Investigation On The Vibration Characteristics Of Machine Tool Structures In Machining Process And Its Effect On Surface Roughness

CNC machine tool is a complex system composed of many substructures,different parts are connected together by coupling bolts or linear guidance,and the joint is formed.The moving parts of CNC machine tools(such as worktable,spindle,etc.)will produce inertial impact in the process of operation,especially in the process of acceleration and deceleration.The inertial impact will cause machine tool vibrations.Due to the coupling between the inertia impact excitation and the cutting excitation,the dynamic characteristics of the machine tool are more complicated in the actual processing.The difference of the structural sensitivity and the dominant frequency vibration characteristics of machine tool will affect the dynamic characteristics of the whole system,which will affect the surface quality of the products.There are several deficiencies in the existing research: First,the absence of the mechanism of inertial impact and the characterization of dynamic characteristics at different feed rates;Second,in the actual processing,the structural vibration characteristics and its effects on the surface quality of the products are needed to be studied further.In order to better understand the characteristics of inertia impact and the vibration the machine tool structure during operation,the main contents of this paper include:(1)Based on the method of self-excitation,we obtained the characteristics of inertial impact produced by moving parts in the process of acceleration and deceleration;(2)For the effect of feed rate to the structural vibration characteristics,this paper put forward the feed rate related dynamic characteristics of machine tool based on ODS modal decoupling;(3)For the effect of structure vibration on surface quality,at first,this paper identified the sensitive structures of machine tool based on the modal mass distribution matrix,and then identified the dominant frequency vibration of the sensitive structures and cutting tool through ODS modal decoupling.Finally,a cutting experiment was carried out on a double-sided lathe to verify the effect of structure vibration on surface roughness.(4)At the end of this paper,a multi axis milling experiments are carried out on a vertical machining centre to verify the trajectory related structural vibration.The theoretical and experimental results show that the inertial impact generated by the moving parts in the process of acceleration and deceleration is a frequency-limited and energy-limited excitation caused by the nonlinear collision of the elastic body,and different feed rates leads to different inertial impact excitations,which makes the dynamic characteristics of the machine related to the feed rates.In actual processing,the multi-mode vibration of the sensitive structures and cutting tool at dominant frequencies directly determine the surface quality of the products.Moreover,the vibration characteristics of the structure are closely related to the machining trajectory.The greater the curvature,the higher frequency of the mode can be more effectively excited,the contribution of higher frequency mode to the vibration of the structure is also greater.