| In recent years,with the rapid development of aerospace,automobile and other fields,the traditional processing methods have been difficult to meet the growing industrial demand of lightweight,low cost and high precision.In this background,a large number of new forming methods emerge,especially flexible medium forming.According to the state of medium,it can be divided into hydraulic forming,viscous medium forming and solid particle forming.However,due to the limited performance of traditional flexible media,it has some limitations in the application process,and it is difficult to be popularized and applied.Under this premise,this paper attempts to expand the flexible medium forming technology,and uses magnetic liquid,one of the typical representatives of intelligent materials,as the force transfer medium to sheet metal forming.Magnetic medium is a new type of controllable intelligent material.Its state can be changed from liquid state to solid state gradually in the magnetic field,which can give full play to the characteristics and advantages of various state medium.The change of this state is instantaneous and reversible under the action of magnetic field.The real-time and controllable characteristics of the magnetic medium make it possible to show different force transfer effects in different stages of the same forming process.In this paper,the law and mechanism of the influence of magnetic medium on sheet metal deep drawing process are studied.A special experimental device with electric and magnetic fields is developed.Taking Al1060 as the blank and cylindrical parts with spherical bottom as the research object,the influence of magnetic medium under different magnetic field strength on the forming performance and quality of the sheet was emphatically investigated.The results show that when the magnetic field is raised from 0 to 0.2T,the maximum thinning rate of the wall thickness is reduced from 24% to 16%,the deformation coordination ability and wall thickness uniformity of each part are significantly improved,the limit forming height is also increased by about 11%,and the springback is also greatly reduced.It can be seen that the sheet metal forming process assisted by magnetic medium provides a scientific guidance and a new idea for the forming of complex special-shaped components.For the special-shaped structure workpiece such as cylindrical parts with spherical bottom,the slab will form a suspended area at the initial stage of drawing because of its special shape at the bottom.The existence of the suspended area will seriously increase the radial tensile stress of the sheet metal in the suspended area,making it easy to thin or even break.In order to solve this problem,this paper attempts to use magnetic medium for reverse pre-bulging before deep drawing.The results show that the pre-bulging can improve the forming performance and the quality of components.When the pre-bulging height increases from 0 to 6 mm,the maximum wall thickness reduction rate is reduced by about 5%,and the coordinated deformation and wall thickness uniformity of all parts are significantly improved.At the same time,the limit forming height is also improved,the springback is obviously reduced,and the shape and size accuracy is improved.However,for this kind of thin-walled deep cavity component,the forming process of reverse pre-bulging with magnetic medium is more complex,and there are many factors affecting the final forming quality,which are generally nonlinear.In order to solve this problem,this paper proposes to combine the gray correlation analysis and response surface method to optimize the parameters in the experiment process.The corresponding prediction model is established,and the reliability and applicability of the model are fully proved.It provides an effective method and thinking for the complex forming of special-shaped sheet metal components. |
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