1. FUNDAMENTALS OF METAL CASTING
SME Video - Forming Processes
Casting (vts_17)
Overview of Casting Technology
Heating and Pouring
Solidification and Cooling
In-class Assignment
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

2. Solidification Processes
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

3. Casting Molten metal Gravity or pressure Solidifies mold cavity
Steps in casting seem simple:
Melt the metal
Pour it into a mold
Let it freeze
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

4. Open Molds and Closed Molds
Closed mold requires a gating system
Molds are made of sand, plaster, ceramic or metal
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

5. Casting Advantages and Disadvantages
External and internal geometries
Net shape & Near net shape
Produce very large parts
Mass production
Disadvantages
Limitations on mechanical properties
Dimensional accuracy and surface finish
Hazards to workers due to hot molten metal
Environmental problems
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

6. Parts Made by Casting Big parts Engine blocks for automotive vehicles
Wood burning stoves
Machine frames
Small parts
Dental crowns
Jewelry
Frying pans
Ferrous and nonferrous metals
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

7. Overview of Casting Technology
Foundry = factory equipped & foundrymen
Making molds
Melting and handling molten metal
Performing the casting process & cleaning
Expendable mold
Intricate geometries possible
Sand plus binders
Permanent mold
Metal molds
Limited part geometry
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

8. Sand Casting Mold Gating system
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

9. Forming the Mold Cavity
Pack sand around a pattern
Remove pattern
Oversized pattern to allow for shrinkage
Shrinkage due to
Solidification
Cooling
Sand for the mold is moist with binder
Cores to create internal geometries
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

10. Cooling Curve for a Pure Metal
Pure metal solidifies at a constant temperature
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

11. Solidification of Alloys
Alloys freeze over a temperature range
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Copper‑nickel phase diagram
Cooling curve for a 50%Ni‑50%Cu

12. Solidification of Metals
Spiral mold test for fluidity
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

13. Solidification of Pure Metals
Skin form due to chilling action of mold wall
Rate of freezing depends on heat transfer
Grain structure
Casting of pure metal
Near mold wall
Randomly oriented grains
Small size
Toward center of casting
Large columnar grains
Oriented toward the center
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

14. Solidification of Alloys
Segregation of alloying components in center of casting
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

15. Shrinkage in Solidification and Cooling
Pattern shrinkage allowance
EXCEPTION:
Cast iron with high C content
Graphitization during freezing causes expansion
Couteracts shrinkage
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

16. External Chills for Directional Solidification
Desirable for regions of the casting most distant from the liquid metal supply to freeze first
Solidification to progress from these remote regions toward the riser
rapid freezing
chill not used
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

17. Solidification Time
TST depends on size and shape of casting by relationship known as Chvorinov's Rule
TST = total solidification time
V = volume of the casting
A = surface area of casting
n = exponent with typical value = 2
Cm = mold constant
Design the riser to have a larger volume‑to‑area ratio
Cm for a given casting based on experimental data
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

18. In-class Example
In the casting of steel under certain mold conditions, the mold constant in Chvorinov's Rule is known to be 4.0 min/cm2, based on previous experience. The casting is a flat plate whose length = 30 cm, width = 10 cm, and thickness = 20 mm. Determine how long it will take for the casting to solidify.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

19. SME Video
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

20. In-class Assignment
A disk‑shaped part is to be cast out of aluminum. The diameter of the disk = 500 mm and its thickness = 20 mm. If the mold constant = 2.0 sec/mm2 in Chvorinov's Rule, how long will it take the casting to solidify?
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

21. Extra Credit – hand in before test 1
A steel casting has a cylindrical geometry with 4.0 in diameter and weighs 20 lb. This casting takes 6.0 min to completely solidify. Another cylindrical‑shaped casting with the same diameter‑to‑length ratio weighs 12 lb. This casting is made of the same steel and the same conditions of mold and pouring were used.
Determine: (a) the mold constant in Chvorinov's Rule, (b) the dimensions, and (c) the total solidification time of the lighter casting. The density of steel = 490 lb/ft3.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

22. Manufacturing Economics
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

23. Time Permitting Content
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

24. Riser Design Reservoir of liquid metal to compensate for shrinkage
Shrinkage due to solidification
Design risers to freeze after the main casting
Riser is waste metal that is later separate
Melt risers to make more castings
Maximize the V/A ratio of riser
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

25. Casting Process Heating the metal in a furnace
Raise temperature to melting point
Heat of fusion converts solid to liquid
Pouring the molten metal
Pouring temperature
Pouring rate and turbulence
Solidification of metals
Transforms molten metal to solid state
Pure element
Alloy
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e