Study On Heat Transfer Coefficients At Metal/Mold Interface During Solidification In Metal Castings

In the heat transfer process, the metal shrinks during solidification while the mold expands when heated, so an air-gap develops at metal/mold interface that enables the desired state of heat transfer not to be achieved, and creates a temperature drop between the two surfaces, accordingly resulting in a thermal resistance. The reciprocal of a thermal resistance is defined as the interfacial heat transfer coefficient which usually describes the effect of a thermal resistance on the interfacial heat transfer in the finite element numerical simulation. Besides, the gap formed often becomes the heat transfer controlling factor during solidification in metal casting. Thus, the interfacial heat transfer coefficient is an important parameter and also the necessary boundary condition, which has a major impact on simulation accuracy.In this paper, a test plan of metal casting being self-designed, and also a temperature test is made. Based on the measured temperature, the finite element software, ANSYS is used to analyze the solidification of metal casting. Based on the nonlinear estimation method the interfacial heat transfer coefficient for the metal casting solidification is solved. The main tasks of this paper are as follows:1. Design and implement the metal-casting temperature test, from which more accurate test datum at different positions of the metal/ mold interface have been obtained. Moreover, a series of measures have been taken to ensure the accuracy of the test data and to improve the anti-ill-posed nature of solution to the inverse problem.2. For the effect of a thermal resistance on the accuracy of simulation, ANSYS is used to simulate the temperature fields of the mold with different thickness for the same casting solidification, and to analyze the influence of the thermal resistant on the temperature distribution. In considering a thermal resistant, the temperature fields are simulated for the metal casting solidification using different interfacial heat transfer coefficients. Then, all the simulated results are compared to the test results, which shows that the interfacial heat transfer coefficient can not be a constant and even the size of its value has a direct impact on the accuracy of the temperature field.3. As the mold thickness will affect the the mold-environment heat transfer, the rule is searched that how the mold thickness influences on the interfacial heat transfer coefficient. Besides, after conducting an investigation into the influence of the space location of the metal/mold contact on the heat transfer, the temperature distributions with different spacial contact positions are respectively simulated, and to be comparatively analyzed.4. Based on the mathematical model related to the inverse problem, the interfacial heat transfer coefficient is determined using the nonlinear estimation method. By applying ANSYS software, the estimation method and the least-squares method, the rule that the interfacial heat transfer coefficient varies with time is enduced. And then, the mathematical model of the interfacial heat transfer coefficient with time for the mold thickness and the spacial contact position can be made up and used to simulate the temperature field. Finally, the simulated results and test results are analyzed, and to find the inherent law between them, so the higher precision is gained. All aboved can provide a workable solution for study on the interfacial heat transfer coefficient for the metal casting.