Asia Billion is a trustworthy partner for the custom precision injection molding and tooling. we service for global market for many years and here we would like to show some our thinking about the precision injection molding and mold making some key points as below.
In the early stage of designing precision plastic products, we need to select the correct engineering material according to their using environment and functions. The appropriate injection molding machine is selected based on the selected plastic raw material, the dimensional accuracy of the finished product, the weight of the part, the quality requirements and the desired mold structure. it is important and need to match for the different combination.
Therefore, design ideals such as flow channel balance, cavity layout, venting and material filling are necessary to reduce the shrinkage error between the different cavities, it is also necessary to extend the allowable range of molding conditions and reduce costs . The cavity layout of the precision injection mold meets the requirements of flow channel balance, the main channel as the center and the cavity layout with the main channel as the symmetry line must be adopted. that mean the different part can be filled material with same conditions.
Since the mold temperature has a great influence on the molding shrinkage rate, it also directly affects the mechanical properties of the injection molded parts, and also causes various molding defects such as flow marks on the surface of the product, so the mold must be kept within the specified temperature range and the mold temperature does not change with different time.
The temperature difference between of the multi-cavity mold must need same for each one. 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 connection cooling and parallel connection cooling.
From the perspective of heat exchange efficiency, the flow of cooling water is turbulent. However, in a parallel cooling circuit, the flow in one circuit that is split is smaller than the flow 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 is 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 not uniform. . 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 entrance of the front 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 depending on the flow rate. For small precision injection molds, it is generally preferable to use a series cooling circuit from the viewpoint of reducing the mold cost.
The mold cavity and core 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, 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 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 can be separately performed when designing the cooling circuit of the cavity and the core.
In order to maintain the precision of the mold under the injection pressure and clamping force, the feasibility of grinding, machining 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 line surface, in addition to the guide pin and guide bushing commonly use in conventional molds, positioning points such as tapered positioning pins or wedge blocks must be added to ensure positioning accuracy is accurate and reliable.
The material for making precision injection molds should be high-quality alloy tool steel with high mechanical properties and small thermal creep. The mold materials for making cavities and runners should be selected with strict heating treatment, high hardness, good wear resistance and strong corrosion resistance. Materials resistant to heat deformation, while also considering the ease of machining and electrical processing and economics. In order to prevent the occurrence of aging changes and to change the dimensional accuracy of the mold, it is necessary to specify a tempering treatment or a low temperature treatment for reducing the retained austenite structure of the heat treatment of the mold material when designing the mold.
For easy damaged parts of precision injection molds, especially for cavities, cores and other often using parts, the possibility of repair should be considered in the design to maintain high precision level after mold repair.
Whether the mold venting design is reasonable or not is also a major factor in determining mold accuracy. Most of the precision products are formed by using engineering plastics. In order to ensure the good fluidity of plastics and the consistency of shrinkage of plastic molecules in the molding process, the mold temperature is generally required to be formed in a certain range. When the temperature of the mold is too high, the expansion of the mold parts will cause difficulty in the gas venting in the mold, it will cause the product to be air trapped, burning, and short shot. Therefore, the cavity of the mold is designed to use more insert parts and ejector accessories. The venting groove should be designed on the moving surface to prevent pin block.
Proper design of precision injection molds is the basis and necessary for obtaining precision injection molding products. By reasonably determining the size and tolerance of the mold, taking actions to prevent shrinkage of the injection molded product, injection molding deformation, demoulding deformation, flash or burrs, etc., as well as technical measures for mold precision, use the correct precision injection molding process parameters, applicable engineering plastics Materials and precision injection molding equipment to achieve the best match for all these combination is great significance. it is the only way to improving the quality, reliability performance of precision plastic parts, reducing production costs and improving production efficiency.
Asia Billion are a small/middle size professional precision injection molding and tooling manufacture as well as metal machined components in South China .Our stability quality, Lower price and good service has given our customer a big confidence to new production development and market competition . ISO 9001 certified and TS 16949 compliance, each project with very competitive price and quality assurance.
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