| As the main primary structure of the large carrier rocket,the manufacturing technology of the fuel tank of rocket reflects the extreme manufacturing capability of our country.Spinning is an international trend in the manufacture of the dome of the fuel tank.It is imperative to develop the spinning technology of large thin-walled curved surface components,in which spinning of the fuel tank dome is taken as a typical model.The structural stiffness of Aluminum alloy large-scale thin-walled surface structure is weak,and the anti-wrinkle ability is poor.The flange is in the unconstrained state and subjected to compressive stress in the circumferential direction during spinning process,so that wrinkling occurs easily.With increasing of diameter-thickness ratio(the ratio of component diameter to blank thickness),wrinkling phenomenon of part with high diameter-thickness ratio is more obvious.Serious wrinkles always appear in the initial stage of wrinkling,which resulting in forming failure.The part with high diameter-thickness ratio poses a higher requirement for flange wrinkling prediction.At present,the research on the spinning of thin-walled curved surface components with high diameter-thickness ratio is rare.The understanding of the influence of the diameter-thickness ratio on the wrinkling of the flange is not deep.Meanwhile,the mechanism of the influence of the relevant process factors on the wrinkling of the flange is not clear,wherefore the process planning is too dependent on the workers' experience and lacks reasonable process guidance.In this way,it is urgent to develop flange wrinkling prediction model for the spinning process,study the mechanism of flange wrinkling,predict the flange wrinkling moment accurately,reveal the influence of the diameter-thickness ratio and key factors on flange wrinkling and realize the theoretical guide of spinning process planning of components with high diameter-thickness ratio.In this research,the aluminum alloy hemispherical part is taken as the research object.The mechanism of flange wrinkling in spinning is revealed from three aspects: flange wrinkling experiment,numerical simulation and theoretical prediction.In the flange wrinkling experiment,in view of the flange wrinkling phenomenon of aluminum alloy hemispherical component during spinning forming,experiments are designed from two aspects to study the influence of the diameter-thickness ratio on the flange wrinkling.The two aspects are constant structure diameter with variable sheet thickness and constant sheet thickness with variable structure diameter.In the numerical simulation,the simulation model of spinning of the hemispherical part is established.Based on the analysis of the characteristics of deformation of sheet during spinning,the assumption of flange wrinkling caused by the instability of the inner ring and outer ring is proposed.In the aspect of theoretical prediction,the instability prediction models of plane ring and curved surface ring are established based on the energy method and plastic buckling theory.Combining with the finite element simulation results,the instability of the inner ring and outer ring is predicted.The mechanism of flange wrinkling during spinning is further clarified.The accurate flange wrinkling prediction of high diameter-thickness ratio aluminum alloy part during the first-pass conventional spinning is achieved.The key influencing factors of flange wrinkling are analyzed theoretically,which provides theoretical support for spinning of high diameter-thickness ratio part.The main contents of this dissertation can be divided into the following four parts:(1)Research on deformation mechanism of hemispherical part in conventional spinningThe flange wrinkling experiments of spinning components with different diameter-thickness ratios were designed to study the influence of the diameterthickness ratio on the flange wrinkling.Based on the ABAQUS finite element simulation platform,the simulation model of the spinning process was established to analyze the stress characteristics of the deformed sheet during the spinning process.The results show that the diameter-thickness ratio has a significant effect on the flange wrinkling.And with the increase of diameter-thickness ratio,flange wrinkles develop more quickly.There are two obvious compressive stress rings in the middle layer of the deformed sheet in circumferential direction during the spinning process-inner ring and outer ring.Flange wrinkling are closely related to the instability of the two rings.And the diameter-thickness ratio has a significant effect on the stress and thickness distribution of the deformed sheet.(2)Research on annular plate instability theoretical model in spinningAccording to the structural characteristics and the stress distributions of the inner and outer rings in the middle layer of the deformed sheet,instability theoretical models of the plane ring and the curved surface ring are established based on the energy method and the plastic buckling theory.According to the boundary characteristics of the stress rings,the corresponding boundary constraint equations are established.Based on the prediction model of instability of annular plate structure,the influence of parameter analysis on the instability of annular plate is carried out.Results show that the established deflection function equation can accurately reflect the boundary constraint condition.With decreasing the thickness of the annular plate,increasing the diameter of the annular plate,reducing the K value,rising the n value,increasing the radial tensile stress and weakening the boundary constraints,the anti-instability of the annular plate decreases.(3)Research on wrinkling prediction and wrinkling mechanism in spinningBased on the finite element simulation,the inner and outer ring instability theory of different diameter-thickness ratio components are predicted.Through the comparison with the flange wrinkling experiments,the relationships between inner and outer ring instability and the flange wrinkling are discussed.The stress distribution characteristics of inner and outer rings in parts with different diameter-thickness ratio are studied,and reasonable stress distribution assumption is proposed to realize the accurate prediction of flange wrinkling for the parts with high diameter-thickness ratio.The results show that the flange wrinkling during the spinning process is caused by the instability of the outer ring.The inner ring instability does not cause flange wrinkling.But it will increase the oscillation of the spinning force.The stress distribution characteristics must be taken into account to predict the flange wrinkling of the parts with high diameter-thickness ratio.The accurate predicting results of the flange wrinkling can be obtained by using the piecewise linear function to describe the stress distribution.(4)Research and application of spinning technology for wrinklesBased on the flange wrinkling prediction method proposed in this dissertation,the influence of parameters such as feed ratio,flange width,roller-mandrel clearance on flange wrinkling are analyzed theoretically.The hemispherical components of multi-pass spinning forming process tests are carried out.Three kinds of multi-pass forming plans are compared.The theoretical guidance of multi-pass spinning forming process is realized for the parts with high diameter-thickness ratio.It is concluded that flange wrinkling will occur ahead of time caused by increasing the feed ratio,reducing the flange width and increasing the deviation of the roller-mandrel clearance from sine law.With the design and optimization method of roller pass and process parameters proposed in this paper,the overall spinning of the aluminum parts with high diameter-thickness ratio can be achieved based on the multi-pass composite spinning plan.In summary,according to the phenomenon of flange wrinkling in spinning of aluminum alloy curved part with high ratio of diameter to thickness,the stress characteristics of deformed sheet during spinning are analyzed by combining with flange wrinkling experiment,numerical simulation and theoretical prediction.An accurate method for predicting flange wrinkling of the parts with high diameterthickness ratio is established.The mechanism of flange wrinkling is further clarified.The influence of diameter-thickness ratio and key process parameters on the flange wrinkling is revealed.Aluminum alloy hemispherical thin-walled part is formed with multi-pass spinning method.These studies can provide theoretical guide and technology support to multi-pass spinning of aluminum alloy curved part with high ratio of diameter to thickness. |
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