What is the composition and structure of plastic injection molds?

Plastic injection molds are basically divided into static molds and dynamic molds. The one with sprue sleeve on the side of the injection head of the injection molding machine is a static mold. The static mold is generally composed of a sprue sleeve, a backing plate, and a template. Simple molds can also use a thicker template without using a backing plate. The sprue sleeve is generally a standard part, and it is not recommended to cancel it unless there are special reasons.

The use of the sprue sleeve is conducive to the installation of the mold, the replacement is convenient, and there is no need to polish it yourself. Some special mold sprue sleeves can be drilled out or cut with a tapered wire. When part of the mold must be released from the static mold, a static mold release mechanism must be added. The structure of the moving mold is generally a moving template, a moving mold backing plate, a demolding mechanism, a mold foot and a fixed plate for installation.

In addition to the stripping rod, there is also a return rod in the demolding mechanism, and some molds also need to add springs to achieve functions such as automatic demoulding. There are also guide pillars, cooling water holes, runners, etc., which are also essential to the basic structure of the mold. Of course, there are also inclined guide boxes, inclined guide columns, etc. When designing a mold for a product, the basic structural dimensions of the mold must first be set to prepare materials to speed up the mold manufacturing. For complex products, the product map should be drawn first, and then the size of the mold should be determined.

The current mold basically needs to be heat treated to increase the hardness of the mold and improve the service life of the mold. Before the heat treatment, the template is preliminarily processed: drill the guide post hole, return hole (moving mold), cavity hole, screw hole, gate sleeve hole (moving mold) cooling water hole, etc., mill the runner, Cavities, some molds should also be milled inclined guide boxes. Now the templates of ordinary precision molds generally use cr12, cr12mov and some professional mold steels. The hardness of cr12 and other molds should not be too high, and they often crack at HRC60 degrees. The common hardness of templates is generally about HRC55 degrees. The hardness of the core can be above HRC58. If the material is 3Cr2w8v, the surface hardness should be nitrided after manufacturing, and the hardness should be above HRC58, and the thicker the nitrided layer, the better.

The gate is directly related to the aesthetics of the plastic part. If the gate design is not good, it is easy to produce defects. It is easy to generate serpentine flow without any obstruction. For products with high requirements, overflow and exhaust should also be designed. The ejector can be used at the overflow, and there should be no overflow flash on the template, so as not to affect the life of the mold.