Abstract
The dynamic characteristics of the bolted joints have a significant influence on the dynamic characteristics of the machine tool. Therefore, establishing a reasonable bolted joint dynamics model is helpful to improve the accuracy of machine tool dynamics model. Because the pressure distribution on the joint surface is uneven under the concentrated force of bolts, a dynamic modeling method based on the uneven pressure distribution of the joint surface is presented in this paper to improve the dynamic modeling accuracy of the machine tool. The analytic formulas between the normal, tangential stiffness per unit area and the surface pressure on the joint surface can be deduced based on the Hertz contact theory, and the pressure distribution on the joint surface can be obtained by the finite element software. Futhermore, the normal and tangential stiffness distribution on the joint surface can be obtained by the analytic formula and the pressure distribution on the joint surface, and assigning it into the finite element model of the joint. Qualitatively compared the theoretical mode shapes and the experimental mode shapes, as well as quantitatively compared the theoretical modal frequencies and the experimental modal frequencies. The comparison results show that the relative error between the first four-order theoretical modal frequencies and the first four-order experimental modal frequencies is 0.2% to 4.2%. Besides, the first four-order theoretical mode shapes and the first four-order experimental mode shapes are similar and one-to-one correspondence. Therefore, the validity of the theoretical model is verified. The dynamic modeling method proposed in this paper can provide a theoretical basis for the accurate dynamic modeling of the bolted joint in machine tools.
Highlights
The dynamic characteristics of machine tool influence the machining accuracy, the machine performance and the machine life significantly
It is necessary to consider the influence of the dynamic characteristics of the joints on the dynamic characteristics of the whole machine during the dynamic modeling of the machine tool, and establishing a reasonable dynamic model of the joints will help to improve the accuracy of the whole machine dynamics model
H Tian et al.[12] simulated the dynamic characteristics of the joint surface as a layer of virtual material that is fixedly connected to the components of the joint, and the elastic modulus, density and poisson’s ratio of the virtual material are deduced based on the fractal theory and the Hertz contact theory
Summary
After investigating various types of CNC lathes, an assembly specimen composed of two blocks is designed and manufactured. The blocks are connected by four M8 bolts, as depicted in FIG. The unit for the dimensions given in FIG. The upper block and the lower block are connected by bolts, so the contact between the upper block and the lower block is a typical bolted joint. The bolted joint in the assembly specimen is used as the research object to study the dynamic modeling method of the bolted joints
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