Some points about designing plastic injection molds

Nowadays, software drawing is generally used. When designing, if there is no product drawing, it is difficult to play the advantages of software drawing in a complicated mold drawing. After the product map is drawn, save the bottom, and then use the size drive or scaling to generate the production graphics. It is also important to save the drawings. The most direct method is to print one copy for a long time, but it can't be modified. There is no guarantee for saving it on the floppy disk. It may be "unformatted" prompts tomorrow; the hard disk is also a consumable item. If you have a burner, it's best to burn it on the CD; now the network is also available to us.

Make your drawings can be stored anywhere in the world. Network hard drives like myspace have stable performance and easy operation. You can use 300M space, but the virtual hard disk I used in China is still not good. You obviously have something stored. However, it refused to recognize it as "database connection error".

Since it is a chain structure, the direction of shrinkage of the plastic during processing is also related to the orientation and cooling shrinkage of the molecular chain of the polymer under stress, and the shrinkage in the flow direction is more than the shrinkage in the vertical direction. Product shrinkage is also related to the shape of the product, gate, thermal expansion and contraction, temperature, holding time and internal stress. Generally, the range of shrinkage provided in the book is wide. In practical applications, the wall thickness and structure of the product and the size and orientation of the temperature and pressure during injection molding are determined. If the general product does not have a core support, the shrinkage should be larger. The plastic injection mold is basically divided into a static mold and a dynamic mold.

In the injection molding machine, the sprue sleeve on the side of the injection head is a static mold. The static mold generally consists of a sprue sleeve, a back plate and a template. The simple mold (especially the mold without a core mold) can also be used without the back plate. Just use a thicker template. The sprue bushings are generally standard and are not recommended for special reasons unless cancelled. The use of the sprue sleeve facilitates the installation of the mold, is easy to replace, and does not need to be polished by itself. Some special mold sprue sleeves can be drilled or cut with taper lines. When some molds must be demoulded, the static mold release mechanism must be added. The structure of the movable mold is generally a movable template, a movable mold plate, a demolding mechanism, and a die and an installation fixing plate.

The gate is directly related to the beauty of the plastic part. If the gate design is not good, it is easy to produce defects. Snake flow is easily generated without any blockage. For products with high requirements, overflow and exhaust should also be designed. The ejector can be used in the overflow, and there is no overflow burr on the stencil to affect the life of the mold.

In addition to the stripping rod and the return rod, the parting mold also adds a spring to realize functions such as automatic demoulding. There is also a basic structure of a mold which is indispensable for a guide post, a cooling water hole, a flow path, and the like. Of course, the oblique guiding mold also has a slanting guide box, a slanting guide column and the like. When designing a mold for a product, the basic structural dimensions of the mold must first be set to prepare the material to speed up the mold manufacturing. Complex products should be drawn first, and then the size of the mold. The current mold is basically subjected to heat treatment to increase the hardness of the mold and increase the service life of the mold. Before the heat treatment, the template is firstly processed: drill the guide post hole, return hole (moving mold), cavity hole, screw hole, gate hole (static mold), pull hole (moving mold), cooling Water holes, etc., milling the flow path, cavity, and some molds should also be milled to the oblique guide box. Today's ordinary precision mold templates generally use Cr12, Cr12Mov and some professional mold steel, Cr12 and other hardness can not be too high, often cracked at HRC 60 degrees, the common hardness of the template is generally about HRC55 degrees. The hardness of the core can be above HRC58. If the material is 3Cr2W8v, the hardness of the surface should be nitrided after manufacture, the hardness should be above HRC58, and the thicker the nitride layer should be.

The design of plastic injection molds must first have a certain understanding of plastics. The main component of plastics is polymers. As we often say, ABS plastic is made of acrylonitrile, butadiene and styrene by emulsion, bulk or suspension polymerization, which has the superior performance and moldability of three monomers. Under the temperature and pressure, it is injected into the mold cavity to generate flow deformation, and the shape of the cavity is obtained. After the pressure is cooled, it is ejected into a plastic product. The molecules of the polymer generally have a chain structure, and the linear molecular chain and the branched molecular molecule are considered to be thermoplastics, which can be repeatedly heated and cooled, and subjected to cross-linking reaction by heating a plurality of molecules to form a network-like molecular structure. Plastics are usually one-time and cannot be re-injected, that is, thermosetting plastics.