Search

Chatter vibration is apt to occur when machining thin-walled parts with insufficient rigidity. The harmful excitation of periodical cutting forces can be mitigated by enhancing the dynamic stiffness or increasing the damping of the part. A composite viscous damper including air damping and eddy current damping is designed, which can be attached on the thin-walled part by the vacuum. Based on the formulations of air damping and eddy current damping, the optimal equivalent viscous damping is derived for achieving the maximum critical depth of cut. Furthermore, the geometries of the damper are determined for damping a specific thin-walled part after investigating its relationship with viscous damping. The modal test indicates that the damper can suppress multiple modes of the cylindrical thin-walled part, and the amplitude of the first mode of the frequency response function (FRF) is reduced by 57%. The composite viscous damper is applied to suppress the chatter and resonant vibration of the thin-walled part during machining. Milling tests demonstrate that the machining vibration is reduced by 55% and 76% after employing single damper and four dampers, respectively. [ABSTRACT FROM AUTHOR]

Nonlinearities have been evidenced during the chatter vibration of milling. Machinability of the thin-walled part is feed rate and position-dependent, and is subject to process damping at low cutting speed. Therefore, chatter stability prediction of milling considering nonlinear cutting force, nonlinear structural stiffness and process damping is investigated. The cutting force and stiffness are established based on the polynomial model and the process damping is investigated based on the dissipated energy. The dynamic cutting force and stability lobes are solved in the time domain with coefficients updated at each iteration. By formulating the displacement as an expanded form via the perturbation method, the time-consuming solution of delay differential equations is avoided. After formulating the identification of the nonlinear model via cutting tests and modal tests, numerical simulations considering nonlinearities are carried out and compared with the analytical method. The proposed method attains high accuracy of classic time-domain solution, but with an improved computational efficiency. Finally, cutting tests are conducted to verify the prediction of cutting force and stability lobes. [ABSTRACT FROM AUTHOR]

A milling cutter with large length–diameter ratio has been essential in machining structural parts with deep cavity and deep hole features. However, chatter vibration is apt to occur with the increase of tool overhang. A damped milling cutter is developed by employing a single-degree-of-freedom passive damper located inside the arbor. The stiffness and damping design of the embedded damper are carried out by following the equal peaks criterion. A novel design is fulfilled to avoid the disequilibrium of the cutter during high-speed rotation, and an accurate experimental tuning of the design parameters is required to achieve the optimum vibration suppression due to a low mass ratio of 2.5%. Modal analysis demonstrates that the damped cutter with an approximate length–diameter ratio of 8 can reach 75% magnitude reduction at all orientations, which is benefical to resist milling force excitation varying with the rotation angle. Chatter stability simulation demonstrates that the damped cutter is able to increase the stability limits based on the evaluation of undamped and Sandvik cutters. Three configurations of machining tests are carried out and the design of the damped cutter is validated by the machining audio signals and machined surface roughness in the end. [ABSTRACT FROM AUTHOR]

• Updated tuning methodology of vibration absorber to improve the machining stability. • Stability pocket relocation to maximize critical cutting depth at specified speed. • Design of stability pocket considering robustness of cutting parameter selection. • Fast and accurate identification of chatter stability boundary. • Two-dimensional chatter stability optimization and milling cutter application. The Equal Real Troughs optimization criterion of vibration absorber improves unconditionally stable cutting depth of single-dimensional chatter vibration. However, the stability pockets within the lobes are decreased after tuning, which therefore causes the machining efficiency reduction at certain spindle speed. Noting that the spindle speed is preferred as a constant in the workshop once the assembly of machine tool/cutter/workpiece are determined, an updated optimization methodology is proposed to maximize the critical cutting depth within specified spindle speed range by utilizing the lobing effect. The optimization routine is formulated based on the boundary identification of stability lobe diagram (SLD), which is derived by the Zero-Order Analytical (ZOA) solution. The tuning methodology is validated on the design of vibration absorber in order to raise the machining stability of slender milling/turning cutter with large length-diameter ratio. The updated methodology enables the stability lobes relocation of single/two-dimensional chatter vibration for achieving higher critical cutting depth at specified spindle speed, and assures the stability width assignable considering the robustness of cutting parameter selection. [ABSTRACT FROM AUTHOR]

Passive control has been effective in damping the machining vibration of thin-walled parts. However, physical addition onto the part causes the dynamics change and limits the engagement of cutting tool, especially in the application of multi-axis machining. Utilizing the non-contact eddy current damping, a two-degree-of-freedom apparatus is designed after experimental investigation into the magnet combination, magnetic flux density and magnetic flux mode on damping behaviors on a specifically designed platform. The apparatus is set up by mounting on the stationary spindle head of a five-axis CNC machine tool. The included neodymium magnets, and then the induced eddy current damping force are able to follow the feeding cutter through the control of two servo motors, keeping out of touch with the thin-walled part to be damped. As the damping force is able to resist the vibration of the machining point induced by the cutting force directly, it allows the design with less volume and mass (i.e. magnets and conductors). In the end, hammer tests are performed to verify the additional damping ratio imposed by the apparatus. Three-axis milling tests of a thin-walled frame are carried out to validate the damping of the apparatus, and five-axis milling tests of thin-walled blade type part are conducted to demonstrate its controllable damping and adaptability to complex tool path. [ABSTRACT FROM AUTHOR]

Thin-walled workpieces are largely manufactured in the aerospace industry. The manufacturing process has been a problem due to its flexibility, and chatter vibrations are apt to occur, which restricts the machining efficiency and quality. A vibration suppression device for thin-walled workpieces is presented based on the electromagnetic induction principle, which utilizes machining vibrations to generate resistant force on the workpiece. The formulated force varies with the workpiece vibration velocity, but in an opposite direction. Excitation tests using the electromagnetic shaker illustrate that the device is effective in vibration attenuation. Finally, machining tests are carried out with applications to two thin-walled structures for further verification. The machining vibrations and surface quality demonstrate the damping promotion of the workpiece assembly, and milling stability limit is increased by more than twofold. [ABSTRACT FROM AUTHOR]

The productivity of many industrial cutting processes is limited by high amplitude chatter vibrations. An optimization technique based on the use of the stability lobes helps to increase the productivity of these processes, improving the life of machine elements and reducing the tool wear as well. The best-known lobes correspond to Hopf bifurcations. However, in case of interrupted cutting, additional lobes appear due to period doubling or flip bifurcation. When the system has more than one dominant vibration mode, important variations can appear in stability due to interaction between modes. The basic mathematics for the appearance of these new lobes are shown in this article. The frequency domain study shows that lobes related to flip bifurcation are a special case of the interaction between modes. The results of these interactions are verified by comparison with semi-discretization method and time domain simulations, respectively. [ABSTRACT FROM PUBLISHER]