Exploring Key Friction Welding Terminologies

Friction welding has been around for a long time, but many are just now discovering it. Because of this, we thought it would be a great idea to discuss some of the key terminology used in the friction welding process along with a few other industry terms.

Friction Welding Classifications

The following are terms used for unique Friction Welding classes: Inertia, Direct Drive, Hybrid, Linear, Stir, Orbital, and Explosion.

Inertia Welding

A solid-state process that joins two materials by using rotation, friction to generate heat, and lateral force to fuse components together.

Solid-State Welding

A set of welding processes which produces fused components at temperatures below the melting point of the base materials that are being joined (Without the use of brazing filler materials).

Linear Friction Welding

Similar to spin welding, except that the moving chuck oscillates laterally instead of spinning. The speeds are much lower in general, which always requires the pieces to be kept under pressure. This also requires the parts to have a high shear strength. Linear Friction Welding requires more complex machinery than spin welding but has the advantage that parts of any shape can be joined, as opposed to parts with a circular meeting point.

Orbital Friction Welding

Orbital Friction Welding is similar to spin welding but uses a more complex machine to produce an orbital motion in which the moving part rotates in a small circle, much smaller than the size of the joint as a whole.

Hybrid Friction Stir Welding

An innovative solid-state joining technology which has great potential to produce effective and defect-free joint for similar materials and dissimilar materials irrespective of high chemical affinity and completely different physical and mechanical properties like aluminum and copper.

Explosion Welding

A solid state (solid-phase) process where welding is accomplished by accelerating one of the components at extremely high velocity through the use of chemical explosives. This process is most utilized to clad carbon steel plate with a thin layer of corrosion resistant material (e.g., stainless steel, nickel alloy, titanium, or zirconium).

Total Indicator Runout (TIR)

Total indicator reading (TIR), also known by the newer name Full Indicator Movement (FIM), is the difference between the maximum and minimum measurements, that is, readings of an indicator, on the planar, cylindrical, or contoured surface of a part, showing its amount of deviation from flatness, roundness (circularity), cylindricity, concentricity with other cylindrical features, or similar conditions.


The material mating surfaces in the Friction Welding Process

Weld Process Sheet (WPS)

The documentation of critical information to control process – Welding parameters and ranges are specified and used to prepare the associated welding procedure.


Combination of Wk2(total moment of inertia of rotating mass), RPM(revolutions per minute), PSI(pressure), and Time.

Friction Weldment

2 or more metal components fused together by the friction welding process.

Ferrous Metals

Indication of metals properties that contain iron – carbon steel, stainless steel, or alloy steel.

Non-Ferrous Metals

Indication of metal properties that do not containing iron – aluminum, copper, lead, nickel, tin, titanium, and zinc.

Upset Metal

Thickened Parent material proud of normal surface for friction welding process.

Total Upset

Total length of upset material removed from friction welding process.


Movement of upset material away from weld interface that curls around a round component.


Mixing of metal materials at the interface.

Bend Test

Engineers conduct a material-bending test before and after welding; it is one of the most crucial steps of friction welding. The test evaluates the quality of the item and the quality of the welded joint.


It is a crucial part used in most aerospace devices like MTI’s LF35-75. Engineers use Blisk as a short word for Bladed disk.

Producing a bladed disk is challenging and expensive when you machine it through a material piece. However, its production becomes relatively cheaper when you produce it with friction welding.

Engineers make a bladed disk (Blisk) by friction welding singular pieces of rotor disk blades to one another.

Direct Drive Friction Welding (DDFW)

DDFW is an old rotator friction welding technique. In this technique, the engineer needs to maintain the speed of the electrical motor. The engineer adds low friction that generates a small amount of heat on the welding interface. It decreases the friction coefficient.


An engineer uses a drawtube to attach a master or a collet to clump on the part. Later, he pulls the drawtube to clamp and pushes to un-clamp.

The engineer will only use the drawtube when parts are longer, and they require extra space in the spindle. The engineer will use the drawtube when chucks. The greatest thing about drawtube is it comes with a built-in actuator.

Grain Refinement

Engineers pass the weld interface to improve its mechanical properties. Grain refinement helps in developing a more robust and reliable material. The best part is that you can reinstate the refined material through the thermal pot weld process.


ITAR is short for International Traffic in Arms Regulation. Their job is to regulate aerospace and defense industries in the country, which are in the interest of national security.


The angle at which two parts of welded materials meet is the orientation. On MIT’s Double-Ended Axe Machine, the material achieves orientation at ±1°.

Final Feedback

Learning about friction is not as challenging as you think. There are a lot of principles to consider, but the overall process is fairly simple. If you want to learn more.

When you learn the terminology, you will start understanding the process.