Research On Parallelism Measurement And Evaluation Method Of Nontransparent Plane Thin-walled Components

With the development of modern manufacturing technology towards high precision and high reliability,the measurement technology used to detect the machining accuracy of parts is becoming more and more important.In order to meet the development needs of modern manufacturing industry,higher precision measurement technology is needed to detect the machining accuracy of key parts,so as to guide the subsequent machining process and improve the machining quality.Flat thin-walled components are widely used in high-end equipment manufacturing,aerospace,optics and other fields,and have high requirements for parallelism.The geometric tolerance of workpiece is an important index reflecting the functional requirements of the measured elements,which has important impact on the machining quality of parts.The new generation Geometrical Product Specification(GPS)specifies the basic principle of face-to-face parallelism evaluation is directional minimum area method.However,due to the different properties of the measured workpiece such as structure,size and transparency,as well as the different reference establishment methods,the measurement and evaluation methods of parallelism are not unified.The nontransparent plane thin-walled components studied in this paper have large size,large diameter thickness ratio and weak rigidity,and the existing parallelism measurement methods are difficult to meet the measurement requirements.Therefore,it is an urgent work to develop an economic and efficient high-precision parallelism measurement system for nontransparent plane thin-walled components.The main research contents of this paper are as follows:A high-precision measurement method for parallelism of nontransparent plane thin-walled parts is proposed.This method measures the thickness data and flatness data of the workpiece respectively in the form of optical noncontact measurement.The surface shape of the workpiece is reconstructed through data screening,splicing,unified benchmark,comparison and superposition.Then,the workpiece surface with good flatness is selected as the fitting object of the reference plane,and the reference plane satisfying the minimum condition is fitted by Particle Swarm Optimization(PSO)algorithm.Finally,the parallelism evaluation mathematical model is established according to the principle of directional minimum area to calculate the face-to-face parallelism error between the two surfaces of the workpiece.Based on the proposed parallelism measurement method,a set of parallelism measurement system for nontransparent plane thin-walled components was developed,mainly including motion unit,measurement unit,control unit,data processing unit and so on.The motion unit is a precision three-axis motion platform.The measurement unit includes laser displacement sensor,flatness meter,special fixture for sensor and special fixture for measurement.The control unit includes motion control software and data acquisition software.The data processing unit is a data processing algorithm developed based on Matlab software.In the development process of parallelism measurement system,the structural design,software development,device construction,geometric accuracy detection,static simulation analysis of key components and so on were carried out.On the developed parallelism measurement system,the parallelism measurement experiment of the measured workpiece(pure copper plane thin-walled part)was carried out to verify the feasibility,stability and applicability of the measurement system.The data processing algorithm is used for data processing to reconstruct the three-dimensional surface shape of the two surfaces of the workpiece under the same reference.The reconstructed surface shape is compared with the measured surface shape,and the maximum surface shape reconstruction error is 0.46 μm.According to the established parallelism mathematical model,the parallelism of the workpiece is calculated to be 7.41 μm.Finally,the uncertainty of the parallelism measurement system is analyzed,and it is concluded that the expanded uncertainty Ut of the parallelism measurement system is ± 0.34 μm,k = 2,that is,the parallelism measurement result is f =(7.41 ± 0.34)μm.