The quality of plastic melt injection is directly related to the effect of gas-assisted injection molding, so the error of the accuracy of the injection molding machine will affect the stability of gas-assisted injection molding.
2. In the injection molding process, pay attention to the following two points
1 The melt thickness dimension at the air passage of the plastic part can be controlled by changing the delay time. The delay time is the period from the end of the injection of the plastic melt to the start of the entry of the high pressure gas, which is very short-lived, but has an important influence on the quality of the molding. Reasonable delay time is beneficial to gas penetration and plastic melt filling. If the delay time is too short, the high pressure gas is easy to diverge, the shape of the air passage is irregular, and the hollowing rate is not guaranteed.
2 The higher injection speed is beneficial to the penetration of high pressure gas and the filling of plastic melt. However, too high an injection speed is likely to cause defects on the surface of the plastic part.
3. The mold should pay attention to the following three points in determining the gas injection speed and pressure:
1 The speed of gas injection should be determined by the size of the airway. The automobile elbow is a plastic piece with a large air passage, and a too high gas injection speed is liable to cause surface flow marks, gas lines and the like. If the air passage of the mold is small or the flow is long, increasing the gas injection speed can improve the quality of the surface of the plastic part, but if the gas injection speed is too fast, the plastic melt may be blown through.
2 The plastic melt will dissolve some gas in the boundary layer in contact with the inert gas. If the plastic melt is not fully solidified after the pressure is maintained, the gas will expand when the pressure is released, resulting in air bubbles on the inner surface of the airway. The more gas is dissolved in the melt surface layer. Therefore, the pressure of the inert gas should be lower when filling the mold. When the pressure is maintained, the pressure of the shrinkage gas is too small, so that the mold filling is insufficient or the surface of the plastic part is shrunk; the gas pressure is too high, and the plastic melt is easy. Blowed through. The gas injection pressure also depends on the fluidity of the plastic melt. The plastic used in the mold has good fluidity, and the injection molding process uses a low injection pressure of 10 MPa.