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Chapter 12 Metal Casting: Design, Materials, and Economics

Chapter 12 Metal Casting: Design, Materials, and Economics. FACTORS AFFECTING QUALITY OF CASTING 1. Flow of molten metal in mold cavities 2. The gating system 3. The rate of cooling 4. The gases evolved.

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Chapter 12 Metal Casting: Design, Materials, and Economics

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  1. Chapter 12Metal Casting: Design, Materials, and Economics

  2. FACTORS AFFECTING QUALITY OF CASTING1. Flow of molten metal in mold cavities2. The gating system3. The rate of cooling4. The gases evolved

  3. DESIGN CONSIDERATIONS IN CASTING1. Corners, angles, thicknesses2. Flat areas3. Ribs4. Shrinkage5. Draft6. Dimensional tolerances7. Lettering and marking8. Finishing operationsEACH WILL BE DISCUSSED SEPARATELY

  4. DESIGN CONSIDERATIONS IN CASTING1. Corners, angles, thicknessesavoid sharp cornersavoid small fillets to decrease stress concentrationavoid large fillets that lead to low cooling rates due to the increase in volume of materialHERE ARE SOME MODIFICATIONS TO AVOID DEFECTS IN CASTING

  5. FIGURE 12.1 Suggested design modifications to avoid defects in castings.Source: Images provided by: North American Die Casting Association, Wheeling, Illinois.

  6. DESIGN CONSIDERATIONS IN CASTING2. Flat areas- avoid plane surfaces as they may warp during cooling- cause poor surface finish due to uneven flow of metal while cooling

  7. FIGURE 12.2 Examples of designs showing the importance of maintaining uniform cross-sections in castings to avoid hot spots and shrinkage cavities.

  8. DESIGN CONSIDERATIONS IN CASTING3. Ribsuse ribs to support structures

  9. FIGURE 12.3 Rib designs for use on thin sections or flat surfaces to reduce or eliminate warping.

  10. DESIGN CONSIDERATIONS IN CASTING4. Shrinkageto avoid cracking during cooling there should be an allowance for shrinkage

  11. TABLE 12.1 Normal Shrinkage Allowance for Some Metals Cast in Sand Molds

  12. DESIGN CONSIDERATIONS IN CASTING5. Draftsa small taper is provided to facilitate the removal of the pattern without damaging the mold

  13. FIGURE 11.5 Taper on patterns for ease of removal from the sand mold.

  14. DESIGN CONSIDERATIONS IN CASTING 6. Dimensional tolerancesdepend on size of castingtolerances are 0.8 mm for small castings  6mm for large castings

  15. DESIGN CONSIDERATIONS IN CASTING7. Lettering and markingscan be sunk into the castingorcan protrude from it

  16. DESIGN CONSIDERATIONS IN CASTING8.Finishing operationsholes (better to be located on a flat surface)type of finishing operationcasting should have features that allow them to be clamped easily on machines if machining operations are necessary

  17. EXAMPLES OF POOR AND GOOD DESIGNSlook at the following slide and state for each design why it is poor

  18. FIGURE 12.4 Examples of undesirable (poor) and desirable (good) casting designs.Source: Images provided by: North American Die Casting Association, Wheeling, Illinois.

  19. EXAMPLES OF POOR AND GOOD DESIGNS(a) lower portion has a thin wall:may fracture(b) Large flat surfacemay warp……use textured surface(c) sharp corners: difficult to produce….small radii at the corners(d) Inner features have no function….also good design is easier to manufacture(e) sharp fillets at base of longitudinal groove(f) thread reaches the right face of casting…some molten metal will penetrate this region

  20. TABLE 12.2 Typical Applications for Castings and Casting Characteristics

  21. TABLE 12.3 Properties and Typical Applications of Cast Irons

  22. TABLE 12.4 Mechanical Properties of Gray Cast Irons

  23. TABLE 12.5 Properties and Typical Applications of Nonferrous Cast Alloys

  24. FIGURE P12.38

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