GMAW Applications 301

“GMAW Applications” provides a comprehensive overview of how to perform gas metal arc welding (GMAW), important variables to consider, and how to prevent common defects. Before beginning GMAW, it is important to prepare by cleaning base metals and selecting an appropriate electrode. During GMAW, the welder controls electrode orientation and travel speed. Welders must also be aware of many variables, such as amperage, voltage, and shielding gas, and their effects. Understanding these variables helps prevent weld discontinuities and defects, including porosity, undercut, incomplete penetration, and incomplete fusion.

The information in this class prepares users to perform GMAW, an extremely common welding process. After taking this class, users will be familiar with many of the considerations and variables that go into GMAW. A good understanding of these concepts helps prevent welders from producing irregular or defective welds.

Class Details

Class Name:
GMAW Applications 301
Version:
2.0
Difficulty:
Advanced
Number of Lessons:
24
Related 1.0 Class:
GMAW Applications 220

Class Outline

  • GMAW Overview
  • Joint Preparation
  • Electrode Selection
  • Electrode Orientation
  • Travel Angles
  • Electrode Orientation: in Action
  • Travel Speed
  • GMAW Bead Types
  • Running a GMAW Bead
  • GMAW Process Review
  • Amperage and WFS
  • Current Density
  • Current Density: in Action
  • Voltage
  • Electrode Extension and CTWD
  • Shielding Gas
  • Shielding Gases and Metal Transfer
  • GMAW Variables Review
  • Discontinuities and Defects
  • Porosity
  • Undercut
  • Incomplete Penetration
  • Incomplete Fusion
  • Discontinuities Review

Objectives

  • Describe GMAW.
  • Describe common methods of preparing a joint for GMAW.
  • Describe how to select the correct electrode for a GMAW application.
  • Contrast work and travel angles.
  • Distinguish between push and drag angles.
  • Contrast work angles and travel angles.
  • Describe travel speed.
  • Describe how to run common GMAW beads.
  • Describe amperage and wire feed speed in GMAW.
  • Describe current density in GMAW.
  • Describe voltage in GMAW.
  • Describe electrode extension and CTWD.
  • Describe shielding gas in GMAW.
  • Explain the relationships between shielding gases and modes of metal transfer.
  • Distinguish between discontinuities and defects.
  • Describe porosity.
  • Describe undercut.
  • Describe incomplete penetration.
  • Describe incomplete fusion.

Job Roles

Certifications

Glossary

Vocabulary Term Definition
active A substance that reacts with other elements. Active and inert gas are both used as shielding in GMAW.
acute angle An angle that measures less than 90 degrees. Acute angles are often used for welding work angles and travel angles.
aluminum A silver-white metal that is soft, light, and thermally conductive. Aluminum is corrosion resistant, has a high strength-to-weight ratio, and has good weldability.
amperage The amount of current flowing in a circuit. Amperage is determined by wire feed speed in GMAW.
arc blow A condition that occurs when the arc does not follow its intended path from the electrode to the workpiece. Arc blow can cause undesirable weld beads.
arc length The distance that electricity must travel from the tip of the electrode to the weld puddle. Longer arcs require more voltage.
arc welding A fusion welding process that uses electricity to generate the heat needed to melt base and filler metals. Arc welding is the most commonly used welding process.
area A measurement of the amount of space contained within a flat, enclosed shape. The cross-sectional area of a wire is expressed in circular mils.
argon An 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 an automatic process, the welder is responsible for setting and controlling the specialized settings for the computer or robot.
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.
backhand technique Positioning the electrode so that it points opposite the direction of welding. The backhand technique uses a drag angle.
bead The end product of a joint that has been welded. Bead formation depends on the movement of the electrode.
brittle fracture The breaking apart of a metal that occurs without appreciable prior plastic deformation. Brittle fracture can be prevented by preheating metals.
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. Circuits for arc welding processes must be closed and allow electricity to flow easily.
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 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.
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 combines electrode extension and arc length.
current density The amount of current carried by an electrode divided by the area of the electrode's cross section. Current density determines how much current an electrode of a particular diameter can carry.
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 source that maintains a constant voltage setting while compensating for changes in amperage. CV power sources are typically used for GMAW.
defect An irregularity in the specified and expected composition of a weld that exceeds the part design's tolerances. A defect is an unacceptable discontinuity.
defects An irregularity in the specified and expected composition of a weld that exceeds the part design's tolerances. Defects are unacceptable discontinuities.
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 or in grams per minute.
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.
discontinuity 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 indicates that a weld joint was not prepared properly.
distortion The undesirable physical change in a material due to excessive temperature changes. Distortion may be caused by excessive amperage.
drag angle A travel angle that points the electrode opposite the direction of welding. Drag angles are used with the backhand technique.
ductility A metal's ability to be drawn, stretched, or formed without breaking. Ductility is unaffected when molybdenum or nickel are added to an electrode to increase strength and hardness.
electrode axis An imaginary line 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 is also called stickout.
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.
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 together at right angles to each other in a lap, T-, or corner joint. Fillet welds are the most common type of welds.
flow rate A fluid power variable that describes how much fluid is being moved and how much work is being performed. Flow rate is usually measured in gallons per minute (gpm) or liters per minute (lpm).
forehand technique Positioning the electrode so that it points in the direction of welding. The forehand technique uses a push angle.
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/MAG 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/MAG welding.
groove weld A type of weld that consists of an opening between two part surfaces, which provides space to contain weld metal. Groove welds are used for many different joints.
helium An inert gas commonly used as shielding for GMAW. Helium is much lighter than air and can escape the weld area quickly.
inches per minute ipm. The rate at which the wire electrode feeds through the welding gun. Inches per minute or millimeters per minute are used to measure wire feed speed.
incomplete fusion The lack of complete integration between a weld metal and base metal or adjoining weld beads. Incomplete fusion can create gaps, which may lead to cracks and joint failure.
incomplete penetration The failure of weld metal to extend through the full thickness of the joint. Incomplete penetration leaves an unfused area that can cause cracking.
inert A substance that does not react with other elements. Inert and active gas are both used as shielding in GMAW.
ipm inches per minute. The rate at which the wire electrode feeds through the welding gun. Ipm or mm/min. are used to measure wire feed speed.
joint preparation A variety of processes that prepare base metals before welding. Joint preparation often includes preheating, cutting, or cleaning.
leading edge The edge of the weld puddle farthest from the finished weld bead. During GMAW, the arc should always be on the puddle’s leading edge.
machining The process of removing metal to form or finish a part. Machining may use abrasives or cutting tools.
mechanical properties The properties that describe a material's ability to compress, stretch, bend, scratch, dent, or break. Mechanical properties include tensile strength and yield strength.
metal transfer The deposition of filler metal into a weld. Metal transfer may occur in several different ways in GMAW.
millimeters per minute mm/min. The rate at which the wire electrode feeds through the welding gun. Millimeters per minute and inches per minute are used to measure wire feed speed.
nonferrous metals A metal that does not contain iron. Nonferrous metals include aluminum and copper.
out-of-position Welding positions that are not classified. Out-of-position welds are often done with electrodes that have smaller diameters to prevent spillage.
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.
oxide scale A film that forms on metals such as aluminum and plain carbon steels due to cutting or heating. Oxide scale must be removed before welding.
oxygen An active gas that is sometimes used in small amounts as shielding for GMAW. Oxygen is never used alone.
parallel Two lines or axes that are equidistant from one another at all points. Parallel lines do not intersect.
penetration The depth to which the arc heat can melt the joint below the surface of the base metals. Penetration is directly affected by the amount of amperage.
perpendicular An intersection of two lines or objects at right angles to one another. Perpendicular lines create angles measuring exactly 90 degrees.
physical properties The characteristics of a material that describes how it responds to forces other than mechanical ones. Physical properties include a metal's magnetic, thermal, and electrical attributes.
plain carbon steels The most basic form of steel containing less than 3.0% alloying elements. The amount of carbon in a plain carbon steel helps determine how it should be welded.
porosity The appearance of tiny holes on a weld bead as a result of trapped gas bubbles. Excessive porosity can weaken a weld.
preheating The application of heat to a base metal immediately before welding. Preheating helps reduce hardness in the metal.
push angle A travel angle that points the electrode in the direction of welding. 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 used as the work angle when welding a flat groove joint.
robot A mechanized device that can be programmed to manipulate materials, parts, tools, and other devices to perform a variety of tasks. Robots are multifunctional and reprogrammable.
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.
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.
short circuit transfer A type of metal transfer in which the electrode produces a short circuit and high current when it touches the workpiece. Short circuit transfer's high current level causes a violent transfer of metal, which creates the weld.
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. Solutions can be used to remove oxide scale from 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 more than 10.5% chromium and exhibits excellent corrosion resistance. Stainless steels have good weldability if the right welding procedures are followed.
stickout The distance from the end of the contact tip to the end of the electrode. Stickout is also called electrode extension.
stringer beads A weld bead formed by moving the electrode in a straight line along the joint. Stringer beads have good wash-in at the toes of the weld.
stub out The condition in which the electrode contacts the base metals before it has melted. Stub out occurs when the WFS is too fast for the set voltage to melt it.
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 or pascals.
tolerances An 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 towards or against direction of welding.
turbulence A disturbance in the even flow of shielding gas to the welding area that causes gas to swirl and mix with outside air. Turbulence is often the result of excessive shielding gas.
turbulence A disturbance in the even flow of shielding gas to the welding area that causes the gas to swirl and mix with outside air. Turbulence is often the result of excessive shielding gas.
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.
voltage The electrical force or pressure that causes current to flow in a circuit. Voltage and arc length are directly proportional in GMAW.
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.
weave beads A weld bead formed by moving the electrode along the joint in a weaving motion. Weave beads are often used when welding out-of-position.
weld axis An imaginary line through the center of the weld. The weld axis forms one side of the travel angle.
weld backing A strip of metal located on the side opposite of the weld. Weld backing protects the back of the weld from atmospheric contamination and provides a surface for depositing the first layer of metal.
weld pass One progression of welding across a joint. Weld passes produce weld beads.
weld toe The point at which the weld face and the base metal meet. Weld toes can experience cracking and undercut.
welding position The position in which the welder performs a weld. The different welding positions include overhead, vertical, flat, and horizontal-position welding.
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 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 perpendicular to the weld axis. The work angle is used to center the weld bead on a given application.
yield strength A metal's ability to resist gradual progressive force without permanent deformation. Yield strength is usually expressed in pounds per square inch or pascals.