Welding is a process that joins metals by heating them to melting point and allowing them to merge together. There are several types of welding including gas welding, arc welding, resistance welding, and solid state welding. Key factors that influence weldability include melting point, thermal conductivity, thermal expansion, surface condition, and changes to microstructure during welding. Common welding joints include butt, corner, lap, tee, and edge joints which are made using fillet, groove, plug, and slot welds. Arc welding and gas welding are two processes that use an electric arc or gas flame to melt metals. Resistance welding uses electric current to heat and join metals and includes spot, seam, and projection welds.

1. WELDING
 Welding is a process of joining similar metals by application of
heat with or without application of pressure and addition of
filler material.
 Weldability has been defined as the capacity of being welded
into separable joints having specified properties such as definite
weld strength,proper structure etc.
 Weldability depends on one or more of five major factors
1) Melting point,
2) Thermal Conductivity,
3) Thermal Expansion,
4) Surface Condition,
5) Change in MicroStructure.

2. TYPES
 Plastic Welding or Pressure Welding:
The piece of metal to be joined are heated to a plastic
stste and forced together by external pressure
EX: Resistance Welding
 Fusion Welding or Non-Pressure Welding:
The material at the joint is heated to a molten state and
allowed to solidify
EX: Gas welding,Arc welding

3. Classification of Welding process
Welding process
Gas Welding Arc Welding Newer Welding Solid State
Resistance Welding
Welding
1.Oxy-Acetylene 1.Electron Beam
2.Air-Acetylene 1.Butt 1.Carbon arc 2.Laser
1.Friction
3.Oxy-Hydrogen 2.Spot 2.Metal arc
2.Ultrasonic
3.Seam 3.Plasma arc
3.Diffusion
4.Projection 4.Gas Metal Arc(MIG)

4. Types of Joints
 Welding produces a solid connection between
two pieces, called a weld joint. Weld joint is the
junction of the edges or surfaces of parts that
have been joined by welding.
 Two classifications related to weld joints are
1. Types of joints
2. The types of welds used to join the pieces
that form
the joints
There are five basic types of joints for bringing
two parts together for joining. The five joint types
are not limited to welding; they apply to other
joining and fastening techniques as well.

5. Butt Joint:
In this joint type, the parts lie in the same plane and are
joined at their edges.
Corner Joint:
The parts in a corner joint form a right angle and are joined at
the corner of the angle.

6. Lap Joint:
This joint consists of two overlapping parts.
Tee Joint:
In a tee joint, one part is perpendicular to the other in the
approximate shape of the letter ‘‘T.

7. Edge Joint:
The parts in an edge joint are parallel with at least one of
their edges in common, and the joint is made at the
common edge(s)....

8. Types of
Welds
 A fillet weld is used to fill in the edges of plates created by
corner, lap, and tee joints.
 Filler metal is used to provide a cross section
approximately the shape of a right triangle.
 It is the most common weld type in arc and oxyfuel
welding because it requires minimum edge preparation—
the basic square edges of the parts are used.
 Fillet welds can be single or double (i.e., welded on one
side or both) and can be continuous or intermittent (i.e.,
welded along the entire length of the joint or with unwelded
spaces along the length).

9. Types of welds
(a) Inside single fillet corner joint; (b) outside single fillet
corner joint; (c) double fillet lap joint; and (d) double fillet tee
joint. Dashed lines show the original part edges

10. Plug Welds and Slot Welds
Plug welds and slot welds are used for attaching flat plates, using
one or more holes or slots in the top part and then filling with filler
metal to fuse the two parts together

11. Groove welds
 Groove welds usually require that the edges of the parts be
shaped into a groove to facilitate weld penetration.
 The grooved shapes include square, bevel, V, U, and J, in
Single or double sides. Filler metal is used to fill in the
joint, usually by arc or oxyfuel welding.
 Preparation of the part edges beyond the basic square edge,
although requiring additional processing is often done to
increase the strength of the welded joint or where thicker
parts are to be welded.
 Although most closely associated with a butt joint, groove
welds are used on all joint types except lap.

12. Types of Groove Welds
(a) Square groove weld, one side; (b) single bevel groove weld;
(c) single V-groove weld; (d) single U-groove weld; (e) single J-groove weld;
(f) double V-groove weld for thicker sections. Dashed lines show the original
part edges.

13. Spot welds and Seam welds
Spot welds and seam welds, used for lap joints. A spot weld is a
small fused section between the surfaces of two sheets or plates.
Multiple spot welds are typically required to join the parts. It is
most closely associated with resistance welding.
A seam weld is similar to a spot weld except it consists of a
more or less continuously fused section between the two sheets or
plates.

14. Spot welds and Seam welds:

15. Gas Welding
 Gas welding is a welding process that melts and joins metals by
heating them with a flame caused by a reaction of fuel gas and
oxygen.
 The most commonly used method is Oxyacetylene welding, due
to its high flame temperature.
 The flux may be used to deoxidize and cleanse the weld metal.
 The flux melts, solidifies and forms a slag skin on the resultant
weld metal.

16. Gas welding Apparatus
1. Oxygen cylinder-125kg/cm2
2. Acetylene cylinder-16kg/cm2
3. Pressure gauges
4. Valves
5. Hose pipes
6. Torch
7. Welding tip
8. Pressure regulators
9. Lighter
10. Goggles

17. Hose pipes
Welding Goggles

18. Oxy-acetylene Welding:
 OAW is a manual process in which the welder
must personally control the the torch movement
and filler rod application
The term oxyfuel gas welding outfit refers to all
the equipment needed to weld.
Cylinders contain oxygen and acetylene gas at
extremely high pressure.

19. Oxy-acetylene welding outfit

21. Gas Cutting
 Ferrous metal is heated into red hot condition and
jet of pure oxygen is projected on to the surface
,which rapidly oxidizes.
 Oxides having lower melting point than metal,
melt
and are blown away by the force of jet, to make cut
Fast and efficient method of cutting steel to a high
degree of accuracy
PIERCING and GOUGING are two important
operations
Piercing,used to cut a hole at the center of the
plateor away from the edge of plate.
Gouging ,to cut a groove in to steel surface

22. Types of gas Cutting

23. Types of Flames
 Oxygen is turned on ,flame immediately changes
into a long white inner area surrounded by a
transparent blue envelop is called carburizing
flame.
 Addition of little more oxygen give a bright whitish
cone surrounded by the transparent blue envelop
is called neutral flame.
 If more oxygen is added the cone becomes
darker and more pointed , while the envelop
becomes shorter and fierce is called oxidizing
flame.
 when acetylene is burned in air it produces a

24. Types of Flames

25.  ADVANTAGES:
1.Equipment has versatile
2.Same equipments can be used for oxy-acetylene cutting
and brazing by varying the torch size
3.Heat can be controlled easily
DISADVANTAGES:
1.Slower process
2.Risk is involved in handling gas cylinders

26. Arc Welding
 Arc Welding is a process that is used to join metal to metal
by using electricity to create enough heat to melt metal, and
the melted metals when cool result in a binding of the
metals.
 Arc is created by low voltage, high current supply, flux
coated electrodes are used which on melting form a
protective gas shield around the electrode tip and molten
weld pool.

27. Basic Steps of Arc Welding
 Prepare the base materials:remove paint and rust
 Choose the right welding process
 Choose the right filler material
 Assess and comply with safety requirements
 Use proper welding techniques and be sure to protect the
molten puddle from contaminants in the air
 Inspect the weld

28. Arc Welding

29. Arc Welding Equipments

30. Metal arc Welding
1.It is a process of joining two metal
pieces by melting the edges by an
electric arc.
2.It is also called as shielded /manual
metal arc welding
3.The electric arc is produced
between two conductors the electrode
is one conductor and work piece is
another conductor.
4.When current is passed an electric
arc is produced between electrode and
work piece.

31. Carbon Arc Welding
1.It is a process which produces
by coalescence of metals by
heating them with an arc
between a non consumable
carbon electrode and the work
piece.
2.It is of two types
a. Twin carbon arc welding
b. Gas carbon arc welding

32. Forging Welding
 Forging is a manufacturing process involving the shaping
of metal using localized compressive forces
 Forging is often classified according to the temperature at
which it is performed cold forging , warm forging , hot
forging.

33. Forge welding
 Forge welding is a solid-state
welding process that joins two
pieces of metal by heating
them to a high temperature
and then hammering them
together.
Steps:
 Metals are heated to the
plastic condition (above 1000
degree Celsius) in a furnace.
 Heated metals are brought to
the anvil from heat source and
superimposed them.
Schematic representation of
FORGE welding using Hammer

34. Classification of forger
1.Hammer:
 Hammering is done by heating the metal to the proper
temperature, coating with flux, overlapping the weld
surfaces, and then striking the joint repeatedly with
hammer.

35. Roll welding
•Here the heated metals are overlapped and passed
through rollers.

36. Die Welding
 Here the pieces of metal are heated and then forced into a
die.

37. Temperature
 Typically 50 to 90 percent of the melting temperature.
 Soft low carbon steel = 1250 to 1300 degree Celsius
 High carbon and alloy steel = 1100 to 1140 degree Celsius
 Wrought iron = little below 1290 degree Celsius
Required Tools:
• Hammers
• Black-smith’s gauge
• Hot chisel
• Brass

38. Advantages
 Good quality welds obtained
 Parts of intricate shape welded
 No filler material required
 Required less matching after welding
 Welded joints have low initial cost
 Welded joints easily repaired
 Noiseless process
 High strength welded joints

39. Disadvantages
 Low carbon steel is welded
 High level of the operator skill is required
 Slow welding process
 Weld is contaminated by the coke used in heating furnace
 Welded joints can not used for collision and vibration
 Can not be assembled and reassembled

40. Submerged Arc
Welding(SAW)
 It is a method in which heat required to fuse the metal
is generated by an arc formed by an electric current
passing between electrode and work piece.
 There is no visible arc and no sparks ,fume .The
electrode may be a solid or a cored wire.
 It is normally a mechanized process.
 Types of SAW: 1.single wire
 2. Twin wire
 3.tandem wire
 4.tandem twin
 5multi wire

41. General scope
 Current :The total welding current can range between 100-
3600A.
 Wires in one molten pool : from 1-6
 Voltage:20-50V
 Speed:30-350cm/min
 Deposition rate:2-100kg/hr

42. Single wire
 Single wire welding is the most
widely used SAW method.
 DC power source is used.
 The solid or cored wires of diameter
is 2-4mm are used.
 A small diameter produces higher
deposition at the same rate.

43. Twin wire
 For twin wire welding two wires
are connected to the same power
source.
 DC power source is used.
 It offers up to 30% higher
deposition rate and can used at
higher currents and speeds.
 Very high welding speeds can be
achieved in fillet welding.

44. Tandem
 In tandem sub arc welding each
of the two wires is connected to
its own power sources and fed
simultaneously by its own feed
unit.
 Both AC and DC source are
used.
 The wires are normally large
diameter(3-5mm) and deposition
rates are about twice that of
single wire welding.

45. Tandem twin
 The tandem twin process
involves two twin wire
heads placed in sequence.
 Both AC and DC source are
used.
 With the use of 4x25mm
diameter,wires depositions
rates of up to 38kg/hr.

46. Multi Wire
 Up to 6 wires can be used together
, each with their own power
source.
 The Pb wire is usually DC
+polarity with the trialing wires
being AC.
 Speeds of upto 2.5m/min can be
achieved giving a max deposition
rate of 90kg/hr.
 It used for longitudinal pipe
welding

47. Advantages Limitations
 High quality.
 Little risk of under cut and
porosity.
 no spatter , higher
deposition rate.
 High thermal efficiency ,
welding speeds.
 No radiations.
 Precise joint preparations
required .
 Irregular wire feed.
 Solidification cracking.
 High operational effort.
 It cannot be used for plates
less than5mm thickness

48. Applications of SAW
 Rail road tank cars
 Shift building
 Beam production
 Structural shapes and cylinders
 Circumferential welding Wind tower fabrication
 Longitudinal pipe welding
 Circular welds

49. Arc Welding

50. Comparision of A.C and D.C arc welding

51. Thermit Welding

52. Principle

53. Composition

54. Preparation

56. Thermit Welding Set-up

57. Working

58. Joining process

61. Applications
 It is mostly used to weld rail
roads.
 It used to weld thick plate before
introduce electroslag welding.
 They are used to repair heavy
casting.
 It is used to joint pipe ,thick plate
etc.. Where power supply is not
available.

63. Advantages Disadvantages
 It is simple and easy
process
 Low cost.
 Metal joining rate is
high.
 It is done where
casting is impossible.
 It is used where
power supply is not
avaliable
 It is used for limited
metals like:Fe,Cu…
 It is uneconomical for
welding light parts.
 Depends on
environmental
condition like:moisture
etc…

64. Resistance welding
 Electric resistance welding refers to a group of
welding processes such as spot and seam
welding that produce coalescence of faying
surfaces where heat to foam the well generated
by the electric resistance of material.
 FORMULA:the heat generated during resistance
welding is
H=I^2*RT

65. Resistance spot welding
 It is used for welding lap
joints , joining
components made from
plate material having
0.025 to 1.25mm in
thickness
 The plate to be joined
together are places
between the two electrode
tips of copper or copper
alloy

66. Resistance seam welding
 When the spot welds on
two over lapping pieces
of metal are spaced ,the
process of welding is
know as roll spot welding
 If the spot welds are
sufficiently made close,
then the process is called
seam welding.
 This process is best for
metal thickness ranging
from0.0.25 to 3mm

67. Resistance projection welding
 It is similar to spot
welding except that
one of the metal piece
to be welded has
projections on its
surfaces at the welds
are to be made in other
words it is a multi spot
welding process

68. Butt welding
 The butt welding is of two
types:
1. upset butt welding
2.Flash butt welding
 The upset butt welding is
especially adopted to rods ,
pipes and many other
components of uniform
sections.
 The flash butt welding is
extensively used in the
manufacture of steel containers
and in the welding of mild steel
shanks to high speed drills and
reamers.