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Friction stir welding head with retractable pin: your new FSW equipment for welds without exit hole

Friction stir welding is a process for welding any aluminium or copper alloy or for dissimilar welds. The advantage of this technology is that it does not reach the melting point of the materials. As a result, the risk of defects is considerably reduced and the mechanical properties of the welded parts are close to those of the base material.

However, one problem that can occur in some applications is the exit hole at the end of the FSW weld. Therefore, FSW welding equipment have been developed, including special machines, which can achieve a weld without an exit hole. However, the investment cost of these special machines is still very high.

Stirweld’s engineers therefore asked themselves how to make FSW with a retractable pin accessible to everyone. A solution was found: an FSW head with retractable pin for machining centres

retractable pin

Fixed-pin FSW process versus retractable-pin FSW process

The standard friction stir welding process is a four-step process: the workpieces are clamped, the tool is rotated and plunged into the material and then moved along the workpieces, stirring the material to perform the welding operation. The tool then moves up vertically leaving an exit hole. In FSW with retractable pin, it is this last step that changes. Before the tool moves upwards, the pin retracts, which allows the exit hole to be filled. This technology opens up new applications. Indeed, thanks to the retractable pin, the welding of variable thicknesses with a single FSW tool is possible.

FSW retractable pin principle

What industrial equipments exist for FSW with retractable pin?

Just like friction stir welding with a fixed pin, there are various types of equipment that can be used to carry out FSW operations with a retractable pin: special FSW machines or industrial robots. However, these equipments involve a high investment cost that is not accessible to most companies.

Therefore, at Stirweld, we wanted to make this technology accessible and allow every company to equip itself with FSW with retractable pin technology. For this purpose, we have developed a new FSW welding head for machining centres: the FSW retractable welding head for CNC.

Our retractable FSW head has all the functions of our standard FSW head: force control and recording, cooling, spindle protection against loads and vibrations. The difference is the retractable pin, which makes it possible to fill the exit hole and weld different thicknesses with one FSW tool.

In addition, just like our fixed pin FSW head, our retractable pin FSW head can be adapted to any machining centre.

Friction stir welding head with retractable pin: technical specifications

Our FSW welding head with retractable pin is a highly technological industrial equipment which combines all the technical characteristics allowing a quality FSW welding. Indeed, it has a force control guaranteeing the quality of the weld from 1 to 18 kN, a rotation speed up to 5000 RPM, a water and compressed air cooling system, and finally a real time display of the forging force to facilitate the adjustment of the welding parameters thanks to its remote control panel.

At the end of this FSW head with retractable pin for machining centre, a tool is attached. This tool is the only consumable of the friction stir welding process. And unlike friction stir welding with a fixed pin, the FSW retractable pin tool consists of two parts. The shoulder and the retractable pin are independent of each other to facilitate tool change, but also to save costs. The pin and the shoulder are synchronised in speed of rotation. In addition, the Whistle Notch attachment system allows the transmission of high torques.

Stirweld FSW head with retractable pin: an intelligent piece of equipment

In addition to its retractable pin, our FSW head has a powerful man-machine interface (HMI) allowing 100% control of the repeatability of the process.

Indeed, through to its basic functions, the HMI of our retractable pin FSW head makes your FSW operation repeatable and qualitative.

The first function is the control of the welding force. Welding force is one of the most important parameters to control in order to achieve a quality FSW weld.

The second function is to control the length of the pin. A must when welding with FSW with a retractable pin, the pin length can be from 0 to 10 mm long with an accuracy of plus or minus 0.05 mm.

Third function: head temperature control. In order to secure your FSW operation, we have set up two different temperature measurements inside our equipment, triggering an alert and then an emergency stop in case of overheating.

Fourth function: the use of the head. The HMI has a complete record of the use of the welding head, its welding time and its usage ratio, essential elements for predictive maintenance.

Fifth function: pop-up alerts. Developed by FSW welders, the FSW Stirweld head has two thresholds: a vigilance threshold when the parameters deviate from the operating window and a protection threshold when the parameters go outside the process protection window.

Sixth and final function: data logging. This function can connect directly to your ERP to record data about your welding operations.

In addition to its 6 basic functions, the Stirweld FSW head with retractable pin offers an advanced function: temperature measurement of your FSW welds for 100% quality control and optimisation of your parameters. To learn more about temperature measurement, go here.

HMI functions: FSW head with retractable pin

Aerospace: a sector that has much to gain from a retractable pin FSW head

Fixed-pin friction stir welding was already a major breakthrough for the aerospace industry as it allows the welding of high-strength aluminium, an aluminium alloy used in the manufacture of aerospace parts.

However, the residual weld hole resulting from a fixed-pin FSW operation was an issue in terms of the fatigue strength or tightness of the welded parts. High fatigue strength is the key parameter for the viability of an aerospace part.

Friction stir welding with a retractable pin allows from now on the welding of several applications in these critical sectors; in particular for the welding of tanks.

The conventional technique for joining aluminium tanks has been arc welding. However, arc welding of aluminium tanks presents several problems in terms of weld efficiency, fatigue resistance and corrosion resistance.

Indeed, it is well known that welding circumferential elements such as tanks is a complicated operation. In the manufacture of aluminium tanks, a minimum of two circumferential welds are required to close the tank. However, it is not possible to weld this element using a fixed-pin friction stir welding operation. The exit hole left at the end of the weld may impact the sealing and fatigue strength of the tank. Friction stir welding with a retractable pin is therefore necessary for the assembly of aluminium tanks since this FSW process does not leave an exit hole.

friction stir welding in aerospace

After the FSW operation with retractable pin, the weld efficiency is guaranteed to be 100% (ratio of the UTS of the circumferential weld to the UTS of the base metal), the fatigue strength is increased, the seal is perfect and the tank is 100% corrosion resistant.

Thus, manufacturers of tanks, whether rocket tanks, cryogenic hydrogen tanks or aeronautical tanks, have an interest in equipping themselves with an FSW welding head with retractable pin for machining centres. Why? Because they can improve the quality of their components at a controlled cost.

To find out more about FSW welding of cryogenic tanks, read our article on the subject.

hydrogen cryogenic tank

Aluminium hydrogen tank welded by FSW

Friction stir welding with retractable pin: get equipped at lower cost

With the Stirweld Friction Stir Welding Head you can equip yourself with FSW with retractable pin at a lower cost. Thanks to this head and its powerful HMI, your welds will be of high quality and will be fatigue and corrosion proof; two essential characteristics to guarantee the quality of critical parts such as tanks for space or aeronautics.

This new FSW head from Stirweld has been designed and engineered by experts in friction stir welding, a guarantee of the effectiveness of this technology. Alexia Grossot, structural design engineer at Avantis, a mechanical engineering company, was able to test this head and here is her testimony.

“We wanted to evolve the tool to suit our needs. Before, we used a robot arm to carry out friction stir welding. However, there are many joints in a robot. This makes it too flexible. It deforms a little when you press on the welded surface. In an operation like FSW, you lose precision. To achieve the precision we want, we needed the stiffness of a machine tool.”

Alexia Grosso

Design Engineer

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