Design And Research Of Frequency Varying Constrained Layer Damping Tool Bar

Vibration is very common in metal cutting process,especially in aerospace and automobile industries.Chatter is hard to avoid for the long overhang tool bar due to its low stiffness,which is generally regarded as an undesirable phenomenon because it reduces the machining stability,quality and surface accuracy.This thesis proposes a passive vibration control solution to develop a constrained layer damping(CLD)tool bar,which has simple structure,good damping performance and strong flexibility.The CLD tool bar can suppress the chatter and improve the machining stability by transforming the vibration energy to heat.The developed tool bar shows better damping performance in high frequency,which has a definite flexibility compared with other passive methods.Firstly,the CLD turning bar and CLD milling bar are preliminarily designed based on the energy dissipation mechanism of CLD structure.The frequency varying damping property of the CLD tool bar is analyzed based on the dynamic mechanical properties of the viscoelastic damping material.The frequency varying damping vibration models both of turning and milling operations are presented.The formulas are deduced to calculate the maximum cutting depth and stable spindle speed.The relationship between the modal parameters and machining stability is analyzed.The design and optimization principle is to increase the first-order dynamic stiffness and to guarantee high value of first-order natural frequency.Secondly,the relationship between dynamic mechanical properties of the viscoelastic material and frequency is determined by experimental test and model fitting.The cantilever beam model and infinitesimal shear dissipation model are built to calculate the modal parameters of the CLD structure.The accuracy of theoretical modeling and computing is verified by the FEM and modal experiments.Thirdly,the geometry parameters of damping layer and the viscoelastic material are optimized to improve the damping performance of CLD turning and CLD milling bars.The optimized CLD turning and CLD milling bars are manufactured and tested by modal experiments,which are compared with the conventional tool bars.It is shown that the first-order dynamic stiffness of CLD turning bar is increased by 82%compared with that of the conventional turning bar,while the first-order dynamic stiffness of CLD milling bar is increased by 23.5%compared with that of the conventional milling bar.Lastly,the stability lobe diagrams of turning and milling operations are drawn.The maximum radial depth of cut for the optimized CLD turning bar is increased by 86.7%compared with that for the conventional turning bar.The maximum axial depth of cut for the optimized CLD milling bar is increased by 22%compared with that for the conventional milling bar.Therefore,the stable machining region is expanded.The cutting parameters of turning and milling experiments are selected in the stability lobe diagrams.From cutting experiments,it is found that the CLD tool bars have better damping performance when the spindle speed and depth of cut are high.The machining operations get more stable and the surface quality is improved.