About Two Shot Injection Molding
Two shot plastic injectio molding is used for manufacturing a single part with two different kinds of materials or colors, like the soft touch holder, key cap, teethbrush and the outer gasket of a electical device etc.. The benefit is that the part can be formed by one time injection process, saving the post moulding process like assembling. To start two shot injectio molding, we need:
- Two shot mold – it can be seen as a combination of two different molds with a rotating table inside. The moving halves of the two molds have the same structure, same runner system and the same height. The fixed halves have the same height but different cavities, different ejecting system and different runner layout. The gate type of the first shot should be point gate or sub gate in order that the harden runner could be removed when ejected.
- Two shot injection molding machine – it is similar with traditional injection molding machine, but has two independent injection units, each of which shoots different materials into two different molds. There is a mechanical system on the machine, for example a pivot shaft, matching the rotating mechanism of the mold to move the molded part from first shot to the second.
- Key points – The metling point of the material on first shot should be higher than the second one and two materials should be adhesive to each other. Shrinkage rate of the second shot can be the same with the first one.