Casting (Week 13) Flashcards
What is Casting?
Process in which molten metal is poured by gravity or other force into a mold or a die cavity where it solidifies in the shape of the mold cavity.
The term casting is commonly used for metals and the term molding is used for plastics
What are 3 common types of Casting Methods?
1-Sand Casting
High-Temperature Alloy, Complex Geometry, Rough Surface Finish
2-Investment Casting
High-Temperature Alloy, Complex Geometry, Moderately Smooth Surface Finish
3-Die Casting
High-Temperature Alloy, Moderate Geometry, Smooth Surface
What is Sand Casting?
Sand Casting is a process in which a cast is formed from a molten metal in a sand mold.
What are the Requirements for Casting?
- Cavity of the desired shape- Mold
- Molten metal
- Proper channels to fill the molten metal
What do we control in Casting?
- Size and shape of cavity and mold
- Mixture composition
- Temperature
- Cooling time
- Carefully remove it
What are some Capabilities and Advantages of Casting?
o Can create complex part geometries
o Can create both external and internal shapes
o Some casting processes are net shape; others are near net shape
o Can produce very large parts
o Some casting methods are suited to mass production
What are the components of a Sand Casting Mold?
Mold consists of two halves:
Cope = upper half of mold
Drag = bottom half
o Two-piece casting flask
o Sand packed around pattern of intended shape
o Gating system for metal flow and escape
What are the steps in Sand Casting?
- Pour the molten metal into sand mold
- Allow time for metal to solidify
- Break up the mold to remove casting
- Clean and inspect casting
- Heat treatment of casting is sometimes required to improve metallurgical properties
What Parameters must be considered when designing the Sand Casting Mold?
- Geometry
- Finishing
- Grain size
- Machining allowance
- Shrinkage factor
- Runner, gating, sprue system
- Wall thickness, Fillet radius
- Mechanical properties
What is Investment Casting?
Investment casting (Lost Wax Casting): is a manufacturing process in which a wax pattern is used to shape a disposable ceramic mold
What are the steps in Investment Casting?
- Make a wax pattern (injection molding)
- Multiple patterns assembled to wax sprue
- Shell bulit => immerse into ceramic slurry => immerse into finse sand (few layers)
- Dry ceramix, melt out the wax, fire ceramic (burn wax)
- Pour molten metal (gravity) => cool, solidify (Hollow casting: pouring excess metal before solidification)
- Break ceramic shell (vibration or water blasting)
- Cut off parts (high-speed friction saw) => finishing (polish)
Differences between Sand Casting and Investment Casting :
Relative cost in high quantities
Sand Casting :
High
Investment Casting :
Low
Differences between Sand Casting and Investment Casting :
Relative cost for small quantities
Sand Casting :
Medium
Investment Casting :
Low
Differences between Sand Casting and Investment Casting :
Weight limit of casting
Sand Casting :
<2000 lb (907 Kg)
Investment Casting :
< 700 lb (317 Kg)
Differences between Sand Casting and Investment Casting :
Thinnest possible Wall (in.)
Sand Casting :
0.1 inch (2.5 mm)
Investment Casting :
0.0625 inch (1.5 mm)
