Mechanism and simulation analysis of preload relaxation in guide-rail bolts

Abstract

Accurate bolt preloading is a critical procedure for ensuring the long-term high-precision assembly, reliable load-bearing capacity, and dynamic stability of high-end machine tools. In the assembly of machine tool guide rails, bolt relaxation directly degrades the straightness of linear-axis motion and is therefore a key factor limiting the precision retention of the machine tool. Focusing on the preload degradation of guide-rail mounting bolt groups, this study establishes a guide-rail installation model for the base structure and investigates, through simulation, the stress degradation behavior of each bolt within the group. The preload loss of bolts over different service periods of the machine tool is quantitatively characterized. The results show that the bolt preload decreases rapidly in the early stage and gradually stabilizes after stress equalization. By 1100 h of service, the relaxation rate of the preload in all bolts reaches 70%–80%.