Improvement and verification of a pin-on-disc tribometer with variable speed and load

Abstract: The use of threaded fasteners can be found throughout the manufacturing industry due to their simplicity. When tightening a threaded fastener, the goal is to reach a desired clamping force. However, the clamping force is not directly measurable in production environments and the tightening torque is instead used to estimate the clamping force. This master thesis covers the development and verification of the control system for a tribometer for simulating the underhead friction of a threaded fastener during the tightening process. The control loop for the tribometer is implemented as a cascaded PI controller, using both speed and current as feedback. Tuning of the controller is performed through numerical optimization with Powell’s method. The experiments are set up to verify the performance of the system as well as test the validity of the measurements that are generated by the tribometer. The results show that the tribometer is capable of simulating tightenings of threaded fasteners. The coefficient of friction was measured for three different coatings: zinc flake, zinc nickel, and zinc phosphate. The zinc flake coating had the smallest coefficient of friction while the zinc nickel coating had the highest.