Research On Local Optimization Of Tool Orientation For Five-axis Machining

Five-axis CNC machine tool is an important equipment for aero-engine impeller,blades and other key parts with complex surfaces.For these surface with abrupt curvature,the planning motion of machine tool often exceed the maximum velocity and acceleration of the drive when using universal CAM(Computer Aided Manufacturing)to plan NC code.This will affect machining efficiency and part quality because of the vibration.In order to take the advantage of adjusting the angle of five-axis machine tool,it is necessary to optimize the orientation of tool while will reduce the vibration of machining processing to improve the machining efficiency and part quality.In this thesis,the kinematics model of machine tool is established by taking the A and C rotary table of five-axis machine tool as research object.Then the velocity and acceleration of each axis of machine tool are calculated by finite difference method.Taking the curved surface model with abrupt curvature as machining object,this thesis analyzes the kinematics characteristics of machine tool and studies the problems of the partial ultra-limit of machine tool.These theories provide theoretical basis for local optimization of tool orientation.There are nonlinear transformation and singular problems when optimizing tool orientation in WCS(Works Coordinate System).The calculation efficiency is low and the machine drive constraints condition may not be satisfied when optimizing tool orientation in MCS(Machine Coordinate System).In this thesis,a local optimization method of tool orientation with minimum rotational axis acceleration under the drive constraints of machine tool is presented.The local optimization model is improved to ensure the kinematics characteristics between optimized sections and non-optimized sections under the drive constraints of machine tool.In the extension simulation experiment of ultra-limit section of velocity in ultra-limit axis,the effect of tool orientation optimization in different optimization sections are compared.A method of selecting local optimization sections by setting acceleration threshold to extend the ultra-limit sections of velocity in ultra-limit axis is obtained in the experiment.Simulation experiment shows the calculation efficiency of local optimization of tool orientation is relatively high.The feedrate before and after the local optimization of tool orientation are analyzed by using the feedrate optimization model under the machine drive constraints,and the influent of the local optimization of tool orientation on the feedrate is studied.Finally,the processing method of straight blade is analyzed,and the finishing trajectory of straight blade is local optimized.The machining effect of blade before and after the local optimization of tool orientation are compared through the experiment of straight blade machining.Experiment shows that blade finishing time is reduced by 15.53% after local optimization of tool orientation.The local optimization method of tool orientation is verified,which is of great significance to improve the machining efficiency of five-axis machine tool.