MELTING & DEFECTS IN

CASTINGS
 WHAT IS FURNACE ?

• Heating device.
• Used for heating and melting.
• For providing heat to chemical reactions for
processes like cracking.
• The furnace may be heated by fuel as in many
furnaces coke is used as a fuel.
• some are operated by electrical energy e.g.
electric arc furnace.
 TYPES OF MELTING FURNACES

• Cupola Furnace
• Electric arc Furnace
• Crucible Furnace
• Induction Furnace
• reverberator Furnace
 CUPOLA FURNACE

• Cupola was made by Rene-Antoine around 1720.

• Cupola is a melting device.
• Used in foundries for production of cast iron.
• Used for making bronzes.
• Its charge is Coke , Metal , Flux.
• Scrap of blast furnace is remelted in cupola.
• Large cupolas may produce up to 100 tons/hour of
hot iron.
 CONSTRUCTION

• Cupola is a cylindrical in shape and placed vertical.

• Its shell is made of steel.
• Its size is expressed in diameters and can range from
0.5 to 4.0 m.
• It supported by four legs.
• Internal walls are lined with refectory bricks.
• Its lining is temporary.
 PARTS OF CUPOLA

• Spark arrester.
• Charging door.
• Air box.
• Tuyeres.
• Tap hole.
• Slag hole.
 ZONES OF CUPOLA

Stack Zone:
The empty portion of cupola above
the preheating zone is called as
stack. It provides the passage to hot
gases to go to atmosphere from the
cupola furnace.

Preheating zone:
This zone is starts from charging door
to the upper end of the melting
zone.
Objective of this zone is preheat the
charges from room temperature to
about 1090°C before entering the
metal charge to the melting zone.
Melting zone:
In this zone the melting is done.
It is located between preheating
zone and combustion zone.
The following reaction take place
in this zone.
3Fe + 2CO → Fe3C + CO2 .

Reducing zone:
Locate between upper level of
combustion zone and upper
level of coke bed.
In this zone temperature is about
1200°C.
In this zone CO2 change in to CO.
CO2 + C (coke) → 2CO
Combustion zone:
Also known as oxidizing zone .
Combustion take place in this zone.
It is located between well and melting
zone.
Height of this zone is normally 15cm to
30cm.
In this zone the temperature is 1540°C
to 1870°C.
The exothermic reactions takes place
in this zone these are
following .
C + O2 → CO2 + Heat
Si + O2 → SiO2 + Heat
2Mn + O2 → 2MnO + Heat

Well:
The space between the bottom of
the Tuyeres and the sand bed.
Molten metals get collected in this
region
 WORKING OF CUPOLA

• Its charge consist of scrap,

coke and flux.
• The charge is placed layer
by layer.
• The first layer is coke,
second is flux and third
metal.
• Air enter through the
bottom tuyeres.
• This increases the energy
efficiency of the furnace.
• Coke is consumed.
• The hot exhaust gases rise
up through the charge,
preheating it.
• The charge is melted.
• As the material is
consumed, additional
charges can be added to
• the furnace.
• A continuous flow of iron
emerges from the bottom
of the furnace.
• The slag is removed from
slag hole.
• The molten metal achieved
by tap hole.
 ELECTRIC ARC FURNACE

• Electric arc furnaces are more suitable for ferrous

materials and are larger in capacity.
• This type of furnace draws an electric arc that
rapidly heats and melts the charge material as
shown
 CRUCIBLE FURNACE

• Smaller foundries generally prefer the crucible

furnace.
• The crucible is generally heated by electric
resistance or gas flame.
• In these the metal is placed in a crucible of
refractory metal and the heating is done to the
crucible thus there is no direct contact between the
flame and the metal charge.
 INDUCTION FURNACE

• The induction furnaces are used for all types of

materials,
• advantage is heat source is isolated from the
charge
• the slag and flux would be getting the necessary
heat directly from the charge instead of the heat
source.
• Coreless induction furnaces use a refractory
envelope that contains the metal, and surround
that by the electric coil.
 REVERBERATOR FURNACE

• These are generally used to melt large amounts of

metal for example, aluminium to supply to holding
furnaces such as those used with pressure die
casting machines.
• These use gas fired burners located generally high
in the furnace transferring the heat by radiation to
the walls and roof
CASTING DEFECTS
 CASTING DEFECTS

• Gas defects
• Shrinkage cavities
• Moulding material defects
• Pouring metal defects
• Metallurgical defects
 Gating design
A good gating design should ensure proper distribution of molten metal without
excessive temperature loss, turbulence, gas entrapping and slags.

If the molten metal is poured very slowly, since time taken to fill the mould
cavity will become longer, solidification will start even before the mould is
completely filled.
If the molten metal is poured very faster, it can erode the mould cavity.

So gating design is important and it depends on the metal and molten metal
composition. For example, aluminium can get oxidized easily.

Gating design is classified mainly into two (modified: three) types:

Vertical gating, bottom gating, horizontal gating

Vertical gating: the liquid metal is poured vertically, directly to fill the mould
with atmospheric pressure at the base end.

Bottom gating: molten metal is poured from top, but filled from bottom to top.
This minimizes oxidation and splashing while pouring.

Horizontal gating is a modification of bottom gating, in which some horizontal

portions are added for good distribution of molten metal and to avoid
turbulence
 Analysis of pouring and filling up mould
(a) Vertical gating

For analysis we use energy balance equation like Bernoulli’s equation

2 2
p1 v1 p v
h1    F1  h3 3  3  F3
g 2g g 2g
Assuming p1 = p3 and level at 1 is maintained constant, so
v1 = 0; frictional losses are neglected.

The energy balance between point 1 and 3 gives,

gh  v 2 / 2 v3  2ght
t 3

Here v3 can be referred as velocity at the sprue base or

say gate, vg

Continuity equation: Volumetric flow rate, Q = A1v1 =A3v3

Above two equations say that sprue should be tapered.

As the metal flows into the sprue opening, it increases in velocity
and hence the cross-sectional area of the channel must be reduced

Otherwise, as the velocity of the flowing molten metal increases

toward the base of the sprue, air can be aspirated into the liquid and
taken into the mould cavity.

To prevent this condition, the sprue is designed with a taper, so that

the volume flow rate, Q = Av remains the same at the top and
bottom of the sprue.

The mould filling time is given by, t  V  V

f
Q Agv 3
Ag = cross-sectional area of gate; V = volume of mould

Note: This is the minimum time required to fill the mould cavity. Since the analysis
ignores friction losses and possible constriction of flow in the gating system; the
mould filling time will be longer than what is given by the above equation.
 (b) Bottom gating
2 2
p1 v1 p v
h1    F1  h3 3  3  F3
g 2g g 2g
Apply Bernoulli’s eqn. between points 1 and 3 and between 3 and
4 is equivalent to modifying V3 equation in the previousgating.

v g  v3  2g(h t  h)
Between 3 and 4:
Assume:
• V4 is very small
• All KE at 3 is lost after the liquid metal
Effective head enters the mould

Assuming in the mould the height moves up by ‘dh’ in a time ‘dt’; Am and Ag are mould
area and gate area, then

A m d h  A g v g dt A
1 dh g
 dt
Combining above two eqns., we get 2g ht  h A m

1
hm
dh Ag
tf Am 1

  dt tf  2( ht  ht  hm )
2g
 ht h Am 0
Ag 2g
0
(Check integration)
Find the filling time for both the mould types. Area of C.S. of gate = 5 cm2

Answer:
tf = 21.86 sec; 43.71 sec.
 Aspiration effect
Aspiration effect: entering of gases from baking of organic compounds present in
the mould into the molten metal stream. This will produce porous castings. Pressure
anywhere in the liquid stream should not become negative.

Free falling liquid

Metal flow with aspiration effect

A tapered sprue without aspiration effect

Case 1: straight Vs tapered sprue

Pressure anywhere in the liquid stream

should not become negative.

R.Ganesh Narayanan, IITG

 Gating ratios
Gating ratio: sprue area : runner area : gate area
Non-pressurized:
has choke at the bottom of the sprue base, has total runner area and gate
areas higher than the sprue area. No pressure is present in the system and
hence no turbulence. But chances of air aspiration is possible. Suitable for
Al and Mg alloys.
In this, Gating ratio = 1 : 4 : 4
Pressurized:
Here gate area is smallest, thus maintaining the back pressure throughout
the gating system. This backpressure generates turbulence and thereby
minimizes the air aspiration even when straight sprue is used.
Not good for light alloys, but good for ferrous castings.
In this, Gating ratio = 1 : 2 : 1
 Gating ratios
Gating ratio: sprue area : runner area : gate area
Non-pressurized:
has choke at the bottom of the sprue base, has total runner area and gate
areas higher than the sprue area. No pressure is present in the system and
hence no turbulence. But chances of air aspiration is possible. Suitable for
Al and Mg alloys.
In this, Gating ratio = 1 : 4 : 4
Pressurized:
Here gate area is smallest, thus maintaining the back pressure throughout
the gating system. This backpressure generates turbulence and thereby
minimizes the air aspiration even when straight sprue is used.
Not good for light alloys, but good for ferrous castings.
In this, Gating ratio = 1 : 2 : 1
Gating ratios used in practice
The flow rate of liquid metal into the downsprue of a mold = 1 liter/sec. The cross-
sectional area at the top of the sprue = 800 mm2 and its length = 175 mm. What area
should be used at the base of the sprue to avoid aspiration of the molten metal?
Ans: A= 540 mm2
• convert Q in lit/sec to mm3/sec
• Find v  2 gh

• Base area, A = Q/v

Molten metal can be poured into the pouring cup of a sand mold at a steady rate of
1000 cm3/s. The molten metal overflows the pouring cup and flows into the
downsprue. The cross-section of the sprue is round, with a diameter at the top = 3.4
cm. If the sprue is 25 cm long, determine the proper diameter at its base so as to
maintain the same volume flow rate.
Ans: D = 2.4 cm
• Find velocity at base, v  2 g h
• find area at base, A = Q/v
• Find D = √4A/π
There are few methods by which damages due to shrinkage can be minimized. They
are directional solidification methods.

Method : Providing chills:

Chills can be provided at appropriate locations in order to have rapid solidification at
those points. Internal and external chills can be provided.

Internal chills: small metal parts are placed inside the mould cavity before pouring so
that the molten metal will solidify first around these parts. The internal chill should
have a chemical composition similar to the metal being poured, so that it can be made
out of same cast metal.

External chills: They are metal inserts kept in mould walls that can extract heat from
the molten metal more rapidly than the surrounding sand in order to promote localized
solidification. They are mainly used in sections of the casting that are difficult to supply
with molten metal.

R.Ganesh Narayanan, IITG

With external chill Without external chill

R.Ganesh Narayanan, IITG

 Solidification of Casting

• During solidification metal experience shrinkage which

results in void formation.
• This can be avoided by feeding hot spot during
solidification.
• Riser are used to feed casting during solidification.
 What Are Risers?

• Risers are added reservoirs designed to feed liquid

metal to the solidifying casting as a means for
compensating for solidification shrinkage.
• Riser must solidify after casting.
• Riser should be located so that directional
solidification occurs from the extremities of mold
cavity back toward the riser.
• Thickest part of casting – last to freeze, Riser should
feed directly to these regions.
Riser Location & Types
Types of Riser
OpenRiser
• The top surface of the riser will be open to the
atmosphere.
• The open riser is usually placed on the top of the
casting.
• Gravity and atmospheric pressure causes the liquid
metal in the riser to flow into the solidifying casting.
Blinder Riser
• It is completely enclosed in the mold and not exposed to the
atmosphere .

• The metals cools slower and stay longer promoting directional

solidification.

• The liquid metal is fed to solidifying casting under the force of

gravity alone.
 Solidification Time For Casting

• Solidification of casting occurs by loosing heat from the

surfaces and amount of heat is given by volume of
casting .
• Cooling characteristics of a casting is the ratio of
surface area to volume.
• Higher the value of cooling characteristics faster is the
cooling of casting.
Chvorinov rule state that solidification time is inversely
proportional to cooling characteristics.

Solidification time
Where
Ts = Solidification time V = Volume of casting
SA = Surface area K = mould constant
• A cylindrical riser must be designed for a sand-casting
mold. The casting itself is a steel rectangular plate
with dimensions 7.5 cm x12.5 cm x 2.0 cm. Previous
observations have indicated that the solidification
time for this casting is 1.6 min. The cylinder for the
riser will have a diameter-to-height ratio as 1.0.
Determine the dimensions of the riser so that its
solidification time is 2.0 min.
• V/A ratio = (7.5 x 12.5 x 2) / 2(7.5x12.5 + 12.5x2 +
7.5x2) = 187.5 / 267.5 = 0.7
 Methods of Riser Design

• Following are the methods for riser design:

1. Caine’s Method
2. Modulus Method
3. NRL Method
 Caine’s Method

• Caine’s equation +

Where
X = Freezing ratio
Y = Riser volume / Casting volume
A, b and c = Constant

Freezing ratio
 Constant For Caine’s Method

• Values of constants are given in table:

Example:
1
 Modulus Method
Modulus is the inverse of the cooling characteristic ( surface area/
Volume) and is defined as
Modulus = Volume / Surface area
In steel casting riser with height to diameter ratio of 1 is generally
used.

Volume of cylindrical riser =

Surface area =

For sound casting modulus of riser should be greater than the

modulus of casting by a factor of 1.2. Therefore Mr = 1.2 Mc
On simplification D = 6 Mc
Considering contraction of metal
MODULI OF SIMPLE SHAPES
 NRL Method
• NRL stand for Naval research Laboratory.
• NRL method is essentially a simplification of Caine’s method.
• In this method shape factor is used in place of freezing ratio.

Shape factor

=
 NRL Method

• Ratio of riser volume to casting volume can be obtained from

graph shown below.
• After obtaining riser volume riser diameter and height can be
obtained.
• Use H/D = 1 for Side riser and H/D =0.5 for Top riser
 Example:2 Design a suitable riser
for the given casting
Solution: Neglecting branch first calculate shape factor
Shape factor = (Length + Width)/ Thickness
= (25+ 12.5)/5 =7.5
Volume of casting VC = 25 x 12.5 x 5
= 1562.5 cm3
Volume of riser VR = 0.575 x VC
= 0.575 x 1562.5
= 898.43 cm3
Volume of riser VR = 2.5 x 2.5 x 10
= 1562.5 cm3
This is a plate feeding bar with a thickness ratio of 0.5,
hence from figure 4.30 (PN Rao), we get parasitic volume
as 30 %
Hence riser volume = 0.30 x 62.5 + 898.43 = 917.2 cm3
Riser diameter D = 10.53 cm
 Riser design
The riser can be designed as per Chvorinov’s rule mentioned earlier. The
following example will illustrate the same.

A cylindrical riser must be designed for a sand-casting mold. The casting

itself is a steel rectangular plate with dimensions 7.5 cm x12.5 cm x 2.0 cm.
Previous observations have indicated that the solidification time for this
casting is 1.6 min. The cylinder for the riser will have a diameter-to-height
ratio as 1.0. Determine the dimensions of the riser so that its solidification
time is 2.0 min.
For casting:
V/A ratio = (7.5 x 12.5 x 2) / 2(7.5x12.5 + 12.5x2 + 7.5x2)

= 187.5 / 267.5 = 0.7

ts
 = 1.6/(0.7)2 = 3.26 min/cm2
V 2
( )
A

M.P. Groover, Fundamental of modern manufacturing Materials, Processes and systems, 4ed
For riser: D/H = 1 and ts = 2 min; V = π D2H/4; A = πDH+2πD2/4
From D/H = 1 => D = H then

V = π D3/4; A = πD2 +2πD2/4 = 1.5 πD2

So, V/A = D/6.
Now by Chvorinov’s rule, 2.0 = 3.26 (D/6)2 =>
D = 4.7 cm and H = 4.7 cm (riser dimensions)

Note that the volume of the riser in this problem is

V = π/4 (4.7)2 (4.7) = 81.5 cm3 , which is just 44% of the volume
of the cast plate, though its solidification time is 25% longer.
 Casting processes
Sand Casting
We have already seen sand casting processes. The steps involved in this
process is shown here briefly.

Riser, runner and

gate making

Melting
and pouring
 Other casting: Two types – (I) Expendable moulding, (II) Permanent moulding

Expendable moulding processes

Shell moulding
The shell moulding is a casting process in which the mould is a thin shell of 9 mm
thick. This is made of sand held together by thermosetting resin binder.

A metal pattern is heated and placed over a box

containing sand mixed with thermosetting resin

The dump box is inverted so that sand and resin mixture

fall on the hot pattern, causing a layer of the mixture to
partially cure on the pattern surface to form a hard shell

The box is positioned to the previous stage, so that loose,

uncured particles drop away

M.P. Groover, Fundamental of modern manufacturing Materials, Processes and systems, 4ed
sand shell is heated in oven for several minutes to complete
curing

The shell mold is removed from the pattern

and two halves of the shell mold are
assembled, supported by sand or metal shot
in a box, and pouring is completed

The part made by this method is shown here

 M.P. Groover, Fundamental of modern manufacturing Materials, Processes and systems, 4ed

•Wax patterns are first made

•several patterns can be attached to a sprue to form a pattern tree, if required
•the pattern tree is coated with a thin layer of refractory material and later covered with
thick coating to make the rigid full mold
•Heating of mold in inverted position to melt the wax and permit it to drip out of the
cavity
•the mold is preheated to a high temperature so that contaminants are eliminated from
the mold
•the molten metal is poured and it solidifies
•the mold is removed from the finished casting
 Die casting
In this process, high pressure of app. 7 to 350 MPa is used to pressurize the molten
metal into die cavity. The pressure is maintained during solidification.
Category: hot chamber machines, cold chamber machines

hot chamber machines:

-Molten metal is melted in a container attached to the machine, and a piston
is used to pressurize metal under high pressure into the die. Typical injection
pressures are between 7 and 35 MPa.
-Production rate of 500 parts/hour are common.
-Injection system is submerged into the molten metal and hence pose
problem of chemical attack on the machine components. Suitable for zinc,
tin, lead, Mg.

Steps in hot chamber casting

cold chamber machines:
- Molten metal is poured from an external unheated container into the mold cavity and
piston is used to inject the molten metal into the die cavity.
- Injection pressure: 14 to 140 MPa.
- Though it is a high production operation, it is not as fast as hot chamber machines.

Steps in cold chamber casting

Die casting molds are made of tool steel, mold steel, maraging steels. Tungsten and
molybdenum with good refractory qualities are also used for die cast steel, CI.

Advantages of die casting:

-high production rates and economical
-Close tolerances possible of the order of ±0.076 mm
-thin section with 0.5 mm can be made
-small grain size and good strength casting can be made because of rapid
cooling
 Centrifugal casting
-In this method, the mold is rotated at high speed so that the molten metal is
distributed by the centrifugal force to the outer regions of the die cavity
-includes : true centrifugal casting, semicentrifugal casting
True centrifugal casting:

-Molten metal is poured into a rotating mold to produce a tubular part

(pipes, tubes, bushings, and rings)
-Molten metal is poured into a horizontal rotating mold at one end. The high-
speed rotation results in centrifugal forces that cause the metal to take the
shape of the mold cavity. The outside shape of the casting can be non-
round, but inside shape of the casting is perfectly round, due to the radial
symmetry w.r.t. forces
Alloy wheels
Valve Body
 Defects in sand castings

Sand blow and Pinholes: defect consisting of a balloon-shaped gas cavity or

gas cavities caused by release of mold gases during pouring. It is present
just below the casting top surface. Low permeability, bad gas venting, and
high moisture content of the sand mold are the usual causes.

Sand wash: surface dip that results from erosion of the sand mold during
pouring. This contour is formed in the surface of the final cast part.

Scab: It is caused by portions of the mold surface flaking off during

solidification and gets embedded in the casting surface.
Penetration: surface defect that occurs when the liquid penetrates into the
sand mold as the fluidity of liquid metal is high, After solidifying, the casting
surface consists of a mixture of sand and metal. Harder ramming of sand
mold minimize this defect.

Mold shift: defect caused by displacement of the mold cope in sideward

direction relative to the drag. This results in a step in the cast product at the
parting line.

Core shift: displacement of core vertically. Core shift and mold shift are
caused by buoyancy of the molten metal.

Mold crack: ‘fin’ like defect in cast part that occurs when mold strength is very
less, and a crack develops, through which liquid metal can seep.
 Common defects in casting

Misruns: castings that solidify before completely filling the mold cavity. This occurs because of
(1) low fluidity of the molten metal, (2) low pouring temperature, (3) slow pouring, (4) thinner
cross-section of the mold cavity.

Cold Shuts: This defect occurs when two portions of the metal flow together but no fusion occurs
between them due to premature freezing.

Cold shots: forming of solid globules of metal that are entrapped in the casting. Proper pouring
procedures and gating system designs can prevent this defect.

Shrinkage cavity: cavity in the surface or an internal void in the casting, caused by solidification
shrinkage that restricts the amount of molten metal present in the last region to freeze. It is
sometimes called as ‘pipe’. Proper riser design can solve this problem.

Microporosity: network of small voids distributed throughout the casting caused by localized
solidification shrinkage of the final molten metal.
RESISTANCE WELDING

electrode

electrode
 Introduction:
• Resistance welding processes are pressure welding processes, heavy
current is passed for short time through the area of interface of metals to be
joined.
• These processes differ from other welding processes that no fluxes are
used, and filler metal rarely used.
• All resistance welding operations are automatic and, therefore, all process
variables are preset and maintained constant.
• Heat is generated in localized area which is enough to heat the metal to
sufficient temperature, so that the parts can be joined with the application of
pressure.
• Pressure is applied through the electrodes.

The heat generated during resistance welding is given by following

expression:
H=I2RT
Where, H is heat generated
I is current in amperes
R is resistance of area being welded
T is time for the flow of current.
Resistance Welding
• The resistance of metal to
the localized flow of
current produces heat
• Process variables
• Current
• Time
• Force
• Spot and seam welding

Spot welding
Electrode Force
• The purpose of the electrode force is to squeeze the
metal sheets to be joined together.
• This requires a large electrode force for better weld
quality
• The force must not be to large as it might cause other
problems.
• The higher electrode force also requires a higher weld
current.
• An adequate target value for the electrode force is 90 N
per mm2.
Squeeze time
• Squeeze Time is the time interval between the initial
application of the electrode force on the work and the first
application of current.
• Squeeze time is necessary to delay the weld current until
the electrode force has attained the desired level.
 Weld time
• Weld time is the time during which welding current is applied to the
metal sheets.
• The weld time is measured and adjusted in cycles of line voltage.
• Weld time should be as short as possible.
• The weld current should give the best weld quality as possible.
• The weld time should be chosen to give as little wearing of the
electrodes
• The weld time shall cause the nugget diameter to be big when
welding thick sheets.
• The weld time might adjusted to fit within the welding equipment
• The weld time shall cause the indentation due to the electrode to be
as small as possible. (This is achieved by using a short weld time.)
 Hold time (cooling time)
• Hold time is the time, after the welding, when the electrodes
are still applied to the sheet to chill the weld.
• Hold time is necessary to allow the weld nugget to solidify
before releasing the welded parts, but it must not be to long as
this may cause the heat in the weld spot to spread to the
electrode and heat it.
• The electrode will then get more exposed to wear.
Electrodes

Truncated cone Dome Pointed

• The diameter of the electrode contact area is also a
consideration: too small an area will produce undersized
welds with insufficient strength; too large an area will
lead to unstable and inconsistent weld growth
characteristics.
• Electrodes must be able to:
• conduct current to the workpiece, mechanically hold the
workpiece, and conduct heat into the workpiece.
• Electrode materials must be able to sustain high loads at
elevated temperatures, while maintaining adequate thermal and
electrical conductivity.
•
Electrode materials
• Class 1 (99% copper, 1% cadmium; 60 ksi UTS (forged);
conductivity 92% IACS) Specifically recommended,
because of its high electrical and thermal conductivity, for
spot welding aluminum alloys, magnesium alloys, brass
and bronze.
• Class 2 (99.2% copper, 0.8% chromium; 62 ksi UTS
(forged), 82% IACS) General purpose electrode material
for production spot and seam welding of most materials.
• Group B contains refractory metals and refractory metal
composites.
• Group C contains specialty materials such as dispersion-
strengthened copper.
 Spot Welding Advantages
• Very little skill is required to operate the resistance welding machine.
• These are very well suited for mass production, as they give a high
production rate.
• High speed, < 0.1 seconds in automotive spot welds
• Excellent for sheet metal applications, < ¼-inch
• No filler metal
• The first advantage is speed.
• When over 5000 welds needed for a car spot weld is easy.
• The process is also adaptable to robotic manipulation
• It is possible to weld dissimilar metals as well as metal plates of
different thicknesses
Process Disadvantages and Limitations
• Higher equipment costs
than arc welding
• Power line demands
• Nondestructive testing
• Low tensile and fatigue
strength
• Electrode wear
• Lap joint requires
additional metal
Seam Welding
Seam Welding
• Resistance seam welding is a variation on resistance spot
welding.
• In this case, the welding electrodes are motor-driven
wheels rather than stationary caps.
• This results in a rolling resistance or seam weld.
• There are three independent parameters in configuring
seam welding machines: power supplies and controls,
welding wheel configuration, and sheet configuration.
• Depending on this frequency and the speed with which the
material is being welded, the weld will be either a continuous
seam weld, an overlapping seam weld, or a roll spot weld.
• Overlapping or Continuous Seam welds are typically used to
produce continuous gas- or water-tight joints in sheet
assemblies, such as automotive gasoline tanks.
• The process is also used to weld longitudinal seams in
structural tubular sections that do not require leak-tight seams.
• In most applications, two wheel electrodes, or one translating
wheel and a stationary mandrel, are used to provide the
current and pressure for resistance seam welding.

Roll spot weld Overlapping seam weld Continuous seam weld

Projection Welding
• One of the sheets to be joined, is provided with a number
of projections to help localise the current at a
predetermined spot.
• The projections are generally very small, of the order of
0.8 mm and are obtained by means of embossing.
• As the welding current passes through these projections,
they soften, get melted and a fusion joint is made under
the pressure applied from the electrode.
FRICTION WELDING
Introduction
Friction welding is a solid state joining process that
produces coalescence by the heat developed between two
surfaces by mechanically induced surface motion.
•It is solid state joining process.
•Mechanical friction between a moving work piece and a
stationary component.
•Lateral force (upset) is applied to plastically displace and
fuse the materials
Advantages
• It is environment friendly process without generation
smoke etc.
• Narrow heat affected zone so no change in properties of
heat sensitive material.
• No filler metal required.
• Welding strength is strong in most cases.
• Easily automated.
• High welding speed.
• High efficiency of weld.
• Wide variety of metal can be weld by this process.
Disadvantages
• This is mostly used only for round bars of same cross
section.
• Non-forgeable material cannot be weld.
• Preparation of work piece is more critical
• High setup cost.
• Joint design is limited.
Application:
• For welding tubes and shafts.
• It is mostly used in aerospace, automobile, marine and oil
industries.
• Gears, axle tube, valves, drive line etc. components are
friction welded.
• It is used to replace forging or casting assembly.
• Hydraulic piston rod, truck rollers bushes etc. are join by friction
welding.
• Used in electrical industries for welding copper and aluminum
equipment’s.
• Used in pump for welding pump shaft (stainless steel to carbon
steels).
• Gear levers, drill bits, connecting rod etc. are welded by friction
welding.
FRICTION STIR WELDING
Introduction
FSW was invented by Wayne Thomas at TWI(The Welding
Institute) Ltd in 1991.
• It overcomes many of the problems associated with
conventional joining techniques.
• FSW is low energy input, capable of producing very high
strength welds in wide range of materials at lower cost.
• FSW process takes place in the solid phase below the
melting point of the materials to be joined.
 WORKING PRINCIPLE
• In friction stir welding (FSW) a cylindrical, shouldered tool with a
profiled probe is rotated and slowly plunged into the joint line between
two pieces butted together.
• The parts have to be clamped onto a backing bar to prevents from
being forced apart.
• Frictional heat is generated between the wear resistant welding tool
and the material of the work pieces.
• This heat causes the latter to soften without reaching the melting point
and allows traversing of the tool along the weld line.
• The maximum temperature reached is of the order of 0.8 of the melting
temperature of the material.
• The plasticized material is transferred from the leading edge of the tool
to the trailing edge of the tool probe and is forged by the intimate
contact of the tool shoulder and the pin profile.
• It leaves a solid phase bond between the two pieces.
• The process can be called as a solid phase keyhole welding
technique since a hole to accommodate the probe is
generated, then filled during the welding sequence.
• The non-consumable tool has a circular section except at the
end where there is a threaded probe or more complicated
flute; the junction between the cylindrical portion and the
probe is known as the shoulder.
• The probe penetrates the work piece whereas the shoulder
rubs with the top surface.
• The tool has an end tap of 5 in 6 mm diameter and a height of
5 to 6 mm (may vary with the metal thickness)
• The tool is set in a positive angle of some degree in the
welding direction.
• The design of the pin and shoulder assembly plays a major
role on how the material moves during the process.
FSW Equipment
FACTORS AFFECTING WELD QUALITY
• Type of metal
• Angle of tool
• Traversing speed of the tool
• Spinning speed of tool
• Pressure applied by the pin tool
Research is going on to combine the above factors in order
to control the process in a better way
IMPORTANT WELDING ZONES
• Friction stir weld consists of three zones:
(a) Nugget, stirred zone,
(b) thermo-mechanically affected zone (TMAZ)
(c)heat affected zone (HAZ).
•The three zones pose distinct mechanical properties and
nugget and TMAZ being the weakest part of the joint.
Material Suitability
 Copper and its alloys
 Lead
 Titanium and its alloys
 Magnesium alloys
 Zinc
 Plastics
 Mild steel
 Stainless steel
 Nickel alloys
Tools Parameters
•H13 steel tools are used
•Tool is strong, tough,
hard wearing at welding
temperature
•Have good oxidation
resistance, thermal
conductivity
Welding Steel using FSW
Advantages
• Good mechanical properties of weld joint
• Avoids toxic fumes, warping, and shielding issues
• Little distortion or shrinkage
• Good weld appearance
• No consumables
• Easily automated on simple milling machines
• Can operate on all positions (vertical,horizontal) etc
• Low environment impact
• High superior weld strength
Disadvantages
• An exit hole is produce when tool is withdrawn
• Heavy duty clamping of parts is required
• Slower traverse rate than fusion welding
APPLICATIONS
• AEROSPACE
• SHIP BUILDING & OFFSHORE
• AUTOMOTIVE
• FABRICATIONS
• RAILWAYS
EXPLOSIVE WELDING
 Introduction
• Explosion welding is also a solid state welding process in
which the welding occurs without application of external heat.
• In this type of welding no additional filler material is used.
• This welding takes place without formation of plastic state.
• It is mainly used to join large surface area of dissimilar
material which cannot be weld by other welding processes.
• This welding finds application to join large metal plates,
cladding one tube on another, plugging of heat exchanger, join
various electric connectors, join two pipes etc.
 Principle:
• This welding process works on principle of metallurgical
bonding.
• A controlled detonation of explosive is used to weld surfaces.
• This explosion generates a high pressure force, which deform
the work plates plastically at the interface.
• This metallurgical bond is stronger than the parent materials.
• The detonation process occurs for a very short period of time
which cannot damage the parent material.
• This welding is highly depend on welding parameters like
standoff distance, velocity of detonation, surface preparation,
explosive etc.
• This welding is capable to join large area due to high energy
available in explosive.
 Basic Terminology:
Base Plate: This is one of the welding plate which is kept stationary on
a avail.
Flyer Plate: This is another welding plate which is going to be weld on
base plate. It has lowest density and tensile yield strength compare to
base plate. It is situated parallel or at an angle on the base plate.
Buffer Plate: Buffer plate is situated on the flyer plate. This plate is
used to minimize the effect or explosion on upper surface of flyer plate.
Standoff distance:It is distance between flyer plate and base plate.
Generally it is taken double of thickness of flyer plate for thin plates and
equal to thickness of flyer plate for thick plates.
Explosive: Explosive is placed over the flyer plate. Mostly RDX, TNT,
Lead azide, PETN etc. used as explosive.
Velocity of detonation: It is the rate at which the explosive detonate.
This velocity should be kept less than 120% of sonic velocity. It is
directly proportional to explosive type and its density.
Types:
1. Oblique Explosion Welding:
In this type of welding process base plate is fixed on an
anvil and filler plate makes an angle with the base plate.
This welding configuration is used to join thin and small
plates.
2. Parallel Explosion Welding:
As the name implies, in this welding configuration filler
plate is parallel to the base plate. There is some standoff
distance between base plate and flyer plate. This
configuration is used to weld thick and large plates.
Advantages:

• It can join both similar and dissimilar material.

• Simple in operation and handling.
• Large surface can be weld in single pass.
• High metal joining rate. Mostly time is used in preparation
of the welding.
• It does not effect on properties of welding material.
• It is solid state process so does not involve any filler
material, flux etc.
Disadvantages:
• It can weld only ductile metal with high toughness.
• It creates a large noise which produces noise Pollution.
• Welding is highly depends on process parameters.
• Higher safety precautions involved due to explosive.
• Designs of joints are limited.
Application:
• Used to weld large structure sheets of aluminum to
stainless steel.
• It is used to weld cylindrical component like pipe,
concentric cylinder, tube etc.
• Weld clad sheet with steel in a heat exchanger.
• Join dissimilar metals which cannot be weld by other
welding process.
• For joining cooling fan etc.
Examples
DIFFUSION BONDING
Introduction:
• Diffusion bonding is a solid state welding process in
which, no liquid or fusion phase involves and the weld
joint is form in pure solid state.
• It does not melt the welding material and mostly a little
plastic deformation takes place at interface surface and
weld is form due to inter-molecular diffusion.
• This bonding process conducted in vacuum or in inert
environment to reduce oxidation.
• This is widely used to join refectory materials in
aerospace and nuclear industries.
• This type of welding can be used to weld both similar and
dissimilar materials with the help of high pressure and
temperature.
 Principle and Working:
• This process works on basic principle of diffusion.
• Diffusion means movement of molecules or atoms from high
concentration region to low concentration region.
• In this welding process both the welding plates are placed one
over other in high pressure and temperature for a long period
of time.
• This high pressure force starts diffusion between interface
surfaces.
• This diffusion can be accelerated by the application of high
temperature.
• This temperature does not melt the welding plates.
• The temperature range is about 50-60% of melting
temperature.
The working of diffusion bonding can be summarized as follow.
• First both the welding plate surfaces prepared for welding.
surfaces made equally flat.
• The surfaces should be machined, cleaned and polished well
• The plates are clamped and placed one over another.
• This assembly placed into a vacuum chamber or in a inert
environment.
• A high pressure and temperature applied to start diffusion.
• The high pressure is applied by a hydraulic press, dead weight
or by the differential gas pressure. This conditions are
maintained for a long duration of time for proper diffusion.
• At the starting stage of this process, local deformation at the
interface surface due to creep and yield take place. Now the
diffusion takes place which form a interface boundary.
• After a long period of time, both the plates properly diffused
into one another which makes a strong joint.
Advantages:
• The joint have same mechanical and physical properties as
parent material.
• This process produces clean joint which is free from interface
discontinuity and porosity.
• Both similar and dissimilar material can be joint by diffusion
bonding process.
• It provides good dimension tolerance. So it is used to make
precision components.
• Low running cost.
• It is simple in working.
• It does not use filler material, flux etc. which are used in arc
welding process.
• It can weld complex shapes.
Disadvantages:
• High initial or setup cost.
• It is time consuming process. It takes more time compare
to other welding process.
• Surface preparations of welding plates are more critical
and difficult.
• Size of the weld is limited according to equipment
available.
• This process is not suitable for mass production.
• Highly depend on welding parameters like surface finish,
welding material, temperature, pressure etc.
Application:
• It is mostly used to weld refectory materials used in
aerospace and nuclear industries.
• Diffusion bonding is used to weld titanium, zirconium and
beryllium metals and its alloy.
• It can weld nickel alloy like Inconel, Wrought Udimet etc.
• It is used to weld dissimilar metals like Cu to Ti, Cu to Al
etc.
THERMIT WELDING
Thermit Welding
• The heat source utilised for fusion in thermit welding is
the exothermic reaction of the thermit mixtures.
• A typical thermit mixture for welding steels is aluminium
and iron oxide.
• When the intimately mixed thermit powder is brought to
its ignition temperature of 1200C, the thermit reaction
starts.
• Aluminium has greater affinity towards oxygen, and as a
result, it reduces the ferric oxide to liberate iron and in the
process, releases heat.
Thermit Welding
• 3 Fe3O4 + 8 Al  9 Fe + 4 Al2O3 + 3.01 MJ/mol

• The temperature reached is of the order of 3000ºC.

• The enormous amount of heat liberated, melts both the
iron and aluminium oxide to a very fluid state.
• Because of the large differential in the densities,
aluminium oxide would be floating on the top with the
molten steel settling below.
• Once started, the reaction continues till all the thermit
mixture in the reaction vessel or ladle is completely
reduced.
Advantages
• It is very portable process.
• No external power supply required.
• It is very cheap process for repairing broken parts of large
metal structures such as rail lines, large parts of ships.
• On site welding can be done for railways.
LIMITATIONS
• Can only be used for ferrous metals.
• It is uneconomical when used for welding cheap metals or
light parts.
• Thermite mixtures can not be stored due to safety
hazards and should be used as soon as prepared.
Thermit Applications
• Repairing fractured rails
• For butt welding pipes end to end
• For welding large fractured crankshafts
• For welding broken frames of machines
• Welding of sections of casting where size prevents there
being caste in one piece
• Replacing broken pieces or large gears
• End welding of reinforcing bars used in huge concrete
constructions
ELECTRON BEAM
WELDING
 Electron Beam Welding
• The cathode within the electron gun is the source of a stream of
electrons.
• These electrons are accelerated towards the anode because of
the large potential difference that exists between them.
• The potential differences that are used are of the order of 30 kV
to 175 kV.
• The higher the potential difference, higher would be the
acceleration.
• The current levels are ranging between 50 to 1000 mA.
• Depending on the accelerating voltage, the electrons would
travel at the speed of 50,000 to 2,00,000 km/s.
• The depth of penetration of the weld depends on this electron
speed which in turn is dependent upon the accelerating voltage.
 Equipment’s:
Power Supply:
• The voltage range of welding is about 5 – 30 kV-175 Kv for low voltage
equipment’s or for thin welding and 70 – 175kV for high voltage equipment’s or
for thick welding.
Electron Gun:
• It is heart of electron beam welding.
• It is a cathode tube generates electrons, accelerate them and focus it on a spot.
This gun is mostly made by tungsten or tantalum alloys.
Anode:
• Anode is a positive pole, just after the electron gun. Its main function is to
attract negative charge, provide them a path and don’t allow them to diverge
from its path.
Magnetic Lenses:
• There are a series of magnetic lenses which allows only convergent electrons
to pass. They absorb all low energy and divergent electrons, and provide a high
intense electron beam.
Electromagnetic lens and deflection coil:
• Electromagnetic lens used to focus the electron beam on work
piece and deflection coil deflect the beam at required weld area.
These are last unit of EBW process.

Work holding device:

• EBW uses CNC table for hold work piece which can move in all
three direction. The welding plates are clamped on CNC table with
the use of suitable fixtures.

Vacuum Chamber:
• As we know, whole this process takes place in a vacuum chamber.
Vacuum is created by mechanical or electric driven pump. The
pressure ranges in vacuum chamber is about 0.1 to 10 Pa.
Advantages of Electron Beam Welding
• Tight continuous weld;
• Low distortion;
• Narrow weld and narrow heat affected zone;
• Filler metal is not required.
• It can weld both similar and dissimilar metals.
• It provides high metal joining rate.
• Low operating cost because no filler material and flux are used.
• It provide high finish welding surface.
• It can used to weld hard materials.
• Less welding defects occur due to whole process carried out in
vacuum.
Disadvantages of Electron Beam Welding
• Expensive equipment;
• High production expenses;
• X-ray irradiation
• High skilled labor required.
• Frequently maintenance required.
• Work pieces size is limited according to vacuum chamber.
Applications of Electron beam welding
• It is used in aerospace industries and marine industries
for structure work
• It is used to join titanium and its alloy.
• This type of welding is widely used to
join gears, transmission system, turbocharger etc. in
automobile industries.
• It is used to weld electronic connectors in electronic
industries.
• This process is also used in nuclear reactors and in
medical industries
FORGE WELDING
 Forge Welding
• Forge welding is a solid state welding process in which metal
joint is created due to inter-molecular diffusion.
• Forging is a technique of shaping any metal by application of
high pressure and temperature.
• This welding process uses fundamental technique of forging to
weld similar or dissimilar metals.
• It has been used from a very old period to join iron or steel
work pieces.
• In this process the ends of the parts to be joined are heated to
a temperature slightly below the solidus temperature and a
pressure is applied so that a fusion joint is obtained.
• The force can be applied in repeated blows manually or by a
machine, or continuously by rotating rolls.
Principle
• This heating deforms the work pieces plastically.
• Now a repeated hammering or high pressurize load is
applied on these plates together.
• Due to this high pressure and temperature, inter-
molecular diffusion takes place at the interface surface of
the plates which make a strong weld joint.
• This is basic principle of forge welding.
Advantages:
• It is simple and easy.
• It does not require any costly equipment for weld small
pieces.
• It can weld both similar and dissimilar metals.
• Properties of weld joint is similar to base material.
• No filler material required.
Disadvantages:

• Only small objects can be weld. Larger objects required

large press and heating furnaces, which are not
economical.
• High skill required because excessive hammering can
damage the welding plates.
• High Welding defects involve.
• It cannot use as mass production.
• Mostly suitable for iron and steel.
• It is a slow welding process.
Application:
• It is used to join steel or iron.
• It is used to manufacture gates, prison cells etc.
• It is widely used in cookware.
• It was used to join boiler plates before introduction of
other welding process.
• It was used to weld weapon like sword etc.
• Used to weld shotgun barrels.
ORBITAL WELDING
MIAB WELDING
Magnetic Impelled Arc Butt Welding (MIAB)

NO EDGE PREPARATION ! NO FILLER MATERIAL !

 Principle of MIAB welding

MIAB welding is a forge welding process that relies on an electric arc to

generate necessary heating to melt the surfaces being welded.
How MIAB welding works?
• Welding arc rotate in the gap between tubes due to the presence of external
magnetic field generated with permanent or electromagnets.
• The maximum Linear Speed of the arc movement is 870 km/hour.
• The spinning arc in combination with thermal conductivity of the welded metal
creates very uniform heating at the joint.
• On completion of welding, the welded parts are rapidly brought under pressure.
 Applications of MIAB welding
• Butt welding of thin-walled tubes

• Butt and T-butt welding of automobile parts

• Butt welding of thick-walled tubes

• Butt welding of solid parts

• Tube to plate welding

• Tube to flange welding

This machine tool based process is attractive to the mass production

industries because of the short cycle times and reproducible quality.
 Materials to be welded

• Steel

• Stainless steel

• Aluminum alloys
 Tube Welding

MIAB welding reduces weld time by 90%

 MIAB welding machines for pipes

MD-1 K-872
Equipment composition Machine МD-1 is intended for welding small
1. Welding Head diameter tubes & pipeline.
2. Pump Station Machine K-872 is intended for welding
3. Control Cabinet pipelines under field conditions.
4. Weld Management System
5. DC Power Source
 Applications
Solid Rods

Solid Rod OD 22mm

Welding Time:12 s

Pull test of weld joint of Reinforcement Rod - OD 32 mm

 Applications
Tubes & Pipelines

Hydraulic Test Result - 72.5MPa.

Tubes OD 22 & 48 mm

“Pipes with OD up to 219mm can be welded using

MIAB”
 Automotive applications
MIAB welding is predominantly used in the European
Automobile Industry

Vehicle drive shafts.

Rear axle assembly.

Wheel bearing housing.

Pipe and tube assemblies.

Shock absorber assemblies.

Threaded sleeves assemblies.

Nuts welded to plates.

Brake pipes
Applications
Shock Absorber

Machine MD-103 and MD-102 type

Shock absorber for MIAB welding of shock absorber
Welded section:
OD53x1,8mm.
Productivity: 200
butts/hour
Welding time: t=2.9 s
Material: Steel 20 +
Steel 35
 Applications Automobile Part: Piston Rod

Piston Assembly: OD22x2.2mm

Welding Time: 3.6 s
Pull Test. Force of break - 12900 kg

HAZ
4.4mm

Line of
Joint

x250
Macro section of welded joint micro section of welded joint
 Applications Automobile part: Drive Shaft

Drive Shaft OD75x2.1 mm Machine K1015 for drive shaft welding OD 70 -

Welding time: 3.8 s 102mm,WT 2-4mm.

“The tests conducted on the drive shaft have indicated that

MIAB welding does not reduce durability of the drive shaft.”
 Applications Automobile Part: Oil
Tank

Welded Joint of Connecting Pipe:

Field for MIAB welding

OD 31.7x 4.1 mm
Welding Time: 7 s
 Applications Liquid Propane Tanks

LP Tank Assembly, Boss Weld

Size: OD 31.7 mm, WT 4.1 mm
Welding Time: 7 Second

LP Tank Assembly, Girth Weld

Size: OD203.2, WT2.1 mm
Welding Time: 12.5 s Welded Joint after Tensile
Elongation Test
Comparison to other welding processes
MIAB has replaced automated TIG, MIG, Resistance and Flash Butt Welding.

Why MIAB scores over other welding process?

 Less internal flash.

 Shorter weld times.
 Less metal loss.
 Reduced machine maintenance.
 Uniform welding.
 Low power consumption
 No rotation of components
 No consumables needed. e.g.. Filler material.
 MIAB- AN
OVERVIEW

• Can weld tube to tube or tube to flange, and can weld irregular or non circular
components as easily as circular.

• One of the fastest methods of welding tube.

• Welds are free from inclusions and impurities.

• An automated process enabling the resulting welds to be highly reproducible.

• The components are not rotated so the alignment can be maintained.

• Uniform heating of the joint results in low distortion.

• Welds a wide variety of materials including dissimilar combinations.

• Can be interfaced with automatic handling systems

SOLDERING &
BRAZING
Soldering and brazing both are metal joining process used in different joining
conditions.
These processes are more confusing to differentiate because both process use filler
material and done below critical temperature.

The basic and main difference between soldering and brazing is that soldering is
used to make a electrically strong joint between metals which can withstand with all
electric loads and brazing is used to make a mechanical strong joint which can
withstand with all mechanic loads and stresses.
Difference between soldering and brazing
 Soldering Brazing

1. It is used in electrical industries 1. It is used to mechanical

to joint capacitor, resistor, wire industries to joint different
etc. to the electronic plate. metals.
2. Soldering is done at 2. Brazing is done at temperature
temperature below 200 C. above 450C but below the
critical temperature of metal.
3. These joints are weaker than 3. It forms stronger joint
brazing joints. 4. In brazing an alloy of copper
4. In soldering an alloy of lead and and zinc is used as filler metal.
tin is used known as solder. 5. It needs special training.
5. It does not need a special 6. It is a expensive process
training to soldering. 7. This process needs preheating
6. It is a cheaper process. of base metal.
7. Soldering does not need to 8. It is used in automotive
preheat of base metal. industries and pipe fitting.
8. It is used to joint electronics
component. 9. it is not so easy for automation
9. This process is very flexible except automation is done at
and easy to automate. automotive industries.
ISO 5817
ISO 5817
• This Standard is for quality levels of imperfections in
fusion-welded joints for steel, nickel, titanium and their
alloys.
• Three quality levels are given in order to permit
application to a wide range of welded fabrication.
• They are designated by symbols B, C and D.
• Quality level B corresponds to the highest requirement on
the finished weld.
• C is medium level
• D is not ok
This International Standard applies to:
• unalloyed and alloy steels;
• nickel and nickel alloys;
• titanium and titanium alloys;
• manual, mechanized and automatic welding;
• all welding positions;
• all types of welds, e.g. butt welds, fillet welds and branch
connections;
Symbols
0 Understand the varieties of fabrication methods used in
manufacturing
0 Utilize gas welding processes for low volume and repair work
0 Select different arc welding processes for large volume
manufacture
0 Use resistance welding processes for sheet metal joints
0 Design welded joints to produce defect free weldments

2
0 Mechanical joining by means of bolts, screws and rivets.
0 Adhesive bonding by employing synthetic glues such as
epoxy resins.
0 Welding, brazing and soldering.

3
4
5
6
7
8
0 Different types of welding joints are classified as butt, lap,
corner, tee and edge joints.

9
10
 Flat

g Vertical
Overhead
Up Vertical
Down

Arrow shows the direction of motion of the electrode / torch.

The torch is held approximately normal to thisdirection.
12
13
14
Need for edge Preparation:
Edge preparation is depends on strength required or to Increase
the load bearing capability of the joint.
In Single square groove the molten liquid will not penetrate fully
into the thickness of the joint. Making the joint weak.

In Case of double v groove Will get full thickness.

15
16
17
18
19
0 Also called as oxy-fuel gas welding (OFW),
derives the heat from the combustion of a
fuel gas such as acetylene in combination
with oxygen.
0 It is a fusion welding process wherein the
joint is completely melted to obtain the
fusion.
0 The heat produced by the combustion of gas
is sufficient to melt any metal and as such is
universally applicable.
20
21
0 In all the oxy-fuel gas welding processes, the combustion
takes place in two stages.
0 The first reaction takes place when the fuel gas such as
acetylene and oxygen mixture burn releasing intense heat.
0 This is present as a small white cone as shown in Fig
0 C2H2 + O2  2CO + H2 + 18.75 MJ/m3

22
0 The carbon monoxide (CO) and hydrogen produced in the
first stage further combine with the atmospheric oxygen
and give rise to the outer bluish flame, with the following
reaction.
0 4 CO + 2H2 + 3O2  4CO2 + 2H2O + 35.77 MJ/m3

Types
0 Neutral flame
0 Carburising flame or Reducing flame
0 Oxidising flame

23
24
 Oxy-Acetylene Welding Equipment

0 The oxygen is normally stored in strong cylinders at a

pressure ranging from 13.8 MPa to 18.2 MPa.
0 Acetylene is normally made available in the following two
forms:
0 Acetylene storage cylinder, and
0 Acetylene generator.

25
26
27
28
Oxy-Acetylene Welding
Technique

29
30
31
32
0 It is versatile.
0 Also the source of heat is separate from the filler rod and
hence, the filler metal can be properly controlled and heat
properly adjusted giving rise to a satisfactory weld.
0 This method of welding is somewhat slower.

33
Recrystallisation
• Under the action of heat and the force, when the atoms
reach a certain higher energy level, the new crystals start
forming which is termed as recrystallisation.
• Recrystallisation destroys the old grain structure
deformed by the mechanical working, and entirely new
crystals, which are strain free are formed.
• The grains are in fact start nucleating at the points of
severest deformation.
Hot Working and Cold Working
• The metal working processes are traditionally divided into
hot working and cold working processes.
• Those processes, working above the recrystallisation
temperature, are termed as hot working processes
whereas those below are termed as cold working
processes.
Hot Working
• Any amount of working can be imparted
• There is no limit on the amount of hot working that can be
done on a material.
• The hot working requires much less force to achieve the
necessary deformation.
• It is possible to continuously reform the grains in metal
working and if the temperature and rate of working are
properly controlled, a very favourable grain size could be
achieved giving rise to better mechanical properties.
Hot Working
• Some metals cannot be hot worked because of their
brittleness at high temperatures.
• Higher temperatures of metal give rise to scaling of the
surface and as a result, the surface finish obtained is
poor.
• The dimensional accuracy in hot working is difficult to
achieve since it is difficult to control the temperature of
workpieces.
• Handling and maintaining of hot metal is difficult and
troublesome.
Cold Working
• Cold working increases the strength and hardness of the
material due to the strain hardening which would be
beneficial in some situations.
• Good surface finish is obtained.
• Better dimensional accuracy is achieved.
• It is far easier to handle cold parts and also is economical
for smaller sizes.
• The amount of deformation that can be given to is limited
by the capability of the presses or hammers used.
• The maximum amount of deformation that can be given is
limited.
• Some materials, which are brittle, cannot be cold worked.
ROLLING
29 March 2019 9

Rolling
• Rolling is a process where the metal is compressed
between two rotating rolls for reducing its cross-sectional
area (Fig 7-5).
• This is one of the most widely used of all the metal
working processes, because of its higher productivity and
low cost.
• Rolling is normally a hot working process unless
specifically mentioned as cold rolling.
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Rolling
• The reduction that could be achieved with a given set of
rolls is designated as the 'angle of bite' and is shown in
Fig 7-5.
29 March 2019 13

Rolling Stand Arrangement

• The arrangement of rolls in a rolling mill, also called rolling
stand, varies depending on the application.
• The various possible configurations are presented in Fig
7-7 and 7-8.
• The names of the rolling stand arrangements are
generally given by the number of rolls employed.
29 March 2019 14
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Rolling Passes
• Break down passes: These are used for reducing the
cross-sectional area nearer to what is desired. These
would be the first to be present in the sequence.
• Roughing passes: In these passes also, the
cross-section gets reduced, but along with it, the shape of
the rolled material comes nearer to the final shape.
• Finishing passes: These are the final passes, which give
the required shape of the rolled section. Generally the
finishing pass follows a leader pass.
29 March 2019 17

Extrusion
• Extrusion is the process of confining the metal in a closed
cavity and then allowing it to flow from only one opening
so that the metal will take the shape of the opening.
• The operation is identical to the squeezing of tooth paste
out of the tooth paste tube.
29 March 2019 18

Extrusion Principle
• The equipment consists of a cylinder or container into
which the heated metal billet is loaded.
• On one end of the container, the die plate with the
necessary opening is fixed.
• From the other end, a plunger or ram compresses the
metal billet against the container walls and the die plate,
thus forcing it to flow through the die opening, acquiring
the shape of the opening.
• The extruded metal is then carried by the metal handling
system as it comes out of the die.
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Cold Extrusion
Forward cold extrusion
• Impact extrusion: The slug for making the component is
kept on the die and the punch strikes the slug against the
die. The metal is then extruded through the gap between
the punch and die opposite to the punch movement.
• Cold extrusion forging: The cold extrusion forging is
similar to impact extrusion but with the main difference
that the side walls are much thicker and their height is
smaller.
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Tooling for Cold Extrusion

• The typical example is the body of spark plugs used in
internal combustion engines. In the process both the
forward as well as backward extrusions are used.
• A typical example of a gear blank as it is produced in cold
forging with its various stages.
• The shapes that can be successfully cold extruded are
the variants of the basic products such as rod, tube and
can.
29 March 2019 28
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Extruding Tubes
• First, the solid ram moves through the heated metal billet
creating a hole at the centre.
• Later, the hollow plunger moves the metal billet through
the die. Because of the presence of the solid ram very
close to the die, the necessary hole is made in the
extruded metal.
29 March 2019 31

Extruding Tubes
• The spider die is essentially an extrusion die with a stub
mandrel, for the hollow portion to be generated.
• It is held to the die by means of thin ribs simulating the
spider legs.
• The material when extruded, flows through the openings
between the legs and form as the central opening
because of the stub mandrel.
• The metal flowing out is actually separated but get
welded together since it is still in plastic state.
29 March 2019 32
29 March 2019 33

Hydrostatic Extrusion
• In this, the metal billet is compressed from all sides by a
liquid rather than the ram.
• The presence of liquid inside the container eliminates the
need for any lubricant and also the material is more
uniformly compressed from all sides throughout the
deformation zone.
29 March 2019 34
29 March 2019 35

Wire Drawing
• A wire by definition, is circular with small diameters so that
it is flexible.
• The process of wire drawing is to obtain wires from rods
of bigger diameter through a die.
• Wire drawing is always a cold working process.
29 March 2019 36
29 March 2019 37

Rod and Tube Drawing

• Rod drawing is similar to wire drawing except for the fact
that the dies are bigger because of the rod size being
larger than the wire. But the rod drawn in coiled form is to
be straightened and then cut into proper lengths.
• The tubes are also first pointed and then entered through
the die where the point is gripped in similar way as the bar
drawing and pulled through in the form desired along a
straight line.
29 March 2019 38
29 March 2019 39

Swaging
• Swaging is a mechanical deformation technique of
reducing or shaping the cross-section of rods or tubes by
means of repeated impacts or blows.
• The swaging process consists of dies which are given the
requisite external shape.
• These dies intermittently hammer the stock to produce the
deformation.
29 March 2019 40
29 March 2019 41

Tube Making
• It is also possible to obtain seamless tubes by a variation
of rolling called roll piercing.
• Here, the billet or round stock is rolled between two rolls,
both of them rotating in the same direction with their axes
at an angle of 4.5 to 6.5 deg as shown in Fig 7-65.
29 March 2019 42
29 March 2019 43

Tube Making
• The tube obtained in the roll piercing mill is further
processed in a plug mill, as shown in Fig 7-66, to obtain
the desired size.
• Plug mill is usually a two high reversing stand.
• It contains a central mandrel to form the tube inner
diameter.
29 March 2019 44
 What is Sheet Metal?

 A piece of metal whose thickness is between 0.006(0.15 mm)
and 0.25 inches(6.35 mm).
 Anything thinner is referred to as a foil and thicker is considered
as a plate.
 Sheet thickness is generally measured in gauge. Greater the
gauge number, thinner the sheet of metal.
 Sheet metal can be cut, bent and stretched into nearly any
shape.
 Generally two types of operations are performed- forming and
cutting.
2
 What is Sheet Metal?

 Sheet metal is a metal formed into thin and flat pieces. It is one
of the fundamental forms used in metalworking, and can be cut
and bent into a variety of different shapes.
 Countless everyday objects are constructed by this material.
 Thicknesses can vary significantly, although extremely thin sheets
are considered as foil or leaf, and sheets thicker than 6 mm (0.25
in) are considered as plate.
 Sheet metal forming is a grouping of many complementary
processes that are used to form sheet metal parts.

3
 Sheet Metal Working & Process

 Bending  Notching  Deep drawing
 Shearing  Perforating  Stretch forming
 Blanking  Nibbling  Roll forming
 Punching  Embossing
 Trimming  Shaving
 Parting  Cutoff
 Slitting  Dinking
 Lancing  Coining

46
 Bending

 Bending is a metal forming process in which a force is applied to
a piece of sheet metal, causing it to bend at an angle and form
the desired shape.

47
Press Brake Machine


48
 Bending Types

Two common bending methods are:
 V-Bending
 Edge bending
 V-Bending - The sheet metal blank is
bent between a V-shaped punch
and die.
 Air bending - If the punch does not
force the sheet to the bottom of the
die cavity, leaving space or air
underneath, it is called “air bending”.

49
 Bending Types

 Edge (or) Wipe Bending - Wipe
bending requires the sheet to be
held against the wipe die by a
pressure pad. The punch then presses
against the edge of the sheet that
extends beyond the die and pad.
The sheet will bend against the radius
of the edge of the wipe die.

50
Bending Operations


51
 Shearing

 Shearing is defined as separating
material into two parts.
 It utilizes shearing force to cut sheet
metal.

53
 Blanking

 A piece of sheet metal is removed
from a larger piece of stock.
 This removed piece is not scrap, it is
the useful part.

54
 Fine Blanking

 A second force is applied
underneath the sheet, directly
opposite the punch, by a "cushion".
 This technique produces a part with
better flatness and smoother edges.

55
Punching Operations


56
 Punching Or Piercing

 The typical punching operation, in
which a cylindrical punch pierces a
hole into the sheet.

57
Blanking & Punching examples


58
 Trimming

 Punching away excess material from the perimeter of a part,
such as trimming the flange from a drawn cup.

59
 Parting

 Separating a part from the remaining sheet, by punching away
the material between parts.

60
 Slitting

 Cutting straight lines in the sheet. No scrap material is produced.

61
 Lancing

 Creating a partial cut in the sheet, so that no material is
removed. The material is left attached to be bent and form a
shape, such as a tab, vent, or louver.

62
 Notching

 Punching the edge of a sheet, forming a notch in the shape of a
portion of the punch.

63
 Perforating

 Punching a close arrangement of a large number of holes in a
single operation.

64
 Nibbling

 Punching a series of small overlapping slits or holes along a path
to cut-out a larger contoured shape.

65
 Embossing

 Certain designs are embossed on the sheet metal.
 Punch and die are of the same contour but in opposite
direction.

66
 Shaving

 Shearing away minimal material from the edges of a feature or
part, using a small die clearance. Used to improve accuracy or
finish. Tolerances of ±0.025 mm are possible.

67
 Cuttoff

 Cutoff - Separating a part from the remaining sheet, without
producing any scrap.
 The punch will produce a cut line that may be straight, angled,
or curved.

68
 Dinking

 Dinking - A specialized form of piercing used for punching soft
metals. A hollow punch, called a dinking die, with beveled,
sharpened edges presses the sheet into a block of wood or soft
metal.

69
 Coining

 Similar to embossing with the difference that similar or different
impressions are obtained on both the sides of the sheet metal.

70
 Deep Drawing

 Deep drawing is a metal forming process in which sheet metal is
stretched into the desired shape.
 A tool pushes downward on the sheet metal, forcing it into a die
cavity in the shape of the desired part.

71
Process overview in deep drawing


72
 Stretch Forming

 Stretch forming is a metal forming process in which a piece of
sheet metal is stretched and bent simultaneously over a die in
order to form large bent parts.

73
 Roll Forming

 Roll forming is a continuous bending
operation in which a long strip of sheet
metal is passed through sets of rolls
mounted on consecutive stands, each
set performing only an incremental
part of the bend, until the desired
cross-section profile is obtained.
 Roll forming is ideal for producing
constant-profile parts with long lengths
and in large quantities.
74
 Dies

 Made up of tool steel and used to cut or shape material.
 Simple die
 Compound die
 Combination die
 Progressive die

75
 Simple Die

 Simple dies or single action dies perform single operation for
each stroke of the press slide.
 The operation may be one of the cutting or forming operations.

76
 Compound Die

 In these dies, two or more operations may be performed at one
station.
 Such dies are considered as cutting tools since, only cutting
operations are carried out.

77
 Combination Die

 In this die also , more than
one operation may be
performed at one station.
 It is different from
compound die in that in
this die, a cutting
operation is combined
with a bending or drawing
operation, due to that it is
called combination die.
78
 Progressive Die

 A progressive has a series of operations.
 At each station, an operation is performed on a work piece
during a stroke of the press.

79
 Rolling Defects

 Wavy edges
 Result from concave roll bending and
 Thinner along its edges than at its center
 Cracks
 Result from poor material ductility
 Convex roll bending
 Severe conditions cause center split
 Alligatoring
 Defects in the original cast material
 Only surface of work is deformed
81
 Forging defects

 Surface crack
 Excessive working at low temperatures
 High sulphur concentration

 Crack at flash
 More prevalent for thinner flash
 Penetrates to work

 Internal cracks
 Secondary tensile stresses
 Cold shuts
 Lubricant residue
2/17/2016 Compiled & Edited by SIVARAMAN VELMURUGAN 82
 Drawing Defects

 Wrinkling in the flange
 Occurs due to compressive buckling in
the circumferential direction (blank
holding force should be sufficient to
prevent buckling.
 Wrinkling in the wall
 Takes place when a wrinkled flange is
drawn into the cup or if the clearance is
very large, resulting in a large
suspended (unsupported) region.

83
 Drawing Defects

 Tearing
 High tensile stresses that cause thinning
and failure of the metal in the cup wall.
 If the die has a sharp corner radius.

 Earring
 When the material is anisotropic
 Varying properties in different directions.

 Surface scratches
 If the punch and die are not smooth
 If the lubrication of the process is poor.

84
 Defects in Extrusions

 Surface Cracking / Fir-tree cracking
 High friction or speed.
 Sticking of billet material on die land.
 Material sticks, pressure increases,
product stops and starts to move
again.
 produces circumferential cracks on

surface, similar to a bamboo

stem.(bambooing).

85
 Defects in Extrusions

 Internal Cracking/ Chevron cracking
 Center of extrusion tends to develop
cracks of various shapes.
 Center-burst, and arrowhead
 Center cracking:

 Increases with increasing die

angle.
 Increases with impurities.
 Decreases with increasing R and
friction.

86