Friction stir spot welding
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The friction stir spot welding ( English friction stir spot welding , FSSW ) is a pressure welding method, below the melting point of working of the workpieces. It is a variant of friction stir welding .
Process description
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With friction stir spot welding, individual spot welds are created by pressing a rotating tool with high force into the upper of two metal sheets that overlap each other. Due to the frictional heat and the high pressure, the workpiece material is plasticized so that the tip of the pin dips into the joining zone between the two sheets and stirs the oxides there . The shoulder becomes like forgingA high pressure is applied by which the components are metallurgically bonded together without melting. The tool is dipped into the sheets until the shoulder is in contact with the surface of the upper sheet. After a short dwell time, the tool is pulled out of the workpieces again so that a spot weld can be created approximately every 5 seconds.
The tool consists of a rotating pen and a shoulder. The pin is the part of the tool that penetrates the material. Both the pin and the shoulder can be profiled to convey the plasticized material in a specific direction and to efficiently break up and stir the oxide skins on the surfaces lying on top of one another. When using one-piece tools, which have already proven themselves in automobile and rail vehicle construction, an end hole remains after the tool is pulled out. The rotating tool is often surrounded by a non-rotating clamping ring, with which the workpieces are firmly pressed together with the clamping force before and when they are immersed. The clamping ring can also be used to reduce the extrusion of plasticized material in order to avoid the formation of burrs or bulges, to apply protective gas or to cool the tool using compressed air.
The most important process parameters are the speed and contact pressure. This results in the immersion speed for a given workpiece material. Modern spot welding guns can be used either via position control or force control or via a product-specific programmed force-displacement control. Position control is often used until a specified immersion depth is reached and then switched to force control during the dwell time. Certain position values can also be specified during the force-controlled dwell time that should not be exceeded or fallen below.
Spot welding guns
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The friction stir spot welding is carried out with spot welding guns that are mounted on a console, flanged to an articulated arm robot or manually guided to the component with a balancer.
Procedural advantages
The friction stir spot welding is characterized by a number of process advantages. Any damage to the material due to the extreme heat, such as occurs with laser or arc welding , does not occur. Particularly in the case of artificially aged aluminum alloys, the strength in the weld seam and the heat-affected zone is much higher than in conventional welding processes.
Industrial use
Friction stir spot welds have a high level of strength, so that they are also suitable for parts that are exposed to particularly high loads. In addition to automobile and rail vehicle construction , aerospace engineering develops the process z. B. for welding deep-drawn sheet metal shells on the seat frame of aircraft seats. In the electrical industry, it can be used to weld aluminum and copper. There are other possible uses in facade and furniture construction , where the low heat input, especially with anodized sheet metal, leads to excellent optical properties.
literature
- Stephan Kallee and Ozan Caliskanoglu: Friction stir spot welding in vehicle construction: New possibilities. The practitioner, 11/2017. Pp. 548-551.
- Wiebke Sophie Junior: Friction spot welding / joining of thermoplastic polymer and aluminum with nanocomposites based on surface-functionalized nanoparticles for lightweight construction applications , Cuvillier , Göttingen 2015, ISBN 978-3-7369-9136-1 (Dissertation Universität Hamburg 2015, 166 pages, illustrations, diagrams, 21 cm).