Welding glossary: 30 terms to know
Arc, weld pool, bevel, throat, tack welding, WPS, shrinkage, cobot… 30 welding and automation terms explained simply, for buyers, designers and workshops.
Welding has its own vocabulary, and it is not always shared between the design office, purchasing and the workshop. Here are 30 essential terms, in alphabetical order, with links to our articles for further reading.
A to F
Arc — An electrical discharge between an electrode and the workpiece that produces the heat needed to melt the metal. It is the basis of the MIG, MAG and TIG processes.
Bevel — An angled edge machined or cut on a part so the molten metal can penetrate the full thickness of a butt joint. Recommended preparations are described in EN ISO 9692-1.
Butt weld — A joint between two parts placed in line with each other, as opposed to a fillet weld.
Cobot — A collaborative robot, designed to work close to people. In welding, it automates the arc while an operator prepares and tacks the parts. See cobot or autonomous cell.
Distortion — A change in the part’s shape caused by the metal shrinking as it cools. It is controlled through design, tacking and weld order.
Electrode — The conductor from which the arc springs. Consumable in MIG/MAG (the wire) and in stick welding, non-consumable in TIG (tungsten).
Fillet weld — A joint between two parts forming an angle, typically a stiffener on a plate or a tube on a plate. It is the most common weld in welded fabrication.
G to M
Gap — The space left between two parts to be joined. Zero or small for a fillet weld, defined by the joint preparation for a butt joint.
Heat-affected zone (HAZ) — The part of the parent metal that did not melt but whose structure has been changed by the heat of welding.
Jig — A fixture that positions and holds the components during tacking and welding. See welding without jigs.
Joint — The area where two parts meet and must be welded. A single assembly contains several joints.
MAG — Metal Active Gas: consumable-wire welding under an active gas, the reference process for steel (number 135). See MIG, MAG, TIG.
MIG — Metal Inert Gas: consumable-wire welding under an inert gas, used in particular for aluminium (number 131).
P to S
Penetration — The depth to which the parent metal has melted. Lack of penetration is a defect.
Run (pass) — Each deposit of metal along a joint. A thick weld is made in several runs: root run, fill runs, capping run.
Shielding gas — Gas that protects the weld pool from the air. Inert (argon) in MIG and TIG, active (argon and CO₂ mix) in MAG.
Shrinkage — The contraction of the welded metal as it cools. It is the cause of distortion.
STEP — A standard exchange format for 3D CAD files (.stp or .step extension), readable by all software. It is the file from which we price and program your parts. See preparing your STEP file.
T to W
Tab and slot — A matching tongue and cut-out, laser cut, that position two components without a jig. See designing for laser cutting.
Tack welding — Laying short welds that temporarily join the components before welding. See the role of tack welding.
Throat (a) — The characteristic dimension of a fillet weld: the height of the largest triangle that fits within the weld cross-section. It determines the strength of the weld.
TIG — Tungsten Inert Gas: welding with a non-consumable tungsten electrode under inert gas, precise and clean, used for stainless steel, aluminium and thin material (number 141).
Torch — The tool held by the welder or mounted on the robot, which brings current, wire and gas to the arc. Its size determines whether welds can be reached.
Weld (bead) — The deposited and solidified metal that joins the parts.
Weld pool — The zone of liquid metal created by the arc, which solidifies to form the weld. The welder, or the robot, guides it along the joint.
Weldment (welded fabrication) — A part made by welding together components in plate, tube or sections, as opposed to casting or machining from solid.
Welding coordinator — The person responsible for welding activities in a workshop, with competences defined by EN ISO 14731.
Welding position — The orientation of the joint during welding (flat, horizontal, vertical, overhead…). The flat position is the easiest and most productive.
WPQR — Welding procedure qualification record: the test report showing that a WPS produces a compliant weld (EN ISO 15614-1 for steels).
WPS — Welding procedure specification: the document that sets the parameters of a weld (process, materials, positions, current, speed, gas). Qualified by a WPQR.
Further reading
These terms come up on our technical capabilities and safety and standards pages and in our article EN ISO 3834 explained for buyers. A term missing? Let us know and we will add it to this glossary.