2. 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.
3. 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
4. Classification of Welding process
Welding process
Gas Welding Newer Welding Solid StateArc Welding
Resistance Welding
1.Butt 1.Carbon arc
1.Electron Beam
2.Laser
2.Spot 2.Metal arc
Welding
1.Oxy-Acetylene
2.Air-Acetylene
1.Friction
3.Oxy-Hydrogen
2.Ultrasonic
3.Seam 3.Plasma arc
3.Diffusion
4.Projection 4.Gas MetalArc(MIG)
5. 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.
6. 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.
7. 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.
8. 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)....
9. Types of
Welds
A fillet weld is used to fill in the edges of plates createdby
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).
10. Types of welds
(a) Inside single fillet corner joint; (b) outside single fillet
corner joint; (c) double fillet lap joint; and (d) double fillettee
joint. Dashed lines show the original part edges
11. 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
12. 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.
13. Types of Groove Welds
(a) Square groove weld, one side; (b) single bevel grooveweld;
(c) single V-groove weld; (d) single U-groove weld; (e) single J-grooveweld;
(f) double V-groove weld for thicker sections. Dashed lines show theoriginal
part edges.
14. Spot welds and Seam welds
Spot welds and seam welds, used for lap joints. A spot weld isa
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.
16. GasWelding
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.
19. 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.
22. 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
24. 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
26. 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
27. ArcWelding
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.
28. Basic Steps of ArcWelding
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
31. Manual Metal arcWelding
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.
32. Carbon ArcWelding
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
33. ForgingWelding
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.
34. 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
35. 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.
38. 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
39. 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
40. 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
41. SubmergedArc 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
42. 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
43. 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.
44. 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.
45. 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.
46. 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.
47. MultiWire
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
beingAC.
Speeds of upto 2.5m/min can be
achieved giving a max deposition
rate of 90kg/hr.
It used for longitudinal pipe
welding
48. Advantages
High quality.
Little risk of under cut and
porosity.
no spatter , higher
deposition rate.
High thermal efficiency ,
welding speeds.
No radiations.
Limitations
Precise joint preparations
required .
Irregular wire feed.
Solidification cracking.
High operational effort.
It cannot be used for plates
less than5mm thickness
49. 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
52. Equipments use in TIG:
Gas supply (cylinder)
Electrical power source
(AC/DC)
Electrode holder, torch or gun
Connection cables
Hose (for gas supply)
Tungsten electrode
Coolant
Filler rods
53. Tungsten inert gas (TIG)
TIG welding is a fusion welding process.
The material is not removed; instead both sides
of the work piece that are to be joined are
heated up until the materials melt and blends.
After stiffening both sides are
permanently connected. Depending on the
welding task filler materials can additionally be
used for joining.
With the suited equipmentTIG
welding is suitable for the joining of almost all
materials that can be melted, ideally for welding
tasks in root and constrained positions
54. Working principle:
An arc is established between the end of a tungsten electrode
and the parent metal at the joint line..
A constant-current welding power supply is used to produces
energy which is conducted across the arc through a column of
highly ionized gas and metal vapors known as a plasma.
Argon and helium are the most commonly used shielding gases.
55. Characteristics of the TIG welding process:
Uses a non-consumable tungsten electrode during the welding process,
Uses a number of shielding gases including helium (He) and argon (Ar),
Is easily applied to thin materials,
Produces very high-quality, superior welds,
Welds can be made with or without filler metal,
Provides precise control of welding variables (i.e. heat),
Welding yields low distortion,
Leaves no slag or splatter.
56. ADVANTAGESAND LIMITATIONS OF
TIG WELDING:
ADVANTAGES:
No flux is used.
Welding is smooth and sound with
fewer scatters.
Very suitable for high quality
welding in thin materials.
Very good process for welding non-
ferrous metals and stainless steels.
The surface finish is good.
The equipments are portable
Tungsten inclusion is hard and
brittle.
Equipment costs are high
In steel welding operations, TIG is
slower and the most costly one
Filler rod end, if by chance comes
out, then inert gas shield can cause
weld metal contamination
LIMITATIONS:
57. MIG:
Metal inert gas (MIG) welding also known as MAG and GMAW.
It is a semi-automatic or automatic arc welding process in which a
continuous and consumable wire electrode and a shielding gas are fed
through a welding gun.
an electric arc forms between the consumable wire electrode and the
workpiece metal(s), which heats the workpiece metal(s), causing them to
melt and join.
58. MIG Welding Process:
MIG welding is a gas shielded metal arc welding process using the heat
of an electric arc between a continuously fed, consumable electrode
wire and the material to be welded.
A wire of copper coated mild steel is fed continuously from a reel
through a gun with a melting rate up to 5m/min.
Current through the wire ranges from 100 to 400 A depending upon the
diameter of thewire.
CO2 is principally used apart from argon or argon-helium mixture as
shielding gas.
The welding machine is a dc constant voltagemachine.
72. 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.
73.
74. 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…
75. 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
76. 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
77. 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
78. 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
79. 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.
