Arc WeldingArc WeldingIntroduction & Introduction & FundamentalsFundamentals

8609-BInstructional Materials Service

Texas A&M University

Importance of Welding

• Serves a variety of purposes across several domains

• Used regularly on many agricultural operations

• Used in construction of fences and livestock trailers

• Used for making quick repairs to many types of agricultural equipment such as combines, hay rakes, and field cultivators

• Not limited to agricultural uses

• Used mostly in industry– Machinery & equipment fabrication– Pipeline and manifold welding– Structural welding– Offshore welding– Ornamental welding

• Industry is always actively seeking certified weldors to enter the workplace and fill vacancies.

Arc Welding

• A person cannot become proficient at arc welding without having some basic knowledge of the components that play a part in the fusing of metal.

• Definition: the process of fusing two or more pieces of metal together through the use of an electric arc welding machine

• Dates back to the end of the nineteenth century

• Uses an electric arc, which is struck between an electrode and metal, to create heat

• The arc heats the metal to a melting point, and the electrode is removed to break the arc, allowing the metal to freeze or solidify.

• This flame (arc) of intense heat is generated as the electric current passes through a highly resistant air gap.– Air gap: space between the lower tip

of the electrode and the base metal

Ice Demonstration• Melt two ice cubes together with a

match.• When the match is removed, the ice

solidifies and freezes.• This is the same process that takes

place when fusing metals together.

Challenge

• Find ways to strengthen the welds that are produced– As metals are heated to very high

temperatures, they become chemically reactive with gases in the air such as oxygen (O2) and nitrogen (N2).

– When these gases come into contact with the molten pool of metal formed during the arc welding process, they destroy the strength properties of welds and the welds become brittle and weak.

Solution

• All arc-welding processes now provide some form of cover or shield for the molten pool of metal.– Shielded Metal Arc Welding (SMAW):

•Coated electrode produces a gas that shields the molten pool from O2 and N2 in the air

– Tungsten Inert Gas Welding (TIG)– Metallic Inert Gas Welding (MIG)

Shielded Metal Arc Welding Process (SMAW)

Quick Vocabulary

• WELDER: describes a welding machine or a person who welds, but in most cases is used to describe the machine

• WELDOR: describes a person who actually performs welds

Benefits

• Enables the utilization of new and recycled metal for construction and repair of items

• Repairs needed quickly on machinery and equipment can be made without delay.

• Cracks or breaks found on machinery can be repaired before breakdowns occur.

• Arc welding repairs are more economical than other types of repair processes.

• Fusing metal is not the only job that an arc welder can perform.

Types of Arc Welding Machines

• The five basic types are:– AC (Alternating Current)– DC (Direct Current)– AC/DC (Alternating and Direct Current)– TIG (Tungsten Inert Gas)– MIG (Metallic Inert Gas)

Alternating Current (AC)

• Alternating Current: current that alternates or changes direction several times per second

• Welding machine found in most on-farm agricultural facilities and agricultural science programs

• Relatively small machine• Used for home construction,

agricultural repair, and light industry & maintenance work

• Most AC welders are usually 180-ampere or 225-ampere units that run best when the power supply is between 220 and 240 volts.– Will produce an arc voltage of 25

• Advantages:– Physical size is small– Portability is high– Can handle most agricultural tasks– Arc blow is generally not as great as

in DC machines

Duty Cycle

• Percentage of a ten-minute period that a welding machine can be safely operated at a given output

• Example:– A 225-ampere AC welder will typically have a

duty cycle of 20% if operating at 200 amp.– A duty cycle of 20% means the machine can

be safely operated for 2 minutes out of a 10 minute period of time when set on 200 amp.

• Rule of thumb:– As amperage increases, duty cycle decreases– As amperage decreases, duty cycle increases

Direct Current (DC)

• Most often used for large industry and heavy equipment

• Adopted primarily because of its portability

• Runs off current that flows steadily and constantly in one direction

• Powered by a motor (usually electric or gas)

• Created out of necessity– American forces needed to weld in order

to make repairs on war machinery and equipment during WWI in Europe.

– AC welders did not work because Europe used electric current on a different cycle.

– DC welders solved the problem.

• Advantages:– Increased portability– Increased output

Polarity

• Direction in which the current flows across an arc

• Will differ according to the type of welding machine that is used

• DC welders can produce straight & reverse polarity.

• Straight: electrode is negative and the work is positive (mild steel)

• Reverse: electrode is positive and the work is negative (cast iron, thin materials, and aluminum)

AC/DC Welders

• Have the ability to produce both types of current from AC current input

• Equipped with a rectifier• Rectifier:

– An electrical device that changes alternating current to direct current

– Most common are silicon diodes which is placed near the output center of the machine

– Not necessary to run at all times

• Transformer/rectifier:– Found in some types of welders– Combination of a transformer and a

rectifier– Transformer: device that is used to

convert high voltage-low amperage inputs to the form of low voltage-high amperage needed for arc welding

– Plays a critical dual role in newer AC/DC welders operating on AC current

• Advantages:– Most efficient machine for general

purpose welding; used in many manufacturing plants

– Noise level is lower during operation than other types of machines

– Allows the individual to select the type of arc and current that will be best for the job

– Practical for any operation in which many different types of tasks will be performed

– Generally inexpensive as compared to DC machines

TIG Welders

• Consist of an electric power unit, a pressure reducing regulator, torch or electrode holder, tungsten electrode, nozzle, gas passages, torch cable, welding cable, water and gas hoses, and gas supply unit

• Commonly used in metal fabrication and repair shops on jobs that require skillful metal joining

• Also used when welding aluminum and stainless steel

• Two gases used:– Argon (Ar18): heavier than air & tends

to blanket the weld zone very well– Helium (He2): much lighter than air &

has a high rate of travel speed that enables it to cover the weld zone very quickly

– Are supplied by a high-pressure cylinder system

– Serve as protection for the Tungsten and weld zone to prevent weakening of the welds due to atmospheric contamination

– Measured and purchased by the ft3

• Uses a non-consumable Tungsten electrode which does not become part of the weld

• TIG welding heats the torch tip to high levels.– Cooling mechanisms required on

machines with a capacity of 200 amps or more

– Cooling mechanism can be either air coolers or water coolers

• Can also be referred to as GTAW (Gas Tungsten Arc Welding) or HeliarcTM welding

• Advantages:– Welds are free of corrosive residue.– Weld is usually stronger and has less

corrosion than other forms of welding.– Weld is free of fumes, sparks, and slag.

Post weld cleaning is eliminated.– Stresses are reduced due to heat

concentration in a small area, so there is little distortion near the weld.

– There is no spatter in this process.

MIG Welders

• Metallic Inert Gas• One of the easiest methods of welding to

put into practice• Made up of a welding machine, wire

drive, wire wheel, gas supply, contractor, gun, hoses, current cable (wire), and a control unit for the wire drive, current & gas flow

• Often referred to as “wire feed” welders• “wire feed” name comes from the basic

process that occurs in MIG welding

• A continuous wire electrode is fed from a spool through a flexible conduit into a welding gun.

• The wire electrode exits the gun through a copper tube called a contact tip (tube) into an electric arc produced by an external power source.

• The wire fed through the tip and into the arc melts and comes into contact with base metals thereby producing a weld.

• Molten pool is protected by Carbon Dioxide (CO2), Argon (Ar18), Helium (He2), or different combinations of the three

• Shielding gases supplied by a nearby high-pressure cylinder or manifold system

• Also possible for a flux located in the core of the wire electrode to produce some shielding gas as it melts during welding

• It is necessary to set the speed at which the wire electrode will be fed through the machine prior to welding.

• Speed will vary and is dependent on the type of metal being welded

• After the initial wire speed has been set, welding is started and stopped by squeezing a trigger on the gun.

• Only job weldor must do is position the gun properly and cross the weld joint at the proper speeds

• Trigger activation takes the place of the “manual striking of the arc”

• It is possible to set up the machine to weld automatically.– Welding is completed with limited labor.– The only labor required from humans is

the initial setup and programming of the equipment.

– Robotic equipment then performs the necessary welds to complete the work.

– Largely practiced in industry

• Very good for welding stainless steel, aluminum, and carbon steel

• Very thin metals can easily be welded• Can also be used to weld heavy metal

• Advantages:– Used in industry as an automatic welder– Similar to the TIG process, however,

there is a slag cover on the weld when using a flux-cored wire

– May be operated by hand

Other Welding Processes

• Laser welding• Submerged arc welding• Electro-slag welding• MIG welders are becoming more widely used• Most commonly used type of arc welding

process today is still the use of a coated electrode that serves as a shield for the weld.– Known as “stick welding”– Process by which most entry-level weldors learn

the technique

Selecting a Welder and Welding Equipment

• Guidelines to follow:– Select a welder that is made by a

respected and reliable manufacturer.– Purchase a welder only from a respected

and reliable dealer.– Compare price and guarantees on

different types of welding machines.– Take notice that the dealer provides

prompt service and information when needed.

– Observe that the dealer has personal protective equipment, electrodes, and operating information readily available.

– Check the duty cycle of weldors to ensure that it matches the requirements of the job.

– Check that the equipment is properly installed and if a used weldor is purchased, check to ensure it has been properly maintained.

– Check that all necessary components such as ground and work cables are present.

• Additional welding equipment:– Safety glasses with side shields– Welding helmet with dark lens– Face shield– Goggles– Hard hat– Anvil– Power grinder– Leather welding gloves– Chipping hammer & Wire brush– C-clamps & pliers– Welding screen– Welding table

Electrodes

• A core wire that can be left bare or covered with flux

• Flux:– Fusible material that covers the electrode

that is meant to produce a shielding gas during the welding process

– Prevents the formation of oxides, nitrides, and other undesirable inclusions during welding

– Floats out the impurities in the air and then settles on top of the weld in the form of slag

– Slag is beneficial in most welding processes because it holds heat and keeps the weld from cooling too quickly, thus preventing the weld from becoming weak.

• It is important to consider the type of base metal and welding current when selecting the proper electrode.

• Electrode selection depends on:– Metal type– Metal thickness– Welding position

• Several tools available to aid in the selection of electrodes

Types of Electrodes

• Coated Electrode:– Covered with flux that is coded for its

properties– Core wire should possess the same

properties as that of the base metal that is begin welded

– Very common type

• Carbon Electrode:– Melts slowly while supplying a stable

arc– Used for special purpose welding

• Bare Electrode:– Not as widely used– Smoke free– Makes weld visible at all times during

the welding process– Requires a tremendous amount of

heat be produced (10,000oF) as it passes across the arc

– Extremely sensitive to voltage change and electrode angle

Electrode Classification

• American Welding Society (AWS) has provided a means of electrode classification to allow for wide spread standardization and application.

• The AWS system was first set up in 1942.• Electrodes are identified by the

manufacturer’s trade name, and/or a combination of letters and numbers from the AWS classification system.

• In order to receive a classification from the AWS, a manufacturer must meet and maintain strict standards.

• These standards call for electrodes that comply with a set of minimum chemical and physical specifications.

• Numbers used for classification represent four different factors:– 1st two digits: minimum tensile

strength of the weld metal– 3rd digit: welding positions in which the

electrode should be used•1=all welding positions, 2=only flat &

horizontal positions, 3=only flat position

– 4th digit: type of welding current that is to be used and the type of flux covering

• Example:– E6010– E: Electrode– 60: tensile strength of the electrode metal

(60,000 pounds/in2)– 1: electrode can be used in all welding positions– 0: a DC and electrode positive current

– E7024– E: Electrode– 70: tensile strength of electrode metal– 2: electrode can be used for flat and horizontal

positions– 4: a DC and electrode positive or negative

current

Electrode Size

• Determined by the diameter of the bare end of a rod

• Diameter of electrode should not exceed the thickness of the metal being welded

•Specifications for electrodes are as follows: (For example E6013)

Standard Size Diameter of Core Wire

# of Electrodes per pound

Standard Length

Amperage Range Setting

1/16 inch 53 18” 20-40

3/32 inch 36 12” 30-80

1/8 inch 17 14” 70-120

5/32 inch 11 14” 12-170

3/16 inch 8 14” 140-240

Electrode Use

• Be familiar with the many types of electrodes and their designed uses in order to maximize the efficiency of the welding process.

• Electrodes can be damaged if they are not stored properly.

• Store electrodes in sealed containers until they are ready to be used.

• Extreme changes in temperatures and moisture in the air can damage or ruin electrodes.

Electrode # Electrode Use

E6010 Used for all-purpose welding and with mild steel. Allows for deep penetration and rapid solidification. Utilizes DC+ current.

E6011 Used for all-purpose welding and with mild steel. Allows for deep penetration and rapid solidification. Utilizes DC and AC current.

E6012 Used on mild steel. Allows for deep penetration and rapid solidification. Utilizes DC or AC current.

E6013 Used with mild steel. Good general-purpose electrode. Allows for medium penetration, medium slag, and a quiet arc. Utilizes DC or AC current.

E7018 Used with high carbon steel. More difficult to weld. Utilizes DC+ or AC current.

E7028 Used with high carbon steel. More difficult to weld. Can only weld in the flat and horizontal positions. Utilizes DC+ or AC current.

Selecting the Correct Electrode

• Pay attention to the following factors when choosing electrodes.– Identification of base metal– Welding current available– Thickness and shape of the base metal– Joint design– Welding position– Job specifications and service

conditions– Deposition rate in relation to

production efficiency– Environmental job conditions– Electrode storage

Safety Practices

• If safeguards are ignored, it is possible to be exposed to such dangers as fumes and gases, overexposure to arc radiation, fire and electric shock.

• General safety rules that should be adhered to at all times during arc welding:– Wear personal protective equipment (PPE) that

allows for freedom of movement but will provide adequate cover against sparks and weld spatters.

– Wear heavy flame-resistant leather gloves.– Flame-resistant welding aprons, suits, and caps

are recommended.– Weld only in well-ventilated areas.

– Protect eyes against “welder’s flash” caused by harmful UV radiation.

– Wear a welding helmet at all times.– Wear earplugs to prevent hearing loss.– Be certain that the welder is properly

grounded.– Do not stand on wet surfaces while welding.– Use electrode holders that are properly

insulated.

– Protect welding cables from hot objects and sharp edges.

– Yell “COVER” prior to striking an arc in order to alert bystanders.

– Use pliers or tongs when handling hot metal.

– Avoid welding on containers that have held combustible materials.

– Properly dispose of used electrodes.

Miscellaneous Safety Rules

• When welding:– Do not lay the electrode holder on the

welding table.– Do not stand on the grounded metal.– Keep the work area free of clutter to

avoid falling accidents.– Keep tools and equipment in a safe

and proper place to prevent accidents.– Do not hold the electrode holder

between the knees or under the arm.

– If the electrode sticks and cannot be twisted free, cut off the machine; allow the electrode to cool and break it loose with pliers.

– Do not cool the electrode holder in water.

– Always wear eye protection.– If foreign particles get into your eyes,

avoid rubbing them.

Arc Welding Fundamentals

• Body Position:– It is impossible to get in a totally

comfortable position on most welding jobs, but the weldor should find a position that allows him/her to be as relaxed and braced as possible.

• Correct Electrode Size:– Consider type, position, and

preparation of the joint, deposition efficiency, and requirements pertaining to weld quality when choosing an electrode.

• Correct Amperage Setting:– If the current is too high, the

electrode melts too fast and the molten pool is large & irregular.

– If the current is too low, there is not enough heat to melt the base metal and the molten pool will be too small, pile up & look irregular.

• Correct Electrode Angle:– When making a flat weld, the correct

angle is 15o from 90o in the direction of travel.

– The electrode should be held perpendicular to the base metal.

• Correct Arc Length:– If the arc is too long, metal melts off the

electrode in large pools that wobble from side to side as the arc wavers, resulting in a wide, spattered, and irregular bead with poor fusion between the original metal and the deposited metal.

– If the arc is too short, there is not enough heat to melt the base metal properly and the electrode will stick to the work, resulting in a high uneven bead with irregular ripples, poor fusion, and slag and gas holes.

– Correct arc length is equal to the diameter of the bare end of the the electrode.

• Correct Electrode Type:– Depends upon type of base metal to be

welded and type of current available

• Correct Travel Speed:– Too fast: puddle does not last long

enough and impurities and gases are locked in; bead will be narrow and ripples pointed

– Too slow: metal will pile up, bead will be high and wide, and ripple will be straight

Preparation of the Work

• Prior to beginning the welding process, take the time to prepare the metal.

• Use a grinder, a metal saw, or a torch for preparation.

• Will result in stronger, more attractive welds than if metal is left unprepared.

Machine Maintenance

• A welder needs preventive maintenance.

• Basic recommendations:– Flush or ventilate the system with clean

compressed air.– Clean the outside of the machine.– Inspect accessories such as the electrode

holder, cables, or wire feeders.– Inspect all dials, knobs,or switches for

damage.– Grease bearings periodically.– For portable machines: check oil daily, fill

fuel tank, and clean the air filter.

Acknowledgements

Kirk Edney, Curriculum Specialist, Instructional Materials Service, edited and reviewed this PowerPoint presentation.

Kristie Weller, Undergraduate Technician, Instructional Materials Service, organized and developed the information used in this PowerPoint presentation.

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Reproduction or redistribution of all, or part,

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Instructional Materials Service

Texas A&M University

2588 TAMUS

College Station, Texas 77843-2588

http://www-ims.tamu.edu

2007