In the die-casting process, injection speed is one of the important parameters that affect casting quality, mold life, and production efficiency. The correct selection of injection speed can not only improve the surface quality and internal compactness of castings but also reduce the occurrence of defects such as porosity and cold shut. Therefore, a deep understanding of the mechanism of action and selection methods of injection speed is of great significance for optimizing the die-casting process.



One, Definition and Function of Injection Speed



Injection speed refers to the speed at which metal liquid is injected into the mold cavity from the injection cylinder of the die-casting machine, which is usually divided into slow injection speed and fast injection speed stages. Slow injection is mainly used for filling gates and runners, reducing the turbulence of metal liquid; fast injection is used for rapid filling of the mold cavity to ensure that the metal liquid is fully filled before cooling.

　　Injection speed directly affects the flow state of metal liquid, filling capacity, and solidification process. A low speed can lead to poor flow of metal liquid, causing cold shut or incomplete filling defects; a high speed can easily cause serious burrs, mold erosion, and an increase in porosity.



Two, Factors Affecting the Selection of Injection Speed



1. Alloy type



The fluidity, solidification characteristics, and viscosity of different alloys vary. For example, zinc alloys have good fluidity and can be selected with higher injection speeds; while aluminum alloys, due to their fast solidification and high viscosity, usually require appropriate reduction in injection speed to avoid cold shut.

　　2. Casting structure and wall thickness



Casting with thin walls and complex structures requires higher injection speeds to ensure complete filling; conversely, for thick-walled castings, the speed can be appropriately reduced to reduce impact and porosity.



3. Mold temperature and structural design

　　When the mold temperature is low, the metal liquid cools quickly, and the injection speed needs to be increased; when the mold structure is complex or the runner design is unreasonable, the injection speed should be adjusted to adapt to the flow characteristics of the metal liquid.



4. Die-casting machine performance



The performance of the injection system of different models of die-casting machines varies, and the injection speed should be reasonably set according to the equipment capabilities to avoid instability in the process due to equipment limitations.



Three, Principles and Methods of Injection Speed Selection



1. Initial setting reference value



Based on experience or industry standards, provide recommended ranges of injection speed for different alloy materials and casting types. For example, the fast injection speed for aluminum alloy die-casting is usually between 3~6m/s, while zinc alloy can reach 6~12m/s.

　　2. Trial molding verification and adjustment



Before actual production, it is necessary to observe the filling effect, casting quality, and mold wear through trial molding, and gradually optimize the injection speed parameters. The use of high-speed camera equipment or simulation software can provide a more intuitive analysis of the metal liquid flow state.



3. Comprehensive optimization of other process parameters



The injection speed should be coordinated with parameters such as injection pressure, mold temperature, and pouring temperature to achieve the best casting effect.



Four, Conclusion



In summary, the selection of injection speed is a systematic project, which requires comprehensive consideration of various factors such as material properties, casting structure, mold conditions, and equipment capabilities. Only through continuous exploration and optimization in practice can the most suitable injection speed parameters be found, thus improving the yield and quality stability of die-castings, and achieving the goal of efficient and high-quality production.