Welding Definitions
Welding requires fusion or melting of the base metals being joined. It can be with or without the use of
filler metals and with or without the use of pressure. The most common welding processes that use an
electric arc in generating the heat are the generic names stick, mig, flux-core, tig and subarc
Brazing uses filler metals that melt above 840°F (450°C) but below the melting point of the base metals
to be joined. The base metals are heated around the joint until the filler metal melts and flows by
capillary attraction into the parallel joint clearance between the base metals. A permanent bond is the
result. Silver brazing is a commonly used term if brazing filler metals contain any percentage of
silver. Brazing fluxes are used to prevent oxidation of the base metals, except for copper to copper
joints that may be brazed with copper/phosphorous filler metals.
Soldering uses filler metals that melt below 840°F (450°C) but below the melting point of the base
metals to be joined. The base metals are heated around the joint until the filler metal melts and flows
by capillary attraction into the parallel joint clearance between the base metals. A permanent bond is
the result. Silver soldering is a correct term if the soldering filler metals contain any percentage of silver.
Soldering fluxes are used to prevent oxidation of the base metals. Soldering is not permitted by the
ASME codes
SMAW- Shielded Metal Arc Welding (Stick welding, arc welding)
GTAW – Tungsten Inert Gas (TIG)
GMAW – Gas Metal Arc Welding (MIG)
OAW- Oxy Acetylene Welding
Oxy-Fuel Cutting Terms
Rapid Oxidation- occurs when metals are heated to their “kindling” point and a jet stream of high
pressure oxygen is directed onto the hot spot.
Drag- the amount the bottom of the kerf lined lags behind the top of the kerf line
Kerf- the width of the cut produced during a cutting process
Kerf lines- visible lines when viewing the cross section of a cut
Torch inclination- the angle at which a cutting torch is held relative to the direction of travel
Neutral flame- The neutral flame has a one-to-one ratio of acetylene and oxygen. It obtains additional
oxygen from the air and provides complete combustion. It is generally preferred for welding. The neutral
flame has a clear, well-defined, or luminous cone indicating that combustion is complete.
Oxidizing flame- Oxidizing welding flames are produced when slightly more than one volume of oxygen
is mixed with one volume of acetylene.
Carburizing flame – a carburizing flame is produced when there is an excess of acetylene gas for the
amount of oxygen being consumed in an oxy-acetylene mixture, producing an acetylene-rich gas. The
carburizing flame may add carbon to the weld metal.
Flashback - Flashback is the combustion of a flame mixture that can occur within your gas management
system (torch, gas lines). This can travel back through the line of your gas management system to you
gas source if a flash back arrestors is not in line. Several factors can cause flash back, including failing to
purge line properly, using improper pressure, leaks in your gas management system and improper
system operation.
Flashback arrestor: A flashback arrestor shuts off gas flow and extinguishes the flame before it can
reach your gas source. Flashback arrestors should be used on your fuel line as well as the oxygen line.
Check Valve- A check valve is a device that is designed to prevent the unintentional backflow of gases.
Non-Ferrous Metals – Metals that will not burn progressively (rapid oxidation), such as copper, brass,
bronze, nickel, aluminum.
Metal Fume Fever- flu like symptoms caused by inhaling fumes of certain metal oxides (galvanized steel,
notably).
SMAW Terms:
Alternating Current (AC) - Current that flows in one direction during any half cycle, then reverses and
flows in the opposite direction during the next half cycle. The rate at which this alternating occurs is
measured as cycles per second (60 cycle AC is common).
Amperage (heat setting) - the strength of a current of electricity measured in amperes. This is the
electrical property that causes the electrode, the parent metal, or both, to be melted. Amperage in arc
welding is responsible for the following:
-
-
Metal deposition rate: If the amperage is increased, there is a proportionate increase in the
metal deposition rate of the electrode. The opposite is true when the amperage is
decreased.
Penetration: Increasing the amperage causes the arc to penetrate or burn deeper into the
parent metal and lowering the amperage causes a decrease in penetration.
Arc- In welding, an arc is created when there is enough amperage and voltage available at the electrode
tip to overcome the natural resistance to the flow of electricity. This resistance is usually caused by the
air gap between the electrode and the work.
Arc Blow- A condition encountered when DC welding that causes the arc to flare uncontrollably from
side to side. Arc blow is caused by magnetic fields being set up around the work. This is due to current
travelling in the same direction for a prolonged period of time. Arc blow is not a problem when welding
with AC because the reversals in the direction of current flow prevent the accumulation of magnetic
fields being set up around the work.
Arc Voltage- is the voltage output of the machine while welding is being done. It is the force that
maintains the arc between the electrode and the work-piece.
Buzz Box- This term is often used to describe an AC transformer type welding machine because of the
typical buzzing sound made when welding with them.
Circuit- Any system of conductors that is designed to complete the path of an electric current is called a
circuit. Current flows in the conductor when voltage is applied to it.
Core- The core is the magnetic link between the primary and the secondary coils of a welding
transformer. The core can be moved into or out of the coil as a method of current control. This type of
current control is called movable shunt. A movable shunt means that the core can be moved into
different positions thus influencing the magnetic link between the primary and secondary coils. The
shunt is usually moved mechanically by an external hand crank that controls its movement on a slide
assembly. This allows for any setting between minimum and maximum of the machine’s output
potential.
Coil- A coil is usually made of insulated copper wire and is designed to have a certain number of turns of
wire. The coil can be moved over or away from the core as a method of adjusting the welding current.
Conductor- A material or substance that is capable of transmitting electricity. Most metals are good
conductors because they offer little resistance to current flow.
Current Flow- is the movement of electrons in an electrical circuit and is measured in amperes.
Cycle- A cycle is one complete rotation of the sine wave pattern. The sine wave begins at zero, climbs to
its maximum positive value, then drops back through zero, and becomes negative. It reaches its
maximum negative value, then proceeds to zero again. This movement is one full cycle of AC current.
With 60-cycle AC, the current changes direction 120 times per second.
Diode- A diode is a one way electrical valve. It allows current to flow in one direction only. In a welding
machine, a diode changes AC to DC (AC-DC rectifier welding machines).
Direct Current (DC) - Electric current that flows in one direction only and has either a positive or
negative value. There is no change of direction as there is with AC. The electron theory states that
current flows from negative to positive since that is the direction that electrons flow in.
Duty Cycle- All welding machines are rated based on maximum output over a ten-minute time period.
This rating is expressed as a percentage of time that the machine can run at maximum rated output
current before it must be allowed to cool down. Exceeding duty cycle ratings can damage or ruin a
welding power source.
Electron- electrons are negatively charged particles that move through a conductor when current is
flowing. Because electrons carry a negative charge, electron theory states that they are attracted by
positively charged bodies and therefore move from negative to positive.
Frequency- Frequency relates to the speed at which alternating current changes its direction of flow. A
high frequency current is used in some welding processes to allow for non-touch arc starting or to
provide a path for the weld current to follow.
Generator- a generator is a machine used to create electricity of sufficient volume for welding. A shaft,
with an electrical conductor, is rotated perpendicular to a magnetic field. Generators produce either AC
or DC depending on their internal configuration.
Inductance- Inductance is the ability of a conductor to transfer current onto a neighboring body without
physical contact. For example, in a transformer welder, current is brought to the primary coil where a
magnetic field is created due to the iron core. The magnetic field induces current flow into the
secondary coil without physical contact.
Insulator- An insulator is any material that does not allow current to flow through it.
Inverter- an inverter is a device that changes DC to AC. In welding machines, inverters are also used to
increase the frequency of AC.
Magnetic Field- A magnetic field is created when current is forced to flow through a coil that is wrapped
around an iron core. The strength of the magnetic field determines the power capacity of welding
machines.
Open Circuit Voltage- When a welding machine is turned on, but no current is flowing in the circuit, the
machine has open circuit voltage at the output terminals. Once voltage is impressed upon the circuit,
current will flow immediately with the circuit is completed (striking an arc).
Primary Coil- The primary coil on a welding transformer takes power directly from the AC input power
line. The current flowing into the primary coil causes a magnetic field to form.
Rectifier- A rectifier is a device that changes AC to DC by allowing current to flow in one direction only.
Relay- A relay is a switch that is operated by an electro-mechanical force rather than by the application
of external mechanical force. Inverter type welding machines use high-speed relays such as transistors
or thyristors. Other types of relays used in gas-shielded welding processes are solenoids or contactors.
Resistance- Resistance is the property of an electrical conductor to oppose the flow of current, causing
electrical energy to be turned into heat. Resistance is measured in ohms and is calculated by dividing
voltage by amperage. The air gap offers resistance to current flow. It is this resistance to the flow of
current across the arc that creates the heat needed for welding.
Reverse Polarity- In a SMAW DC welding circuit, reverse polarity occurs when the electrode cable is
connected to the positive terminal of the welding machine, thus making the electrode positive, in
relation to the work-piece.
Straight Polarity- In a SMAW DC welding circuit, straight polarity occurs when the electrode cable is
connected to the negative terminal of the welding machine, thus making the electrode negative, in
relation to the work-piece.
Secondary Coil- the secondary coil is located on the main transformer core of an AC welding machine.
The energy created in the magnetic field by the primary coil is induced into the secondary coil.
Switch- A switch is a device having points of contact that can complete a circuit. When the contact
points are open, no current can flow. When the contact points are closed, current can flow because the
circuit is complete.
Thyristor- A thyristor, or silicon-controlled rectifier, is a diode variation with a trigger called a gate. It is
non-conducting until a positive electrical signal is applied to the gate.
Voltage- Voltage is the electrical pressure or force that causes current to flow in a conductor, or to cross
a gap, as occurs in welding. Voltage is often called EMF, which stands for electromotive force. Voltage in
arc welding is responsible for the following:
-
Starting the arc
Maintaining the arc
Puddle fluidity and puddle flow (the amount of voltage is determined by the type and size of
electrode being used)
Volt-Amp Curves- Volt-amp curves are graphical illustrations that indicate the output of a welding
machine. Voltage is plotted on the vertical axis and amperage on the horizontal axis. Machines that
produce a steep or drooping type of volt-amp curve (constant current) are used for SMAW or GTAW.
Machines that produce a fairly flat volt-amp curve (constant voltage) are used for most of wire feed
welding processes.
Welding machine- a welding machine is an apparatus that is specifically designed to deliver voltage and
amperage of sufficient capacity for welding.