Introduction to GMAW 251

“Introduction to GMAW” provides a comprehensive overview of the gas metal arc welding 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 polarity (DCEP). In GMAW, there are several modes of metal transfer: 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
Version:
2.0
Difficulty:
Intermediate
Number of Lessons:
21
Related 1.0 Classes:
What Is Arc Welding? 110, Arc Welding Processes 120, Electrical Power for Arc Welding 140, GMAW Applications 220, Arc Welding Power Sources 260

Class Outline

  • Gas Metal Arc Welding
  • GMAW: in Action
  • Advantages and Disadvantages of GMAW
  • GMAW Equipment
  • Power Sources
  • Power Circuits
  • GMAW Setup Review
  • GMAW Gun
  • GMAW Gun Components
  • Inside a GMAW Gun
  • 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: in Action
  • 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.
  • Explain the AWS classification system for GMAW electrodes.
  • Describe GMAW wire feeders.
  • Describe the characteristics and function of shielding gas 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

Glossary

Vocabulary Term Definition
active A substance that reacts with other elements. GMAW uses both active and inactive gas as shielding.
active A substance that reacts with other elements. GMAW uses both active and inert gas as shielding.
American Welding Society AWS. The non-profit society that regulates the industrial standards for welding and promotes the welding industry. AWS specifications include classification systems for welding electrodes.
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 the electricity must travel from the tip of the electrode to the weld puddle. Longer arcs require more voltage.
argon An inert gas commonly used as shielding for GMAW. Argon is much heavier than air, so it effectively shields the weld area.
automatic process 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.
AWS American Welding Society. The non-profit society that regulates the industrial standards for welding and promotes the welding industry. AWS specifications include classification systems for welding electrodes.
axial spray transfer method 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 An 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 in which electricity can easily flow.
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 source that uses current that varies slightly with changes in voltage. Constant current power sources are often used in gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW).
constant voltage CV. A power source 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 a filler metal. GMAW uses a consumable wire electrode.
consumable electrode A device that conducts electricity from the contact tip to the arc but also melts into the weld as a filler metal. GMAW uses a consumable wire electrode.
contact tip The device located inside the welding gun that conducts electricity to the electrode. The contact tip is usually made of copper.
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 metal's ability to resist attack by other elements and chemicals. 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.
cylinder pressure gauge The device that indicates the amount of shielding gas present in the gas cylinder. The pressure gauge detects the level of gas pressure and displays it on a dial.
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 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 is the weight of material deposited in a unit of time.
direct current DC. Current that flows in one continuous direction. Gas metal arc welding (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 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 percentage of a ten-minute period that an electrical device can perform work before it must rest to prevent overheating. Welding guns are rated by their duty cycle.
electric shock The flow of electricity that occurs when a part of the human body contacts a source of electricity. Electric shock can be fatal.
electrode A device that conducts electricity in an electrical circuit. In GMAW, electrodes are wires that also serve as the filler metal.
electrode cable The path used in arc welding to conduct electricity to the electrode. The electrode cable connects the power source or wire feeder to the gun.
electrode extension The distance from the end of the contact tip to the end of the electrode. Electrode extension is also called stickout.
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 freezing welds are more easily performed 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 for GMAW is the filler metal.
flux A non-metallic material used to protect the weld puddle and solid metal from atmospheric contamination in some welding processes. GMAW does not use flux.
gas cylinder An external device used to house shielding gas. Shielding gas flows from the gas cylinder, to the gas hose, 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 joint through a welding gun. Gas metal arc welding is also referred to as MIG/MAG welding.
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. GTAW is also known as TIG welding.
globular transfer method 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 joint through a welding gun. GMAW is also referred to as MIG/MAG welding.
hardness A material's ability to resist penetration, indentation, or scratching. Hard materials tend to be very strong and resistant to wear.
inches per minute ipm. The rate at which the wire electrode feeds through the welding gun. 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.
MAG welding Metal active gas 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. MAG welding is a type of GMAW.
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 transfer The deposition of filler metal into a weld. Metal transfer may occur in four different ways in GMAW.
metal transfer The deposition of filler metal into a weld. Metal transfer may occur in three different ways in GMAW.
MIG welding Metal inert gas 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. MIG welding is another name for GMAW.
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, silvery 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 can melt 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.
semi-automatic process 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.
shielding gas A gas that protects the weld puddle and arc from reacting negatively with the atmosphere. GMAW shielding gas is supplied to the power source and flows through the welding gun.
shielding gas flowmeter The device that indicates the amount of shielding gas that flows to the weld area. A valve connected to the flowmeter controls gas flow.
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 method A type of metal transfer in which the electrode produces a short circuit and high current when it touches the workpiece. The high current level causes a violent transfer of metal, which creates the weld.
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 does not use flux, and as a result, does not have slag.
spatter Liquid metal droplets expelled from the welding process. Spatter can leave undesirable particles of metal on a workpiece surface.
stickout The distance from the end of the contact tip to the end of the electrode. Stickout is also called electrode extension.
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.
trigger A lever on the welding gun that starts and stops the welding process. For GMAW, the trigger controls the delivery of electricity, the electrode, and 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 beads 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. A weld puddle is also called a weld pool, molten pool, or molten puddle.
welders The person who performs welding. The term "welder" may also be used to refer to the power source.
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 the welder performs a weld. The different 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 wire electrode to the welding gun. The wire feeder may be built either inside the power source or 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 The component that, along with the electrode, can come in direct contact with the workpiece during welding. The work clamp is connected to the power source by the work cable and provides ground for the GMAW circuit.