Abstract
Bolted connections are widely used in the machine tool manufacturing and equipment. As it is well known, bolt preload will be attenuated by the vibration of machine tools, which will degenerate the working life of machine tools. In this paper, a new experimental design method is introduced into the study on bolt preload attenuation: the quadratic general rotary unitized design. The dynamic analysis of the bolted connection is carried out based on a finely fragmented numerical model to interpret the generation of fretting slip and the reason for the loosening of bolts. The alternating load cyclic vibration test, implemented on the bolted joints, can provide the vibration response under the influence of different working factors. Statistical test and analysis are performed on the quadratic regression mathematical model of the bolt preload attenuation, and the principal working factor that affecting the bolt preload attenuation under vibration can be obtained. Based on the analytical result, the combination of the working factors at the lowest bolt preload attenuation rate, which can effectively slow the bolt looseness, is investigated. The results of this study can provide an experimental basis for improving the machining stiffness of machine tools.
Highlights
CNC machine tools are the core equipment for lightweight and high-precision production of key components in the high-end equipment manufacturing industry and the assembly form is mainly bolted connection
In order to investigate the effect of vibration on bolt preload attenuation of the bolted connection in machine tools, a connection structure that is commonly used in machine tools was designed to perform bolt looseness tests
The quadratic general rotary unitized design (QGRUD) method was used to investigate the pre-tightening torque, cyclic load and load frequency effects on bolt preload attenuation rate in order to obtain the results of bolt preload variations
Summary
CNC machine tools are the core equipment for lightweight and high-precision production of key components in the high-end equipment manufacturing industry and the assembly form is mainly bolted connection. In order to meet the requirements of machining stiffness retention in CNC machine tools, it is necessary to study the working factors and the relaxation mechanism that affect the bolt preload force attenuation. In response to this problem, domestic and foreign scholars have conducted a lot of studies on the factors affecting the loosening of the bolted connection. In 2009, Nassar and Yang [17,18,19,20] solve the tangential force and friction moment at the support surface and the thread, under lateral cyclic load, through accurate mathematical modelling, while the looseness analysis criterion of the bolt structure is obtained. The research results provide an important experimental basis for improving the machining stiffness of machine tools, while they are very significant for the study of the loosening mechanism of the bolted connection in machine tools
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