Points of plastic mold design.
Public: 2019-09-30 15:22:39 Views: 242Plastic injection molds are now widely used in all plastic molds and can form complex high-precision plastic products. 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. Plastic injection molds are basically divided into static molds and dynamic molds.
In the injection molding machine, the sprue bushing on the side of the injection head is a static mold. The static mold generally consists of a sprue bushing, a backing plate and a template. The simple mold (especially the mold without the core in the static mold) can also be used without the backing 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 bushing is conducive to the installation of the mold, easy to replace, without polishing. Some special mold sprue sleeves can be drilled or cut with a taper line. When some molds must be demoulded, the static mold release mechanism must be added. The structure of the movable mold is generally a movable formwork, a movable formwork plate, a demolding mechanism, and a die and an installed fixed 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 are also basic structures 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.