GMAW Applications 301

active

A substance that reacts with other elements. Active gases used as shielding gas for GMAW include argon and helium.

acute angle

An angle that measures less than 90 degrees. Acute angles are often used for welding work angles and travel angles.

aluminum oxides

A chemical compound made of aluminum and oxygen that forms a thin film on the surface of aluminum when it is exposed to the oxygen in the air. Aluminum oxides should be removed from base metals before welding.

amperage

The amount of current flowing in a circuit. Amperage is measured in amperes (A), or amps.

amperes

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amperes are also called amps.

amps

A. A unit of measurement that indicates the amount of current flowing in a circuit. Amps is another name for amperes.

arc length

The distance that electricity must travel from the tip of the electrode to the weld puddle. Arc length is directly proportional to voltage in GMAW.

area

A measurement of the amount of space contained within a flat, enclosed shape. The cross-sectional area of an electrode wire is expressed in circular mils.

argon

Ar. A heavy inert gas commonly used for shielding in arc welding processes. Argon is much heavier than air, so it effectively shields the weld area.

automatic

A type of welding process in which a computer or a robot controls both the welding equipment and the weld variables. In an automatic process, the welder is responsible for setting and controlling the specialized settings for the computer or robot.

axial spray transfer

GMAW-Spray. A type of GMAW metal transfer in which the metal at the end of the electrode melts into small, fine droplets that transfer to the weld puddle. Axial spray transfer creates a stable arc and little spatter.

backhand technique

A method of moving the electrode along the workpiece that points the electrode opposite the direction of travel. The backhand technique uses a drag angle.

burnthrough

A discontinuity that occurs when weld metal from one side of a joint melts through to the other side, leaving an open hole. Burnthrough is caused by excessive penetration, but not all excessive penetration results in burnthrough.

carbon dioxide

CO₂. A heavy active gas commonly used for shielding in arc welding processes. Carbon dioxide is inexpensive but yields a violent arc.

carbon steel

A common metal that is an alloy of iron and carbon. Carbon steel is one of the most commonly welded metals.

circuit

A controlled path for electricity. All arc welding processes require a closed electrical circuit that includes a source, path, load, and control.

constant voltage

CV. A power supply in which the voltage is set at a fixed level and the amperage varies to maintain the relatively constant voltage. With constant voltage power, the wire feed speed (WFS) is also set at a fixed rate and maintained by the varying amperage.

consumable electrode

A device that conducts electricity from the contact tip to the arc and melts into the weld as a filler metal. The consumable electrodes used for GMAW come in the form of wires.

contact tip

The device located inside the welding gun that conducts electricity to the electrode. The contact tip is usually made of copper.

contact tip to work distance

CTWD. The distance from the contact tip to the workpiece surface. Contact tip to work distance includes both electrode extension and arc length.

contaminants

Any element or substance not original to a weld that may impact the quality and strength of a finished weld. Contaminants in welds include oxygen and nitrogen.

convex

Curving outward like the exterior surface of a circle or sphere. Many weld beads have a convex surface.

copper

A reddish metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper may be used as weld backing.

current

The flow of electricity through a circuit. Current controls the heat of the arc.

current density

The amount of current carried by an electrode divided by the area of the electrode's cross section. Current density is limited by the diameter of the electrode.

current saturation

The point at which an electrode has reached maximum current density. Current saturation indicates that amperage can no longer increase.

CV

Constant voltage. A power supply in which the voltage is set at a fixed level and the amperage varies to maintain the relatively constant voltage. With CV power, the wire feed speed (WFS) is also set at a fixed rate and maintained by the varying amperage.

defects

An irregularity in the specified and expected composition of a weld that exceeds the part design's tolerances. A defect is an unacceptable discontinuity.

deoxidizers

A material that removes oxygen from the molten weld puddle and arc. Deoxidizers prevent oxygen from ruining a weld bead.

deposition rate

The rate at which filler metal melts off the electrode into the weld puddle. Deposition rate can be measured in pounds per hour (lb./hr.) or in grams per minute (g/min).

direct current electrode positive

DCEP. Current that always flows in one continuous direction from the negative workpiece to the positive electrode. Direct current electrode positive polarity is also known as reverse polarity, but this is a nonstandard term.

direction of travel

The direction in which welding occurs. The travel angle determines whether the electrode points towards the direction of travel or away from it.

discontinuities

An irregularity in the specified and expected composition of a weld. A discontinuity that exceeds the part design's tolerances is a defect.

distortion

A condition in which a weld's structure or appearance differs from specifications. Distortion can be caused by using incorrect welding variables.

drag angle

A travel angle that points the electrode opposite the direction of travel. Drag angles are used with the backhand technique.

electrode axis

An imaginary line that runs through the center of the electrode. The electrode axis forms one side of both the work and travel angles.

electrode extension

The distance from the end of the contact tip to the end of the electrode. Electrode extension combined with arc length is equal to the contact tip to work distance.

electrode orientation

The position of the electrode in relation to the workpiece and direction of travel. Electrode orientation includes the work angle and the travel angle.

ferrous metals

A metal that contains iron. Ferrous metals, such as steel, are the most common type of welded metal.

fillet weld

A type of weld that is triangular in shape and joins two surfaces at right angles to each other in a lap, T-, or corner joint. Fillet welds are the most common type of welds.

fit-up

A measure of the closeness between two parts that are to be welded. Proper fit-up occurs when parts fit together without extra spaces or gaps.

flow rate

The amount of shielding gas that is delivered in a specific amount of time. Flow rate is usually measured in standard cubic feet per hour (SCFH) or liters per minute (l/min).

forehand technique

A method of moving the electrode along the workpiece that points the electrode in the direction of travel. The forehand technique uses a push angle.

gas envelope

A pocket of shielding gas intended to surround the weld puddle, arc, and electrode tip. Drafty or windy conditions and excessive gas flow rates can disturb the gas envelope.

gas metal arc welding

GMAW. An arc welding process in which a bare wire electrode and shielding gas are fed to the weld through a welding gun. Gas metal arc welding is also referred to as MIG or MAG welding, although these terms are nonstandard in the United States.

globular transfer

GMAW-Globular. A type of GMAW metal transfer in which the metal at the end of the electrode melts into a large ball and drops to the workpiece. Globular transfer deposits large amounts of metal into the weld puddle.

GMAW

Gas metal arc welding. An arc welding process in which a bare wire electrode and shielding gas are fed to the weld through a welding gun. GMAW is also referred to as MIG or MAG welding, although these terms are nonstandard in the United States.

groove angles

The angle of the groove between two workpieces being welded together. Increasing the groove angle can improve joint access when welding thicker metals.

groove faces

The exposed surface of the groove between two workpieces. The groove face must experience complete fusion to create a quality weld.

groove weld

A type of weld made in the opening between two part surfaces that provides space to contain weld metal. Groove welds are used on all joints except lap joints.

heat input

The amount of thermal energy transferred to the workpiece during welding. Heat input is measured in kilojoules per inch (kJ/in.) or kilojoules per millimeter (kJ/mm).

helium

He. A lightweight inert gas commonly used for shielding in arc welding processes. Helium is much lighter than air and can escape the weld area quickly.

inches per minute

ipm. A unit of measurement for speed that indicates how many inches of wire electrode feed through the welding gun in one minute. The units inches per minute and millimeters per minute are used to measure wire feed speed.

incomplete fusion

A discontinuity that occurs when the weld metal and base metal or adjoining weld beads are not fully fused. Incomplete fusion can create gaps, which may lead to cracks and joint failure.

incomplete joint penetration

IJP. A discontinuity characterized by an unpenetrated and unmelted area in a joint that occurs when weld metal does not extend through the full thickness of the joint. Incomplete joint penetration leaves an unfused area that can cause cracking.

inert

A substance that does not react with other elements. Inert gases used as shielding gas for GMAW include carbon dioxide and oxygen.

ipm

Inches per minute. A unit of measurement for speed that indicates how many inches of wire electrode feed through the welding gun in one minute. The units ipm and mm/min. are used to measure wire feed speed.

leading edge

The edge of the weld puddle farthest from the finished weld bead. Keeping the arc on the leading edge of the weld puddle helps prevent discontinuities.

machining

The process of removing metal to form or finish a part. Machining may be used to remove surface contaminants from base metals.

mechanical properties

A characteristic of a material that describes its ability to compress, stretch, bend, scratch, dent, or break. Mechanical properties include tensile strength and yield strength.

melt-through

An undesirable sagging of weld metal caused by overheating. Using weld backing helps minimize the effects of melt-through.

metal transfer

The deposition of filler metal into a weld. There are several different modes of metal transfer for GMAW, including short circuiting, globular, and axial spray.

mill scale

A tough surface contaminant found on metals that is composed mainly of iron oxides. Mill scale can contaminate a weld and cause porosity.

millimeters per minute

mm/min. A unit of measurement for speed that indicates how many millimeters of wire electrode feed through the welding gun in one minute. The units millimeters per minute and inches per minute are used to measure wire feed speed.

multi-pass weld

A weld that is formed by running two or more weld beads over top of one another. Multi-pass welds often use both stringer and weave beads.

nonferrous metals

A metal that does not contain iron. Nonferrous metals include aluminum and copper.

oscillating

Moving back and forth from side to side. Oscillating an electrode from side-to-side along a joint will create a weave bead.

out-of-position welding

Welding that is performed in a position other than flat or horizontal. Out-of-position welding may be vertical, overhead, or inclined.

overlap

A weld discontinuity in which the weld metal protrudes beyond the weld toe or weld root. Overlap is nearly always unacceptable in a finished weld.

oxidation

A metal's chemical reaction with oxygen. Oxidation can cause tarnish and rust on a metal's surface.

oxygen

O₂. An active gas that is sometimes used in small amounts for shielding in arc welding processes. Oxygen is never used alone.

penetration

The depth to which the arc heat melts the joint below the surface of the base metals. Penetration is directly affected by the amount of amperage.

perpendicular

Intersecting at right angles to one another. Perpendicular lines create angles measuring exactly 90 degrees.

physical properties

A characteristic of a material that describes how it responds to environmental, electrical, magnetic, and thermal forces. Physical properties include corrosion resistance and conductivity.

porosity

A discontinuity characterized by the appearance of tiny voids or cavities in a weld bead, resulting from trapped gas. Excessive porosity can weaken a weld.

pulsed spray transfer

GMAW-P. A type of GMAW metal transfer that alternates rapidly between two different current levels. During pulsed spray transfer, one droplet of metal forms on the end of the electrode at a time.

push angle

A travel angle that points the electrode in the direction of travel. Push angles are used with the forehand technique.

resistance

The force that opposes the flow of electrical current. Resistance also affects voltage.

right angle

An angle that measures 90 degrees. Right angles are formed by perpendicular lines.

root openings

The separation between base metals at the root of a joint. The size of the root opening determines how much weld metal is needed to obtain fusion at the root.

root pass

The first pass of a multi-pass weld. The root pass may use a different work angle than subsequent passes.

sanding

A gentle grinding process that uses an abrasive with a fine grain, usually sandpaper, to remove small amounts of surface material. Sanding can be used to remove surface contaminants from welding base metals.

semi-automatic

A type of welding process in which the power source maintains a uniform arc and a wire feeder controls the wire feed speed of the electrode. In semi-automatic welding, the welder is responsible for controlling the position of the welding gun as well as the direction and speed of travel.

shielded metal arc welding

SMAW. An arc welding process that uses a flux-coated electrode. Shielded metal arc welding is also referred to as stick welding or manual welding.

shielding gas

A gas that protects the weld puddle and arc from reacting negatively with the atmosphere. GMAW shielding gas is supplied by a cylinder and flows through the welding gun.

short circuiting transfer

GMAW-S. A type of GMAW metal transfer in which the electrode touches the workpiece to produce a short circuit and high current that causes a violent transfer of metal. Short circuiting transfer uses low amperages and small electrodes.

single-pass weld

A weld that is formed by running a single weld bead. Single-pass welds often use stringer beads.

slag

Cooled flux that forms on top of the weld bead and must be chipped off. Slag does not occur with GMAW because it does not use flux.

solution

A mixture of liquids. A solution can be used to remove some surface contaminants from base metals.

spatter

Liquid metal droplets expelled from the welding process. Spatter can leave undesirable particles of metal on a workpiece surface.

stainless steels

A type of steel that contains at least 10.5% chromium and exhibits excellent hardness and corrosion resistance. Stainless steels have good weldability if the right welding procedures are followed.

stress

A force that attempts to deform an object. Excess stress may cause a part to break.

stringer bead

A weld bead formed by moving the electrode in a straight line along the joint. Stringer beads can also be created by using a slight back and forth motion.

stub out

To contact the base metals before melting. An electrode may stub out if the WFS is too fast.

tensile strength

A metal's ability to resist forces that attempt to pull it apart or stretch it. Tensile strength is usually expressed in pounds per square inch (psi) or pascals (Pa).

tolerances

An unwanted but acceptable deviation from a desired dimension that still meets specifications. Tolerances indicate the allowable difference between a physical feature and its intended design.

travel angle

The acute angle between the electrode axis and a line vertically perpendicular to the weld axis. The travel angle points the electrode in the same or opposite direction as the direction of travel.

travel speed

The rate at which the electrode moves along the joint to make a weld. Travel speed determines the size of the weld bead.

turbulence

A disturbance in the even flow of shielding gas to the welding area that causes the gas to swirl and mix with atmospheric gases. Turbulence is often the result of using an excessively fast flow rate.

undercut

A groove melted into the base metal at the weld toe or root that is left unfilled by weld metal. Undercut concentrates stress on the weld and can weaken it.

venturi effect

The initial decrease and then subsequent increase in pressure that occurs when a gas or fluid passes through a constriction. Leaking or damaged shielding gas system components can create a venturi effect that sucks outside air into the system and contaminates the shielding gas.

vertical-down welding

Welding that progresses downwards along a vertical surface. Vertical-down welding on ferrous metals uses a drag angle measuring between 5 and 10 degrees.

voltage

The electrical force or pressure that causes current to flow in a circuit. Voltage and arc length are directly proportional in GMAW.

volts

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts indicate voltage.

wash-in

The section of deposited weld metal that aligns evenly with the weld toe. Wash-in should be smooth and even along the joint, which is easy to achieve with metals that wet easily.

weave bead

A weld bead formed by moving the electrode side to side along the joint in an oscillating motion. Weave beads are often used for out-of-position welding.

weld axis

An imaginary line that runs through the center of the weld. The weld axis and the electrode axis are used to determine the work and travel angles.

weld backing

A strip of metal located on the side of the joint opposite the weld that stops molten metal from escaping through the joint. Weld backing is used for complete penetration welds.

weld bead

The end product of a joint that has been welded. Weld beads are formed using a variety of different techniques.

weld passes

One progression of welding across a joint. Weld passes produce weld beads.

weld puddle

The small area of molten metal that forms during welding. The cooled weld puddle forms the permanent joint.

weld root

The point at which a weld intersects the surfaces of the base metals, opposite the face of the weld. The weld root may have an opening or be internal.

weld toes

The point at which a weld's face meets the base metals. Weld toes can experience cracking and undercut.

welding codes

A collection of standards that outline practices for particular welding applications. Welding codes ensure safe welding practices and high-quality welded products.

welding position

The position in which the welder performs a weld. Welding positions include overhead-, vertical-, flat-, and horizontal-position welding.

welding procedure specification

WPS. A written document that contains all the necessary and specific information for creating a qualified weld. A welding procedure specification must be approved and tested before welding can begin.

WFS

Wire feed speed. The rate at which the wire electrode is fed through the welding gun. WFS determines amperage and the amount of heat in the arc in GMAW.

wire brushes

A tool with wire filaments used to clean the surface of a workpiece. Wire brushes can be used to prepare base metals before welding or to clean finished welds.

wire feed speed

WFS. The rate at which the wire electrode is fed through the welding gun. Wire feed speed determines amperage and the amount of heat in the arc in GMAW.

work angle

The acute or right angle between the electrode axis and a line horizontally perpendicular to the weld axis. The work angle positions the weld bead in the joint.

yield strength

A metal's ability to resist gradual progressive force without permanent deformation. Yield strength is usually expressed in pounds per square inch (psi) or pascals (Pa).