This document provides an overview of major manufacturing processes including casting, forming and shaping, machining, joining, and finishing. It focuses on describing various metal casting processes such as sand casting, shell molding, vacuum molding, expanded polystyrene casting, investment casting, plaster mold casting, and ceramic mold casting. It also discusses permanent mold casting processes and die casting. Finally, it covers metal forming processes such as rolling, extrusion, forging, and thread rolling.
1. Principles of Major
Manufacturing Processes
Prepared By
Bilal Hussain
Msc Mechanical Design
Department of Mechanical Engineering
University of Engineering & Technology Lahore
3. University of Engineering & Technology Lahore
METAL CASTING PROCESSES
1. Sand Casting
2. Other Expendable Mold Casting Processes
3. Permanent Mold Casting Processes
4. University of Engineering & Technology Lahore
Two Categories of Casting
Processes
1. Expendable mold processes - mold is sacrificed to
remove part
Advantage: more complex shapes possible
Disadvantage: production rates often limited by
the time to make mold rather than casting itself
2. Permanent mold processes - mold is made of metal
and can be used to make many castings
Advantage: higher production rates
Disadvantage: geometries limited by need to
open mold
5. University of Engineering & Technology Lahore
Overview of Sand Casting
Most widely used casting process, accounting for a
significant majority of total tonnage cast
Nearly all alloys can be sand casted, including metals
with high melting temperatures, such as steel, nickel,
and titanium
Castings range in size from small to very large
Production quantities from one to millions
6. University of Engineering & Technology Lahore
Sand casting weighing over 680 kg (1500 lb) for an
air compressor frame (photo courtesy of Elkhart
Foundry).
7. University of Engineering & Technology Lahore
Steps in Sand Casting
1. Pour the molten metal into sand mold
2. Allow time for metal to solidify
3. Break up the mold to remove casting
4. Clean and inspect casting
Separate gating and riser system
5. Heat treatment of casting is sometimes required to
improve metallurgical properties
8. University of Engineering & Technology Lahore
Making the Sand Mold
The cavity in the sand mold is formed by packing
sand around a pattern, then separating the mold into
two halves and removing the pattern
The mold must also contain gating and riser system
If casting is to have internal surfaces, a core must be
included in mold
A new sand mold must be made for each part
produced
9. University of Engineering & Technology Lahore
Sand Casting Production
Sequence
Production sequence in sand casting, including
pattern-making and mold-making
10. University of Engineering & Technology Lahore
Foundry Sand
Silica (SiO2) or silica mixed with other minerals
Good refractory properties - for high temperatures
Small grain size for better surface finish on cast part
Large grain size is more permeable, allowing gases
to escape during pouring
Irregular grain shapes strengthen molds due to
interlocking, compared to round grains
Disadvantage: interlocking reduces permeability
11. University of Engineering & Technology Lahore
Binders Used with
Foundry Sand
Sand is held together by a mixture of water and
bonding clay
Typical mix: 90% sand, 3% water, and 7% clay
Other bonding agents also used in sand molds:
Organic resins (e g , phenolic resins)
Inorganic binders (e g , sodium silicate and
phosphate)
Additives are sometimes combined with the mixture
to increase strength and/or permeability
12. University of Engineering & Technology Lahore
Other Expendable Mold
Processes
Shell Molding
Vacuum Molding
Expanded Polystyrene Process
Investment Casting
Plaster Mold and Ceramic Mold Casting
13. University of Engineering & Technology Lahore
Shell Molding
Casting process in which
the mold is a thin shell
of sand held together by
thermosetting resin
binder
Steps: (1) A metal
pattern is heated and
placed over a box
containing sand mixed
with thermosetting resin
14. University of Engineering & Technology Lahore
Steps in Shell Molding
(2) Box is inverted so
that sand and resin
fall onto the hot
pattern, causing a
layer of the mixture to
partially cure on the
surface to form a
hard shell
15. University of Engineering & Technology Lahore
Steps in Shell Molding
(3) Box is
repositioned so
loose uncured
particles drop
away
16. University of Engineering & Technology Lahore
Steps in Shell Molding
(4) Sand shell is
heated in oven for
several minutes to
complete curing
17. University of Engineering & Technology Lahore
Steps in Shell Molding
(5) shell mold
is stripped
from pattern
18. University of Engineering & Technology Lahore
Steps in Shell Molding
(6) Two halves of the shell
mold are assembled,
supported by sand or
metal shot in a box, and
pouring is accomplished
19. University of Engineering & Technology Lahore
Steps in Shell Molding
(7) Finished casting
with sprue removed
20. University of Engineering & Technology Lahore
Shell Molding: Advantages and
Disadvantages
Advantages:
Smoother cavity surface permits easier flow of
molten metal and better surface finish
Good dimensional accuracy
Mold collapsibility minimizes cracks in casting
Can be mechanized for mass production
Disadvantages:
More expensive metal pattern
Difficult to justify for small quantities
21. University of Engineering & Technology Lahore
Vacuum Molding
Uses sand mold held together by vacuum pressure
rather than by a chemical binder
The term "vacuum" refers to mold making rather than
casting operation itself
Developed in Japan around 1970
22. University of Engineering & Technology Lahore
Vacuum Molding: Advantages
and Disadvantages
Advantages:
Easy recovery of the sand, since no binders
Sand does not require mechanical
reconditioning done when binders are used
Since no water is mixed with sand,
moisture-related defects are avoided
Disadvantages:
Slow process
Not readily adaptable to mechanization
23. University of Engineering & Technology Lahore
Expanded Polystyrene Process
Uses a mold of sand packed around a polystyrene foam
pattern which vaporizes when molten metal is poured
into mold
Other names: lost-foam process, lost pattern
process, evaporative-foam process, and full-mold
process
Polystyrene foam pattern includes sprue, risers,
gating system, and internal cores (if needed)
Mold does not have to be opened into cope and drag
sections
24. University of Engineering & Technology Lahore
Steps in
Expanded Polystyrene Process
(1) Polystyrene
foam pattern is
coated with
refractory
compound
25. University of Engineering & Technology Lahore
Steps in
Expanded Polystyrene Process
(2) Foam pattern is
placed in mold box,
and sand is
compacted around
the pattern
26. University of Engineering & Technology Lahore
Steps in
Expanded Polystyrene Process
(3) Molten metal is
poured into the portion
of the pattern that
forms the pouring cup
and sprue
As the metal enters the
mold, the polystyrene
foam is vaporized
ahead of the advancing
liquid, thus filling the
mold cavity
27. University of Engineering & Technology Lahore
Expanded Polystyrene Process:
Advantages and Disadvantages
Advantages of expanded polystyrene process:
Pattern need not be removed from the mold
Simplifies and speeds mold-making, because
two mold halves are not required as in a
conventional green-sand mold
Disadvantages:
A new pattern is needed for every casting
Economic justification of the process is highly
dependent on cost of producing patterns
28. University of Engineering & Technology Lahore
Expanded Polystyrene Process
Applications:
Mass production of castings for automobile
engines
Automated and integrated manufacturing
systems are used to
1. Mold the polystyrene foam patterns and then
2. Feed them to the downstream casting
operation
29. University of Engineering & Technology Lahore
Investment Casting
(a.k.a. Lost Wax Process)
A pattern made of wax is coated with a refractory
material to make the mold, after which wax is melted
away prior to pouring molten metal
"Investment" comes from a less familiar definition of
"invest" - "to cover completely," which refers to
coating of refractory material around wax pattern
It is a precision casting process
Capable of producing castings of high accuracy
and intricate detail
30. University of Engineering & Technology Lahore
Steps in Investment Casting
(1) Wax patterns are
produced
(2) Several patterns
are attached to a
sprue to form a
pattern tree
31. University of Engineering & Technology Lahore
Steps in Investment Casting
(3) Pattern tree is
coated with a thin
layer of refractory
material
(4) Full mold is
formed by covering
the coated tree with
sufficient refractory
material to make it
rigid
32. University of Engineering & Technology Lahore
Steps in Investment Casting
(5) Mold is held in an
inverted position and
heated to melt the wax
and permit it to drip out
of the cavity
(6) Mold is preheated
to a high temperature,
the molten metal is
poured, and it solidifies
33. University of Engineering & Technology Lahore
Steps in Investment Casting
(7) Mold is broken
away from the finished
casting and the parts
are separated from
the sprue
34. University of Engineering & Technology Lahore
One-piece compressor stator with 108
separate airfoils made by investment
casting (photo courtesy of Howmet Corp.)
35. University of Engineering & Technology Lahore
Investment Casting:
Advantages and Disadvantages
Advantages:
Parts of great complexity and intricacy can be cast
Close dimensional control and good surface finish
Wax can usually be recovered for reuse
This is a net shape process
Additional machining is not normally required
Disadvantages:
Many processing steps are required
Relatively expensive process
36. University of Engineering & Technology Lahore
Plaster Mold Casting
Similar to sand casting except mold is made of plaster
of Paris (gypsum - CaSO4-2H2O)
In mold-making, plaster and water mixture is poured
over plastic or metal pattern and allowed to set
Wood patterns not generally used due to
extended contact with water
Plaster mixture readily flows around pattern,
capturing its fine details and good surface finish
37. University of Engineering & Technology Lahore
Plaster Mold Casting:
Advantages and Disadvantages
Advantages:
Good accuracy and surface finish
Capability to make thin cross sections
Disadvantages:
Mold must be baked to remove moisture
Moisture can cause problems in casting
Mold strength is lost if over-baked
Plaster molds cannot stand high temperatures
Limited to lower melting point alloys
38. University of Engineering & Technology Lahore
Ceramic Mold Casting
Similar to plaster mold casting except that mold is made
of refractory ceramic material that can withstand
higher temperatures than plaster
Can be used to cast steels, cast irons, and other
high-temperature alloys
Applications similar to those of plaster mold casting
except for the metals cast
Advantages (good accuracy and finish) also similar
39. University of Engineering & Technology Lahore
Permanent Mold
Casting Processes
Economic disadvantage of expendable mold casting:
A new mold is required for every casting
In permanent mold casting, the mold is reused many
times
The processes include:
Basic permanent mold casting
Die casting
40. University of Engineering & Technology Lahore
The Basic Permanent Mold
Process
Uses a metal mold constructed of two sections
designed for easy, precise opening and closing
Molds used for casting lower melting point alloys are
commonly made of steel or cast iron
Molds used for casting steel must be made of
refractory material, due to the very high pouring
temperatures
41. University of Engineering & Technology Lahore
Steps in
Permanent Mold Casting
(1) Mold is preheated and coated for lubrication and
heat dissipation
42. University of Engineering & Technology Lahore
Steps in
Permanent Mold Casting
(2) Cores (if any
are used) are
inserted and
mold is closed
43. University of Engineering & Technology Lahore
Steps in
Permanent Mold Casting
(3) Molten metal is
poured into the mold,
where it solidifies
44. University of Engineering & Technology Lahore
Permanent Mold Casting:
Advantages and Limitations
Advantages of permanent mold casting:
Good dimensional control and surface finish
Rapid solidification caused by metal mold results in
a finer grain structure, so castings are stronger
Limitations:
Generally limited to metals of lower melting point
Simpler part geometries compared to sand casting
because of need to open the mold
High cost of mold
45. University of Engineering & Technology Lahore
Die Casting
A permanent mold casting process in which molten
metal is injected into mold cavity under high pressure
Pressure is maintained during solidification, then
mold is opened and part is removed
Molds in this casting operation are called dies; hence
the name die casting
Use of high pressure to force metal into die cavity is
what distinguishes this from other permanent mold
processes
46. Metal forming processes
Large set of manufacturing processes in which the
material is deformed plastically to take the shape of
the die geometry. The tools used for such
deformation are called die, punch etc. depending on
the type of process.
University of Engineering & Technology Lahore
47. Three Basic Bulk Deformation
Processes
Rolling – slab or plate is squeezed between opposing
rolls.
Forging – work is squeezed and shaped between
opposing dies.
Extrusion – work is squeezed through a die opening,
thereby taking the shape of the opening
University of Engineering & Technology Lahore
48. Rolling
Deformation process in which work thickness is
reduced by compressive forces exerted by two
opposing rolls .
University of Engineering & Technology Lahore
49. The Rolls
Rotating rolls perform two main functions:
Pull the work into the gap between them by friction
between workpart and rolls.
Simultaneously squeeze the work to reduce its cross
section
University of Engineering & Technology Lahore
50. Types of Rolling
Based on workpiece geometry :
Flat rolling - used to reduce thickness of a
rectangular cross section.
Shape rolling - square cross section is formed into a
shape such as an I-beam’
Based on work temperature :
Hot Rolling – most common due to the large amount
of deformation required.
Cold rolling – produces finished sheet and plate
stock
University of Engineering & Technology Lahore
52. Diagram of Flat Rolling
University of Engineering & Technology Lahore
Side view of flat rolling, indicating before and after
thicknesses, work velocities, angle of contact with rolls,
and other features.
53. Rolling Mills
Equipment is massive and expensive .
Rolling mill configurations:
Two-high – two opposing rolls
Three-high – work passes through rolls in both
directions
Four-high – backing rolls support smaller work rolls.
Cluster mill – multiple backing rolls on smaller rolls.
Tandem rolling mill – sequence of two-high mills
University of Engineering & Technology Lahore
55. Thread Rolling
Bulk deformation process used to form threads on
cylindrical parts by rolling them between two dies
Important commercial process for mass producing
bolts and screws.
Performed by cold working in thread rolling
machines.
Advantages over thread cutting (machining):
Higher production rates
Better material utilization
Stronger threads and better fatigue resistance due to
work hardening
University of Engineering & Technology Lahore
58. Forging
Deformation process in which work is compressed
between two dies Oldest of the metal forming
operations, dating from about 5000 B C’
Components: engine crankshafts, connecting rods,
gears, aircraft structural components, jet engine
turbine parts Also, basic metals industries use forging
to establish basic form of large parts that are
subsequently machined to final shape and size
Forging today is done either with presses or with
hammers powered by compressed air, electricity,
hydraulics, or steam.University of Engineering & Technology Lahore
59. Forging can be broken down into
two main types; cold and hot
forging
Hot forging.
University of Engineering & Technology Lahore
61. Forging operation
Drawing out:
In this operation in which the metal get elongated
with a reduction in the cross sectional area. For this
purpose, the force is applied in the direction
perpendicular to the length of the axis.
Upsetting:
In this operation, cross sectional area of the work
piece increases by decreasing length. For this
purpose is force is applied in the direction parallel to
the length of the axis
University of Engineering & Technology Lahore
63. Upsetting
Smith forging: Traditional operation, done by
manual hammering in open dies.
Drop Forging or Impression : done by serious of
blows by means drop hammers -die contains cavity
or impression that is imparted to work during this
process flash is created.
Machine forging: in case of drop and press forging
the material would be continuously drawn out where
as in this case only upsetting take place.
Press forging : similar to the drop forging expect
force is applied continuously (squeezing type).University of Engineering & Technology Lahore
65. Drop forging or Impression-Die
Forging
University of Engineering & Technology Lahore
66. Drop forging or Impression-Die
Forging
University of Engineering & Technology Lahore
67. Drop forging
It uses closed impression dies to get the desire
shape of the component.
The shaping is done by serious of hammering given
to the material to form a desired shape.
The equipment used for this : Drop hammers.
Apply impact load against work.Two types:
Gravity drop hammers - impact energy from falling
weight of a heavy ram
Power drop hammers - accelerate the ram by
pressurized air or steam.
University of Engineering & Technology Lahore
69. Drop forging Cont…..
The required impression are machined in the die.
During hammering the between the stock is
compressed, because of continuous blows the metal
will completely spread over the die
Complex shape can be possible.
Depending upon the requirement of grain shape and
complex shape number of pass will be decided.
Application: crank, connecting rod, crank shaft and
crane hook.
University of Engineering & Technology Lahore
70. Drop forging Cont…..
Disadvantages: in a single stretch it is not possible to
get the final product and huge force will be
transmitted to the building.
University of Engineering & Technology Lahore
71. Advantages and Limitations
Advantages of impression-die forging compared to
machining from solid stock:
Higher production rates
Less waste of metal
Greater strength
Favorable grain orientation in the metal
Limitations:
Not capable of close tolerances
Machining often required to achieve accuracies and
features neededUniversity of Engineering & Technology Lahore
72. Press forging
Similar to the drop forging, it uses closed dies. Incase
of drop forging the force will be supplied as a serious
of blows where as in this case the force will be
applied as a squeezing force with the help of
hydraulic operation.
University of Engineering & Technology Lahore
73. Machine forging
Some times it is called upset forging
Even though the drop and press forge are done by
machine, historically upsetting process is called
machine forging.
University of Engineering & Technology Lahore
74. Upsetting and Heading
Forging process used to form heads on nails, bolts, and
similar hardware products
More parts produced by upsetting than any other
forging operation
Performed cold, warm, or hot on machines called
headers or formers
Wire or bar stock is fed into machine, end is headed,
then piece is cut to length
For bolts and screws, thread rolling is then used to
form threads
University of Engineering & Technology Lahore
75. Extrusion
Compression forming process in which work metal is
forced to flow through a die opening to produce a
desired cross-sectional shape
Process is similar to squeezing toothpaste out of a
toothpaste tube
In general, extrusion is used to produce long parts of
uniform cross sections
Two basic types:
Direct extrusion
Indirect extrusion
University of Engineering & Technology Lahore
77. Comments on Direct Extrusion
Also called forward extrusion
As ram approaches die opening, a small portion of
billet remains that cannot be forced through die
opening
This extra portion, called the butt, must be separated
from extrudate by cutting it just beyond the die exit
Starting billet cross section usually round
Final shape of extrudate is determined by die
opening
University of Engineering & Technology Lahore
80. Comments on Indirect Extrusion
Also called backward extrusion and reverse extrusion
Limitations of indirect extrusion are imposed by
Lower rigidity of hollow ram
Difficulty in supporting extruded product as it exits die
University of Engineering & Technology Lahore
81. Hot vs. Cold Extrusion
Hot extrusion - prior heating of billet to above its
recrystallization temperature
Reduces strength and increases ductility of the metal,
permitting more size reductions and more complex
shapes
Cold extrusion - generally used to produce discrete
parts
The term impact extrusion is used to indicate high
speed cold extrusion
University of Engineering & Technology Lahore
82. Extrusion Ratio
Also called the reduction ratio, it is defined as
where
rx = extrusion ratio; Ao = cross-sectional area of the
starting billet; and Af = final crosssectional area of the
extruded section
Applies to both direct and indirect extrusion
University of Engineering & Technology Lahore
84. Comments on Die Angle
Low die angle - surface area is large, which increases
friction at die-billet interface
Higher friction results in larger ram force
Large die angle - more turbulence in metal flow during
reduction
Turbulence increases ram force required Optimum
angle depends on work material, billet temperature,
and lubrication
University of Engineering & Technology Lahore
85. Orifice Shape of Extrusion Die
Simplest cross section shape is circular die orifice
Shape of die orifice affects ram pressure
As cross section becomes more complex, higher
pressure and greater force are required
Effect of cross-sectional shape on pressure can be
assessed by means the die shape factor Kx
University of Engineering & Technology Lahore