Global Stability Analysis on Combination Self-Excited Vibration of BTA Deep-Hole Boring Rotor Materials

Abstract

Cr, Ni, Mo, V exist in materials of high, medium and low pressure turbine rotor. Its composition contains higher carbon content, so leads to poor hardenability. Shear characteristics of martensite phase transformation is caused by a large number of micro defects inside crystal of microstructure in rotor during the service status. Martensite phase transformation is by strengthening because of plastic deformation in cutting process. Mechanical properties and phase transformation plasticity in cutting process show that rotor is hard machining material. Plastic deformation aggravates tool wear, and leads to an increased cutting force; hard points of uneven material internal organization lead to fluctuation of cutting force, and induced cutting chatter. During the course of machining critical or ultra-supercritical rotor, boring bar becomes a flexible system surrounded by rotating stirred vortex cutting fluid inside and outside it. BTA processing system is in a complicated hydraulic-solid coupling environment. Whether or not BTA deep hole boring processing system is stable, the essence is converted into estimating dynamic stability of BTA boring bar coupled fluid--solid with multi-physics environment. The system will be triggered cutting chatter, fluid flutter and self-excited vibration combination. This paper establishes nonlinear mathematical physics model on BTA deep hole processing system. The perturbation equation and Lyapunov function of BTA system are obtained, through introducing the stable Rumjantsev part variables analysis theory. Based on stability characteristic under the significance of Lyapunov, the constraint condition undisturbed stability is gotten and the global bifurcation analysis is finished. Hyperbolic periodic orbit and heteroclinic connection are found throughout the entire phase space of Hamiltonian system. The bifurcation condition on quadratic heteroclinic is acquired, by analyzing intersection relationship between hyperbolic stable manifold and its unstable manifold of Poincare mapping. The intersection critical conditions are shown on hyperbolic fixed stable manifold and its unstable manifold, by using computer numerical simulation to draw 3-D surface relationship among resonant frequency, cutting fluids flow velocity and the radius of free surface. The result could provide a reference on multi-machining parameters optimization for BTA deep hole boring process practical production.