Optimization Design And Wear Analysis Of Roller Cavities For Rolling Net-shape Blade

Blade is an important component in aero-engine.The different blades forms by different manufactuting processes.The thin-walled and small sized blades of high pressure compressor are usually formed by the net-shape cold rolling.During blade rolling process,the workpiece suffers plastic deformation in the inverse rotatory rolling motion of a pair of the dies and achieves a formed blade with the definited shapes and mechanical property.Due to the high accuracy requirement,the manufacturing accuracy of the blade is very sensitive to the profiles of the roller cavities.Hence,it is necessary to research the optimization design method of the roller cavities and monitor the geometric evolution of the cavities during service life in order to improve the manufacturing accuracy,shorten the design period and prolong the service life of roller,and develop the theory of the design method and life prediction for the plastic forming die.In this thesis,a new optimization design method is proposed to improve the forming precision of the net-shape cold rolling compressor blade based on the evolution of the blade’s geometrical characteristic and the conjugate movement between the roller cavities and the blade’s profile.Moreover,a forward slip compensation model and a springback compensation model are presented based on the rolling deformation and bending springback theory to optimize the designed roller cavity.The optimization design method achieves the precise modeling of the roller cavities for the net-shape rolling blade.Meanwhile,the contact responses of roller cavities are investigated based on a valid finite element model of blade rolling processes.The wear distribution and evolution of roller cavities are also investigated based on a revisional wear model.Finally,a lifetime prediction model is proposed to predict the service life of the rollers based on the wear distributions of the roller cavities.According to studying the optimization design method and the wear evolution of the blade rolling cavities,the design accuracy and stable period of the cavities are improved,and the manufacturing accuracy and uniformity of a batch of blade are guaranteed.The main research contents and innovation achievements of the thesis are as follows:(1)The design method of the cavities for rolling blade.A new design method for the blade rolling cavities is proposed based on the rolling theory and the the conjugate movement between the roller cavities and the blade.Firstly,a process model of blade is built by adding machining allowance at the leading and trailing edges,and the root and tip of the blade.Then,a transformational model is proposed based on the conjugate movement between the roller cavities and the blade,and section curves of the pressure and suction surfaces are mapping transformation to the corresponding section curves of the roller cavities respectively.The roller cavities are reconstructed based on the transformed section curves.(2)The forward slip compensation method of the roller cavities for rolling blade.The causes of the rolling forward slip are analyzed and an analytic model is proposed to calculate the forward slip coefficient for a symmetric rolling.The blade process model are dispersed into sequential units along the stacking direction,and the forward slip coefficients of every units are calculated based on the analytic model.Then,a forward slip compensation model which relates the center angles of cavity section and the corresponding stacking heights of the blade’s section is proposed to optimizate the roller cavities.The calculated center angles are used in the mapping transformation of the section curves.The forward slip compensation method improves the blade forming accuracy along rolling direction.(3)The springback compensation method of the roller cavities for rolling blade.The causes of the springback in bending are analyzed and a springback calculation method of a bended unit is presented based on the geometric parameters and material properties.The springback compensation theory is also analyzed.One of the blade section is dispersed into sequential units along the chordwise direction of the blade.The geometric parameters of every units are extracted to calculate the springback,and predict the corresponding geometric parameters of the springback compensated units based on the springback compensation theory.The springback compensated units are reconstructed sequentially to achieve springback compensation for the section.All sections of process model are reconstructed based on the springback compensation method,and mapping transformed to the corresponding section contour of the springback compensated roller cavities.The springback compensation method of roller cavity improves the forming precision of blade profile.(4)The contact responses distribution and evolution of roller cavities in blade rolling process.The contact responses model and the rolling contact model are analyzed,and the symmetric rolling contact responses are investigated.Then,a finite element model of the blade rolling processes is set up,and the result convergences of the model are checked.At last,the distributions and evolutions of the contact pressure,shear stress and local sliding on the roller cavities are investigated based on the result of finite element model.It provides necessary dates for studying the wear of roller cavities.(5)The wear distribution and evolution of roller cavities in blade rolling process.An adhesive wear model and its modified model are analyzed.A pin-disk experiment is used to replace the local contact between the roller and blade,and the wear of the ball pin is measured.The wear coefficient and the exponent coefficients are calculated based on the experiment.Then,the distributions of transient wear on the cavities are investigated based on the contact responses and the wear model.The evolutions of wear on the cavities are investigated with the rotation of roller.The distributions of wear on the roller cavities in one rolling cycle are calculated by summating all of the transient wear.Finally,a lifetime prediction model of the roller is proposed based on the maximum permissible wear.The wear distribution on a pair of used rollers are measured and compared with the lifetime prediction model,and the results show that the lifetime prediction model is efficient.