Composition and structure of plastic injection mold

Plastic injection molds are basically divided into static molds and moving molds. On the injection head side of the injection molding machine, the gate with the gate sleeve is a static mold. The static mold generally consists of a gate sleeve, a backing plate, and a template.

The structure and composition of the plastic injection mold

The gate sleeve is generally a standard part, and it is not recommended to cancel it unless there is a special reason. The use of the gate sleeve is conducive to the installation of molds and easy replacement, without having to polish it by yourself. Some special mold gate sleeves can be drilled out or cut with a taper line. When some molds must be demolded statically, a static mold release mechanism must be added. The structure of the movable mold is generally a movable template, a movable mold backing plate, a demolding mechanism, a mold foot and a mounting plate.

In addition to the ejection lever and the return lever in the ejection mechanism, some molds also need to add springs to achieve functions such as automatic ejection. There are also guide pillars, cooling water holes, flow channels, etc., which are also essential mold structures. Of course, the slanted guide mold also has a slanted guide box, a slanted guide post, and the like. When designing a mold for a product, the basic structure size of the mold must first be set to prepare materials to accelerate the speed of mold manufacturing. For complex products, product drawings should be drawn first, and then the size of the mold should be determined.

The current molds are basically heat treated to increase the hardness of the molds and increase the service life of the molds. Before the heat treatment, the template is preliminarily processed: drill guide 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 oblique guide box. At present, the templates of ordinary precision molds generally use cr12, cr12mov and some professional mold steels. The hardness of cr12 should not be too high. It often cracks at 60 HRC, and the common hardness of the template is generally about HRC 55. The hardness of the core can be above HRC58. If the material is 3Cr2w8v, the hardness of the surface should be nitrided after manufacturing. 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, defects will easily occur. It is easy to produce a serpentine flow without any obstruction. For demanding products, overflow and exhaust should also be designed. The overflow can be used with a ejector pin, do not have an overflow flash on the template, so as not to affect the mold life. Software for designing molds is also increasing, and most people rarely use pencils to draw mold drawings.
Plastic mold is an abbreviation for a combination mold for compression molding, extrusion, injection, blow molding and low foam molding. The coordinated changes of the convex and concave molds and the auxiliary molding system can process a series of plastic parts of different shapes and sizes. In order to meet the needs of molded parts, we need to pay attention to some matters when purchasing plastic molds , and put forward corresponding requirements. The following selection of a more suitable plastic mold needs to meet the following six requirements.

How to buy plastic injection mold?

1. High corrosion resistance Many resins and additives have a corrosive effect on the surface of the cavity. This corrosion causes the surface of the cavity to dissolve and peel off the metal, the surface condition becomes worse, and the quality of the plastic parts becomes worse. Therefore, it is best to use corrosion-resistant steel or chrome-plated and samarium-nickel on the cavity surface.

2. Good abrasion resistance The gloss and accuracy of the surface of plastic and plastic parts are directly related to the abrasion resistance of the surface of the cavity of the plastic mold, especially when some plastics are added with glass fiber, inorganic fillers and certain pigments. Together with the plastic melt, it flows at a rapid speed in the flow channel and the mold cavity, and the friction on the surface of the cavity is very large. If the material is not abrasion-resistant, it will wear quickly and damage the quality of the plastic part.

3. Good dimensional stability During plastic molding, the temperature of the cavity of the plastic mold must reach above 300 ° C. For this reason, it is best to select a tool steel (heat-treated steel) that has been appropriately tempered. Otherwise, the microstructure of the material will be changed, which will cause the size change of the plastic mold.

4, easy to process mold parts are mostly made of metal materials, and some structural shapes are still very complex. In order to shorten the production cycle and improve efficiency, mold materials are required to be easily processed into the shape and accuracy required by drawings.

5. Good polishing performance Plastic and plastic parts usually require good gloss and surface conditions, so the roughness of the cavity surface is very small. In this way, the surface of the cavity must be surface processed, such as polishing and grinding. Therefore, the selected steel should not contain rough impurities and pores.

6. Little influence by heat treatment In order to improve the hardness and abrasion resistance, plastic molds are generally heat treated, but this treatment should make the size change small. Therefore, it is best to use pre-hardened steel that can be machined.