In-situ wear-progression measurement in POM-steel gear contacts

Wear is the dominant failure mechanism in polymer–steel gear pairs. This study presents an in-situ optical method for measuring the wear-progression of a polyoxymethylene (POM) gear meshing with a steel pinion on a real-scale gear test rig under controlled operating conditions. The method enables imaging of the individual teeth without removing the gears from their operating environment. Experiments were performed for a range of operating parameters (torque: 1/2 Nm, rotational speed: 1200/1800 rpm, temperature: 30/70 ° C ). The in-situ profiles reveal three distinct wear regimes: (1) a running-in phase with nearly uniform material removal and a steep decrease in the wear coefficient during the first 30,000 load cycles, (2) a position-dependent regime dominated by dedendum and tip wear with delayed wear in the pitch area, and (3) a steady-state regime where wear progresses approximately linearly at all characteristic flank positions. Contact analyses using imported measured profiles show a redistribution of the contact pressure toward the pitch area, consistent with the observed transition to steady-state wear. Higher torque and speed reduce the number of cycles to the wear-failure criterion, whereas a higher temperature extends the lifetime and promotes a more uniform flank engagement for the investigated material pairing and operating conditions. Scanning electron microscopy (SEM) observations support a milder wear morphology at 70 ° C compared to 30 ° C . The method provides time- and position-resolved wear data that are difficult to reconstruct from ex-situ techniques and is suitable for supporting flank wear modeling and optimization.