Plastic injection molding solutions to problems

In the injection molding process, mainly due to product defects is

1) molding plastic parts design is not

(2) mold design, manufacturing unreasonable;

Nature (3) of the plastic itself;

4) the inappropriate choice of molding process conditions;

(5) injection molding machine model matching unreasonable. Therefore, to solve the problem of plastic injection molding bad, we can start from the injection machine, molding conditions and mold (including product design), plastics and so on. However, the reasons for seeking to defect from the plastic is very difficult, because the defect molded parts are often made in front of several reasons why the mutual coupling formed by the action (see Table 1), it causes the defect depends on the vast project experience and judgment of the technical staff

Countermeasure

1, the rational design of plastic parts

Design of plastic parts to uniform thickness, it is because the molding cycle cooling time is never a given thickness of plastic parts, if a part of the thick, partially affected by the thickness of the cooling time and extended cycle times, reduce the efficiency of the molded ; Also, if uneven wall thickness, is caused by uneven shrinkage, resulting in reduced pit or internal stress, as well as deformation or cracking. Plastic stripping designed to have a certain slope to ensure the smooth stripping of plastic parts. Because the internal stress tends to be concentrated at the intersection of the surface and the surface, i.e., focused on the corner, in order to reduce distortion in the root fillet can design stress dispersion, while also improving the fluidity of the plastic, but also conducive to the release. Sometimes in order to enhance the plastic parts or to increase the fluidity of plastics, set the ribs, pay attention to the stripping direction to be provided with a reverse slope.

2. Improved mold design

Gate design is an important and complex issue, in the form of a direct gate, side gate, submarine gate, gate and other points. How to choose the actual manufacturing arrangement runner, gate type and position, mostly by the shape of plastic parts, dimensional accuracy and appearance requirements and decisions, while its runner-type system is varied. In order to make the plastic filling process ends at the same time, the gate and the runner must be balanced. In the injection molding process, the injection into the mold cavity of the molten plastic temperature is about 200300 ℃, but when removed from the mold cavity after the plastic parts which cure temperature 60 0C or less, the mold temperature is lowered due to the cooling water through the heat away, so a reasonable cooling system directly affects the dimensional accuracy of plastic parts and mechanical properties. In the actual injection mold exhaust problem must also be considered, if the injection mold cavity gas can not be discharged smoothly, will make products bubble, loose, filling dissatisfaction, welding is not strong, the workpiece surface fat bird, or at the time of the injection due produced by high-temperature gas is compressed so that the bottom parts of the charred charring. Common exhaust many ways, for example using an exhaust vent grooves, with the gap such as exhaust. Set the top of the system should be considered in order to avoid distortion, bleaching, catching phenomenon.

3, adjusting the injection molding process

For the different types and grades of plastics, which drying and molding the melt temperature are clearly defined, and therefore in the development of the molding process, according to the specific requirements of products used in plastics, to determine its drying and heating barrel temperature. Pressure is also forming important process parameters, the pressure into the injection pressure and holding pressure in two stages. Injection pressure is pushing the screw will melt into the mold cavity pressure used, packing pressure is nearing completion filling in, inject the melt is cooled and solidified to complement the products due to volume shrinkage caused by replenishment process of pressure used, in molding process, the right choice injection pressure and holding pressure and injection speed, is the key to the success of the molding process. Currently, most computer-controlled injection molding machines, injection to the decentralized approach.

4, the choice of efficient equipment

Selection of the injection molding machine should consider matching the mold clamping force is necessary to meet the requirements can not be too large, each injection is not less than the plastic parts plus runner condensate material weight. Pay attention to regular maintenance of equipment to ensure the normal operation of the production. IV Conclusion

Since the injection molding is a complex process, a lot of factors affecting the molding products, often a result of improved product defects caused by forming factors, may cause another previously insignificant factors stand out, make the product the emergence of new defects. Thus, in the development and adjustment molding process, not only to build pressure, speed, the right combination of temperature and the right choice for screw speed, injection pressure screw each position, holding pressure. Back pressure and cooling time and other issues should be fully valued. Advanced tooling, efficient equipment and reasonable modern injection molding process is the production of three elements. Therefore, in addition to research as a mold designer and mold structure and processing technology, but also a certain amount of injection molding technology, especially for products in the molding process common defects and solutions should have a full understanding.

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