The Welder's Lexicon
Every trade has its language. Welding has more than most. This glossary covers 123 essential welding terms — from fundamental processes and joint types to advanced certifications and quality standards. Whether you are running your first bead or prepping for a CWI exam, this is your reference.
A
Adaptive Welding
Adaptive welding refers to automated welding systems that use real-time sensing (laser vision, arc voltage sensing, through-arc seam tracking, or camera syst...
Aluminum
Aluminum is a lightweight, corrosion-resistant metal widely used in aerospace, automotive, marine, and consumer products. Welding aluminum presents unique ch...
Amperage
Amperage (current, measured in amps) is the primary control for heat input in welding. Higher amperage means more heat into the workpiece, deeper penetration...
Arc Blow
Arc blow is the deflection of the welding arc from its intended path by magnetic fields in the workpiece. The arc wanders, flickers, or pushes to one side, c...
Arc Force and Hot Start
Arc force (also called dig or arc control) is an adjustable feature on stick welding machines that automatically increases amperage when the arc length short...
Arc Length
Arc length is the distance between the tip of the electrode and the surface of the weld pool. It is one of the most important variables a welder controls in ...
Argon
Argon is an inert (chemically non-reactive) gas that is the foundation of most welding shielding gas applications. It is the exclusive shielding gas for TIG ...
ASME
ASME (American Society of Mechanical Engineers) publishes the Boiler and Pressure Vessel Code (BPVC), which governs the design, fabrication, and inspection o...
Auto-Darkening Helmet
An auto-darkening helmet is a welding helmet with an electronically controlled lens that automatically transitions from a light shade (typically shade 3-4) t...
AWS (American Welding Society)
AWS (American Welding Society) is the primary standards-developing organization for the welding industry in the United States. Founded in 1919, AWS publishes...
AWS D1.1
AWS D1.1 (Structural Welding Code — Steel) is the most widely referenced welding code in the United States for structural steel construction. It covers the w...
B
Back Purge
Back purging is the practice of flooding the backside (root side) of a weld joint with inert gas — typically argon — to prevent oxidation of the root pass du...
Backing Strip
A backing strip (also called a backing bar) is a strip of material placed behind a weld joint to support the root pass, contain the weld pool, and enable com...
Bevel
A bevel is an angled cut on the edge of a plate or pipe that creates a groove when two beveled pieces are placed together for welding. Beveling is the most c...
Brazing
Brazing is a metal-joining process that uses a filler metal with a melting point above 840°F (450°C) but below the melting point of the base metals being joi...
Burn-Through
Burn-through occurs when excessive heat melts completely through the base metal, leaving a hole or severely thinned area in the workpiece. It is the most com...
Butt Joint
A butt joint is a welding joint formed when two pieces of metal are placed edge to edge in the same plane and welded along the seam. It is the most fundament...
C
Cap Pass
The cap pass (also called the cover pass or final pass) is the last weld bead deposited on a groove weld — the visible surface that represents the finished w...
Cast Iron
Cast iron is a family of iron-carbon alloys with carbon content typically above 2%, making it extremely hard and brittle compared to steel. Welding cast iron...
Chromoly
Chromoly (chromium-molybdenum steel, most commonly 4130) is a high-strength alloy steel used in applications where a superior strength-to-weight ratio is nee...
CO2 Shielding Gas
CO2 (carbon dioxide) is an active (reactive) shielding gas used in MIG welding, primarily on mild steel. Unlike inert argon, CO2 is a molecule that dissociat...
Cold Lap
Cold lap (also called overlap or rollover) occurs when weld metal flows over the base metal surface without fusing to it. The weld bead sits on top of the ba...
Contact Tip
A contact tip is the small copper or copper-alloy tube at the business end of a MIG gun through which the welding wire passes. It transfers welding current t...
Corner Joint
A corner joint is formed when two pieces of metal meet at an angle (typically 90°) to form an L shape. It is common in box structures, frames, enclosures, an...
Crater Crack
A crater crack is a crack that forms in the depression (crater) left at the end of a weld bead when the arc is extinguished. As the small remaining pool soli...
CWI (Certified Welding Inspector)
CWI (Certified Welding Inspector) is the premier welding inspection credential administered by the American Welding Society. A CWI is qualified to inspect we...
D
Destructive Testing
Destructive testing (DT) evaluates weld quality by physically testing specimens to failure. The test piece is intentionally destroyed to measure mechanical p...
Drive Roll
Drive rolls are the grooved rollers inside a wire feeder that grip and push the welding wire from the spool through the liner and out the contact tip. They a...
Duty Cycle
Duty cycle is the percentage of a 10-minute period that a welding machine can operate at a given amperage before it must cool down to prevent overheating. A ...
E
E6010
E6010 is a cellulosic-coated stick electrode known for deep penetration, a driving arc, and excellent performance on dirty, rusty, or painted steel. It is th...
E7018
E7018 is the most widely specified stick welding electrode in structural steel fabrication. It is a low-hydrogen, basic-coated rod that produces strong, duct...
Edge Joint
An edge joint is formed when two pieces of metal are placed side by side with their edges aligned and welded along the shared edge. It is the least common of...
Electrode
An electrode in welding is a conductor through which welding current flows to create and maintain the arc. Electrodes are classified as consumable (they melt...
Electrode Holder
An electrode holder (commonly called a stinger) is the clamping device used in stick welding (SMAW) to grip the electrode and conduct welding current to it. ...
ER308L
ER308L is the standard filler metal for welding 304 and 304L stainless steel — the most common stainless alloy encountered in fabrication. The "L" designates...
ER70S-6
ER70S-6 is the most commonly used solid MIG wire for welding mild and low-carbon steel. It is also widely used as TIG filler rod. The designation breaks down...
F
FCAW
FCAW (Flux-Cored Arc Welding) is the AWS designation for flux-core welding. It uses a continuously fed tubular electrode with flux inside, combining the spee...
Filler Metal
Filler metal is the general term for any metal added to a weld joint to fill the gap and create the weld deposit. Filler metal comes in many forms depending ...
Filler Rod
A filler rod is a length of bare metal wire manually fed into the weld pool during TIG welding and oxy-fuel welding to add material to the joint. Unlike MIG ...
Fillet Weld
A fillet weld is a triangular cross-section weld deposited in the internal corner formed by two surfaces meeting at an angle — most commonly at a tee joint o...
Fire Blanket
A welding fire blanket (also called a welding blanket or spatter blanket) is a heat-resistant fabric used to protect surrounding surfaces, equipment, and mat...
Flash Burn
Flash burn (arc eye, welder's flash, or photokeratitis) is a painful eye injury caused by exposure to the intense ultraviolet radiation produced by a welding...
Flat Position
Flat position (designated 1G for groove welds and 1F for fillet welds) is the welding position where the weld face is approximately horizontal and the weld i...
Flux
Flux is a chemical cleaning agent used in welding, brazing, and soldering to remove oxides from metal surfaces, prevent new oxidation during heating, and imp...
Flux-Core Welding
Flux-core welding (FCAW — Flux-Cored Arc Welding) is a wire-feed process similar to MIG but using a tubular wire filled with flux instead of a solid wire. Th...
Foot Pedal
A foot pedal is a variable amperage control used primarily in TIG welding that allows the welder to adjust heat input in real time by pressing the pedal, muc...
Fume Extractor
A fume extractor is a ventilation device that captures welding fumes at or near the source and filters them before exhausting clean air. Fume extraction is a...
G
Gas Lens
A gas lens is a TIG torch component that replaces the standard collet body and uses a series of fine mesh screens to produce a smooth, laminar flow of shield...
Gas Regulator
A gas regulator reduces the high pressure inside a shielding gas cylinder (typically 2,000-3,000 PSI) to a usable working pressure and flow rate for welding....
GMAW
GMAW (Gas Metal Arc Welding) is the official AWS designation for the process commonly known as MIG welding. The name describes exactly what happens: gas (shi...
Groove Weld
A groove weld is a weld deposited in a groove (channel) between two pieces of metal, typically formed by beveling one or both edges. Groove welds provide com...
Ground Clamp
A ground clamp (formally called a work clamp or work lead connection) attaches the work cable from the welding machine to the workpiece, completing the elect...
GTAW
GTAW (Gas Tungsten Arc Welding) is the formal AWS designation for TIG welding. The name breaks down as: gas (argon/helium shielding) + tungsten (non-consumab...
H
Heat-Affected Zone
The heat-affected zone (HAZ) is the area of base metal adjacent to the weld that is not melted but has had its microstructure and mechanical properties alter...
Helium
Helium is an inert shielding gas used in welding, primarily in blends with argon, to increase arc energy and heat input. Helium has higher thermal conductivi...
Horizontal Position
Horizontal position (2G for groove welds, 2F for fillet welds) is welding on a vertical surface where the weld axis runs horizontally. The weld pool tends to...
Hydrogen Cracking
Hydrogen cracking (also called cold cracking, delayed cracking, or hydrogen-induced cracking — HIC) is one of the most serious and insidious weld defects. It...
I
Interpass Temperature
Interpass temperature is the temperature of the weld zone measured before depositing the next weld pass in a multi-pass joint. It is specified as both a mini...
Inverter Welder
An inverter welder uses high-frequency electronic switching (typically IGBT or MOSFET transistors) to convert incoming power into welding output. This techno...
L
Lack of Fusion
Lack of fusion (LOF, also called incomplete fusion) occurs when the weld metal fails to properly fuse with the base metal or with a previous weld pass. It cr...
Lap Joint
A lap joint is formed when two pieces of metal overlap each other and are welded along the edge of the overlapping piece. It is one of the easiest joints to ...
M
MIG Welding
MIG welding (Metal Inert Gas) is a semi-automatic arc welding process that feeds a continuous solid wire electrode through a welding gun into the joint while...
Mild Steel
Mild steel (also called low-carbon steel or A36 steel) is the most commonly welded metal in the world. It contains less than 0.30% carbon, making it highly w...
Multi-Process Welder
A multi-process welder is a single welding machine capable of performing two or more welding processes — typically MIG, TIG, stick, and sometimes flux-core. ...
N
Non-Destructive Testing
Non-destructive testing (NDT, also called non-destructive examination — NDE) encompasses inspection methods that evaluate weld quality without damaging the w...
Nozzle
A nozzle (also called a gas nozzle or shroud) is the cylindrical component on the end of a MIG gun that directs shielding gas around the arc and weld pool. I...
O
Overhead Position
Overhead position (4G for groove welds, 4F for fillet welds) is the most challenging welding position — the welder works beneath the joint, depositing weld m...
Oxy-Fuel Cutting
Oxy-fuel cutting (also called oxy-acetylene cutting or torch cutting) is a thermal cutting process that uses a fuel gas flame to preheat steel to its kindlin...
P
Passive Lens Helmet
A passive lens helmet (also called a fixed shade or traditional helmet) uses a static filter lens at a fixed dark shade — the lens does not change when the a...
Penetration
Penetration refers to the depth to which the weld metal extends into the base metal from the surface. Complete or full penetration means the weld fuses throu...
Plasma Cutting
Plasma cutting is a thermal cutting process that uses a constricted arc and high-velocity ionized gas (plasma) to melt and blow away metal. The plasma jet re...
Porosity
Porosity refers to gas pockets trapped within a solidified weld bead. These voids form when dissolved gases (hydrogen, nitrogen, oxygen) cannot escape the we...
Post-Weld Heat Treatment
Post-weld heat treatment (PWHT, also called stress relief) is a controlled heating cycle applied to a weldment after welding to reduce residual stresses, tem...
Preheat
Preheat is the application of heat to the base metal before welding to slow the cooling rate in the weld zone. By raising the base metal temperature before t...
Push vs Pull Technique
Push technique (forehand) moves the torch with the electrode pointing backward, away from the direction of travel — the torch pushes the puddle forward. Pull...
R
Remote Amperage Control
Remote amperage control allows a welder to adjust the machine's output current from a location away from the machine — either from a foot pedal, a fingertip ...
Resistance Welding
Resistance welding is a family of welding processes that generate heat through electrical resistance at the interface between two overlapping metal pieces cl...
Respirator
A welding respirator protects the welder's lungs from welding fumes — the fine metal particles, metal oxides, and gaseous byproducts generated by the welding...
Robotic Welding
Robotic welding uses programmable industrial robots equipped with welding torches to perform welds automatically, with consistent speed, angle, and position ...
Root Pass
The root pass is the first weld bead deposited in a groove joint — it bridges the root opening at the very bottom of the joint preparation. The root pass is ...
S
Shielding Gas
Shielding gas is a gas or gas mixture used in MIG and TIG welding to protect the molten weld pool and arc zone from atmospheric contamination. Without shield...
Six-G Certification
6G certification is the gold standard welder qualification test — a groove weld on pipe set at a 45° fixed angle that forces the welder to weld in all positi...
Slag
Slag is the glassy, non-metallic residue that forms on the surface of a weld made with flux-bearing processes — stick welding (SMAW), flux-core welding (FCAW...
Slag Inclusion
Slag inclusion occurs when slag (the solidified flux residue) becomes trapped within the weld metal instead of floating to the surface. Slag inclusions creat...
SMAW
SMAW (Shielded Metal Arc Welding) is the AWS designation for stick welding. The shielding comes from the flux coating on the electrode — as it melts, it prod...
Soldering
Soldering is a joining process that uses a filler metal (solder) with a melting point below 840°F (450°C) to bond metals without melting the base material. T...
Spatter
Spatter consists of small droplets of molten metal expelled from the weld zone during welding that solidify on the surrounding base metal and workpiece surfa...
Spool Gun
A spool gun is a specialized MIG gun with a small wire spool (typically 1 pound) mounted directly at the gun body, keeping the wire feed path to just a few i...
Spot Welding
Spot welding (Resistance Spot Welding, RSW) is a process that joins overlapping metal sheets by clamping them between two copper electrodes and passing a hig...
Stainless Steel
Stainless steel is a family of corrosion-resistant alloys containing at least 10.5% chromium. The chromium forms a passive oxide layer on the surface that se...
Stick Welding
Stick welding is an arc welding process that uses a consumable electrode coated in flux to lay a weld bead. Its formal designation is SMAW (Shielded Metal Ar...
Stick-Out
Stick-out (also called CTWD — Contact Tip to Work Distance, or electrode extension) is the distance between the contact tip inside the MIG gun nozzle and the...
Stringer Bead vs Weave Bead
A stringer bead is a weld bead deposited in a straight line with no side-to-side manipulation — the torch or electrode travels in a direct path along the joi...
Submerged Arc Welding
Submerged arc welding (SAW) is a high-productivity welding process where the arc burns beneath a blanket of granular flux, completely submerging and hiding t...
T
Tack Weld
A tack weld is a small, temporary weld used to hold parts in position during fit-up and assembly before the final production weld is made. Tack welds maintai...
Tee Joint
A tee joint (T-joint) is formed when one piece of metal is placed perpendicular (at 90°) to another, forming a T shape. It is one of the most common joint co...
TIG Welding
TIG welding (Tungsten Inert Gas) is a precision arc welding process that uses a non-consumable tungsten electrode to produce the arc while the welder manuall...
Transformer Welder
A transformer welder uses a conventional iron-core transformer to convert incoming line voltage to welding output voltage. This is the original welding machi...
Travel Speed
Travel speed is the rate at which the welding torch or electrode moves along the joint during welding. It is one of the three primary variables (along with a...
Tri-Mix Gas
Tri-mix refers to three-component shielding gas blends used primarily for MIG welding stainless steel. The most common tri-mix is 90% helium, 7.5% argon, and...
Tungsten Electrode
A tungsten electrode is the non-consumable electrode used in TIG welding (GTAW). Tungsten's extremely high melting point (6,170°F / 3,410°C) allows it to sus...
V
Vertical Position
Vertical position (3G for groove welds, 3F for fillet welds) is welding on a vertical surface where the weld axis runs up and down. Gravity pulls the molten ...
Voltage
Voltage in welding controls arc length and arc characteristics. In MIG welding (constant voltage process), voltage is set on the machine and determines the a...
W
Walking the Cup
Walking the cup is a TIG welding technique used primarily in pipe welding where the welder rocks the ceramic cup from side to side against the pipe surface, ...
Warping and Distortion
Warping and distortion are dimensional changes in a weldment caused by the uneven heating and cooling inherent in welding. As the weld zone heats, the metal ...
Weld Pool
The weld pool (also called the weld puddle) is the localized volume of molten metal created during welding. Reading and controlling the weld pool is the fund...
Welder Qualification Test
A welder qualification test (also called a welder performance qualification or WPQ) is a practical test that demonstrates a welder's ability to produce sound...
Welding Boots
Welding boots are protective footwear designed to shield the welder's feet from falling objects, hot sparks, molten metal spatter, and electrical hazards. Pr...
Welding Cart
A welding cart is a purpose-built mobile platform designed to hold a welding machine, gas cylinder, cables, and accessories in an organized, portable package...
Welding Gloves
Welding gloves protect the welder's hands from burns, UV radiation, electrical shock, and sharp metal edges. Different welding processes require different gl...
Welding Jacket
A welding jacket is a protective garment made from flame-resistant material (leather, flame-resistant cotton, or FR-treated fabric) that shields the welder's...
Welding Lens Shade
Welding lens shade numbers indicate the darkness level of a welding filter lens, which protects the welder's eyes from the intense ultraviolet, visible, and ...
Welding Machine
A welding machine (also called a welding power source or welder) is the device that provides the electrical energy needed to create and maintain a welding ar...
Welding Procedure Specification
A welding procedure specification (WPS) is a formal written document that defines exactly how a specific weld is to be made. It specifies every essential var...
Welding Symbol
A welding symbol is a standardized graphical notation used on engineering drawings and blueprints to communicate exactly what type of weld is required, where...
Welding Table
A welding table is a heavy, flat, heat-resistant work surface designed specifically for welding and fabrication. Unlike a regular workbench, a welding table ...
Welding Torch
A welding torch is the handheld device that delivers the welding arc, shielding gas, and (in MIG/flux-core) the filler wire to the workpiece. In TIG welding,...
Wire Feed Speed
Wire feed speed (WFS, measured in inches per minute — IPM) is the rate at which the welding wire is fed from the spool through the MIG gun to the arc. In con...
Wire Feeder
A wire feeder is the mechanism that pushes welding wire from the spool through the MIG gun cable and out the contact tip at a controlled, adjustable speed. W...