The experimental and modeling studies on the heat transfer behavior and pressure transfer law of the casting die interface in squeezewere carried out
(1) A set of methods for obtaining the heat transfer coefficient and pressure at the interface by measurement and back calculation are established. Through the design of temperature measurement unit and the installation of pressure sensor, the accurate measurement of mold temperature and interface pressure is realized. Through the data processing based on fast Fourier transform filtering and accurate back calculation model, the estimation of interface heat transfer coefficient is realized, and the quantitative data of interface heat transfer coefficient and interface pressure are obtained.
(2) The effects of process parameters (including process pressure, pouring temperature, mold initial temperature and coating thickness) on the interfacial heat transfer coefficient were systematically studied, and a complete set of quantitative data was obtained. The pouring temperature has little effect on the interface heat transfer coefficient and the interface pressure; with the increase of the initial temperature of the die, the peak value and the average value of the interface heat transfer coefficient increase, and the peak value and the action time of the pressure increase obviously. The coating thickness has a great influence on the interfacial heat transfer coefficient. When the coating thickness is thin, the effect of applied pressure on the interfacial heat transfer coefficient is obvious. When the coating thickness increases to about 125 μ m, the effect of applied pressure on the interfacial heat transfer coefficient is very small.
(3) Based on the theory of micro geometry / contact mechanics, a model was established to describe the interface heat transfer between squeeze casting and die. By considering the contact stress, effective heat transfer area, material mechanical properties and related thermal parameters on the micro scale, and using the data obtained from squeeze casting experiments, the relationship between the interface heat transfer coefficient and the interface pressure and temperature was established The quantitative relationship between the two factors. The relationship between the heat transfer coefficient and the average temperature of the interface is obtained by fitting.
(4) Through experiments and numerical simulation, the influence of solidification process and material mechanical properties on the pressure transfer law in squeeze casting process is revealed. Through the simulation of magnesium alloy and aluminum alloy, the difference of pressure transfer law between them is clarified: the latent heat of magnesium alloy is less than that of aluminum alloy, which makes the solidification time of magnesium alloy faster, and the deformation resistance of magnesium alloy is higher, which leads to the difference between magnesium alloy and aluminum alloy The results show that the difference of interface pressure and heat transfer coefficient is the main factor. Due to the high deformation resistance of magnesium alloy, the ability of magnesium alloy to compensate volume shrinkage by extrusion deformation is weaker than that of aluminum alloy in the solidification process. Therefore, under the same conditions, the tendency of magnesium alloy forming shrinkage defects is greater.