In the injection molding process, there are a series of important process parameters that have a profound impact on the final quality of plastic products. These parameters include mold temperature, injection pressure, injection speed, holding time, etc., each of which plays an indispensable role in the molding effect and quality of the product. By reasonably adjusting these parameters, the appearance, dimensional accuracy, and quality of the plastic mold can be optimized to meet customer needs.
1. Injection volume

Injection volume, that is, the amount of melt injected into the mold by the screw of the injection molding machine during the injection molding process, is a crucial parameter. Its calculation formula is: Injection volume = Screw advance volume × ρ × C, where ρ represents the density of the injection material, and C varies depending on the type of polymer. For crystalline polymers, it is 0.85, and for amorphous polymers, it is 0.93. It is worth noting that injection molding machines are not suitable for processing products smaller than 1/10 of the injection volume or exceeding 70% of the injection volume.
2. Metering stroke (plasticizing stroke)

After each injection cycle, the screw remains at the front end of the barrel. Once the plasticizing program starts, the screw begins to rotate, pushing the material towards the screw head. Under the reaction force of the material, the screw moves backward until it touches the limit switch. This series of actions constitutes the metering process.

The size of the injection volume is closely related to the accuracy of the metering stroke. If the metering stroke is too small, it will lead to insufficient injection volume; if it is too large, it may cause too much material to remain in the front part of the barrel after each injection, which may lead to uneven melt temperature or overheating decomposition. In addition, there are temperature differences in both the longitudinal and radial directions of the plasticized melt, and the screw speed, plasticizing back pressure, and barrel temperature will all have a significant impact on this temperature difference.
3. Anti-sag volume

Anti-sag volume, that is, after the screw is metered in place, it will retract a certain distance linearly. The purpose of this is to increase the specific volume of the metering chamber, reduce the internal pressure, and prevent fluid from flowing out of the metering chamber. In addition, it also helps to reduce the pressure of the nozzle flow path system when the injection nozzle does not retract for plasticizing, reduce internal stress, and make it easier to remove the plastic part when the mold is opened. However, excessive anti-sag volume may cause air bubbles to enter the metering chamber, so for materials with high viscosity, anti-sag volume may not be set. By reasonably adjusting these parameters, we can produce products that meet quality requirements. For example, by adjusting the injection pressure, mold temperature, injection speed, and back pressure to control the dimensions of the product.