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Which method of friction welding is best? In previous sessions we talked about how most applications can be welded with any of the friction welding technologies. Now, let’s explore several standard rotary friction welding geometries and which rotary technique is best suited for each: inertia, direct drive, or hybrid.

Typically, there are two important criteria to consider when talking about which rotary friction welding application to use:

1. MATERIAL CONSIDERATIONS – What materials are the parts made from?
2. GEOMETRY CONSIDERATIONS – What are the shapes of the parts at the weld interface?

For the following examples, let’s consider that the materials are pretty similar to each other so that we can focus on the geometry aspects.

In the case of a bar-to-bar application, there is no relative motion at the center of a rotating bar during the process. Therefore, all of the heat is going to be coming from the outside and moving in because the outer edge of the rotating bar is where the relative motion is the greatest. That means a long heating process is desired, so welding with a constant energy input using an electric motor is advantageous. This lends itself to direct drive or hybrid friction welding.

Small bars can be welded with the inertia cycle; however, additional energy and additional load will be required for the inertia cycle in order to develop heat at the center of the parts. This is referred to as a load or energy penalty.

A tube-to-tube application can be welded using any of the rotary techniques if the parts have a small enough diameter.

As the tube’s diameter gets larger and larger, there may be issues with the electric motor being able to provide enough torque. So adding the flywheels for the hybrid cycle or using the inertia cycle would lend itself to larger diameter tubes.

When considering a tube-to-bar application, the same issue with torque arises for the larger parts. So as the tube gets larger, the use of flywheels with either the hybrid or inertia process would be advantageous.

The direct drive cycle is useful for relatively small parts because there is no center heating issue at the center of the bar.

A bar-to-plate application will also have an issue with center heating. So, consider using the direct drive technique or the hybrid cycle with an electric motor providing constant energy input to complete the weld. Make sure the plate isn’t acting like too much of a heat sink by getting the energy in quickly. Penetration of the bar into the plate is important for a good weld.

The hybrid cycle may work best for larger parts.

The tube-to-plate application is a classic example of an inertia friction welding geometry. The plate is going to act as a heat sink, so fast energy input in order to penetrate that tube into the plate is important for a good weld. This lends itself to inertia, with the second choice being the hybrid cycle.

Again, anyone of these geometries can be welded with the three rotary friction welding techniques. MTI offers all three of the technologies so that we can optimize your application for the best possible results.


MTI Can Solve Your Problems
These applications are only a small look into the wide-array of what is possible with MTI. We specialize in custom engineering parts to solve your specific manufacturing needs. Contact us today to discuss those needs and see how MTI can help improve your processes and save you money. We’ll build a machine that makes your part, we’ll make the part for you, or we’ll help you make the part even better.

To learn more about friction welding,  discover the MTI process or watch how friction welding can be put to work for you.

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