1. Plastic material
The complexity of the properties of plastic materials determines the complexity of the injection molding process. The performance of plastic materials varies greatly according to different varieties, different brand sizes, different manufacturers, and even different batches. Different performance parameters can lead to completely different molding results.
2). Injection temperature
The melt flows into the cooled cavity, dissipateing heat due to thermal conduction. At the same time, due to shearing and the generation of heat, this part of the heat may be more or less heat loss than heat transfer, mainly depending on injection molding conditions. The viscosity of the melt becomes lower as the temperature increases. Thus, the higher the injection temperature, the lower the viscosity of the melt and the less filling pressure is required. At the same time, the injection temperature is also limited by the temperature of thermal degradation and decomposition.
3). Mold temperature
The lower the mold temperature, the faster the heat is lost due to thermal conduction, the lower the temperature of the melt and the worse the flow. This is particularly true when lower injection rates are used.
4). Injection time
The effect of injection time on the injection molding process is expressed in three ways:
(1) Shorten the injection time, the shearing rate in the melt will also be increased, in order to fill the cavity required injection pressure should also be increased.
(2) Shorten the injection time, the shearing rate in the melt is increased, because of the shearing thinning characteristics of the plastic melt, the viscosity of the melt is reduced, in order to fill the cavity required injection pressure should also be reduced.
(3) Shorten the injection time, the shearing rate in the melt increases, the greater the shear heat, and the less heat is lost due to heat conduction, so the melt temperature is high, the viscosity is lower, in order to fill the cavity required injection pressure should also be reduced. As a result of the joint action of the above three cases, the curve of injection pressure required to fill the cavity is presented in a “U” shape. That is, there is an injection time at which the minimum injection pressure is required