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- AC Current – Common throughout the world, AC in the United States switches polarity at 60 cycles per second.
- Acetylene - Highly flammable, gaseous, hydrocarbon used in combination with oxygen as the fuel source in Oxy-Acetylene gas torch welding.
- Alloy - A metal manufactured by combining a base metal with other metals or chemical elements in order to alter or improve its properties.
- Amperage - A measure of electrical current. In electric welding, the higher the amperage measure, the higher the arc-heat applied at the weld.
- Annealing - The process of slowly cooling a hot piece of metal until it has softened into a workable condition.
- Arc Welding - Also known as STICK, or SMAW, welding. An electric welding process by which metal work-pieces are melted together with a consumable electrode creating an arc between itself and the work-pieces. The coating on the rod protects the weld from oxidation and deposits slag over the weld. Once the weld has cooled, the slag must be removed.
- Argon - An inert gas used in MIG and TIG welding to protect the weld from oxidation.
- Bead – The fused metal deposited over the seam where two metals are welded together. It will look like a series of tight, overlapping ovals.
- Brazing - A metal joining process in which a filler metal, usually brass, is melted into the seam fusing two heated pieces together.
- Burn Through - Holes burnt through a weld seam when the amperage is set too high for the thickness of the metals being joined.
- Butt Weld - The standard welding position: Two edges being joined are butted up against each other after being laid flat on a table.
- Cast Iron – A common, high-carbon, silicon steel alloy used to cast molded parts (e.g. engine blocks). Welding cast iron requires special rods or MIG wires.
- Current - The flow of electricity, generally defined as AC or DC, alternating or direct.
- DC Current – Direct current. Common throughout the world, DC is defined by its polarity, or direction of flow, which can either be straight, meaning the ground clamp is negative, or reverse, meaning it is positive.
- Ductility - The property of metal indicating its flexibility, how thin it can be hammered out or stretched into wire without breaking.
- Duty Cycle - The amount of time in which an electric welder can be operated before it must be turned off and cooled down. Expressed as a percentage of a 10 minute test period, a 40% Duty Cycle indicates a 4 minute operating, 6 minute cooling cycle. Industrial equipment operates on a 100% Duty Cycle.
- Electrode – The conductive element creating the electric arc between itself and the work-pieces. The stick, or rod, in ARC welding and the tungsten rod in TIG welding.
- Eye-Flash - Caused by even the briefest exposure to ultraviolet and infrared radiation after observing a welding arc without wearing protective glasses. This can create a burning sensation as much as 6-8 hours after exposure and cause permanent eye-damage.
- Ferrous Metals – Metals, such as wrought and cast iron, steel and cast steel, that combine iron and other elements in their makeup. Magnets attach to these types of metals easily.
- Filler Metal - The additional metal most weld-seams require, filler metal is added by melting filler rod or wire in to the weld-joint.
- Fillet Weld - A 90° or T-joint weld where the bead fills a triangle-shaped space. A multiple-pass weld on thick, beveled plates is also known as a fillet weld.
- Flowmeter - A clear glass tube with a floating colored ball acting as a gauge indicating shielding gas flow-rates in MIG welding processes.
- Flux - A chemical coating applied to the outside of ARC rods and inside flux-cored MIG wire that cleans the hot base metal and produces a shielding gas to protect the weld from oxidation.
- Forge-Welding - The welding process by which a blacksmith hammers near-molten metals together to create a weld.
- Gas Welding – The welding process in which metals are fused with an oxygen-acetylene mixture concentrated in an intensely hot flame at the end of a torch.
- GMAW - Gas Metal Arc Welding, also known as MIG (Metal Inert Gas) welding, is a wire-feed, torch-welding process by which a consumable wire, acting as both filler and electrode, is mechanically fed into the weld zone with a shielding gas.
- GTAW - Gas Tungsten Arc Welding, also known as TIG (Tungsten Inert Gas) welding, is a torch-welding process by which a non-consumable tungsten electrode, making the arc, a hand-held filler rod, and either a helium or argon shielding gas are used to fuse the work pieces.
- Ground Clamp - The heavy cable attached to an electric welding machine that can be clamped either to the work-piece or a conductive metal work-table completing the circuit between the machine, the work-piece, and the electrode.
- Gun - The hand-held torch used in the MIG welding process. Shaped like a gun, it shoots the wire out of the barrel and into the weld bead.
- Hard Surfacing – An ARC welding process using special rods to apply multiple, overlapping beads over a large area, creating a very hard, abrasion-resistant surface on heavy-duty work tools and farm implements.
- Heat-Affected Zone - The area, running along either side of a weld affected by heat. A visible discoloration will occur on welded ferrous metals.
- Heat-Treating - Scientifically monitored heating and cooling process designed to change the characteristics of a metal, generally making it harder.
- Heli-Arc - Popular generic term for GTAW, or TIG welding, derived from trade name belonging to equipment manufacturing company L-TEC, formerly Linde. (See GTAW or TIG Welding)
- Helium - A non-flammable gas, light and colorless, used in electric welding to shield the weld from oxidation.
- Jig – An apparatus used by welders to align and hold parts in a fixed position while the weld is being made.
- Joint - Where two or three metal parts, or two sides of a crack being repaired, are welded together.
- Kerf – The width of the cut made in a metal surface using a rod or plasma cutter.
- Lap Weld – Two pieces of metal overlapped, rather than butted together to accept a weld. Common brazing procedure, lap welding produces exceptionally stiff, thin sheet metal joints.
- Malleability – The formability, or responsiveness, of heated metal when being shaped.
- MIG Welding - Metal Inert Gas Welding. A welding process in which a wire fed from a role inside the welding machine passes through the gun along with the inert gas, creating a shielded arc that melts and joins the work-pieces. (See GMAW)
- Mild Steel - Same as low-carbon steel. Common throughout the world, it is highly malleable.
- Molybdenum - An alloying metal used to strengthen and make steel and stainless steel more corrosion resistant.
- Multiple-Pass Weld - Successive beads laid down upon each other until a beveled joint is filled, multiple passes are required when welding thick metal plates or repairing large casting cracks.
- Nickel – An alloying metal used to increase steel and stainless steel corrosion resistance as well as tolerance for low and high temperature extremes.
- Normalizing - Heat-treating process used to refine and strengthen hard steel grain structures removing stress from the weld zone.
- Nozzle - The component of TIG, MIG and plasma torches that aims and concentrates the shielding gas over the weld zone protecting it from oxidation.
- Out of Position Welding – Any welding operation, such as vertical or overhead welding, in which the parts are not laid out flat in front of the operator.
- Oxidation - The natural disintegration process that occurs when metals are exposed to oxygen. On steel it produces a reddish-brown residue of rust: on aluminum, it is grayish-black.
- Oxygen - The colorless, odorless, tasteless gas making up about 20% of the air we breathe. In a concentrated combination, equal parts oxygen to acetylene, combusting at 3315° C (5999° F), a torch-flame will cut and weld metal.
- Penetration – Describes the extent of the depth into each piece of metal the welding fusion penetrates: The deeper the penetration, the stronger the joint.
- Pickling - Chemical treatment to remove dangerous fume-creating chemical or metal elements produced during the welding process. All plated parts should be stripped in swimming-pool acid before welding.
- Plug Weld - Also called a rosette weld, two pieces of tubing are welded together, one inside the other, through holes drilled in the outer sheath.
- Polarity - The directional flow of electrical current during the welding process, which varies depending on the current being used. (See AC and DC Current)
- Porosity - Tiny, undesirable holes caused by welding dirty metal, water in the electrodes, or a welding torch coming too close to the weld joint.
- Post-Heating - Reheating welded metal parts, after fusion, in order to relieve the stress incurred during the welding process.
- Pre-Heating - A common process in which either the weld zone, or whole pieces of thick metal, aluminum or iron castings are preheated in an oven or with a large torch-flame to prevent thermal stresses or uneven expansion and contraction.
- Puddle - The active welding bead melting the heated parent metal and the filler rod together. The finished weld is a hardened row of overlapping puddles.
- Resistance Welding – Welding method in which sheet-metal pieces are joined together with a short burst of electricity passed between copper electrodes on either side of the sheet-metal. Heat and pressure creates the weld.
- Rod - The consumable filler steel used to weld metals. In stick welding the rod is coated with shielding flux and often called an electrode. In gas and TIG welding it is usually uncoated.
- Root - The base of the weld bead at the point of deepest penetration.
- Root Pass - The first bead of a multiple-pass weld.
- Reverse Polarity - A Direct Current arrangement in which the work-piece is made negative and the ground clamp is made positive (DCRP). The opposite is straight polarity where the work-piece is made positive and the ground clamp is made negative (DCSP).
- Seam Welding – Often called stitching, a welding procedure where the weld bead is composed of a series of overlapping, inline spot welds.
- Sheet Metal - Thin metals, generally between 12 and 24 gauge, used in auto bodies, household appliances and HVAC applications.
- Shielding Gas - Inert, non-flammable, non-reactive gas forced out of a MIG or TIG gun, or released from the flux of an electrode, around the weld zone protecting the arc area from oxidation and other impurities.
- Shielded Metal Arc Welding - Also known as stick welding (SMAW). Flux coating on the outside of the consumable electrode vaporizes producing a protective gas that shields the weld zone.
- Slag - A hard coating of oxidized impurities produced when welding or cutting metal. Slag produced when arc welding must be chipped away with a hammer before further finishing or additional weld beads are applied.
- Spatter - Tiny balls of melted filler, rod or wire scattered around a weld zone. Unavoidable in arc welding, it's otherwise generally formed through poor welding technique primarily caused by the rod or MIG tip being held too far from the surface and creating too long of an arc.
- Spot Welding - Small, circular welds made with an electrode or MIG gun that fuses overlapping panels of sheet-metal through holes drilled in the top panel. Also can be made with a resistance welding machine which does not require a hole being drilled in the top panel.
- Stick Welding - (See Arc Welding)
- Stitch Welding - Short strips of welding bead that are separated by regular gaps along the seam when a full weld is not required.
- Straight Polarity - A Direct Current arrangement in which the work-piece is made positive and the ground clamp is made negative (DCSP). The opposite is reverse polarity where the work-piece is made negative and the ground clamp is made positive (DCRP).
- Tack Welds – Small, preliminary welds located at both ends and the middle of a seam meant simply to align and secure metal work-pieces before the final weld is begun. This is a precautionary measure. Tack welds are easily broken when design alterations become apparent.
- Tempering - Secondary heating and cooling of an already heat-treated metal to a degree just below the transformation temperature that restores toughness in metals that may have become brittle in the original welding process.
- Tensile Strength - The amount of stress a weld, weld zone, joint or metal alloy can resist before breaking, becoming deformed or being pulled apart.
- TIG Welding - Tungsten Inert Gas welding, also known as (GTAW), is a torch-welding process by which a non-consumable tungsten electrode, making the arc, and a hand-held filler rod, are heated, with either a helium or argon shielding gas, to make the weld. (See Heli-Arc or GTAW)
- Titanium - Extremely strong, light-weight metal, often used in the aerospace and race-car industries. Titanium requires special welding techniques, generally achieved through TIG welding.
- Tungsten - Corrosion resistant, non-consumable rod or electrode used in TIG welding.
- Undercut – Weld defect characterized by eroding parent metal, and too much penetration on the back side, caused by the welding current or amperage setting being to high.
- Voltage – A characteristic of an electrical current arrived at by multiplying the number of amps (current) by the number of ohms (resistance). Input current on a welding machine is usually described in volts and the output in amps. Formula: Volts = amps X ohms.
- Wrought Iron – Soft, highly malleable, form of iron that includes some slag in its makeup. It is the welder’s choice for working and shaping in or outdoor decorative pieces.