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

2. FACTORS AFFECTING QUALITY OF CASTING 1
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

3. DESIGN CONSIDERATIONS IN CASTING 1. Corners, angles, thicknesses 2
DESIGN CONSIDERATIONS IN CASTING 1. Corners, angles, thicknesses 2. Flat areas 3. Ribs 4. Shrinkage 5. Draft 6. Dimensional tolerances 7. Lettering and marking 8. Finishing operations EACH WILL BE DISCUSSED SEPARATELY

4. DESIGN CONSIDERATIONS IN CASTING 1
DESIGN CONSIDERATIONS IN CASTING 1. Corners, angles, thicknesses avoid sharp corners avoid small fillets to decrease stress concentration avoid large fillets that lead to low cooling rates due to the increase in volume of material HERE ARE SOME MODIFICATIONS TO AVOID DEFECTS IN CASTING

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

6. DESIGN CONSIDERATIONS IN CASTING 2
DESIGN CONSIDERATIONS IN CASTING 2. 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 Examples of designs showing the importance of maintaining uniform cross-sections in castings to avoid hot spots and shrinkage cavities.

8. DESIGN CONSIDERATIONS IN CASTING 3. Ribs use 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 CASTING 4
DESIGN CONSIDERATIONS IN CASTING 4. Shrinkage to 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 CASTING 5
DESIGN CONSIDERATIONS IN CASTING 5. Drafts a 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
DESIGN CONSIDERATIONS IN CASTING 6. Dimensional tolerances depend on size of casting tolerances are 0.8 mm for small castings  6mm for large castings

15. DESIGN CONSIDERATIONS IN CASTING 7
DESIGN CONSIDERATIONS IN CASTING 7. Lettering and markings can be sunk into the casting or can protrude from it

16. DESIGN CONSIDERATIONS IN CASTING 8
DESIGN CONSIDERATIONS IN CASTING 8.Finishing operations holes (better to be located on a flat surface) type of finishing operation casting should have features that allow them to be clamped easily on machines if machining operations are necessary

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

18. FIGURE 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 surface may 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