Introduction to GMAW 251

“Introduction to GMAW” provides a comprehensive overview of the gas metal arc welding (GMAW) process and its equipment. GMAW is a semi-automatic or automatic process that uses a consumable electrode and a shielding gas. GMAW equipment includes a power source, wire electrode, wire feeder, shielding gas, and welding gun. GMAW typically uses a constant voltage power source and direct current electrode positive (DCEP) polarity. There are three main modes of metal transfer used with GMAW: short circuit, globular, and axial spray.

GMAW is one of the most popular arc welding processes. Because it is semi-automatic or automatic, it is also one of the easiest to learn. After taking this class, users will be familiar with GMAW equipment and the various modes of metal transfer. This information provides the foundation necessary to learn how to perform GMAW. A good understanding of GMAW is also helpful when learning about related types of welding such as gas tungsten arc welding (GTAW).

Class Details

Class Name:
Introduction to GMAW 251
Difficulty:
Intermediate
Number of Lessons:
19

Class Outline

  • Gas Metal Arc Welding
  • Advantages and Disadvantages of GMAW
  • GMAW Equipment
  • Power Sources
  • Power Circuits
  • GMAW Setup Review
  • GMAW Gun Components
  • GMAW Gun Operation
  • GMAW Electrodes
  • Electrode Classification
  • Wire Feeder
  • Shielding Gases
  • GMAW Components Review
  • The Arc and Metal Transfer
  • Short Circuit Transfer
  • Globular Transfer
  • Axial Spray Transfer
  • Metal Transfer Methods
  • Metal Transfer Review

Objectives

  • Describe GMAW.
  • Distinguish between advantages and disadvantages of GMAW.
  • Describe common GMAW equipment.
  • Describe GMAW power sources.
  • Describe GMAW power circuits.
  • Describe components of the GMAW gun.
  • Describe GMAW electrodes.
  • Identify electrodes based on the AWS classification system.
  • Describe GMAW wire feeders.
  • Describe the shielding gas used in GMAW.
  • Describe the process of GMAW.
  • Describe the short circuit metal transfer method.
  • Describe the globular metal transfer method.
  • Describe the axial spray metal transfer method.

Job Roles

Certifications

MSSC
  • MSSC Fast Track Maintenance

Glossary

Vocabulary Term Definition
active A substance that reacts with other elements. GMAW uses both active and inert gas as shielding.
alloys A metal consisting of a mixture of two or more elements, one of which must be a metal. Alloys combine the beneficial properties of the mixed elements.
American Welding Society AWS. The non-profit organization that regulates the industrial standards for welding. The American Welding Society also promotes the welding industry in the United States.
amperage The amount of current flowing in a circuit. Amperage is determined by wire feed speed in GMAW.
arc The area in which electricity transfers from the electrode to the workpiece. The heat generated by the arc melts the base metals and filler metal during welding.
arc length The distance that electricity must travel from the tip of the electrode to the weld puddle. Longer arc lengths require more voltage.
argon A colorless, odorless inert gas commonly used as shielding for GMAW. 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 automatic welding, the welder is responsible for setting and controlling the specialized settings for the computer or robot.
AWS American Welding Society. The non-profit organization that regulates the industrial standards for welding. The AWS also promotes the welding industry in the United States.
axial spray transfer A type of 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.
carbon dioxide A colorless, odorless active gas commonly used as shielding for GMAW. Carbon dioxide is inexpensive but yields a violent arc.
circuit A controlled path for electricity. All arc welding processes require a closed electrical circuit that includes a source, path, load, and control.
code A collection of laws or standards that outline practices for a particular application. Welding codes ensure safe welding practices and high-quality welded products.
constant current CC. A power supply that maintains a flow of current that varies only slightly with changes in voltage. Constant current power sources are often used in GTAW and SMAW.
constant voltage CV. A power supply that maintains a constant voltage setting while compensating for changes in amperage. Constant voltage power sources are typically used for GMAW.
consumable electrode A device that conducts electricity from the contact tip to the arc and melts into the weld as filler metal. GMAW uses a consumable electrode in the form of a wire.
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 of the welding gun to the workpiece surface. Contact tip to work distance combines electrode extension and arc length.
control cable The path used in some arc welding processes to provide communication between the power source and wire feeder. The control cable is used when the wire feeder is an external device, rather than being built into the power source.
coolants A substance, usually liquid, used to reduce or maintain the temperature of a component during a manufacturing process. Coolants are used to keep some GMAW guns from overheating.
copper A reddish metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper and copper alloys are usually used to make the contact tip in a welding gun.
corrosion resistance A material's ability to resist deterioration caused by exposure to a particular environment. Adding nickel to a GMAW electrode improves corrosion resistance.
crater An undesirable depression in the weld bead. A crater can cause cracking if it is not properly filled.
CTWD Contact tip to work distance. The distance from the contact tip of the welding gun to the workpiece surface. CTWD combines electrode extension and arc length.
current The flow of electricity through a circuit. Current is measured in amperes (A), or amps, and controls the heat of the arc.
DCEP Direct current electrode positive. Current that always flows in one continuous direction with reverse polarity. With DCEP, electricity flows from the negative workpiece to the positive electrode.
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 an electrode melts into the molten weld puddle to form a weld. Deposition rate can be measured in pounds per hour or in grams per minute.
diffusible hydrogen The maximum amount of hydrogen, given in milliliters, that will be present per 100 grams of weld metal. An electrode's classification may indicate diffusible hydrogen.
direct current DC. Current that flows in one continuous direction. GMAW requires direct current.
direct current electrode positive DCEP. Current that always flows in one continuous direction with reverse polarity. With direct current electrode positive, electricity flows from the negative workpiece to the positive electrode.
drive rolls Wheels that direct a wire electrode as it moves through a wire feeder. Drive rolls are specially designed for various types and sizes of wires.
ductility A metal's ability to be drawn, stretched, or formed without breaking. Adding molybdenum or nickel to an electrode increases strength and hardness without affecting ductility.
duty cycle The amount of time in a ten-minute period that an electrical device can perform work before it must rest to prevent overheating. Duty cycle ratings are given as a percentage of the ten-minute period.
electric shock The flow of electricity through the body. Electric shock can be fatal.
electrode A device that conducts electricity in an electrical circuit. In GMAW, electrodes are wires that also serve as filler metal.
electrode cable The path used in arc welding to conduct electricity from the power source to the electrode. The electrode cable connects the power source to the wire feeder or to the gun.
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 liner The insulated lining that surrounds the wire electrode. The electrode liner supports the electrode from the wire feeder to the contact tip.
electrode orientation The position of an electrode in relation to the workpiece and direction of travel. Electrode orientation refers to the work angle and the travel angle.
fast-freeze weld A weld that solidifies quickly. Fast-freeze welds are easier to perform out-of-position, and they reduce the risk of a leaking weld puddle.
filler metal Metal deposited into the weld that often adds strength and mass to the welded joint. The wire electrode used for GMAW also acts as filler metal.
fillet welds A type of weld that is triangular in shape and joins two surfaces at right angles to one another. Fillet welds are the most common types of welds.
flat-position A welding position used to weld from the upper side of the joint. During flat-position welding, the face of the weld is horizontal.
flowmeter The device that indicates and controls the volume of shielding gas that flows to the welding gun. The flowmeter consists of a flow gauge that measures the volume and an adjustment valve that controls the volume.
flux A non-metallic material used to protect the weld puddle and cooling metal from atmospheric contamination in some welding processes. GMAW does not use flux.
fumes Potentially hazardous gases and particulate matter generated at the electric arc during welding processes. Fumes include particulates from the electrode, shielding gas, base metal, and any coatings included in a process.
gas cylinder An external device used to house shielding gas. Shielding gas flows from the gas cylinder to the gas hose and then to the welding gun.
gas diffuser The device inside the welding gun through which shielding gas flows. The gas diffuser regulates the flow of gas.
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.
gas nozzle The device positioned directly over the contact tip and gas diffuser in a welding gun. The gas nozzle forces shielding gas to surround the electrode and arc.
gas tungsten arc welding GTAW. A precise arc welding process that uses a non-consumable tungsten electrode. Gas tungsten arc welding is also known as TIG welding.
globular transfer A type of 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.
hardness A material's ability to resist penetration, indentation, or scratching. Hardness in a metal may change due to the heat generated during welding.
horizontal-position A common welding position in which the weld is performed on the upper side of a horizontal surface and against a vertical surface. Horizontal-position welding is often used for fillet and groove welds.
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. Wire feed speed is measured in inches per minute.
inert A substance that does not react with other elements. GMAW uses both inert and active gas as shielding.
insulator A non-conductive material that prevents the flow of electricity. A small insulator inside the welding gun prevents the gas nozzle from becoming electrically charged.
kilopounds per square inch ksi. A unit of pressure used in the English system that is equal to thousands of pounds per square inch. Kilopounds per square inch measures the amount of load pressure that is applied over an area of one square inch to describe the tensile strength of a material.
manganese A hard, brittle, gray-white metal often added to GMAW electrodes. Manganese acts as a deoxidizer and increases strength and hardness in the weld.
metal active gas welding MAG welding. An arc welding process in which a bare wire electrode and an active shielding gas are fed to the weld through a welding gun. Metal active gas welding is a nonstandard term that is sometimes used to refer to gas metal arc welding (GMAW).
metal inert gas welding MIG welding. An arc welding process in which a bare wire electrode and an inert shielding gas are fed to the weld through a welding gun. Metal inert gas welding is a nonstandard term that is sometimes used to refer to gas metal arc welding (GMAW).
metal transfer The deposition of filler metal into a weld. Metal transfer may occur in three different ways in GMAW.
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. Wire feed speed is measured in millimeters per minute.
molybdenum A hard, silver-white, metallic alloying element. Molybdenum is often added to GMAW electrodes to increase strength and hardness without decreasing ductility.
nickel A hard, malleable, silver-white metal. Nickel is often added to GMAW electrodes to increase strength and hardness without decreasing ductility.
oxidation A material's chemical reaction with oxygen. Oxidation can ruin a weld bead.
penetration The depth to which the arc heat melts the joint below the surface of the base metals. The amount of amperage directly affects weld penetration.
polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.
power source The device that provides the electricity needed to perform arc welding. Power sources may also contain the wire feeder for the electrode.
pressure gauge The device that indicates the amount of shielding gas present in a gas cylinder. The pressure gauge detects the level of gas pressure and displays it on a dial.
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 rod as its electrode. Shielded metal arc welding is also called 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 circuit A circuit in which current takes a shorter, unintended path between two conductors, interrupting the intended flow of electricity. A short circuit causes excess current flow.
short circuit transfer GMAW-S. A type of 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 circuit transfer uses low amperages and small electrodes.
silicon A non-metallic material that does not conduct electricity. Silicon is often added to GMAW electrodes to act as a deoxidizer.
slag Cooled flux that forms on top of the weld bead and must be chipped off. GMAW weld beads do not have slag because GMAW electrodes do not use flux.
spatter Liquid metal droplets expelled from the welding process. Spatter can leave undesirable particles of metal on a workpiece surface.
tensile strength A material's ability to resist forces that attempt to pull it apart or stretch it. Electrodes must create welds that at least meet the minimum tensile strength required to prevent the finished part from deforming or failing.
travel speed The speed at which the welder moves the electrode along the seam to make a weld. Travel speed determines the size of the weld bead.
trigger A lever on the welding gun that starts and stops the welding process. The trigger on a GMAW gun controls the delivery of electricity, the electrode, and the shielding gas.
voltage The electrical force or pressure that causes current to flow in a circuit. Voltage and arc length are directly proportional in GMAW.
weld bead The end product of a joint that has been welded. Weld bead formation depends on the movement of the electrode.
weld puddle The small area of molten metal that forms during welding. The cooled weld puddle forms the permanent joint.
welding cables The path used in welding to create a closed electrical circuit. Welding cables include work cables and electrode cables.
welding gun A welding instrument that conducts electricity, guides the electrode, and, in some cases, releases shielding gas. Welding guns are used in some automatic and semi-automatic welding processes, such as GMAW.
welding positions The position in which a welder performs a weld. Welding positions include overhead-, vertical-, flat-, and horizontal-position welding.
wire feed speed WFS. The rate at which the wire electrode is fed through the welding gun. In GMAW, wire feed speed determines amperage and the amount of heat in the arc.
wire feeder The device that feeds a supply of wire electrode to the welding gun. The wire feeder may be either built inside the power source or an external device set beside it.
work cable The path used in arc welding to conduct electricity from the power source to the workpiece. The work cable attaches to the workpiece via the work clamp.
work clamp A component that connects the work cable to the workpiece. The work clamp provides ground for the GMAW circuit.