Welding Notes_new.pdf

Welding machine

1. WELDING
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

2. Classification of Manufacturing Processes
Ingot Casting
Shape Casting
Power Metallurgy
Turning, Boring
Drilling, Milling
Grinding
Forging
Extrusion
Sheet Metal Forming S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Joining
Processes
Forming
Processes
Machining
Processes
Casting
Processes
Manufacturing
Processes

3. Classification of Joining Processes
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

Welding

Brazing
Adhesive
Joining

Soldering
Mechanical
Fastening
Joining
Processes

4. Different Welding Processes
Welding:
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Gas Welding:
Oxy fuel, Hydrogen

Beam Processes:
LBW, EBW

Resistance Welding:
Spot, Seam, Projection

Solid state
USW, FRW, EXW
Arc Welding:
SMAW, GMAW,
GTAW, SAW,
FCAW, PAW
Welding
Processes

5. Five basic joint designs
BUTT
LAP TEE
EDGE
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

CORNER

6. Four basic types of fusion welds
Bead / Surface Weld Groove Weld
Fillet Weld
Plug Weld
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

7. Bead / Surface Welds
•
•
•
•
•
For butt welds
No edge preparation
Thin sheets of metal
Building up surfaces
Bead / Surface Weld
Weld overlay
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

8. Groove preparations
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

9. Five Welding Positions
Flat
g Vertical
Up
Overhead
Vertical
Down
Arrow shows the direction of motion of the electrode / torch.
The torch is held approximately normal to this direction.
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

10. Classification of Welding
Autogenous
Consumable
Electrode
Non-consumable
Electrode
Filler
Single Pass
Flux protected
Multi Pass
Inert gas
protected
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Fusion
Welding

11. S. G
Dr.
A weld can be defined as a coalescence of metals produced by
heating to a suitable temperature with or without the application
of pressure, and with or without the use of a filler material.
hosh, Lecturer in ME
MSIT, Haldia

12. Some terminology
Traverse rate : velocity of the welding source
Heat Input : ratio of power to velocity : J/m
•
•
•
•
: m/s
Rate of heat input or heat intensity : W/m
2

Heat intensity distribution : Q(x,y)
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

13. Overview of few welding processes
SMAW : Shielded (Manual) Metal Arc Welding
GMAW: Gas Metal Arc (MIG) Welding







GTAW: Gas Tungsten Arc (TIG) Welding
PAW:
SAW:
EBW:
LBW:
Plasma Arc Welding
Submerged Arc Welding
Electron Beam Welding
Laser Beam Welding
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

14. Arc Welding
 A fusion welding process in which coalescence of the metals is
achieved by
the work
the heat from an electric arc between an electrode and
 Energy from the arc produces
enough to melt any metal
temperatures ~ 10,000 F (5500ᵒ C), hot
 Most Arc Welding processes add filler metal to increase volume and
strength of weld joint
S. Ghosh, Lecturer
Dr. MSIT, Haldia
in ME
S.Ghosh

15. Electric Arc
An electric arc is a discharge of electric
current, upon application of voltage
and separated by a small distance.
• Electrode
65% to 75% heat is generated
anode.
Presence of ionisable gas
Sustained electric discharge
through ionized gas (plasma)
at the •
•
column between
electrodes
the two
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

Workpiece

16. Longer Arc
Shorter Arc
Arc Characteristics
OCV
Current
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Ref: Principles of Welding Technology, 3
rd
Edition by L. M. Gourd, ISBN: 8176490296
V
o
lt
a
g
e


Normal Operating range

17. Two Basic Types of Electrodes
• Consumable
consumed during welding process
Source of filler metal in arc welding
o
o
• Non-consumable
not consumed during welding process
Filler metal must be added separately if it is
o
o
o
added
This type of welding is called Autogenous welding
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

18. CONSUMABLE
ELECTRODE
HOLDER
TYPE ELECTRODE
WELDING
Electrode is made
anode (high heat
concentration) to
melt more and
penetrate the
fast
joint
mixed with
low voltage 
short arc length
High current
faster melting
Base metal
is HEAT
AFFECTED
AREA
made cathode(-) S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh
WELD POOL
filler metal
molten metal
and penetrates
the joint
Flux mixes with
the impurities
and rises to top
of weld pool
SHIELDING GAS
PROTECTION

POWER
SUPPLY
STEP DOWN
TRANSFORM
ER

19. Arc Shielding
•At high temperatures in Arc Welding, metals are chemically
reactive to oxygen, nitrogen, and hydrogen in air
 Mechanical properties of joint can be degraded by these reactions
To protect operation, arc must be shielded from surrounding air in
AW processes
•Arc shielding is accomplished by:
 Shielding gases, e.g., argon, helium, CO
2
 Flux
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

20. Flux
•A substance that prevents formation of oxides and other
contaminants in welding, or dissolves them and facilitates removal. During welding, the
flux melts and becomes liquid slag, covering and protecting the molten weld pool. The
slag hardens upon cooling and removed later by chipping or brushing.
 Provides protective atmosphere for welding
 Stabilizes arc
 Reduces spattering
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

21. Various Flux Application Methods
• Pouring granular flux onto welding operation
• Stick electrode coated with flux material that melts during welding to
cover operation
• Tubular electrodes in which flux is contained in the core and released
as electrode is consumed
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

22. Power Source in Arc Welding
Direct current (DC) vs. Alternating current (AC)
•AC machines less expensive to purchase and operate, but generally
restricted to ferrous metals
•DC equipment can be used on all metals and is generally noted for
better arc control
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

23. S. Ghosh, Lecturer i
Dr. MSIT, Haldia
n ME

24. S. Ghosh, Lectur
Dr. MSIT, Hald
er in ME
ia

25. Electrode
Direct Current Straight Polarity
Deeper penetration.
Direct Current Reverse Polarity
Polarities
(DCSP) : Electrode • is negative.
• (DCEP) : Electrode is positive.
Enhanced deposition rate for consumable electrode.
Alternating Current (AC) : Polarity is switched at a frequency. •
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

26. AC DCEP DCEN
+ -
+ - - +
30% Heat to workpiece
70% Heat to Electrode,
Shallow penetration,
Surface Cleaning
70% Heat to workpiece
30% Heat to Electrode
so more penetration
50% Heat to workpiece
50% Heat to Electrode
Surface cleaning half-the-time
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

Workpiece

Workpiece

Workpiece

27. S. Ghosh, Le
Dr. MSIT, H
cturer in ME
aldia

28. Arc Welding Processes
Consumable Electrode Non-Consumable Electrode
• Shielded Metal Arc Welding (SMAW)
• Gas Tungsten Arc Welding (GMAW)
• Gas Metal Arc Welding (GMAW)
• Plasma Arc welding
• Flux-Cored Arc Welding (FCAW)
• Submerged Arc Welding (SAW)
• Electrogas Welding
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

29. S. Ghosh,
Dr. MSIT,
Shielded Metal Arc Welding (SMAW)
Electrode holder
Power
source
and
controls Arc
Shielding gas
Coating Electrode
Electrode
Work cable
Arc
Work
Solidified slag
Electrode cable
Weld metal
Base metal
Lecturer in ME
Haldia

30. SMAW
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Photographs from the
facilities in Materials
Joining Laboratory,
Department of MME,
IIT Madras

31. SMAW or MMAW
S.Ghosh
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

32. Shielded Metal Arc Welding (SMAW)
•
•
It is the simplest, versatile, and the most widely used welding process.
Uses a consumable electrode consisting of a filler metal rod coated with chemicals that
provide flux and shielding
Sometimes called "stick welding"
Alternating current or direct current forms an arc between the electrode and the base
metal creates the required heat.
The flux coating disintegrates and gives off vapors that serve as a shielding gas and
provides a protective layer of slag.
Both protect the weld area from atmospheric contamination. As the metal rod inside the
electrode melts it forms a molten pool which becomes the weld after solidification.
It can be used in all positions:
•
•
•
•
•
1. Flat 2. Vertical 3. Horizontal 4. Overhead
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

33. • SMAW Arc Welding (stick welding) uses the arc heat to melt the base metal and tip of a
consumable electrode. The
circuit.
This circuit includes:
electrode and base metal are part of an electric circuit or welding
•






Power source
Welding cables
Electrode holder
Ground clamp
The work or base metal
Arc welding electrode
• One cable is attached to the work and the other to the electrode holder.
• Welding starts when an arc is struck between the tip of the electrode and base metal.
• The heat melts the tip and the surface of the work. Tiny globules of molten metal form on
the electrode tip then transfer through
electrode is consumed.
the arc into the molten pool. Filler is deposited as the
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

34. SMAW Applications
 Used for steels, stainless steels, cast irons, and certain
nonferrous alloys
 Not used or rarely used for aluminum and its alloys,
copper alloys, and titanium
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

35. S. Ghos
Gas Metal Arc Welding or MIG
Feed control
Control system
Wire
Gas out Shielding gas source
Shielding gas
Solid wire electrode
Current conductor
Travel
Gun
control
Gas in
Shielding gas
Nozzle
Gun
Voltage
control
Arc
Work piece
Welding machine
Base metal
Wire feed drive motor
h, Lecturer in ME Solidified weld metal
Molten weld metal
Dr. MSIT, Haldia

36. GMAW
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Photographs from the facilities in
Materials Joining Laboratory,
Department of MME, IIT Madras

37. GMAW
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

38. Gas Metal Arc Welding (GMAW) or MIG
• Uses a consumable bare metal wire as electrode with shielding by
flooding arc with a gas
• Wire is fed continuously and automatically from a spool through the
welding gun
• Shielding gases include argon and helium for aluminum welding, and
CO
2 for steel welding
• Bare electrode wire plus shielding gases eliminate slag on weld bead
S. Ghosh, Lecturer in ME
S.Ghosh
Dr. MSIT, Haldia

39. Metal transfer modes
Globule transfer •
–
–
–
Droplets close to or larger than diameter of the electrode
Reach base material
Leads to spatter
by gravity
• Spray transfer
– Fine droplets
– Reach base material by EM force
• Short-circuit transfer
– Small and fast solidifying weld pools
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

40. GMAW Advantages over SMAW
• Better arc time because of continuous wire electrode
• Sticks must be periodically changed in SMAW
• Better use of electrode filler metal than SMAW
• End of stick cannot be used in SMAW
• Higher deposition rates
• Eliminates problem of slag removal
• Can be readily automated
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

41. Flux-Cored Arc Welding (FCAW)
 Adaptation of shielded metal arc welding, to overcome
stick electrodes - two versions
limitations of
Self-shielded FCAW - core includes compounds that produce
shielding gases
Gas-shielded FCAW - uses externally applied shielding gases
 Electrode is a continuous consumable tubing (in coils) containing flux
and other ingredients (e.g., alloying elements) in its core
S. Ghosh, Lecturer in ME
S.Ghosh
Dr. MSIT, Haldia

42. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia FCA
S.GhW
osh

43. Submerged Arc Welding (SAW)
• Uses a continuous, consumable bare wire electrode, with arc shielding
by a cover of granular flux
• Electrode wire is fed automatically from a coil
• Flux introduced into joint slightly ahead of arc by gravity from a hopper
• Completely submerges operation, preventing sparks, spatter, and
radiation
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

44. S. Ghosh, Lecturer in
SAW
ME
Dr. MSIT, Haldia

45. Submerged
Wire reel
Arc welding
Flux hopper
Unused flux recovery tube
Wire feed
motor
Contact tube Voltage and current control
Work piece
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Ground
Granular flux covers the
weld and the arc

46. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

47. SAW Applications
• Steel fabrication of structural shapes (e.g., I-beams)
• Seams for large diameter pipes, tanks, and pressure vessels
• Welded components for heavy machinery
• Most steels (except hi C steel)
• Not good for nonferrous metals
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

48. ARC WELDING – NONCONSUMABLE
ELECTRODES
- GTAW (Gas tungsten arc welding) or TIG welding
- Plasma arc welding
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

49. NON-CONSUMABLE
TYPE ELECTRODE
WELDING FILLER
ROD
ELECTRODE
HOLDER
Electrode is made
cathode (-)to
prevent electrode
melting
the impurities
Low voltage 
Short arc length
high current
Faster melting
Base metal is
made anode
(high heat
concentration)
S. Ghosh, Lecturer in ME
S.Ghosh
AREA Dr. MSIT, Haldia
WELD POOL HEAT
AFFECTED
Flux mixes with
and rises to top
of weld pool
SHIELDING
GAS
PROTECTION
filler metal
mixed with
molten metal
and penetrates
the joint
POWER
SUPPLY
STEP DOWN
TRANSFORM
-ER

50. Gas tungsten arc welding
Inert gas supply
Cooling water supply
Travel
AC or DC Welder
Drain
Torch
Filler wire
Tungsten
electrode
Work piece
Arc Molten weld metal
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Foot pedal (optional Solidified weld

51. TIG
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Photographs from the
facilities in Materials
Joining Laboratory,
Department of MME, IIT
Madras

52. TIG WELDING or GTAW
Electrodes: various types of tungsten alloys used
1.
2.
Pure tungstenis used on nonferrous metals, such as aluminum and magnesium
Thoriated tungsten, with 1 or 2 % thorium, the most common type of tungsten electrode used on
carbon and stainless steel
Zirconiated tungsten, typically used for welding with higher AC currents on nonferrous metals. 3.
•
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Typical flow rate of shielding inert gas may varyS.fGrhoshm 5-50 liters/min.

53. GTAW Process Characteristics
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding
process that uses a non-consumable tungsten electrode (autogenous) to produce the weld.
•
• The arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon
or helium. The small intense arc provided by the pointed electrode is ideal for high quality and precision
welding.
• When filler metal is required, it must be added separately to the weld pool.
• The weld area is protected from atmospheric contamination by a shielding gas, usually an inert gas such as
argon, helium and helium/argon mixtures - adding helium to argon will raise the temperature of the arc. This
promotes higher welding speeds and deeper weld penetration.
• A drooping, constant current power source - either DC or AC. A constant current power source is
essential to avoid excessively high currents being drawn when the electrode is short-circuited on to the
workpiece surface.
• However, GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
slower than most other welding techniques.

54. Operation Modes
GTAW can use a positive direct current, negative direct current or an alternating current, depending
on the power supply set up.
•
• A negative direct current from the electrode (DCEN) causes a stream of electrons to collide with the
surface, generating large amounts of heat at the weld region. This creates a deep, narrow weld.
• In the opposite process where the electrode is connected to the positive power supply terminal
(DCEP), positively charged ions flow from the part being welded to the tip of the electrode instead, so
the heating action of the electrons is mostly on the electrode. This mode also helps to remove oxide
layers from the surface of the region to be welded, which is good for metals such as Aluminium or
Magnesium. A shallow, wide weld is produced from this mode, with minimum heat input.
• Alternating current gives a combination of negative and positive modes, giving a cleaning effect and
imparts a lot of heat as well.
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

55. GTAW Applications
• The aerospace industry is one of the primary users of gas tungsten arc welding, It is used
extensively in the manufacture of space vehicles.
• Many industries use GTAW for welding thin workpieces, especially nonferrous metals.
• TIG has played a major role in the acceptance of Aluminum and Magnesium for high quality
structural applications. welding and
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

56. Plasma Arc Welding
Tungsten electrode
(PAW)
Plasma gas
Shielding gas
Power supply
Power supply
Work piece
Non transferred arc
Transferred arc
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

57. PAW
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
Photographs from the
facilities in Materials
Joining Laboratory,
Department of MME, IIT
Madras

58. • Plasma welding is very similar to
TIG as the arc is formed between a
pointed tungsten electrode and the
workpiece.
• However, The key difference
from GTAW is that in PAW, by
positioning the electrode within
the body of the torch, the plasma
arc can be separated from the
shielding gas envelope.
• Plasma is then forced through a
fine-bore copper nozzle which
constricts the arc.
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

59. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

60. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

61. PROPERTIES OF ELECTRODES, SHIELDING GAS AND FLUX
• Consumable electrodes materials are selected such that finished weld metal
should have similar mechanical properties that of base metal with no defects,
Consumable Electrodes contains de-oxidising metals (Si, Mn, Ti, Al) and
de-nitriding metals (zirconium) in small percentages to prevent entrapment of
oxygen and nitrogen in the weld, reducing the
weld.
porosity and giving continuous
• Shielding gas is necessary to protect weld area from atmospheric gases,
thereby reducing porosity and cracking.
EG. argon, helium, carbon dioxide etc
Flux when melted by the arc, mixes with the impurities in the weld
forms slag and covers the weld pool from contamination.
• pool and
E.G. lime, silica, manganese dioxide, calcium flouride etc
flux is either coated on the electrode surface, or inside
or provided additionally(non-consumable electrodes).
S.Ghosh
the electrode,
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

62. GAS WELDING
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

63. OXY – ACETELYNE
OXYGEN +
ACETELYNE
GAS WELDING
FILLER
MATERIAL
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

64. S. Ghosh
S.Ghosh
OXY-ACETELYNE GAS WELDING SETUP
, Lecturer in ME
Dr. MSIT, Haldia

65. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

66. • Gas welding is a fusion welding process.
• Acetylene burned in oxygen is used as source of heat. This heat is used to fuse the metal joints.
ADVANTAGES
1.
2.
3.
Simple
Portable
Easy maintenance
DISADVANTAGES
Very low welding speed,
Large amount of heat is required,
over a large area.
large heat affected zones.
1.
2. some amount of heat is wasted, since heat is distributed
3.
4. Should not be used with reactive metals like Titanium and Zirconium.
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

67. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

68. NEUTRAL FLAME
A neutral flame is produced when the ratio of oxygen
to acetylene, in the mixture leaving the torch, is almost
exactly one-to-one. The temperature of the neutral
flame is of the order of about 5900ºF.
•
• There are two clearly defined zones in the neutral
flame. The inner zone consists of a luminous cone that
is bluish-white. The inner cone is where the acetylene
and the oxygen combine. Surrounding this is a light
blue flame envelope or sheath. This neutral flame is
obtained by starting with an excess acetylene flame in
which there is a "feather" extension of the inner cone.
When the flow of acetylene is decreased or the flow of
oxygen increased the feather will tend to disappear.
The neutral flame begins when the feather disappears.
• Applications:





Mild steel
Stainless steel
Cast Iron
Copper
Aluminum
• The tip of the inner is the hottest part of the flame and
is approximately 5850ºF, while at the end of the outer
sheath or envelope the temperature drops to
approximately 2300ºF.
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

69. Carburizing Flame
The reducing or carburizing flame is obtained when slightly less than
one volume of oxygen is mixed with one volume of acetylene.
•
• The carburizing flame is characterized by three flame zones; the hot
inner cone, a white-hot "acetylene feather", and the blue-colored outer
cone.
• The feather is adjusted and made ever smaller by adding increasing
amounts of oxygen to the flame. A welding feather is measured as 2X or
3X, with X being the length of the inner flame cone. It has a temperature
of approximately 5500ºF (3149ºC) at the inner cone tips. The feather is
caused by incomplete combustion of the acetylene to cause an excess of
carbon in the flame.
Applications:
 High carbon steels
• The carburizing flame may add carbon to the weld metal and will tend to
remove the oxygen from iron oxides which may be present. With iron
and steel it produces very hard, brittle substance known as iron carbide.
 Oxygen free copper alloys
 Non ferrous alloys like nickel and
Monel
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
This chemical change makes the metal unfit for many applications
which the weld may need to be bent or stretched. Metals that tend
absorb carbon should NOT be welded with reducing flame.
in
to

70. Oxidizing Flame
• The oxidizing flame is produced when more than one
volume of oxygen is mixed with one volume of acetylene.
• An oxidizing flame can be recognized by the small white
cone which is shorter, much bluer in color and more pointed
than that of the neutral flame. The outer flame envelope is
much shorter and tends to fan out at the end. The temperature
of this flame
cone tip.
is approximately 6300ºF (3482ºC) at the inner
Applications:
• An oxidizing flame tends to be hotter than the other two
causes the
 Copper base metals
flames. This is because of excess oxygen which
temperature to rise as high as 6300°F.
 Zinc base metals, and
• An oxidizing flame is of limited use in welding. It
in the welding of steel.
is not used
 manganese steel
 Brass S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

71. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

72. RESISTANCE WELDING
Resistance welding is a fusion welding process makes use of the electrical
resistance for generating heat required for melting the workpiece. It is generally
used for
welding,
joining thin plates and structures. It has different variants such as Spot
Seam welding and Projection welding.
H = Heat
I = Welding Current
R = Resistance
t= Time S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

73.  Electrode tips are made of copper alloys
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

74. • The weld is made by a combination of heat, pressure, and time. The resistance of the base metal to
electrical current flow through the electrode tips causes localized heating at the interface of the joint,
and the weld nugget is formed. The pressure of the electrode tips on the workpiece holds the part in close
and intimate contact during the making of the weld.
• The secondary portion of a resistance spot welding circuit, including the parts to be welded, is actually a
series of resistances. The total additive value of this electrical resistance affects the current output of the
resistance spot welding machine and the heat generation of the circuit.
•
1.
2.
3.
4.
5.
6.
There are six major points of resistance in the work area.
The contact point between the electrode and top workpiece.
The top workpiece.
The interface of the top and bottom workpieces.
The bottom workpiece.
The contact point between the bottom workpiece and the electrode.
Resistance of electrode tips.
• The resistances are in series, and each point of resistance will retard current flow. The amount of
resistance at point 3, the interface of the workpieces, depends on the heat−transfer capabilities of the
material, the material’s electrical resistance, and the combined thickness of the mSa.
tGehroiashls,
LaetctthureerwinelMd
E joint. It is at this part of the circuit that the nugget of the weld is formed. Dr. MSIT, Haldia

75. 



Squeeze Time: Time between pressure application and weld.
Heat Or Weld Time: Weld time in cycles.
Hold Time: Time that pressure is maintained after weld is made.
Off Time: Electrodes separated to permit moving of material for next spot
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

76. S. Ghosh, Lec
Dr. MSIT, H
.
turer in ME
aldia

77. S. Ghosh, Lecturer in M
S.Ghosh
Dr. MSIT, Haldia
ADVANTAGES
DISADVANTAGES
E

78. RESISTANCE SEAM WELDING
Seam
series
consists of a
of spot welds
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia
S.Ghosh

79. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

80. S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia

81. S.
D
Projection Welding
In Projection welding size and shape of individual welds are determined by the presence of projections,
embossments or intersections on the metals to be joined.

 Metals are heated and coalescence is achieved through the metals’ resistance to electrical currents passing
through them as they are held together with pressure by electrodes.
 In projection welding the pieces to be joined areclamped between two electrodes under force, and electrical
current is sent through them.
Ghosh, Lecturer in ME
r. MSIT, Haldia

82. http://nptel.ac.in/courses/112107144/welding/lecture13.htm
Welding Defects
The defects in the weld can be defined as irregularities in the weld
metal produced due to incorrect welding parameters or wrong
welding procedures or wrong combination of filler metal and parent
metal.
Fig 13.1: Various Types of Cracks in Welds
Weld defect may be in the form of variations from the intended weld
bead shape, size and desired quality. Defects may be on the surface
or inside the weld metal. Certain defects such as cracks are never
tolerated but other defects may be acceptable within permissible
limits. Welding defects may result into the failure of components
under service condition, leading to serious accidents and causing the
loss of property and sometimes also life.
Cracks may be developed due to poor ductility of base metal, high
sulpher and carbon contents, high arc travel speeds i.e. fast cooling
rates, too concave or convex weld bead and high hydrogen contents
in the weld metal.
2. Porosity
Porosity results when the gases are entrapped in the solidifying weld
metal. These gases are generated from the flux or coating
constituents of the electrode or shielding gases used during welding
or from absorbed moisture in the coating. Rust, dust, oil and grease
present on the surface of work pieces or on electrodes are also
source of gases during welding. Porosity may be easily prevented if
work pieces are properly cleaned from rust, dust, oil and
grease.Futher, porosity can also be controlled if excessively high
welding currents, faster welding speeds and long arc lengths are
avoided flux and coated electrodes are properly baked.
Various welding defects can be classified into groups such as
cracks, porosity, solid inclusions, lack of fusion and
penetration, imperfect shape and miscellaneous defects.
inadequate
1. Cracks
Cracks may be of micro or macro size and may appear in the weld
metal or base metal or base metal and weld metal boundary.
Different categories of cracks are longitudinal cracks, transverse
cracks or radiating/star cracks and cracks in the weld crater. Cracks
occur when localized stresses exceed the ultimate tensile strength of
material. These stresses are developed due to shrinkage during
solidification of weld metal.

83. Fig 13.3: Slag Inclusion in Weldments
4. Lack of Fusion and Inadequate or incomplete penetration:
Lack of fusion is the failure to fuse together either the base metal
and weld metal or subsequent beads in multipass welding because
of failure to raise the temperature of base metal or previously
deposited weld layer to melting point during welding. Lack of fusion
can be avoided by properly cleaning of surfaces to be welded,
selecting proper current, proper welding technique and correct size
of electrode.
Fig 13.2: Different Forms of Porosities
3. Solid Inclusion
Solid inclusions may be in the form of slag or any other nonmetallic
material entrapped in the weld metal as these may not able to float
on the surface of the solidifying weld metal. During arc welding flux
either in the form of granules or coating after melting, reacts with the
molten weld metal removing oxides and other impurities in the form
of slag and it floats on the surface of weld metal due to its low
density. However, if the molten weld metal has high viscosity or too
low temperature or cools rapidly then the slag may not be released
from the weld pool and may cause inclusion.
Fig 13.4: Types of Lack of Fusion
Incomplete penetration means that the weld depth is not upto the
desired level or root faces have not reached to melting point in a
groove joint. If either low currents or larger arc lengths or large root
face or small root gap or too narrow groove angles are used then it
results into poor penetration.
Slag inclusion can be prevented if proper groove is selected, all the
slag from the previously deposited bead is removed, too high or too
low welding currents and long arcs are avoided.
Fig 13.5: Examples of Inadequate Penetration
5. Imperfect Shape
Imperfect shape means the variation from the desired shape and
size of the weld bead.

84. During undercutting a notch is formed either on one side of the weld
bead or both sides in which stresses tend to concentrate and it can
result in the early failure of the joint. Main reasons for undercutting
are the excessive welding currents, long arc lengths and fast travel
speeds.
Underfilling may be due to low currents, fast travel speeds and small
size of electrodes. Overlap may occur due to low currents, longer arc
lengths and slower welding speeds.
Fig 13.6: Various Imperfect Shapes of Welds
Excessive reinforcement is formed if high currents, low voltages,
slow travel speeds and large size electrodes are used. Excessive
root penetration and sag occur if excessive high currents and slow
travel speeds are used for relatively thinner members.
Distortion is caused because of shrinkage occurring due to large
heat input during welding.
6. Miscellaneous Defects
Various miscellaneous defects may be multiple arc strikes i.e.
several arc strikes are one behind the other, spatter, grinding and
chipping marks, tack weld defects, oxidized surface in the region of
weld, unremoved slag and misalignment of weld beads if welded
from both sides in butt welds.

85. Thank You
S. Ghosh, Lecturer in ME
Dr. MSIT, Haldia