The complexity of plastic material properties often determines the complexity of the injection molding process. Under normal circumstances, the complexity of the material is not what we want. The performance of plastic materials varies greatly due to different varieties, different grades, different manufacturers of injection molded parts, and even different batches.
Therefore, corresponding adjustments should be made according to the performance of the material. Different performance parameters can lead to completely different injection molding results. This is also a different situation that everyone likes to see.
This is an important item. The melt flows into the cooled cavity and loses heat due to heat conduction.
At the same time, heat is generated due to shearing, and this part of heat may be more or less than the heat lost by heat conduction, mainly depending on the conditions of the injection molded part. This also results in a loss of some heat.
The viscosity of the melt decreases with increasing temperature. In this way, the higher the injection temperature, the lower the viscosity of the melt, and the smaller the required filling pressure. At the same time, the injection temperature is also limited by the thermal degradation temperature and decomposition temperature. This limitation causes a change in temperature.
Is the higher the mold temperature the better or the lower the better? The lower the temperature of the injection mold, the faster the heat will be lost due to heat conduction, the lower the temperature of the melt, and the worse the fluidity. The temperature also affects the speed of fluidity. This phenomenon is especially evident when using lower injection rates. If you don't believe it, you might as well do a test if conditions permit.
The length of time also has a certain impact on injection molding.
The influence of injection time on the injection molding process is manifested in three aspects:
1. Shorten the injection time, and the shear strain rate in the melt will also increase, so the injection pressure required to fill the cavity should also increase.
2. The injection time is shortened, the shear strain rate in the melt increases, and due to the shear thinning characteristics of the plastic melt, the viscosity of the melt decreases, and the injection pressure required to fill the cavity also decreases. This is exactly the opposite of the first point.
3. The shorter the injection time, the higher the shear strain rate in the melt, the greater the shear heat, and the less heat lost due to heat conduction, so the higher the temperature of the melt, the lower the viscosity, and the lower the injection pressure required to fill the cavity.
As a result of the combined action of the above three conditions, the curve of the injection pressure required to fill the cavity presents a "U" shape. That is, there is an injection time at which the minimum injection pressure is required. This is the aspect of injection time that affects the injection molding process.
The influence of injection molding process conditions on products is as described above. Injection molding has special significance for plastic materials, injection temperature, mold temperature, and injection time. The plastic material determines the complexity of the injection molding. Injection temperature results in high or low viscosity. The difference in fluidity is caused by the temperature of the mold. The injection pressure is different depending on the injection time.
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