Understanding Injection Speed in Molding Processes

Injection speed during the molding process refers to the rate at which polymeric material moves within the mold cavity under a specific injection pressure. It plays a crucial role in the effective filling of the mold cavity, impacting the quality and efficiency of the final product. The speed can vary based on the material, mold type, and operating temperature, and it is typically determined by the setup technician for each individual job.

Factors Influencing Injection Speed

The injection speed is a dynamic parameter that can be adjusted to suit the specific requirements of the molding job. Factors such as the material's flow properties, the mold design, and the operating temperature all contribute to the optimal injection speed. In some cases, it may take a full shift to set up a machine for a particular job run, especially if detailed shop notes are available. For brand new jobs, an engineer may assist the technician to achieve the desired injection speed.

Injection Rate and Fuel Injector Delivery Volume

Injectors in other industrial applications, such as fuel injection systems, operate based on a similar principle. The fuel injector delivery volume is determined by the duty cycle, which is the proportion of time the injector is open versus closed, the fuel pressure, and the size of the pintle opening orifice. In the context of injection molding, the performance of the injection unit itself is often expressed in terms of the injection rate (volume of molten plastic injected per second, cm3/s) and the injection speed (speed of forward movement of the plunger, mm/s).

Observing the High-Speed Injection Process

Visualizing the injection process can help in understanding its complexity. You will observe the molds moving at high speeds during the injection process. These videos provide a clear illustration of how the machine controls the injection and the post-injection stages, including dwell pressure after the plastic has filled the cavities.

Control During Injection and Dwell Phases

Once the required amount of molten plastic is accumulated, the injection process begins. While the molten plastic flows into the mold, the machine controls the movement speed of the screw (or injection speed) to ensure appropriate filling. The machine also manages the dwell pressure after the plastic fills the cavities, ensuring optimal cooling and solidification before part ejection.