CFD Analysis of Fluid Flow in Sand Casting

In Casting process filling and solidification is difficult to visualize by experimental methods. The fluid flow, phase transfer, temperature distribution and velocity gradient is undesirable. So we are going to CFD software to control the solidification parameters. According to finite element theory, using FLUENT software and three dimensional model to simulate liquid metal free surface and temperature field of casting filling process numerically. Boundary and initial conditions, such as velocity, pressure, temperature, etc., was reasonably calculated by theoretically. The feasibility of using FLUENT to simulate three dimensional casting was studied the fluctuation of molten metal free surface was observed. The temperature distribution data on the end of filling was recorded, for further numerical simulation of casting solidification process which provided an accurate initial condition.


III.
Design specifications A. Flange Design specifications of the flange is specified in fig 2. This represents the 2D View of the flange.   Height of A pulley=18.5mm Height of B pulley=10mm Height of C pulley=13.5mm C. Gating system Turbulence can be avoided by incorporating small changes in the design of gating system. The Sharp changes in the flow should be avoided & making smooth change. The gating system must be designed always full with liquid metal.

OBJECTIVES OF GATING SYSTEM:
1. Clean molten metal. 2. Smooth filling of the casting cavity. 3. Uniform filling of the casting cavity. 4. Complete filling of the casting cavity. 5. The mold cavity must be filled with a clean metal so that it prevents the entry of slag and inclusions into the mold cavity, which in turn minimizes the surface instability. 6. If the mold has smooth filling then it helps to reduce the bulk turbulence. If it has a uniform filling it means that the casting fill is in a controlled manner. Complete filling of the cavity makes the metal thin with minimum resistance at the end sections.
Commonly Preferred Gating System from Industries is BOTTOM GATING SYSTEM.
In bottom gating molten metal enters from the bottom of the casting cavity. It is recommended for tall casting where free fall of molten metal has to be avoided. The advantage of the bottom gating is that molten metal enters the bottom of the cavity gradually with minimal disturbances. The only disadvantage is that casting cavity is filled with variable filling rate, having high velocity of molten metal at the start of filling and gradually decreasing velocity as the molten metal fills the cavity.

DESIGN CONSIDERATION OF BOTTOM GATED SYSTEM:
1. Air forced up and out of mold.
3. As metal is poured the system, effective head reduced.   E. Design specification of pouring and sprue 1. Sprue wells are built with a different material than the one used in the mold for higher resistance to erosion 2. In the case of deep molds, the sprue may be offset at several points rather than using a straight sprue.

D. Design specification of flange
The two dimensional and three dimensional views of pouring & sprue are shown in figure 10. The ratio (Volume / surface area) 2 of the Riser must be greater than that of the casting. 2. However, when this condition does not meet the metal in the riser can be kept in liquid state, by heating it externally or using exothermic materials in it. 3. The way the riser is connected to the casting is very important, the connection called neck. So, it solidify first, so that the shrinkage cavity is located in the riser itself.
The removal of the riser should be made simpler making the neck smaller. Carbon

Properties of cast iron:
A number of properties such as mechanical, physical and service properties are of important in assessing materials suitably for any application. The mechanical properties of interest are tensile strength proof stress, elongation, hardness, impact strength, elastic modulus, and fatigue strength, notch sensitivity while the physical properties of interest are damping capacity, machinability and conductivity. The service properties generally involved are wear resistance, heat resistance, corrosion resistance.

FILLING AND FEEDING SYSTEM:
Molten metal is filled into the molding cavity from pouring series of filling channels which is called filling/runner system. Feeding is the process after filling up of liquid metal till to freezing of metals. Both of them are curtail for getting good quality of castings. A proper designed runner system can eliminate generation of casting defects such as porosity, inclusion, etc. and feeding mechanism is mainly to deal with shrinkage problems. Figure 14 explains briefly about the filling and feeding system used for this purpose. CFD Analysis Process The general process for performing a CFD analysis is outlined below so as to provide a reference for understanding the various aspects of a CFD simulation. The process includes: 1. Formulate the Flow Problem 2. Model Geometry and Flow Domain 3. Establish the Boundary and Initial conditions 4. Generate the Grid 5. Establish the Simulation Strategy 6. Establish the Input parameters and Files 7. Perform the Simulation 8. Monitor the Simulation for Completion 9. Post-process the Simulation to get the Result 10. Make the comparison of the result 11. Repeat the process to examine the sensitivities 12. Document

FORMULATE THE FLOW PROBLEM:
The first step of the analysis process is to formulate the flow problem by seeking answers to the following questions: What is the objective of the analysis? What is the easiest way to obtain those objectives? What geometry should be included? What are the free stream and/or operating condition? What dimensionality of the spatial model is required? (1D, quasi-1D, 2D, axisymmetric, 3D) What should the flow domain look like? What temporal modeling is appropriate? (steady or unsteady) What is the nature of the viscous flow? (inviscid, laminar, turbulent) How should the gas be modeled?

MODEL THE GEOMETRY AND FLOW DOMAIN:
The body about which flow is to be analyzed requires modeling. This generally involves modeling the geometry with a CAD software package. Approximation of the geometry and simplification may be required to allow an analysis with reasonable effort. Concurrently, decisions are made as to the extent of the finite flow domain in which the flow is to be simulated. Portions of the boundary of the flow domain coincide with the surfaces of the body geometry.
Other surfaces are free boundaries over which flow enters or leaves.

ESTABLISH THE BOUNDARY AND INITIAL CONDITIONS:
Since a finite flow domain is specified, physical condition are required on the boundary of the domain. The simulation generally starts from an initial solution and uses an iterative method to reach a final flow field solution.

GENERATE THE GRID:
The flow domain is discretized into a grid. The grid generation involves defining the structure and topology and then generating a grid on that topology. Currently all cases involve multi-block, structured grids; the grid blocks may be abbuting, contiguous, non-contiguous, and over lapping. The grid should exhibit some minimal grid quality as defined by measures of orthogonality (especially at the boundaries), relative grid spacing (15% to 20% stretching is considered a maximum value), grid skewness, etc… further the maximum spacing should be consistence with the desired resolution of important features. The resolution of boundary layers requires the grid clustered in the direction normal to the laminar sub-layer of the boundary layer. For turbulent flows, the first point off the wall should exhibit a y+ value of less than 1.0.

ESTABLISH THE SIMULATION STRATEGY:
The strategy for performing the simulation involves determining such things as the use of space-marching, the choice of turbulence or chemistry model, and the choice algorithms.

ESTABLISH THE INPUT PARAMETERS AND FILES:
A CFD codes generally requires that an input data file be created listing the values of the input parameters consisted with the desired strategy. Further the grid file containing the grid boundary condition information is generally required. The files for the grid and initial flow solution need to be generated.

PERFORM THE SIMULATION:
The simulation is performed with various possible with options for interactive or batch processing and distributed processing.

MONITOR THE SIMULATION FOR COMPLETION:
As the simulation proceeds, the solution is monitored to determine if a "converged" solution has been obtained, which iterative convergence is. Further discussion can be found on the page entitled examining iterative convergence.

POST-PROCESS:
Post-processing involves extracting the desired flow properties (thrust, lift, drag, etc…) from the computed flow field.

COMPARISONS OF THE RESULT:
The computed flow properties are then compared to results from analytic, computational, or experimental studies to establish the validity of the computed results.

REPEAT THE PROCESS TO EXAMINE SENSITIVITIES:
The sensitivity of the computed results should be examined to understand the possible differences in the accuracy of results and / or performance of the computation with respect to search things as: dimensionality, flow condition, initial condition, marching strategy, algorithms, grid topology and density, turbulence model, chemistry model, flux model, artificial viscosity, boundary condition, computer system.

DOCUMENT:
Documenting the findings of an analysis involves describing each of these steps in the process. . Select define -model-viscous-select k-epsilon then click ok 8. Select the type of fluid copy the data and past 9. Select define-boundary condition-type of fluid-inlet velocity-outlet pressure 10. Next select solve-controls-solutions 11. Select solve-initialize-initialize-then select unit 12. Select-monitors-residual-plot-increase absolute value 13. File-write-auto save-for every 100 iteration 14. Now select -solve -iterate 15. Particular iteration the result are taken

SIMULATION OF FLANGE:
In this simulation of casting filling process, multiphase flow (VOF), energy, turbulence and solidification options were chosen. Also, reasonable numerical simulation formula was chosen. Liquid surface tension was controlled. Casting, mold material properties and calculation boundary conditions were applied. The whole calculation domain state was initialized. Flow field and temperature field were coupling simulated. The time of 3D model of cell body finished filling process consisting with actual production of filling were obtained after using FLUENT simulation.

FREE SURFACE OF FILLING PROCESS:
In the whole simulation of casting filling process, the flow of molten metal can be divided into five parts.
Liquid metal enters from gate entrance liquid surface rises steadily in the gate liquid metal fills the whole gate at 0.003s Liquid metal begins to flow smoothly in to the bottom of die cavity from centre after 0.003s. Liquid metal flows in the die cavity the first contact with bottom of the cavity. When the flow of liquid metal begins to flow back to the middle part of the die cavity. From the wall of pouring basin bottom of the cavity will be filled with mold metal in 0.1s or and the top along cavity of walls being to be casted. However, the floe state of liquid metal is still unstable at this moment. At 0.3s the liquid metal is filled in the outer surface of the die cavity of air and turbulence flow is interface.

TEMPERATURE FIELD OF FILLING PROCESS OF FLANGE:
The change of temperature field in filling process. It can be found that, after liquid metal has entered the bottom of cavity, the transfer direction of temperature is in keeping with flow direction of liquid metal and they are all transferred placidly from center to all around, When temperature has passed to the wall, transfer speed of temperature of a, b wall is faster than c. The warming rate at the intersection of two walls is faster than other locations of model. When observed comprehensively, the temperature changes intensively in during the seconds of the whole filling process, with the filling process gradually becoming stable. Temperature changes will also become stable. According to previous research, this simulation result conforms to actual situation because the fluid is the carrier of temperature and the change of temperature field is decided by the change of flow field. Figure 19 explains the temperature distribution of flange.

SIMULATION OF PULLEY:
In this simulation of casting filling process, multiphase flow (VOF), energy, turbulence and solidification options were chosen. Also, reasonable numerical simulation formula was chosen. Liquid surface tension was controlled. Casting, mold material properties and calculation boundary conditions were applied. The whole calculation domain state was initialized. Flow field and temperature field were coupling simulated. The time of 3D model of cell body finished filling process consisting with actual production of filling were obtained after using FLUENT simulation.

FREE SURFACE OF FILLING PROCESS:
In the whole simulation of casting filling process, the flow of molten metal can be divided into five parts.
Liquid metal enters from gate entrance liquid surface rises steadily in the gate liquid metal fills the whole gate at 0.  Figure 24 shows the change of temperature field in filling process. It can be found that, after liquid metal has entered the bottom of cavity, the transfer direction of temperature is in keeping with flow direction of liquid metal and they are all transferred placidly from center to all around, When temperature has passed to the wall, transfer speed of temperature of a, b wall is faster than c. The warming rate at the intersection of two walls is faster than other locations of model. When observed comprehensively, the temperature changes intensively in during the seconds of the whole filling process, with the filling process gradually becoming stable. Temperature changes will also become stable. According to previous research, this simulation result conforms to actual situation because the fluid is the carrier of temperature and the change of temperature field is decided by the change of flow field.  Figure 25 shows the change of velocity field in filling process. It can be found that, after liquid metal has entered in the bottom of the cavity, the transfer direction of velocity is in keeping with flow direction of liquid metal.

CONCLUSIONS:
According to the Flange and Pulley simulation for flow field and temperature field of 3D model in casting filling process, visual simulation of casting process can be made well, especially for the accuracy and the visibility of the change of liquid metal free surface by using FLUENT solver in common software ANSYS. Due to the fluid is the carrier of temperature, the change of temperature field is decided by the change of flow field. The results of FLUENT simulation show that, solidification process and flow distribution identification of velocity vector in the early stage of filling process, the liquid level is volatile, especially when Liquid metal first contact with the wall of mold. It is possible to generate blowhole, slag inclusion and other casting defects in this stage. After filling enters the stable stage, the speed slows down and liquid level rises reposefully. The probability of defects caused by strong turbulent is decreased. Comparisons between experimental and simulation has been done. Overall experimental and simulation tell us about the fluid flow, temperature distribution and velocity vectors are identified. This identification shows to control the mould filling process.