Demonstrate Proper Care

1Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

PowerPoint to accompany

WeldingPrinciples and PracticesThird Edition

Sacks and Bohnart

Gas Metal Arc Welding Practice: Jobs 22-J1–J23 (Plate)

Chapter 22

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Objectives

1. Describe GMAW operating variables

2. Describe GMAW weld defects

3. Describe GMAW safe operation

4. Describe and demonstrate proper care, use, and troubleshooting of equipment

5. Describe and demonstrate welding techniques

6. Make various groove and fillet welds with the various modes of metal transfer with both solid and metal cored electrodes

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Operating Variables That Affect Weld Formation

• Factors that affect operation of arc and weld deposit

• Sound welding of good appearance results when variables in balance

• Necessary to become familiar with all variables

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Direct Current Electrode Positive (DCEP)

• Generally used for gas metal arc welding– Provides maximum heat input into work allowing relatively

deep penetration to take place

– Assists in removal of oxides from plate

– Low current values produce globular transfer of metal from electrode

• On carbon steel shielding gas must contain minimum of 80% argon

• Ferrous metals need addition of 2 to 5% oxygen to gas mixture

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Gas Metal Arc DCEP Welding: Wire Positive, Work Negative

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Direct Current Electrode Negative (DCEN)

• Limited use in welding of thin gauge materials

• Greatest amount of heat occurs at electrode tip

• Wire meltoff rate great deal faster than DCEP

• Penetration also less than with DCEP

• Arc not stable at end of filler wire– Corrected by use of shielding gas mixture of 5%

oxygen added to argon– Meltoff rate reduced so benefit cancelled

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Gas Metal Arc DCEN Welding: Wire Negative, Work Positive


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Alternating Current

• Seldom used in gas metal arc welding

• Arc unstable because of current reversal

• Combination of both DCEN and DCEP polarity, rate of metal transfer and depth of penetration falls between those polarities

• Found some use for welding of aluminum

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Shielding Gas

• Argon and helium first used for gas metal arc– Continue to be basic gases

• Argon used more than helium on ferrous metals to keep spatter at minimum– Also heavier than air so good weld coverage

• Oxygen or carbon dioxide added to pure gases to improve arc stability, minimize undercut, reduce porosity, and improve appearance of weld

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Shielding Gas

• Helium added to argon to increase penetration

• Hydrogen and nitrogen used for only limited number of special applications

• Carbon dioxide has following advantages:– Low cost– High density, resulting in low flow rates– Less burn-back problems because of its shorter arc

characteristics

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Specific Metal Recommendations

• Aluminum alloys: argon

• Magnesium and aluminum alloys: 75 percent helium, 25 percent argon

• Stainless steels: argon plus oxygen

• Magnesium: argon

• Deoxidized copper: 75 percent helium, 25 percent argon preferred

• Low alloy steel: argon, plus 2 percent oxygen

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Specific Metal Recommendations

• Mild steel: 15 percent argon, 25 percent carbon dioxide (dip transfer); 100 percent CO2 may

also be used with deoxidized wire

• Nickel, Monel®, and Inconel®: argon

• Titanium: argon

• Silicon bronze: argon

• Aluminum bronze: argon

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Joint Preparation

• Joint design should provide for most economical use of filler metal

• Correct design for job depends on:– Type of material being welded– Thickness of material– Position of welding– Welding process– Final results desired– Type and size of filler wire– Welding technique

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Joint Preparation

• Arc in gas metal arc welding more penetrating and narrower than arc in shielded metal arc welding therefore, smaller root openings may be used for groove welds– Change in joint design increase speed of welding

• 100% penetration may be secured in ¼" plate in square butt joint welded from both sides

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Joint Preparation

• No root face recommended for 60º single- or double-V butt joints– Root opening should range from 0 to 3/32"– Double-V joints may have wider root openings

than single-V

• Plates thicker than 1 inch should have U-groove preparation– Require less weld metal; root face thickness should

be less than 3/32" and root spacing 1/32 and 3/32"

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V-Groove, Butt Joint Comparison


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Joint Preparation

• Multipass welding easier since absence of slag ensures easier cleaning

• For fillet welds deposit smaller weld beads on surface of material

• Certain types of joints backed up to prevent weld from projecting through back side– Blocks, strips and bars of copper, steel or ceramics

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Comparison of Penetration in a Fillet Weld

Carbon dioxide shieldedMAG weld versus coated

electrode weld.


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Electrode Diameter

• Influences size of weld bead, depth of penetration, and speed of welding

• General rule– For same current, arc becomes more penetrating as

electrode diameter decreases and deposition rate increases

• To get maximum deposition rate at given current density, use smallest wire possible consistent with acceptable weld profile

• Wire 0.045" and larger provide lower deposition rate and deposit wider beads than small wires

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Electrode Diameter

• Filler wires should be same composition as materials being welded

• Position of welding may affect size of electrode• Welding thin material

– Wires with diameters: 0.023/0.025, 0.030, 0.035"• Medium thick materials

– Wires with diameters: 0.045" or 1/16"• Heavy materials

– Wire with diameter: 1/8"• Small diameters recommended for vertical and

overhead positions

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Electrode Extension

• Length of filler wire that extends pas contact tube• Area where preheating of filler wire occurs• Also called the stickout• Controls dimensions of weld bead since length of

extension affect burnoff rate• Exerts influence on penetration through its effect on

welding current– As extension length increased, preheating of wire increases

and current reduced which in turn decreases amount of penetration into work

• Stickout distance may vary from 1/8 to 1 1/4"

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Electrode Extension

• Short electrode extensions (1/8–1/2 inch) used for short circuit mode of transfer, generally with smaller diameter electrodes (0.023–0.045 inches)

• Stainless steel favors shorter electrode extension because of its higher resistivity (1/8–1/4 inch)– Longer and larger diameter electrode extensions used for

spray arcs (1/2–11/4 inches)

• Excessive long arcs with active gases reduce the mechanical properties in weld– Various alloys being burned out as metal transferred across

longer arc

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Electrode Extension

• Tests indicated that when electrode extension increased from 3/16 to 5/8 inch, welding current then drops approximately 60 amperes

• Current reduced because of change in amount of preheating that takes place in wire– As electrode extension increased, preheating of wire increases – Thus less welding current required from power source at a

given feed rate – Because of self-regulating characteristics of constant voltage

power source, welding current decreased – As welding current decreased, depth of penetration also

decreases

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Nomenclature of Area Between Nozzle and Workpiece


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Position of the Gun

• Expressed by two angles: travel and work• Bead shape changed by changing direction of wire as

goes into joint in line of travel• Gun Angle

– Can be compared to angle of electrode in shielded metal arc welding

– Drag technique results in high narrow bead with deeper penetration (10º drag angle)

– As drag angle reduced, bead height decreases, width increases

– Increased travel speeds characteristic of push technique

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Travel and Work Gun Angles

Axis of Weld


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Travel and Work Gun Angles


Travel Angle(T.A.)

Axis of Weld

(Drag) Travel Direction

(Push) Travel Direction

Work Angle(W.A.)

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Drag and Push Gun angles


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Work Angle

• Position of wire to joint in plane perpendicular to line of travel

• Filler weld joints: work angle normally half of included angle between plates forming joint

• Butt welds: work angle normally 90º to surface of plate being joined

• Utilizes natural arc force to push weld metal against vertical surface to prevent undercut and provide good bead contour

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Work and Gun Angles


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Arc Length

• Constant voltage welding machine used for gas metal arc welding provides for self-adjustment of arc length– Arc length shortened, arc voltage reduced– Arc length lengthened, arc voltage increased

• No change in wire-feed speed occurs• Corrected by automatic increase or decrease of

burnoff rate of filler wire• Welder has complete control of welding current and

arc length by setting wire-feed speed on wire feeder and voltage on welding machine

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Arc Voltage

• Decided effect upon penetration, bead height, and bead width

• Chief function to stabilize welding arc and provide smooth, spatter-free weld bead

• Higher or lower causes arc to become unstable– Higher: produces wider, flatter bead and increases

possibility of porosity and increases spatter and increases undercut in fillet welds

– Lower: causes bead to be high and narrow

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Arc Voltage

• High arc voltages result in globular transfer– Spatter prone and reduces deposition efficiency

• Has sharp crackling sound when proper arc voltage for short circuit transfer– Spray arc have hissing sound

• Not set to control penetration

• Better control of weld profile and arc stability

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Relationship of Arc Length to Weld Bead Width


High VoltageLow Voltage

Arc LengthArc Length

Electrode

Electrode

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Penetration Comparisons


Arc voltage too highfor travel speed.

Arc voltage too slowfor travel speed

Proper arc voltagefor speed

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Wire-Feed Speed

• Fixed relationship between rate of filler wire burn off and welding current

• Electrode wire-feed speed determines welding current– Current set by wire-feed speed control on wire feeder

• Excessive speed, welding machine cannot put out enough current to melt wire fast enough– Stubbing or roping of wire occurs– Causes convex weld beads and poor appearance

• Decrease in speed results in less electrode being melted• Generally – high setting of filler wire speed rate results in

short arc, slow speed in long arc

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Effect of Wire-Feed Speeds


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Welding Current

• Determines amount of current delivered at arc• Often related to current density

– Amperage per square inch of cross-sectional area of electrode

• At given amperage, current density of electrode 0.035" in diameter higher than of electrode 0.045" in diameter

• Area of current-carrying sheath of metal cored electrode more complex to calculate– Current densities much higher with metal cored

electrodes than solid wire

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Welding Current

• If going to maintain given amperage and switch from solid wire to metal core, either jump one wire diameter size and keep wire-feed speed same or keep same wire size and increase wire-feed speed

• Each type and size of electrode has minimum and maximum current density– Best working range lies between

• Direct relationship between welding current and penetration– Welding current increases, penetration increases

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Welding Current

• Table 22-3 gives comparative current ranges and other parameters for welding carbon steel, stainless steel, and aluminum

• Increases in current will increase bead height and width (voltage must also be increased)

• Too high– Possibility of electrode burn-back into tube, arc unstable

and gas shielding disturbed, spatter

• Too low– Arc unstable, poor fusion, electrode becomes red hot, arc

may be extinguished, less penetration

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Travel Speed

• Has decided effect on penetration, bead size, and appearance

• At given current density, slower travel speeds provide proportionally larger weld beads and more heat input in base metal per unit length of weld– Too slow, unusual weld buildup occurs

• Progressively increased travel speeds have opposite effects– Less weld metal deposited with lower heat input per unit

length of weld– Produces narrower weld bead and lower contour

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Travel Speed

• Excessively fast speeds causes undercut

• Influenced by thickness of metal being welded, joint design, cleanliness, joint fitup, and welding position

• If increased, necessary to increase wire-feed speed, which increases current and burnoff rate

• Too low produces overlap of base metal and even burn-through on this material

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Arc Position

Arc must be on leading edge of

weld pool to assure penetration

and fusion.


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Optimum Travel Speed


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Summary of Operating Variables

• Height and width of bead depend on adjustment of these variables– Joint preparation– Gas flow rate– Voltage– Speed of travel– Arc length– Polarity

• Variables adjusted on basis of type of material being welded, thickness of material, position of welding, deposition rate required, and final weld specifications

– Gun angle– Size and type of filler wire– Electrode extension– Characteristics of the shielding

gas– Wire-feed speed (current)

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Summary of Operating Variables

• Welding current and travel speed have similar effect on both bead height and width– Each variable increases or decreases both bead

height and width at same time

• Arc voltage– As arc voltage increases, bead height decreases and

bead width increases, flattening bead– Affects shape and size of bead

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Weld Defects

• Defects found in welds made by gas metal arc process similar to those in other welding– Causes and corrective action entirely different

• Incomplete penetration– Result of too little heat input in weld area– Correct by increasing wire-feed speed and reducing

electrode extension to obtain maximum current for particular wire-feed setting

– Also causes by improper welding techniques

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Excessive Penetration

• Usually causes excessive melt-through• Result of too much heat in weld area

– Reducing wire-feed speed to obtain lower amperage or increasing speed of travel

• Another cause is improper joint design– Root opening too wide or root face too small– Correct by checking position of welding and root face and

opening

• Remedied during welding by increasing electrode extension distance and weaving gun

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Whiskers

• Short lengths of electrode wire sticking through weld on root side of joint

• Caused by pushing electrode wire past leading edge of weld pool

• Can be prevented by– Reducing wire-feed speed– Increasing electrode extension distance– Weaving gun

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Voids

• Referred to as wagon tracks because of resemblance in radiographs to ruts in dirt road

• May be continuous along both sides of weld• Found in multipass welding

– Underneath pass has bead with large contour or bead with too much convexity or undercut

– Next bead does not completely fill void between previous pass and plate

• Prevent by making sure edges of all passes filled in so undercut cannot take place and arc melts previous bead and fuses into sides of joint

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Incomplete Fusion

• Also referred to as overlap• Result of improper gun handling, low heat and

improper speed of travel• To prevent:

– Direct arc so it covers all areas of joint

– Keep electrode at leading edge of pool

– Reduce size of pool as necessary by adjusting travel speed

– Check current values carefully; keep short electrode extension

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Porosity

• Most common defect in welds• Exists on face of weld readily detected• Below surface must be determined by

radiograph ultrasonic or other testing methods • Causes of most porosity are contamination by

atmosphere, change in physical qualities of filler wire, and improper welding technique

• Also caused by entrapment of gas evolved during weld metal solidification

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Causes of Porosity

• Travel so fast that part or all of shielding gas lost, and atmospheric contamination occurs

• Shielding gas flow rate too low so gas does not fully displace all air in arc area

• Shielding gas flow rate too high drawing air into arc area and causing turbulence

• Shielding gases must be of right type for metal being welded

• Shielding gases must be pure and dry

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Causes of Porosity

• Gas shield may be blown away by wind or drafts

• May be defects in gas system

• Excessive voltage for arc required can cause loss of its deoxidizers and alloying elements

• Foreign material such as oil, dirt, rust, grease, and paint on wire or material to be welded

• Improper welding techniques are used

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Other Defects

• Warpage– Occurs when forces of expansion and contraction

poorly controlled

• Spatter– Made up of very fine particles of metal on plate

surface adjoining weld area– Usually caused by high current, long arc, irregular

and unstable arc, improper shielding gas, improper gun angle, electrode extension, or clogged nozzle

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Other Defects

• Weld cracking– Comes from compositional problems, poor joint design, and

poor welding technique– Prevent by making sure filler metal has composition

suitable for base metal and providing for expansion and contraction forces during welding

• Irregular weld shape– Include too wide, too narrow, excessively convex or

concave surface and those with coarse, irregular ripples– Caused by poor gun manipulation, too fast or too slow

speed of gun travel, too high or too low current, improper arc voltage, improper shielding gas, improper extension

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Undercutting

• Cutting away of base material along toes of weld• May be present in cover pass weld bead or in

multipass welding• Condition usually result of high current, high voltage,

excessive travel speed, low wire-feed speed, poor gun technique, improper gas shielding, or wrong filler wire

• To correct, move welding gun from side to side in joint, and hesitate at each side before returning to opposite side

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Safe Practices

• Safety most important consideration to both worker and employer

• Welding no more dangerous than other industrial operations

• Safety precautions and protective equipment required for MIG/MAG process essentially same as for any other electric welding process

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Eye, Face, and Body Protection

• Welding helmets and protective clothing necessary

• Radiant energy produced by gas-shielded process 5 to 30 times more intense than produced by shielded metal arc welding– Lowest intensities produced by gas tungsten arc– Highest by gas metal arc– Argon produces greater intensities than helium

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Clothing Regulations

• Standard arc welding helmets with lenses ranging in shade from no. 6 for work using up to 30 amperes to no. 14 for work using more than 400 amperes should be worn– Arc should never be viewed with the naked eye when

standing closer than 20 feet

• Skin should be covered completely to prevent burns and other damage from ultraviolet light– Back of the head and neck should be protected from

reflected radiation – Gloves should always be worn

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Clothing Regulations

• Shirts should be dark in color to reduce reflections– Have tight collar and long sleeves– Leather, wool and aluminum-coated cloth can

withstand action of radiant energy reasonably welld

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Handling of Gas Cylinders

• Stored cylinders should be in protected area away from fire, cold, and grease and away from general shop activity

• Cylinders must be secured to equipment to prevent their being knocked over

• Proper regulators and flowmeters must be used with each special type of cylinder

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Handling of Gas Cylinders

• Cylinders should not be dropped, used as rollers, lifted with magnets, connected into electric circuit, or handled in any other way that might damage cylinder or regulator

• When cylinders empty, should be stored in upright position with valve closed

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Ventilation

• Ozone generated in small quantities, generally below allowable limits of concentration

• Nitrogen dioxide also present around area of arc in quantities below allowable limits

• Carbon dioxide shielding may create hazard from carbon monoxide and carbon dioxide if welder’s head in path of the fumes or if welding done in confined space– Special ventilation should be provided

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Ventilation

• Eye, nose, and throat irritation can be produced when welding near such degreasers as carbon tetrachloride, trichlorethylene, and perchloroethylene– Break down into phosgene under action of powerful rays

from arc

– Locate degreasing operations far away from welding activities

• Much of welding smoke and fumes can be engineered out of GMAW arc by use of higher argon percent and pulse-spray mode of transfer

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Ventilation

• During welding, certain metals emit toxic fumes that may cause respiratory irritation and stomach upset – Most common toxic metal vapors given off by

welding of lead, cadmium, copper, zinc, and beryllium

– Fumes can be controlled by general ventilation, local exhaust ventilation, or respiratory protective equipment

• Welding guns can be purchased with smoke extractor capability

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Electrical Safety

• Hazard less than that with shielded meal arc process– Open circuit voltage considerably less

• Electrical maintenance should be done only by qualified person– NEVER worked on in electrical HOT condition

22 - 68

Wire-Feeder Safety

• Turn power off when aligning and adjusting drive rolls

• Avoid pinch points when working near drive rolls

• Remember force being applied to wire sufficient to push it through your hand or other body parts

• Never let exposed wire come in contact with or be pointed at your body

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Fire Safety

• Welding should not be done near areas where flammable materials or explosive fumes present

• Paint spray or dipping operations should not be located close to any welding operation

• Combustible material should not be used for floors, walls, welding tables, or in immediate vicinity of welding operation

• When welding on containers that have previously contained combustible materials, special precautions should be taken

• Use “hot work permit” as required

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Care and Use of Equipment

• Do not push gun into arc like an electrode – Wire feeder pushes wire into arc

• Either push or drag travel angle can be used • If possible, welding should be done in flat welding

position to take advantage of increased penetration and deposition rate characteristic of the MIG/MAG process

• Small fillets and butt welds should be positioned so arc can run slightly downhill

• Equipment has to be kept clean, in proper adjustment, and in good mechanical condition

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Drag and Push Methods

Produces large wide beads Produces flatter bead shape


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Care of Nozzles

• Keep the gun nozzle, contact tube, and wire-feeding system clean to eliminate wire-feeding stoppages– Nozzle is natural spatter collector

• If spatter builds up thick enough, it can actually bridge gap and electrically connect insulated nozzle to contact tube

• To remove spatter, use soft, blunt tool for prying


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Care of Nozzles

• Spatter almost falls out by itself if nozzle kept clean, shiny and smooth

• Antispatter compound may be applied to gun nozzle and contact tube end

• Do not clean by tapping or pounding on solid object– Bends gun nozzles, damages threads and high

temperature insulation in nozzle can break

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Care of Contact Tubes

• Transfers welding current to electrode wire• Hole has to be big enough to allow wire with slight

cast to pass through easily• Wire wears hole to oval shape

– Wire slides more easily, but transfer of current not as good and arcing in tub results

– Spatter flies up into bore and wire slows down because of friction

– Must be replace; secure tightly in gun and check periodically for tightness

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Care of Wire-Feed Cables

• Wire-feed conduit flexible steel tube that does not stretch

• Main source of friction in wire-feed system

• Should be kept clean and straight as possible– Clean with dry compressed air

• Lubricate with dry powdered graphite reduces friction

• Clean every time spool or coil changes

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Bird Nesting

• Wire coils sideways between wire-feed cable and drive rolls

• Prevent by accurate alignment of wire-feed cable inlet guide– Aligned exactly with rollers so wire does not have

to make reverse bend– Notch in drive rolls must be in perfect alignment to

provide smooth passage for wire

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Cleanliness of Base Metal

• Clean area thoroughly before welding

• Remove all rust, scale, burned edges and chemical coatings– Gas producers– Porosity is result

• Intense heat of arc burns away some of the contaminants

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Arc Blow

• Arc blown to one side or other by condition of pull and counter-pull as magnetic field is distorted– Ionized gases carrying arc from end of electrode wire to work

act as flexible conductor with magnetic field around it– When placed in location such as corner of joint or end of

plate, magnetic field distorted and pulls in another direction– Magnetic field tries to return to state of equilibrium

• Does not occur with a.c. welding arcs– Forces exerted by magnetic field reversed 120 times per

second thus keeping magnetic field in equilibrium

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Connecting Work to Minimize Arc Blow

Suggestions to shorten trial-and-error process to correct or minimize arc blow

• Attach work lead or leads directly on workpiece if possible

• Connect both ends of long, narrow weldments

• Use electrical conductors of proper length

• Weld away from work connection

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• On parts that rotate, use rotating work connection or allow work cable to wind up no more than one or two turns

• In making longitudinal welds on cylinders, use two work connections—one on each side of the seam as close as possible to point of starting

• If multiple work connections necessary, make sure cables are same size and length and have identical terminals

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• On multiple-head installations, all heads should weld in same direction and away from work connection

• Use individual work circuits on multiple-head installations

• Do not place two or more arcs close to one another on weldments that are prone to magnetic disturbance with one arc such as tubes or tanks requiring longitudinal seams

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Setting Up Equipment

• Constant voltage d.c. power source• Wire-feeding mechanism with controls and spooled or

reeled filler wire mounted on fixture• Gas-shielding system consisting of one or more

cylinders of compressed gas, pressure-reducing cylinder regulator, flowmeter assembly

• Combination gas, water, wire, and cable control assembly and welding gun of correct type and size

• Connecting hoses and cables, work lead, and clamp• Face helmet, gloves, sleeves (if necessary), and

assortment of hand tools

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Assumed Safety Precautions

• Welding equipment installed properly

• Welding machine in dry location, and no water on floor of welding booth

• Welding booth lighted and ventilated properly

• All connections tight, and all hoses and leads arranged so they cannot be burned or damaged

• Gas cylinders securely fastened so they cannot fall over and not part of electrical circuit

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Starting Procedure

1. Check power cable connections; connect gun cable to proper welding terminal on welding machine and work cable end connected to proper terminal on welding machine

2. Start welding machine by pressing on button or, in case of engine drive, start engine

3. Turn on wire-feed unit4. Check gas-shielding supply system5. Check water flow if gun water cooled

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Starting Procedure

5. Set wire-feed speed control for type and size of filler wire and for job

6. Voltage rheostat should be set to conform to type and thickness of material being welded, diameter of filler wire, the type of shielding gas, and type of arc

7. Adjust for proper electrode extension beyond contact tube

8. To start arc, touch end of electrode wire to proper place on weld joint, usually just ahead of weld bead, with current shut off; lower helmet and press gun trigger on torch

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Shutting Down the Equipment

1. Stop welding and release gun trigger2. Return feed speed to zero position3. Close gas outlet valve in top of gas cylinder4. Squeeze welding gun trigger, hold it down,

and bleed gas lines5. Close gas flowmeter valve until finger-tight6. Shut off welding machine and wire feeder7. Hang up welding gun and cable assembly

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Starting the Weld

• Running start– Arc started at beginning of weld

– Electrode end put in contact with base metal

– Trigger on torch pressed

– Tends to be too cold at beginning of weld

• Scratch start– Arc struck approximately 1 inch ahead of beginning of weld

– Arc quickly moved back to starting point of weld, direction of travel reversed, and weld started

– Arc may also be struck outside of weld area on starting tab

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Finishing the Weld

• Arc should be manipulated to reduce penetration depth and weld pool size when completing weld bead– Decreases final shrinkage area

– Reduction accomplished by rapidly increasing speed of welding for approximately 1 to 2 inches of weld length

– Trigger released, stopping wire feed and interrupting welding current

• Gun trigger can be turned on and off several times at end of weld to fill crater

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Gun Angle

• Push angle of 5° to 15° generally employed when welding in flat position– Take care push angle not changed as end of weld

approached

• Work angle equal on all sides when welding uniform thicknesses

• Welding in horizontal position, point gun upward slightly

• Thick-to-thin joints, direct arc toward heavier section• Slight drag angle may help when welding thin

sections

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Control of Arc

• Arc voltage controls penetration, bead contour, and such defects as undercutting, porosity and weld discontinuities

• Arc should be occasionally noisy for most applications of spray arcs

22 - 91

Process and Equipment Problems

• Study tables 22-6 which lists problems with MIG/MAG short arc process and their correction

• Table 22-7 lists problems with MIG/MAG process and equipment, their causes, and possible remedies

22 - 92

Practice Jobs

• Practice gas metal arc welding on mild steel, aluminum, and stainless steel

• Specifications given in Job Outline in order assigned by instructor

• Beyond these job, practice other forms of joints in all positions– Use various types and sizes of filler wire and

different shielding gases

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Precautions to Observe When Doing Practice Jobs

• Avoid excessive current values• Check your welding speed• Make sure that gas flow adequate• Keep wire centered in gas pattern and in center of

joint; make sure correct electrode angle maintained at all times

• Select proper filler wire for material being welded and for such situations as rust, scale, and excessive oxygen

• When welding from both sides of plate, be sure root pass on first side deeply penetrated by root pass on second side

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MIG/MAG Welding of Carbon Steel

• Bulk of all welding done on carbon steel

• MIG/MAG welding on increase– Welders find it relatively easy to master– Consistently produces sound welds at high rate of

speed

22 - 95

Groove Welds: Jobs 22-J1 and J2

• Plate up to 1/8" thick may be butt welded with square edges with root opening of 0 to 1/16"

• Heavier plate, 3/16 and 1/4 inch may be welded without beveling edges if 1/16 to 3/32" opening provided

• Bead should be wider than root spacing for proper fusion

• Two passes, one from each side usually needed

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• For code welding, plate thicknesses from 3/16 to 1" should be beveled– 60º single- or double-V without root face

recommended– Root opening of 0 to 1/16" should be maintained– Wider root openings may be provided for double-V

joints– Single-V grooves backing pass from reverse side

generally required• Less distortion when welding from both sides

of joint

22 - 97


• Open root joint should be run using short circuit or pulse spray for ferrous metals

• Practice 3G using both uphill and downhill techniques

• U-grooves used on plate thicker than 1 inch– Root spacing between 1/32 and 3/32" maintained– Root face of 3/32" or less to assure penetration– Requires less filler metal than V groove butt joint

22 - 98


• Argon-oxygen mixture containing 1-5% oxygen recommended for spray arc welding– Oxygen improves flow of weld metal and reduces tendency

to undercut

• Argon with 10% CO2 sometimes used

• Carbon dioxide at 100% used by arc not true spray arc– Popular for MAG small wire welding

• Short arc welding of carbon steel uses mixture of 75% argon and 25% carbon dioxide

22 - 99

Fillet Welds: Jobs 22-J3-J10

• Used in T-joints, lap joints, and corner joints• Deposit rate and rate of travel high with deep

penetration• Permits smaller fillet welds than with stick electrode

welding• Position of nozzle and speed of welding important• Welding may be single pass or multipass

– Multipass may be done with stringer or weave beads

• Each pass must be cleaned carefully

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Inspection and Testing


Outside corner joint in steel plate welded with gas metalarc welding process in the flat position.

Penetration through back side of corner joint weldedin the flat position.

22 - 101


Fillet weld on lap joint in steel platewelded with gas metal arc weldingprocess in 2F position.


Fillet weld on lap joint in steel plate weldedwith gas metal arc welding process in 3Fposition, downhill. Note porosity caused

by poor gas shielding.

22 - 102



Fillet weld on T-joint weldedin the 2F position with the

gas metal arc welding process in steel plate.

Penetration through back side of a V-groove butt joint welded

in the 1G position.

The first (root) pass of a V-groovebutt joint welded in the 1G position

with the gas metal arc welding process in steel plate.

22 - 103

Fillet and Groove Welding Combination Project:

Job Qualification Test 1

• Purpose– Ability to read print– Develop bill of materials– Thermally cut– Fit components together– Tack and weld carbon steel project

• Follow instructions found in Fig. 22-26

22 - 104

Fillet and Groove Welding Combination Project:

Job Qualification Test 1

• Inspection and testing (visual inspection only)– Shall be no cracks or incomplete fusion– Shall be no incomplete joint penetration in groove welds

except as permitted for partial joint penetration groove welds

– Undercut shall not exceed lesser of 10% of base metal thickness or 1/32 inch

– Frequency of porosity shall not exceed one in each 4 inches of weld length, and maximum diameter shall not exceed 3/32 inch

– Welds shall be free from overlap– Only minimal weld spatter shall be accepted

22 - 105

Fillet and Groove Welding Combination Project: Job Qualification Test2

• Purpose– Ability to read print– Develop bill of materials– Thermally cut– Fit components together– Tack and weld carbon steel project– Use spray arc mode of metal transfer– Note on Fig. 22-27

22 - 106

Fillet and Groove Welding Combination Project: Job Qualification Test2

• Inspection and testing (visual inspection only)– Shall be no cracks or incomplete fusion– Shall be no incomplete joint penetration in groove welds


– Undercut shall not exceed lesser of 10% of base metal thickness or 1/32 inch

– Frequency of porosity shall not exceed one in each 4 inches of weld length, and the maximum diameter shall not exceed 3/32 inch


22 - 107

Groove Weld Project: Job Qualification Test 3

• Project– Ability to read print– Fit components together– Tack and weld carbon steel unlimited thickness test

plate– Using spray arc mode of metal transfer– Instructions in notes in Fig. 22-28

22 - 108


• After tacking, have it inspected• After complete welding, use visual inspection

and cut specimens for bend testing• Use side bend test procedures and check:• Testing criteria:

– No cracks or incomplete fusion– No incomplete joint penetration in groove welds


22 - 109


• Testing criteria (cont.): – Undercut shall not exceed lesser of 10 percent of

base metal thickness or 1/32 inch– Frequency of porosity shall not exceed one in each

4 inches of weld length and maximum diameter shall not exceed 3/32 inch


22 - 110

Side Bend Acceptance Criteria as Measured on Convex Surface of Bend Specimen

• No single indication shall exceed 1/8 inch measured in any direction on surface

• Sum of greatest dimensions of all indications on surface, which exceed 1/32 inch, but are less than or equal to 1/8 inch, shall not exceed 3/8 inch

• Cracks occurring at corner of specimens shall not be considered unless there definite evidence that they result from slag inclusions or other internal discontinuities

22 - 111

MIG Welding of Aluminum

• Readily joined by welding, brazing, soldering, adhesive bonding, and mechanical fastening

• Lightweight• Alloyed readily with many other metals• Highly ductile and retains ductility at subzero

temperatures• High resistance to corrosion, no colored salts, not toxic• Good electrical and thermal conductivity• High reflectivity to both heat and light• Nonsparking and nonmagnetic

22 - 112


• Easy to fabricate• May be given wide variety of mechanical,

electrochemical, chemical and paint finishes• Needs high heat input for fusion welding• Aluminum and its alloys rapidly develop oxide

film when exposed to air (melting point 3600ºF)– Must be removed during welding

• Removed by fluxes, action of arc in inert gas atmosphere or mechanical and chemical means

22 - 113


• MIG and TIG replaced stick electrode welding for aluminum and its alloys– Small percentage still using stick electrodes

• Type of joint and position of welding determines process to used on thicknesses 1/8 inch and under

22 - 114

Factors that Make Gas Metal Arc Welding Desirable Joining Process for Aluminum

• Cleaning time reduced because there no flux on weld

• Absence of slag in weld pool eliminates possibility of entrapment

• Weld pool highly visible due to absence of smoke and fumes

• Welding can be done in all positions

22 - 115

Joint Preparation

• Designed like those for steel• Narrower joint spacing and lower welding currents

used• Foreign substances must be removed

– Wiped off or removed by vapor degreasing– Oxide film removed by chemical and mechanical cleaning

methods

• Weld as soon as possible before oxide film has chance to form again

• Sheared edges can also cause poor quality welds

22 - 116

Shielding Gas

• Argon preferred for welding aluminum plate thicknesses up to 1 inch

• Plate thicknesses 1-2 inches may use:– Pure argon, mixture of 50% argon and 50% helium, or

mixture of 75% argon and 25% helium– Helium provides high heat and argon excellent cleaning

action• Plate thicknesses from 2-3 inches

– Mixture of 50% argon and 50% helium or 25% argon and 75% helium

• Plate thicknesses greater than 3 inches– Mixture of 25% argon and 75% helium

22 - 117

Spray Arc Welding

• Weld metal deposited continuously• More arc energy and greater heat provided for melting

filler wire and base material• Helium, helium-argon mixtures and argon used as

shielding gases– Choice dependent upon type of material, thickness and

welding position

• Welding can be done in all positions• GMAW-P very effective when welding aluminum

22 - 118

Out-of-Position Welding

• Horizontal position– Care must be taken to penetrate to root of joint

when welding butt joints and T-joints– Overheating in any one area causes sagging,

undercutting or melt-through to back of joint– Weld metal should be directed against upper plate– In multipass welding, be sure fusion between

passes

22 - 119

Horizontal Position

Welding T-joint in aluminumplate in 2F position

Welding V-groove butt jointin aluminum plate in 2G position.


22 - 120

Out-Of-Position Welding

• Vertical position– Travel-up technique on fillet and groove welds

– Do not use too high welding current nor deposit too large weld bead

– Slight side-to-side motion helpful

• Overhead position– No problem with fillet and groove welds

– Welding current and travel speed lower than flat position

– Gas flow rate higher because gas has tendency to leave area

– Somewhat awkward – assume relaxed position as possible

22 - 121

Out-Of-Position Welding


Welding V-groove butt joint inaluminum plate in 3G position, uphill.

Welding T-joint in aluminum plate in 3F position, uphill.

22 - 122

Butt Joints: Jobs 22-J11 and J12

• Easy to design• Require minimum of base material• Perform better under fatigue loading• Require accurate alignment and edge preparation• Usually necessary to bevel edge on thicknesses of ¼"

or more to permit root pass penetration– On heavier plate, chipping back side and welding back side

with one pass– Sections with different thicknesses should be beveled

before welding

22 - 123

Lap Joints: Job 22-J13

• More widely used on aluminum alloys than on other materials

• Use double-welded, single-lap joints in thicknesses of aluminum up to ½"

• Require no edge preparation

• Easy to fit

• Require less jigging than butt joints

22 - 124

T-Joints: Jobs 22-J14-J16

• Seldom require edge preparation on material ¼" or less in thickness

• Fully penetrated if weld fused into root of joint• Easily fitted and normally require no back chipping• Jigging usually quite simple• Better to put small continuous fillet weld on each side

of joint rather than one large weld on one side• Continuous fillet welding recommended over

intermittent welding for longer fatigue life

22 - 125

Edge and Corner Joints

• Economical from standpoint of preparation, base metal used, and welding requirements

• Harder to fit up

• Prone to fatigue failure

• Edges do not require preparation

22 - 126


• Inspect carefully for defects

• Use same inspection and testing procedures used previously

• Look for surface defects

• High quality welds in aluminum can be produced only if proper welding conditions and good cleaning procedures been established and maintained

22 - 127

Effect of Current on Aluminum Welds


Aluminum weld bead made with current

too high

Aluminum weld bead made with current

too low

Aluminum weld bead made with

correct current

Kaiser Aluminum & Chemical Corporation Kaiser Aluminum & Chemical Corporation Kaiser Aluminum & Chemical Corporation

22 - 128

Main Causes of Cracking in Aluminum Welds

• Generally in crater or longitudinal form• Crater cracks

– Cause: arc broken sharply and leaves crater– Cure: manipulate gun properly

• Longitudinal cracks caused by– Incorrect weld metal composition– Improper welding procedure– High stresses imposed during welding by poor joint

design or poor jigging

22 - 129

Main Causes of Porosity in Aluminum Welds

• Hydrogen in the weld area• Moisture, oil, grease, or heavy oxides in the weld area• Improper voltage or arc length• Improper or erratic wire feed• Contaminated filler wire (Use as large a diameter as

possible and GMAW-P if lower heat is needed.)• Leaky gun • Contaminated or insufficient shielding gas

22 - 130

Major Causes of Incomplete Fusion of Weld Metal with Base Metal

• Incomplete removal of oxide film before welding

• Unsatisfactory cleaning between passes

• Insufficient bevel or back chipping

• Improper amperage (WFS) or voltage

22 - 131

Causes of Inadequate Penetration at Root of Weld and Into Side Walls of Joint

• Low welding current (WFS)

• Improper filler metal size

• Improper joint preparation

• Too fast travel speeds for the selected wire-feed speed

22 - 132

Causes of Metallic and Nonmetallic Inclusions in Aluminum Welds

• Copper inclusions caused by burn-back of electrode to contact tube

• Metallic inclusions from cleaning weld with wire brush which leaves bristles in weld

• Nonmetallic inclusions from poor cleaning of base metal

• Always use push gun travel angle when welding aluminum

22 - 133

Groove Weld Project: Job Qualification Test 4

• Purpose– Ability to read print– Fit components together– Tack– Weld aluminum test plates– Using spray arc mode of metal transfer

• Inspection and testing– Visual inspection– Perform side bend tests

22 - 134Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Performance QualificationTest GMAW Spray Transfer, Aluminum3G and 4G Positions

AWS SENSE

Shown only to illustrate what a qualification test wouldlook like. Follow it and inspect and test as listed in text.

22 - 135

MAG Welding of Stainless Steel

• Heat and corrosion resistant alloy– Always contains high percentage of chromium in

addition to nickel and manganese

• Excellent strength-to-weight ratios• Many alloys possess high degree of ductility• Widely used in products such as tubing, piping,

kitchen equipment, ball bearings• Supplied in sheets, strip, plate, shapes, tubing,

pipe and wire extrusions

22 - 136

MAG Welding of Stainless Steel

• Lower rate of thermal conductivity than carbon steel– Heat retained in weld zone longer

• Thermal expansion greater than carbon steel– Causes greater shrinkage stresses and warpage

• Has tendency to undercut• All standard forms of joints used in fabrications• Copper backing bars necessary for welding sections

up to 1/16" thick• No air must be permitted to reach underside of weld

while weld pool solidifying (air weakens it)– If no backing bar, argon should be used as purge gas shield

22 - 137

Advantages of MAG Welding Stainless Steel

• Absence of slag-forming flux reduces cleaning time and makes it possible to observe weld pool

• Continuous wire feed permits uninterrupted welding

• MAG lends itself to automation• Welding may be performed with short-

circuiting, spray, or pulsed spray modes of transfer

22 - 138

Spray Arc Welding

• Electrode diameters as large as 3/32" can be used for stainless steel– 1/16" wire used with high current to create spray arc

transfer of metal• DCEP used for most stainless-steel welding• Most common gas: mixture of Ar and 1 to 2% O

– Recommended for single-pass welding• Push travel angle should be employed on plate ¼"

thick or more• Gun should be moved back and forth in direction of

travel and slightly from side to side

22 - 139

Short Arc Welding (GMAW-S)

• Requires low current ranging form 20 to 175 amperes; low voltage of 12 to 20 volts, small diameter wires

• Metal transfer occurs when filler wire short circuits with base metal

• Ideally suited for most stainless-steel welding on thicknesses from 16 gauge to 1/16"– Also for first pass in which fitup is poor or copper

backing unsuitable

– Very desirable in vertical and overhead positions for first pass

22 - 140

Short Arc Welding (GMAW-S)

• For stainless steel in light gauges, triple mixture of gas gives good arc stability and excellent coalescence– 90% helium, 7 ½% argon and 2 ½% carbon dioxide– Produces small heat-affected zone that eliminates

undercutting and reduces distortion– Does not lower corrosion resistance– Flow rates must be increased because of lower

density of helium

22 - 141

Pulse Spray Arc (GMAW-P)

• Can be done with lower current levels and higher wire-feed speeds

• Can be used on all thickness ranges• Spray-type gas: 1 and 2% oxygen with

remainder being argon most common• Weld more fluid and flows well because arc on

all the time• Spatter reduced on thin base metals as

compared to short-circuiting mode of transfer

22 - 142

Hot Cracking

• Tendency of some stainless steels– More welding passes needed– Stringer beads recommended instead of weave

• Reduce contraction stresses and cooling more rapid

• Can reduce when welding sections 1 inch or thicker by preheating to 500ºF– Also reduce by GMAW-S or P welding

22 - 143

Stainless-Steel Sensitization

• Carbide precipitation– Sensitizing chromium out of individual grains of austenitic

types of stainless steel

– Occurs most readily in 1,200ºF heat range

• To reduce situation– Use GMAW process with its rapid speed and high

deposition rate

– Use stabilized and low carbon grades of stainless steel

– Using proper filler metals such as ER308L which is low in carbon

22 - 144

Inspection and Testing: Jobs 22-J17-J23

• Inspect each weld carefully for defects

Fillet weld on lap joint in 3/8" stainless-steel plate weldedin the 1F position with the gas metal arc welding process.


22 - 145

Inspection and Testing: Jobs 22-J17-J23

Fillet weld on T-joint in 3/8" stainless-steel platewelded in 1F position with gas metal arc welding process.

Fillet weld on T-joint in 3/8" stainless-steel platewelded in 2F position with gas metal arc welding process.


22 - 146

Copper and Its Alloys

• May be welded successfully by gas metal arc process• Electrolytic copper can be joined by using special

techniques, but weldability not good• Various grades of deoxidized copper readily weldable

with MIG process– Deoxidized filler wires necessary

• Filler wires of approximately matching chemistry used

• Argon preferred shielding gas for material 1" and thinner– Flow of 50 cubic feet per hour sufficient– Heavier material uses 65% and 35% argon

22 - 147


• Joint design like any other metal– Steel backup necessary for sheets 1/8" or thinner

• Welding currents on high side required– Preheat not required when welding ¼" or less

• Always provide good ventilation when welding copper and its alloys– Beryllium-copper alloy dangerous

22 - 148


• GMAW-B– Variation of GMAW process where B indicates

brazing or just MIG brazing– Uses silicon-bronze type electrode with inert

shielding with Argon 100% most common– Main application for coated carbon steel sheet

metal (light gauge)– Zinc coating applied for corrosion resistance – Base metal not melted (hence brazing operation)

22 - 149

Nickel and Nickel-Copper Alloys

• Can be welded using gas metal arc process• Remove all foreign material in vicinity since

susceptible to severe embrittlement and cracking when come in contact with foreign materials

• Argon generally preferable for welding up to about 3/8 inch in thickness – Above that thickness, argon-helium mixtures

usually more desirable• Joint preparation like other metals

22 - 150

Magnesium

• Silvery white metal, two-thirds weight of aluminum and one-quarter weight of steel

• Melting point of 1,204ºF• Strength-to-weight ratio high when compared to steel• Welding techniques like aluminum

– Rate of expansion greater– Care taken that surface clean before welding

• Arc characteristics of helium and argon with magnesium different than with other metals– Argon recommended in most cases

22 - 151

Titanium

• Bright white metal that burns in air

• Only element that burns in nitrogen

• Melting point of about 3,500ºF

• Most important compound titanium dioxide– Used extensively in welding electrode coatings

• Used as stabilizer in stainless steel

22 - 152

Zirconium

• Bright gray metal

• Melting point above 4,500ºF

• Very hard and brittle and readily scratches glass

• Used in hard-facing materials

• Often alloyed with iron and aluminum

• Argon or helium-argon mixtures used for gas shielding

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