Fuente: WIPO "tomato" There is described a welding head (17) configured to weld a cap (6) to a pouring collar (5) and comprising: a support portion (20) configured to be advanced along an operative path (P) for following the sealed package (2) along an advancement direction (D); a welding portion (22) movably coupled to the support portion (20) and including a welding device (23) configured to interact with the cap (6) for welding the cap (6) thereon (5); the welding portion (22) is configured to move, with respect to the support portion (20), between a first position in which it is aligned in a resting configuration with the support portion (20), and a plurality of second positions in which it is displaced relatively to the support portion for assuming a corrected configuration thereby adapting to an actual positioning of the cap (6) with respect to the advancement direction (D); the welding head (17) further comprises a magnetic device (25) configured to bias the welding portion (22) towards the first position.