MANUFACTURING
PROCESSES
Processing
BMM3643
Manufacturing Processes
Shaping
processes
Assembly
Surface
Technology
Topic 1 :
Fundamentals of Metal Casting
Solidification
processes
Cleaning &
surface
treatments
Forming
processes
Coating &
deposition
processes
LECTURER:
Nur Azhani Abd Razak
Department of Mechanical Engineering
azhani@ump.edu.my
Particulate
processing
Solidification of Metals
Involves liquid metal turning back into solid
metal.
The significant factors;
Type of metals
Thermal properties (metals & the mold)
Relationship volume & surface area
Shape of the mold
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.
Mechanical
fastening
Permanent
joining
processes
Threaded
fasteners
Welding
Permanent
Fastening
methods
Brazing &
soldering
Adhesive
bonding
Material
removal
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.
Cast Structures of Metals
Preferred Texture Development
Figure 10.1 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: G. W.
Form, J. F. Wallace, J. L. Walker, and
A. Cibula.
Development of a preferred texture at a cool mold wall; note that only favorably oriented grains grow
away from the surface of the mold.
Source: Kalpakjian (2016). Manufacturing Engineering and Technology, 8th edition.
Alloy Solidification
Solidification Patterns
(a)
Figure 10.3 Schematic
illustration of alloy
solidification and
temperature
distribution in the
solidifying metal.
Note the formation of
dendrites in the mushy
zone.
Solidification in alloys begins when
the temperature drops below the
liquidus TL and is complete when it
reaches the solidus, TS.
Within the TL and TS temperature
range, the alloy is like a slushy with
columnar dendrites.
(b)
Solidification patterns for gray cast iron in a 180-mm (7-in.) square casting. Note that after 11
minutes of cooling, dendrites begin to reach each other, but the casting is still mushy throughout. It
takes about 2 hours more 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 of
the metal increases.
Source: H. F. Bishop and W. S. Pellini.
Cast Structures
(a)
(b)
Riser-gated Casting
(c)
Schematic illustration of three basic types of cast structures: (a) columnar dendritic;
(b) equiaxed dendritic; and (c) equiaxed nondendritic. Source: D. Apelian.
Schematic illustration of a typical risergated casting. Risers serve as reservoirs,
supplying molten metal to the casting as it
shrinks during solidification.
Source: American Foundrymen’s Society.
Schematic illustration of cast structures in (a) plane front, single phase, and (b) plane front, two
phase. Source: D. Apelian.
Fluidity Test
1. Sprue – is a vertical channel
though which the molten
metal flows downward in the
mold.
2. Runners – channels that
carry the molten metal from
the sprue to the mold cavity.
3. Gate – is the portion of the
runner though which the
molten metal enters the mold
cavity.
4. Risers – serve as reservoirs
to supply the molten metal
necessary to prevent
shrinkage.
Temperature Distribution
Temperature distribution at the interface of the mold wall and the liquid metal
during the solidification of metals in casting.
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.
Solidification Time
Hot Tears in Casting
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 regions to avoid hot tearing.
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.
Casting Defects
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.
Internal & External Chills
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).
Solubility of Hydrogen in Aluminum
Solubility of hydrogen in aluminum. Note the sharp decrease in solubility as the
molten metal begins to solidify.
Thank You