When injection molds are produced, there are often many factors that affect the quality of the product. In summary, there are four main points:
1). Plastic materials
The complexity of the properties of plastic materials determines the complexity of the injection molding process. The performance of plastic materials varies greatly depending on the variety, grade, manufacturer, or batch. Different performance parameters can result in completely different molding results.
2). Injection temperature
The melt flows into the cooled cavity, dissipating heat due to heat conduction. At the same time, heat is generated due to shearing, which may be more or less less than heat transfer, depending on the 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 the required filling pressure. At the same time, the injection temperature is also limited by the thermal degradation temperature and the decomposition temperature.
3). Mold temperature
The lower the mold temperature, the faster the heat loss due to heat conduction, and the lower the temperature of the melt, the worse the fluidity. This phenomenon is especially noticeable when using lower injection rates.
4). Injection time
The impact of injection time on the injection molding process is manifested in three areas:
(1) Shortening the injection time, the shear strain rate in the melt is also increased, and the injection pressure required to fill the cavity is also increased.
(2) Shortening the injection time, the shear strain rate in the melt is increased, and the viscosity of the melt is lowered due to the shear thinning property of the plastic melt, and the injection pressure required to fill the cavity is also lowered.
(3) Shortening the injection time, the shear strain rate in the melt is increased, the shear heat is increased, and the heat lost due to heat conduction is small, so the melt temperature is high, the viscosity is lower, and the injection required for filling the cavity The pressure should also be reduced. As a result of the combination of the above three conditions, the curve of the injection pressure required to fill the cavity assumes a "U" shape. That is, there is an injection time at which the injection pressure required is the smallest.
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