3. Injection temperature

Injection temperature is an important factor affecting injection pressure. The barrel of the injection molding machine has 5 to 6 heating sections, and each raw material has its appropriate processing temperature (see the data provided by the material supplier for detailed processing temperature). The injection temperature must be controlled within a certain range. If the temperature is too low, the melt will not plasticize well, which will affect the quality of the molded parts and increase the process difficulty; If the temperature is too high, the raw material is easy to decompose. In the actual injection molding process, the injection temperature is often higher than the barrel temperature, and the higher value is related to the injection rate and material properties, up to 30 ℃. This is caused by the high heat generated by the shearing of the molten material when it passes through the injection port. There are two ways to compensate for this difference in mold flow analysis. One is to try to measure the temperature of the melt during injection molding into the air, and the other is to include the nozzle in modeling.

           4. Holding pressure and time

At the end of the injection molding process, the screw stops rotating and just pushes forward. At this time, the injection molding enters the pressure-holding stage. During the pressure maintaining process, the nozzle of the injection molding machine continuously replenishes the mold cavity to fill the empty volume due to the shrinkage of the parts. If the cavity is filled and the pressure is not maintained, the part will shrink by about 25%, especially the shrinkage trace will be formed at the rib due to excessive shrinkage. The pressure retaining pressure is generally about 85% of the maximum filling pressure, which should be determined according to the actual situation.

           5. Back pressure

Back pressure refers to the pressure to be overcome when the screw reverses and reverses to store material. The use of high back pressure is conducive to the dispersion of pigments and the melting of plastics, but it also prolongs the screw retraction time, reduces the length of plastic fibers, and increases the pressure of the injection molding machine. Therefore, the back pressure should be lower, generally not more than 20% of the injection molding pressure. When injecting foamed plastics, the back pressure should be higher than the pressure formed by the gas, otherwise the screw will be pushed out of the barrel. Some injection molding machines can program back pressure to compensate for the reduction of screw length during melting, which will reduce the input heat and make the temperature drop. However, because the result of this change is difficult to estimate, it is not easy to make corresponding adjustments to the machine.