Department of Mechanical Engineering Emam Hossain University
One of the main factors in poor performance of machine tools is undesirable vibrations. Unbalancing in rotary elements of machine tools cause induced vibration in machine head that influences on precision of processing material. The work presented in this paper is intended to resolve this problem. In this paper, a 3- DOF system has been modeled with design parameters in a machine tool. Based on technical specification of material used in this milling machine real amount of parameters were calculated. The equations solved and the amplitude movement of machine head in a crucial condition of vibration obtained. The main aim of optimization in this work is to reduce this amplitude by considerable amount. For this purpose, two approaches have been suggested. The first approach is solving the dynamic equations of 3-DOF model and changing stiffness and damping property of machine body material so that reduce the head movement to the desired level. It was found that such an especial material is not easy available and in case of finding, is not economical. Therefore, the second approach was suggested, i.e. adding a dynamic absorber to the drilling machine in three different positions to improve the situation. In this approach, only one DOF is added to the model and solve four differential equations with unknowns of mass (MD) and stiffness constant of spring (KD) for dynamic absorber. The mechanical impedance was used for these equations and the results obtained in complex coordination. In MATLAB, a procedure for optimization of MD and KD of dynamic absorber has been developed. Finally, the range of available MD and KD in industrial market was defined. The results have shown that adding dynamic absorber both more effective and more economical than changing material. The final achievement is though, the place of installing dynamic absorber. If the dynamic absorber install on the machine head is much more effective than putting in the base of machine tools, as a regular practice. Finally, a design criteria has been suggested for mass and stiffness of the dynamic absorber.