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Problem 2: Thermal Solidification of a Casting University of Puerto Rico at Mayagüez Department of Mechanical Engineering Modified by (2008): Dr. Vijay.

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Presentation on theme: "Problem 2: Thermal Solidification of a Casting University of Puerto Rico at Mayagüez Department of Mechanical Engineering Modified by (2008): Dr. Vijay."— Presentation transcript:

1 Problem 2: Thermal Solidification of a Casting University of Puerto Rico at Mayagüez Department of Mechanical Engineering Modified by (2008): Dr. Vijay K. Goyal Associate Professor, Department of Mechanical Engineering University of Puerto Rico at Mayagüez Thanks to UPRM students enrolled in INME 4058 sections 2006-08

2 Workshop This is the 10.0 ANSYS Product Launcher main window. Select the Working Directory and type the name of work shop on Job Name.

3 Workshop Click the button Customization/ Preferences. On the item of Use custom memory settings type 128 on Total Workspace (MB): and type 64 on Database (MB):. Then click the Run bottom.

4 Workshop This is the main window of ANSYS University Intermediate Utility Menu.

5 Chapter 3. Thermal Solidification of a Casting Problem Description This is a transient heat transfer analysis of casting process. The objective is to track the temperature distribution in the steel casting and the mold during the solidification process, which occurs over a duration of 4 hours. The casting is made in an L-shaped sand mold with 4 inch thick walls. Convection occurs between the sand mold and the ambient air. Steel piece to be cast

6 Chapter 3. Thermal Solidification of a Casting Given: Material Properties for Sand Conductivity (KXX)0.025 Btu/(hr-in- o F) Density (DENS)0.054 lb/in 3 Specific heat (C)0.28 Btu/(lb- o F) Conductivity (KXX) for Steel at 0 o F1.44 Btu/(hr-in- o F) at 2643 o F1.54 at 2750 o F1.22 at 2875 o F1.22 Enthalpy (ENTH) for Steel at 0 o F0.0 Btu/in 3 at 2643 o F128.1 at 2750 o F163.8 at 2875 o F174.2 Initial Conditions Temperature of steel2875 o F Temperature of sand80 o F Convection Properties Film coefficient0.014 Btu/(hr-in 2 - o F) Ambient temperature80 o F

7 Approach and Assumptions You will perform a 2-D analysis of a one unit thick slice. Half symmetry is used to reduce the size of the model. The lower half is the portion you will model. The mold material (sand) has constant material properties. The casting (steel) has temperature-dependent thermal conductivity and enthalpy; both are input in a table of values versus temperature. The enthalpy property table captures the latent heat capacity of the metal as it solidifies. Radiation effects are ignored. Solution control is used to establish several nonlinear options, including automatic time stepping. Automatic time stepping determines the proper time step increments needed to converge the phase change nonlinearity. This means that smaller time step sizes will be used during the transition from molten metal to solid state. Chapter 3. Thermal Solidification of a Casting Steel casting Sand Mold Model Symmetry plane

8 Chapter 3. Thermal Solidification of a Casting Thermal Analysis Step 1: Change the title of the work: Click File \ Change Title \ click. On the new window enter the new name of the work “Thermal steady state analysis of a composite slab” then click OK

9 Chapter 3. Thermal Solidification of a Casting Step 2: Set preferences. 1. Main Menu > Preferences 2. (check) “Individual discipline(s) to show in the GUI” = Thermal 3. [OK] 1 2 3

10 Chapter 3. Thermal Solidification of a Casting Step 2: Draw the geometry of the casting. In order to draw the geometry quicker, we specify the keypoints by telling ANSYS the coordinates of those points. 1. Main Menu > Preprocessor > Modeling > Create > Keypoints > In Active CS 2. “Keypoint number” = 1 3. “X,Y,Z Location in active CS” X=0, Y=0, Z=0 4. [Apply] 1 2 3 4

11 Chapter 3. Thermal Solidification of a Casting Repeat the same procedure for keypoints 2, 3, 4, 5, 6, 7, and 8. Keypoint #XYZ 20120 310120 42200 5440 6480 71480 81840

12 Chapter 3. Thermal Solidification of a Casting After entering all keypoints your drawing should look like this:

13 Chapter 3. Thermal Solidification of a Casting Step 3: Define the mold area. In order to define the areas. We have to tell ANSYS that the keypoints 1, 2, 3, 7, 6, 5, 8, 4 define a closed loop of the vertex AREA 1. For this: 1. Main Menu > Modeling > Create > Areas > Arbitrary > Through KPs 2. Write the keypoints numbers separated by comas = 1, 2, 3, 7, 6, 5, 8, 4 3. [OK] 1 2 3

14 Chapter 3. Thermal Solidification of a Casting Step 4: Define the cast area. In order to define AREA 2, do the same as for AREA 1. Now, the area has as vertex the keypoints 5, 6, 7, and 8. 1. Main Menu > Modeling > Create > Areas > Arbitrary > Through KPs 2. Write the keypoints numbers separated by comas = 5, 6, 7, 8 3. [OK] 1 2 3

15 Chapter 3. Thermal Solidification of a Casting Step 5: Show area numbers. 1. Utility Menu > PlotCtrls > Numbering 1

16 Chapter 3. Thermal Solidification of a Casting In the “Plot Numbering Controls” windows: 1. “Area numbers” = ON 2. (first drop down) = Element numbers 3. [OK] 1 2 3

17 Chapter 3. Thermal Solidification of a Casting The numbered areas are shown like this: Note that the numbering A1 and A2 appears in the same area ( the purple area ). This is because ANSYS puts the area’s number in the centroid of the respective area. It is important to remember that A1 is the mold area (blue) and that A2 is the cast area (purple).

18 Chapter 3. Thermal Solidification of a Casting Step 6: Define mold material properties. Define the sand mold material properties as material NUMBER 1. These are not functions of temperature.material properties 1. Main Menu> Preprocessor> Material Props> Material Models 2. (double-click) “Thermal”, then “Conductivity”, then “Isotropic” 3. “KXX” = 0.025 4. [OK] 1 2 3 4

19 Chapter 3. Thermal Solidification of a Casting 5. (double-click) “Specific Heat” 6. “C” = 0.28 7. [OK] 5 6 7

20 Chapter 3. Thermal Solidification of a Casting 8. (double-click) “Density” 9. “DENS” = 0.54 10. [OK] 8 9 10

21 Chapter 3. Thermal Solidification of a Casting Step 7: Define cast material properties. The metal casting is defined as material number 2. These properties change significantly as the metal cools down from the liquid phase to the solid phase. Therefore, they are entered in a table of properties versus temperature. 1. Material> New Model 2. “Define Material ID” = 2 3. [OK] 1 2 3

22 Chapter 3. Thermal Solidification of a Casting 4. (double-click) “Isotropic” 5. [Add Temperature] three times to create fields for the four temperatures. 6. Fill the blanks with the table values. 7. [OK] T1T2T3T4 Temperatures0264327502875 KXX1.441.541.22 7 5 6 4

23 Chapter 3. Thermal Solidification of a Casting Next, define the temperature dependent enthalpy. 8. (double-click) “Enthalpy” 9. [Add Temperature] three times to create fields for the four temperatures. 10. Fill the blanks with the table values. 11. [OK] T1T2T3T4 Temperatures0264327502875 ENTH0128.1163.8174.2 8 9 10 11

24 Chapter 3. Thermal Solidification of a Casting Step 8: Plot material properties vs. temperature. We now want to see how varies the conductivity of Material 2 vs. temperature. For this: 1. (double-click) “Thermal conduct. (iso)” under Material Model Number 2. 2. [Graph] 3. [OK] Graph will look like this: 1 2 3

25 Chapter 3. Thermal Solidification of a Casting We now want to see how varies the enthalpy of Material 2 vs. temperature. For this: 4. (double-click) “Enthalpy” under Material Model Number 2. 5. [Graph] 6. [OK] Graph will look like this: Then: Material> Exit 4 5 6

26 Chapter 3. Thermal Solidification of a Casting Step 9: Define element type. You will now define the element type as PLANE55.element typePLANE55 1. Main Menu> Preprocessor> Element Type> Add/Edit/Delete 2. [Add...] 3. “Thermal Solid” (left column) 4. “Quad 4node 55” (right column) 5. [OK] 6. [Close] 1 2 3 4 5 6

27 Chapter 3. Thermal Solidification of a Casting Step 10: Mesh the model. 1. Utility Menu> Plot> Areas Specify a SmartSize of 4. This will allow a slightly finer mesh than the default and yet the resulting number of elements will be within the ANSYS ED program limits for the maximum number of elements.ANSYS ED 2. Main Menu> Preprocessor> Meshing> MeshTool 3. (check) “Smart Size” 4. (slide) “Fine Course” = 4 5. [Mesh] 1 2 3 4 5

28 Chapter 3. Thermal Solidification of a Casting Mesh the mold area first. Note that the material attribute reference number defaults to 1 and there is no need to set attributes before meshing the area. 6. Pick the mold area A1 (Hint: Place the mouse cursor on top of the A1 label when you pick -- this is the picking "hot spot," based on the centroid of the area.). 7. [OK] 6 7

29 Chapter 3. Thermal Solidification of a Casting Before meshing the casting area, set the material attribute to that of steel (material 2). 8. (drop down in MeshTool) “Element Attributes” = Global, then [Set] 9. (drop down) “Material number” = 2 10. [OK] 8 9 10

30 Chapter 3. Thermal Solidification of a Casting 11. Utility Menu> Plot> Areas 11

31 Chapter 3. Thermal Solidification of a Casting 12. [Mesh] in MeshTool 13. Pick area A2 14. [OK] 12 13 14

32 Chapter 3. Thermal Solidification of a Casting 15. [Close] in MeshTool 16. Utility Menu> Plot> Elements 15 16

33 Chapter 3. Thermal Solidification of a Casting 17. Utility Menu> PlotCtrls> Numbering 18. (drop down) “Elem / Attrib numbering” = Material numbers 19. [OK] 17 18 19

34 Chapter 3. Thermal Solidification of a Casting Note that the elements of material 1 form the sand mold. The elements of material 2 form the steel casting. You can also plot the elements showing materials in different colors without displaying the associated material numbers.

35 Chapter 3. Thermal Solidification of a Casting 20. Utility Menu> PlotCtrls> Numbering 21. (drop down) “Numbering shown with” = Colors only 22. [OK] 20 21 22

36 Chapter 3. Thermal Solidification of a Casting Step 11: Apply convection loads on the exposed boundary lines. Apply the convection to the lines of the solid model. Loads applied to solid modeling entities are automatically transferred to the finite element model during solution. 1. Utility Menu> Plot> Lines 1

37 Chapter 3. Thermal Solidification of a Casting 2. Main Menu> Preprocessor> Loads> Define Loads> Apply> Thermal> Convection> On Lines 3. Pick the three lines that are exposed to ambient air. 4. [OK] 2 3 4

38 Chapter 3. Thermal Solidification of a Casting 5. “Film coefficient” = 0.014 6. “Bulk temperature” = 80 7. [OK] 5 6 7

39 Chapter 3. Thermal Solidification of a Casting Step 12: Define analysis type. 1. Main Menu> Solution> Analysis Type> New Analysis 2. (check) “Type of analysis” = Transient 3. [OK] 2 1 3

40 Chapter 3. Thermal Solidification of a Casting 4. (check) “Solution method” = Full 5. [OK] 4 5

41 Chapter 3. Thermal Solidification of a Casting Step 13: Specify initial conditions for the transient. The mold is initially at an ambient temperature of 80oF and the molten metal is at 2875oF. Use select entities to obtain the correct set of nodes on which to apply the initial temperatures. First select the casting area, then select the nodes within that area and apply the initial molten temperature to those nodes. Next, invert the selected set of nodes and apply the ambient temperature to the mold nodes. 1. Utility Menu> Plot> Areas 2. Utility Menu> Select> Entities 1 2

42 Chapter 3. Thermal Solidification of a Casting 3. (first drop down) “Areas” 4. [OK] 5. Pick area A2, which is the casting. 6. [OK] 3 4 5 6

43 Chapter 3. Thermal Solidification of a Casting 7. Utility Menu> Select> Everything Below> Selected Areas 8. Utility Menu> Plot> Nodes 7 8

44 Chapter 3. Thermal Solidification of a Casting 9. Main Menu> Solution> Define Loads> Apply> Initial Condit'n> Define 10. [Pick All] to use selected nodes. 11. (drop down) “DOF to be specified” = TEMP 12. “Initial value of DOF” = 2875 13. [OK] 9 10 11 12 13

45 Chapter 3. Thermal Solidification of a Casting 14. Utility Menu> Select> Entities 15. (first drop down) “Nodes” 16. (second drop down) “Attached to” 17. (check) “Areas, all” 18. [Invert] This is an action command; the selected set of nodes is immediately inverted. 19. [Cancel] to close the dialog box. 15 16 17 18 19

46 Chapter 3. Thermal Solidification of a Casting 20. Utility Menu> Plot> Nodes 21. Main Menu> Solution> Define Loads> Apply> Initial Condit'n> Define 22. [Pick All] to use all selected nodes. 21 22

47 Chapter 3. Thermal Solidification of a Casting 23. “Initial value of DOF” = 80 24. [OK] Remember to always select Everything again when you are finished selecting the nodes! 25. Utility Menu> Select> Everything 23 24 25

48 Chapter 3. Thermal Solidification of a Casting Step 14: Set time, time step size, and related parameters. Stepped boundary conditions simulate the sudden contact of molten metal at 2875 oF with the mold at ambient temperature. The program will choose automatic time stepping that will enable the time step size to be modified depending on the severity of nonlinearities in the system (for example, it will take smaller time steps while going through the phase change). The maximum and minimum time step sizes represent the limits for this automated procedure. 1. Main Menu> Solution> Load Step Opts> Time/Frequenc> Time-Time Step 2. “Time at end of load step” = 4 Note: This represents 4 hours. 3. “Time step size” = 0.01 4. (check) “Stepped or ramped b. c.” = Stepped 5. “Minimum time step size” = 0.001 6. “Maximum time step size” = 0.25 7. [OK] 1 2 3 4 5 6 7

49 Chapter 3. Thermal Solidification of a Casting Step 15: Set output controls. 1. Main Menu> Solution> Load Step Opts> Output Ctrls> DB/Results File 2. (check) “File write frequency” = Every substep 3. [OK] 1 2 3

50 Chapter 3. Thermal Solidification of a Casting Step 16: Solve. 1. Main Menu> Solution> Solve> Current LS 2. Review the information in the status window. 3. [OK] to initiate the solution. 1 2 3

51 Chapter 3. Thermal Solidification of a Casting 4. [Close] when the solution is done. 4

52 Chapter 3. Thermal Solidification of a Casting While ANSYS is solving the analysis, the Graphical Solution Tracking (GST) monitor plots the "Absolute Convergence Norm" as a function of the "Cumulative Iteration Number." Notice that the solution is assumed to have converged for values less than or equal to the convergence criteria.

53 Chapter 3. Thermal Solidification of a Casting Review Results


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