Manufacturing Methods MAE 4500 Chapter 7 - Metal Casting
Jan 28, 2016
Manufacturing Methods MAE 4500
Chapter 7 - Metal Casting
FIG. 6-5
FIG. 7-1
FIG. 7-3
FIG. 7-4
Casting PropertiesFundamental Properties:
ViscosityThe flow of the liquid metal inside the mold is controlled by its viscosity.
a. T>Tm
Viscosity is a function of superheat.
Superheat = (T - Tm) / Tm
b. TS < T < TL
Viscosity is a function of the structure and hence a function of the freezing
range.
Freezing range = (TL - TS) / TL
Viscosity low Viscosity high
Variation of viscosity in an eutectic system
FIG. 7-5
Gases and Solidification
Solid
Alloy
LiquidSolubility
TTm
S Pg1/2
Pg is the partialpressure of the gas over the melt
Similar to FIG. 6-17
To eliminate:1. Reduce pg ----> vacuum2. Melting with insoluble gas
(inert gas such as argon)3. Adding elements that react with the gas and form oxides
Al, Si, Ca with steelsPhosphorus with Cu and
bronze
Technological PropertiesFluidity:
This term indicates the capability of the molten metal to flow into the cavities of the system before freezing.
Fluidity is a function of:a. Fluid flow (viscosity)
• Heat transfer• Superheat• Mold temperature• Mold type
b. Solidification mechanism
Pure metalsand eutectic
alloys
Solid solutionalloys
Improvedfluidity
Fluidity Evaluation
Fluidity indexIt is measured by the length of the solidifiedspiral or length of the solidified thin plate.
FIG. 7-6
Heat Extraction and SolidificationProgressive vs. Directional Solidification
Directional solidification is important for the quality of the casting (solidification proceeds from the most remote section to the points of feeding).1. Feeder heads (risers)
They serve as wells of liquid metal to compensate for shrinkage during
solidification.2. Chills
They are heat-absorbing devices for fast freezing.
Risers (feeder heads) should have a high volume-to-area ratio compared to the product.
Directionalsolidification
Progressivesolidification
Aids to directionalsolidification
Improper positioningof riser
Chill
Effect of Process Parameters on Product Properties
1. Mold temperature2. Nucleating agents3. Breaking dendrites
a. Vibration during solidificationb. Centrifugingc. Forced flow (pressure die casting)d. Shearing (rheocasting)e. Pressure application during solidification
(squeeze casting)
(Grain size, porosity, and homogeneity control)(Grain size, porosity, and homogeneity control)
Fl
uidi
ty
Effect of mold temperature on properties and production rate
FIG. 7-7
Classification of casting processes
FIG. 7-12
Sequence of Operations of Sand Casting
FIG. 7-19
Similar to FIG. 7-15
Pattern Design
Match Plate Cope and Drag Plates
(a)
Characteristics of a Sand Mold
Similar to FIG. 7-17
FIG. 7-14
Investment Casting (Lost-wax Process)
FIG. 7-22
Centrifugal Casting
FIG. 7-26
Permanent molds
SIMILAR TO FIG. 7-24 and FIG. 7-25
Hot Chamber Die Casting
Cold Chamber Die Casting
Illustration of a Die Casting Machine