Research On Contact On-Machine Measurement And Error Compensation Method Of Complex Thin-Walled Parts

Complex thin-walled parts are widely used in products with lightweight and high performance(pneumatic,structural strength,etc.)requirements in the fields of automobile,aerospace,shipbuilding,electronics,etc.Due to the complex structure and large machining allowance of thin-walled parts,especially in the final finishing stage,due to its poor structural rigidity and mostly cantilever clamping mode,even small cutting force will produce deformation,resulting in machining errors.How to strictly control and accurately evaluate the machining error of thin-walled parts and ensure good surface accuracy has become the focus of the inspection process.In the process of machining,the on-machine measurement is used to detect the complex thin-walled parts with high efficiency and high precision.Then the thin-walled parts can realize the closed-loop processing of ’processing→measurement→modification ’ with only one clamping.In this paper,the typical complex thin-walled parts(turbine blades)are taken as the research object.In order to improve the accuracy,flexibility and efficiency of the measurement of thin-walled parts,aiming at the error analysis and compensation of the on-machine measurement process of thin-walled parts,the theoretical research is combined with simulation and experiment to study the adaptive on-machine measurement strategy and error compensation method of complex thin-walled parts.The main research contents of this paper are as follows:(1)Research on adaptive sampling method of thin-walled parts.According to the data point set of the designed thin-walled part surface,the NURBS surface configuration method is used to carry out three-dimensional parametric modeling for the planning and arrangement of sampling points.In order to solve the problem of severe curvature change and sampling at both ends of thin-walled parts,a curve sampling method based on modified chord height difference method is proposed.Considering the influence of curvature gradient on the sampling process,the control factor group is adjusted to control the sampling process,and the distribution density of profile measuring points is determined adaptively.It is extended to the whole surface to obtain the measurement point set of the whole surface.Simulation and on-machine measurement experiments verify the effectiveness and feasibility of the method.By comparing the sampling results with the equal parameter method,the equal arc length method and the chord height difference method,it is shown that the adaptive sampling method based on the modified chord height difference can fit the theoretical model of thin-walled parts to the greatest extent,and has the smallest sampling error,which can effectively improve the accuracy and efficiency of onmachine measurement.According to the analysis of the on-machine measurement results,it is found that the on-machine measurement trigger force will cause the blade deformation to produce measurement error,resulting in inconsistent machining accuracy between the top and the root of the blade(fixture fixed end),so further research is carried out.(2)Analysis of trigger on-machine measurement error.Aiming at the problem of triggering force-induced deformation in the process of on-machine measurement of thin-walled parts,the error source of on-machine measurement system is analyzed,and the existence of triggering force-induced error is verified by on-machine measurement experiment.The simulation of triggering force-induced error is carried out by solving the outer normal vector of thin-walled parts.The neural network NARX is used to establish the triggering force-induced error model.The simple thin plate is used as the prior model to simulate and model the triggering forceinduced error.The calibration experiment of the simple thin plate is carried out to obtain the calibration coefficient,and the deformation experiment is carried out to verify the rationality of the method.The simulation and experimental data are compared to grasp the influence of the triggering force-induced error on the on-machine measurement results of thin-walled parts.(3)Research on on-machine measurement error compensation method.Aiming at the problem of trigger force-induced error compensation in the process of on-machine measurement,the geometric error of machine tool is analyzed.The geometric error of five-axis CNC machine tool is measured by laser interferometer and compensated by G code.The on-machine measurement system is calibrated and compensated.The motion topology and forward and inverse kinematics model of five-axis CNC machine tool are established.Based on the inverse kinematics solution of five-axis CNC machine tool,the trigger force-induced error vector at each sampling point is compensated to the motion of each axis of five-axis CNC machine tool to improve the machining accuracy of thin-walled parts.