Research On Adaptive Adjustment Of Castings Base On Photoelectric Measurement

Precision casting,supplementary machining assembly contact surface only,is becoming widely used in aviation manufacturing.However,finished products tend to have large plastic deformation and uneven wall thickness since it is still in early stage,which results in long process preparation cycle,high cost and even scrapped parts.That’s to say,conventional milling methods are not applicable to the supplementary machining of precision casting blank.This thesis aims to find a new machining method which could attain more accurate casting block shape including deformation degree and wall thickness dimension before supplementary machining.Moreover,casting block shape could be adjusted to ensure the machining allowance and technical requirements of other characteristic elements,so as to improve product quality and reduce costs.Therefore,following investigation has been conducted.(1)Research on photoelectric measurement technologyApply photoelectric measuring technology,instead of the traditional three coordinate measuring machines,to achieve full-scale measurement for casting block.Through combining the structural characteristics(such as profile,shading area,etc.)of castings and analyzing the commonly used photoelectric measuring technology TRITOP system,ATOS system,Handyprode portable coordinate measuring system,the best measurement method was acquired: global location-main surface measurement-local area measurement-measurement data integration.(2)Research on digital module reconstruction of blockCombined with the measured data points,the technologies such as data preprocessing,data segmentation,curve surface fitting and curve surface editing were investigated to achieve the digital module reconstruction of blank.And then true shape and position of block have been obtained.(3)Research on optimal allocation of process allowanceAlignment method was studied by comparing the block digital module and CAD design to ensure the machining allowance and technical requirements of other characteristic elements during the sequent process of blocks.During this stage,allowance analysis software based on CATIA software has been developed.It could realize the initial alignment,unconstrained alignment,constrained alignment between the blank and CAD design,and then automatically deliver the allowance analysis report(4)Research on positioning technology of processThrough comparing the coordinate system established by the aligned mathematical model with the coordinate system formed automatically by the machine tool,the alignment method has been studiedBy selecting typical precision castings,this thesis has overall verified all the technologies involved in the process including photoelectric measurement technology,block digital module reconstruction technology,process margin optimal allocation technology and process benchmark positioning technology.Moreover,selected typical precision castings have been further supplementary machined,and the test report has demonstrated that all the characteristic elements met the technical requirements.