Casting, Forming & Welding
(ME31007)
Jinu Paul
Dept. of Mechanical Engineering
CFW- Welding marks distribution
CFW Total Marks = 100
Casting =33, Forming = 33, Welding =33
End semester exam 50 %
Mid semester exam 30 %
Class test 1 (Before midsem) 5 %
Class test 2 (After midsem) 5 %
Attendance + Assignments - 10 %
2
Course details: Welding
Topic Hours
1. Introduction to welding science & technology 2-3
2 Welding Processes 4
3 Welding Energy sources & characteristics 1-2
4 Welding fluxes and coatings 1
5 Physics of Welding Arc 1
6 Heat flow in welding 2
7 Design of weld joints 1
8 Defects, Testing and inspection of weld joints 2
9 Metallurgical characteristics of welded joints,
Weldability, Brazing, soldering, adhesive joining 2
Total 19
3
References
Principles of Welding, Robert W Messler
Metallurgy of Welding, J.F. Lancaster
Welding Science and Technology, Md.
Ibrahim Khan
Welding Technology-O.P. Khanna
Manufacturing Engineering and
Technology, S. Kalpakjian
4
Lecture 1
22 July 2013, Monday, 10.30-11.30 am
Introduction to welding
5
Overview of Joining processes
Joining
processes
Mechanical
Brazing
Assembly
Welding Soldering
(e.g., Threaded
Adhesive bonding
fastners, rivets)
6
Joining processes-overview
Riveted Joint
Threaded fastner
Welded Joint
Brazed Joint 7
What are the joints that
were used in the Eiffel Tower?
Some application areas of welding
Ship building
Aircraft industry
Automotive industry 9
Welding: Application areas
Applications in Air, Underwater & Space
Automobile industry, aircraft industry,
ships and submarines
Buildings, bridges, pressure vessels,
girders, pipelines, machine tools, offshore
structures, nuclear power plants, etc.
House hold products, farm, mining, oil
industry, jigs & fixtures, boilers, furnaces,
railways etc.
10
Welding process-Features
Permanent joining of two materials through
localized coalescence resulting from a
suitable combination of Temperature &
Pressure
Formation of Common metallic crystals at
the joints/interface
With or Without filler material
11
Welding process-Features
Continuity: absence of any physical
disruption on an atomic scale
Not necessarily homogeneous but same in
atomic structure, thereby allowing the
formation of chemical bonds
Material Metals Ceramic Polymer
(similar/dissimilar)
Type of bond Metallic Ionic/coval Hydrogen, van der
ent Waals, or other
dipolar bonds
12
Welding Process: Advantages
Exceptional structural integrity, continuity,
fluid tightness, portable equipments
Strength of joints can approach or exceed
the strength of the base material(s)
Wide range of processes & approaches
Can be performed manually, semi
automatically or completely automatically
Can be performed remotely in hazardous
environments (e.g., underwater, areas of
radiation, outer space) using robots
13
Welding Process: Disadvantages
Precludes disassembly
Requirement for heat in producing many
welds can disrupt the base material
microstructure and degrade properties;
may induce residual stresses
Requires considerable operator skill
Capital equipment can be expensive (e.g.,
laser beam, vacuum chambers etc.)
14
Types of joints in welding
Butt joint
Corner joint Lap joint
Tee joint Edge joint
15
Types of welds
1) Fillet weld
Fillet weld Fillet weld
Fillet weld on corner joint
on lap joint on T-joint
16
Types of welds
2) Groove weld
(c) single
(a) square groove weld, (b) single bevel
V-groove weld
groove weld
(d) single (e) single (f) Double V- groove
U-groove weld J-groove weld weld for thicker
sections
17
Types of welds
3) Plug & slot weld
Drill hole/slot on the top plate only
Hole/slot is filled with filler metal
18
Types of welds
4) Spot weld
5) Seam weld
Fused section between the surfaces of two sheets
Mostly associated with resistance welding
19
Types of welds
6) Flange weld & Surfacing weld
Surfacing weld is not for joining parts
The purpose is to increase the thickness of the plate or
to provide a protective coating on the surface.
20
Weld symbols
Fillet weld Flush/Flat contour
Convex contour
Square Butt
Concave contour
Single V Butt
G Grinding Finish
Double V Butt
M Machining Finish
Single U
C Chipping Finish
Single Bevel Butt
21
Weld Specification
22
Lecture 1-Summary
Overview of Joining processes,
welding
Welding - applications, advantages
Welded Joint types
Basic Classification of welding
Weld symbols & specifications
23
Lecture 2
29 July 2013, Monday, 10.30 am-11.30 am
Elements of welding set up,
power density & heat transfer
24
Basic elements of a welding setup
1. Energy source to create union by
pressure/heat
2. Method to remove surface contaminants
3. Protect metal from atmospheric
contamination
4. Control of weld metallurgy
25
1. Energy source
Classification of Fusion welding based on energy source
Energy Types of welding
source
Oxy fuel gas welding, Exothermic welding/ Thermite
Chemical
welding, Reaction brazing/Liquid phase bonding
Radiant Laser beam welding, Electron beam, Infrared welding/
energy brazing, Imaging arc welding, Microwave welding,
Electric-Perm. Gas tungsten arc welding, plasma arc welding, Carbon
electrode arc arc welding, atomic hydrogen welding, Stud arc welding
Electric- Gas metal arc welding, Shielded metal arc welding,
Consumable Submerged arc welding, Electrogas welding, Electroslag
electrode welding, Flux cored arc welding
Electric- Resistance spot, resistance seam, projection welding,
Resistance flash/ upset welding, Percussion, Induction welding
26
1. Energy source
Classification of solid state welding based on energy source
Energy Types of welding
source
Cold welding, Hot pressure welding, Forge welding, Roll
welding, Friction welding, Ultrasonic welding, Friction stir
Mechanical
welding, Explosion welding, Deformation diffusion welding,
Creep isostatic pressure welding, Super plastic forming
Chemical + Pressure gas welding, Exothermic pressure welding,
Mechanical Pressure thermit forge welding
Stud arc welding, Magnetically impelled arc butt welding,
Electrical + resistance spot welding, resistance seam welding,
Mechanical projection welding, flash welding, upset welding,
percussion welding, resistance diffusion welding
27
2. Removal of Surface
contaminants
Surface contaminants may be organic films,
absorbed gases or chemical compounds of the
base metals (usually oxides)
Heat when used as source of energy removes
organic films and absorbed gases
Fluxes are used to clean oxide films and other
contaminants to form slag
Slag floats and solidifies above weld bead
protecting the weld from further oxidation
28
3. Protection from atmospheric
contamination
Shielding gases are used to protect molten
weld pool from atmospheric contaminants
like O2 & N2 present in air
Shielding gases could be Ar, He,CO2
Alternatively, welding could be carried out in
an inert atmosphere.
29
4. Control of weld metallurgy
Microstructures formed in the weld and
HAZ determines the properties of the weld
Depends on heating, cooling rates (power,
weld travel speed)
Can be controlled by preheating/ post heat
treatment
De-oxidants, alloying elements etc. added
to control weld metal properties
30
Power density
Defined as the power transferred to work per
unit surface area (W/mm2)
Time to melt the metal is inversely proportional
to power density
Welding Process Approx. Power density
(W/mm2)
Oxy-fuel welding 10
Arc welding 50
Resistance welding 1000
Laser beam welding 9000
Electron beam welding 10,000
31
Heat transfer mechanisms in
Fusion Welding
Heat transf. factor f1= Heat transf. to work / Heat gen. by source
Melting Factor f2 = Heat used for melting / Heat tranf. to work
Useful heat or energy = f1.f2
32
Example 1
The power source in a particular welding setup generates
3500 W that can be transferred to the work surface with
a heat transfer factor f1 = 0.7. The metal to be welded is
low carbon steel, whose melting temperature is 1760K.
The melting factor in the operation is 0.5. A continuous
fillet weld is to be made with a cross-sectional area of 20
mm2. Determine the travel speed at which the welding
operation can be accomplished?
Heat capacity of low carbon steel (Cp)=480 J/Kg.K
Latent heat of melting Lm =247 kJ/Kg
Density = 7860 kg/m3
Initial sample temperature T0 = 300 K
33
Example 1-Solution
Rate of heat input to the weld bead = 3500 f1 f2
= 3500 0.7 0.5 = 1225 J/s
Heat input = Energy used for heating to Tm + Energy used
for melting
1225 = [Cp(Tm-T0) + Lm ] A v
1225 = [480(1760-300) + 247 103] 7860 20 10-6 v
Travel speed v = 0.0082 m/s = 8.2 mm/s
34
Lecture 3
05 Aug 2013, Monday, 10.30 am-11.30 am
Weld Microstructure & Concept
of continuity
35
Some material science basics
Atoms Lattice Grains
Grain size, Grain boundaries,
Recrystalization ~0.4-0.6 Tm Atoms remain in lattice,
but new grains will be formed
Melting Atoms displaced from lattice, free to move
36
Some material science basics
Metals are crystalline in nature and
consists of irregularly shaped grains of
various sizes
Each grain is made up of an orderly
arrangement of atoms known as lattice
The orientation of atoms in a grain is
uniform but differ in adjacent grains
37
Basic Classification of welding
(a) Fusion welding (b) solid-state welding
a) Fusion Welding
Uses heat to melt the base metals
A filler metal is mostly added to the molten
pool to facilitate the process and provide bulk
and strength to the welded joint.
e.g., Arc welding, resistance welding, Gas
welding, Laser beam welding, Electron beam
welding
38
Basic Classification of welding
b) Solid state Welding
Coalescence results from application of
pressure alone or a combination of heat and
pressure
If heat is used, the temperature in the process
is below the melting point of the metals being
welded
No filler metal is used
e.g., Diffusion welding, friction welding,
ultrasonic welding
39
Micro-structural zones in Fusion
welding
1) Fusion zone 2) Weld interface/partially melted zone
3) Heat affected zone 4) Unaffected base metal
40
Grain growth in Fusion welding
Fusion Zone Directional solidification Epitaxial grain
growth Columnar grains
HAZ Possible recrystallization/ grain refinement or
phase change
Slow cooling Coarse grains; Fast cooling Fine grains
Shrinkage of fusion zone Residual stress on the base
metal surrounding HAZ 41
Micro-structural zones in Solid
state welding
No Fusion zone
Little or no HAZ
Mechanically upset region (Flash)
Plastic deformation at the interface
42
Role of Temperature in Fusion/
solid state welding
Drives off volatile adsorbed layers of gases,
moisture, or organic contaminants
Breaks down the brittle oxide through differential
thermal expansion
Lowers yield/flow strength of base materials
helps plastic deformation
Promotes dynamic recrystallization during plastic
deformation (if T > Tr)
Accelerates the rates of diffusion of atoms
Melts the substrate materials, so that atoms can
rearrange by fluid flow (if T > Tm) 43
Role of Pressure in solid state
welding
Disrupts the adsorbed layers of gases/organic
compound or moisture by macro- or
microscopic deformation
Fractures brittle oxide or tarnish layers to
expose clean base material atoms
Plastically deform asperities (lattice) to increase
the number of atoms that come into intimate
contact (at equilibrium spacing)
44
Mechanisms for obtaining
material continuity
(1) Solid-phase plastic deformation,
without or with recrystallization
Solid state welding
(2) Diffusion, Brazing, Soldering
(3) Melting and solidification
Fusion Welding
45
Obtaining continuity
1a) Solid-phase plastic deformation (with no heat)
Atoms are brought together by
plastic deformation
Sufficiently close to ensure that
bonds are established at their
equilibrium spacing
Significant lattice deformation
Lattices are left in the strained
state (distorted) in cold (1a) Cold deformation
deformation and lattice strain
Prevailing mechanism in solid state welding
with out heat 46
Obtaining continuity
1b) Solid-phase plastic deformation (with heat)
In hot state (0.4-0.5 Tm), the
strained lattice recover from the
distorted state
Atomic rearrangement &
Recrystallization
Grain growth across original
interface (1b) hot deformation and
Eliminates the original physical dynamic recrystallization
interface
Prevailing mechanism in solid state welding
with heat 47
Obtaining continuity
2) Diffusion
Transport of mass through atom
movement
Can occur entirely in solid
phase or with liquid phase
For dissimilar materials thin
layer of alloy at the interface
Rate of diffusion Difference in Solid-phase diffusion across
composition (Ficks law), the original interface (dotted
line)
Temperature
Prevailing mechanism in brazing/soldering
48
Obtaining continuity
3) Melting and solidification
Liquid provided by melting Establishing a bond upon
the parent materials without epitaxial solidification of
or with additional filler this liquid
Solidifying crystals take up the grain structure &
orientation of substrate/unmelted grains
Prevailing mechanism in most fusion welding process
49
Summary: Lectures 1-3
Overview of welding, applications,
advantages, Welded Joint types
Weld specifications, Symbols
Fusion & Solid state welding
Elements of weld setup, Heat Balance,
Power density
N.B: Characteristics, micro-structural
zones and concept of lattice continuity in
fusion & solid state welding
50
Course details: Welding
Topic Hours Status
1. Introduction to welding science & 2-3
technology
2 Welding Processes 4
3 Welding Energy sources & characteristics 1-2
5 Welding fluxes and coatings 1
4 Physics of Welding Arc 1
5 Heat flow in welding 1-2
6 Design of weld joints 2
7. Testing and inspection of weld joints 2-3
Metallurgical characteristics of welded
8 joints, Weldability and welding of various 2
metals and alloys
Total 19
Lecture 4
12 Aug 2013, Monday, 10.30 am-11.30 am
Welding Processes
1) Oxy-Fuel gas welding
52
Welding Processes-
1) Oxy-Fuel gas welding
Uses oxygen as oxidizer
Acetylene, H2 or Natural gas, methane,
propane, butane or any hydrocarbon as
fuel
Fuel + Oxidizer Energy
Acetylene is preferred (high flame
temperature-3500 C)
53
Gases used in Oxy-gas welding
Fuel Peak Heat of
reaction combustion
Temp (C) (MJ/m3)
Acetylene 3500 54.8
Methylacetylene- 2927 91.7
propadiene (C3H4)
Hydrogen 2660 12.1
Propylene 2900 12.1
Propane 2526 93.1
Natural gas 2538 37.3
54
Oxy-acetylene welding (OAW)
operation
55
Reactions in Oxy-acetylene welding
Flame in OAW is produced by the chemical
reaction of C2H2 and O2 in two stages
Stage 1 C2H2 + O2 2CO + H2 + heat
Stage 2 2CO + H2 + 1.5O2 2CO2 + H2O + heat
56
Flames in OAW
57
Flames in OAW
Neutral flame is used for most applications 58
Flames in OAW- Reducing flame
Reducing flame for removing oxides
from metals, such as aluminium or
magnesium
Preventing oxidation reactions during
welding
To prevent decarburization (i.e., C to
CO,) in steels.
Low carbon, alloy steels, monel metal
(Ni+Cu+), hard surfacing
59
Flames in OAW-Oxy. flame
The oxidizing flame causes the metal
being welded to form an oxide.
Useful for preventing the loss of high
vapor-pressure components, such as
zinc out of brass, through the formation
of an impermeable oxide skin (here,
copper oxide)
Brass (Cu + Zn)
Bronze, Cu, Zn & Sn alloys
60
OAW set up
Pressurized cylinders of
O2 and C2H2
Gas regulators for
controlling pressure and
flow rate
A torch for mixing the
gases
Hoses for delivering the
gases from the cylinders to
the torch
61
OAW Torch
62
Example 1 - OAW
An oxyacetylene torch supplies 0.3 m3 of acetylene per
hour and an equal volume rate of oxygen for an OAW
operation on 4.5-mm-thick steel.
Heat generated by combustion is transferred to the work
surface with a heat transfer factor f1 = 0.20. If 75% of
the heat from the flame is concentrated in a circular
area on the work surface that is 9.0 mm in diameter,
find
(a) rate of heat liberated during combustion,
(b) rate of heat transferred to the work surface, and
(c) average power density in the circular area.
(Heat of combustion of Acetylene in O2 = 55106 J/m3)
63
Example 1 - OAW
(a) The rate of heat generated by the torch is the product
of the volume rate of acetylene times the heat of
combustion: RH = (0.3 m3/hr) (55106) J/m3 = 16.5106
J/hr or 4583 J/s
(b) With a heat transfer factor f1 = 0.20, the rate of heat
received at the work surface is
f1 RH = 0.204583 = 917 J/s
(c) The area of the circle in which 75% of the heat of the
flame is concentrated is A = Pi. (9)2/4 = 63.6 mm2
The power density in the circle is found by dividing the
available heat by the area of the circle:
Power density = 0.75 917/63.6 = 10.8 W/mm2 64
OAW-Advantages
The OAW process is simple and highly
portable
Inexpensive equipment
Control over temperature
Can be used for Pre-heating, cutting &
welding
65
OAW-Disadvantages
Limited energy welding is slow
Low protective shielding welding of reactive
metals (e.g., titanium) is generally impossible
Low power density, Energy wastage, total heat
input per linear length of weld is high
Unpleasant welding environment
Weld lines are much rougher in appearance
than other kinds of welds Require more
finishing
Large heat affected zones
66
OAW-Applications
Preheating/post heat treatment
Can be used for cutting, grooving, or piercing
(producing holes), as well as for welding
Oxyfuel gas processes can also be used for
flame straightening or shaping
Oxidizing flame for welding Brass, bronze, Cu-
Zn and Tin alloys
Reducing flame for low carbon & alloy steels
67
Pressure Gas welding
(Special case of OAW)
Oxyfuel gas used for preheating the weld
interface
68
