In automotive industry, the development of a feasible and reliable solution to produce free-shape hollow box profiles in low thickness AA5754, typical in automotive applications, represents an important innovation opportunity. The main challenge is to produce sound welds between thin plates in a corner joint design, when the activation of the FSW joining mechanisms demands application of a significant mechanical energy. The innovation is based on a new clamping system enabling the use of a conventional tool architecture. The innovation enables to produce hollow box profiles in a wide range of aspect ratios. The cross-section dimensions implemented for the test specimens are 100 mm × 50 mm, with a thickness of 3 mm. The thermal history is monitored at strategic positions along the joint. Metallographic analysis of the weld zone includes EBSD and grain size evaluation. The mechanical properties of the joints are assessed via microhardness and a specially designed bending test: corner opening test (COT). The structural behavior of the final profile is tested with a quasi-static crashworthiness test. The results demonstrate the feasibility of the concept, by presenting a sound weld zone. The FSW components clearly overcome the COT and crashworthiness resistance of similar structures welded by TIG.