Research On Press-bending With Internal Pressure Of Thin-walled Unsymmetrical 5083 Aluminium Alloy Tubal Component With Large Diameter Thickness Ratio

As the aerospace industry continues to increase the weight reduction requirements of aircraft,the diameter-to-thickness ratio of tubular parts gradually increases.Taking aluminum alloy tubes as an example,the diameter-to-thickness ratio(D/t)gradually increases from 40-50 to 70-80,and the difficulty of forming gradually increases.The bending method with internal pressure reduces the axial stress by increasing the liquid pressure support inside the tube,thereby avoiding wrinkles on the inner side of the bend.When the diameter of the tube exceeds 200 mm,due to the large diameter of the tube,the axial hydraulic reaction force generated by the internal pressure increases,and the friction value is limited,and the polyurethane friction method cannot be used for sealing.In addition,for variable-curvature bends,multiple bends are formed at the same time,which makes it more difficult to avoid the bending wrinkles.To this end,this paper proposes three kinds of bending forming schemes with internal pressure for tubes with pressing plates at both ends,serrations at both ends,and closed heads at both ends,which provides a new forming process for the forming of large-size,large-diameter-thickness ratio and variable-curvature aluminum alloy thin-walled bent tubular componets.This paper takes 5083 aluminum alloy tube as the research object.The diameter-to-thickness ratio of the variable curvature tube is 74.2,the bending angle is 24°,and the relative bending radius is 2.77.The inner side of the tube is prone to wrinkling defects.Based on the analysis of the geometrical dimensions of the bent tubular componet and the bending forming with internal pressure,three kinds of bending forming schemes with internal pressure are designed: pressure plate restriction at both ends,serration restriction at both ends,and closed head at both ends.All three experimental schemes restrict the axial displacement of tube end.Directional displacement,sawtooth restriction at both ends and closed head at both ends provide more significant axial tensile stress to the tube.Using the Abauqs finite element software,three kinds of tube bending forming schemes are numerically simulated,and the tube wrinkling defects,wall thickness distribution,cross-sectional distortion,axial feed and stress and strain distribution of different schemes are analyzed.Due to the lack of axial restraint at the tube end of scheme 1,the axial feed of the tube is relatively high,which is prone to wrinkle defects on the inner side of the tube bending.Scheme 2 and scheme 3 add axial constraints,in which the tube axial feed of scheme 2 is zero,and the tube axial feed of scheme 3 is between schemes 1 and 2.The introduction of axial restraint eliminates the wrinkling defects on the inner side of the tube bending.A large-size,large-diameter-to-thickness ratio and variable curvature 5083 aluminum alloy bent tubular component was carried out in a bending forming experiment with internal pressure.The final formed part of the tube has three bends.The relative errors of the tubular components of the schemes 2 and 3 are respectively 1.46 % And 1.52%.The thickness of the inner wall of the tube is increased while the thickness of the outer wall is reduced.The maximum wall thickness reduction rate of the second scheme is 5.9%,and the minimum wall thickness is 2.776 mm;the maximum wall thickness reduction rate of the third scheme is 6.24%,and the minimum wall thickness is 2.766 mm.The tube end restraint imposed by scheme 2 and scheme 3 produces axial tensile stress,which has a significant inhibitory effect on wrinkling.