Solidification Simulation of Investment Castings of Single Crystal Hollow Turbine Blade

The three-dimensional solidification simulation of the investment castings of single crystal hollow turbine blade at the withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min has been performed with the finite element thermal analysis. The calculated results are in accordance with the experimental ones. The results show that with the increase of withdrawal rate the concave curvature of the liquidus isotherm is larger and larger, and the temperature gradients of the blades increase. No effects of withdrawal rate on the distribution of the temperature gradients of the starter and helical grain selector of the blades are observed at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min. The relatively high temperature gradient between 500℃/cm and 1000℃/cm in the starter and helical grain selector is obtained at three withdrawal rates.

Solidification Simulation of Single Crystal Investment Castings

The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7 mm祄in was performed with the finite element thermal analysis method. The calculated results were in accordance with the experimental ones. The results showed that with the increase of with-drawal rate the concave curvature of the liquidus isotherm was bigger and bigger and the temperature gradient of the castings decreased. No effects of withdrawal rate on the distribution of the temperature gradient of the starter and helical grain selector of the castings were observed at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7mm祄in. The relatively high temperature gradient between 500癈礳m and 1000癈礳m in the starter and helical grain selector was obtained at three withdrawal rates. The study indicates the three dimensional solidification simulation by finite element method is a powerful tool for understanding solidification and predicting defects in single crystal investment castings.

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

Shrinkage Behaviour of Spheroidal Graphite Cast Iron in Green and Dry Sand Molds for the Benchmarking of Solidification Simulation

The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.

Numerical simulation of solidification morphologies of Cu-0.6Cr casting alloy using modified cellular automaton model

The purpose of this study is to predict the morphologies in the solidification process for Cu-0.6Cr(mass fraction,%)alloy by vacuum continuous casting(VCC)and verify its accuracy by the observed experimental results.In numerical simulation aspect, finite difference(FD)method and modified cellular automaton(MCA)model were used to simulate the macro-temperature field, micro-concentration field,nucleation and grain growth of Cu-0.6Cr alloy using real data from actual casting operations.From the observed casting experiment,the preliminary grain morphologies are the directional columnar grains by the VCC process.The solidification morphologies by MCAFD model are in agreement with the result of actual casting experiment well.

Simulation of Dendritic Growth with Melt Convection in Solidification of Ternary Alloys

A cellular automaton-lattice Boltzmann coupled model is extended to study the dendritic growth with melt convection in the solidification of ternary alloys. With a CALPHAD-based phase equilibrium engine, the effects of melt convection, solutal diffusion, interface curvature and preferred growth orientation are incorporated into the coupled model. After model validation, the multi dendritic growth of the Al-4.0 wt%Cu-1.0 wt%Mg alloy is simulated under the conditions of pure diffusion and melt convection. The result shows that the dendritic growth behavior, the final microstructure and microsegregation are significantly influenced by melt convection in the solidification.

Numerical Simulation of Transport Phenomena in Solidification of Multicomponent Ingot Using a Continuum Model

A continuum model proposed for dendrite solidification of multicomponent alloys, with any partial solid back diffusion, was used to numerically simulate the macroscopic solidification transport phenomena and macrosegregations in an upwards directionally solidified plain carbon steel ingot. The computational results of each macroscopic field of the physical variables involved in the solidification process at a middle solidification stage were presented.

Radiation heat transfer model for complex superalloy turbine blade in directional solidification process based on finite element method

For the sake of a more accurate shell boundary and calculation of radiation heat transfer in the Directional Solidification(DS) process, a radiation heat transfer model based on the Finite Element Method(FEM)is developed in this study. Key technologies, such as distinguishing boundaries automatically, local matrix and lumped heat capacity matrix, are also stated. In order to analyze the effect of withdrawing rate on DS process,the solidification processes of a complex superalloy turbine blade in the High Rate Solidification(HRS) process with different withdrawing rates are simulated; and by comparing the simulation results, it is found that the most suitable withdrawing rate is determined to be 5.0 mm·min^(-1). Finally, the accuracy and reliability of the radiation heat transfer model are verified, because of the accordance of simulation results with practical process.

A Computer Aided System for Simulating Weld Metal Solidification Crack

A computer-aided system for simulating weld solidification crack has been developed by which a welding engineer can carry out the welding solidification crack simulation on the basis of a commercial finite element analysis software package. its main functions include calculating the heat generations of the moving arc. mesh generation, calculating stress-strain distributions with element rebirth technique.

CA Investment Casting Process of Complex Castings

CA (Computer aided) investment casting technique used in superalloy castings of aerospace engine parts was presented. CA investment casting integrated computer application, RP (Rapid Prototyping) process, solidification simulation and investment casting process. It broke the bottle neck of making metal die. Solid model of complex parts were produced by UGII or other software, then translated into STL(Stereolithography) file, after RP process of SLS(Selective Laser Sintering), wax pattern used in investment casting can be acquired without metal die in short time. These can reduce period and cost greatly of complex superalloy parts development of engine. The key processes of CA investment casting were discussed. The accuracy of model translation should match that of RP system. Choice of RP material, surface polishing, sintering parameter plays important role in RP process. Other processes, like solidification simulating and optimization of gate system were introduced. The conclusion was that complex parts can be produced by CA investment casting with lots of advantages. The accuracy of castings can reach CT5～7,and the smoothness can get Ra3～13 mm. These parts of engines worked well.

PREPARATION OF Al－Si INGOTS WITH FULL EUTECTIC－LIKE MICROSTRUCTURE AT LOW COOLING RATE

A self-designed computer-aided solidification simulation system for large-size ingots was employed to determine the eutectic coupled-zone of Al-(7-14 wt%) Si alloys at low freezing rate with a temperature gradient of liquid on solidification interface tower than 20 K cm￣(-1). Experimental parameters for the formation of a fully eutectic microstructure in a dia.38×70 mm ingot have been successfully obtained under various conditions for Al-(11.3 -13.0 wt%) Si alloys.Eutectic coupled growth charactersitics under this condition was also discussed.

Investigation of Solidification and Segregation Characteristics of Cast Ni-Base Superalloy K417G

Differential scanning calorimetry （DSC） analysis, isothermal solidification experiment and Thermo-Calc simulation were employed to investigate solidification characteristics of K417G Ni-base superalloy. Elec- tron probe microanalysis （EPMA） was employed to analyze the segregation characteristics. Liquidus, solidus and the formation temperatures of main phases were measured. In the process of solidification, the volume fraction of liquid dropped dramatically in the initial stage, while the dropping rate became very low in the final stage due to severe segregation of positive segregation elements into the residual liquid. The solidification began with the formation of primary γ. Then with solidification proceeding, Ti and Mo were enriched in the liquid interdendrite, which resulted in the precipitation of MC carbides in the interdendrite. A1 accumulated into liquid at the initial stage, but gathered to solid later due to the precipitation of γ/γ＇ eutectic at the intermediate stage of solidification. However, Co tended to segregate toward the solid phase. In the case of K417G alloy, combining DSC analysis and isothermal solidification experiment is a good way to investigate the solidification characteristics. Thermo-Calc simulation can serve as reference to investigate K417G alloy.

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product.The multiphase flow phenomena of molten steel,steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation,and the effect of electromagnetic brake（EMBR） and argon gas blowing on the process were investigated.The relationship between wavy fluctuation height near meniscus and the level fluctuation index F,which reflects the situation of mold flux entrapment,was clarified.Moreover,based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification,the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux,temperature and stress of shell in slab continuous casting mold were described.