It's no secret Friction Welding is a highly scientific process; it involves a lot of calculations, engineering and research to get it right. But thanks to the MTI-engineered control system found on each of our friction welding machines, you can trust our technology to do the complex work for you on your shop floor!
Friction welding is a solid state joining process. It’s actually a forging process: not a welding process. In the Friction Welding process we use relative motion and high force in order to create frictional heat at the weld interface. This heats the materials being joined to the point where they will plasticize without melting. The result is molecular intermixing at the weld interface and a forged quality joint.
In friction welding, we always strive toward repeatability—even when there are differences in the length of incoming parts. This is especially true in the automotive and aerospace industry where finished parts are held to rigid standards. Using Torque Modulation with Dynamic Profile Modification, we’re able to ensure our first welded part is the same length as our last welded part.
Our customers—especially those in the automotive industry—rely on repeatable upset in order to meet tight part tolerances. Remember, upset is the amount of shortening of the two parts as a result of friction welding.
When it comes to friction welding, we want to work towards repeatability, even when there are incoming part variations. But how can we do that? One way is through pressure modulation.
Over the course of this series on upset control, we’ve discussed the repeatability of upset control and part variation in rotary friction welding. Remember, upset is the amount of shortening you get in the part as a result of friction welding. Upset is different than overall length, which is the total length of the part after welding.
In Part One of this series, we talked about how upset is the amount of shortening of a part resulting from friction welding. Remember, if we had perfect incoming parts then we could fix the amount of energy used to make that weld, and get very repeatable upset. However, incoming parts variations such as area differences, surface conditions, material differences, or even interface “squareness” can cause subtle variations in upset.
In previous Whiteboard Wednesday videos, we discussed the various types and benefits of rotary friction welding. The two most common types that have been discussed are Inertia and Direct Drive Friction. In this post, we’re going to look at an important aspect of these friction welding types: upset control.
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During the friction welding process, the combination of heat and force applied between two parts produces more than just a solid-state weld. One of the most notable results of the process is the formation of flash.
As two parts are heated and the material at the weld interface softens, the excess material starts to extrude away from the weld interface. That extruded material is called flash. Flash formation varies from part to part due to shape, type of friction welding process, and the material used. Here are a few common variations:
Two buzz words in the manufacturing industry today are near net shape manufacturing and additive manufacturing. Both terms are manufacturing processes that save time and money when producing parts.
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One of the key differentiators between friction welding and other welding techniques is the ability to join dissimilar metals or two different materials that may be impossible to join by other techniques. Doing so is a cost effective way of getting the benefits from both materials. Typically we can use any of the friction welding technologies to weld dissimilar metals, and the following are some common bi-metallic combinations and applications:
Linear friction welding is similar to direct drive rotary friction welding since both are a constant energy input process. But unlike rotary, linear friction welding uses linear oscillation (a repeated back and forth motion) to create a solid state weld. There are two components of the oscillation that drives the energy input:
The hybrid friction welding cycle is a type of rotary friction welding, and is a combination of the direct drive process and the inertia process. The direct drive process has a constant energy input using an electric motor. The inertia friction welding cycle, on the other hand, has rotating flywheels that store the energy needed for the weld, which makes it a fixed energy cycle. Hybrid friction welding is a combination of both.
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.
Friction Stir Welding is another friction welding technique that has beneficially impacted the aerospace, transportation and electronics industries. Like other friction welding processes, friction stir welding uses frictional heat and force to forge materials together creating extremely high-quality, solid-state joints.
Linear friction welding is a solid-state joining process that uses relative motion and high force in order to create enough heat to create a two-piece forging. In linear friction welding, one part is moved back and forth rapidly in a linear reciprocating motion while the other part is forced into it, generating enough heat between the two parts to forge them together.
Direct Drive Friction Welding is the oldest form of the rotary friction welding process. Direct Drive friction welding can be used to join a variety of part geometries and materials, making a high quality, solid state joint. Here is the MTI process for direct drive welding:
Inertia friction welding is 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, a set of heavy rotating wheels that are used to store rotational energy.
Rotary friction welding is a flexible technique that can provide many advantages over traditional fusion welding processes. In order to use the rotary friction welding process, you must have one part that is symmetric around its rotating axis. The non-rotating component, can also be symmetrical but does not have to be.
There are three main types of rotary friction welding—Inertia, direct drive and hybrid friction welding. Each technique offers a unique advantage depending upon the type of materials being welded as well as the shape or geometries of the materials. Let’s take a look at some application examples.
You may not realize it, but friction welded parts are part of your everyday life. A good example of an everyday application of friction welding can be found in a component used with automobile air bag inflators. This component is found in steering , wheels, glove boxes, dash boards, seats, and side panels, and since every car needs air bags, this component has a very high volume demand. The tricky part is that, due to the intricacy of the specific component shown in the video, it could not be made from a single piece.
One small part — the lift screw — is a great example of what makes friction welding so useful. It’s a part you might find in an automobile power seat, or in the wing of an airplane, where it helps raise and lower the flaps.
There are a couple traditional ways to produce a lift screw:
Friction welding in the United States started in the late 1960s when Caterpillar Tractor Company wanted to produce hydraulic cylinder rods, or piston rods.
A key challenge they faced was that many of these parts were made out of single-piece forgings, which were — and still are — very expensive to produce. When they examined all of their parts, they found they had a smaller number of eyes than clevises, and they wanted to be able to weld these rods to different lengths and diameters. Friction welding allowed them to create two-piece forgings that would be much less expensive to produce.