A GD&T and Manufacturing Methodology to Optimize Resistant Torque in Car Doors Hinges

The remarkable characteristics of polytetrafluoroethylene (PTFE) have made it one of the most widely used materials in various fields, especially in industry. PTFE has a low coefficient of friction, a high degree of anti-adhesive properties, excellent resistance to external agents, above all a high degree of resistance to low and high temperatures that guarantee long-lasting performance. In this research, a geometric dimensioning and tolerance (GD&T) and manufacturing methodology was presented to optimise the resistant torque in car doors hinges. The manufacturing technology of a PTFE-coated bronze bushing inserted with an FeZnNi pin inside the hinges of a car door was analysed and optimised. A predictive mathematical model was developed and validated with measurements using an appropriate experimental set-up created by the authors. Specifically, the experimental tests were performed by simulating and automating the rotation of the hinge, using software and electronic cards connected to an electric stepper motor; this made it possible to accurately assess the resistant torques due to assembly errors, tightening torques, geometric tolerances, etc. A correct assessment of the resistant torque and especially the friction torque is crucial, both at the design and production stages, to correctly calibrate the door drive loads (opening-closing), and to correctly predict the fatigue life of the components. Through the proposed methodology, the resistant torque was related to the correct manufacture and assembly of the hinge components.