How to choose my FSW tool for my application?

Since the emergence of friction stir welding, many innovations have been made to improve the quality of FSW tools. These improvements result in better quality, more stable welds, and a certified lifetime. Today, many people are asking how to choose their FSW tool and how this choice will influence the quality of their weld. We propose to answer this legitimate question throughout this article. To start with, it is important to detail the composition of an FSW tool.

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The different components of a FSW tool: what is a shoulder and what is a pin?

A FSW tool consists of three parts: the body, the shoulder and the pin.

The shoulder is the part that heats the material by friction in order to soften the workpieces and thus enable the welding operation. This is its primary function. The larger the diameter of the shoulder, the larger the contact area, which increases the frictional capacity of the tool. However, too large a shoulder will cause the workpiece to heat up too much and reduce the strength of the weld. The size of the shoulder will therefore depend on the thickness to be welded.

In addition, the shoulder with its counter-cyclical spiral shape allows the material flow to be pushed back towards the centre to prevent it from leaving the welding area. This second feature will improve the surface finish of the weld and the quality of the weld. With this feature, there is no need to tilt the tool during the welding operation. This is because the spirals pull the material towards the axis, which prevents the material from slipping (see infographic below: “No more tilt angle required on the FSW tool”).

Tool attachment – Whistle notch systemShoulderPin

In addition, the spiral shape improves tolerance to weld seam offset, reduces burrs and makes variable thickness welds possible.

Second part: the pin – the extremity of the tool.

The pin is the part of the tool that will penetrate the material by mixing it through a shearing effect: this is the stirring. Indeed, due to its conical shape and its grooves, the pin heats the material and softens it in order to ensure the mixing of the materials and the quality of the weld. The flat tip of the pin allows better penetration of the tool and therefore reduces the risk of lack of penetration. The pin and its flutes allow stirring in the direction of tool rotation as well as vertical mixing of the material.

Heat is generated by the friction between the workpiece and the tool, which produces plastic deformation of the workpiece and welds the two parts together.

How does the quality of my FSW tool contribute to the quality of my weld?

The quality of the weld depends directly on the quality of the tool and the choice of the tool. We will see later how to choose the right tool for your specific application.
But first, let’s see how the quality of the tool affects the quality of your FSW weld. To understand this, it is important to keep in mind how a FSW welding operation works.

Friction Stir Welding in 4 steps

1

Clamping of the parts to be welded: side by side in a butt welding configuration, one on top of the other in a lap welding configuration. The tool does not depend on the welding configuration. The same tool is used for butt and lap welding.

2

The tool penetrates the material: the shoulder heats the material by friction and the pin seals the parts together.

3

Welding operation: the tool advances along the weld seam and mixes the parts together.

4

End of welding: the tool moves up vertically, leaving a hole.

As you can see, the tool geometry has an impact on the weld quality. The tool will directly contribute to the mechanical strength of the weld. How? By the strong mixing of the material by the pin and by the heat generated by the shoulder. These two phenomena will cause a recrystallisation of the aluminium which will result in the precipitation of fine grains and thus contribute to the very good mechanical strength of FSW welds.

However, at the end of the weld, the tool will leave an exit hole as you can see in step 4 of the infographic above. This is not a quality issue, but for some applications it is better to remove it. The solution: the retractable pin tool. Where a conventional FSW tool leaves an exit hole at the end of the weld, a retractable pin tool seals the hole directly at the end of the weld, without any further intervention.

Finally, a last improvement has been made to the FSW tools: temperature measurement of the weld in real time. The temperature measurement tool allows you to control your FSW weld in real time: it is a quality tool.

Smart tool holder – the temperature measuring tool: precision for successful welding

In addition to the functionality of a standard tool, the temperature measurement tool allows you to precisely measure the temperature of the weld in order to adjust your welding parameters finely and check 100% of the parts.

How does the temperature measurement tool work?

The FSW temperature measurement has two holders, one fixed and one rotating, each containing an electronic card. These electronic boards receive and send the signal from the probe in the tool to the software. Thanks to this system, it is possible to control the temperature of the weld in order to optimise all the welding parameters (rotation speed, feed speed, Z force).

The benefits of the Stirweld temperature measurement tool are:

• Real time temperature measurement for demanding FSW parts (space, aerospace and automotive applications),
• 100% quality control of FSW parts – compatible with EN ,
• Optimisation of welding parameters: increase of welding speed (from 20 to 100%).

As an example, the temperature measurement tool is very useful for the assembly of aerospace components according to EN .

How to choose my friction stir welding tool according to my application?

To choose your FSW tool, you need to take into account 4 parameters:

• The distance to be welded,
• The depth to be welded, which will determine the size of the pin and the shoulder,
• The tool geometry: for this point, Stirweld experts are present to help you define the tool geometry that will best suit your welding configuration – optimal heat and material stirring.
• The material of the parts to be welded: standard aluminium alloys, high strength aluminium alloys, aluminium casting, copper, aluminium-steel or aluminium-stainless steel dissimilar.

Stirweld has developed a range of standard tools for different markets and materials to be welded. To give you an idea of which FSW tool is best suited to your application, here are some examples of FSW tool choices depending on the application sector, the material used and the thickness to be welded.

FSW tool for your application

For example, for the aerospace sector, the FSW tool will be made of a high-strength alloy to suit the more demanding aluminium parts (2xxx and 7xxx series).

You will get efficient and thoughtful service from World Wide Welding.

Another example is the automotive sector, where most parts are produced in aluminium casting. These alloys contain silicon, which is inherently abrasive. For this type of aluminium, we use tools made of ceramic, a material that is highly resistant to abrasion.

Stirweld supports you with a complete range of high quality FSW tools. One of our main references, the Ariane company, leader in the aerospace field.

What is the lifetime of an FSW tool?

There are two factors that influence the lifetime of an FSW tool:

• Cyclic fatigue: Fatigue exerted at the base of the pin causing the pin to pull out prematurely. It is due to the drag force, i.e. the force exerted as the tool moves through the workpiece.

• Abrasive wear: Fatigue exerted on the whole tool by friction in the welded material. This will cause wear on the shoulder spiral which affects the quality of the weld.

The life of the tool will also depend on the materials being welded: aluminium/aluminium, aluminium/copper, copper/copper, aluminium/steel.

FSW Stirweld tools have an average life of  metres of weld in a “classic” Al/Al welding configuration with a thickness of less than 8mm. In order to guarantee the quality of its tools, Stirweld uses a test bench.

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Materials for friction stir welding: how to choose?

The right choice of materials for friction stir welding is essential to guarantee the integrity and durability of welds. They react differently in terms of plasticity, thermal conductivity and mechanical behavior.

Unlike traditional welding methods involving the melting of metals, friction stir welding (FSW) uses the heat generated by the friction of a rotating tool to weld in a solid state, without the addition of material.

FSW can be used to join materials that are difficult to weld using conventional processes, such as aluminum, magnesium, copper, titanium or steel. It produces high-quality welds with minimal deformation, even on thick materials.

But which materials are most commonly used in FSW? What are the selection criteria to consider? And what are the specific features of each? TRA-C industrie, experts in FSW welding, shares their advice on choosing the right materials for your application.

Selection criteria of materials for friction stir welding

The choice of materials for friction stir welding will depend not only on their properties, but also on their specific application. Here are the main factors to consider:

• Mechanical properties: the tensile strength, hardness and ductility of materials primarily determine their ability to withstand the forces applied during the welding process. But clamping tools help to overcome these limitations;
• Thermal properties: materials with high thermal conductivity, such as aluminum or copper, require low-temperature assembly to avoid excessive dissipation;

• Metal similarity: similar alloys, such as aluminum, generally weld well together. Significant differences in material properties can lead to faulty welds;
• Operating conditions: the conditions to which the weld will be exposed also determine the choice of materials. These include extreme temperatures, corrosive environments and mechanical loads;

• Processing: some materials require special preparation and treatment before assembly. This is the case with steel, for example, from which oxides must be removed first;
• Plasticity: finally, it is better to choose materials with sufficient plasticity to allow them to deform without cracking during the welding process.

Materials commonly used in FSW welding

FSW welding is a technique that is suitable for a wide range of metallic and composite materials. Here’s an overview of the most commonly used materials for friction stir welding:

• Aluminum: aluminum is one of the most popular materials for friction stir welding. Lightweight, it offers excellent thermal and electrical conductivity and good resistance for corrosion. FSW can weld both standard and high-density aluminum (2xxx, 5xxx, 6xxx, 7xxx);
• Copper: copper is highly conductive, both thermally and electrically, which makes it necessary for certain electrical applications;
• Titanium: it has excellent mechanical strength, comparable to that of steel, but it is much lighter. Titanium is also resistant to corrosion in many aggressive environments, including seawater and chemical environments;
• Steel: although more difficult to weld with FSW than aluminum, steel offers excellent mechanical strength and good durability, but lower thermal conductivity.

Comparison of materials for friction stir welding

In order to adapt welding parameters, it is essential to consider the behavior of materials for friction stir welding. Here’s a comparison of the advantages and drawbacks of the FSW process:

• Aluminum: FSW can be used to join aluminum alloys that are difficult to weld using conventional methods. However, welding parameters must be precisely controlled to avoid defects such as cavities and cracks;
• Copper: FSW produces high-quality welds with low distortion and improved mechanical properties. But the assembly temperature must be controlled because of copper’s high thermal conductivity;
• Titanium: welding this material is difficult due to its hardness, low melting temperature and contamination when exposed to air. By adjusting weld parameters, FSW makes it possible to meet these challenges while guaranteeing optimum quality;
• Steel: finally, steel welds are more resistant to impact and fatigue with FSW than with conventional welding methods. However, FSW requires wear-resistant tools, due to the density of the material.

Industrial applications of FSW based on materials

Materials for friction stir welding are used in a variety of sectors, depending on their mechanical properties and ease of processing. The main industrial applications include:

• Aerospace industry: aluminum is widely used for fuselage and wing assembly. It reduces aircraft weight while maintaining structural integrity. Titanium alloys offer excellent mechanical properties, particularly in high-temperature environments such as engine components;
• The automotive sector: aluminum is used to manufacture light, resistant chassis and body structures. This improves vehicle performance and energy efficiency, particularly in e-mobility. FSW is also suitable to the assembly of battery trays, as it allows welding around electrical components without damaging them;
• Shipbuilding: corrosion-resistant aluminum is used for ship hulls and superstructures. Stainless steel, on the other hand, is perfect for tanks and piping in aggressive marine environments;
• The rail industry: here again, aluminum’s properties make it the ideal material for designing lightweight, high-strength train bodies. Components requiring high mechanical strength, such as frames and structures, are made of steel;
• The energy sector: heat exchangers and piping are often made of copper or aluminum, excellent thermal conductors. With its high conductivity, copper is also used for electrical components.

Recent innovations and research on FSW materials

FSW is a constantly evolving field. Ongoing innovation and research are aimed at improving materials for friction stir welding and processes. This enables to meet the growing challenges of modern industries.

Major advances include the development of new aluminum alloys, such as the series (Al-Zn-Mg). They offer mechanical strength comparable to that of certain steels, but they are lighter.

At the same time, studies on the effects of microalloying and numerical modelling are interesting to predict the thermal and mechanical behavior of steel welds. High-performance stainless steels are more resistant to corrosion and wear.

Friction stir welding of steel is particularly demanding due to the temperatures required and the mechanical strength of this material. Tools made of nickel-based superalloys or including internal cooling systems can withstand high temperatures and wear.

Aluminum, on the other hand, has a low melting temperature. New welding tools are designed to reduce friction and heat generation. This minimizes deformation of aluminum welds. Finally, the use of adjustable shoulders can adapt to variations in the thickness of the parts to be welded.

TRA-C industrie guides you in your choice of materials for friction stir welding

The right choice of materials for friction stir welding enables engineers to improve the performance, durability and efficiency of their assemblies. All while reducing production and maintenance costs!

Expert in friction stir welding for over 20 years in Europe, certified ISO and  in compliance with NF EN ISO , TRA-C industrie offers you its expertise in selecting the right materials for your applications.

We’re at your side at each stage of your project, from design to management of all your welding operations. We can also design, integrate, manufacture and maintain your machines, industrial robots and automation systems...

Thanks to our technical design office and R&D department, we also imagine innovative FSW solutions. Finally, we offer training and technical assistance in France and abroad.

Are you interested in learning more about robotic friction stir welding? Contact us today to secure an expert consultation!

Mathilda