Modern CNC (Computer Numerical Control) equipment has the property of high-speed, high precision and high reliability, while its supplementary machine tool component’s performance has hindered the development of China’s machine tool industry for long. As one of the most important functional components of machine tool, the CNC turret directly influences the machine tool’s precision and stiffness matching. It is shown that bolted joint interface has a significant effect on the dynamics of machine tool or CNC turret system. Due to its low cost and easy fabrication, bolted joint has been widely used in modern structural equipment, and its dynamics directly influences the whole machine’s performance. The modelling of bolted joint interface is one of the most subject problems that need to be solved for machine tool or servo turret’s modeling.
In order to establish a more accurate model of machine tool, modeling of bolted joint interface must be considered for investigation of machine tool’s dynamic characteristic. The modeling of bolted joint interface and its nonlinear property are investiaged under the fund of “National Science and Technology major projects” （No.2012ZX04002032,No.2013ZX04012032）. The project begans with the finite element modeling of bolted joint interface, the vibration peoperty and nonlinear behavior of bolted joint is studied then. Some subjects are carried out in this paper , such as the effect of preload, exterior loading and corresponding design method of bolted joint’s dynamics, nonlinear parameter identification method, modeling of bolt joint interface and optimization of CNC turret. The main contents are as follows:
1、Seven kinds of finite element modeling methods for bolted joint interface are studied, such as preload model, thermal stress model, beam element model, MPC constraint, equivalent contact area method and virtual material method, which can be validated by modal test process. The modelling accuracy of different modelling technique is compared with each other according to modal test results, which supplies the finite element technique for subsequent turret’s modeling and indexing tool optimization.
2、The effect of bolted joint interface on structural dynamic response is investigated by hammer and sine sweep test procedure, and the effect of both preload and external loading on vibration transmission is also studied. It shows that the vibration property of bolted joint interface is directly affected by preload and external loading levels, and the nonlinear behavior of bolted joint interface can be observed during test procedure, which provides the foundation of subsequent nonlinear parameter identification and vibration test for bolted joint interface. Meanwhile, the effects of some design parameters, such as nominal diameter, number of bolted joints on the vibration response are discussed, and the welded joints’ dynamics are compared with bolted joints.
3、The equivalent linear function method based on the first-order approximation of harmonic balance method is proposed for nonlinear parameter identification, which shows a satisficed identification precision and promising engineering value. The nonlinear stiffness and damping will be regarded as the function of response amplitude, proposes a representation of the internal non-linear force and provide its harmonic response prediction, which can be used for the nonlinear parameter identification and non-linear inspection. Some numerical simulation of typical nonlinear numerical models, such as cubic stiffness, five order stiffness, coulomb damping, pieacwise stiffness, bilinear stiffness and combined nonlinearity are carried out by simulation process for validity of this method. The equivalent linear function method can be used for parameter identification for various nonlinearities according to numerical results, and the identification resuts is so satisfied that it can be used for inspecting and modelling of nonlinear structures and solution of problems within characterization of nonlinearity of bolted jont interface.
4、An experimental platform is founded for dynamic investigation for bolted joint interface. The equivalent linear function method is utilized for nonlinear parameter identification of bolted joint interface in dynamic property test. And the identification result is so satisfied that it can reveal the softening nonlinear stiffness and hardening nonlinear damping and validate the existence of nonlinear spring and damping force in polynomials form along bolted joint interface. The control system continually adjusts the level of basic input excitation to conduct the response control harmonic test, which is suitable for nonlinear test for precision equipment. The equivalent linear function method is proved experimentally that it can be used for nonlinear parameter identification for other industrical instrument.
5、Servo turret’s structural characteristics, working principle and loading condition is analyzed, and the finite element model of CNC turret is simplified to optimize the structural parameters of the end-tooth plate such as tooth profile angle, tooth number, teeth length ratio and tooth width by considering the modeling of bolted joint. According to the national standard static stiffness test platform of CNC turret is set up to complete the CNC turret performance test, which will identify the low stiffness part of the CNC turret, improve its operation performance and validate finite element model. Experimental results will provide reliability data and optimization analysis for the CNC turret structure and indexing plate.
The investigation of mechanical property of bolted joint is carried out in this study, which begans with the modelling of CNC turret. Some meaningful research results of bolted joint interface have been obtained during this invstigation, such as finite element modeling method, influencing factors, nonlinear dynamic test and the nonlinear parameter identification procedure .