the only injection machine injects two kinds of plastic material. The product forms by 2 times but depanning once. Generally this molding craft is called double material injection, which is finished by only one mold. But it must be implemented in the special double color injection machine.
B, over molding
two kinds of plastic material may not injected by only one machine, and the product forms by 2 times. It will be injected in the other mold after being removed from first mold for the first injection. So generally this type of injection craft is finished in two sets of molds but doesn’t need special injection machine.
Designing over molding, we should pay attention to the fixed position of hard plastic pieces. There must be anti rank hole on the piece which can prevent frictional pullar from deformation.
Double color injection mold becomes more and more popular. Because the outlook of products can be more nice by this craft. and it is easy to change colors, without spraying as well. However the cost of manufacture is high and technical requirements are needed more.
1, cavity has 2 different shapes that form different products separately. 2 shapes on the core are totally same.
2, front and back mold must be coincided after both of them rotate 180 degree. This checking action must be designed in advance.
3, we should pay attention to the position of ejector pin hole, of which min distance is 210mm. the number of ejector pin holes should be increased in bigger mold. Because ejector pin of injection machine is not long enough, we must length it when we are designing the mold. Ejector pin can reach 150mm higher than mold base plate. Back mold base plate is made with 2 locating rings.
4, the total thickness of front mold panel and plate a is not less than 170mm. please check this specification and other reference data of machine, such as max and min mold containing thickness, distance of ejector pin hole etc.
5, the gate of three plate mold had better demold automatically. Especially for the soft plastic material.
6, the depth of former sprue can’t be over 65mm. the distance from the top of upside sprue (side gate) to the centre of mold base is not less 150mm.
7, when designing the second shape, we can design a part of clearance on the cavity for fear of scratching sprue position of first formed product. We also consider the intensity of sealing carefully.
8, when first injecting, product dimensions can be molded little bigger which can let the product press to the other cavity more closely, for sealing of second injection.
9, when second injecting, we must be sure whether the plastic flow will rush out the first forming product, if it is possible; we must try to find way.
10, before a and b plate closing, please pay attention to slider and lifter of front mold which returns to crush the product. Thus, slider and lifter should return after a and b closing.
11, waterway of 2 parts on both cavity and core must be arranged fully and evenly.
12, because soft plastic reformat easily, mostly we inject hard plastic part on product firstly and then soft plastic part.
Lucia
focaremould@yahoo.com
