Plastic injection mold is basically divided into static mold and dynamic mold. The mold with gate sleeve on the injection head side of the injection molding machine is static mold. The static mold is generally composed of gate sleeve, backup plate and template. Simple mold can also use thicker template instead of backup plate. Generally, the gate sleeve is a standard part, and it is not recommended to cancel it except for special reasons. The use of the gate sleeve is conducive to the installation of the mold, easy to replace, without polishing. Some special mold gate sleeve can be drilled out or cut with taper line. When part of the mold must be demoulded by the static mold, the demoulding mechanism of the static mold must also be added. The structure of the moving die is generally the moving die plate, the backing plate of the moving die, the demoulding mechanism, the die foot and the fixed plate of the installation machine.

In the demoulding mechanism, in addition to the stripper bar, there is a return bar, and some molds also need to add springs to realize functions such as automatic demoulding. There are guide pillars, cooling water holes, flow channels, etc. are also essential to the basic structure of the mold. Of course, there are inclined guide box, inclined guide pillar and so on. When designing a mold for a product, we should first set the basic structure size of the mold to prepare materials, so as to speed up the speed of mold manufacturing. Complex products should first draw a good product drawing, and then determine the size of the mold.

Now the mold basically to heat treatment, increase the hardness of the mold, improve the service life of the mold. Before the heat treatment, the template should be preliminarily processed: drill the guide post hole, return hole (dynamic mold), cavity hole, screw hole, gate sleeve hole (dynamic mold) cooling water hole, etc., mill the runner and cavity, and some molds should also mill the inclined guide box, etc. At present, Cr12, Cr12MoV and some professional die steel are generally used for the formwork of ordinary precision die. The hardness of Cr12 can not be too high, and it often cracks at HRC60 degree. The common hardness of the formwork is about HRC55 degree. The hardness of the core can be above hrc58. If the material is 3Cr2W8V, the hardness of nitrided surface should be above hrc58, and the thicker the nitrided layer, the better.

Gate directly related to the beauty of plastic parts, gate design is not good, easy to produce defects. Snake like flow is easily produced without any obstruction. For products with high requirements, overflow and exhaust shall also be designed. The top bar can be used at overflow place, and there is no overflow edge on the formwork, so it will not affect the die life. More and more software is used to design die, and most of them seldom use pencil to draw mold diagram.