材料科学与工程学院 College of Materials Science & Engineering Page 1 Page 1 Fundamental of Materials Forming - Metal Casting: Design, Materials, and Economics

材料科学与工程学院 College of Materials Science & Engineering Page 2 Page 2 Metal Casting: Design, Materials, and Economics Design Considerations Casting Alloys The Economics of Casting

材料科学与工程学院 College of Materials Science & Engineering Page 3 Page 3 Casting Design Modifications Figure 12.1 Suggested design modifications to avoid defects in castings. Note that sharp corners are avoided to reduce stress concentrations. 1. Corners, angles, and section thickness

材料科学与工程学院 College of Materials Science & Engineering Page 4 Page 4 Casting Cross-Sections Figure 12.2 Examples of designs showing the importance of maintaining uniform cross- sections in castings to avoid hot spots and shrinkage cavities.

材料科学与工程学院 College of Materials Science & Engineering Page 5 Page 5 2.Flat areas

材料科学与工程学院 College of Materials Science & Engineering Page 6 Page 6 Avoiding Shrinkage Cavities Figure 12.3 Examples of design modifications to avoid shrinkage cavities in castings. Source: Steel Castings Handbook, 5th ed. Steel Founders' Society of America, Used with permission. 3.Shrinkage

材料科学与工程学院 College of Materials Science & Engineering Page 7 Page 7

材料科学与工程学院 College of Materials Science & Engineering Page 8 Page 8 Chills Figure 12.4 The use of metal padding (chills) to increase the rate of cooling in thick regions in a casting to avoid shrinkage cavities. Source: Steel Castings Handbook, 5th ed. Steel Founders' Society of America, Used with permission.

材料科学与工程学院 College of Materials Science & Engineering Page 9 Page 9 Normal Shrinkage Allowance for Some Metals Cast in Sand Molds

材料科学与工程学院 College of Materials Science & Engineering Page 10 Page 10 Figure 12.5 Redesign of a casting by making the parting line straight to avoid defects. Source: Steel Casting Handbook, 5th ed. Steel Founders' Society of America, Used with permission. 4.Parting Line

材料科学与工程学院 College of Materials Science & Engineering Page 11 Page 11 Casting Design Modifications Figure 12.6 Examples of casting design modifications. Source: Steel Casting Handbook, 5th ed. Steel Founders' Society of America, Used with permission.

材料科学与工程学院 College of Materials Science & Engineering Page 12 Page 12 Desirable and Undesirable Die-Casting Practices Figure 12.7 Examples of undesirable and desirable design practices for die-cast parts. Note that section- thickness uniformity is maintained throughout the part. Source: American Die Casting Institute.

材料科学与工程学院 College of Materials Science & Engineering Page 13 Page 13 6.Dimensional tolerances Dimensional tolerances depend on the particular casting proce ss, size of the casting, and type of pattern used. tolerances are s mallest within one region of the mold, but because they are cu mulative, increase between different regions of the mold. Toler ances should be as wide as possible, within the limits of good pa rt performance; otherwise, the cost of the casting increases. In commercial practice, tolerances are usually in file range of 8m m for small castings and increaae withthe size of castings. Tole rances for large castings, for instance, may be 6 mm

材料科学与工程学院 College of Materials Science & Engineering Page 14 Page 14 7.Machining allowance Because most expendable-mold castings require some addi tional finishing operations, such as machining, allowances s hould be made in casting design for these operations. Mac hining allowances, which are included in pattern dimensions, depend on the type of casting and increase with the size a nd section thickness of castings. Allowances usually range f rom about 2 mm to 5 mm for small castings to more than 25 mm for large castings.

材料科学与工程学院 College of Materials Science & Engineering Page 15 Page 15 8.Residual stresses The different cooling rates within the body of a casting cause residual stresses.Stress relie ving may thus be necessary to avoid distortio ns in critical applications.

材料科学与工程学院 College of Materials Science & Engineering Page 16 Page 16 Aluminum Piston Aluminum piston for an internal c ombustion engine. (a) As cast; (b) after machining. Schematic illustration of the permanent mold used to produce aluminum piston s, showing the position of four cooling c hannels.

材料科学与工程学院 College of Materials Science & Engineering Page 17 Page 17 Mold Filling and Solidification Simulation of mold filling and solidification. (a) 3.7 seconds after start of pou r. Note that the mushy zone has been established before the mold is compl etely filled. (b) Using a vent in the mold for removal of entrapped air five sec onds after pour.

材料科学与工程学院 College of Materials Science & Engineering Page 18 Page 18 CASTING ALLOYS Nonferrous Casting Alloys Aluminum-based alloys Magnesium-based alloys Copper-based alloys Zinc-based alloys High-temperature alloys Ferrous Casting Alloys Cast irons Ductile (nodular) iron White cast iron Malleable iron Compacted graphite iron Cast steels Cast stainless steels