Diagnostic Study on the Rooftop Assembly Process in the Automotive Industry

My thesis presents a diagnostic study of the rooftop assembly process of the second- generation Maserati GranTurismo (M189 platform), carried out during an industrial internship at the Maserati plant in Modena. The roof to body interface is a customer- significant, fully visible joint, and its dimensional quality, expressed through the flush between the roof rail and the surrounding body, is a primary indicator of perceived build quality in a luxury sportscar. The aluminium roof is joined to the body using a one- component polyurethane structural adhesive, which makes the joint sensitive to panel geometry, bead application, fixturing, and curing conditions. The work was motivated by the transfer of GranTurismo body production from the Mirafiori plant to Modena. Baseline bodies arriving from Mirafiori were characterised using Statistical Process Control (SPC) on a sample of vehicles. X ̄ and R control charts, process capability and performance indices (Cp, Cpk, Pp, Ppk), parallelism analysis, and normality testing identified two systematic bottlenecks: a recurring flush deficit at the rear extremity (point P7) and an undershoot at the A-pillar interface (point P1), together with a left to right asymmetry along the roof axis. A 4M Ishikawa analysis was used to structure the root-cause investigation, leading to three corrective actions: a load-distributed roof mounting tool, a revised adhesive application trajectory, and an operator retraining and standard operating procedure update. The corrected process at Modena was validated on a fresh production sample using the same statistical framework, complemented by a destructive adhesion test on a complete vehicle to confirm joint integrity. The results show a measurable improvement in capability and performance indices, a reduction in the per point flush deficit at the critical rear and A-pillar locations, and improved bilateral parallelism, demonstrating that the bottlenecks identified at baseline were effectively addressed.