Research On Kinematic Transformation And Post-processing Methods Of Five-axis CNC Machine Tools

Five-axis CNC machine tools are widely used in aerospace,national defense,automobile manufacturing and other fields.Because the five-axis CNC machine tool adds two rotating axes,the machining method is more flexible,the movement of the cutter is more complex,and it can be used for the machining of complex and precise parts,but at the same time,it also introduces the unique nonlinear error problem of the five-axis CNC machine tool.It can reduce the non-linear error when using the adaptive encryption method of tool contact,but the NC program with tool contact cannot be generated when UG and other commercial CAM software post process the tool position file,so it is necessary to develop a special post processor.When the machining tool of five-axis CNC machine tool enters into the singular region,the small change of tool position will lead to the drastic change of the rotating axis,which will produce a large nonlinear error and reduce the machining quality.The singular phenomenon should be avoided in actual machining.Because of the periodicity of the trigonometric function,each cutter axis vector can correspond to different angles.The rotation axis angle range of the non modal machine tool is limited to a certain extent.The angle value of the NC program generated by UG may exceed the allowable range.Therefore,it is necessary to develop a post processor to optimize the angle,so that the optimized angle value is within the allowable range of the machine tool.The main contents of this paper are divided into the following three parts:(1)This paper analyzes the kinematic transformation of three different machine tools,and obtains the mathematical model containing the calculated tool contact through the homogeneous coordinate transformation.Using visual basic to develop the special postprocessor of five-axis CNC machine tool,creating the software operation interface,inputting the relevant parameters of the machine tool,and processing the cutter position file generated by UG software to get the CNC program with cutter contact.(2)Taking A-C double turntable machine tool as an example,this paper analyzes the cause of singularity,and puts forward a method to judge the singularity region by detecting the cutter position file of five-axis NC machine tool.By using adaptive interpolation between adjacent cutter axis vectors in singular region,the change of rotation angle of adjacent cutter is reduced,so that the nonlinear error of machining is less than the allowable error.It is proved that this method can obviously reduce the angle and nonlinear error between adjacent cutter positions in the singular region,make the machining process stable and improve the machining quality.(3)Taking A-C double turntable machine tool as an example,through the kinematic transformation of the machine tool,the mathematical expression for calculating the angle of rotation is obtained,the values of angle A and angle C are analyzed,and the optimal combination of the angle is carried out without changing the cutter position.By using Visual Basic language,a postprocessor which can optimize the turning angle of machine tool is developed to solve the problem that the turning angle is limited during the processing of non modal machine tool and improve the use range of NC machine tool.The validity of the method is verified by the simulation of universal wheel seat with VERICUT software.