Die casting gate speed
The die-casting ingate velocity refers to the flow rate of molten metal as it enters the mold cavity through the ingate. Second only to injection speed, it is a critical parameter in the die-casting process, directly impacting the cavity filling efficiency and the inherent quality of the casting. As the “throat” connecting the runner to the cavity, the magnitude and distribution of its velocity alter the flow pattern of the molten metal, thereby determining whether the casting will exhibit defects such as undergiving, porosity, and shrinkage. For example, if the ingate velocity is too low, the molten metal may lose fluidity due to cooling before reaching the end of the cavity, resulting in incomplete filling. Excessively high velocity, on the other hand, can cause splashing and turbulence in the molten metal, increasing the risk of air entrapment and oxidation.
The calculation of the ingate velocity is closely related to the ingate’s cross-sectional area. Given a constant injection speed and molten metal flow rate, the smaller the ingate cross-sectional area, the higher the velocity; conversely, the smaller the ingate cross-sectional area, the lower the velocity. Therefore, during mold design, engineers need to accurately calculate the ingate size based on the casting’s volume, wall thickness, and complexity to match the required ingate velocity. For example, for small, thin-walled castings, a smaller ingate cross-sectional area is typically required to achieve a higher velocity to ensure efficient filling. For large, thick-walled castings, however, a larger ingate cross-sectional area is required to reduce the velocity and minimize turbulence.
The uniformity of the gate velocity distribution is also crucial. If the velocities of different parts of the gate vary significantly, the molten metal will form an asymmetric flow front after entering the cavity, resulting in localized over- or underfilling, which can lead to cold shuts or air holes. To ensure uniform velocity distribution, the shape of the gate must be designed symmetrically, avoiding sharp corners or sudden dimensional changes. Furthermore, the connection between the gate and the cavity can also affect velocity distribution. Using a smooth transition connection can reduce flow resistance, allowing the molten metal to enter the cavity more smoothly and improving the uniformity of velocity distribution.
In actual production, the gate speed is affected by factors such as the molten metal temperature and mold temperature. When the molten metal temperature is low, its viscosity increases, and even if the gate size remains unchanged, the actual flow rate will decrease. In this case, the injection speed must be increased to compensate. When the mold temperature is too high, the molten metal cools slower and its fluidity increases, which may lead to a relatively high gate speed, requiring appropriate adjustment of the injection parameters or gate size. Therefore, operators need to dynamically monitor and adjust the gate speed according to real-time process conditions to maintain stable production.
Optimizing the gate speed is a systematic process that requires comprehensive consideration of both casting quality requirements and production efficiency. By employing numerical simulation technology, engineers can simulate the flow of molten metal at different gate speeds before mold manufacturing, predicting potential defects and optimizing parameters in advance. For example, computer simulation software can intuitively observe the filling sequence, velocity distribution, and gas discharge of the molten metal within the mold cavity, allowing precise adjustment of the gate size and injection parameters to determine the optimal gate speed range. This digital optimization method not only shortens the process debugging cycle, but also significantly improves the quality stability of castings, laying the foundation for efficient production.
