Friction Stir Welding (FSW) requires specialized equipment and expertise, which can make the process costly to set up. Because of its reliance on friction, FSW may produce excessive heat in some applications that can cause problems such as warping or cracking. This is particularly true when welding metals that are not well-matched. FSW may also be more difficult to inspect due to the narrowness of the welds and lack of visible fusion lines, making it harder to identify any flaws in the welded joint.