Bolt Tightening Methods on the Combined Surface of Assembly Structure

Machine tools are assembled by thousands of components. The surface between two components is the mating surface. The bolt tightening methods will affect the stress and deformation of mating surface which influences the accuracy and rigidity of machine tools. In the precision machinery industry, if the structure needs to tighten in line such as linear guideway, the senior engineers will tighten the bolts from sides to the middle or middle to sides instead of tightening in order. Furthermore, engineers use two-step of tightening rather than one-step of tightening. Based on their experience, these tightening methods will reduce the stress of mating surface and increase the rigidity of entire structure. In this study, the three bolts tightening model is used to investigate these tightening methods. Three bolts tightening CAD model is created by using the SolidWorks software. The finite element analysis is used the ANSYS workbench R19 software to simulate the bolt tightening methods (tightening sequences and pre-tightening force ratio) on the mating surface and entire model. From the simulation results, the minimum stress is observed in the tightening sequence from sides to middle and maximum stress is obtained in the tightening sequence in order. The experimental results of bolt tightening sequences match the simulation results. The stresses of mating surface and entire model drastically decrease when the tightening step is two-step of tightening. In two-step tightening process, the pre-tightening force ratio 1:1 is the optimal tightening methods for reducing the stress of mating surface compared to another pre-tightening force ratio.