A substantial portion of the peripheral edges of two panels forming a component of a motor-vehicle body, in particular a front bonnet of a motor-vehicle, is joined by interposing a thermosetting adhesive. Polymerisation of the adhesive is obtained by heating, without introducing the structure into an oven, by means of one or more induction heating coil, which are shaped and arranged in proximity and along the peripheral edges of the two panels. The quality of the induction heating process is controlled according to signals output by a thermographic detection camera which is positioned adjustable at a point from which it can acquire a thermographic image of the entire extension of said peripheral edges of the panels to be joined, so as to allow simultaneously controlling the temperature reached by each portion of the peripheral edges of the panels.