| With the development of automotive,aerospace and a lot of other fields to the direction of lightweight,sheet metal parts are also developing in the direction of large size,thin wall,deep cavity,complex surface and difficult deformation materials.For the application of aluminum alloy material in automotive,aerospace and other areas,it effectively solves the demand of lightweight structure,especially for the complex parts such as aluminum alloy body covering parts and aircraft large complex double curvature aluminum alloy skin,this kind of complex parts formed by aluminum alloy material is highly favored for research.For aircraft stepped thin-walled parts,automobile motor shell,oil bottom box and other stepped parts,these parts are more complex in shape,it is necessary to improve the formability of stepped parts by using pre-bulging hydroforming method.In this dissertation,the stepped part is taken as the research object,and the forming process analysis is carried out for this part.The 0.8 mm thick 1060 Al sheet is used as the investigation material,and the hydraulic drawing process principle of hydraulic punch and rigid body die is designed based on the principle of pre-bulging liquid deep drawing.The forming law of the stepped part is studied by the method of test research and numerical simulation.The forming process of the stepped part is studied by the principle of pre-bulging hydroforming,supplemented by numerical simulation.Based on the specific process size of stepped part,a hydraulic punch drawing and forming device for stepped part was designed and developed,and a test platform was built based on the device for experimental research.The deformation distribution and variation law of stepped part in deep drawing process are analyzed.The influence of pre-bulging parameters on the formability of stepped part was further revealed.Based on the test results,the optimal process parameter combination and hydraulic loading curve were obtained by orthogonal experiment,and the parts with excellent forming quality and good adhesion were obtained.Finally,based on the test results,the failure forms of stepped part during deep drawing were analyzed,the conclusions of this analyze are as follows:(1)The test result show that the reasonable matching of pre-bulging height and pre-bulging pressure can not only improve the formability of the part,but also restrain the occurrence of failure forms to a certain extent.When the pre-bulging height is 6 mm and the pre-bulging pressure is 3 MPa,the part have good formability and the forming height is28.9 mm.Excessive thinning occurs at the top of the stepped part,the wall thickness is the minimum,the hardness is the maximum at the transition corner,and the hardness are the minimum at the top and flange of the first step.(2)The orthogonal experiment of four factors and four levels was designed and the simulation analysis was carried out by DYNAFORM software.The result showed that the degree of the influence of each factor on the minimum wall thickness was as follows: liquid chamber pressure C> blank holding force D> pre-bulging pressure B> pre-bulging height A.The orthogonal test result was analyzed,and the optimal parameter combination was obtained.Under this process parameters,the part have better moldability.(3)Based on the principle of pre-bulging hydroforming,the hydraulic loading path of pre-bulging and then deep drawing was adopted,and different pre-bulging pressures and liquid chamber pressure loading paths were designed.It was found that reasonable hydraulic loading curve played an important role in improving the formability of part.(4)In order to improve the forming quality of part,the influence of each parameters on the failure forms of the part was analyzed.It was found that the typical failure forms during the forming process of the stepped part were wrinkling and crack.The main failure forms were wrinkling at the flange and folding at the top,and crack at the top of the part and the first step.From the above study,it can be seen that the formability of stepped part can be effectively improved by selecting the appropriate pre-bulging height and pre-bulging pressure and matching the pre-bulging height and pre-bulging pressure reasonably. |
