Manufacturing Processes
Welding
BITS Pilani
Hyderabad Campus
Soldering, Brazing and
Welding Technology
32-34
Soldering, Brazing and
Welding Technology
ARC welding, gas welding, Soldering,
Brazing,
T1-Ch 12
T1 Serope Kalpakjian, Steven R. Schmid, “Manufacturing Processes for Engineering
Materials”, Pearson Education (Low Price Edition), 2003
T2 or R1. Manufacturing Science by Amitabha Ghosh and Asok Kumar Mallik,
East-West Press Pvt Ltd
BITS Pilani, Hyderabad Campus
Classification of joining processes
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Welding Process
Definition:
• Welding is a joining process which produces coalescence of
materials by heating them to suitable temperatures with or
without the application of pressure or by the application of
pressure alone, and with or without the use of filler material
Applications:
• It is used in the manufacture of automobile bodies, aircraft
frames, railway wagons, machine frames, structural works,
tanks, furniture, boilers, general repair work and ship
building.
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Liquid state welding
• The liquid state joining processes involve localized melting
and solidification of workpiece materials with or without the
addition of external filler material.
• The liquid state joining processes are commonly referred to
as fusion welding.
• Based on the characteristics of the external filler (electrode)
material, the welding processes can also be classified as
• consumable electrode and
• non-consumable electrode welding processes.
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Principles of Fusion Welding
• Material around the joint is melted in both the parts to be
joined
• Molten filler material may also be added
• Three distinct zones in weld part as shown:
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…continued
Important factors governing fusion welding:
• Characteristics of heat source
• Nature of deposition of filler material in fusion zone
• Heat flow characteristics
• Cooling of fusion zone
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Electric Arc Welding
• An arc is generated between two conductors of
electricity, cathode and anode when they are touched to
establish the flow of current and then separated by small
distance
• Anode (positive electrode)--workpiece
• Cathode (negative electrode)--electrode rod
• Temperature of order 6000oC generated at anode
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Arc Welding schematic
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Electrodes
• Electrodes are used for providing heat input in
arc welding
• Types:
• Consumable
• Non consumable
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Consumable
Non Consumable
• Tip of electrode melts
• Acts as filler rod also to
provide filler metal
• Made of steel, Cast Iron,
Copper, brass, Bronze,
Aluminum
Types
– Coated
• No melting of electrode
tip
• Filler metal to be
deposited through
separate filler rod
• Made of carbon,
graphite, tungsten
• Used in TIG
o Used SMAW
– Bare
o Used MIG/GMAW
Arc welding
•Arc is struck
Cathode (-)
(-) Charged
electrons
Air gap
DC
Power
Supply
(+) Charged
ions
Anode (+)
•Electrons travel form
cathode to Anode at very
high speed
•K.E of electrons converted
to Heat
•Positively charged ions from
anode to Cathode provide
protecting shield
ARC welding
Straight Polarity
&
Reverse Polarity
WELD PENETRATION
Bead
Base
Metal
(a) DC straight polarity (positive workpiece)
Penetration depth
(b) DC reverse polarity (negative workpiece)
(c) AC source
Arc welding
The actual heat utilized by the joint depends
upon how this heat is transferred from the tip of the
electrode to the joint .Hence ,a factors of heat
tranfers efficiency ,f1 is defined to take into account
of any losses in between such that the net heat
.
available
at the weld joint,
Numerical
Calculate the melting efficiency in the case of
arc-welding of steel with a potential of 20 V and
a current of 200 A. The travel speed is 5 mm/s
and the cross-sectional area of the joint is 20
mm2.Heat required to melt steel may be taken
as 10 J/mm3 and the heat transfer efficiency as
0.85.
Open and short circuit provide two useful points on the V-I curve.
In particular: The open circuit voltage is the voltage difference measured
between two terminals when no current is drawn or supplied.
The short circuit current is the current that flows when the terminals are forced
to have zero voltage difference.
NUMERICAL
The arc length-voltage characteristic of a DC arc is
given by the equation V=24 + 4l where V is the arc
voltage and l the arc length in mm. The static voltampere characteristic of the power source is
approximated by a straight line with no load voltage of
80 volts and the short-circuit current of 600 amperes.
Determine the optimum arc length for maximum power.
Resistance Welding
Resistance welding is the joining of metals by applying pressure and passing
current for a length of time through the metal area which is to be joined. The key
advantage of resistance welding is that no other materials are needed to create
the bond, which makes this process extremely cost effective.
Resistance welding
Resistance welding is the joining of metals by applying pressure and passing
current for a length of time through the metal area which is to be joined. The key
advantage of resistance welding is that no other materials are needed to create
the bond, which makes this process extremely cost effective.
In case of resistance welding the heat input is given by
H=I2 R t
Where
R is the resistance of the joint in Ohms
t is the time in seconds for which the current is flowing
through the joint
Numerical
Two steel sheets of 1.0 mm thickness are resistance
welded in a projection welding with a current of
30000 A for 0.005 second. The effective resistance
of the joint can be taken as 100 micro ohms. The
joint can be considered as a cylinder of 5 mm
diameter and 1.5 mm height .The density of steel is
0.00786 g/mm3 and heat required for melting steel is
10 J/mm3.
Calculate:
1) Heat required for melting
2) heat lost to surroundings
The term duty cycle is used to
describe the amount of time spent
depositing weld metal (the arcing
period) as a percentage of the total
time taken to complete a weld.
Question
At what duty cycle need a 300A welding power source rated 60% duty cycle be
operated to get an output current of 400A.
Question
What maximum output current can be drawn at 100% duty cycle from a welding power
source rated at 500A at 60% duty cycle?
Solution:
NUMERICAL
A shielded metal arc welding operation is
performed on steel at a voltage = 30 volts
and a current = 225 amps. The heat
transfer factor = 0.85 and melting factor =
0.75. The unit melting energy for steel =
10.2 J/mm3. Solve for (a) the rate of heat
generation at the weld and (b) the volume
rate of metal welded.
Solution:
(a) H = f1f2VI = (0.85)(0.75)(30)(225) = 4303.1 W
Solution:
(a) H = f1f2VI = (0.85)(0.75)(30)(225) = 4303.1 W
(b) V = (4303.1 W)/(10.2 J/mm3) = 421.9 mm3/sec
In an arc welding process, the voltage and current are 25 V and 300 A
respectively. The arc heat transfer efficiency is 0.85 and welding speed is 8
mm/sec. The net heat input (in J/mm) is :
(A) 64
(B) 797
(C) 1103
(D) 79700
A direct current welding machine with a linear power source characteristic
provides open circuit voltage of 80 V and short circuit current of 800 A. During
welding the machine, the measured arc current is 500 A corresponding to an arc
length of 5.0 mm and the measured arc current is 460 A corresponding to an arc
length of 7.0 mm. the linear voltage (E)-arc length (L) characteristic of the
welding arc can be given as (where E is in volt and L is in mm)
(A) E=20+2L
(B) E=20+8L
(C) E=80+2L
(D) E=80+8L
In arc welding of a butt joint, the welding speed is to be selected such that
highest cooling rate is achieved. Melting efficiency and heat transfer efficiency
are 0.5 and 0.7 respectively. The area of the weld cross-section is 5 mm2 and
the unit energy required to melt the metal is 10J/mm3 . If the welding power is 2
kW, the welding speed in mm/s is closest to
(A) 4
(B) 14
(C) 24
(D) 34
GAS WELDING PROCESSES
When mixture of gases
are burned to
produce the required
temperature for
welding , the process
is known as Gas
Welding.
TYPES OF FLAMES