| In aerospace manufacturing,reducing the structure weight of the aircraft means improving the maneuverability of the aircraft,increasing the load carrying capacity and the flight distance.Therefore,the thin-walled parts,represented by skins,are widely used in the aerospace field.Because of their large size,complex shape,thin thickness and poor rigidity,the parts will be difficult to manufacture.The traditional chemical milling process has the disadvantages of chemical pollution,complex process,high energy consumption and the inability to recycle aluminum materials.In recent years,the mirror milling technology,as a new technology of aircraft skin processing,is a highly efficient and green processing method.It has gradually replaced chemical milling,and is becoming the research hotspot of many industrial developed countries.Mirror Milling System(MMS)involves a lot of basic theories and key technologies,but for the sake of national defense and the economic interests of the state and company,most of the research results obtained abroad are limited.In order to break the blockade of the foreign companies and realize the technology and equipment of the independent research in our country,it is necessary to carry out basic research on the mechanism of the milling machining,the mirror support technology and system,the law of mirror milling force,the matching relationship between the force and the support system,the surface forming mechanism,and the surface quality control method.The main contents and conclusions of this paper are as follows:(1)According to the characteristics of mirror milling,a milling force model is established.The workpiece deformation is fed back to the milling force model,and the milling deformation is predicted by iterative calculation.A simplified control method for the mirror milling test rig of thin-walled parts is proposed,and a mirror milling test rig is set up.A non-contact measurement method for the thickness of the unknown surface shape workpiece is proposed,and a device for measuring the thickness of the mirror milling workpiece is set up.(2)It is proposed that the thickness consistency of machined workpiece can be used as an index for judging the quality of machining,which makes it possible to realize the precise NC machining of the parts.The surface topography prediction model of thin-walled parts processed by mirror milling is established,the influence of the support location on the surface topography is studied,and the relative location of the milling head and the support head is optimized.The results show that the optimal arrangement is to make the workpiece's stiffness near the cutting path consistent with the milling force,so that the best consistency of workpiece can be made.Less support points and smaller support area will make the pressure of the support head on the support surface of the workpiece greater than the yield strength of the workpiece material,so that the workpiece will produce plastic deformation and leave the indentation on the support surface.(3)On the basis of summarizing the research status,analyzing technical problems and difficulties of mirror milling support technology,two kinds of support systems with rolling contact or hydrostatic pressure are developed.The support stiffness,the action state of the support element and the surface of the workpiece,and the control mode of the supporting force and the position of the support are studied.For the rolling contact support system,with the increase of the number of support points,the average and minimum of the size error caused by the elastic deformation gradually decreases,and the indentation of the supporting surface is obviously improved.No matter the support head is single point,two point or three point,the support can get a smoother surface at the optimized sitting position.For the hydrostatic support system,using the static pressure support of the multi liquid cavity with constant pressure inlet,the throttle can be set separately on the liquid path of each liquid cavity,which can balance the changing milling force,optimize the pressure of the inlet liquid,make the liquid film stiffness maximum,and minimize the inconsistency of the workpiece thickness caused by the variation of the milling force.(4)Error compensation method for mirror milling thin-walled parts is determined.For the rolling contact support system and the hydrostatic support system,the error compensation calculation and the mirror milling experiment is carried out respectively.The results show that the elastic deformation error is further reduced when the tool path is corrected by single level cycle. |
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