The speed at which the punch in the aluminum alloy die casting chamber pushes the molten metal is called the injection speed. In the aluminum alloy die casting process, the injection speed is directly affected by the pressure, and together with the pressure, it plays an important role in the intrinsic quality, surface requirements and contour clarity of the aluminum alloy die casting.

Aluminum alloy die casting injection speed is divided into slow injection speed and fast injection speed.

1. Slow injection speed for aluminum alloy die casting
The speed from the start of the aluminum alloy die casting punch until the metal liquid in the pressure chamber is sent to the inner gate. In this stage, the metal in the pressure chamber is required to be filled. Under the principle of not reducing the temperature of the alloy liquid too much and facilitating the removal of gas in the pressure chamber, the low injection speed should be used as much as possible. Generally, the slow injection speed is less than 0.3m/s.

2. Fast injection speed of aluminum alloy die casting
Determined by the characteristics of aluminum alloy die casting machines, the maximum injection speed given by domestic aluminum alloy die casting machines is generally 4~5m/s (GB/T 21269-2007 stipulates ≥6~7m/s), while the speed of foreign die casting machines can reach 10m/s.

3. The role and influence of fast injection speed in aluminum alloy die casting
Increasing the injection speed converts kinetic energy into thermal energy, improves the fluidity of the alloy liquid, helps eliminate defects such as flow marks and cold shuts, and improves mechanical properties and surface quality. However, if the speed is too fast, the mechanical properties will decrease.

4. The influence of injection speed on filling characteristics of aluminum alloy die casting
Increasing the injection speed increases the temperature of the alloy liquid when filling the cavity, which is beneficial to improve the filling conditions. Complex thin-walled castings require fast injection speeds, but when the injection speed is too high, the filling conditions deteriorate, which is particularly obvious in thick-walled castings.

5. Factors to consider when selecting the fast injection speed for aluminum alloy die casting
(1) Characteristics of aluminum alloy die casting alloy (latent heat of fusion, specific heat and thermal conductivity of alloy, solidification temperature range).
(2) Mold temperature (the injection speed can be appropriately reduced when the mold temperature is high. The injection speed can be appropriately limited according to the heat conduction condition of the mold, the mold design structure and production quality, and to extend the life of the mold).
(3) Quality requirements of die castings (aluminum alloy die castings with thin-walled complex parts with high surface quality requirements can use a higher injection speed).