Influence of Injection Molding Process Conditions on Products

1) Plastic Materials

The complexity of plastic material properties determines the complexity of the injection molding process. Moreover, the properties of plastic materials can vary greatly depending on the type, grade, and even batch. Different performance parameters may lead to different molding results.

2) Injection Temperature

As the molten plastic enters the cooled mold cavity, it loses heat due to thermal conduction. At the same time, heat is generated due to shear, and this heat may be more or less than the heat lost through conduction, mainly depending on the injection molding conditions. The viscosity of the molten plastic decreases as the temperature rises. Thus, the higher the injection temperature, the lower the viscosity of the melt, and the lower the required filling pressure. However, the injection temperature is also limited by the thermal degradation and decomposition temperatures.

3) Mold Temperature

The lower the mold temperature, the faster the molten plastic loses heat through conduction, resulting in lower melt temperatures and poorer flowability. This phenomenon is especially evident when using lower injection speeds.

4) Injection Time

The effect of injection time on the injection molding process is reflected in three aspects:

(1) Shortening the injection time increases the shear rate in the melt, which requires higher injection pressure to fill the mold cavity.

(2) Shortening the injection time increases the shear rate in the melt. Due to the shear-thinning behavior of the plastic melt, its viscosity decreases, so the required injection pressure to fill the mold cavity also decreases.

(3) Shortening the injection time increases the shear rate in the melt, generating more shear heat while less heat is lost through conduction, resulting in a higher melt temperature and lower viscosity, which reduces the required injection pressure to fill the mold cavity.

The combined effect of these three situations results in a 'U'-shaped curve for the injection pressure required to fill the mold cavity. In other words, there is an optimal injection time at which the required injection pressure is minimal.