I. Utilising a Segmented Injection Method (Fast-to-Slow)
Initially, employ a rapid injection stage to complete approximately 90% of the filling. This substantially reduces the overall filling time, prevents premature melt cooling, and overcomes flow resistance.
At the conclusion of the filling process, transition to a gradual injection stage. This results in a decrease in pressure and velocity, which enables the gas to escape through the venting channels. This prevents the accumulation of trapped gas, burning, and flash defects that are the result of rapid filling. Additionally, it compensates for resistance variations in various cavities, rendering it appropriate for multi-cavity moulds.
Utilise an in-mold pressure sensor to precisely regulate the timing of the fast-to-slow speed switch by monitoring the pressure curve in real time. This prevents the transition from occurring too early, which can result in a decrease in the filling speed, or too late, which can lead to quality issues.
II. Accurate Temperature Regulation
Keep the raw material in a consistent and stable molten state by maintaining a consistent temperature in all sections of the barrel. This guarantees that the melt maintains a consistent flow state, even at high injection rates, by preventing localised high temperatures that result in excessive fluidity or low temperatures that cause slow feeding.
To reduce flow resistance and support higher filling speeds, it is necessary to adjust the mould temperature to match the material properties. For high-viscosity materials (e.g., PC, PA66), the mould temperature should be increased to 80-120℃. For low-viscosity materials (e.g., PE, PP), the mould temperature should be decreased to 40-60℃ to accelerate cooling and reduce filling quality fluctuations caused by temperature gaps between cavities.
III. Enhancing the parameters of plasticization and pressure
To ensure consistent melt density and viscosity for each injection, reduce batch-to-batch flow performance fluctuations, and support stable high-injection-speed filling, employ moderate back pressure and a stable screw speed during the plasticising stage.
Utilising multi-stage injection pressure control: In the filling stage, a high injection speed and high pressure are employed to ensure that the melt quickly fills the cavity. During the holding pressure stage, the pressure is gradually reduced to prevent overfilling and flash, while also compensating for cooling shrinkage and stabilising the dimensional accuracy of the product.
Control the holding pressure switching point with strictness: After all cavities are filled synchronously, switch to holding pressure uniformly to prevent uneven shrinkage caused by premature pressure on some cavities, thereby eliminating the need to deliberately prolong the filling time to balance holding pressure.
IV. Modifications to Process Details for Multi-Cavity Moulds
Low-pressure, low-speed filling tests should be prioritised during the trial moulding phase of a new machine. Before progressively optimising parameters, the filling status of each cavity should be observed individually, and discrepancies in filling speed should be recorded. This prevents the occurrence of bulk quality defects that are brought about by the direct implementation of high-pressure, high-speed mass production.
A new filling balance adjustment should be implemented when transitioning to raw materials with varying flowability. In order to guarantee a dynamic equilibrium between quality and filling speed, the injection parameters must be adjusted to correspond with the viscosity of the source material.
Your current precision multi-cavity mould injection moulding production line is entirely compatible with this process adjustment scheme. The product yield can be stabilised at over 98%, and the overall filling efficiency can be enhanced by over 20% after implementation.
