1. Melting temperature

Melting temperature is very important in injection molding processes. The melting temperature can be measured at the injection molding machine nozzle or roughly estimated using the air injection method. The temperature setting at the material barrel depends on the melting temperature of the plastic melt, screw speed, back pressure, injection volume, and injection cycle. If the operator has no experience in processing a specific plastic, the test should start from the minimum allowable temperature setting. In order to accurately control the melting temperature, the material barrel is generally divided into multiple heating zones, and each heating zone can be set with different temperatures. If the injection time is long or operated at high temperatures, the temperature of the first zone should be set to a lower value, which will prevent premature melting and splitting of the plastic. Before starting injection molding, ensure that the hydraulic oil, hopper closure, mold, and injection cylinder are all at the correct set temperature.

2. Injection pressure

Injection pressure is a type of pressure that promotes the flow of plastic melt, which can be measured using sensors located on nozzles or hydraulic equipment. It does not have a fixed value, and the more difficult it is to fill the mold with melt, the injection pressure should also increase accordingly.

The injection pressure can be divided into several stages, and during the filling stage of an injection cycle, the first and second stage pressures may require the use of high pressure to maintain a higher injection speed. After the melt fills the mold, the pressure can be lowered. However, when injecting some semi crystalline thermoplastic plastics (such as PA and POM), sudden changes in pressure can cause adverse changes in the internal structure of the product, so sometimes stage pressure is not necessary.

3. Locking pressure

In order to combat injection pressure, the mold must maintain a certain pressure during mold locking, but the locking pressure should not be too high, otherwise the equipment may operate under high pressure for a long time, which may cause damage to the mold and equipment. When calculating the locking pressure, it is necessary to consider the projected area of the plastic product and calculate a suitable pressure value based on this. The projected area of an injection molded part is the maximum area visible from the direction of application of the locking force. However, if the height of the injection molded part is large, the side wall area must also be taken into account.

4. Back pressure

Although using high back pressure is beneficial for the uniform dispersion of fillers such as pigments and the melting of plastics, it also prolongs the screw return time and can cause losses to the fibers in fiber-reinforced plastics. The setting of back pressure should not be too high, and under no circumstances should it exceed 20% of the injection pressure (maximum rating) of the injection molding machine.

5. Injection speed

When injecting thin-walled products, it is necessary to use a high injection rate to fully fill the mold when the melt from the gate is not solidified. However, the injection speed should not be too high. A stepped injection speed can be used to avoid defects such as melt injection or trapped gas.