Research On Deep Drawing Of 2A12 Aluminum Alloy Hemispherical Parts With Reverse Bulging

Due to the tensile and compressive stress in the hanging area,the aluminum alloy hemispherical parts are prone to plastic instability,which leads to wrinkling and cracking defects.In this paper,a novel deep drawing method is proposed to suppress the wrinkling of the suspended area.In deep-drawing process,the rigid lifting-up ring is used to form the sheet in the suspended area,and the shape of the sheet in the suspended area is adjusted to make it in a reasonable double tensile stress state to avoid wrinkling and cracking.The theoretical analysis under the reverse expansion of the lifting-up ring was carried out,and the rigid loading tooling with lifting-up ring was designed.The deep drawing process of 2A12 aluminum alloy hemispherical part was deeply studied by finite element simulation and experiment.The geometric model of bulge forming in suspended zone is established.The relationship between bulge height,lifting speed and punch loading displacement is deduced by geometric relationship.It is found that bulge height is related to drawing depth and punch shape parameters;Through the stress analysis of the counter expansion zone,the calculation formula of lifting force is deduced.In this paper,the simulation model of the semi-spherical drawing process is established,and the numerical simulation of semi-spherical drawing with reverse bulging is carried out.The effects of lifting force loading path,lifting ring size and lifting ring number on wall thickness and wrinkling are analyzed.Before the middle stage of deep drawing,the instability and wrinkling of the suspended zone and the sheet metal thinning can be effectively restrained by using larger lifting force;In the later stage of deep drawing,the change of lifting force has no obvious effect on wrinkling inhibition,and the increase of lifting force will lead to the increase of sheet thinning trend.On this basis,the optimized loading path,the size and the number of lifting rings are obtained by numerical simulation.An experimental device with follow-up lifting-up function was designed to carry out the deep drawing experiment of 2A12-O aluminum alloy with 0.8mm thickness(thickness diameter ratio 2.35 ‰).The deformation behavior under different lifting loading paths is studied.It is found that before the middle stage of deep drawing,the number and height of wrinkles in the suspended area decrease with the increase of the lifting force.When the lifting force is less than 22 MPa,wrinkles will appear in the suspended area.When the lifting force is 44 MPa,hemispherical parts with good surface quality can be formed;The influence of the number of lifting rings on the wall thickness of hemispherical parts is studied.It is found that the wall thickness distribution is more uniform when three-stage lifting rings are used,and the maximum thinning rate is 9.88%;At the same time,the experimental device was used to carry out the deep drawing of hemispherical parts with different thickness diameter ratio and different sheet metal;With the increase of the yield strength of sheet metal,the lifting force needed to resist the instability is greater.