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The world of friction welding is vast -- and so is the vocabulary used to describe it! We've compiled a list of the most commonly used friction welding terms -- from machine components to MTI's processes -- to help you grow your engineering mind!

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Acceleration Phase
On a friction welding machine, this refers to the start of acceleration to weld speed.

Attaches the drawbar to the collet or master collet.

A safety and operating standard based on the ISO 9001 quality system requirements. Companies holding this certification are held to high and precise standards set by the aerospace industry. See MTI's certification here

Axial Force
Force between two parts during friction weld.

Axial Pressure
Pressure (force per unit area) on the parts being friction welded.

Bend Test 
A crucial step of the pre and post-weld process. The test, which involves bending the material, evaluates the quality of the material and weld joint.

A part that is made up of more than one metal. For example, a turbocharger with an Inconel wheel and a Steel shaft would be considered a bimetallic part. One of the leading advantages of friction welding is the ability to join dissimilar metals. Bimetallic parts often offer stronger welds and can lead to cost savings.

Blade Collar
A geometric shape that creates datum surfaces, in relation to the finished airfoil, for which to measure and clamp a single blade for the welding process to a hub.

Short for "bladed disk," a blisk is a crucial aerospace part comprised of a rotor disk with individual blades friction-welded to it. Because each blade is separately welded, it's often cheaper to develop blisks through friction welding instead of machining them from a solid piece of material. MTI's LF35-75 is the ideal machine on which to weld blisks.

Braking Delay
The period of time between the cessation of the drive producing relative motion of the workpieces and the start of external braking.

Breaking Strength
The stress coordinate on the stress-strain curve at the point of rupture.

Burn-off Length
Loss of length in the friction phase.

Burn-Off Rate 
The rate of shortening of the components during application of the friction force.

Buy-to-Fly Ratio 
A popular term used in the aerospace industry, this refers to the weight ratio between the raw material used to make a part and the weight of the finished part.

Holds the collet or master collet in place.

Short for Computer Numerical Control. At MTI, CNC machines are used in the post-weld process, primarily for flash removal. 

A sleeve used for holding pieces in a lathe or machine.

Collet Pad
Clamps down on a part to hold it in place. Collet pads are attached to a master collet and can come in different diameters and shapes to hold different parts.

A single item before friction welding.

Component-Induced Braking
Reduction in rotational speed resulting from friction between the interfaces.

Contact Force
Axial force on contact of components.

Contact Torque
Reaction torque after friction start.

Contract Friction Welding
Another term to describe MTI's Manufacturing Services division.  It focuses on part production instead of machine build. See all of the benefits of this value-added location here

Controls System
Responsible for all data acquisition and machine control. The system can detect issues related to operator error before the welding process begins. The system displays data, diagnostic messaging, parameter input and data storage. On MTI-built machines, the software consists of a choice of Phoenix, Siemens or Allen Bradley systems.

Test materials used for friction weld trials and research. 

Cycle Time
The total time required to complete a friction welding cycle on a machine.

Direct Drive Friction Welding (DDFW)
The oldest form of rotary friction welding, the rotating component is accelerated up to the desired weld speed using an electric motor. The speed is maintained through most of the process. A low friction force is added in order to generate some heat at the weld interface, decreasing the coefficient of friction.

Attaches to the actuator, which attaches to the collet or master collet to clamp onto a part. The drawbar is pulled in to clamp and pushed out to un-clamp.

Attaches to the actuator which attaches to the collet or master collet to clamp onto a part. The drawtube is pulled in to clamp and pushed out to un-clamp. The drawtube is usually used when a part is long enough in length and needs extra room inside the spindle. The drawtube can only be used with some chucks. A drawtube has the actuator built into it.

External Braking
Reduces the rotational speed.

Face Plate
Holds the collet or master collet in place in a knee fixture. They come in different sizes to fit different collets.

Faying Surface
A surface of one component that is to be in contact with a surface of another component to form a joint.

First Friction
A reduced friction welding force at the beginning of the welding cycle.

Fixture/Jaw Inserts
Clamp down on a part to hold it in place. Inserts are installed on the master fixture jaws. They can have fixture pads to help align these components. In some cases, they can be used on their own to clamp onto a part.

Fixture Pad
Clamps down on a part to hold it in place. Fixture pads are usually installed to fixture inserts, but in some cases they can be directly attached to the master fixture jaws. They come in different diameters to fit a variety of parts.

The extruded material after two parts are heated and the material at the weld interface softens. The excess material extrudes away from the weld interface. 

Flash Removal
The process of removing flash from a welded material. Popular techniques include sheering, turning and milling.

Steel disks that add Wk² to a spindle to allow more energy to be stored for a weld.

Flywheel Adapter
Attaches the chuck to the flywheel on the spindle.

Forge Force
The force applied normal to the faying surfaces at the time when relative movement between the components is ceasing or has ceased.

Forge Length
The amount by which the overall length of the components is reduced when forge force is applied.

Forge Phase
The interval between the start and finish of application of the forge force during the friction welding cycle.

Forge Pressure
The pressure (force per unit area) on the faying surfaces resulting from the axial forge force.

Forge Rate
The rate of shortening of the components during the application of forge force.

Forge Time
The time for which the forge force is applied to components.

Friction Phase
The interval in which the heat necessary for making a weld is generated by relative motion and the friction force(s) between the components, i.e. from contact of components to the start of deceleration. 

Friction Pressure(s)
The pressure(s) (force per unit area) on the faying surfaces resulting from the axial friction force.

Friction Stir Welding (FSW)
Using a pin tool, this solid-state joining process creates extremely high-quality, high-strength joints with low distortion. Friction Stir Welding "stirs" the pin tool between two materials to join them. The process is ideal for extrusions, castings, plates, and sheets for applications ranging from railcars to aerospace.

Friction Time
The time during which relative movement between the components takes place at rotational speed and under application of the friction force(s.)

Full-Scale Part Development
Achievable on the MTI-built LF35-75. Read about the machine's specifications and possibilities here

Grain Refinement
This process can improve the mechanical properties at the weld interface and in some cases, results in a stronger, more reliable material. In other cases, the refined grained material can be restored through post-weld thermal processing.

Heat-Affected Zone (HAZ)
The area of the base material that has not been melted but has had its microstructure and properties altered from welding.  A key advantage of friction welding is the ability to achieve a narrow heat-affected zone.

Human Machine Interface (HMI) 
A screen or component that allows a machine operator to perform a variety of functions on a friction welding machine.

Hybrid Friction Welding
A form of friction welding in which the energy required for welding is provided by more than one source.

Inertia Friction Welding (IFW)
A variation of the rotary friction welding process, Inertia Friction Welding uses kinetic energy with applied force to join parts together. The kinetic energy is achieved by the use of flywheels.

Integrally Bladed Rotors (IBRs)
Widely used in military gas turbine engines. They replace rotors with inserted blades. These can be easily welded on MTI's LF35-75.

The contact area developed between the faying surfaces after completion of the welding operation.

International Traffic in Arms Regulation.  ITAR-controlled jobs and parts typically belong to the defense and aerospace industries and details of which may not be shared outside the country in the interest of national security.

Knee Fixture
Uses collets and collet pads to clamp onto a part, just like the spindle.

Length Allowance
Extra material to allow for loss of length during friction welding process.

Loose Backup
Acts like a space filler between the bolt down backup and the part being friction welded. It doesn't get bolted down and can come in a large variety of sizes. The general rule of thumb is to use only one loose backup. The diameter of the loose backup must be smaller than the diameter of the part being clamped, otherwise the backup might get clamped instead of the part.

Low Force Friction Welding
MTI's newest form of friction welding. It uses an external energy source to raise the interface temperature of the parts being welded, reducing the process forces required to make a solid-state weld compared to traditional friction welding.

The concept and process of creating more lightweight parts and materials, primarily of interest in the automotive and aerospace industries. Lightweighting can lead to better fuel efficiency for vehicles.  An MTI-built machine is helping accomplish this at a groundbreaking lightweighting facility in Detroit. 

Linear Friction Welding (LFW)
A solid-state process in which one part moves in a linear motion at a high speed and is pressed against another part held stationary. The resulting friction heats the parts, causing them to forge together.

Master Collet
Uses the help of collet pads to clamp down on a part to hold it in place. There are a few different size master collets and each can have only certain sized collet pads installed.

Master Fixture Jaws
Clamp down on a part to hold in place. They are only used in self-centering fixtures. Master fixture jaws can have fixture/jaw inserts installed and/or fixture pads installed. They can have pins installed in them through the fixture insert or fixture pads to help align these components. In some cases, they can be used on their own to clamp onto a part.

A scientist specializing in metals. Highly skilled in identifying metals, their metallurgical components and whether they can be joined with other metals. 

The study and science of metals and their unique properties. 

Short for National Aerospace and Defense Contractors Accreditation Program, this ensures companies serving customers in the aerospace and defense sectors are following strict quality and safety standards. See MTI's Nadcap certification here.

Near-Net Shape
A major advantage of friction welding, this process enables the joining of several parts that form a larger part, minimizing the amount of machining to produce the finished product. For example, instead of machining an entire lift screw from a solid bar of metal, MTI can weld a threaded rod to a flange, saving time, money and materials.

The angle at which two parts come into contact for a weld. MTI's Double-Ended Axle Machine, for example, accomplishes orientation to ±1°.

Overall Length
Total length of a part after welding.

The distance a component projects from the fixture or chuck in the direction of the mating component.

Part Geometries
The geometry of which two materials are welded. For example: bar to bar, tube to tube, tube to bar, etc. 

Peripheral Velocity
Velocity of outer diameter of faying surfaces to be welded.

Plug Welding
The process of forging material into a hole, using rotary friction welding.

Pot Chuck
Holds irregular-shaped parts in place. They are custom-made to hold a particular-shaped part. Instead of the part, the pot chuck is clamped in place and can be used in self-centering or knee fixtures. Inside the pot chuck, the part can be held in place by using a key or by pressing the part against a face plate.

Pre & Post- Weld Processing
Crucial, often necessary steps that parts or materials must go through before and after being welded that ensure optimal strength.  Read about MTI's pre and post-weld offerings here.

Pressure Contact Area
The surface contact area of the components through which the force is transmitted.

Pressure Modulation
Indirectly controls upset by modulating the amount of weld pressure.

A precise refinement of a production process that enables machines to repeat their processes and functions with no variance between runs.

Rotary Friction Welding (RFW)
A solid-state process in which one part is rotated at a high speed and is pressed against another part that is held stationary. The resulting friction heats the parts, causing them to forge together.

Rotational Speed
Revolutions per minute of rotating component.

Second Friction
The portion of the friction welding cycle which, in conjunction with the first friction phase, comprises the friction phase. This term is only relevant when the first friction phase is used.

Self-Centering Fixture
Uses a set of master fixture jaws, fixture/jaw inserts, and/or fixture pads to clamp onto a part to hold it in place.

Size Collet
Clamps down on a part to hold it in place. A size collet can come in different sizes and diameters to fit different chucks and hold on to different parts. A size collet does not use collet pads.

Rotating components pieces used to hold workpieces.

Spindle Bolt Down Backup
Gets bolted to the actuator inside the chuck and must have the correct key to do so. If a portion of the spindle bolt down backup fits inside the collet pads or size collet, the diameter must be smaller than the diameter of the part being clamped otherwise the backup might get clamped instead of the part.

Solid-State Joining
The process of joining two materials that do not need to melt to successfully forge. Instead, they soften (or plasticize) to join. 

Stopping Phase
The interval in which the relative motion of the components is decelerated to zero.

Stress Relief
A heat-treating process that consists of heating the steel to a temperature below the critical range to relieve the residual stresses resulting from friction welding. Stress relieving does not change the material properties as does annealing and normalizing.

Tensile Strength
A measurement of the force required to pull something such as rope, wire or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress that it can take before failing or breaking.

Tensile Tester
A machine that tests the tensile strength of a material or weld. MTI uses one in its in-house metallurgical lab.

Short for Total Indicator Runout. The difference between the maximum and minimum values measured across an entire rotating surface about a reference axis.

Tools and modifications added to a machine to ensure parts and components fit for each unique job.

Tooling Envelope
An area of a machine where tooling can be installed. 

Torque Curve
Torque characteristic between the two interfaces based on time (contact, equilibrium, final torque.) 

Torque Modulation
Directly controls upset by modulating the amount of energy—through motor torque—that a rotary friction welder’s electric motor will apply.  

Total Weld Time
Time elapsed between component contact and end of forging phase.

Travel Speed
The rate at which the Friction Stir Welding tool translates through the material.

Ultimate Strength
The maximum stress a material can withstand.

Unit Energy
The stored flywheel energy of an inertia friction welder divided by the area of the faying surfaces.

Unit Force
The compressive force applied to the faying surfaces divided by the area of the faying surfaces.

The amount of shortening between two parts as a result of friction welding.  The sum of the burn-off length and the forge length.

Upset Profile 
Created by performing a standard inertia weld without the use of any control techniques.

Weld Cross-Section
The areas to be welded.

Welding Cycle
The succession of operations affected by the machine for making a weldment and the return to the initial position (excluding component-handling operations.) 

Weld Development
A process in which engineers and metallurgists examine specifications and parameters of a proposed welding job and determine exactly what is needed to successfully join two metals.

Two or more components joined by welding.

Weld Parameters
Specifications of a particular friction welding job.

Welding Procedure Specification (WPS)
Provides details of how a welding operation is to be performed and contains all pertinent details about the welding job.

Weld Speed
The RPM at which the weld force is applied in inertia friction welding.

Weld Zone
The total area impacted by a weld.

Inertia measurement of the rotor. When combined with load inertia, it determines acceleration time and required torque.

Yield Strength
The stress a material can withstand without permanent deformation. This is not a sharply defined point. Yield strength is the stress that will cause a permanent deformation of 0.2% of the original dimension.

MTI credits ISO and the American Welding Society for some of these definitions.

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