Spot Welding Glossary

4 RW

RWMA Taper Spec for Welding Electrodes (#1 Morse Taper)

5 RW

RWMA Taper Spec for Welding Electrodes (#2 Morse Taper)


An Air Storage Tank mounted on the Resistance Welding Machine which supplies consistent air pressure regardless of fluctuations in the Plant Air System

ACME Spot Welder

A Household name in Spot Welding Machines. The most well-known and popular Resistance Welding Machines manufactured in the USA


A System which converts standard available Plant Pressure to a high Welding Force in a compact Weld Gun


In Resistance Welding, an electrical unit of measurement depicting the required Weld Intensity


In Resistance Welding, to slowly cool the Base Metals at the weld interface using a lower post secondary heat so as to eliminate cracking and brittleness at or near the welded joint.

Back-Up Electrode

Typically used for "Cosmetic" or "Markless" Welds. A large flat Electrode which makes contact with the exterior Base Metal during the welding process to provide a return path for Welding Current. The end result is a Spot Weld that is nearly invisible

Butt Weld

The joining of two wires, end for end, to make a continuous fluid connection

C Gun

A Weld Gun with a fixed "C" shaped Secondary. Weld Force is transmitted directly from the movable Electrode to the Stationary Electrode

Cap Electrode

An Electrode used in a production welding environment. Requires a Shank


In Resistance Welding, to fire more than one Welding Transformer in one Welding Sequence using multiple SCRs

Circumferential Seam Weld

A welded joint around the circumference of two or more overlapping Base Metals

Class I Copper


Class II Copper

Copper-Chromium, most commonly used as an Electrode Base Material for welding low carbon or high carbon steel

Class III Copper

Copper-Chromium-Byrilium, used as an Electrode Base Material where high Weld Forces are present

Closed Loop Feedback

Typically used in Mid-Frequency DC Resistance Welding. A method of process control where the Secondary Output is monitored and managed in real time during the entire Welding sequence to produce optimal Welded Joint Characteristics

Conduction Angle

A Function of an AC Resistance Welding Control. The precise moment in time at a specific Amplitude of the 50 or 60 Hz incoming Sine Wave in which the SCR begins Conducting to generate the required intensity of Welding Current

Constant Current

A type of Closed Loop Feedback where the Secondary Welding Current remains steady regardless of changes in Material Resistance, Inductive Losses (Part entering the throat depth), or Line Voltage Fluctuations


Typically, an Electrode. The "throw-away" component of a Resistance Welding Machine

Cosmetic Weld

A Spot Weld where very little marking or deformation occurs in the joining process

Current Collector Head

A Resistance Seam Weld Head of the highest quality, producing the most constant method of Weld Current Transfer from a Stationary to a Rotating Member

Diaphragm Weld Cylinder

An Air Cylinder used in critical Resistance Spot Welds and Projection Welds. Compared to standard Piston Cup Air Cylinders, Diaphragm Cylinders produce extremely "Fast-Follow-Up" due o the absence of Friction that is produced by Cup Drag on the Cylinder Bore

Differential Pressure

The Pressure on the top of the Cylinder (when present) minus the Pressure on the bottom of the Cylinder. In Resistance Welding, This would also be known as the Net Force, or Welding Force

Direct Drive

In Resistance Welding, a method by which to drive a Seam Weld Head where a Motor, coupled to a Gear Reduction, is mechanically connected directly to the Seam Weld Head. Without some form of Feedback Device, as the Wheel Diameter changes due to wear, the Weld Speed is altered

Direct Weld

Weld Current is transferred from the Welding Transformer, through Secondary 1, through Electrode 1, through the Part, through Electrode 2, through Secondary 2, and back to the Welding Transformer


In Resistance Welding, the measurement of the Weld Nugget Growth (expansion) in a Spot Weld or the collapse of a Projection(s) in a Projection Weld


In a Resistance Welding Control, the gradual "ramping down" of the Weld Current directly after Weld Time or Heat Time

Duty Cycle

In Resistance Welding, the On Time of the Welding Transformer or IGBT vs the Off Time relative to a production environment


In Resistance Welding, the "throw away" Component, usually made of RWMA Copper Alloy, which makes contact with the work while under the applied Welding Force


Also known as "Flashing". During the Welding Sequence, molten metal is projected due to lack of Weld Pressure, excessive Weld Current, or contamination on the Weld Face of the Electrode(s)

Fast Follow Up

In Resistance Welding, a term describing the capability of the Movable Electrode to react to the expansion of the Weld Nugget or the Collapse of a Projection(s) during the Welding Sequence

Flow Control

A Device integrated into the pneumatic System of a Resistance Welding Machine used to control the speed at which the stroke of an Air Cylinder travels to reduce impact

Force Gauge

An Instrument used to measure the actual Welding Force at the Electrodes

Forge Force

In a Differential Pressure System, The Gross Force or the Forge Force present at the Electrodes when the Pressure at the bottom of the Cylinder is "dumped" at a precise moment during the Welding Sequence. This higher Force assures the integrity of the Welded Joint

Gun Transformer

A standard Welding Transformer with a higher than normal Secondary Voltage (up to 20 Volts) in order to accommodate Voltage Drops present in lengthy Weld Cables

Half Cycling

In Resistance Welding, an Electronic malfunction in the Welding Control Circuitry (usually the SCR) resulting in Core Saturation of the AC Welding Transformer most noticeable by a distinct grunting noise and lack of Welding Current during the Welding Sequence

Heat Decay

In a Low Frequency Converter Welding Machine such as a SCIAKY, Heat Decay is a timing function of the Welding Control to allow for the stored energy in the Welding Transformer to dissipate between Impulses. Lack of Heat Decay may result in the misfiring of one SCR causing the Welding Transformer to "Thump" or in extreme cases, knock out the Breaker

Heat Time

In Resistance Welding, Heat Time denotes the amount of time in which the Welding Transformer is Short-Circuited or Conducting through the Base Materials. The Time Base is programmed into the Welding Control in Cycles (1/50th or 1/60th of a second) or milliseconds. 1 Cycle is equal to 16 milliseconds in a 60 Hz Frequency and 20 milliseconds in a 50 Hz Frequency

Hold Time

Administered by the Welding Control, the time duration after Heat Time in which the Welding Electrodes are held at the applied Welding Force prior to release. Programmable in Cycles. (1 Cycle = 1/60 of a second or 16 milliseconds)


Short for Insulated Gate Bipolar Transistor. In a Medium Frequency Inverter Welding Control, a device used to convert a Rectified D.C. Primary Voltage into an A.C. Medium Frequency (1K Hz) Primary Voltage which drives the Welding Transformer during the Welding Sequence

Indirect Weld

Similar to a Direct Weld except Electrode 1 makes contact with the part at a location other than at the actual Weld Interface. This Method is usually utilized as a consequence of Part Geometry.


Also known as M.F.D.C. (Medium Frequency Direct Current), The newest Technology In Resistance Welding, where the Secondary Welding Current is a highly concentrated pure D.C. Output precisely controlled in real time during the entire Welding Sequence. Inverter Technology is more efficient than standard A.C. Systems due to a high Power Factor which can significantly lower operational costs as a result of Reduced Primary Demand. Today, Inverter Technology leads the way in the advancement of total Process Control in the Resistance Welding Industry


Short for Joint Industrial Council. JIC Standards were written in the early 1950s by a joint committee of major machine tool builders and users. The purpose was to provide a uniform set of basic practices which would result in a well-built machine tool. Four standards were written: Electrical (EMP-1-67/EGP-1-67); Electronic EL-11-1971); Hydraulic (H-1-1973); and Pneumatic (P-1-1975).

Kickless Cable

Also known as a Dual Conductor Welding Cable. Copper conductor ropes insulated from each other are arranged in alternate polarity relationship to achieve an excellent balance of electrical forces which virtually reduces the pulsing vibration or "KICK"

Knurl Drive

In a Seam Welder, the method by which to drive one or both Weld Wheels. Two advantages of a Knurl Drive are: Constant Wheel Speed regardless of change in Wheel Diameter and continuous Dressing of the Weld Wheel via the Knurl Drive


Short for Kilo-Volt-Amp. In Resistance Welding, KVA denotes Rating or Size of a Resistance Welding Machine. Actually, KVA is the Kilo-Volt-Amp Capacity of the Welding Transformer

Laminated Shunt

Constructed of Copper Laminations, the Flexible Joint on the Secondary of a Resistance Welding Machine to accommodate the Movable Electrode

Load Distribution

In Resistance Welding, the capability of a single phase Welding Control to drive more than one Welding Transformer across more than one Phase in a single Welding Sequence.

Longitudinal Seam Weld

A welded joint along the length of the overlapping Base Metal(s)


Short for Line Voltage Compensation. The capability of the Welding Control to compensate for abnormal fluctuations in Supply Power that may occur during the Welding Sequence

Mil-Spec Welding

A Resistance Welding Standard developed and published by and for the United States Military as a basis for Quality Assurance of Critical Resistance Welded Joints. Most Aerospace Manufacturers adhere to Mil-Spec Resistance Welding Standards and Guidelines


In Resistance Welding, to oversee actual results of specific data such as: Secondary Weld Current, Secondary Weld Voltage at the Electrodes, Secondary Resistance, Welding Force, and Displacement during the entire Welding Sequence


Occurs when the Welding Electrodes loose shape as a result of Weld Force and Weld Current. This is unavoidable and can be maintained by properly dressing the Electrodes


Short for National Electrical Code. A standard for the safe installation of electrical wiring and equipment

Nose Type

In Resistance Welding, the RWMA description of the Welding Electrode Geometry

Nugget Expansion

The growth of the Welded Joint that can be measured during the Welding Sequence

Off Time

In Resistance Welding, Off Time denotes the amount of time in which the Electrodes open after the Welding Sequence and remain open prior to the welding sequence automatically repeating. Programmable in Cycles. (1 Cycle = 1/60 of a second or 16 milliseconds)


Short for Occupational Safety & Health Administration. Federally funded by the U.S. Government, OSHA constitutes and governs standards for Workplace Environments to protect all Laborers from work related injury or death caused by faulty equipment or worker negligence

Pass Through

In Resistance Welding, a type of Multi-Spot Welding Machine that allows for the Part, as it is welded, to "Pass" or "Index" Through the Machine for production purposes

Ped Welder

See Press Welder

Percent Heat

In Resistance Welding, a programmable parameter in the Welding Control that is used to increase or decrease the Secondary Weld Current

Phase Rotation

Synching the Three Phase Power Source with the Resistance Welding Machine. Proper Phase Rotation is essential on Frequency Converter Resistance Welding Machines

Plain Copper

Also known as Alloy 110. In Resistance Welding, Alloy 110 Copper is the base material used to construct the Secondary Welding Circuit


On a Press Welder, a T-Slotted Base on the upper and lower Secondary used to attach tooling for part specific applications


Short for Programmable Logic Controller. A fully programmable CPU that is used to administer machine function in an industrial and automated environment

Power Factor

The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 to 1 inclusive. The significance of power factor lies in the fact that utility companies supply customers with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts). This increases generation and transmission costs. Good power factor is considered to be greater than 0.85 or 85%. Utilities may charge additional costs to customers who have a power factor below some limit

Press Welder

A Type of Resistance Welding Machine where the Weld Cylinder is directly connected to the movable Electrode resulting in a smooth and guided method of generating Weld Force

Process Control

In Resistance Welding, to refine a Weld Schedule and continuously verify the results using a capable Weld Monitoring Instrument


A stamped Protrusion in a piece of metal

Projection Weld

In Resistance Welding, to set down or burn-in a projection using a suitable Welding Current and Force. This process is normally used in applications where part geometry prohibits typical Spot Welding

Pull Test

A destructive test used to validate the strength of a Welded Joint. The Test is usually performed using a Pull Tester which measures and displays the results


Typically used on a Multi-Spot Resistance Welding Machine. A Welding Transformer configuration which permits the Part, as it is being welded, to unobstructedly pass through the Machine in a fluid productive manner

Quench Time

In Resistance Welding, Quench Time is the time lapse between Heat Time and Temper Time also known as Post Heat. The Time Base is programmed into the Welding Control in Cycles (1/50th or 1/60th of a second) or milliseconds. 1 Cycle is equal to 16 milliseconds in a 60 Hz Frequency and 20 milliseconds in a 50 Hz Frequency


Short for Rough Oversized to Finish. A term used when ordering Forged Copper Weld Wheel Blanks. The machined O.D. and Thickness of the Wheel is given as the R.O.T.F. dimensions when ordering


A Mechanical Link which guides and transfers the Welding Force from the Weld Cylinder to the Upper Electrode or Tooling


In a Resistance Welding Control, to continually sequence the weld schedule as the Initiation switch is held closed when the Repeat Switch is in the on position. See Off Time

Resistance Weld

See Spot Weld


An option available on most Resistance Welding Machines. Retraction is an extended Electrode Opening for the purpose of accommodating Parts with geometry too large to enter into the standard Electrode Opening which is usually 1/4" - 3/8" aprox

Rise Time

In an Inverter Welding Control, Rise Time refers to the time required, in milliseconds, for the Secondary Welding Current to change from zero to the programmed value

Rocker Arm Spot Welder

A Type of Resistance Welding Machine where the Weld Cylinder is indirectly connected to the movable Electrode through a Fulcrum

Roller Ram

A low inertia precision Mechanical Link which guides and transfers the Welding Force from the Weld Cylinder to the Upper Electrode or Tooling


Short for Resistance Welding Manufacturing Alliance. Develops equipment standards for the protection and benefit of buyers and users of Resistance Welding Equipment and Accessories. Resistance Welding Manufacturing Alliance encourages the highest standards of ethics in the resistance welding industry

Scissor Gun

In Resistance Welding, a Portable Weld Gun which is based on the same mechanical principles as a Rocker Arm Spot Welder


Short for Silicon Controlled Rectifier. A 4-layer solid state device that controls current flow. In an A.C. Resistance Welding Machine, a SCR is used to switch the Welding Transformer on during Heat Time

Seam Weld

A uniform continuous chain of Resistance Welds. The Welding Electrodes are usually in the form of Copper Wheels which index the Base Metals at a precise rate of speed to perform a very consistent Welded Joint

Secondary Circuit

In Resistance Welding, the entire Electrical Connection and Structure that is attached to the Secondary of the Welding Transformer

SEEDORFF Rapid Gun Adjust

On a Multi-Spot Resistance Welding Machine, an ingenious Weld Gun Mounting System which allows for infinite, effortless, and swift Weld Gun Adjustability

Series Weld

Weld Current is transferred from the Welding Transformer, through Secondary 1, through Electrode 1, through the Part, through the Series Back-Up Bar, through the Part, through Electrode 2, through Secondary 2, and back to the Welding Transformer. This Method produces two simultaneous Spot Welds


In Resistance Welding, a Component used to hold a Cap Electrode


See Laminated Shunt

Sleeve Bearing Head

In Resistance Welding, a type of Seam Weld Head usually constructed of a Class III Copper Shaft which rotates in Class II Copper Sleeve Bearings. Conductive Grease is used to minimize friction and allow smooth Shaft rotation


Short for Statistical Process Control. a method for achieving quality control in manufacturing processes. It employs control charts to detect whether the process observed is under control.

Spot Weld

A Spot Weld or a Resistance Weld is a Metal Joining Process requiring no Filler Medium. This process is based solely on the principle of OHMS LAW where V(voltage) = I(current) x R(resistance). Most Base Metals have very low Resistance (micro-ohms). Low Voltage Secondary Outputs (up to 30 VAC in a Spot Welding Transformer) in conjunction with the Low Resistance in the Base Material can produce a very High Current (Kilo-Ampere) Draw through the interface of the stack of two or more metals to be joined. This high "Welding Current" almost instantly liquefies the metal at the interface where the electrodes make contact under pressure with the base materials. When the Welding Current is turned off, the water circulating through the electrodes, while still under pressure, secures the welded joint. And this is the basis behind Resistance Welding, also known as Spot Welding

Squeeze Time

The time allotted for the Movable Electrode to make contact with the work and develop the required Welding Force. Programmable in Cycles. (1 Cycle = 1/60 of a second or 16 milliseconds)


A programmable function in the Welding Control which automatically increases or decreases the Welding Current in programmed Step Counts based on the rate of Electrode wear

Surface Resistance

The Electrical Resistance at the surface of the Base Metal prior to Resistance Welding

Swivel Electrode

A Back-Up Electrode used on a Rocker Arm Spot Welder for producing Cosmetic Welds

Tap Switch

The coarse mechanical heat adjustment of the Welding Transformer

Temper Heat

Also known as Post Heat. In the Resistance Welding of High Carbon Steel or Heat Treated Non-Ferrous Alloys, a function of the Welding Control in which a second lower Heat is applied in order to anneal the Welded Joint

Temper Time

The programmable time in which the Temper Heat is applied during the Welding Sequence

Throat Depth

In a Resistance Welding Machine, the Throat Depth accommodates the physical dimensions of the Work at the Welded Joint and is defined as: the unobstructed reach from the Electrodes to the Machine


See Electrode

Tip Dresser

A Tool designed to clean and reface a Resistance Welding Electrode

Trans Gun

A Weld Gun with an integrated, on-board Welding Transformer. Also known as Robot Weld Gun or Roboterpunktschweißung Gewehr

Turns Ratio

In a Resistance Welding Transformer, the Ratio of Primary Windings to Secondary Windings. Usually, the Secondary is 1 (ie 50:1, 50 Turns primary to 1 Turn Secondary)


A term used in Butt Welding, where the square end of one wire is forced, under pressure, into the square end of another wire during the Welding Sequence. The end result is a welded joint with a minor bulge around the circumference of the wire at the connection


In Resistance Welding, a programmable parameter in the Welding Control that is used to gradually ramp up the Welding Current to "Burn Through" the coating of Galvanized, Galvaneal, or Aluminized Sheet Metal

Water Chiller

In Resistance Welding, a programmable stand-alone Water Recirculating System that provides precise temperature-controlled water-cooling to the Resistance Welding Machine and Electrodes/Weld Wheels

Weld Face

The physical area of the Electrode or Weld Wheel that makes contact with the Work. The Weld Face directly influences the size and characteristics of the Weld Nugget

Weld Force

The required physical Force at the Electrodes, Tooling, or Seam Welding Wheels during the Welding Sequence to produce a qualified Resistance Welded Joint

Weld Force Gauge

An Instrument used to measure Weld Force at the Electrodes or Seam Welding Wheels

Weld Gap

In a Resistance Welding Machine, the Weld Gap accommodates the physical dimensions of the Work at the Welded Joint and is defined as: the unobstructed area between the Upper and Lower Secondary

Weld Nugget

The created tangible Joint of two or more separate base metals produced by a Resistance Welding Machine

Weld Time

Begins automatically after Squeeze Time. The time allotted for the Electrical Source to "short circuit" or "conduct" through the stack of weldable metals under applied force. Programmable in Cycles. (1 Cycle = 1/60 of a second or 16 milliseconds)

Weld Wheel

A round Electrode used on a Resistance Seam Welder to produce uniform in-line Welds

Welding Cable

A high-ampicity flexible Conductor used to transfer Welding Current from the Welding Transformer to a Weld Gun. Welding Cables are constructed of Hi-Con Copper Rope and can be water-cooled to reduce the physical size of the Cable

Welding Control

In Resistance Welding, a Micro-processor based Electronic Device responsible for administering precise Resistance Welding Timing Sequences and magnitude of Welding Current

Welding Current

In Resistance Welding , a Unit of Measurement (Ampere) of Heat Intensity during the Welding Sequence required to make a successful Weld

Welding Transformer

The Main Component in a Resistance Welding Machine which generates the required Welding Current by "short-circuiting" through the Part Interface. The Size or Rating of the Welding Transformer is based on the physical Kilo-Volt-Ampere (KVA) capacity and efficiency of the Device

X Gun

A Weld Gun where the Weld Cylinder is indirectly connected to the movable Electrode through a Fulcrum

Zero Gravity Balancer

In a manual Resistance Weld Gun Station, an adjustable suspension system which allows the Weld Gun to float at a desired work level for ease of manipulation

Zirconium Electrode

An Electrode used for Welding Galvanized, Galvaneal, or Aluminized Coated Sheet Metals. The Zirconium Electrode provides a non-stick Weld Face Surface which reduces Tip Contamination caused by the burn-off of the Coating during the Welding Sequence.