This topic explains the processes of metal works and casting. It also describes the types and purpose of heat treatment for steels and the effects of heat treatment on mechanical properties of steels.
3. Metal works is a forming
process by plastic deformation
process in which the volume
and mass of metal are
conserved and the metal is
displaced from one location to
another.
Metal Works
4. Types of Metal Works
Cold Work :
Mechanical
working/forming of
metals below its
recrystallisation
temperature.
Hot Work :
Mechanical
working/forming of
metals above its
recrystallisation
temperature.
5. 1.Better dimensional control than hot working
is possible because the reduction in size is not
much.
2. Surface finish of the component is better
because no oxidation takes place during the
process.
3. Strength and hardness of the metal are
increased.
4. It is an ideal method for increasing
hardness of those metals which do not
respond to the heat treatment.
Advantages of Cold Work:
6. 1. Only ductile metals can be shaped through
cold working.
2. Over-working of metal results in brittleness
and it has to be annealed to remove the
stress because the grain structure.
3. Subsequent heat treatment is mostly
needed to remove the residual stresses set
up during cold working.
4. Need high power/force in forming process.
Disadvantages of Cold Work:
8. Cold rolling is generally employed for
providing a smooth and bright surface
finish to the previously hot rolled steel.
It is also used to finish the hot rolled
components to close tolerances and
improve their toughness and hardness.
Reduce the thickness of metals.
Cold Rolling
9. Typically it's a process in which the
metal sheet or strip stock is placed
between rollers and then compressed
and squeezed. The amount of strain
generated determines the hardness of
the finished product. There can be
numerous types of cold rolling mill,
which can produce different types of
rolled product, with thicknesses as low
as 0.05mm.
Cold Rolling
10. Cold rolling produces sheet, plate and
foil.
Foil- The Thickness is less than 0.2 mm
Sheet- .Thickness ranges from 0.2 mm
and 6mm
Plate-It is the rolled product, which is
over 6mm in thickness.
Cold Rolling
12. Wire drawing is a process used to
reduce the diameter of a wire by
pulling the wire through a single, or
series of, drawing die(s).
Drawing is different from extrusion,
because in drawing the wire is pulled,
rather than pushed, through the die.
Wire drawing
13. Wire drawing process is quite simple in
concept. The wire is prepared by
shrinking the beginning of it, by
hammering, filing, rolling or swaging, so
that it will fit through the die; the wire is
then pulled through the die.
As the wire is pulled through the die, its
volume remains the same, so as the
diameter decreases, the length
increases.
Wire drawing
14. Tube drawing is a metalworking process to size tube by
shrinking a large diameter tube into a smaller one,
by drawing the tube through a die. This process
produces high quality tubing with precise dimensions,
good surface finish, and the added strength of cold
working.
Tube drawing
15. Tube drawing is a reduction process in which one end of a
tube is grasped and pulled through a die that is smaller
than the tube diameter. To obtain the desired size, a series
of successive reductions, or passes, may be
necessary. Because of its versatility, tube drawing is suited
for both small and large production runs.
Process Characteristics
Stock is pulled through a die, reducing its diameter,
increases length as diameter decreases.
Typically requires several passes. Results in improved
material properties through cold working and is suitable
for small production runs of long workpieces.
Tube drawing
19. 1. Larger deformation can be accomplished
and more rapidly by hot working since the
metal is in plastic state.
2. Porosity of the metal is considerably
minimized.
3. Concentrated impurities, if any in the
metal are disintegrated and distributed
throughout the metal.
4. Grain structure of the metal is refined and
physical properties improved.
Advantages of Hot Work
20. 1. Due to high temperature a rapid oxidation or scale formation
takes place on the metal surface, leading to poor surface
finish and loss of metal.
2. On account of the lost of carbon from the surface of the
steel piece being worked the surface layer loses its strength,
which is a disadvantage when the part is put to service –
fatigue failure.
3. Close tolerances cannot be maintained.
4. It involves excessive expenditure on account of high
cost of tooling. This, however, is compensated by the
high production rate and better quality of products.
Disadvantages of Hot Work:
21. Forge and Smith forge
Hot Rolling
Extrusion
Example of hot work:
23. Smith Forge also known as open-die
forging.
In open-die forging, a hammer strikes
and deforms the workpiece, which is
placed on a stationary anvil.
Therefore the operator needs to
orient and position the workpiece to
get the desired shape.
Forge & Smith Forge
24. Impression-die forging is also called
closed-die forging.
Metal is placed in a die resembling a
mold, which is attached to the anvil.
Usually the hammer die is shaped as well.
The hammer is then dropped on the
workpiece, causing the metal to flow and
fill the die cavities.
Forge & Smith Forge
25. Excess metal is squeezed out of the
die cavities, forming what is referred
to as flash. This also forces the metal
to completely fill the die cavity. After
forging the flash is removed
Forge & Smith Forge
26.
27. Hot rolling is a metalworking process that
occurs above the recrystallisation
temperature of the material.
After the grains deform during processing,
they recrystallize, which maintains
an equiaxed microstructure and prevents
the metal from work hardening.
The starting material is usually large pieces
of metal, like semi-finished casting
products, such as slabs, blooms, and
billets.
Hot Rolling
28.
29. Extrusion is a process where the
materials is pushed or drawn through
a die of the desired cross-section.
The two main advantages of this
process over other manufacturing
processes are its ability to create very
complex cross-sections . It also forms
finished parts with an excellent
surface finish.
Extrusion
31. Direct extrusion is also called forward
extrusion and it is the most general
extrusion process. Its work operation
includes the placement of the billet in
a container, which is heavily walled.
Ram or screw is used to push the billet
through the die. In between the billet
and ram, there is a dummy block,
which is reusable and is used for
keeping them separated.
Direct Extrusion
33. Indirect extrusion is also called
backwards extrusion and in this
process, the die is constant whereas
the billet & container move together.
As the billet movement is along with
the container, all the frictional forces
are easily eliminated.
Indirect Extrusion
35. What is casting?
Casting is
a manufacturing process by which
liquid material is usually poured
into a mold, which contains a
hollow cavity of the desired
shape, and then allowed to
solidify.
Casting
40. Place a pattern in sand to create a mold.
Incorporate the pattern and sand in a gating system.
Remove the pattern.
Fill the mold cavity with molten metal.
Allow the metal to cool.
Break away the sand mold and remove the casting.
Sand Casting
43. The process is capable of making parts
from prototypes to high volume.
Cast tolerance is better (+/- .005 per
inch).
Cast surface finish is smooth.
Excellent cast details with regards to
cast letter i.e. logo, names, part
number, etc.
Benefit s of Lost-wax Casting
44. Reduced machining due to castings
designed to near net shape. Investment
castings can have undercuts, blind
holes, thru holes with almost any
geometric shape or size.
All of the above advantages reduce your
casting costs.
Benefit of Lost-wax Casting
45. What is die casting?
Die casting is the process of forcing
liquid metal under pressure into
cavities known as dies.
The die casting method is especially
suited for applications where a large
volume of small to medium sized parts
are needed with good detail, a fine
surface quality and dimensional
consistency.
Die Casting
46. The mould is sprayed with lubricant and
closed. The lubricant has two purposes,
firstly to help control the temperature of
the die and secondly, to assist in the
removal of the casting from the mould.
Molten metal is then shot into the die
under high pressure. Once the die is filled
the pressure is maintained until the
casting has cooled and hardened.
The die is then opened and the shot is
ejected.
Die Casting Process
47. Finally, excess material which includes
the gate, runners, sprues and flash, must
be separated.
Often a secondary operation is
performed to produce features not
readily castable, such as tapping a hole,
polishing, plating, buffing, or painting.
Die Casting Process
49. What is heat treatment?
Heat treatment is the controlled heating and cooling of
metals to alter their physical and mechanical properties
without changing the product shape.
Heat treatment is sometimes done inadvertently due to
manufacturing processes that either heat or cool the
metal such as welding or forming.
Heat treatment
50. What is the purpose of doing heat treatment to the steels?
The purpose of heat treating carbon steel is to change the
mechanical properties of steel, usually ductility, hardness,
yield strength, or impact resistance and sometimes is
to alter certain manufacturability objectives such as improve
machining, improve formability, restore ductility after a cold
working operation.
Heat Treatment
51. Heat Treatment Cycle:-
Heat treatment is an operation involving heating,
soaking and cooling of metal obtain desirable structure
and mechanical properties. Heat treatment cycle consist
of the following steps.
Heat the metal and alloys to a definite temperature.
Soaking/holding at the temperature for a sufficient time
to allow uniform temperature of core (centre) and
surface.
Cooling at a rate necessary to obtain desire structure
and mechanical properties.
Heat Treatment - cycle
53. It involves, heating the steel up to 950 to 1000º C (.i.e.
austeniting temperature).
Then soaking or holding the steel at that temperature
for a definite time so that the steel (Job) become
completely austenite (.i.e. core and outer surface
become austenite).
Then cooling it to room temperature in a furnace (i.e.
very slow cooling) this whole process is called
"Annealing Process".
It improves the structure of steel specially ductility and
toughness.
Heat Treatment - Annealing
54. Full annealing is the process of slowly raising the
temperature about 50 ºC (90 ºF) above the Austenitic
temperature line A3 or line ACM in the case of
Hypoeutectoid steels (steels with < 0.77% Carbon) and 50
ºC (90 ºF) into the Austenite-Cementite region in the
case of Hypereutectoid steels (steels with > 0.77%
Carbon).
It is held at this temperature for sufficient time for all the
material to transform into Austenite or Austenite-
Cementite as the case may be. It is then slowly cooled at
the rate of about 20 ºC/hr in a furnace to about 50 ºC into
the Ferrite-Cementite range. At this point, it can be
cooled in room temperature air with natural convection.
Full annealing
55. The grain structure has coarse Pearlite with ferrite or
Cementite (depending on whether hypo or hyper
eutectoid). The steel becomes soft and ductile.
Full annealing
56. Stress Relief Anneal is used to reduce residual
stresses in large castings, welded parts and cold-
formed parts. Such parts tend to have stresses due to
thermal cycling or work hardening. Parts are heated
to temperatures of up to 600 - 650 ºC (1112 - 1202 ºF),
and held for an extended time (about 1 hour or more)
and then slowly cooled in still air.
Stress Relief Annealing
57. Spheroidization is an annealing process used for
high carbon steels (Carbon > 0.6%) that will be
machined or cold formed subsequently. This is
done by one of the following ways:
1.Heat the part to a temperature just below the Ferrite-
Austenite line, line A1 or below the Austenite-Cementite
line, essentially below the 727 ºC (1340 ºF) line. Hold the
temperature for a prolonged time and follow by fairly
slow cooling. Or
2.Cycle multiple times between temperatures slightly
above and slightly below the 727 ºC (1340 ºF) line, say for
example between 700 and 750 ºC (1292 - 1382 ºF), and
slow cool. Or
3.For tool and alloy steels heat to 750 to 800 ºC (1382-1472
ºF) and hold for several hours followed by slow cooling.
Spheroidizing
58. All these methods result in a structure in which all the
Cementite is in the form of small globules (spheroids)
dispersed throughout the ferrite matrix. This structure
allows for improved machining in continuous cutting
operations such as lathes and screw machines.
Spheroidization also improves resistance to abrasion.
Spheroidizing
59. It involves, heating the steel 40 to 50 ºC above the
annealing temperature for a short time and then
cooling in air up to room temperature (cooling rate is
slightly faster then annealing).
It improves the structure and mechanical properties
of steel. It is slightly harder than annealed steel.
Also used to soften and relieve internal stresses after
cold work and to refine the grain size and
metallurgical structure.
Normalizing
60. Quenching is a heat treatment process in which steel is
heated (up to 1000-1050 ºC like normalizing). Then steel
is hold at that temperature for uniforming the
temperature then cooling in quenching media e.g,
water, brine, oil etc.
After rapid cooling steel will become hard and brittle
and its structure will be martensite. Steel is hardened to
increase the wear-resistance.
Heat Treatment - Quenching
61. Quenching media used to prevent quench fracture:
1. Air
2. Brine (salt water)
3. Oil
4. Water
5. Polymer quench
Heat Treatment - Quenching
