The shrinkage rate will change due to injection pressure, therefore, for single cavity molds, the cavity pressure inside the cavity should be as consistent as possible; As for multi cavity molds, the pressure difference between the cavities should be very small. In the case of single cavity multi gate or multi cavity multi gate, it is necessary to inject with the same injection pressure to ensure consistent cavity pressure. To achieve this, it is necessary to ensure that the gate position is balanced. In order to maintain consistent pressure within the mold cavity, it is best to keep the pressure at the entrance of the sprue consistent. The balance of pressure at the gate is related to the flow resistance in the runner, so before the gate pressure reaches balance, the flow should be balanced first.

Due to the influence of melt temperature and mold temperature on the actual shrinkage rate, it is necessary to pay attention to the arrangement of the mold cavity when designing precision injection mold cavities in order to facilitate the determination of molding conditions. Because molten plastic brings heat into the mold, the temperature gradient distribution of the mold is generally around the cavity, forming a concentric circle shape centered on the main channel.

Therefore, design measures such as channel balance, cavity arrangement, and concentric circular arrangement centered on the main channel are necessary to reduce shrinkage errors between cavities, expand the allowable range of molding conditions, and reduce costs. The cavity arrangement of precision injection molds should meet the requirements of balanced flow channels and centered arrangement around the main flow channel, and must adopt a cavity arrangement with the main flow channel as the symmetrical line, otherwise it will cause differences in the shrinkage rate of each cavity.

Due to the significant impact of mold temperature on molding shrinkage rate, it directly affects the mechanical properties of injection molded products and can also cause various molding defects such as surface discoloration. Therefore, it is necessary to keep the mold within the specified temperature range and ensure that the mold temperature does not change over time. The temperature difference between each cavity of a multi cavity mold must not change. Therefore, in mold design, temperature control measures must be taken for heating or cooling the mold. In order to minimize the temperature difference between each cavity of the mold, attention must be paid to the design of the temperature control cooling circuit.

In the temperature control circuit of the cavity and core, there are mainly two connection methods: 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 the diverted circuit is smaller than that in the series cooling circuit, which may result in laminar flow. Moreover, the actual flow rate entering each circuit may not be the same. Due to the same temperature of the cooling water entering each circuit, the temperature of each mold cavity should also be the same. However, in reality, due to the different flow rates in each circuit and the varying cooling capacities of each circuit, the temperature of each mold cavity cannot be consistent.

The disadvantage of using a series cooling circuit is that the flow resistance of the cooling water is high, and there is a significant difference in the temperature of the cooling water at the inlet of the front cavity compared to the inlet of the last cavity. The temperature difference between the inlet and outlet of the cooling water varies with the flow rate.

For small precision injection molds for molding plastic parts, it is generally more suitable to use a series cooling circuit to reduce mold costs. If the performance of the mold temperature machine used can control the flow rate of cooling water within 2 ℃, the maximum temperature difference between each cavity can also be maintained within the range of 2 ℃.

The mold cavity and core should have their own cooling water circuit systems. In the design of the cooling circuit, due to the different heat absorbed from the cavity and core, the thermal resistance of the circuit structure is also different, resulting in a significant temperature difference between the water temperature at the entrance of the cavity and core. If the same system is used, the design of the cooling circuit is also difficult. The cores of small injection molds used for general plastic parts are very small, making it difficult to use cooling water systems. If possible, beryllium bronze material can be used to manufacture the core, and insert cooling method can be used for solid beryllium bronze cores.

In addition, when taking measures to prevent warping of injection molded products, it is also desirable to maintain a certain temperature difference between the cavity and the core. Therefore, when designing the cooling circuit for the cavity and core, it should be possible to separately adjust and control the temperature. In order to maintain the accuracy of the mold under injection pressure and locking 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 core has met the requirements of high precision, and the shrinkage rate is also as expected, due to the center offset during molding, the relevant dimensions of the inner and outer sides of the molded product are difficult to meet the design requirements of plastic parts. In order to maintain the dimensional accuracy of the dynamic and fixed model cavities on the parting surface, in addition to setting conventional guide columns and guide sleeve centers, it is also necessary to install positioning pins such as conical positioning pins or wedge-shaped blocks to ensure accurate and reliable positioning accuracy.

Precision injection molding technology is the main and key production technology for plastic components, and the design of precision injection molding molds is a major part of this production technology. Reasonable design of precision injection molding molds is the foundation and necessary prerequisite for obtaining precision injection molded products. By reasonably determining the size and tolerance of the mold, taking technical measures to prevent shrinkage errors, injection deformation, demolding deformation, overflow, etc. in injection molded products, and ensuring mold accuracy, and using the correct precision injection molding process, applicable engineering plastic materials, and precision injection molding equipment, the best match can be achieved!