1. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Chapter 10 Fundamentals of Metal Casting

2. First used about six thousand years ago, casting continues to be an important manufacturing process for producing very small, as well as very large and complex, parts. The first topic discussed is solidification of molten metals, including the differences between solidification of pure metals and alloys, as well as concepts such as grain nucleation and freezing range. Fluid flow in casting is then described, with Bernoulli’s and the continuity equations being applied to establish a framework for analyzing molten metal flow through a mold. The concept and importance of turbulence versus laminar flow is introduced. Heat transfer and shrinkage of castings are also discussed, including Chvorinov’s rule for solidification time. The chapter ends with a description of the causes of porosity in castings and common methods of reducing them to improve cast-metal properties.

3. Topics Introduction Solidification of Metals Fluid Flow Fluidity of Metals Heat Transfer Defects

4. Fundamentals of Metal Casting One of the oldest processes is casting, which basically involves pouring molten metal into a mold cavity. Upon solidification, the metal takes the shape of the cavity. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

5. Fundamentals of Metal Casting Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

6. Overview of Casting Casting uses the idea that a liquid metal can take the shape of any vessel containing it. When the metal cools it has taken the shape of its container Casting is one of the most versatile manufacturing processes

7. Advantages of Casting Low cost and quick Easier to manufacture Can produce intricate shapes and internal openings Can produce parts in one piece Best suited for composite components

8. Introduction Important Considerations –Flow of Molten Metal –Solidification and Cooling –Type of Mold Material

9. Solidification of Metals  Involves liquid metal turning back into solid metal  The process is different for pure metals and alloys  Can be divided into two steps:  Formation of stable nuclei  Growth of crystals Pure Metals Have a clearly defined melting point Temperature remains constant during freezing Solidifies from the walls of the mold toward the center of the part

10. Grain Structure for Pure Metals Two types of grains are formed for a pure metal –Fine equiaxed grains –Columnar Rapid cooling at the walls produces fine equiaxed grains Columnar grains grow opposite of the heat transfer throughout the mold following the chill zone Equiaxed Grains If crystals can grow approximately equally in all directions – equiaxed grains will grow. Large amounts of under cooling is needed near the wall of the mold.

11. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Solidification of Pure Metals Figure 10.1 (a) Temperature as a function of time for the solidification of pure metals. Note that the freezing takes place at a constant temperature. (b) Density as a function of time

12. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Cast Structures of Solidified Metals Figure 10.2 Schematic illustration of three cast structures of metals solidified in a square mold: (a) pure metals; (b) solid-solution alloys; and (c) structure obtained by using nucleating agents. Source: After G. W. Form, J. F. Wallace, J. L. Walker, and A. Cibula Figure 10.3 Development of a preferred texture at a cool mold wall. Note that only favorably oriented grains grow away from the surface of the mold

13. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Alloy Solidification Figure 10.4 Schematic illustration of alloy solidification and temperature distribution in the solidifying metal. Note the formation of dendrites in the mushy zone.

14. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Solidification of Iron and Carbon Steels Figure 10.5 (a) Solidification patterns for gray cast iron in a 180-mm (7-in.) square casting. Note that after 11 minutes of cooling, dendrites reach each other, but the casting is still mushy throughout. It takes about two hours for this casting to solidify completely. (b) Solidification of carbon steels in sand and chill (metal) molds. Note the difference in solidification patterns as the carbon content increases. Source: After H. F. Bishop and W. S. Pellini

15. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Basic Types of Cast Structures Figure 10.6 Schematic illustration of three basic types of cast structures: (a) columnar dendritic; (b) equizxed dendritic; and (c) equiaxed nondendritic. Source: Courtesy of D. Apelian

16. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Cast Structures Figure 10.7 Schematic illustration of cast structures in (a) plane front, single phase, and (b) plane front, two phase. Source: Courtesy of D. Apelian

17. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Fluid Flow and Solidification Time Sprue design Mass continuity Bernoulli’s theorem Reynolds number Chvorinov’s Rule

18. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Casting Design and Fluidity Test Figure 10.8 Schematic illustration of a typical riser-gated casting. Risers serve as reservoirs, supplying molten metal to the casting as it shrinks during solidification. Figure 10.9 A test method for fluidity using a spiral mold. The fluidity index is the length of the solidified metal in the spiral passage. The greater the length of the solidified metal, the greater is its fluidity.

19. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Temperature Distribution during Metal Solidification Figure 10.10 Temperature distribution at the interface of the mold wall and the liquid metal during the solidification of metals in casting

20. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Solidified Skin on a Steel Casting Figure 10.11 Solidified skin on a steel casting. The remaining molten metal is poured out at the times indicated in the figure. Hollow ornamental and decorative objects are made by a process called slush casting, which is based on this principle. Source: After H. F. Taylor, J. Wulff, and M. C. Flemings

21. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Solidification Contraction or Expansion

22. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Hot Tears in Castings Figure 10.12 Examples of hot tears in castings. These defects occur because the casting cannot shrink freely during cooling, owing to constraints in various portions of the molds and cores. Exothermic (heat-producing) compounds may be used (as exothermic padding) to control cooling at critical sections to avoid hot tearing

23. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Common Casting Defects Figure 10.13 Examples of common defects in castings. These defects can be minimized or eliminated by proper design and preparation of molds and control of pouring procedures. Source: After J. Datsko.

24. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Types of Internal and External Chills used in Casting Figure 10.14 Various types of (a) internal and (b) external chills (dark areas at corners) used in castings to eliminate porosity caused by shrinkage. Chills are placed in regions where there is a larger volume of metal, as shown in (c).

25. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Solubility of Hydrogen in Aluminum Figure 10.15 Solubility of hydrogen in aluminum. Note the sharp decrease in solubility as the molten metal begins to solidify.

26. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Casting of an Aluminum Piston Figure 10.16 Aluminum piston for an internal combustion engine: (a) as- cast and (b) after machining. Figure 10.17 Simulation of mold filling and solidification. (a) 3.7 seconds after start of pour. Note that the mushy zone has been established before the mold is filled completely. (b) Using a vent in the mold for removal of entrapped air, 5 seconds after pour.

27. http://www.youtube.com/watch?v=9l7JqonyoKA&feature=related http://www.youtube.com/watch?v=mx1qteRUYwI&feature=relatedInvestment%20cast inghttp://www.youtube.com/watch?v=mx1qteRUYwI&feature=relatedInvestment%20cast ing http://www.youtube.com/watch?v=BX8w-GUPz1w http://www.youtube.com/watch?v=STl8aYYcpb4 Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.