The process uses a non-consumable tool comprised of two rotating components – probe and shoulder. Although one continuous process, RFSSW occurs over four stages: the first of which sees the tool move to the surface of the top sheet, where it rotates to produce the initial frictional pre-heating. Once the pre-heating stage is complete, the material is sufficiently soft, allowing the shoulder to plunge to a pre-determined depth in the base material while the probe retracts to create a gap into which the displaced material can flow. The third stage of the process involves the rotating components returning to the top surface, consolidating the weld material. Finally, the weld cycle finishes when the tool is retracted from the top surface of the material.

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The key industrial drivers for this technology are to replace mass-adding fastening processes, such as riveting, and to join a range of dissimilar materials, which are currently difficult to join using fusion welding processes.

RFSSW has been primarily used to join heat treatable aluminium alloys and to join dissimilar material combinations, such as aluminium alloys to magnesium, steel, titanium and copper. Carbon fibre composites have also been joined.

The RFSSW process offers a number of advantages over current spot joining methods, especially for the joining of aluminium alloys. For example, RFSSW avoids many of the defects associated with melting and solidification of metals, owing to the material remaining in the solid-state; no filler material or third body is added to the weld, reducing component mass; No fumes, porosity or spatter are generated; and the process is easily automated, making it suitable for production.

Refill Friction Stir Spot Welding (RFSSW)

Refill Friction Stir Spot Welding (RFSSW) is a solid-state welding process suitable for spot joining of lightweight metallic alloys [e.g., Aluminum and Magnesium alloys as well as polymer and composite materials.], which is a development of Friction Stir Welding (FSW). 

Unlike FSW, there is no traversing motion associated with the RFSSW process. 

This results in a localized ‘spot’ weld.

The welding tool consists of three parts: pin, sleeve, and clamping ring. 

By controlling the relative movement of the pin retraction and sleeve pressing down, there is a back-filling pressing process at the end of the welding process, pushing the base material back into the welding hole during the welding process.

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Refill Friction Stir Spot Welding

As a new type of spot welding technology, the welding process does not require current, and the RFSSW head has a stirring and crushing effect on the surface oxide film of aluminum alloy materials. 

At the same time, it can backfill the extruded material, eliminating the keyhole problem of traditional friction stir welding, thereby increasing the effective bearing area of the joint, improving mechanical properties, and prolonging fatigue life. 

It is widely used in manufacturing fields such as automobiles, shipbuilding, and aerospace.

The RFSSW process offers a number of advantages over current spot joining methods, especially for the joining of aluminium alloys. 

For example, RFSSW avoids many of the defects associated with melting and solidification of metals, owing to the material remaining in the solid-state; 

No filler material or third body is added to the weld, reducing component mass; 

No fumes, porosity or spatter are generated; and the process is easily automated, making it suitable for production.

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