Precision Mold Processing And Forming Process Characteristics

The injection molding machine must be able to precisely control the injection molding clamping force of its clamping system, otherwise, too large or too small clamping force will have a negative impact on the accuracy of plastic parts. For example, when the clamping force is too large, the precision of precision injection molding will decrease due to the excessive elastic deformation of the mold. The silent injection molding machine must have a strong plasticizing ability, and also ensure that the material can get a good plasticizing effect. Therefore, in addition to the screw must adopt a larger driving torque, the control system should also be able to stepless speed regulation of the screw.

      Increasing the injection pressure can increase the allowable flow distance ratio, so it helps to improve the specific molding properties of plastic parts and can form ultra-thin wall thickness plastic parts. For example, for polycarbonate, when the injection pressure is 77MPa, the wall thickness of the plastic part that can be formed is about 0.2-0.8mm, and when the injection pressure is increased to 392MPa, the wall thickness of the plastic part can be reduced to 0.15-0.6mm.

      The control system of the precision injection molding machine generally has a high control precision, which is required by the precision of the precision injection molding itself. The injection molding machine control system must ensure that various injection molding process parameters have good repeatability to avoid changes in precision injection molding accuracy due to fluctuations in process parameters. For this reason, precision injection molding machines generally adopt multi-stage feedback control for process parameters such as injection volume, injection pressure, injection speed, as well as holding pressure, screw back pressure and screw speed, and for barrel and nozzle temperature. PID controller.

      Increasing the injection pressure helps to give full play to the effect of the injection speed. This is because plastic parts with complex shapes generally have to use a faster injection speed, and the faster injection speed must be guaranteed by a higher injection pressure. During injection molding, if a faster injection speed is used, it can not only mold plastic parts with complex shapes, but also reduce the dimensional tolerance of plastic parts. This conclusion has been confirmed.

      Temperature has a great influence on the molding quality of plastic parts. For precision injection molding, there is not only the problem of temperature, but also the problem of temperature control accuracy. Obviously, in the precision injection molding process, if the temperature control is not accurate, the fluidity of the plastic melt and the molding performance and shrinkage rate of the plastic part will not be stable, so the accuracy of the plastic part cannot be guaranteed. From a different point of view, when using precision injection molding, both for barrels and nozzles, or for injection mold manufacturing, their temperature range must be strictly controlled.

Increasing the injection pressure can increase the volume compression of the plastic melt, increase its density, reduce the linear expansion coefficient, and reduce the shrinkage rate of the plastic part and the fluctuation value of the shrinkage rate. For example, for polyoxymethylene with a temperature of 209 °C, when a plastic part with a wall thickness of 3 mm is formed by a warm mold of 60 °C and an injection pressure of 98 MPa, the shrinkage rate of the injection molded part is close to 2.5%. , When the injection pressure is increased to 392MPa, the shrinkage rate of the plastic part can be reduced to about 0.5%.

In the production of precision injection molding, in order to ensure the accuracy of the plastic parts, in addition to strictly controlling the temperature of the barrel, nozzle and mold, it is also necessary to pay attention to the influence of the ambient temperature on the accuracy of the plastic parts after demolding. Because precision injection molding has high precision requirements, they generally need to be carried out on a special precision injection molding machine. Precision injection molding machines generally use relatively large injection power. In addition to meeting the requirements of injection pressure and injection speed, the injection power itself will also play a certain role in improving plastic parts.