Browsing by Author "Tien-Dat Hoang"

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Coupled lateral and torsional vibrations of the micro-drilling spindle systems
(2016-11)
Lee, An-Chen
;
Tien-Dat Hoang
;
機械工程學系
;
Department of Mechanical Engineering
In this research, the coupled lateral and torsional micro-drilling spindle system was analyzed by the finite element method (FEM). The Timoshenko beam finite element with five degrees of freedom at each node is applied to perform dynamic analysis of the system containing cylinder, conical symmetric elements, and flute asymmetric elements. The three-dimensional flute of the Union MDS drill with 0.1 mm diameter is defined by specifying the Cartesian coordinates of the specific points. In addition, the system model comprehensively includes the effects of continuous mass eccentricity, shear deformation, gyroscopic moments, and rotational inertia with external thrust force and torque during machining. In particular, the consideration of continuous mass eccentricity gives a more realistic model for system investigation. The Hamilton\'s equations of the system involving both symmetric and asymmetric elements were established and utilized to find shape functions of each element. The transient and steady-state lateral and torsional responses of drill point were estimated by Newmark\'s method. Simulation studies were attentively conducted to investigate the coupled lateral and torsional effect on the system vibration behavior. The results show that during design stage, the coupled lateral and torsional vibration associated with the above external forces should be considered carefully to prevent unexpected damage to the spindle system.
Structure optimization of a micro drill bit with nonlinear constraints considering the effects of eccentricity, gyroscopic moments, lateral and torsional vibrations
(2017-01-01)
Danh-Tuyen Nguyen
;
Tien-Dat Hoang
;
Lee, An-Chen
;
機械工程學系
;
Department of Mechanical Engineering
A micro drill structure was optimized to give minimum lateral displacement at its drill tip, which plays an extremely important role on the quality of drilled holes. A drilling system includes a spindle, chuck and micro drill bit, which are modeled as rotating Timoshenko beam elements considering axial drilling force, torque, gyroscopic moments, eccentricity and bearing reaction force. Based on our previous work, the lateral vibration at the drill tip is evaluated. It is treated as an objective function in the optimization problem. Design variables are diameter and lengths of cylindrical and conical parts of the micro drill, along with nonlinear constraints on its mass and mass center location. Results showed that the lateral vibration was reduced by 15.83 % at a cutting speed of 70000 rpm as compared to that for a commercial UNION drill. Among the design variables, we found that the length of the conical part connecting to the drill shank plays the most important factor on the lateral vibration during cutting process.