Most of the plastic electronic components are injection-molded. Since these plastic parts have high design precision and are processed by special engineering plastics, conventional injection molding cannot be used for these plastic parts, and precision injection molding technology must be adopted. In order to ensure the performance, quality and reliability of these precision plastic parts and the stability of long-term use, injection molding of plastic products with high quality and meeting product design requirements must be applied to plastic materials, injection molding equipment and mold design and injection molding, and injection molding. The site management is perfected.
We usually say that precision injection molding means that the precision of the molded product should meet strict dimensional tolerances, geometric tolerances and surface roughness. There are many relevant conditions for precision injection molding, and the most essential are the four basic factors of plastic materials, injection molds, injection molding processes and injection molding equipment. When designing plastic products, engineering plastic materials should be selected first, and engineering plastics capable of precision injection molding must use materials with high mechanical properties, dimensional stability, good creep resistance and environmental stress cracking resistance. Secondly, the appropriate injection molding machine should be selected according to the selected plastic material, the dimensional accuracy of the finished product, the weight of the part, the quality requirements and the expected mold structure. In the process of processing, the factors affecting precision injection molding products mainly come from the temperature of the mold, the control of the injection molding process, and the variation range of the ambient temperature and humidity at the production site and the annealing treatment of the acquired products.
For precision injection molding, mold is one of the keys to obtain precision plastic products that meet the quality requirements. The molds for precision injection molding should meet the requirements of product size, precision and shape. The mold materials should be strictly selected. However, even if the precision and size of the mold are the same, the actual size of the molded plastic product may be inconsistent due to the difference in the amount of shrinkage. Therefore, effective control of shrinkage of plastic products is very important in precision injection molding technology.
The reasonable design of the injection mold will directly affect the shrinkage of the plastic product. Since the mold cavity size is determined by the size of the plastic product plus the estimated shrinkage rate, the shrinkage rate is determined by the plastic manufacturer or engineering plastics manual. A recommended range of values ​​that are related not only to the gate form of the mold, to the location and distribution of the gate, but also to the crystal orientation (anisotropic) of the engineering plastic, the shape and size of the plastic product, and the distance to the gate. It is related to the location and is closely related to the mold cooling distribution system. The main factors affecting plastic shrinkage are heat shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery. These factors are related to the molding conditions or operating conditions of precision injection molded products. Therefore, the relationship between these influencing factors and injection molding conditions and their apparent factors must be considered when designing the mold, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature, mold structure and gate form and distribution. And the influence of the cross-sectional area of ​​the gate, the wall thickness of the product, the content of the reinforcing filler in the plastic material, the crystallinity and orientation of the plastic material. The influence of the above factors is also different due to different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in the injection molding machine.
Because the injection molding process is the process of converting plastic from solid (powder or pellet) to liquid (melt) to solid (product). From the pellets to the melt, from the melt to the product, through the temperature field, stress field, flow field and density field, under the joint action of these fields, different plastics (thermosetting or thermoplastic, crystalline) Or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structural morphology and rheological properties. Any factors that affect the above "field" will affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products. Thus, the intrinsic link between process factors and polymer properties, structural morphology, and plastics is manifested by plastics. Analysis of these intrinsic links is of great significance for the rational preparation of injection molding process, rational design and manufacturing of molds according to drawings, and even the selection of injection molding equipment. Precision injection molding and ordinary injection molding also differ in injection pressure and injection rate. Precision injection molding often uses high pressure or ultra high pressure injection and high speed injection to obtain a small molding shrinkage. In view of the above various reasons, in addition to considering the design elements of general molds, the following points must be considered when designing precision injection molds: 1 using appropriate mold dimensional tolerances; 2 preventing mold shrinkage error; 3 preventing injection molding deformation; Prevent demoulding from occurring; 5 minimize mold manufacturing errors; 6 prevent mold accuracy errors; 7 maintain mold accuracy.
The shrinkage rate will change due to the injection pressure. Therefore, for a single cavity mold, the cavity pressure in the cavity should be as uniform as possible; as for the multi-cavity mold, the cavity pressure between the cavities should be small. In the case of single cavity multi-gate or multi-cavity multi-gate, it must be injected at the same injection pressure to make the cavity pressure uniform. To do this, you must ensure that the gates are balanced. In order to make the cavity pressure in the cavity uniform, it is preferable to keep the pressure at the gate entrance consistent. The equilibrium of the pressure at the gate is related to the flow resistance in the runner. Therefore, before the gate pressure reaches equilibrium, the flow should be balanced first.
Since the melt temperature and the mold temperature have an effect on the actual shrinkage rate, in order to facilitate the determination of the molding conditions, it is necessary to pay attention to the arrangement of the cavities when designing the precision injection mold cavity. Because the molten plastic brings heat into the mold, the temperature gradient of the mold generally surrounds the cavity, forming a concentric shape centered on the main channel.
Therefore, design measures such as flow channel equalization, cavity arrangement, and concentric circular arrangement centered on the main channel are necessary to reduce the shrinkage error between the cavities, to extend the allowable range of molding conditions, and to reduce costs. . The cavity arrangement of precision injection molds should meet the requirements of flow channel equalization and centering on the main channel, and the cavity arrangement with the main channel as the symmetry line must be adopted, otherwise the shrinkage rate difference of each cavity will be caused. .
Since the mold temperature has a great influence on the molding shrinkage rate, and also directly affects the mechanical properties of the injection molded article, and also causes various molding defects such as fading on the surface of the product, it is necessary to keep the toucher within the specified temperature range, and also The mold temperature is not changed with time. The temperature difference between the cavities of the multi-cavity mold must also not change. For this reason, temperature control measures for heating or cooling the mold must be taken in the mold design, and in order to minimize the temperature difference between the mold cavities, the design of the temperature control-cooling circuit must be paid attention to. In the cavity and core temperature control loop, there are mainly two connection modes: series cooling and parallel cooling.
From the perspective of heat exchange efficiency, the flow of cooling water should be turbulent. However, in a parallel cooling circuit, the flow rate in one circuit that is split is smaller than the flow rate in the series cooling circuit, which may result in laminar flow, and the flow actually entering each circuit is not necessarily the same. Since the temperature of the cooling water entering each circuit is the same, the temperature of each cavity should be the same, but in fact, the flow rate in each circuit is different, and the cooling capacity of each circuit is also different, so that the temperature of each cavity is impossible. Consistent. The disadvantage of using a series cooling circuit is that the flow resistance of the cooling water is large, and the temperature of the cooling water at the inlet of the frontmost cavity is significantly different from the temperature of the cooling water at the inlet of the last cavity. The temperature difference between the cooling water inlet and outlet varies with the flow rate. For small precision injection molds for processing plastic parts, it is generally preferable to use a series cooling circuit from the viewpoint of reducing the mold cost. If the performance of the mold temperature control controller (machine) used can control the flow rate of the cooling water within 2 ° C, the temperature difference of each cavity can be maintained at a maximum of 2 ° C.
The mold cavity and core should have their own cooling water circuit system. In the design of the cooling circuit, the thermal resistance of the circuit structure is different due to the difference in heat taken from the cavity and the core, and the temperature of the water at the inlet of the cavity and the core generates a large temperature difference. If the same system is used, the design of the cooling circuit is also difficult. In general, small injection mold cores for plastic parts are very small, and it is very difficult to use a cooling water system. If possible, cores made of bronze may be used, and for solid bronze cores, plug-in cooling may be used. In addition, when taking measures against warpage of the injection molded article, it is also desirable to maintain a certain temperature difference between the cavity and the core. Therefore, the temperature adjustment and control should be separately performed when the juice cavity and the core cooling circuit are set. In order to maintain the accuracy of the mold under the injection pressure and clamping force, the feasibility of grinding, grinding and polishing the cavity parts must be considered when designing the mold structure. Although the processing of the cavity and the core has reached the requirement of high precision, and the shrinkage rate is the same as expected, due to the center deviation during molding, the relevant dimensions of the inside and the outside of the formed product are difficult to reach the plastic. Design requirements for components. In order to maintain the dimensional accuracy of the dynamic and fixed model cavity on the parting surface, in addition to the guide column and guide sleeve centering commonly used in conventional molds, it is necessary to add a positioning position such as a tapered positioning pin or a wedge block to ensure accurate positioning accuracy. ,reliable.
Precision injection molding technology is the main and key production technology of plastic parts, and the design of precision injection mold is the main part of this production technology. Reasonable design of precision injection mold is the basis and necessary prerequisite for obtaining precision products. By reasonably determining the size and tolerance of the mold, taking measures to prevent shrinkage of the injection molded product, injection molding deformation, demoulding deformation, overflow, etc., as well as technical measures such as ensuring mold precision, and adopting the correct precision injection molding process, applicable engineering Plastics Materials and precision injection molding equipment to achieve the best match!
Lathe And Milling Processing Parts
Lathe and milling processing parts refer to precision metal parts that are manufactured using lathe and milling machines. These machines use computer numerical control (CNC) to produce parts to exacting specifications with high accuracy and precision.
Lathe machines are used to produce parts that have a cylindrical shape, while milling machines are used to produce parts with complex shapes and irregular surfaces. The combination of these two machining processes allows for the creation of parts with different shapes, sizes, and complexities.
Lathe and milling processing parts are used in a wide range of industries, including aerospace, automotive, electronics, and medical. These parts are typically produced from a variety of metals, including steel, aluminum, brass, and copper.
The advantages of lathe and milling processing parts are their high accuracy and precision. The CNC machines used in their production are programmed to make precise cuts and movements, resulting in parts that are consistent and accurate. This is especially beneficial in industries where quality control is essential for safety and reliability.
Another benefit of lathe and milling processing parts is their versatility. The combination of the two machining processes allows for the creation of a wide range of parts with complex shapes and irregular surfaces. These parts can also be produced in large quantities, allowing for efficient mass production.
Lathe and milling processing parts provide a cost-effective solution for many manufacturing needs. The precision of these machines means that parts can be manufactured to exact specifications, minimizing the need for additional processing or finishing. This can result in significant cost savings for manufacturers and ultimately lower prices for consumers.
In conclusion, lathe and milling processing parts are essential components in the manufacturing industry. These precision parts provide accuracy, versatility, and cost-effectiveness for a wide range of applications. With the ability to produce parts with high accuracy and precision, lathe and milling processing parts offer a powerful solution for many manufacturing needs.
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