Research On Parameters Identification Of Heat Conductioninverse Problem In The Casting Solidification Process

The numerical simulation of temperature field in the solidification process is one of key contents of the casting CAE technology, which is the foundation to predict the defects. The accurate material properties, initial and boundary conditions are essential to the simulation. It's difficult to acquire the accurate parameters only by experiments. Especially, the Interfacial Heat Transfer Coefficient (IHTC) is influenced by many factors. Up to present, no theories can be sophisticatedly employed to determine it quantitatively, and no equipments can be used to measure it directly. It's more difficult to acquire the parameters of sand casting process because of various sand materials. Consequently, it's necessary to develop one new method to solve the Inverse Heat Conduction Problem (IHCP) and to identify the parameters based on the new research achievements and experiments.The research survey and development trend of the casting CAE technology and IHCP were firstly represented systematically. The research on the IHCP of solidification process was carried out to the widely used sand casting process.The IHCP belongs to the class of ill-posed problems which represents as the amplification of solution to the errors. Namely, the solution will be amplified even if the input data (measured temperatures) has a little oscillation. One new inverse method was presented according to the Tikhonov regularization theory, and one new regularized functional was established. The expression of regularization parameter was individually deduced by a-priori and a-posteriori strategy. The solution method of the new regularized functional was deduced by employing the sensitivity coefficient.In order to verify the new regularization technology, the Least Square Method, the Maximum A Posteriori and the new regularization method were employed to parameters identification of one-dimensional massive plate and steel solidification process, and convective heat coefficient, IHTC, conductivity and specific heat of sand were identified. The results indicated the new regularization method had higher precision and efficiency.In order to verify the priori regularization parameter, the Simulated Annealing Algorithm was employed to optimize the identification process of one-dimensional massive plate to acquire the optimal regularization parameter. Subsequently, the optimum parameter was used to identification process so as to distinguish between it and the priori one. The detailed demonstration indicated the priori parameter had higher precision and efficiency.The measured temperatures are requisite input data to the IHCP. Three kinds of casting projects were designed, and aluminium ZL101 and ZL102 were used to pour each project. It's analyzed the errors of measured temperatures quantitatively, and the principle was determined that the measured temperatures in the casting should be employed to the IHCP as input data, and the ones in the core and sand mold were only used to validation process.The IHTC was defined as segments linear function of casting temperature according to alloy ZL101 solidification feature.The Orthogonal Experimental Design (OED) was employed to estimate the initial value and variation domain of the variables. The IHTC, conductivity and specific heat of sand were identified based on the measured temperatures of ZL101 hollow cylindrical casting. The results indicated it could decrease the number of iteration and improve the precision and efficiency by combining the new regularization technology with OED when there were several variables.The IHTC was defined as exponential function of casting temperature according to alloy ZL102 solidification feature. The IHTC was identified based on the measured temperatures of ZL102 cylindrical casting, and it was used to temperature field simulation of hollow cylindrical casting and H-shape one. The results indicated the simulation temperatures were coincident to the corresponding measured ones. It implied that the identification results had universality to the same materials of casting and sand mold.The successful application of new regularization technology indicated it could overcome the ill-posedness and guarantee the precision and stability of solution. It provides one new method to identify the material properties and the IHTC so as to improve the simulated accuracy and promote the casting CAE technology.