Advanced GMAW Applications 302

AC aluminum pulse welding

An advanced GMAW process that uses alternating current (AC) and a pulse waveform to weld aluminum. AC aluminum pulse welding has a lower heat input because of the alternating polarity of AC.

active gas

A substance that reacts with other elements. Active gases used as shielding gas for GMAW include carbon dioxide and oxygen.

adaptive control

A type of waveform control that monitors the arc and increases or decreases current in response to changes in the arc. Adaptive control uses a feedback loop between a sensor lead and the power source.

alloy steels

A steel that contains small percentages of purposely added materials that change its properties. Alloy steels commonly include chromium, manganese, molybdenum, and nickel.

alloys

A material consisting of a mixture of two or more elements, at least one of which must be a metal. Alloys combine the beneficial properties of the mixed elements.

alternating current

AC. Electricity that switches direction at regularly recurring intervals of time. Alternating current is typically not used for GMAW processes.

aluminum

A lightweight, highly conductive, nonferrous, silvery metal. Aluminum has good weldability, but certain factors, such as its melting point, can make the process difficult.

aluminum oxide

A thin film that forms on the surface of aluminum when it reacts with oxygen in the air. Aluminum oxide is often removed before welding to improve weld quality.

amperage

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

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 pool. Arc length is directly proportional to voltage in GMAW.

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 robot controls both the welding equipment and the welding variables. In an automatic process, the welder is responsible for setting and controlling the specialized settings for the computer or robot.

automation

The use of self-regulated equipment, processes, or systems that perform manufacturing operations with limited human intervention. Automation methods include robotic and computer numerical control (CNC) processes, but robotic automation is most common in welding applications.

axes

An imaginary line that is used to define the locations of objects in three-dimensional space. Axes are used to track locations and movements of objects in the Cartesian coordinate system.

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 pool. Axial spray transfer creates a stable arc and little spatter.

background current

The lower nominal amperage of metal transfer with waveform control. Background current maintains the arc.

backing strips

A strip of metal located on the side opposite of the weld. Backing strips protect the back of the weld from atmospheric contamination and provide a surface for depositing the first layer of metal.

burnback time

An end option that controls how long welding output continues after the wire stops feeding. Burnback time prevents the wire from sticking to the pool and prepares the wire to start the next arc.

burnthrough

A discontinuity that occurs when weld metal from one side of a joint melts through to the other side. Burnthrough can leave an open hole in the joint, which must then be ground down and re-welded.

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.

chromium

A shiny, gray nonferrous metal with high corrosion resistance. Chromium is a common alloying element used in metals such as stainless steel.

chromium carbide

A solid, gray metal compound formed by chromium and carbon. Chromium carbide formation can weaken corrosion resistance in stainless steel.

chromium oxide

A protective film that forms on the surface of stainless steel when chromium reacts with oxygen. Chromium oxide helps prevent corrosion.

CO₂

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

coefficient of thermal expansion

A value that indicates the degree to which a material increases in size as temperature increases. Higher coefficients of thermal expansion can lead to distortion in metals.

constant current

CC. A power supply in which the amperage is set at a fairly fixed level and varies only slightly with changes in voltage. Constant current power sources are often used in gas tungsten arc welding (GMAW) and shielded metal arc welding (SMAW).

constant voltage

CV. A power supply in which the voltage is set at a fixed level and the amperage varies to maintain 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

An electrode that conducts electricity to the arc and melts into the weld as 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.

controller

The main device that processes information and communicates instructions to a robot. A controller operates the entire robotic system.

coordinate system

A system that uses axes to describe the location of an object in three-dimensional space. A coordinate system expresses the location of any point as the distance from it to the origin, or the fixed intersection of axes.

corrosion resistance

The ability of a material to resist deterioration and chemical breakdown due to surface exposure in a particular environment. Corrosion resistance is an important physical property of finished welds.

current

The flow of electricity through a circuit. Current strength is called amperage and is measured in amperes (A), or amps.

CV

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

DCEP

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

deposition rates

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

direct current

DC. Electricity that flows in one continuous direction. Direct current is typically used in GMAW.

direct current electrode positive

DCEP. Electricity 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.

distortion

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

downtime

A period of time during which production stops, often due to mechanical failure or maintenance needs. Downtime reduces the efficiency of a manufacturing operation and should always be limited as much as possible.

drive rolls

A wheel that directs the wire electrode as it moves through a wire feeder. Drive rolls are specially designed for various types and sizes of wires.

ductility

A material's ability to be drawn, stretched, or formed without breaking. Ductility is more common in softer metals.

duty cycle

The percentage of a ten-minute period during which an electrical device can perform work before it must rest to prevent overheating. Power sources are rated by their duty cycle.

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 in a welding gun that surrounds the electrode and supports it from the wire feeder to the contact tip. Electrode liners are often used for aluminum and can be either permanent or interchangeable.

electrode negative

EN. The stage of the alternating current cycle during which electricity flows from the negative electrode to the positive workpiece. The electrode negative stage concentrates heat in the workpiece and improves penetration.

electrode positive

EP. The stage of the alternating current cycle during which electricity flows from the negative workpiece to the positive electrode. The electrode positive stage improves fusion and provides a cleaning effect.

end effector

A device attached to the end of a robotic arm that allows it to interact with a part, component, or material. An end effector, also known as an end of arm tool, may be a gripper, a welding gun, or another tool that performs work.

end option

Various settings used to control variables, such as shielding gas and current, after welding output stops or the welding gun trigger has been released. End options, such as postflow time and burnback time, help protect the weld pool, prevent electrode adhesion, and produce quality welds.

ethernet

A common local area network standard that is the most popular type of network for office communication. Ethernet cables can be used to connect robotic welding equipment for communication and internet connectivity.

feedback loop

A method of monitoring and controlling a process by gathering information and sending signals to the power source. In welding, feedback loops provide information that allows the power source to automatically adjust the waveform.

ferrous

A metal that contains iron. Ferrous metals are the most common type of welded materials.

fixed automation

The use of mechanized devices to automate a process for one particular task. Fixed, or hard, automation is capable of only linear movements.

fixture

A customizable, modular workholding device created by configuring locators, supports, and clamps. Fixtures are used to hold and often move workpieces or welding tools in automated welding applications.

flat-position

Welding that is performed on the upper side of a joint. During flat-position welding, the face of the weld is horizontal.

flexible automation

The use of reprogrammable mechanized devices to automate a task. Flexible, or soft, automation includes robotic processes.

frequency

A measurement of the number of times a waveform repeats in one second. Frequency is measured in Hertz (Hz).

frost line

A clean border around an aluminum weld bead where the welding current has blasted off aluminum oxide. Frost lines indicate that a bead was welded properly.

gantry

A bridge-like overhead structure with a platform for supporting equipment. Gantries may be used to move robotic arms for welding.

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 metal inert gas (MIG) welding or metal active gas (MAG) welding, although these terms are nonstandard in the United States.

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 pool.

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 metal inert gas (MIG) welding or metal active gas (MAG) welding, although these terms are nonstandard in the United States.

hard automation

The use of mechanized devices to automate a process for one particular task. Hard, or fixed, automation is capable of only linear movements.

heat dissipation

The loss or transfer of heat. Heat dissipation can help control thermal expansion.

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.

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.

hydrogen

H. A colorless, odorless gas that is the most abundant element on the planet. Hydrogen can cause weld metal to crack and should not be used with aluminum.

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.

inert gas

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

inverters

A component in a welding machine that can run in constant current or constant voltage modes with variable frequencies, amplitudes, and AC/DC output. Inverter power sources are energy efficient.

joints

The location at which two or more parts of a robotic arm make contact. Joints allow robots to move in different directions along the axes of a coordinate system.

lead-through programming

An online robot programming method during which the programmer physically moves a robot through the different positions required for an operation. Lead-through programming, also known as hand guiding, is a less accurate type of online programming.

machine interface

The input device on a machine that operators use to interact with the machine's control system. The machine interface may be complex, such as a computer touchscreen, or simple, such as a control panel with just a few buttons.

metal transfer

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

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 or how many millimeters of a joint are welded in one minute. The units millimeters per minute and inches per minute are used to measure wire feed speed and travel speed.

nonferrous

A metal that does not contain a significant amount of iron. Common nonferrous metals include aluminum, titanium, copper, and nickel.

nylon

A semicrystalline thermoplastic that gains strength when the fibers are stretched. Nylon can be used as an electrode liner.

offline programming

A method of creating instructions for a robot during which the programmer uses simulation software to write the program and then uploads it to the controller. Offline programming can involve writing instructions manually but using simulation software is more common.

online programming

A method of manually creating instructions for a robot during which the programmer interacts with a robot in real time. Online programming methods include teach pendant programming and lead-through programming.

out-of-position

Welding that takes place is any position besides the flat or horizontal position. Out-of-position welding includes welding in the vertical and overhead positions.

overhead

Welding that is performed from the underside of a joint. Overhead welding requires extra safety precautions.

overshoot

The part of a waveform during which current increases above peak current. Overshoot increases pinching forces.

oxygen

O. A colorless, odorless, tasteless active gas that naturally exists in the atmosphere. A small amount of oxygen is sometimes used as shielding gas.

peak current

The higher nominal amperage of metal transfer with waveform control. Peak current helps form and pinch the molten metal.

personal protective equipment

PPE. Any clothing or device used to minimize exposure to hazards and prevent injury. Common personal protective equipment includes safety glasses, welding helmets, and hearing protection.

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.

pinch current

The part of a waveform during which current increases in order to squeeze or pinch a molten droplet off the electrode. Pinch current forms metal droplets during Surface Tension Transfer.

plasma force

The force of an electromagnetic field generated by the surge of current during peak current. Plasma force, sometimes called pinch effect, helps detach a controlled metal droplet and propel it across the weld pool.

polarity

The state of having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.

positioner

The component that holds and moves the workpiece fixture in a robotic welding system. Positioners ensure robots can access all necessary parts of the workpiece.

postflow time

An end option that controls the duration of gas shielding after welding stops. Postflow time determines how long gas flows after the welding output ends.

precision pulsed transfer

An advanced type of GMAW metal transfer in which metal droplets form on the electrode one at a time at a fixed frequency. Precision pulsed transfer provides more control and consistent transfer than traditional pulse spray transfer.

preflow time

A start option that controls the duration of gas shielding before welding begins. Preflow time determines how long gas flows after the trigger is pulled but before the wire begins feeding and the arc is initiated.

pulsed spray transfer

GMAW-P. An advanced type of GMAW metal transfer that alternates rapidly between different current levels to precisely form metal droplets. During pulsed spray transfer, one droplet of metal is deposited during each cycle.

push-pull wire feed systems

A wire drive system that uses one motor to push the electrode out of the feeder and another motor to pull the electrode. Push-pull wire feed systems are often used when welding aluminum.

radiation

Energy emitted in the form of particles or waves. Radiation exposure for prolonged periods of time can cause serious health problems.

ramp-up

The part of a waveform during which current increases. The speed of ramp-up affects the stiffness of the arc.

robot body

The casing and parts that provide structural support for the other components in the robot. The body shape of a robot varies greatly depending on the type of robot.

robot manipulator

An automated mechanism with joints that allow movement along different axes. Robot manipulators are also known as robotic arms.

robotic arm

An automated mechanism with joints that allow movement along different axes. Robotic arms are also known as robot manipulators.

robotic welding

type of automated welding that uses robots to move the welding gun or torch. Robotic welding is a form of flexible automation often used in automobile production.

robots

A multifunctional device that uses highly adaptable programmed motions to perform various processes. Robots are commonly used to automate welding operations.

run-in WFS

A start option that controls wire feed speed at the beginning of welding. Run-in WFS determines the speed of the wire from when the trigger is pulled to when the arc is established.

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.

sensitization

A reduction in corrosion resistance in the heat-affected zone due to carbide formation and precipitation. Sensitization is caused by overheating stainless steel.

sensor lead

A welding sensor attached to a workpiece and connected to the power source. Sensor leads are used in adaptive control to monitor the arc and welding parameters.

sensors

A device that detects a change in a physical stimulus and turns it into a signal that can be measured or recorded. Sensors allow robots and other devices to interact with their environment and monitor operations.

shielding gas

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

short circuit

A condition 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

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.

simulation software

A program that allows the user to observe an operation virtually without actually performing that operation. Simulation software is commonly used for robot programming.

smut

A black soot made of aluminum and manganese oxide that may form on aluminum base metals. Smut is expected in some locations, but excess smut indicates a problem.

soft automation

The use of reprogrammable mechanized devices to automate a task. Soft, or flexible, automation includes robotic processes.

spatter

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

spool guns

A welding gun with an integrated wire drive system that feeds wire electrode from self-contained spools mounted on the gun. Spool guns are mainly used for smaller diameter, softer wires, such as aluminum.

stainless steel

A type of steel that contains 10.5-30% chromium and exhibits excellent hardness and corrosion resistance. Stainless steel can be welded with many different welding processes.

start option

Any setting used to control different variables, such as WFS and shielding gas, before the arc is initiated. Start options include preflow time and run-in WFS.

stepoff

The part of a waveform during which current goes from tail-out to background current. Stepoff is optional and reduces spatter.

surface tension

A property of a liquid that causes it to minimize its surface area by pulling inward on itself. Surface tension enables compact metal droplets that spread evenly across the weld pool with reduced spatter.

Surface Tension Transfer

STT. An advanced type of GMAW metal transfer that uses a specialized form of short circuit transfer and adaptive control. Surface Tension Transfer relaxes the surface tension of the weld pool to improve transfer.

synergic control

A feature of some advanced power sources that calibrates all welding parameters in response to one setting. Synergic control devices allow the welder to set wire feed speed (WFS) and then adjust all other variables accordingly using the trim value.

tail-out

The part of a waveform during which current decreases. The speed of tail-out affects average current and pool fluidity.

teach pendant

A hand-held machine interface that can be used to program a robot or control its movements. Teach pendants are used in online programming.

teach pendant programming

An online robot programming method during which the programmer uses a machine interface to move a robot through the different positions required for an operation. Teach pendant programming is more accurate than lead-through programming.

Teflon

A fluorocarbon solid that may be used to coat surfaces. Teflon can be used as an electrode liner.

thermal conductivity

The ability of a material to act as a medium for conveying heat. Materials with superior thermal conductivity include aluminum and copper.

travel speeds

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.

trim

A value used to represent and control all of the welding variables that affect arc length in synergic processes. Trim is a value between 0.5 and 1.5, but 1.0 is the standard setting.

ultraviolet light

UV light. Light that is not visible to the naked eye because it consists of wavelengths shorter than those of visible light. Ultraviolet light is harmful and can damage vision and burn skin.

vertical

The welding position in which welding is done on a vertical surface, moving up or down. Vertical welding is more difficult than flat- or horizontal-position welding.

voltage

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

waveform

A visual representation of how current behaves over time. A waveform represent cycles, or the time it takes for current to flow and change levels to form and deposit molten metal.

waveform control

A feature of some advanced power sources that increases or decreases current to achieve different arc and weld characteristics. Waveform control helps transfer metal cleanly and minimize spatter.

weld backing

Protection on one or both sides of a joint that prevents weld metal from escaping or becoming contaminated. Weld backing may be in the form of backing strips or inert gas.

weld bead

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

weld pool

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

weld toe

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

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 output

The current and voltage provided by a welding machine to create the arc necessary for joining metals. Welding output controls metal deposition and penetration.

wet-in

The process of a liquid filler metal spreading across and adhering to a solid base metal surface in a thin continuous layer. Wet-in provides even metal distribution and can decrease spatter.

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 drive system

The device that feeds a supply of wire electrode to the welding gun. Wire drive systems are typically either built inside or set beside the power source.

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.

workcell

The area composed of a robot and any external devices or equipment that interacts with the robot, including additional robots. Robotic workcells can include multiple robots controlled by a single interface.