, but the cost is expensive and the technical requirements are high.

1. The shapes of the two cavities of the overmoldare different, and one product is molded separately, while the shapes of the two cores are identical.
2. After the front and rear dies of the mold are rotated 180 ° in the center, they must be aligned. This inspection must be performed during design.
3. Pay attention to the position of the ejector pin hole, with a minimum distance of 210mm. The number of ejector pin holes shall be appropriately increased for large moulds. Moreover, because the ejector pin attached to the injection molding machine itself is not long enough, we must design an extended ejector pin in the mold, which is about 150 mm longer than the mold base plate. Two locating rings must be designed on the bottom plate of the rear mold.
4. The total thickness of front formwork panel plus A plate shall not be less than 170mm. Please carefully check other reference data of this model of injection molding machine, such as the maximum mold holding thickness, the minimum mold holding thickness, the distance between the ejector pin holes, etc.
5. The nozzle of the three plate mold should be designed to automatically demould. Pay special attention to whether the demoulding action of the soft rubber nozzle is reliable.
6. The depth of the front gate shall not exceed 65mm. The distance from the top of the upper side gate to the center of the mold embryo shall not be less than 150mm.
7. When designing the cavity for the second injection molding, in order to avoid the cavity scratching the rubber position of the first molded product, a part of the cavity can be designed to avoid void. However, the strength of each sealing position must be carefully considered, that is, during injection molding, will the plastic deform under high injection pressure, which may lead to the possibility of batch front for the second injection molding?
8. During injection molding, the product size of the first injection molding can be slightly larger, so that it can be pressed more tightly with another cavity during the second molding to achieve the role of sealant.
9. Note that during the second injection, will the flow of plastic impulse the first molded product to deform its rubber position? If this is possible, we must find ways to improve.
10. Before clamping plates A and B, pay attention to whether the front die slider or inclined jack will reset first and crush the product. In this way, it is necessary to find a way to make sure that the sliding block or inclined roof of the front die can be reset only after the A and B plates are closed first.
11. The water delivery arrangement of the two cavities and cores shall be as adequate as possible, and shall be balanced and the same.

plastic injection mold

12.99% of the time, the hard rubber part of the product is injected first, and then the soft rubber part of the product is injected, because the soft rubber is easy to deform.