Deep Drawing Forming Law Of 7075 Aluminum Alloy Double-layer Sheets At Cryogenic Temperature

The new generation of equipment urgently needs thin-walled curved parts with integral structure,but its integral forming has serious defects of wrinkling and crack,which has always been the bottleneck restricting the industrial application of such components.In order to solve the forming problem of ultra-thin curved surface parts of high-strength aluminum alloy,a new method of ultra-low temperature deep drawing of aluminum alloy double-layer sheets is proposed in this paper.Taking 7075 aluminum alloy ball bottom parts as the object,the deep drawing rules under the superposition of double-layer sheets and ultra-low temperature are expounded through process test and numerical simulation system,and the mechanism of restraining the instability and wrinkling in the suspended area and improving the deformation uniformity of double-layer sheets are revealed,It provides theoretical guidance and technical support for the integral forming and manufacturing of aluminum alloy ultra-thin curved parts.The ultra-low temperature mechanical properties of sheet and cladding materials were tested by ultra-low temperature uniaxial tensile test.Under ultra-low temperature conditions,three kinds of cladding materials with different strength levels(1Cr18Ni9Ti stainless steel,5052 aluminum alloy,1060 pure aluminum)and 7075 aluminum alloy sheet all show excellent mechanical properties,which is conducive to the formation of thin-walled components.The forming law of double-layer sheets under the condition of temperature,clad material,size and blank holder coupling was studied through the ultra-low temperature drawing process test of double-layer sheets.The double increasing effect of aluminum alloy at ultra-low temperature can not only improve the formability and cracking limit of aluminum alloy sheet,but also restrain the occurrence of wrinkling defects to a certain extent.When the clad plate is1Cr18Ni9 Ti stainless steel,the maximum drawing force reaches 176 t,which is nearly 4 times that of 5052 aluminum alloy,and the tonnage of forming equipment is too high;Compared with 5052 aluminum alloy clad plate,the accuracy of sheet profile and wall thickness distribution are also poor.In addition,the cladding needs to have a certain strength to effectively suppress the wrinkling of the sheet and improve the forming limit of the sheet.When the blank diameter is constant,only when the selected thickness of the clad plate is not less than its critical wrinkling thickness,can the specimen without wrinkling defects be formed under low blank holder force;The wrinkling free specimen can also be formed by reducing the thickness of the cladding,but a larger blank holder force is required.Through the numerical simulation of ultra-low temperature deep drawing of double-layer sheets,the circumferential stress distribution law of ultra-low temperature deep drawing of double-layer sheets is clarified,and the wrinkling suppression mechanism of ultra-low temperature deep drawing of double-layer sheets is revealed: the introduction of clad plate exerts normal contact pressure and interface friction on the thin plate,which on the one hand reduces the circumferential compressive stress in the suspended area,and on the other hand improves the ability of the formed part to resist instability and wrinkling,The two aspects work together to effectively suppress the wrinkling defects.Through stress-strain analysis,the improvement mechanism of deformation uniformity under ultra-low temperature drawing forming of double-layer sheets is revealed: the cladding can not only exert normal contact pressure on the suspended area of the sheet,but also provide beneficial friction for the sheet,so that the radial stress and strain gradient of the sheet are reduced,and the distribution of deformation and wall thickness are more uniform.