WELDING PROCESS -ANB

WELDING PROCESS
GAS,SMAW,GMAW,FCAW,
SAW & RESISTANCE WELDING

Indian Institute of Welding-ANB

Refresher course : Module-06

Gas Welding, Brazing,

Soldering and Cutting
IIW-ANB refresher course for Transition candidates

Contents
Part-1 : Introduction
Part-2 : Welding & related processes
Part-3 : Brazing and soldering
Part-4 : Cutting & edge preparation
Part-5 : Plasma Cutting
Part-6 : Thermal Cutting Standards
Part-7 : Safety

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Part-1

Introduction
Oxy-gas equipment

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Introduction
Oxy gas processes are based on controlled

combustion of fuel gas and oxygen mixture,

and consequent generation of heat

Oxy gas processes are popular for welding,

brazing, soldering and cutting of steel

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Fuel Gases
Acetylene ( C2H2 )
Propane ( C3H8 )
LPG ( Mixture of propane and butane )
Methane (CH4 ) - Natural gas
Hydrogen ( H2 )
Propylene ( C3H6 )
Butane ( C4H10 )
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Combustion Chemistry of Acetylene

Fuel gas + Oxygen

CO2 + H2 O

Acetylene C2 H2 + O2

2 CO + H2

4CO + 2H2 + 3O2

overall

C2 H2 + 2.5O2

4 CO2 + 2H2 O

2 CO2 + H2 O

However, maximum flame temperature for

Acetylene is reached at 55% oxygen stoichiometry
Actual oxygen to fuel gas ratios used are :
Acetylene 1.5
: 1
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Fuel gases and their characteristics

Oxygen:FG

Flame
Temperature
Deg C

Heat of
combustion
MJ/m

Acetylene

2.5

3087

55

Propane

2526

104

Hydrogen

0.5

2660

12

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Types of flames
Correct mixture
Neutral

Oxidising

Greenish, rounded
inner cone

Excess of O2
Blueish, sharp
inner cone

Excess of FG
Reducing
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Long white
luminous feather
9

Hottest point of flame

Acetylene = 3160 deg
C

Primary flame
(or inner cone)

LPG = 2826 deg C

Nozzle

Secondary flame (or outer cone)

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Heating Effect of Fuel Gases

OXY-LPG

OXY-ACETYLENE

HEAT CONCENTRATION

HEAT CONCENTRATION

TOTAL
Kj/m3
Primary
Secondary
Flame Temp
C

TOTAL
Primary
Secondary
Flame temp

54,772
18,890
35,882
3,160 deg

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95,758 Kj/m3
10,433
85,325
2,820 deg C
11

Gas Equipment
CYLINDER VALVE
OXYGEN REGULATOR

ACETYLENE REGULATOR

FLASHBACK ARRESTOR
FLASHBACK ARRESTOR
CUTTING TORCH
WELDING TORCH

FLASHBACK
ARRESTORS

OXYGEN AND
ACETYLENE
HOSES
ACETYLENE
(CYLINDER PAINTED
MAROON)

OXYGEN
(CYLINDER PAINTED
BLACK)
T-CQ3-2

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Cylinders
Service

Max
Pressure
(Kg)

Construction

Connection

Colour

Oxygen

150

Steel body

RH

Black

15

Steel body with

kisselghur &
acetone inside for
dissolving
acetylene

LH

Maroon

Dissolved
Acetylene

A cylinder normally contains about 6 cu.m of gas

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Cylinder manifolds

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Part-2

Oxy-gas welding
and
related processes

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Gas Welding
Torch
Tip

Oxy-acetylene welding - commonly

referred to as gas welding - is a

process which relies on the
combustion of oxygen and acetylene.

Because steel melts at a temperature

Filler
Flame

greater than 1500oC, oxy-acetylene is

the only gas combination hot enough
to weld steel.

When mixed in the correct

proportions, an extremely hot flame is

produced with a temperature of
around 3200oC
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Joint design for welding

Thickness

Joint recommendation

< 4 mm No special preparation. Butt joint OK

No special preparation.
4-6 mm
Slight root opening recommended
Bevel of 35-45 deg
>6 mm Root upto 3 mm depending on plate
thickness
>19 mm Double bevel with 3 mm root
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Welding techniques
Technique

Suitability

Upto 3mm plate thickness

Forehand Pipe welding <10mm wall
thickness
Above 3mm plate thickness
Pipe welding >6 mm wall
Backhand
thickness
For faster welding
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Gas welding - Flame types

For most applications, a neutral flame is

used, however some materials are different:

Welding brass, and bronze

Nickel, and alloys

Oxidising flame
Neutral to slightly carburising (reducing)

Copper

Neutral to slightly carburising (reducing)

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Gas welding
FLAME
SETTING

FLUX

FILLER

Cast Steel

Neutral

No

Steel

Steel Plate

Neutral

No

Steel

Slightly
High Carbon Steel
Oxidising

Yes

Bronze

Cast Iron (Gray)

Yes

Cast Iron

Yes

Base
metal

METAL

Chrome steel

Neutral
Neutral

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Special techniques
Cleaning

Fishtail burners are normally used

Preheating

Large handheld heating blowpipes

are used. Custom built burners are
used which are configured as per
requirement for heating large
irregular areas.

Large handheld heating blowpipes

Straightening
are convenient for local heating
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Part-3

Brazing and soldering

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Brazing
Economical for complex assemblies
Simple way to join for large joints
Excellent stress and heat distribution
Ability to join dissimilar metals
Ability to join non metals to metals
Ability to join different thickness parts
Joints require no finishing
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Principle of brazing
Parts must be joined without

melting

Melting point of filler metal >

450 deg C

Molten filler metal must be

able to wet surface of base

metals

Capillary flow is the dominant

physical principle

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Brazing methods
Single/ multiple torch : suitable for low volume

and maintenance jobs.

Furnace: Suitable for batch production and

automation
Induction: Suitable for continuous automated

production
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Braze-welding
Braze welding is a process similar to fusion

welding but a filler wire is used which has a

melting point lower than the parent metal
and no fusion or capillary attraction takes
place.

The main difference between brazing and

braze welding is in the joint clearance.

Brazing, for most commonly used brazing
alloys,requires a joint clearance of between
0.04-0.20mm. This allows the liquid filler
alloy to be drawn between the two closely
fitted surfaces by capillary action.

Braze welding does not require such a close

fitting joint and hence larger quantities of

filler alloy are used.

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Problems in brazing
Problems
>>>>>>

Causes
>>>>>>

No flow
No wetting
Wrong filler
Low temp.
Dirty parts
Poor fit-up
Too little flux
Bad vacuum

Excess flow or
wetting

Erosion of
parent metal

Wrong filler
High temp.
High temp.
Excess filler Time too long
Time too long Excess filler
Wrong filler
No stop-off

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Soldering
Parts must be joined without melting
Melting point of solder (filler) < 450 deg C
Molten solder must be able to wet surface of

base metals and flow by capillary action

between the surfaces to be joined.
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Soldering methods
Method

Application

Air-FG torch

manual working, low volume and

maintenance jobs

Soldering iron

manual working, electrical &

maintenance jobs

Furnace

batch production and automation

Wave
soldering

automatic soldering of electronic PCB

Vapour phase
soldering

in-line continuous process for electronic

parts

Induction

continuous automated production

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Selection of flux for soldering

Rosin

Organic Inorganic Special

Al & Al bronze

Brass

Copper

Steel/SS

Cast iron

Tin & Tin bronze

Zinc

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Fluxes
Inorganic fluxes

Organic fluxes

Zinc chloride

Stearic acid

Ammonium chloride

Oleic acid

Tin chloride

Glutamic acid

HCl

Hydrazine hydrobromide

Phosphoric acid

Acid based or acid

forming organics

Metal chloride

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Solders
Solder

Workpiece

Sn-Sb-Pb
Sn-Zn
Sn-Ag, Sn-Cu
Cd-Ag
Zn-Al

Copper, brass
Aluminium
SS, copper,
Aluminium
Aluminium

Indium-Sn

Glass to glass,
glass to metal
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Brazing and Soldering

Soldering is a joining process which uses

a filler material which melts at a

temperature lower than the parent
material and lower than 450oC.

Brazing is a joining process which uses a

filler material which melts at a

temperature lower than the parent
material but at a temperature greater than
450oC.

In brazing the molten filler metal is drawn

into the gap between the pieces of metal

to be joined by capillary attraction.

Bonding between the base metal and

filler metal takes place by surface alloying

through diffusion
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Soldering & brazing - comparison

Brazing

Soldering

Mech. strength

Higher

Lower

Working temp

Higher

Lower

Less

More

Versatile

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Part-4

Oxy-cutting and other

edge preparation
processes

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Various cutting processes

MS

OXY

PLASMA

LASER

SS
TITANIUM
ALUMINIUM
CERAMIC
RUBBER

KEVLAR
GLASS
LAMINATES

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WATER
JET

ROUTER

36

Oxygen cutting process

Preheat job to cherry red (around 850C)
Release pure oxygen stream
Oxidation of hot metal starts which is
exothermic Helps sustain reaction
Oxide produced should be molten at that
temperature
Kinetic energy of O2 removes molten oxide
producing kerf

These conditions are satisfied by Steel & Titanium.

Therefore these metals can be cut by this process
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Oxy-fuel gas cutting

Most widely used cutting
process
Can be used for cutting
MS and low alloy steels
Uses a wide range of fuel
gases acetylene, propane,
LPG, Methane, Hydrogen
Used in foundries for
cutting off runners and risers
Used for machine cutting
or hand cutting
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Oxy-cutting Torch
Nozzle mix system

Torch head
Cutting oxygen
Heating oxygen
Acetylene

Mixed gas
Cutting oxygen
Pre-heat flame

Cutting Nozzle

View from the bottom

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Oxygen cutting
NOZZLE

DIRECTION OF CUT

PRE-HEAT
FLAME

DRAG
LINES

FUEL GAS AND

PREHEAT OXYGEN
MIXTURE

CUTTING OXYGEN

CUTTING STREAM
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Drag Lines
As well as the roughness of the cut face, drag lines across the
surface of the cut can give the operator an indication if the cutting
speed is correct and the right cutting oxygen velocity is being
used.

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Common defects in Oxy-cutting

DEFECTS

CAUSES

Fluted cut
Low speed
-gouging at the bottom
Top edge melt

Large preheat flame

Oxygen pressure low

Heavy slag

Large preheat flame

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Common defects in Oxy-cutting

If the pre-heat temperature is too high it can have an effect on
the top edge of the cut. Too fierce a flame can cause melting of
the face or upper edge, this defect is called 'top edge melt'

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Common defects in Oxy-cutting

Example of a good quality cut

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Effects of alloying elements

ALLOYING ELEMENT

MAX LIMIT (%)

Carbon

0.3

Manganese

10

Silicon

Chromium

Nickel

3
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Effects of oxygen purity

SPEED / CONSUMPTION
(%)

17
5
15
0
12
5
10
0
75

O2 CONSUMPTION

50
2
510
0

CUTTING SPEED
99.5

99

98.5

O2 PURITY %
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9
8
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Cutting parameters
High speed vs standard nozzle

CUTTING SPEED

m/min

1.0
0.7
5

HIGH SPEED

0.5

0.2
5

STANDAR
D

10

20

PLATE

30

40

50

T IIW-ANB
H I Crefresher
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>>

70
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Plate Edge Preparation

Flame Planing Machine

Torch
Carriages

CONTROLS

TBA

WORKPIECE
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Triple Burner Assembly

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Profile Cutting & Nesting

OPTIMISE PLATE UTILISATION

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Programming Station
CUSTOMERS
ORDER

DESIGN

DXF
FILES

BOM
FINISHED
GOODS

RAW
MATERIAL
S

PROGRAMMING
STATION

PRODN
PLANNIN
G

PART
LIBRARY

NESTIN
G

GRAPHIC
EDITOR

MIS

TOOL PATH
GENERATION

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CNC
CUTTIN
G

MIS

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Part-5

Plasma and other

cutting processes

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Plasma Cutting

Originally introduced in around 1950s for non ferrous cutting

Often only method for non-ferrous (SS, Alu)

Suitable for profile or straight cutting

Suitable for Machine/hand cutting

Can also cut MS

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Plasma cutting of MS

Produces a taper cut which is often not acceptable

Advantage- high cutting speed at lower thickness

Taper not prominent in thin sheets. Therefore, popular for

cutting sheet metal, using low priced air plasma.

May be used low thickness MS (upto 20mm) for speed

advantage, compromising quality

WI produces good quality cut at high speed upto 40mm

thickness

Suitable for profile/straight cutting

Suitable for machine cutting or hand cutting

Normally used for square edge cutting

Possible to cut V edge with expensive equipment

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Plasma cutting equipment

PLASMA
GAS

SECONDARY
GAS
RECTIFIER
POWER
SOURCE

PLASMA
CUTTING
TORCH

HIGH
FREQUENCY
SOURCE
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Plasma cutting
CUT QUALITY

T-1>T-2>T-3>T-4
T-1
T-2
T3

WORKPIECE

T-4
TAPER CUT
SURFACE
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Air plasma
-

Hot ionised gas stream = plasma

(Temp = 30-40 thousand degC)

+
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Dual flow plasma

-

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Water injection plasma

-

Steam Layer

+
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Water Injection Plasma

Underwater cutting

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Plasma Cutting parameters

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Commonly used plasma gases

Open-arc

WI

Plasma gas Secondary Plasma gas

Air
Nitrogen
Argon
Argon+Hydrogen
(60% + 40%)

Nitrogen
(99.999%)
Oxygen

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Plasma cutting
Further developments

WATER
MUFFLER
WATER TABLE
UNDERWATER
CUTTING
O2 PLASMA
WITH WATER
INJECTION
FINE PLASMA

REDUCE UV, NOISE

REDUCE NOISE
FURTHER
REDUCE UV, NOISE
FURTHER
FASTER CUTTING
OF MS
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NARROW KERF

63

Oxy vs plasma cutting of MS

OXY FUEL

OPEN PLASMA

WI-PLASMA

UV, IR, Noise

Max Thickness
Kerf
HAZ (mm)
Suitable for

Low
>200
0.9-3
0.6
MS

Contained
30-50
--MS, SS

Cut Squareness

Good

Cut Surface

Good

V. High
30-50
3
0.4
MS, SS, Alu, etc.
Acceptable < 6mm
Bevelled > 6mm
Good < 6mm
Fair > 6mm
High
High

Cutting speed
Equipment cost

Low
Low

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Good
Good
High
V. High
64

Water-jet cutting

High pressure (30-60 K PSI) water is forced

through 0.1-0.6 dia orifice

Velocity achieved : 1700-3000 ft/sec

Efficiency increased by adding abrasive

powder with water

Effective upto 3mm thickness

Can cut metals & non metals

Profile cutting possible using CNC machine

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Laser cutting and drilling

The heat is provided by laser

Assist gas removes the vaporised/molten

material to form the kerf

O2 used as cutting gas for MS cutting (1max)

CO2 Lasers are most popular

Can be used for profile cutting

Provides high quality clean cut. Low HAZ

Pulsed LASER used for drilling

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Other cutting processes

PROCESS

APPLICATION

High alloy steel where normal

oxy-cutting is not possible
Flame gouging Removal of weld deposit in MS
Scarfing
Removal of surface defects in MS
Carbon arc
Severing of MS,SS,CI, Bronze,
cutting/gouging Al/Mg alloys. Gouging.
Oxy-arc
Severing MS, alloy steel
cutting/ gouging
Plasma arc
Gouging of MS, SS, alloy steel, Alu.
gouging
Powder cutting

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Flame gouging nozzle

Pre-heat flame
Oxygen stream

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Part-6

Thermal Cutting
Standards

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Thermal cutting standards

DIN EN 28206

Acceptance testing of
Oxygen cutting machines
testing the accuracy and
operational characteristics

DIN EN ISO
9013

Classification of thermal cuts

- Geometrical product
specification and quality
tolerances

WES 2801

Quality standard for gas cut

surface
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DIN EN ISO 9013

1

Indication of quality of cut

surface & tolerance class
1

Main
Perpendicularity/ Mean height
number of
angularity
of profile RZ5
standard
tolerance, u
ISO 9013

Angularity of
cut surface to
plate surface

4
Tolerance
class

Roughness of
cut surface Dimensional
along cutting accuracy
direction

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Part-7

Safety

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Safety in oxy-cutting & welding

PERSONAL PROTECTION
Protection
of

Protection
from

Recommendation

Use correct goggles

Eyes

IR Radiation, Spatter -shade # 3-6 for cutting

-shade # 4-8 for welding

Skin

IR Radiation,
Spatter,
Hot metal, Burn

Wear leather gloves

& apron

Apparel

Spatter, Fire

Wear apron

Feet

Spatter, Burn

Wear safety shoes

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Safety in oxy-cutting & welding

USE OF ACETYLENE

Do not draw more than 15% acetylene content per

hour from a cylinder

Always use cylinder in upright position
Always use correct hose, regulator & fittings
Do not use oxy-acetylene torch in a closed space
Do not use copper piping/parts in acetylene line
Never use Acetylene at a pressure higher than 1kg.
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Safety in oxy-cutting & welding

BACKFIRE

Flame burns back inside torch, usually with a

shrill sound, or flame is extinguished with a
loud pop. Sustained flashback indicates
something seriously wrong.
In the event of backfire:
Immediately shut of the oxygen supply, then

shut off FG supply

Set the pressures correctly
Clean the nozzle and seat, start again
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Safety in oxy-cutting & welding Flashback

A flame and its pressure wave (75x gas pressure in bar) travel
back through the torch and into the gas system.
Flame

Symptoms

A bang

Pressure
Wave
Hose

MIXED
GAS
Direction of Flashback
Toward Regulator

Cause: Improper purging & pressures of O2 & DA lines.

The flame speed is too fast to be blocked by the check valve in

the hose and proceeds right past it through the hose to the FBA
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Safety in brazing
For manual brazing safety requirements are

essentially same as in gas welding

Use goggles for eye protection (shade # 3-4

for gas brazing)

Additional safety measures must be taken

for protection against flux & toxic metal

vapours by assuring ventilation & respiratory
protection as required
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Safety in soldering
Precautions for fire hazard, specially when

flame is used,
Use goggles for eye protection (use shade #

1.5 - 3 for soldering with gas torch)

Ventilation to remove toxic metal & chemical

vapours,
Precaution from hot metal and burns.
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Safety in plasma cutting

Protection
from

Protection
of

Recommendation

Use correct goggles

(shade # 8-14)

Eyes

IR, UV Radiation,
Spatter

Skin

IR, UV Radiation,
Wear leather gloves
Spatter, Hot metal, Burn & apron

Apparel

Spatter, Fire

Wear apron

Ear

Sound

Use ear plug

Feet

Spatter, Burn

Wear safety shoes

Body

Electric shock

Follow safety
instructions
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Eye protection

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Contributors to this presentation:

1)

S. Ghoshal

1)

Ranajoy Banerjee

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Thank You

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Indian Institute of Welding ANB

Refresher Course Module 07

MMAW and SAW

Process and Practice

Contents

Manual Metal Arc Welding

Submerged Arc Welding

Manual Metal Arc

Welding
Process and Practice

Advantages of MMAW
Equipment used is simple,

inexpensive.
Electrode provides and
regulates its own Flux.
This process has excellent
suitability for outdoor use
lower sensitivity to wind
and even for use under
water.
All position capability

Principles of MMAW
An electric arc is maintained

between the end of a coated

metal electrode and work
piece.
The flux covering melts
during welding and forms gas
and slag to shield the arc and
molten weld pool
The flux also provides a
method of adding
scavengers, deoxidizers and
alloying elements to the weld
metal

Drooping characteristics power

source
Designed to give stable operation where the electrode moves

up and down with the welders hand eg MMAW and GTAW

processes.
Variation in arc voltage with movement of the welders hand
results in very little change in current
Stable current gives consistent arc heat and weld pool

ISO line of the power

source is V= 20+ 0.04xI

OCV
Open circuit voltage ( ocv )is the voltage across

the output terminals of the power source when it

is under no load condition.
In case of AC welding ocv plays an important
role in ensuring easy arc starting and good arc
stability. Higher is the ocv better is the arc
stability. However higher ocv poses danger of
electric shock and hence its value is restricted to
100 v max
Commercially available transformers generally
have ocv values 60 v to 70 v.
Commercially available rectifiers generally have
ocv values 65 v to 80 v

Equipment And Accessories

EQUIPMENT AND ACCESSORIES
1.
2.
3.
4.
5.
6.
7.
8.

Power source
Welding and ground cables
Electrode holder
Ground clamp
Chipping hammer and steel wire brush
Hand-shield / welding helmet / head-shield
Welding electrode
Re-drying oven

MMAW Electrode
Core Wire
Electrode core wire: C 0.10 max; Mn 0.38-0.62; Si
0.03 max; S 0.03 max; P 0.03 max
Important feature: low level of C, Si, S & P
Coating
Arc characteristics Stability, Striking & Restriking, Force, Capability to work in positions, and
in AC & DC sets
Slag characteristics Good shielding, Capability
to bring impurities out of molten weld metal, Good
detachability, Flowability as well as quick freezing
nature

Functions of the Flux coating

Stabilises and maintains Arc
To improve metal transfer and reduce spatter
They also reduce operating voltage for the electrode.
Shielding: Provided by gases produced by the flux and slag
covering during welding

Weld Pool Control

Slag fluidity determines the ease of positions welding
Fast freezing slag is more suitable for welding in vertical
and overhead positions.
Alloying Elements: May contain elements which can improve
mechanical properties of the joint

Coating Constituents
Arc stabilisers
Slag formers
Deoxidisers
Gas forming materials
Binders
Alloying elements
Deposition efficiency improvers
Extruding/slipping agents

Coating types
Rutile
Basic
Cellulosic
Acid
Acid-rutile
Oxidising

Merits/Demerits of coating types

Rutile: Merits
Easy striking/restriking
Good slag control
Good slag detachability
Good positional welding capabilities
Usable in low OCV sets
More welder friendly
Demerits

Limitation in mechanical properties

Alloy transfer difficult
High hydrogen level

Coating Factor
CF = Electrode diameter / Core wire

diameter
Thin coated: CF <= 1.3
eg. Ferrospeed

Medium coated: CF 1.3 1.5

eg. Ferrospeed Plus
Heavy coated: CF 1.5 2.2
eg. Vordian

Super heavy coated: CF > 2.2

Merits/Demerits of coating types

Basic: Merits
Good mechanical properties
Low hydrogen level
Alloy transfer effective
Higher deposition efficiency
Demerits
Greater welder skill required
AC welding difficult, especially in low OCV
High temperature preheating before welding
necessary
Slag detachability not as good as rutile type

Merits/Demerits of coating types

Cellulosic: Merits
High arc force good penetration
Thin coating good manouverability in roots
Less slag volume
Good positional welding
Alloy transfer possible
Demerits

DC based
High hydrogen level
Operator skill is important

Production Of Electrodes
The powdered coating materials are dry mixed and then liquid

silicate is added to form a paste.

The flux paste is extruded onto the core wire in an hydraulic
extruder. The two ends are brushed and linished for gripping
by the electrode holder and easy striking of arc.
The electrodes are then dried at between 110 130 C in
continuous or batch type ovens before packing.
Low hydrogen basic coated, stainless steel and other special
electrodes are further baked at 350 450 C to remove
moisture to very low levels.
Cellulose coated electrodes are dried at 80 90 C so that the
cellulose is not damaged and there is some residual moisture
to augment the arc force.

Handling And Storage Of Electrodes

1. Bending of electrodes causes weakening of bonding of coating
to be discouraged
2. Striking the electrode tip hard with base plate can cause peeling
of flux of electrode tip.
3. Use of higher current than recommended can cause
overheating of coating in end portion causing coating
decompose or disintegrate.
4. Contamination of electrodes by oil, grease, shop floor dirt to be
avoided.
5. Re-dry the electrode as per recommendation before use

Handling And Storage Of

Electrodes
SOURCE OF WATER IN COATING
1. Chemically combined water [ water of crystalisation of certain

ingredients of coating ] to remove it very high temp. [ Say 900 deg.

C or more ] is needed.

2. Hygroscopic water partly retained by the silicates used as binder

and partly as free moisture originated from atmosphere and settled
into the pores of coating -3 Can be removed by heating the electrode at 110 to 450 deg.C.
Hygroscopic water varies as the relative humidity of atmosphere of
storage area.
Regular consumer of electrodes are advised to maintain special
storage rooms which are dehumidified to 50% RH maximum and are
kept 5 to 10 deg. C above ambient temperature.

Handling And Storage Of Electrodes

Type of electrode

Redrying temp &

time

Remarks

Rutile E6012 / E6013

100 110 C for 1 hr

Cellulosic E6010 / 6011

Not recommended

If wet 70 C for 30
min

Low hydrogen 10-15 ml H2

250 C for 1 - 2 hrs

Transfer to holding
oven at 125 150 C

Low hydrogen 5 -10 ml H2

350 C for 1 - 2 hrs

Transfer to holding
oven at 125 150 C

Low hydrogen below 5 ml H2

400 - 450 C for 1 - 2

hrs

Transfer to holding
oven at 125 150 C

Stainless steel Exxx-16/17

250 C for 1 hr

Stainless steel Exxx-15

300 350 for 1 hr

Classification - AWS A5.1 - 1991

Example : E 6013
Letter E indicates covered electrode for MMAW

process manufactured by extrusion process.

Digits 60 indicate minimum weld metal UTS of 60,000
psi
Digit 1 indicates the position all positions except Vdown
Digit 13 indicates the type of coating, current
condition High titania, Potassium & AC, DC

Classification - IS 814 - 1991

Example : EB5426H3JX
Letter E indicates covered electrode for

MMAW process manufactured by extrusion

process.
Letter B indicates Basic coating.
Digit 5 indicates UTS 510-610N/mm2 & Y.S.
360 N/mm2 (min)
Digit 4 indicates a min elongation as 20% with
impact strength as min 27J at 300c.

Classification - IS 814 - 1991

Digit 2 indicates that electrode can be used in all

positions except vertical down.

Digit 6 indicates that electrode is usable in DC
with electrode positive & on AC with min. 70 OCV
Letter H3 indicates that max. H2 level will be 5 ml
per 100 gm weld metal.
Letter J indicates that electrode efficiency is in
the range 110-129%.
Letter X indicates that electrode deposits
radiography quality welds.

Selection Of Covered Electrodes

For Applications
MMAW PROCESS IS BEING SUCCESSFULLY

USED FOR WELDING OF

1.
2.
3.
4.
5.
6.
7.
8.

MILD AND CARBON MANGANESE STEELS

LOW ALLOY STEEL
HIGH ALLOY STEELS AND STAINLESS
STEELS.
CAST IRONS
SURFACING APPLICATIONS
COPPER AND COPPER ALLOYS
ALUMINIUM AND ALUMINIUM ALLOYS
NICKEL AND NICKEL ALLOYS

Selection Of Covered Electrodes

For Applications
To ensure compatible property with base material
A.

Strength / toughness related compatibility

B.

Environment / specific environment related

compatibility eg. Corrosion / high or low
temperature related applications

C.

Welding procedure / position related

compatibility eg. V-up / v-down / oh welding

D.

Crack resistant weld during welding in

specific cases SS / cast iron / dissimilar
welding

Factors to be Considered for

selecting electrodes
Chemical composition of base material
Mechanical properties required
Service requirements of the joint
Position of Welding
Deposition requirements
Joint design / fit up
Penetration requirements

Selection of electrodes
Use an all position Electrode when welding job involves all

position
Use high deposition electrodes when the job is to be done in

down hand and large amount of deposition is to be done.

High deposition electrodes will have limitations on welding
position.
Use deep penetration electrodes, cellulosic type electrodes

to achieve higher penetration (or) to make one side welding

respectively.

Selection of electrodes for C-Mn Steels

Group contains

- Mild steels to IS : 2062

- Boiler quality steel to IS: 2002
- Micro-alloyed steels to IS : 8500
- Weathering steels to IS : 11587
For mild steel non-critical, applications in static
loading upto 40 mm combined thickness E6013
medium coated electrodes
For mild / boiler quality steel for all applications above
40 mm combined thickness and sub-zero conditions
E 7018 electrodes + pre-heat as required for higher
thicknesses

Selection of electrodes for Microalloyed steels

Range of medium and high tensile steel developed to give

improved strength and toughness without impairing

weldability. Covered by IS:8500 - 1991
Small amounts of carbide forming elements eg. Nb, V, Ti etc
added Total amount 0.20% max as such called Microalloyed steels
Controlled rolling at low finish roll temperatures results in
very fine grain size ASTM 12 14.
Properties :
UTS
450 600 MPa
YS
400 500 MPa
Elongation
20 22 %
Weld all sections with E7018 / E8018 G electrodes
depending on minimum yield requirements

Selection of electrodes for

Weathering steels
These are medium tensile steels with Cu, Cr & small amount of

Phosphorous added to improve atmospheric corrosion

resistance. However P gives hot shortness and lower impacts
and latest grades have reduced P levels
Example - Corten A, B & C and Sailcor HR & CR steels used
for rolling stock in railways and other transportation sectors.
Corten B & C with lower P levels have better weldability
For the lower strength Corten A & B type use E7018 W1
electrodes
For higher strength Corten C use E8018 W2 electrodes.
Note the electrode weld metal does not contain P

MMAW Best practice

Selection of welding parameters
Current
Current selected is dependent on
Size & type of electrode
Thickness of base material
Welding position

Voltage
Try to use highest voltage setting available,
specially for basic coated low hydrogen
electrodes.

MMAW Best practice contd.

Operator control

Quality of welding
highly dependent on the
skill of operator
A high level of manual
dexterity is required to
co-ordinate the
electrode to match the
burn off rate and to
maintain a constant
ARC length.

MMAW Best practice contd.

Defects due to lack of operator control
Porosity
Undercut
Insufficient / excess penetration
Lack of fusion
Slag inclusion
Undercut
Incorrect weld size
Incorrect weld profile

MMAW Best practice contd.

Operator control points
Set correct current.

Too low current - lack of fusion, convex bead

Too high current spatter, undercut in H-V fillets
overheating & damage to flux coating.
Maintain shortest arc possible for basic electrodes
Avoid excessive weaving may lead to slag entrapment.
Use work-back technique at start for Basic coated LH
electrodes
Always fill crater at end of run
Maintain correct welding speed to ensure optimum weld
size. Avoid over-welding.

Position of Electrode Good Practices

Position of Electrode Good Practices

Cleaning Of Joints
To avoid porosity and attain satisfactory

welding speed , remove excessive scale ,

oxide films, rust, moisture , paint , oil and
grease , dirt and other contaminations before
welding.
The cleaning procedure may involve light to
heavy brushing/grinding and removal of the
metal by goughing electrode .
In case of some non ferrous materials
chemical cleaning is recommended

Process Limitations of MMAW

Highly dependent on manual skill of welder

Variability in implementation of qualified

welding procedure
Low deposition rate

Effect of Welding parameters

A- Proper amperage, arc length, travel speed

B- Amperage - too low
C- Amperage - too high
D- Arc Length - too short
E- Arc Length - too long
F- Travel Speed - too slow
G- Travel speed - too fast

Indian Institute of Welding - ANB

Refresher Course Module 08

Gas Metal Arc and Flux

Cored Arc Welding
Processes

Contents
Gas Metal Arc Welding
Flux Cored Arc Welding

Major Arc welding processes

MMAW / SMAW

GMAW / FCAW *

Gas Metal Arc Welding ( MIG / MAG )

Flux Cored Arc welding

GTAW *

Manual Metal Arc Welding / Shielded Metal Arc

Welding

Gas Tungsten Arc welding

SAW

Submerged Arc Welding

Electro slag

*Gas shielded processes

Weld Metal Deposited By Major Arc

Welding Processes

Developed
Countries
India

Gas Metal Arc Welding the Dominant Process

Improved productivity with flexibiity
High weld quality with low hydrogen deposit
Suitable for semi-automatic and automatic welding
Increased penetration and deposition rates
Amenable to mechanisation and robotic applications
Adaptable to microprocessor based feed back

control

Gas Metal Arc ( MIG ) Welding

Uses continuous wire
0.6 2.0 mm as
electrode
Gas shielded, inert or
active gas
Manual,automatic or
semi-automatic
process
High productivity

GMAW process

GMAW equipment

Power Source Characteristics

Power Sources of Constant Current type having

drooping characteristics are used for

- MMAW process
- GTAW process
- Plasma processes

Power sources of constant voltage type having flat

characteristics are used for

- GMAW & FCAW processes
- SAW process

V-A Relationship CV power source

for GMAW / SAW

Automatic arc length regulation

Wire Feed Speed / Current.

Constant potential power sources are used for

GMAW and have no built in means of changing the

current. The current adjusts itself to burn off the
quantity of wire delivered. If the wire feed speed is
increased more current is drawn to burn it off . In
this way adjusting the wire feed speed also adjusts
the current supplied.

The current dictates the amount of heat generated

by the arc. Increasing the current increases the arc

energy and therefore the heat input. This in turn
increases fusion and penetration, wire deposition
rate and travel speed.

Shielding Gases
Shielding gases provide a
protection to the weld metal
from the atmosphere and
have a pronounced effect on:
Arc characteristics
Mode of metal transfer
Penetration and weld bead profile
Speed of welding
Undercutting tendency
Cleaning action
Weld metal mechanical properties

Types of shielding
gases used in GMAW
Carbon Dioxide (CO2)
Argon
Helium
Oxygen
Nitrogen
Mixtures of the above
gases

GMAW Filler Wire

GMAW filler wire for welding carbon-manganese and low alloy steels
require additional quantities of silicon and Manganese as de-oxidisers.
Some stainless steel wires may also have higher silicon, otherwise
chemistry of GMAW wire generally match the plate material
AWS specifications covering GMAW wire
SFA-5.7 for copper and copper alloys
SFA-5.9 for stainless steels
SFA-5.10 for aluminium and aluminium alloys
SFA-5.14 for nickel and nickel allos
SFA-5.18 for carbon manganese steels
SFA-5.28 for low alloy steels

Modes of metal transfer

The mode of transfer is determined by a number of

factors:
Magnitude, type and polarity of welding current
Electrode diameter
Electrode composition
Electrode extension and
Shielding gas composition

Influence of welding current & gas on

metal transfer mode in GMAW
DIP

CO2 /
Ar Mix

GLOBULAR

CO2

SPRAY

Argon Mix

Modes Of Metal Transfer

DIP TRANSFER

Low current - low voltage used to produce

short circuiting arc, freq. 200 times / minute.
Used for sheet metal and postional welding
SPRAY TRANSFER

Higher currents and voltage used , droplet size

same as or lower than the wire diameter.
Higher deposition rate penetration and fluidity
of the molten pool , increases the productivity

Dip or Short Circuit Transfer

Occurs with carbon dioxide, argon and argon mixtures as

the shielding gas and the current density is low.

Molten droplets forms on the tip of the electrode, but
instead of dropping to the weld pool, they bridge the gap
between the electrode and the weld pool as a result of the
greater wire feed rate.
This causes a short circuit and extinguishes the arc, but it
is quickly reignited after the surface tension of the weld
pool pulls the molten metal bead off the electrode tip.
The metal is transferred from the electrode only during the
period in which the electrode is in contact with the weld
pool.
No metal is transferred across the arc.
The electrode contacts the weld pool in the range of 20- to
200 times per second.

GMAW Metal Transfer modes

Spray Transfer

4 steps in
Short
circuiting
transfer

Globular Transfer

Spray Transfer
Spray transfer GMAW occurs when the molten

metal from the electrode is propelled axially

across the arc in the form of minute droplets.
With Argon-rich gas shielding it is possible to
produce a very stable, spatter-free axial spray
transfer mode.
The mode requires Direct current with a positive
electrode (DCEP) and a current level above a
critical value termed the spray transition current.
Below this level, the transfer is globular.

Axial Spray Transfer

Molten metal is
propelled axially
across the arc in
minute droplets
Argon-rich gas
shielding produces
stable spatter free
axial spray transfer
mode

Argon Mixed Gas Spray Transfer

Modes Of Metal Transfer

Contd.

GLOBULAR TRANSFER

An intermediate stage between dip and spray

transfer. Droplet sizes are more than the wire dia.
Produces excessive spatter and erratic arc
behaviour
PULSED TRANSFER

Controlled method of spray transfer. Heat input to

the job is controlled by low background current
with high pulses using special type of equipment

Globular transfer
Globular transfer is normally encountered with CO2 as shielding

gas at higher current and voltages.

The higher surface tension of molten metal with CO2 produces
a larger size droplet greater than the wire diameter.
The CO2 gas also dissociates in the welding arc to CO and
oxygen and then recombines back on top of the weld.
This sets up some electro-magnetic forces in the upward and
tangential directions which act on the metal droplet. It also
produces greater heat due to the burning of the CO.
When the droplet finally detaches by gravity or it falls in an
uneven manner on to the workpiece, This causes higher spatter
and a more uneven bead.
As a result of the large molten droplets this mode of transfer is
generally limited to flat and horizontal welding positions.

CO2 Globular Transfer

Pulse Transfer

Combines the control on heat input of short arc with the higher
deposition rate of open arc.
Gives extremely precise control on metal transfer and penetration
to give superior weld quality
In synergic pulsed systems wire feed rate synchronised with
pulsed current to control individual droplet detachment.

Problems of using CO2 as Shielding

Gas
Unstable arc with high level of spatter
High fume formation rate
Higher level of reinforcement
Reduced speed due to high viscosity
Undercut / sharp notch at the toe of weld

Spatter generated
1 metre of weld at 260 amps
using 1.2mm dia. A18 solid wire

Carbon dioxide
17.1 g

Argon - 20 CO2
8.6 g

Argon-12 CO2
5.5 g
T-GK 3 (10)

Problems in using pure Argon

as Shielding gas
Stable and Soft arc with a tendency to wander
Finger shaped penetration profile
Poor fusion and penetration due to low heat

input
Comparatively high bead profile

Finger Profile of pure Argon arc

Oxygen

Pure Argon Profile

Carbon di-oxide

20%

10%

Modified by oxygen and CO2

Development of Shielding Gas

Mixtures
For welding mild and alloy steels which can tolerate some amount of
oxidising gases the pure Argon arc is modified by adding
1 5% oxygen to reduce surface tension and improve weld pool
fluidity to give a flatter bead and increase welding speeds.
5 25% CO2 to increase arc heat to improve fusion and penetration
and round out the penetration profile of pure argon. However the
greater is the amount of CO2 added higher is the spatter.
For welding stainless steels
Upto 2% oxygen or 3% CO2 added to improve weld fluidity and
give flatter weld bead.
10 - 40% helium added in modern gases for improved penetration &
bead shape and increased welding speeds,
For welding aluminium, copper, nickel and other non-ferrous
alloys where no oxidising gas can be tolerated
25 75% helium added to improve fusion, penetration and welding
speeds.

Argon - Helium Mixtures used for

Aluminium and Non-ferrous metals
Helium

Argon

Effect of CO2 and O2 on welding speed

( 4mm throat fillet on 6mm plate)

CO2 and Argon mixture profiles

CO2

Argon mixture

Shielding gas profiles &

effect on weld length
weld length
1.2 m

weld length
1.15 m

Ar-CO2-O2

weld length
1m

Ar-CO2

CO2

Savings with Argon / CO2 / O2 gas mixtures

CASE STUDY - 2

Heavy Fabrication

Reduction in direct weld costs - 16.6 %

All weld deposit properties

with ER70S-6 wire

Benefits of using gas mixtures

Improved arc stability leading to lower spatter loss
Improved weld bead geometry leading to weld metal saving
Faster welding speeds leading to higher productivity and

reduced labour costs

Improved weld quality leading to lesser rejects
Reduced clean up time
Lower distortion
No heaters required for individual cylinders

Gas Metal Arc Welding Parameters

Current ( amps )
Voltage ( volts )
Shielding gas flow rate. ( litres / min )
Stick out
Torch angle
Welding speed

Balancing the wire feed speed

As the wire feeds toward the weld it is melted by

the arc which burns up the wire. This is shown

below.

Balancing welding parameters

Wire Feed
Rate

Arc Burn Back Rate

Balancing the wire feed speed

Two options are available to balance the

wire feed rate

Adjusting the arc voltage to increase or
decrease the burn off rate - used when the
current is OK for the job
Adjusting the wire feed speed if the
current is too high or low.

Torch angle.
15 - 25

Direction of travel
This rake angle should be utilised for the welding of all joint types in the
flat and overhead position.

Influence of wire angle

The wire angle influences
penetration
weld convexity
tendency to undercutting
porosity.
Backhand gives high penetration,
narrow and high weld convexity, and
relatively high risk for undercutting
Vertical welding gives optimum
performance
Forehand gives low penetration, wide
and low weld convexity, and relatively
slight risk for undercutting

Backhand Vertical

Forehand

Process Variations
Gas metal arc spot welding is a technique in

which two overlapping work-pieces are fused

together by penetration of the arc
Heavier sections can also be welded by
punching a hole in the upper work-piece. This
is know as plug-welding
As against resistance spot welds, access to
only one side of the joint is necessary for Gas
metal arc spot welding.

MIG Brazing
MIG brazing is a variation of the MIG

welding process used for brazewelding. It

uses the heat generated by an arc struck
between a continuously fed consumable
filler wire and the workpiece to fuse the
metal in the joint area.
The consumable wire used in MIG brazing
is solid and an additional shielding gas is
required to protect the arc and weld area in
the same manner as that used for MIG
welding.
The main features of the process are low
welding currents, low heat input and high
deposition rates.
The filler wire is usually of copper-silicon
alloy, although other copper alloy wires
have also been used.

High Productivity GMAW Processes

Conventional GMAW limited to deposition rates

upto 6kg / hr and speeds upto 600 mm / min.

To achieve higher productivity

- Modified single wire processes

Speeds upto 2m/min, deposition rate 14kg/hr
- Two wire processes
Speeds upto 5m/min, deposition rates 20kg/hr

RAPID ARC / RAPID MELT / T.I.M.E

PROCESSES
Characterised by high wire feed rates upto 30

m/min with high stick out

3 voltage ranges : Low - Forced short arc
High - Moderated spray arc
V.High - Rotating arc
Special gas mixture compositions
Ar - 26.5He - 8CO2 - 0.5O2
Ar - 30He - 10CO2 - 300ppm NO
Ar - 8CO2

Two Wire Processes

Two wires, leading and trailing forming common

elongated weld pool.

Twin wire GMAW Power sources coupled in parellel with common

control. Parameters cannot be set independently
Equipotential contact tubes - same volts for both
wires. Magnetic attraction of arc roots.
Optimum inter wire spacing 4-7mm.
Mostly used with Pulsed - Arc and Spray Arc

Multi-wire GMAW Process

Tandem

Wire Technologies
came to the GMAW process
in early Nineties .
2 electrically isolated wires,
one behind the other (lead &
trail
electrodes),
closely
spaced, deposit metal in
single weld pool
Lead wire generates most of
base metal penetration, trail
wire controls bead contour
and edge wetting-also adds
to Depo. Rate.
Managed
by
specialized
Power control software

Two Wire Processes

Tandem MIG
Independently controlled power sources
frequency coupled - master and slave operation.
Electrically seperated contact tubes allows
independent volts and parameter settings.
Phase shift in pulsed welding achieves high
quality spatter free welding
Argon - 5O2 and Argon - 18CO2 gas mixtures
used
Applications in Ship building, tank welding, truck
wheels, rail coaches

FCAW PROCESS

FCAW Process Features

Uses tubular wire with flux

inside
Gas shielded (FCAW-G) or self
shielded (FCAW-S)
The flux produces a protective
slag and/or gas cover
Combination of benefits of
MMAW and GMAW
High productivity process with
low spatter. Smooth arc with
CO2. Argon mixtures give
superior performance
Problem of high fumes which
need to be extracted in
enclosed areas

Application of FCAW
For fabrication of

- mild and low alloy steels

- stainless steels
- high nickel alloys
For surfacing

- for wear or corrosion/oxidation resistance

- wide range of hardness / compositions available
- self shielded wires mainly used here

FCAW application areas

Out-of-position welding
Solid wire GMAW has to use dip-transfer which is slow with
tendency for lack-of-fusion or expensive pulsed-arc power
sources
Rutile type gas shielded E71T-1 wires can deposit over 3 kgs/hr
vertically up and are extensively used in shipbuilding, structural
and general fabrication applications.
Outdoors field welding
Gas shielded, solid wire or FCAW processes cannot be used
due to windy conditions
Self shielded E71T-8 wires used which can deposit upto 2
kgs/hr vertically up.

FCAW application areas

Down-hand welding
For applications not requiring Charpy impact properties
E70T-4, self shielded wires used. Deposits upto 18 kg/hr
in mechanised operation
For applications requiring impact properties E70T-1
wires used. Deposits upto 14 kg/hr in mechanised
operation.
For welding coated and galvanized sheet
Self shielded E71T-14 wires used. Breaks up and
volatilizes the coating avoiding porosity and cracks
For high impact requirements and low alloy steels
E70T-5 wires used with gas shielding

Typical welding Parameters for FCAW

E71T-1 wire
Wire
Size

Down-hand

Vertical-up

Overhead

0.9 mm

26V 200A

23V 150A

26V 200A

1.2 mm

27V 240A

25V 200A

27V 210A

1.4 mm

28V 260A

25V 210A

28V 220A

1.6 mm

28V 275A

25V 220A

28V 240A

Acknowledgements
We gratefully acknowledge the contributions of
the following faculty members for developing
this module
Mr.R.Banerjee
Mr.R.Srinivasan

THANK YOU

Submerged Arc
Welding
Process and Practice

SAW Process Principles

Application of SAW process

Uses continuous wire
2.0 6.3 mm as
electrode.
Automatic process
Down-hand position
and H-V fillets only
Heavy section welding
of straight sections
Circumferential
welding

SAW Features
High Productivity, high
amperages may be used
Easy de-slagging
High Quality
Deep penetration
Excellent mechanical
properties
Environment friendly
Very little fume
No radiation
Easy operation

SAW Equipment

Equipment And Accesories

1.
2.
3.
4.
5.
6.
7.

WIRE FEEDER
WELDING POWER SOURCE
FLUX HOLDER AND FEEDER
MEANS FOR TRAVERSING THE WELD
JOINT
REDRYING ARRANGEMENT FOR
FLUX
FLUX RECOVERY UNIT .
OTHER ACCESORIES

Consumables
Wire : solid / fluxcored
Soilid wires for mild and low alloy steel applications are

normally copper coated.

Flux cored wires are often referred as composite

electrodes and comes under EC designation in wire flux
classification.
Flux :
A. Fused flux :
Ingredients ( ground minerals ) are mixed and melted in a

pot / furnace at high temperature [ 1600 1800 deg.C ].

melt is rapidly solidified and fragmented by quenching in
water. These flux fragments are dried , crushed , sieved ,
sized and packed.

Consumables contd.
B. Agglomerated flux ;

finely powdered ingredients are mixed and mix is steadily

moistened with liquid alkaline silicates.The mixer blades
are designed to assist agglomeration.
The green agglomerates are baked in rotary oven gradually
with final exposure at 600 to 800 deg.C.While baking the
water evaporates leaving the binder as bridges between
particles. The flux is then sieved , graded and packed.
C. Sintered flux :
Produced by grinding the dry charge together, pressing
into small balls and heating to just below melting point
[ 1000 1100 deg. C ] in furnace. These semi fused masses
are crushed, sieved, sized and packed.

SAW Fluxes
Fused
Heavier, higher bulk

densities, hence less

volume for same weight
Thicker slag cover,
more consumption
Higher manufacturing
temperature and so
ferro-alloys, alloy
addition not possible.

Agglomerated
Lighter, lower bulk

densities, hence volume

is more for same weight
Thinner slag cover, less
consumption
Lower manufacturing
temperature and hence
ferro-alloys, alloys
additions possible

Neutral , Active And Alloy

Fluxes
A change in arc voltage will change the quantity of flux

interacting with a given quantity of electrode resulting change

in composition of weld metal

Neutral fluxes :
These fluxes do not produce any significant change in the weld
metal chemical composition due to a large change in arc
voltage or arc length / stick out.
Active fluxes :
These contain manganese and / or silicon bearing ingredients
as de-oxidiser and changes the weld metal chemical
composition with change in arc voltage / stick out.
Alloy fluxes :
contain alloying ingredients in the flux and when used with non
alloyed carbon steel electrode give alloy weld metal.

Basicity Index ( B.I )

B.I = BASIC OXIDES / ACIDIC OXIDES =
[CaO+MgO+Na2O+CaF2+1/2(MnO+FeO)]
-------------------------------------------------------------------- [SiO2+1/2 (Al2O3+TiO2+ZrO2)]
B.I < 0.9 , ACIDIC

B.I = 0.9 to 1.2 , NEUTRAL

B.I > 1.2 -2.0 , BASIC
B.I > 2.0 , HIGH BASIC

SAW Wire - Flux Classification

F 7A6 EM 12K
F Indicates SAW flux
7 UTS minimum 70,000 psi
A As welded condition
( P post weld heat-treated condition )
6 Impact minimum 20 ft-lbf at 60 F
E Solid wire electrode
M Medium manganese level wire
12K specific composition wire

Flux consumption in SAW

kg/m

0,4

0,3

0,2

0,1

0
40

60

80

100

120

140

Welding speed in m/h

160

Handling and Storage of Fluxes

A. Wires : should be free from rust , oil , grease

etc. Before welding.

B. Flux : to be redried depending on flux type in

line with manufacturers recommendation

Care should be taken while storing agglomerated

flux - if bags containing flux are stacked one upon
other the bag at the bottom should not
experience heavy load .

Welding Parameters
1.

2.
3.
4.
5.
6.

WELDING CURRENT
ARC VOLTAGE
SPEED OF ARC TRAVEL
SIZE OF ELECTRODE
ELECTRODE STICK OUT
HEAT INPUT RATE

TO GET OPTIMUM RESULTS , EFFECTS OF

THESE PARAMETERS AND TO SELECT AND

CONTROL THOSE PROPERLY TO BE
UNDERSTOOD CAREFULLY.

Parameters for SAW welding

Typical parameters for square-butt weld on 19

mm MS plate
Plate thickness
Pass

19 mm
1

5 mm

5mm

Current ( amps )

800

900

Voltage ( volts )

36

37

Travel speed ( cm/min )

56

56

Wire size

Arc Starting in SAW

Unlike MMAW arc start in SAW may be difficult due to flux cover
Few common methods are
A.

Use of steel wool / iron powder

B.

Sharp wire start- wire tip made chisel like

for high current density

C.

Scratch start carriage starts just before current

flow starts

D.

Molten flux start arc starts inside molten flux used

for multi wire technique

E.

Wire retract start

F.

High frequency start

Control points of SAW process

The plates have to be straight
The plates have to be clean, preferably ground or
shot blasted
The positioning of the wire is of utmost
importance
The flux should cover the arc completely (not
necessarily cover the wire completely)
The flux should be dry

SAW Typical Defects

Porosity
Inadequate flux depth, moisture or
contaminants
in the flux or weld joint
Excessive travel speed
Slag residue from tack welds made with
covered electrodes
Slag
-

Inclusion
Contaminants of flux, Usage of cold flux.
Improper joint geometry
Viscosity of the slag
Inadequate interpass cleaning

Influence of Amperage and Voltage

Higher amperage gives deeper penetration

Higher voltage gives wider penetration. The arc

length gets extended

Influence of polarity and wire diameter

Deepest penetration with positive electrode. Normally, the
welding machine is equipped with DC positive electrode.

At constant amperage, the penetration gets deeper with

smaller wire diameter, due to the higher current density.

Influence of stick-out
Longer stick-out gives higher deposition rate, but
also more shallow penetration.

Above: Penetration at different stick-out

Right: Deposition rate at different stick-outs.
A: 25 mm
B: 57 mm
C: 83 mm

Deposition rate
Recommended current range and deposition rate (kg/h)
for different wire diameters

Deposition rate
As a function of wire diameter and amperage
Kg/
h

Wire
diameter
a = 1,6 mm
b = 2,0 mm
c = 2,4 mm
d = 3,2 mm
e = 4,0 mm
f = 5,0 mm
g = 6,0 mm

16
14

12
a

10

c
b

8
6
4
2
200

400

600

800

1000 Amp

SAW - Process Variations

Tandem SAW
Twin / Multiple wire SAW
SAW with auxiliary hot wire feeding
SAW with metal powder addition
Narrow Gap SAW

SAW Process Limitations

Limitation welding position
Limited to higher thickness
Limited to few materials
Elaborate arrangement for equipments

& accessories - expensive

Acknowledgements
We gratefully acknowledge the contributions of
the following faculty members for developing
this module
Mr.R.Senguta
Mr.R.Banerjee
Mr.R.Ravi
Mr.N.K.Mukherjee

THANK YOU

Indian Institute of Welding ANB

Refresher Course Module 06
__________________________

Resistance Welding

212

IIW-ANB refresher course for

Transition candidates

Resistance welding

213

IIW-ANB refresher course for

Transition candidates

What is resistance welding?

Spot welding
Butt welding

Spot Welding

Seam welding
Flash butt

Resistance welding is a process where heat is generated by

the resistance of the parts being welded to the flow of a
localized electric current.
214

IIW-ANB refresher course for

Transition candidates

Spot welding applications

Car body

Resistance spot welding is extensively applied for car

body manufacture.
215

IIW-ANB refresher course for

Transition candidates

Spot welding applications

Rail car body panels

216

IIW-ANB refresher course for

Transition candidates

Spot welding applications

Complete side walls of rail coach

217

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Transition candidates

Spot Welding Machine

218

IIW-ANB refresher course for

Transition candidates

Spot Welding Process

219

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Transition candidates

Spot welding in progress

220

IIW-ANB refresher course for

Transition candidates

PORTABLE

SPOT WELDING GUNS

X-GUN

C-GUN
221

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Transition candidates

Portable Spot Welding Machine

T ROLEY

G A NTRY

,AIR
,

SPRING
BALANCE

T/R

SELECT S/W
3

GUN S/W

A IR
Cylin
- der

KICKNESS
CABLE

2
1

SHUNT

T /C

POINT HO LDER
Guide Rod

CAP T IP

G A NT RY

SHANK

SCR
BOX

ADAPT O R
HOLDER
GUN BODY
MOTO R

222

IIW-ANB refresher course for

Transition candidates

Portable spot welders

for side wall arch

223

IIW-ANB refresher course for

Transition candidates

Robotics Spot Welding

LHB side wall

224

IIW-ANB refresher course for

Transition candidates

Spot welding process

Overlapping steel sheets are positioned between

Cu-based electrodes.
225

IIW-ANB refresher course for

Transition candidates

Spot welding process

P

Pressure is applied to ensure adequate contact resistance

between the parts being welded.
226

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Transition candidates

Spot welding process

P

Key parameters: Squeeze pressure, Current, Weld

time, Hold time
227

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Transition candidates

TIMES INVOLVED IN SPOT WELDING

Squeeze Time is the time interval between the initial

application of the electrode force on the work and the
first application of current. Squeeze time is necessary
to delay the weld current until the electrode force has
attained the desired level.

228

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TIMES INVOLVED IN SPOT WELDING

Weld time is the time during which welding current is
applied to the metal sheets. The weld time is measured
and adjusted in cycles of line voltage as are all timing
functions. One cycle is 1/50 of a second in a 50 Hz
power system.
As the weld time is, more or less, related to what is
required for the weld spot, it is difficult to give an exact
value of the optimum weld time.
229

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TIMES INVOLVED IN SPOT WELDING

Hold time is the time, after the welding, when the electrodes are
still applied to the sheet to chill the weld. Considered from a
welding technical point of view, the hold time is the most
interesting welding parameter.
Hold time is necessary to allow the weld nugget to solidify before
releasing the welded parts, but it must not be to long as this may
cause the heat in the weld spot to spread to the electrode and
heat it.
The electrode will then get more exposed to wear. Further, if the
hold time is to long and the carbon content of the material is high
(more than 0.1%), there is a risk the weld will become brittle.
When welding galvanized carbon steel a longer hold time is
recommended.
230

IIW-ANB refresher course for

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TIMES INVOLVED IN SPOT WELDING

231

IIW-ANB refresher course for

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Parameter nugget size relationship

No nugget
Pressure

Splash

Good
weld
Explosion

Welding current

Pressure control is critical for good quality joints

232

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Transition candidates

Process range weld lobe

Welding time, ms

140
120
100
80
60
6

Welding current, kA

0.9mm thick IF-bare steel

0.8mm thick IF-coated steel

Weld lobe is the permissible operating range

for a given pressure condition.
233

IIW-ANB refresher course for

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Effect of weld time on nugget diameter

Increase in weld time increases nugget size

IIW-ANB refresher course for Transition
candidates

234

DETERMINATION OF SPOT WELDING PARAMETERS

Sheet
thickness,
t [mm]

Electrode
force, F [kN]

Weld
current, I
[A]

Weld time
[cycles]

Hold time
[cycles]

Electrode
diameter, d [mm]

0.63 + 0.63

2.00

8 500

0.71 + 0.71

2.12

8 750

0.80 + 0.80

2.24

9 000

0.90 + 0.90

2.36

9 250

1.00 + 1.00

2.50

9 500

10

1.12 + 1.12

2.80

9 750

11

1.25 + 1.25

3.15

10 000

13

1.40 + 1.40

3.55

10 300

14

1.50 + 1.50

3.65

10 450

15

1.60 + 1.60

4.00

10 600

16

1.80 + 1.80

4.50

10 900

18

2.00 + 2.00

5.00

11 200

3x7+2

2.24 + 2.24

5.30

11 500

3x8+2

2.50 + 2.50

5.60

11 800

3x9+3

2.80 + 2.80

6.00

12 200

4x8+2

3.00 + 3.00

6.15

12 350

4x9+2

3.15 + 3.15

6.30

12 500

4x9+2
235

8
IIW-ANB refresher
course for
Transition candidates

Joule heating

H=I2Rt
H=Heat
I=Current
R=Resistance
t=time

The high contact resistance at the interface of the

two
sheets cause heating during237passage of highIIW-ANB
current.
refresher course for

Transition candidates

Resistance and heating

The temperature varies from electrode to the

238
IIW-ANB refresher course for
interface.
Transition candidates

Nugget shape and size

The nugget diameter should ideally be between 3.5t and

5t in order to provide proper strength.
240

IIW-ANB refresher course for

Transition candidates

Temperature profile

Fusion temperatures at center of nugget exceed 2000oC

IIW-ANB refresher course for Transition
candidates

241

Characteristics of welding machines

242

IIW-ANB refresher course for

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Process control monitor

Weld checker

Current and voltage monitors help in proper process control.

243

IIW-ANB refresher course for

Transition candidates

Welding defects

Identifying causes for defects helps in their prevention.

245

IIW-ANB refresher course for

Transition candidates

Electrode - types and shapes

Cap tips

Electrodes

246

IIW-ANB refresher course for

Transition candidates

Electrode dimension and parameter

247

IIW-ANB refresher course for

Transition candidates

Welding parameters BS1140

IIW-ANB refresher course for Transition

candidates

248

Welding parameters BS1140

249

IIW-ANB refresher course for

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Specific testing

Shear-tension

Cross-tension

Mechanical properties indicate about the quality of the product.

250

IIW-ANB refresher course for

Transition candidates

Cross-tension test

Load bearing capacity of nugget under Mode-I condition.

251

IIW-ANB refresher course for

Transition candidates

Shear tensile test

Load bearing capacity of nugget under shear (Mode-II) condition

252

IIW-ANB refresher course for

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What is the intent ?

Sufficiently large size nugget

Strong nugget
A button failure indicates good weld.
253

IIW-ANB refresher course for

Transition candidates

Shear strength of spot welds

Steel: IF-GA

Bigger nuggets are stronger.

IIW-ANB refresher course for Transition
candidates

254

Shear strength of spot welds

IIW-ANB refresher course for Transition

candidates

255

PROJECTION WELDING PROCESS

256

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Seam welding machine

Electrodes

All resistance welding processes work on almost the

same principle.
257

IIW-ANB refresher course for

Transition candidates

Butt Seam Welding

IN BUTT SEAM WELDING, THE ELECTRODES ARE TWO COPPER

ROLLERS DRIVEN BY AN ELECTRIC MOTOR.

THE PARTS TO BE WELDED ARE CLAMPED BETWEEN THE

ROLLER ELECTRODES.

WITH THE ROLLERS ROTATING AND THE CURRENT SWITCHED

ON AND OFF, A WELD IS PRODUCED EITHER IN THE FORM OF A
SERIES OF CLOSELY SPACED STITCHES, OR AS OVERLAPPING
SPOTS, OR AS A CONTINUOUS WELD NUGGET.

258

IIW-ANB refresher course for

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Seam Welding Machine

CARRIAGE

COPPER
RAILS
MAGNETIC
TABLE

FOIL
SPOOLS

GUIDE

ELECTRODE ROLLER

SERVO DRIVE
259

FEEDERS

TELESCOPIC
COVER

IIW-ANB refresher course for

Transition candidates

Butt-Seam Welding of Roof Sheets

260

IIW-ANB refresher course for

Transition candidates

Butt Seam Welded Joint

261

IIW-ANB refresher course for

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Butt Seam Welding

Work in progress

262

IIW-ANB refresher course for

Transition candidates

Butt Seam Welding

Work in progress

263

IIW-ANB refresher course for

Transition candidates

Seam welding of galvanized steel

264

IIW-ANB refresher course for

Transition candidates

Flash butt welding machine

265

IIW-ANB refresher course for

Transition candidates

Flash butt welding machine

266

IIW-ANB refresher course for

Transition candidates

Flash Butt Welding Machine

Flash butt welding of pull rod

267

IIW-ANB refresher course for

Transition candidates

Flash butt welding of pull rod

setting up

268

IIW-ANB refresher course for

Transition candidates

Flash butt welding of pull rod

Actual welding

269

IIW-ANB refresher course for

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Flash butt welding of pull rod

Welding just completed

270

IIW-ANB refresher course for

Transition candidates

Joint configurations of processes

Resistance spot - Overlap
Resistance seam - Overlap
Projection Lap attachment
Flash butt - Butt

271

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Friction Stir Welding

A non-consumable rotating tool is

pushed into the materials to be

welded.
Then the central pin, or probe,
followed by the shoulder, is
brought into contact with the two
parts to be joined.
The rotation of the tool heats up
and plasticises the materials it is
in contact with.
As the tool moves along the joint
line, material from the front of the
tool is swept around this
plasticised annulus to the rear, so
eliminating the interface.
272

IIW-ANB refresher course for

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Advantages Of Friction Stir Welding

Weld is formed across the entire cross-sectional area of

the interface in a single shot process.

The process is completed in a few seconds with very high

reproducibility - an essential requirement for a mass

production industry

Friction heating is generated locally, so no widespread

softening of the materials,

Capable of joining dissimilar materials.

The main advantage is low distortion & ability to weld

awkward material combination

Increasing use for aluminium & copper based alloys

research going on welding of ti & SS also

273

IIW-ANB refresher course for

Transition candidates

Applications Of FSW

FRICTION STIR WELDED

ALUMINIUM CONNECTOR

274

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Acknowledgements
We gratefully acknowledge the contributions of
the following faculty members for developing
this module
Dr.A.K.Das
Dr.M.Shome
Mr.R.Ravichandran
Mr.Swapan Ghoshal

275

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Thank you

276

IIW-ANB refresher course for

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