Welding

• Welding is a materials joining process which producescoalescence of materials by heating them to suitabletemperatures with or without the application of pressure orby the application of Heat alone, and with or without the useof filler material. . Heat may be obtained by chemicalreaction, electric arc, electrical resistance, frictional heat,sound and light energy. If no filter metal is used duringwelding 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 bywelding.

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.

Choice of welding process

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

Oxyacetylene Welding

Acetylene (C2H2)

• Most popular fuel among OFW group because it is capable of higher temperatures than any other

• Up to 3480C (6300F)

• 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 CylindersPressure

Oxygen – 125 kg/cm2

Acetylene – 16 kg/cm2

2. RegulatorsWorking 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

Oxy-Acetylene welding

Typical Portable Oxygen/ Fuel Cutting Rig

Oxygen/ Fuel Hose

Green = Oxygen

Red = Fuel

Typical Cutting Torch

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

1. Fore hand Welding

2. Back hand welding

Advantages of gas welding

• It is probably the most versatile processes. It can be applied to awide variety of manufacturing and maintenance situations.

• Since the sources of heat and of filler metal are separate, the welderhas control over filler- metal deposition rates.

• The equipment is versatile, low cost, self- sufficient and usuallyportable.

• The cost and maintenance of the welding equipment is low whencompared 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 operationsproduce fumes that are irritating to the eyes, nose, throatand lungs.

• Refractory metals (e.g., tungsten, molybdenum, tantalum,etc.) and reactive metals (e.g., titanium and zirconium) cannot be gas welded.

• More safety problems are associated with the handling andstoring 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 = I R

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 forGMAWFCAW

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 VoltageArc 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 - PolarityPolarity (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 cycleof the power supply.

• Duty cycle is based on a 10 minute interval.

• Many power supplies have a sloping duty cycle.

2: Duty cycleThe percentage of time in a 5 min period that a welding

machine can be usedat 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 oxidecalled Thermit is ignited to produce the required quantity of molten metal By an exothermic non violent reaction .

Arc Welding processes

MIG

• 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

1Arc2

Weld Puddle

3

Shielding Gas4

5Solidified 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 astungsten inert gas (TIG) welding, is an arc weldingprocess that uses a non-consumable tungsten electrodeto produce the weld. The weld area is protected fromatmospheric contamination by an inert shielding gas(argon or helium), and a filler metal is normally used,though some welds, known as autogenous welds, donot require it. A constant-current welding power supplyproduces energy which is conducted across the arcthrough a column of highly ionized gas and metal vaporsknown as a plasma.

TIG

TIG

Water cooled torch of TIG

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

SAW

• The molten weld and the arc zone are protected from atmosphericcontamination by being "submerged" under a blanket of granularfusible flux consisting of lime, silica, manganese oxide, calciumfluoride, and other compounds. When molten, the flux becomesconductive, and provides a current path between the electrode andthe work. This thick layer of flux completely covers the molten metalthus preventing spatter and sparks as well as suppressing the intenseultraviolet radiation and fumes that are a part of the shielded metalarc 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

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

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

TIG

• Gas tungsten arc welding (GTAW), also known astungsten inert gas (TIG) welding, is an arc weldingprocess that uses a non-consumable tungsten electrodeto produce the weld. The weld area is protected fromatmospheric contamination by an inert shielding gas(argon or helium), and a filler metal is normally used,though some welds, known as autogenous welds, donot require it. A constant-current welding power supplyproduces energy which is conducted across the arcthrough a column of highly ionized gas and metal vaporsknown as a plasma.

TIG

TIG

Water cooled torch of TIG

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.

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

SAW

• The molten weld and the arc zone are protected from atmosphericcontamination by being "submerged" under a blanket of granularfusible flux consisting of lime, silica, manganese oxide, calciumfluoride, and other compounds. When molten, the flux becomesconductive, and provides a current path between the electrode andthe work. This thick layer of flux completely covers the molten metalthus preventing spatter and sparks as well as suppressing the intenseultraviolet radiation and fumes that are a part of the shielded metalarc welding (SMAW) process.

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.

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.