Research On Motion Trajectory Control Of Profile Accuracy For Five-axis Additive And Subtractive Hybrid Manufactering

In view of the wide application of high-complexity parts in advanced technology industries such as aerospace,energy power,defense military,and biomedicine,the performance,accuracy,and efficiency requirements of manufacturing are becoming more and more accurate.The traditional casting,powder metallurgy,machining and other processes show problems such as difficulty forming,complex processes,and long manufacture-cycle,especially for the high-performance difficult to machine materials,gradient functional materials,and internal structural parts.The hybrid additive/subtractive manufacturing is considered to be a promising technical means because of the advantages of additive manufacturing and subtractive manufacturing.However,the current additive/subtractive manufacturing also faces many problems such as trajectory control,multi-process coordinate coordination,lack of dedicated multi-function post-processing software,and severely restricts the contour accuracy of the hybrid formed parts.In order to solve the above problems,based on the deeply analysis of additive manufacturing and subtractive manufacturing process,a five-axis additive and subtractive hybrid forming contour precision control method is proposed based on motion trajectory;The composite kinematics model of the five-axis additive and subtractive hybrid machine tool was established,and the coordinate coordination of the kinematics models is carried out.With the goal of controlling the high-precision contour of the forming part,the key technical problems such as the tool axis vector,nonlinear error,tool error and cutting speed which affect the running accuracy of the tool's motion trajectory are discussed in depth,and corresponding control algorithm is established.It is verified by virtual simulation and cutting experiment of complex parts such as impeller and blade,and a special post-processing software is developed based on post-processing technology.The main research work of the paper is as follows:(1)on the basis of analyzing the structure of the five-axis machine tools,the paper studies the motion characteristics of five-axis additive/subtractive machine tools and explores the principle of linkage of five-axis machine tools.On account of the principle of inverse kinematics,the paper constructs the kinematics model of five-axis additive/subtractive hybrid machine tools.According to the non-coordination of the two process coordinate systems,the paper carries out the process coordinate coupling analysis,and proposes the process coordinate coordination strategy.(2)In order to improve the contour accuracy of the parts during the additive process and eliminate the step effect caused by the traditional three-axis layered cladding,the paper proposes a five-axis spiral dynamic tool axis vector control method.By analyzing the principle of contact between the tool and the surface of the workpiece during the five-axis linkage process,a five-axis spiral dynamic vector calculation method is established and verified by a single-channel multi-layer cladding experiment of a blade.(3)In order to improve the contour accuracy of the five-axis subtractive process,the paper explores the mechanism of nonlinear error generation with the principle of rotary axis linear interpolation,and establishes a mathematical model of nonlinear error.By analyzing the limitations of existing nonlinear error processing methods,a tool vector interpolation algorithm is proposed.When the error exceeds the set allowable value,the vector interpolation plane is established by two adjacent points,thereby obtaining the interpolation point position and the vector for error compensation.It is verified by virtual simulation and cutting experiment of a blade.In order to reduce the influence of tool wear on the contour accuracy of the five-axis subtractive process,the contact mode of the tool in the space cutting process is studied.The three-dimensional wear of the tool error compensation model is established according to the relationship among the tool core,the tool contact point and the tool axis vector,and is verified by a virtual simulation and cutting experiments of a blade.(4)In order to analyze the influence mechanism of the cutting speed on the precision of the forming process of complex curved parts,the paper establishes the speed interpolation model by analyzing the five-axis speed interpolation principle,and proposes the control method of the constant surface tool contact speed based on the speed and acceleration constraints.It is verified by a cutting experiment of a blade.(5)In order to solve the NC code problem required for the additive/subtractive manufacturing process,according to the established composite kinematics model,combined with the dynamic tool axis vector algorithm,the nonlinear error control algorithm,the tool 3D error compensation algorithm,the speed control algorithm,the paper develops a special and multi-functional five-axis post-processing software which bases on the high-level language,and is verified by the function of an impeller.At the same time,the paper discusses the error measurement method of the coordinate system of the additive/subtractive manufacturing process,and proposes the judging criteria of coordinate coordination error.The basic experiments of process synergy in composite manufacturing is carried out with ring parts.