Research On Post-processing Technology Of Five-axis CNC Machine Denture Machining

In today's increasingly developed life,with the gradual increase in the demand for denture,the accuracy of the denture is also increasingly high.The CAM system of five-axis CNC machine tool has been applied to the denture machining because of its high machining accuracy and the ability to process complex surfaces.As one of the important links of CNC machining CAM system,post processing technology assumes the role of converting the output file data of the system into NC code which can be recognized by CNC machine tool,and plays a very important role in improving the accuracy of CNC machining.For this reason,based on the indepth study of the model of CNC machine tools,the mechanism of post processing algorithm is analyzed.This thesis proposes a nonlinear error compensation algorithm based on error modeling and according to the maximum limit shaft speed to change speed control algorithm of programming instructions,and further designs and develops the denture processing and post processing software system.In order to solve the problem of CNC denture machining,this thesis analyzes three types of five-axis CNC machine tools,namely double swinging head,turntable-swinging head and double turning table,and analyzes their advantages and disadvantages,and selects double turning table type as the CNC machine tool for denture machining.According to the movement mechanism of CNC machine tool and the relationship between coordinate systems,the mathematical model of five-axis CNC machine tool with double turntable is established by using the principle of computer graphics,combining the translation and rotation transformation of coordinates.In post-processing,due to the existence of linear interpolation motion and rotation axis of five-axis CNC machine tool,the actual machining trajectory between two points will deviate from the ideal straight line segment,resulting in nonlinear errors.In order to compensate the nonlinear errors effectively,an online prediction and compensation method for nonlinear errors based on error modeling is proposed by this thesis.According to the nonlinear errors generated by any two adjacent tool bit points,the distribution characteristics of the errors are obtained,and the error distribution model is established.Furthermore,the mathematical expression of the nonlinear error is solved by using the least square method,and the new tool point is determined by comparing with the maximum allowable error,so as to realize the online prediction and compensation of the nonlinear error.Taking the actual processing data as an example,the simulation research is carried out in the MATLAB environment,and the effectiveness of the proposed method is verified.In order to ensure the machining efficiency and safety of CNC machine tools,this thesis further studies the speed control of CNC machine tools.By analyzing the instruction principle of G93 and G94,combined with the tool location data file and the motion information of each axis obtained by the postposition algorithm,a speed control strategy is established to change the programming instruction according to the maximum limit speed of each axis.The simulation study is carried out in the MATLAB environment,and the effectiveness of the strategy is verified.The post-processing system of denture machining is designed and developed under the Qt environment,and the CLSF file,that is,tool location data file,is converted into NC code which can be recognized by CNC machine tool by applying the post-processing algorithm,and the basic function of code conversion is realized.