Development of a phenomenological equation to predict tool wear in friction stir welding by steel grades in Al/Steel lap joining

Since its introduction in the industry, the amount of structures being joined by friction stir welding (FSW) are in progression. Even if low-melting point materials such as aluminium or magnesium represents the highest number of applications, this method can also successfully join materials with different melting point as in the case of aluminium to steel. As lightweigthing structures gained ground in the last few years and will still continue to grow, joining processes combining aluminium to steel effectively need to be developed further. When it comes down to join aluminium to steel, the most common configuration is lap joint which the FSW pin enters into the bottom sheet substrate, thus the steel material. In order to have a FSW tool that lasts a sufficient amount of time, the material needs to sustain high stresses and temperatures and still be affordable, such as WC-based tools. The wear rate of the tool used during the process needs to be known and understood as it dictates the applicability of the FSW method depending of the application. As an example, the sub-frame assembly of the Honda Accord 2013 is joined using aluminium to steel FSW lap joining. Be able to predict when the tool reaches a point where it is no longer effective to produce a sound weld can certainly help to evaluate tool life. Actually, a few papers have produced a series of equations or processes that can predict material losses but they are constraints at the application designed for and will be presented further. This study will assess FSW tool life prediction upon different material configurations, mainly steel grades as it impacts greatly the wear behavior of the tool.
12th International Friction Stir Welding (FSW) Symposium, June 26-28, 2018, Saguenay, QC, Canada