Analysis of torque variation in bolt fastening on coated steel surfaces

Abstract

As the number of parts ever increases, the push for automation in assembly processes is intensifying in advanced manufacturing industries. The drive to improve productivity through manufacturing automation is relentless, and minimizing torque variation in automated bolt fastening is crucial for achieving successful assembly. Therefore, a precise understanding of the mechanisms of interfacial friction between bolts and coated steel plates, along with a torque analysis based on the interactions of various involved parameters, is essential. This study examines the interactions between surface topography and mechanical properties of bolts and coated steel plates. We explain three primary friction modes (plowing, sliding, and penetrating) within the defined contact areas and propose a prediction model based on contact mechanics to estimate the frictional torque under the bolt head on coated surfaces. Additionally, we quantitatively evaluate how the proportions of these friction modes change under various axial loads and coating conditions, and how these variations affect torque values. We also assess how variations in key parameters influence changes in friction modes, providing insights into the critical factors that should be monitored for effective control of fastening torque. This study presents methods for analyzing and calculating friction torque, offering guidelines for monitoring bearing surfaces to address bolt topography deviations and solving key industrial challenges in automated assembly.