Research On Forming Limit Of Radial Extrusion Of Outer Wall Boss Based On Tube Blank

Tubular parts with boss on the outer wall are widely used in key engineering fields such as aerospace,weaponry,mining and oilfields,and automobiles,especially occupying an important position in the lightweighting of key components.These key structural parts often withstand the impact force,inertial force,additional stress generated by vibration and other forces,so their safety and reliability are very strict.Tubular parts with bosses on the outer wall manufactured by the integral plastic forming method can meet the requirements of use.However,defects such as folding and cracks in the forming directly affect the quality of the components.Therefore,it is very necessary to study the influencing factors of folding,crack defects,generation mechanism,forming limit,etc.In this paper,a combination of numerical simulation,theoretical analysis,and physical experiments is used to carry out the following research and obtain relevant results:The influence of factors such as inner diameter d₀,outer diameter d₁,tube wall thickness t,boss cavity height h,width w,boss cavity fillet radius r,friction coefficient?,extrusion speed v and other factors on forming is studied through Deform-3D numerical analysis software.The results show that:the inner wall of the tube blank is recessed and folding defects are easy to be generated in the initial upsetting stage,the boss edge crack defects are easily generated in the stable filling stage,and the forming force will rise sharply in the final forming stage.The forming load increases obviously with the increase of friction force,and the strain uniformity of the boss is better under the condition of lower extrusion speed and smaller friction coefficient.There are critical conditions for the influence of the width and height of the boss cavity on folding defects.In terms of the generation mechanism of defects,the sag and fold of the tube blank are related to the force distribution in the wall thickness direction of the tube blank.The direction of the force on the wall thickness of the tube blank is divided into inside and outside.Analysis of the micro-unit mechanical model in the deformation zone of the boss shows that reducing the friction coefficient or increasing the height and width of the boss cavity can increase the limit length of the boss.In terms of forming limit,the shape and area of the axial section of the boss cavity determine whether the inner wall of the tube blank is dented and folded during the initial upsetting stage,and the radial length of the boss cavity has no obvious effect on whether the inner wall depression occurs during the initial upsetting stage;The tube size d₀,d₁ and t determine the maximum value of the axial cross-sectional area w×h of the defect-free boss that can be formed.Definition S=?h/t?×?w/t?characterizes the safety of the initial upsetting stage of the outer wall boss of the radial extrusion of the billet,each d₀/d₁ has a certain forming safety limit value S_d,S_d value It has nothing to do with the wall thickness t of the billet;when S>S_d,the inner wall of the billet will be depressed and folded,and when S<S_d,the inner wall of the billet will not be depressed and folded.The forming limit diagram of the initial upsetting stage of the outer wall boss of the radial extrusion of the tube blank is obtained,and the safe area and dangerous area of the forming parameter selection are determined.Through the numerical simulation experiment,the influence of the number of bosses,the distribution position and the number of loaded punches on the forming quality is analyzed.The results show that the strain of the boss area under the axisymmetric distribution and bidirectional loading conditions is more uniform,and the damage to the mold is small during the forming process.Through the design of physical experiments,the correctness of the above-mentioned forming limits and other conclusions were verified and successfully applied in actual production.