Research On Accuracy Inspection Method Of Five Axis Machine Tool Based On Ruled Surface Test Pieces

Five-axis CNC machines are widely used in the processing of complex space surfaces such as aircraft parts and marine propeller because of the excellent spatial accessibility.In the manufacture of aerospace,shipbuilding and high precision instruments,the five-axis CNC machining level has become an important symbol showing the manufacturing industry level in a country.The traditional measurement accuracy such as geometric accuracy and positioning accuracy are considered in the quasi-static evaluation of CNC machine performance,which cannot reflect the accuracy of CNC machine tool in processing.With the appearance of five-axis manufacturing and requirement of efficiency,the machine's dynamic error are becoming the main part of total error,especially in the complex surface processing.At present,ISO five-axis machine tool precision inspection standards are only concerned with the quasi-static geometric accuracy and positioning accuracy detection,lacking of precision for the machine tool dynamic accuracy.In order to guarantee the five-axis machine's processing ability of the complex surface,it is very important to design a test specimen which can reflect the working performance of the machine tool based on the study of dynamic performance of the machine tool when machining part surface with different characteristics.In this paper,taking the flank milling of complex ruled surface as research target,a variety of geometric features of surface are extracted.And the mapping between the contours error of the parts and the features above are constructed based on the kinematics laws of machine tools under different characteristics.Finally,a new type of test specimen for dynamic performance detection of machine tool is reconstructed.The main contents of the thesis are as follows:The analysis of the kinematics mapping between the axes and the calculation method of contour error based on NC code are studied.By analyzing the structures of linear axis and the rotary axis feed system,a feeding model including the servo control system,the mechanical transmission system and the feedback system is established.Based on the multi-body system theory combined with the displacement of each axis,the tool posture calculation model is established.Based on these models above,a machine tool kinematics simulation platform is developed in the MATLAB environment,which can calculate real position of the tool tip based on calculation results of the real-time speed,acceleration and jerk of axis according to the NC code in the processing and the given machine tool's static error factors.Then the tool tip trajectory error can be calculated,which is considered as the foundation for the dynamic performance analysis of the machine tool under the processing of different surface features.The relationship between the curvature-related characteristics and the kinematics of each axis of the machine is studied.In this paper,three kinds of geometric features including curvature,curvature change rate and different continuity are proposed.The expressions of the linear axis velocity,acceleration and jerk under several conditions are deduced based on the simple two-axis motion taken as an example.Then the constant curvature specimen,the rate-changing curvature specimen and the different continuity specimen are designed and machined to verify the theoretical results based on the simulation model and actual processing.Based on the motion prediction of the rotary axis,the curvature characteristic integrated specimen is designed.Under the support of the Siemens 840 D numerical control system and the simulation result,the correspondence between the motion and the curvature-related characteristics of each axis is verified.The relationship between the curvature-related features and the contour errors of the parts is studied.Based on the simulation of the tool tip trajectory,the calculation method of the part contour considering the tool envelope is established.Taking the curvature-related feature specimen established in Chapter 3 as an example,the contour error of the tool in real motion is calculated,and the distribution law of the processing quality of the parts based on the curvature,the curvature change rate and the different continuity characteristics is given.By extending three types of topology structure machine and cutting experiment,the general law of the curvature feature is verified.The influence of surface opening and closing angle on the dynamic performance and contour error of the machine is studied.Taking consideration of the postures of the cutting tools during complex curved surfaces processing,the characteristics of the surface called opening and closing angle are proposed,and then the geometrical characteristics of the twist and singular regions are analyzed.For the twist,a midline drived method which can reduce the principle error of the processing is proposed.For the singular point feature,the mechanism of the mutation movement of axis-C for CA double pendulum machine is analyzed.Cutting experiments and simulation are carried out on the BA and CA structural machines respectively using the designed test specimen which has the opening and closing angle conversion characteristic have verified the motion and error distribution law of the machine.The advantages and disadvantages of the dynamic performance test of the five-axis CNC machine tool at present based on dynamic test specimen are studied,and proposes a new type of test specimen which integrates many kinds of surface features.Aiming the five-axis machine tool specimens commonly used in China and abroad,the modeling methods and geometric characteristics of each specimen are analyzed,and the limitations of the existing test specimen are expounded by comparing with the research results in the previous chapter,thus,A S-shaped test specimen with a variety of surface features(referred to as "S" specimen)is proposed.The geometrical modeling,clamping and processing techniques and measurements of the "S" specimen are all described in details.Through the kinematic analysis of the machine tool,it shows that the geometrical characteristics of the "S" specimen produce rich dynamic changes in each axis of the machine,and scientifically reflect the superiority of the "S" specimen in the machine tool inspection.Cutting experiments on different machines show that the contour error of "S" specimen is larger than that of other specimens,which can reflect more comprehensive performance of the machine.