I-CAR SWQT key terms

A process that joins overlapping steel panels by clamping them between copper-alloy electrodes and passing a high current for a short time; the electrical resistance at the sheet interface generates the heat that forms a molten nugget.

The amperage delivered through the electrodes during a spot weld. Too little produces a cold, undersized nugget; too much causes expulsion, electrode wear, and sometimes surface cracking in high-strength grades.

The clamping pressure applied by the spot welder before, during, and briefly after current flow. Adequate force contains the molten nugget and prevents expulsion; low force allows the sheets to separate and the weld to be porous.

The interval between the electrodes contacting the panel and the start of current flow. It lets force build to the set value so the sheets are fully seated before heating begins.

The period after current stops during which electrode force is still applied, allowing the nugget to solidify under pressure. Releasing too early can leave a brittle, cracked, or porous weld.

The measured width of the fused zone in a peeled or sectioned spot weld. It is the primary acceptance criterion because it correlates directly with joint strength and must meet the OEM's specified minimum.

Molten metal ejected from the faying surface or the outer surface during a spot weld, often as sparks or a small crater. It signals excessive current, insufficient force, poor fit-up, or contaminated surfaces.

Reshaping the copper electrode faces to restore their contact area and profile after repeated welds. Mushroomed or pitted tips reduce current density and produce inconsistent nugget size.

The mating surfaces of two overlapping panels where fusion occurs during spot welding. Coating, adhesive, sealer, oil, or oxide on this interface raises resistance and can cause weak or expelled welds.

Current that bypasses the intended weld location and flows through an adjacent existing weld or metal path. It reduces current density at the new spot and yields an undersized nugget unless spacing is controlled.

A conductive zinc-rich coating applied to faying surfaces before assembly so corrosion protection remains between panels while still permitting acceptable spot welds. Non-conductive coatings must be removed from weld locations.

An arc welding process in which a continuously fed consumable wire electrode melts into the joint while a shielding gas protects the molten pool. Automotive body work commonly uses its short-circuiting transfer mode on thin sheet steel.

A GMAW mode in which the wire touches the puddle, extinguishes the arc, and transfers metal before re-establishing the arc many times per second. It suits thin sheet because heat input stays low and the puddle is easy to control.

A gas or gas mixture fed through the gun to displace air and stabilize the arc. Common automotive mixes contain argon with carbon dioxide or oxygen; the choice affects penetration profile, spatter level, and bead appearance.

The volume of shielding gas delivered per unit time, usually set in liters or cubic feet per hour. Too low allows atmospheric contamination and porosity; too high creates turbulence that also draws air into the arc.

The distance from the end of the contact tip to the workpiece. Holding it steady at the value used to set voltage keeps arc length and penetration consistent; long distances reduce current and destabilize the arc.

The rate at which the consumable electrode is pushed into the weld, expressed in inches or meters per minute. It primarily controls deposition rate and, together with voltage, determines arc stability and bead shape.

A condition where the arc melts the wire back to or into the contact tip, fusing them together and stopping wire feed. It results from excessive voltage, a stuck or worn liner, or a loose drive roll.

Void cavities trapped in solidified weld metal, visible as pinholes on the surface or revealed by destructive testing. Causes include lost shielding gas, contaminated base metal, moisture, and paint or sealer in the joint.

A discontinuity where weld metal fails to bond to the base metal or to the previous pass. It typically stems from travel speed too high, current too low, or an incorrect gun angle that leaves the arc off the root.

The depth to which fusion extends into the base metal from the joint surface. It is controlled by current, travel speed, joint gap, and material thickness, and is verified by destructive testing against OEM criteria.

The thermal energy delivered per unit length of weld, governed by current, voltage, and travel speed. Excess heat input softens heat-treated steel and widens the heat-affected zone, weakening the surrounding structure.

The band of base metal alongside a weld whose microstructure is altered by welding heat without melting. In advanced and ultra-high-strength steels it can lose substantial strength, so OEM procedures limit its size and location.

The temperature of the work piece measured before laying a subsequent pass or adjacent weld. OEMs may cap it to prevent cumulative softening and distortion when multiple welds are made close together.

A family of automotive sheet steels with tensile strengths roughly 500 MPa and above, produced by microstructures such as dual phase, TRIP, or complex phase. Their strength-to-weight ratio makes them common in crash structures.

The highest-strength class of automotive steel, typically above 780 MPa tensile strength and often martensitic or press-hardened. Many grades are heat sensitive and may require MIG brazing, rivet bonding, or adhesive instead of fusion welding.

Boron-alloyed steel formed and quenched in the die to create a martensitic structure with very high strength, used in safety cages and B-pillars. Welding can locally soften it, so OEM repair methods frequently specify alternatives to fusion welding.

A joining process using a copper-based filler wire that melts and bonds to the steel without melting the base metal. Its low heat input preserves the strength of heat-sensitive high-strength panels and limits the heat-affected zone.

A mild or high-strength steel whose strength increases when the paint-bake oven heats the formed body. Repair welding that adds heat in the wrong place can alter this condition, so OEM guidance should be checked before welding.

A weld made by filling a hole punched or drilled in the outer panel to fuse it to the panel beneath. It is used where a squeeze-type spot welder cannot reach and must match OEM size, count, and spacing.

A joint in which two members overlap and are joined along the overlap. It is the standard configuration for spot welds and plug welds, and the overlap width must follow the OEM's sectioning and joining plan.

A square-groove joint where two members meet edge to edge and a backing plate or strip supports the root. Common in sectioned structural members, it demands full penetration and a backing material of compatible thickness and strength.

The alignment and gap condition of parts before welding. Poor fit-up creates gaps that exceed tolerance, causing burn-through, incomplete penetration, distortion, and expulsion in spot welding.

Cutting a damaged structural member at an OEM-approved location and joining a replacement section rather than the whole part. The procedure specifies cut points, backing, weld type, and count that must be followed exactly.

The standardized notation on an engineering drawing that shows joint type, weld size, length, spacing, and process. Reading it correctly tells the technician where and how to weld, including whether welding is on the arrow side or other side.

The horizontal line in a welding symbol to which the arrow, tail, and weld details attach. Symbols placed below the line indicate the arrow side; those above indicate the other side of the joint.

A small circle placed at the junction of the arrow and reference line, meaning the weld continues around the entire perimeter of the joint. It is common on tubular and boxed sections.

The optional fork at the end of the reference line used to carry a process reference, specification number, or note. It tells the technician which process or procedure governs the weld shown.

A destructive test in which a spot-welded flange is pried apart so the nugget can be examined and measured. The weld must tear a button from one sheet rather than separate cleanly, confirming fusion.

A destructive check in which a chisel is driven between spot-welded panels to verify the weld holds and the nugget is sound. Excessive separation or a clean pop-out indicates an unacceptable weld.

Physically breaking or sectioning a test weld to inspect fusion, penetration, and nugget size. Technicians make test coupons on scrap of the same material and thickness before welding the vehicle.

A piece of matching scrap material welded with the same equipment settings as the repair, then destroyed and inspected. It verifies that the machine, consumables, and technique produce an acceptable weld before work begins on the vehicle.

The vehicle maker's published position statement or procedure specifying approved joining methods, weld counts, materials, and sectioning locations. Following it is mandatory because generic practices can compromise structural integrity and warranties.

Reapplying zinc-rich primer, seam sealer, and cavity wax to areas disturbed by welding, cutting, or grinding. Skipping it leaves bare steel and heat-affected coatings that corrode rapidly from the inside out.

Steel coated with zinc to resist corrosion. Welding it produces zinc oxide fume that requires ventilation and can cause porosity and poor fusion if coating is not removed from the weld zone as the OEM allows.

Local exhaust ventilation that captures welding smoke at the arc before it reaches the technician's breathing zone. It is essential when welding coated, primed, or galvanized steel in a collision shop.

The gear worn during welding and cutting, including a filtered helmet, flame-resistant clothing, leather gloves, and safety glasses. It protects against arc radiation, spatter, burns, and electrical shock.

A designated person who monitors the work area for smoldering material during and after hot work, with extinguishing equipment ready. Sparks can travel into hidden cavities and ignite long after welding stops.