Nonlinear Dynamic Behavior Of Drilling Shaft System In Deep Hole Drilling

The study on the drilling shaft system is increasingly emphasized due to the increasing demand on high efficiency, high precision and high reliability for metallurgical industry, nuclear power and ordnance industry. However, it is crucial content of nonlinear performance analysis of drilling shaft system to calculate the movement trajectories of the drilling shaft, nonlinear hydrodynamic forces and their Jacobians etc. efficiently without losing dynamic analysis precision due to complexity of the problem. The availability of various approaches such as analytical or numerical Euler-Bernoulli beam equation and empirical equation for solving the dynamic characteristic of drilling shaft just indicate that there is no universally accepted opinion on this point. Based on the relevant mathematical theory and previous research works, some key technologies are presented in this thesis for solving the rich and complex dynamic behaviors of drilling shaft system, the results can make a good reference for the dynamic design of drilling shaft system in practical drilling process and have important significance of the theory and engineering application.The hydrodynamic pressure of cutting fluid in deep hole drilling was investigated. According to characteristics of Reynolds equation arising in cutting fluid to satisfy the finite length drilling shaft and taking approximate analytical pressure function as the basic solution, hydrodynamic pressure was modeled. The effects of parameters such as the rotational speed of drilling shaft and its whirling velocity, eccentric velocity etc., can be taken into consideration in the model of hydrodynamic pressure. By using the theoretical analysis and computation for the distribution rules of the hydrodynamic pressure as changing the structural and the moving parameters of drilling shaft, a quantitative elucidation of the dynamic characteristics of hydrodynamic pressure was implemented, and the whirling condition and instability of drilling shaft are discussed. Finally, the rules of selecting drilling shaft parameters are derived, so has significant guidance to the production.The equivalent variational approach is proved by revising the variational form of Reynolds equation in hydrodynamic forces of cutting fluid with rupture boundary. Then, according to the physical character of cutting fluid, a revise variational form of Reynolds equation and its disturbed equation are formulated by using isoparametric finite element method with 8 nodal points. So, nonlinear hydrodynamic forces of cutting fluid and their Jacobian matrix are obtained simultaneously without increasing the computational costs. The applicable range and the approximate degree of the current model of nonlinear hydrodynamic forces are discussed by comparing the analytical model with finite element model of nonlinear hydrodynamic forces.Based on the solving thought of traditional shooting method, the generalized shooting procedure is implemented, the period takes part in the iterations of the shooting method as a parameter. The iterations give the periodic orbit and its period simultaneously. The increments of the state variables and period T are selected for iterations using the optimization method, and then the periodic orbit and its period are determined rapidly. For the structural style of round hole and slot hole, the local stability and dynamic behaviors of periodic motion with the change of the drilling shaft design parameters value are obtained by combining the presented method of nonlinear hydrodynamic forces and their Jacobian matrix, improvement shoot method with Floquet theory. The rich and complex dynamic behaviors of the drilling shaft system are presented and further analyzed in depth and scope, such as periodic, quasi-periodic, jumped solution etc. The stability, bifurcation characteristics and whirling motion behaviors of drilling shaft system are analyzed when the rotating speed of drilling shaft is used as the bifurcation parameter. The effect of the increasing stability of eccentricity on the drilling shaft system is discovered Through the combination of theories with experiment, the correctness and effectiveness of the above methods are verified.Based on the extended Hamilton principle, the variational problem of lateral vibration of drilling shaft system is deduced and the finite element model of lateral vibration of drilling shaft is established using Timoshenko element model. The shear deformation and rotary inertia are taken into account in the model of drilling system. Mode synthesis technique with free-interface is modified to represent a reduced method of degrees-of-freedom. The practical flexible deep-hole drilling shaft system with multi-support is used as subject to test the presented reduced method. The results show that the presented reduced method can reduce a large number of degrees-of-freedom of flexible drilling shaft system, effectively save the computational costs under the condition of maintain nonlinear analysis precision for the system, and may satisfy the dynamic design demand of the large-scale complex deep hole drilling machine. By using the theoretical analysis and computation, the natural frequency influence rules of the drilling shaft system as changing the structural parameters of drilling shaft and the relative distance of intermediate support are discussed. For the structural style of round hole and slot hole, the stable region, unstable boundary and unstable mode of drilling shaft system are analyzed under the different rotating speed and drilling depth parameter in drilling process.The finite element model of drilling tool is established as flexible vibratory shaft with multi-support in deep hole drilling process. Considering the machining characteristic in vibrating drilling process, the axial vibration of drilling shaft containing flowing cutting fluid in pipe and vibrating cutting force are taken into account in the model of drilling system. Under the given initial value of pilot bush misalignment and the support misalignment, the relationship between the axial hole straightness deviation and cutting parameters as drilling shaft length and drilling depth is analyzed. Finally, the rules for change of the axial hole straightness deviation are derived with drilling length increasing, so provide a basis for the design of deep hole drilling machine and analysis of the errors of mechanical process.