Types of welding

• Welding is a materials joining process which produces
coalescence of materials by heating them to suitable
temperatures with or without the application of pressure or
by the application of Heat alone, and with or without the use
of filler material. . Heat may be obtained by chemical
reaction, electric arc, electrical resistance, frictional heat,
sound and light energy. If no filter metal is used during
welding then it is termed as Autogenous Welding Process
• Welding is used for making permanent joints.
• It is used in the manufacturing of automobile bodies, aircraft frames,
railway wagons, machine frames, structural works, tanks, furniture,
boilers, general repair work and ship building.

 During ‘Bronze Age' parts were joined by forge welding to produce tools, weapons and
ornaments
 First application of welding with carbon electrode was developed in 1885 while metal arc
welding with bare electrode was patented in 1890.
 In the mean time resistance butt welding was invented in USA in the year 1886. Other
resistance welding processes such as spot and flash welding with manual application of load
were developed around 1905.
 With the production of cheap oxygen in 1902, oxy – acetylene welding became feasible in
Europe in 1903.
 When the coated electrodes were developed in 1907, the manual metal arc welding process
become viable for production/fabrication of components in the industries on large scale.

Subsequently other developments are as follows:
• Thermit Welding (1903)
• Arc Stud Welding (1918)
• Seam Welding of Tubes (1922)
• Mechanical Flash Welder for Joining Rails (1924)
• Extruded Coating for MMAW Electrodes (1926)
• Submerged Arc Welding (1935)
• Air Arc Gouging (1939)
• Inert Gas Tungsten Arc (TIG) Welding (1941)
• Iron Powder Electrodes (1944)
• Inert Gas Metal Arc (MIG) Welding (1948)
• Electro Slag Welding (1951)

• Flux Cored Wire with CO 2 Shielding (1954)
• Electron Beam Welding (1954)
• Constricted Arc (Plasma) for Cutting (1955)
• Friction Welding (1956)
• Plasma Arc Welding (1957)
• Electro Gas Welding (1957)
• Short Circuit Transfer for Low Current, Low Voltage Welding with CO2
Shielding (1957)
• Vacuum Diffusion Welding (1959)
• Explosive Welding (1960)
• Laser Beam Welding (1961)
• High Power CO2 Laser Beam Welding (1964)

Advantages of welding
• A good weld is as strong as the base metal.
• General welding equipment is not very costly.
• Portable welding equipment's are available.
• A large number of metals/alloys both similar and dissimilar can be joined by
welding.

Disadvantages of welding
• Welding gives out harmful radiations (light), fumes and spatter.
• Welding results in residual stresses and distortion of the work
pieces.
• Jigs and fixtures are generally required to hold and position the
parts to welded.
• Edge preparation of the work pieces is generally required before
welding them.
• A skilled welder is a must to produce a good welding job.

GAS WELDING
• Gas welding process was introduced in 1903.
• Gas welding is a fusion welding process.
• It join metals, using the heat of combustion of an oxygen/air and
fuel gas (i.e. acetylene, hydrogen, propane or butane) mixture.
• Intense heat (flame) thus produces melts and fuses together the
edges of the parts to be welded, with addition of a filler metal.
• Oxy-acetylene flame temp 3480 degree Celsius

Oxyfuel Gas Welding (OFW)
Group of fusion welding operations that burn various fuels mixed with
oxygen
• OFW employs several types of gases, which is the primary distinction
among the members of this group
• Oxyfuel gas is also used in flame cutting torches to cut and separate
metal plates and other parts
• Most important OFW process is oxyacetylene welding

Fuels
• Propane (LPG) C3H8
• Natural Gas CH4
• Acetylene C2H2
• MAPP (Methylacetylene-propadiene)
• Hydrogen

Oxyacetylene Welding (OAW)
Fusion welding performed by a high temperature flame from
combustion of acetylene and oxygen
• Flame is directed by a welding torch
• Filler metal is sometimes added
• Composition must be similar to base metal
• Filler rod often coated with flux to clean surfaces and prevent oxidation

Acetylene (C2H2)
• Most popular fuel among OFW group because it is capable of higher
temperatures than any other
• Up to 3480C (6300F)
• Two stage reaction of acetylene and oxygen:
• First stage reaction (inner cone of flame)
C2H2 + O2  2CO + H2 + heat
• Second stage reaction (outer envelope)
2CO + H2 + 1.5O2  2CO2 + H2O + heat

• Maximum temperature reached at tip of inner cone, while outer
envelope spreads out and shields work surface from atmosphere
• Shown below is neutral flame of oxyacetylene torch indicating
temperatures achieved
Oxyacetylene Torch

GAS WELDING EQUIPMENT...
1. Gas Cylinders
Pressure
Oxygen – 125 kg/cm2
Acetylene – 16 kg/cm2
2. Regulators
Working pressure of oxygen 1 kg/cm2
Working pressure of acetylene 0.15 kg/cm2
Working pressure varies depends upon the thickness of the work
pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve

Typical
Portable
Oxygen/ Fuel
Cutting Rig

Oxygen/ Fuel Hose
Green = Oxygen
Red = Fuel

TYPES OF FLAMES…
• Oxygen is turned on, flame immediately changes into a long white inner
area (Feather) surrounded by a transparent blue envelope is called
Carburizing flame (30000c)
• Addition of little more oxygen give a bright whitish cone surrounded by the
transparent blue envelope is called Neutral flame (It has a balance of fuel
gas and oxygen) (32000c)
• Used for welding steels, aluminium, copper and cast iron
• If more oxygen is added, the cone becomes darker and more pointed, while
the envelope becomes shorter and more fierce is called Oxidizing flame
• Has the highest temperature about 34000c
• Used for welding brass and brazing operation

Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting
operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

Three basic types of oxyacetylene flames used in oxyfuel-gas welding and
cutting operations:
(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

Gas Welding Techniques
1. Fore hand Welding 2. Back hand welding

Advantages of gas welding
• It is probably the most versatile processes. It can be applied to a
wide variety of manufacturing and maintenance situations.
• Since the sources of heat and of filler metal are separate, the welder
has control over filler- metal deposition rates.
• The equipment is versatile, low cost, self- sufficient and usually
portable.
• The cost and maintenance of the welding equipment is low when
compared to that of some other welding processes.

Disadvantages
• Heavy sections cannot be joined economically.
• Flame temp is less than the temp of the arc.
• Fluxes used with certain welding and brazing operations
produce fumes that are irritating to the eyes, nose, throat
and lungs.
• Refractory metals (e.g., tungsten, molybdenum, tantalum,
etc.) and reactive metals (e.g., titanium and zirconium) can
not be gas welded.
• More safety problems are associated with the handling and
storing of gases.

Arc Welding (AW)
• A fusion welding process in which coalescence of the metals is
achieved by the heat from an electric arc between an electrode and
the work
• Electric energy from the arc produces temperatures ~ 10,000 F (5500
C), hot enough to melt any metal
• Most AW processes add filler metal to increase volume and strength
of weld joint

What is an Electric Arc?
• An electric arc is a discharge of electric current across a gap in a
circuit
• It is sustained by an ionized column of gas (plasma) through which
the current flows
• To initiate the arc in AW, electrode is brought into contact with work
and then quickly separated from it by a short distance

• A pool of molten metal is formed near electrode tip,
and as electrode is moved along joint, molten weld
pool solidifies in its wake
Arc Welding

Manual Arc Welding
and Arc Time
• Problems with manual welding:
• Weld joint quality
• Productivity
• Arc Time = (time arc is on) divided by (hours
worked)
• Also called “arc-on time”
• Manual welding arc time = 20%
• Machine welding arc time ~ 50%

Two Basic Types of AW Electrodes
• Consumable – consumed during welding process
• Source of filler metal in arc welding
• Nonconsumable – not consumed during welding
process
• Filler metal must be added separately if it is added

Consumable Electrodes
• Forms of consumable electrodes
• Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter
and must be changed frequently
• Weld wire can be continuously fed from spools with long lengths of wire,
avoiding frequent interruptions
• In both rod and wire forms, electrode is consumed by the arc and
added to weld joint as filler metal

Nonconsumable Electrodes
• Made of tungsten which resists melting
• Gradually depleted during welding (vaporization is principal
mechanism)
• Any filler metal must be supplied by a separate wire fed into weld
pool

Arc Shielding
• At high temperatures in AW, metals are chemically reactive to oxygen,
nitrogen, and hydrogen in air
• Mechanical properties of joint can be degraded by these reactions
• To protect operation, arc must be shielded from surrounding air in AW
processes
• Arc shielding is accomplished by:
• Shielding gases, e.g., argon, helium, CO2
• Flux

Flux
A substance that prevents formation of oxides and other contaminants
in welding, or dissolves them and facilitates removal
• Provides protective atmosphere for welding
• Stabilizes arc
• Reduces spattering

Various Flux Application Methods
• Pouring granular flux onto welding operation
• Stick electrode coated with flux material that melts during welding to
cover operation
• Tubular electrodes in which flux is contained in the core and released
as electrode is consumed

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

Consumable Electrode
AW Processes
• Shielded Metal Arc Welding
• Gas Metal Arc Welding
• Flux-Cored Arc Welding
• Electrogas Welding
• Submerged Arc Welding

Arc Welding Electrical Terms
1. Electrical Circuit
2. Direct current (DC)
3. Alternating current (AC)
4. Ampere
5. Volt
6. Resistance
7. Ohms Law
8. Constant potential
9. Constant current
10. Voltage drop
11. Open circuit voltage
12. Arc voltage
13. Polarity
14. Watt
To understand how an electric arc welder produces the correct heat
for arc welding, you must understand the following fourteen (14)
electrical terms.

Terms
1 - Electrical Circuit
• An electrical circuit is a complete
path for electricity.
• Establishing an arc completes an
electric circuit .
Current will not flow through an open circuit.

2 - Direct Current
• Direct current: A type
of current where the
flow of electrons is in
one direction.
• In arc welding the direction
of flow is called the polarity.

3 - Alternating Current
• Alternating current: The type
of current where the flow of
electrons reverses direction
at regular intervals.

4 - Ampere
• Amperes: the unit of measure for current flow.
• One ampere is equal to 6.24150948×1018
electrons passing by a point per second.
• Electricity passing through a resistance causes
heat.
• An air gap is a high resistance
Arc welding requires large electrical currents 100-1000A.

5 - Voltage
• Voltage is the measure of
electromotive force (Emf).
• Emf is measured in units of volts
• The voltage at the electrode for MAW
determines the ease of starting and
the harshness of the arc.

6 - Resistance
• Resistance is the characteristic of a material that
impedes the flow of an electrical current.
• Measured in units of Ohm’s (  )
• When an electrical current passes through a resistance
heat is produced.

7 - Ohm’s Law
• Commonly expressed as:
• Voltage is equal to amps x
resistance
• For arc welding rearranged
as:
• Amperage is the voltage
divided by the resistance.
E = IR

I =
E
R

8 - Constant Potential
A constant potential power supply is designed to produce
a relatively constant voltage over a range of amperage
changes.
Primarily used for
GMAW
FCAW

Constant Current
• In a constant current power supply, the current (amperage)
stays relatively constant over a narrow range of voltages.
• Primarily used for:
SMAW
TIG

10 - Voltage Drop
• Voltage drop is the reduction in voltage in an electrical circuit
between the source and the load.
• Primary cause is resistance.
• Excessive voltage drop reduces the heat of the arc.

11 - Open Circuit Voltage
• Open circuit voltage is the potential voltage between the
electrode and the work when the arc is not present.
• The higher the OCV the easier the arc is to start.
• The higher the OCV the steeper the volt – amp curve.

12 - Arc Voltage
Arc voltage is the electrical potential between the electrode
and the metal after the arc has started.
The arc voltage depends only upon the arc length
V = k1 + k2l Volts
Where l is the arc length in mm and k1 and k2 are constants,
k1 = 10 to 12; and k2 = 2 to 3
The minimum Arc voltage is given by
Vmin = (20 + 0.04 l) Volt

13 - Polarity
Polarity (positive & negative) is present in all electrical circuits.
Electricity flows from negative to positive
Controlling the polarity allows the welder to influence the location
of the heat.
When the electrode is positive (+) it will be slightly hotter than the
base metal.
When the base metal is positive (+) the base metal will be slightly hotter
than the electrode.
What abbreviations are used to indicate the polarity of the electrode?
DCEN or DCSP [direct current electrode negative or direct current straight
polarity]
DCEP or DCRP [direct current electrode positive or direct current reverse
polarity]

Arc welding equipment's
1. Droppers: Constant current welding machines
Good for manual welding
2. Constant voltage machines
Good for automatic welding
58

14 - Watt
Watts are a measure of the amount of electrical energy being
consumed.
Watts = Volts x Amps
The greater the Watts of energy flowing across an air gap the
greater the heat produced.
Power to drive the operation is the product of the current I passing
through the arc and the voltage E across it.
This power is converted into heat, but not all of the heat is
transferred to the surface of the work.
Convection, conduction, radiation, and spatter account for losses
that reduce the amount of usable heat

Arc Welding Power Supplies
The type of current and the polarity of the welding
current are one of the differences between arc
welding processes.
• SMAW Constant current (CC), AC, DC+ or DC-
• GMAW Constant voltage (CV) DC+
• FCAW Constant voltage (CV) DC-
• GTAW Constant Current (CC) ), AC, DC+ or DC-

1: Amperage
Output
• The maximum output of the power
supply determines the thickness of
metal that can be welded before
joint beveling is required.
• 185 to 225 amps is a common size.
• Welding current depends upon: the
thickness of the welded metal,
type of joint, welding speed,
position of the weld, the thickness
and type of the coating on the
electrode and its working length.
• Welding current, I = k. d, amperes;
d is dia. (mm)

2: Duty cycle
• The amount of continuous welding time a power
supply can be used is determined by the duty cycle
of the power supply.
• Duty cycle is based on a 10 minute interval.
• Many power supplies have a sloping duty cycle.

2: Duty cycle
The percentage of time in a 5 min period that a welding
machine can be used
at its rated output without overloading.
Time is spent in setting up, metal chipping, Cleaning and
inspection.
For manual welding a 60% duty cycle is suggested and for
automatic welding
100% duty cycle.
63

Atomic hydrogen welding
An a.c. arc is formed between two tungsten electrodes along which streams of
hydrogen are fed to the welding zone.
The molecules of hydrogen are dissociated by the high heat of the arc in the gap
between the electrodes.
The formation of atomic hydrogen proceeds with the absorption of heat:
This atomic hydrogen recombines to form molecular hydrogen outside the arc,
particularly on the relatively cold surface of the work being welded,
releasing the heat gained previously:
64

Atomic hydrogen welding
• Temperature of about 3700 ˚C.
• Hydrogen acts as shielding also.
• Used for very thin sheets or small diameter wires.
• Lower thermal efficiency than Arc welding.
• Ceramics may be arc welded.
• AC used.
67

THERMIT WELDING
It is a process in which a mixture of aluminum powder and a metal oxide
called Thermit is ignited to produce the required quantity of molten metal
By an exothermic non violent reaction .

• GMAW stands for Gas Metal Arc Welding
• GMAW is commonly referred to as MIG or Metal Inert Gas welding
• During the GMAW process, a solid metal wire is fed through a welding
gun and becomes the filler material
• Instead of a flux, a shielding gas is used to protect the molten puddle
from the atmosphere which results in a weld without slag

GMAW Equipment
• Power Supply
• Wire Feeder
• Electrical mechanical device that feed required amount of filler material at a
constant rate of speed

GMAW Equipment
• Welding filler electrode
• Small diameter consumable electrode that is supplied to the welding gun by
the roller drive system
• Shielding Gas
• Gas used to protect the molten metal from atmospheric contamination
• 75%Argon (inert gas) & 25% Carbon Dioxide most common gas used for GMAW

GMAW Components
• Let’s look a little closer at the GMAW process
Travel direction
Electrode
1
Arc2
Weld Puddle
3
Shielding Gas4
5
Solidified Weld Metal
Generally, drag on thin sheet metal
and push on thicker materials

1 - Electrode
• A GMAW electrode is:
– A metal wire
– Fed through the gun by
the wire feeder
– Measured by its diameter
GMAW electrodes are commonly
packaged on spools, reels and coils

2 - Arc
• An electric arc occurs
in the gas filled space
between the electrode
wire and the work
piece
Electric arcs can generate
temperatures up to 10,000°F

3 - Weld Puddle
• As the wire electrode
and work piece heat up
and melt, they form a
pool of molten material
called a weld puddle
• This is what the welder
watches and
manipulates while
welding
.045” ER70S-6 at 400 ipm wire feed
speed and 28.5 Volts with a 90% Argon/
10% CO2 shielding gas

4 - Shielding Gas
• GMAW welding
requires a shielding gas
to protect the weld
puddle
• Shielding gas is usually
inert gases , CO2 or a
mixture of both
The gauges on the regulator show gas
flow rate and bottle pressure

5 - Solidified Weld
Metal
• The welder “lays a
bead” of molten metal
that quickly solidifies
into a weld
• The resulting weld is
slag free
An aluminum weld done
with the GMAW process

Advantages of GMAW
• High operating factor
• Easy to learn
• Limited cleanup
• Use on many different
metals: stainless steel,
mild (carbon) steel,
aluminum and more
• All position
• Great for small scale
use with 115V and
230V units

Limitations of GMAW
• Less portable
• GMAW equipment is more
expensive than SMAW
equipment
• External shielding gas can
be blown away by winds
• High radiated heat
• Difficult to use in out of
position joints

TIG
• Gas tungsten arc welding (GTAW), also known as
tungsten inert gas (TIG) welding, is an arc welding
process that uses a non-consumable tungsten electrode
to produce the weld. The weld area is protected from
atmospheric contamination by an inert shielding gas
(argon or helium), and a filler metal is normally used,
though some welds, known as autogenous welds, do
not require it. A constant-current welding power supply
produces energy which is conducted across the arc
through a column of highly ionized gas and metal vapors
known as a plasma.

TIG Shielding Gases
Argon
• Good arc starting
• Good cleaning action
• Good arc stability
• Focused arc cone
• Lower arc voltages
• 10-30 CFH flow rates
Helium
• Faster travel speeds
• Increased penetration
• Difficult arc starting
• Less cleaning action
• Less low amp stability
• Flared arc cone
• Higher arc voltages
• Higher flow rates (2x)
• Higher cost than argon

TIG Shielding Gases
Argon/Helium Mixtures
• Improved travel speeds over pure argon
• Improved penetration over pure argon
• Cleaning properties closer to pure argon
• Improved arc starting over pure helium
• Improved arc stability over pure helium
• Arc cone shape more focused than pure helium
• Arc voltages between pure argon and pure helium
• Higher flow rates than pure argon
• Costs higher than pure argon

SAW
• The molten weld and the arc zone are protected from atmospheric
contamination by being "submerged" under a blanket of granular
fusible flux consisting of lime, silica, manganese oxide, calcium
fluoride, and other compounds. When molten, the flux becomes
conductive, and provides a current path between the electrode and
the work. This thick layer of flux completely covers the molten metal
thus preventing spatter and sparks as well as suppressing the intense
ultraviolet radiation and fumes that are a part of the shielded metal
arc welding (SMAW) process.

Advantages
• High deposition rates (over 100 lb/h (45 kg/h) have been reported).
• High operating factors in mechanized applications.
• Deep weld penetration.
• Sound welds are readily made (with good process design and control).
• High speed welding of thin sheet steels up to 5 m/min (16 ft/min) is possible.
• Minimal welding fume or arc light is emitted.
• Practically no edge preparation is necessary.
• The process is suitable for both indoor and outdoor works.
• Low distortion
• Welds produced are sound, uniform, ductile, corrosion resistant and have good impact value.
• Single pass welds can be made in thick plates with normal equipment.
• The arc is always covered under a blanket of flux, thus there is no chance of spatter of weld.
• 50% to 90% of the flux is recoverable.

Limitations
• Preferred for ferrous (steel or stainless steels) and some nickel-based
alloys.
• Normally limited to long straight seams or rotated pipes or vessels.
• Requires relatively troublesome flux handling systems.
• Flux and slag residue can present a health and safety concern.
• Requires inter-pass and post weld slag removal.

Also Known AS
• Wire Feed
• MIG = Metal Inert Gas
• Inert Gas= Inactive gas that does not combine chemically with base or filler
metal
• MAG= Metal Active Gas
• Active Gas= Gas will combine chemically with base or filler metal

Advantages
• Variety of Metals
• All Position Welding
• Quality Welds
• Little to No Slag
• Low Spatter
Disadvantages
• Cost
• Portability
• Clean Base Material

Principles of the GMAW Process

GMAW Process Parameters
Steel Material .035” wire Short-Arc Mode
Thickness Gas
75%AR-
25%CO2
Amps Wire
Speed
Volts
1/8” 18-19 140-150 280-300 23-24
3/16” 18-19 160-170 320-340 24-25
1/4” 21-22 180-190 360-380 24-25
5/16” 21-22 200-210 400-420 25-26
3/8” 23-24 220-250 420-520 26-27

The tungsten arc process is being employed widely for the precision joining of
critical components which require controlled heat input. The small intense heat
source provided by the tungsten arc is ideally suited to the controlled melting of
the material. Since the electrode is not consumed during the process, as with the
MIG or MMA welding processes, welding without filler material can be done
without the need for continual compromise between the heat input from the arc
and the melting of the filler metal.

Fluxes are fused or agglomerated consisting of MnO, SiO2, CaO, MgO, Al2O3,
TiO2, FeO, and CaF2 and sodium/potassium silicate
The ratio of contents of all basic oxides to all acidic oxides in some
proportion is called basicity index of a flux. CaO, MgO, BaO, CaF2, Na2O,
K2O, MnO are basic constituents while SiO2, TiO2, Al2O3 are considered to be
acidic constituents.

Electrode wire size, welding voltage, current and speed are four most
important welding variables apart from flux.
Welding voltage has nominal effect on the electrode wire melting rate but high
voltage leads to flatter and wider bead, increased flux consumption and resistance
to porosity caused by rust or scale and helps bridge gap when fill up is poor. Lower
voltage produces resistance to arc blow but high narrow bead with poor slag
removal. Welding voltages employed vary from 22 to 35 V

If the welding speed is increased, power or heat input per unit length of
weld is decreased, less welding material is applied per unit length of
weld, and consequently less weld reinforcement results and penetration
decreases. Travel speed is used primarily to control bead size and
penetration. It is interdependent with current.
Excessive high travel speed decreases wetting action, increases
tendency for undercut, arc blow, porosity and uneven bead shapes while
slower travel speed reduces the tendency to porosity and slag inclusion.

Influence of Welding Parameters on Bead Shape.

Types of welding

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