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MTI's Comprehensive Weld Development

Practice makes perfect: it’s an old saying, but one that continues to ring true in just about every aspect of life – especially when it comes to manufacturing.

At MTI, we wouldn’t necessarily label our weld development process as practice, but the concept follows a similar flow – plan, detect, adjust.

It’s true, our experienced team of engineers would certainly be able to offer predictions based on historical experience about what might happen if certain materials and geometries were to be joined through friction welding. After all, our team has a combined 300 years of friction welding experience. However, we couldn’t be certain about the results until we studied each angle of the project and considered each of the customer’s requests.

This thorough testing process is known as a weld development.

Why You Need a Weld Development 

While MTI has decades of experience successfully joining countless materials for all industries, no two jobs are the same. For example, the performance needs of a drive shaft are different from a shock absorber body, even if the materials are identical.

Each material combination, weld geometry, incoming part condition and tooling concept must be proven with experimental data in order to avoid a lengthy post-weld testing process. This saves not just time, but also money because we are cutting down on material wastage by identifying solutions earlier in the friction welding process.

The main purpose of a weld development is to optimize the results that ensure the production parts are fit for purpose. This promotes extended part life, reduces scrap, and fosters a strong weld and design.

A special emphasis is placed on our aerospace customers who may be utilizing powdered materials in their applications. In addition to the different complexities of those materials, we realize all aerospace applications require a foundation of weld data and destructive testing to prove that each weld is fit for purpose based upon machine data collected during welding.

Already familiar with friction welding? Skip ahead to the “Beginning the Weld Development Process” section of this article. Otherwise, read on to learn about the different forms of friction welding and explore which one may be best for your application.

What is Friction Welding?

Before we dive into the weld development process, let’s talk about friction welding and how it’s different from other welding methods.

Friction welding is a solid-state process and comes in several different forms: Rotary friction welding, Linear friction welding, Friction Stir welding, plug welding, and our newest technology, Low Force friction welding.

Friction welding creates a 100-percent bond of the contact area and creates joints of forged quality. The weld properties are superior to welds created with fusion processes, such as MIG or TIG welding, because a friction weld does not result in melting. The absence of melting helps create a higher strength bond and greatly increases the design flexibility of each part.

Additionally, friction welding requires minimal joint preparation, is a repeatable process, produces faster cycle times and can join dissimilar metals.

In fact, one of the best reasons to take advantage of a weld development is for joining bimetallics, since the material properties can vary greatly from one metal to another.

Now that you’re familiar with how friction welding works, let’s talk about what to expect when you contact MTI to begin a weld development program.

Beginning the Weld Development Process

When you sit down with MTI for the first time to discuss your project, you will need to provide us with a few pieces of information, including:

  • The materials to be joined
  • Specifications of the materials to be joined to your supplier's expectations
  • The geometries to be joined
  • The area at the weld interface (diameter and wall thickness for tubular weld geometries)
  • The purpose the finished part will serve
  • Annual part volume expectations

One of the best ways to begin this conversation is to offer a part print or sketch of the application you want to create or improve. Having a sketch is much more beneficial and will provide more detail than if you described your part over the phone or an email.

Identifying a Timeline

Our team should be able to give you a rough estimate of the time required for a weld development while the conversation is in its earliest stages.

How much time it takes to elevate each part from concept to completion relies on many factors, including:

  • Whether MTI has friction welded your application before
  • Whether MTI has friction welded your materials before
  • The complexity of your parameters
  • The number of industry quality certifications your application must meet
  • Whether you want a machine built for your application

MTI’s weld development program is comprised of three phases. However, this multi-phase approach is generally only needed when we are doing something new. It may not be required for Rotary friction welding. We may enter a Boundary Condition Phase where we determine how to use weld development data to ensure weld quality for machine data during production.

The traditional three phases are classified as:

Phase 1 – Proof of Concept: In this phase, our team determines, through a variety of different tests, whether it’s feasible to join your materials and geometries.

Phase 2 – Small-Scale Development: In Phase 2, we develop small-scale portions of your part to test their strength and durability.

Phase 3 – Large-Scale Development: In this phase, we develop full-scale parts to test their viability on our friction welders. This is the final step before producing production parts.

Now, let’s explore each phase of the weld development to learn more about each step of the process.

Phase 1 - Proof of Concept

At MTI, we define a successful weld as a joint that meets the performance requirements that are fit for the purpose of the welded assembly we’re creating.

The fit-for-purpose performance requirements may include:

  1. Heat Affected Zone (HAZ) width
  2. The hardness of the HAZ
  3. Tensile strength at the weld line
  4. High and low cycle fatigue
  5. Elongation
  6. Yield strength
  7. Residual stress
  8. Microstructure

These qualities can be determined through metallurgical testing. Both MTI’s US and UK locations have in-house metallurgical labs equipped with various equipment to complete these tests.

Without identifying the relevant qualities listed above, the designer of a production part assembly cannot design the joint. That’s why it’s critical that MTI identifies these details before the design process begins.

It’s important to note that the process forces in friction welding are significantly different than other processes, so the part must be designed to withstand those forces – that’s why there are so many layers to our initial steps.

Plus, the resulting metallurgical and physical properties are different than any other joining process, so those must also be considered for the part design. Redesigning the part for optimized properties will change the process forces and redesigning the part for process forces can change the metallurgical and physical properties of the resulting weld.

Phase 2 - Small-Scale Development

Once we have gathered all the required knowledge of the materials and the assembly, we can begin working toward developing small-scale parts for testing. This step also involves fine-tuning the tooling required to fit your part on an MTI friction welder.

If we use the same material and choose the correct parameters for evaluation, then these parameters are not specific to a geometry of a weld – they are scalable to larger welds. This is especially important later when we are ready to move on to larger-scale development parts.

Friction welding is a repeatable process because there are only two variables the machine must control – energy and forge force. These are tweaked to produce the intended result. The combination of forge force and energy leads to upset, which is a loss of length in the part. That upset often translates into weld flash, which is the extrusion of plasticized material at the weld line. Flash may form as a smooth curl or jagged ribbon in traditional friction welding. With Low Force friction welding, there may be no flash at all.

With some additional evaluations surrounding the upset, we can ensure that slight non-machine variations to the process do not change the material properties of the application.

This process will ensure each weld produced by the machine is a good weld. This will also produce the data that the designer needs to create the part while the manufacturing team focuses on the design of the process.

In this stage of weld development, upset can be used as a quality assurance tool if you have the data to show that the pressure and energy produced a good-quality weld, as demonstrated by the mechanical and physical testing done ahead of time.

Once we weld sample parts, we will conduct a post-weld inspection. This looks for flaws that may not show up on machine data, such as incoming flaws in the forging or a lack of proper clean-up in post-weld machining.

To Contract or Not to Contract?

Also at this point in the process, we should be able to identify whether you want MTI to handle your project with our Contract Friction Welding services or if you are interested in joining your new parts on your own MTI-built friction welder.

If you choose to purchase a dedicated friction welder for your project, we will handle the weld development on our in-house machines while yours is being built.

Alternatively, you have the option of purchasing a lab machine, which is designed to facilitate the foundation of the data needed for your project.

In that case, we would begin the development on our machines until your lab machine was ready.

Phase 3 - Large-Scale Development

Once you and our team are satisfied with the data and results produced in the Proof of Concept and Small-Scale Development phases, we can move on to full-scale development. These parts will mirror your final product and will serve as the last step before achieving production-ready parts.

While the small-scale development may focus on one portion of the part, such as the weld, in this phase, we observe how the entire part reacts to the process in its entirety to ensure the quality is maintained.

Ready to Begin?

By now, you should have a solid understanding of MTI’s weld development process and what to expect in each phase. However, it’s important to note that there is a lot more depth to our process than is represented in this document. To explore your application further, we would sign a mutual NDA so we can learn more about your application and you can gain a better understanding of our process.

Contact MTI to start the conversation about your weld development and learn why we are the global leaders in friction welding!

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