Injection speed-pressure (vp) switching
injection speed and pressure (VP) is a critical step in the injection molding process, directly impacting part quality, production efficiency, and mold life. During the injection molding process, speed control is primarily used to ensure that the melt quickly and evenly fills every corner of the cavity. When the melt nears fullness, pressure control must be promptly switched to prevent defects such as flash and mold bulge caused by overfilling, while also ensuring part dimensional accuracy and density. Therefore, accurately grasping the timing and method of VP switching is a crucial prerequisite for achieving high-quality injection molding production.
Determining the timing of vp switching is the core issue of this link, and there are usually three judgment methods: position-based, pressure-based, and volume-based. Position-based switching is the most commonly used method, that is, a screw position is preset as the switching point, and when the screw advances to this position, it automatically switches to pressure control. This method is simple to operate and highly stable, and is suitable for most plastic parts with relatively simple structures. Pressure-based switching monitors the cavity pressure or nozzle pressure, and switches when the pressure reaches the preset value. It can respond more accurately to the filling status of the melt in the cavity, and is especially suitable for plastic parts with thin walls and complex cavities. It can effectively avoid quality problems caused by insufficient or excessive filling. Volume-based switching determines the switching point based on the calculation of the cavity volume and the melt injection volume. It is suitable for the production of precision plastic parts with extremely high filling requirements, but it requires high metering accuracy of the equipment.
The parameters set during the VP switching process significantly impact part quality, primarily including switching speed, pressure, and holding time. The switching speed should be minimal, as this can cause the melt to generate shock pressure at the moment of switching, leading to internal stress concentration or surface ripples. However, too low a speed can affect filling efficiency and increase production cycle time. The holding pressure after switching should be determined based on factors such as the part’s material properties, wall thickness, and shrinkage. Excessive pressure can increase internal stress, leading to cracking and deformation. Excessive pressure can’t effectively compensate for melt shrinkage, resulting in undersized parts or surface depressions. Furthermore, the holding time must be appropriately set: too long will extend the production cycle, while too short will fail to achieve the desired holding effect.
In actual production, the VP switching process may be disrupted by various factors, such as fluctuations in raw material properties, changes in mold temperature, and equipment wear. This can lead to reduced switching accuracy and compromised part quality. To address these issues, modern injection molding machines are typically equipped with advanced closed-loop control systems. These systems monitor parameters such as screw position, pressure, and temperature in real time, dynamically adjusting switching timing and control parameters to ensure stability and accuracy during the switching process. For example, adaptive control algorithms can automatically adjust the next switching parameters based on the results of the previous molding cycle, continuously optimizing the molding process. The combined monitoring of pressure and speed sensors enables more precise switching control, effectively compensating for the effects of various interfering factors.
With the continuous advancement of injection molding technology, VP switching technology is also moving towards intelligent and refined features. On the one hand, computer simulation and emulation technologies enable virtual optimization of the VP switching process during mold design and process debugging, predicting potential problems and taking preemptive measures, reducing mold trials and lowering production costs. On the other hand, the integration of the Industrial Internet and big data analysis enables centralized management and analysis of VP switching parameters across multiple injection molding machines, identifying optimal process solutions and achieving consistent quality across large-scale production. In the future, with the application of artificial intelligence, the VP switching process is expected to be fully autonomously optimized, further improving the efficiency and quality of injection molding production.
