The initial temperature of the die represents the initial state of the die before the start of squeeze casting, and this initial state directly affects the speed of the temperature reduction in the solidification process of the casting, so the initial temperature of the die has a great influence on the quality of the casting, and because it affects the solidification process of the casting, it must have a great influence on the interface heat transfer.
In squeeze casting process, the initial temperature of die is usually about 250 ℃. Too low initial temperature of the mold will make the high-temperature metal melt be cooled, and a hard solidified shell will be formed soon. Due to the deformation resistance of the solidified shell, it is difficult for the casting to compensate the volume shrinkage caused by solidification shrinkage by plastic deformation under the action of external pressure, which leads to shrinkage defects in the casting. The high initial temperature of the mold slows down the solidification of the high temperature melt, and the high temperature melt is easy to enter the mold gap under the action of external pressure, which leads to the difficulty of casting demoulding. Therefore, it is necessary to set the appropriate initial temperature of the mold. In the experiment of squeeze casting in this chapter, under the premise of ensuring the casting quality and avoiding the difficulty of demoulding, the minimum initial temperature of the die is 190 ℃ and the maximum is 300 ℃.
As shown in Fig. 1 and Fig. 2, the influence of die initial temperature on the peak value and average value of interface heat transfer coefficient after applying external pressure is shown. It can be seen from the figure that the peak value and average value of the interface heat transfer coefficient increase with the increase of the initial temperature of the die.
As shown in Fig. 3 and Fig. 4, it shows the influence of initial mold temperature on the peak value and action time of interface pressure. It can be seen from the figure that the peak value and action time of interface pressure increase with the increase of initial mold temperature, and the greater the applied pressure is, the greater the increase range of peak value and action time of interface pressure is. The main reason is that the increase of the initial temperature of the die slows down the temperature drop of the casting, and the overall temperature of the casting is higher. Because of the slow down of casting temperature, the solidification process is prolonged, and the action time of pressure is also prolonged. When the interface pressure is larger, the interface heat transfer is improved, and the average value of the interface heat transfer coefficient will be higher when the action time is longer.