Welding of aluminium castings in the automotive industry is done by Friction Stir Welding (FSW). The requirements for the quality of the welds are high, so for the manufacture of high-quality joints the shape of the tool and technological parameters are important. The company investigated the influence of tool geometry on the quality of butt welds, the surface of which must be pretreated due to dimensional matching. Eight different geometric designs were used for the tests. The welding parameters were adjusted to the external appearance of the weld itself. Each welded joint was visually inspected. The products were tested on pressure test until failure. On these samples, welded joints were metallographically examined and defects in the weld and bursting sites were analysed. We found out that by increasing the grinding of the spiral, we get a higher energy intake. With increased energy input, the required welding speed increases. With the pressure test, we found that the strength of the welds meets the requirements, as the test subject always made concessions on the base material and not on the weld.
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