Research On Forming Bending Parts Based On The Stepped Rubber Forming Method

Rubber forming technology is a common method in the manufacturing of aviation sheet metal parts.It is mainly divided into fixed container and mobile container.In the mobile container rubber forming process,the rubber pad is wrapped in the whole container to form the part.Because of the incompressibility of the rubber pad,the rubber will naturally generate a certain bending radius in the forming process,which makes it difficult to stick the mold and affects the forming accuracy.On the contrary,the fixed rubber forming method mainly uses the hydraulic oil filled rubber bag as the forming medium,which has a high film sticking degree and is favored by the factory.At present,most of the researches on rubber forming technology are based on the large tonnage fixed container rubber bag forming process and the influence of the related process parameters on the part forming,such as die gap,rubber hardness,loading speed,sheet thickness,etc.There are still some shortcomings in the fixed container rubber bag forming technology.The equipment has a large tonnage and covers a large area.However,there is less research on the technology of movable container rubber forming method.The whole frame is used in traditional one-step forming.This paper proposes a stepped rubber forming method based on the traditional movable container one-step rubber forming technology.Based on the traditional rubber forming method,the rubber container is divided into blocks to realize the local stepped loading.And the stepped rubber forming equipment is developed.Based on the numerical simulation analysis of sheet rubber forming with different flange heights and thicknesses,the influence of the rubber hardness on the film forming of the straight edge bending of the sheet was analyzed,and a number of forming experiments with different relative bending height were completed.With the same amount of vertical depression,the situation of the sticking of the form part under the traditional rubber forming method and the stepped rubber forming method is analyzed.Based on ABAQUS finite element analysis software,the effects of rubber hardness A and die fillet radius R on sheet metal wrinkling were studied.At the same time,the correlation between the hardness of rubber,the radius of the corners of the mold and the amount of depression of the frame and the wrinkle were obtained based on the orthogonal test and the gray correlation analysis method.Combined with the simulation and the experiments,the forming results of the traditional rubber forming method and the stepped rubber forming method are compared and analyzed,as well as the influence of the horizontal cylinder feed on the wrinkling of the sheet in the stepped rubber forming.The results of numerical simulation and experiment show that the stepped rubber forming method can effectively improve the sticking degree of sheet metal,and the longer the bending length of sheet metal,the more obvious the film sticking effect.When the relative height of the flange is h t(27)4,the traditional one-step rubber forming method is used to form the sheet,which is prone to curling and uneven bending.But the stepped rubber forming method has a certain correction effect on the curling angle.And with the increase of the loading of the horizontal side cylinder,the greater the crushing effect of the rubber,which makes it more fully contact with the deformed part of the sheet flange,which is beneficial to the film control of the straight edge of the sheet.In the process of rubber forming,the hardness of the rubber and the corner radius of the mold have a greater effect on the wrinkling of the sheet.With the increase of rubber hardness,the peak height of wrinkling point increases or decreases,otherwise,the width of wrinkling point increases.The larger the radius of die fillet is,the smaller the peak height of wrinkling point is.Based on the orthogonal test and grey correlation analysis,the correlation degree of hardness of rubber,radius of round corner of die and the amount of pressure under the frame to the number of wrinkle points,width and peak height of wrinkle points was analyzed.The stepped rubber forming method can effectively control the wrinkling of sheet metal,and the size of wrinkling point decreases with the increase of feeding of horizontal cylinder.When f = 2mm,the peak height of the wrinkle point is reduced by 41.15% on compared with traditional rubber forming method.When f = 4mm,the peak height of the wrinkle point is reduced by42.77%.The height is reduced by 58.61%.When f = 8mm,the wrinkle point of the plate is basically eliminated and the plate completely attached.