Research On The Roll-drawing Forming Behavior For Large-section Thin-walled Square Box With Inner Longitudinal High Ribs By 6061 Aluminum Alloy

The lightweight of major aerospace and national defense equipment has become an important guarantee of national strategy and a main means of improving tactics level.Major equipment key components using lightweight alloys and large integrated,thin-walled lightweight complex structure is an objective demand.The large-sized thin-walled components with inner high ribs made of lightweight alloys with force-bearing structures and protective functions are preferred as key components for major equipment due to their high structural efficiency and reliability.Aiming at the large cross-section thin-walled square box with inner high longitudinal ribs for projectile equipment,the traditional split welding manufacturing process has the problems of high residual stress,poor precision and poor air tightness,which can not meet the requirements of high bearing capacity,high reliability and high efficiency.In view of the above manufacturing bottlenecks,this paper proposes a roll-drawing forming method for large-section thin-walled square boxes with inner high longitudinal ribs.The variation of force and stress with parameters was studied,and the calculation formula of roll-drawing force and forming limit diagram were established.The influence of different rolldrawing dies and process parameters on the stress-strain distribution and the filling effect of the inner ribs was revealed,and the deformation behavior of the square box was clarified.The influence of the blank on the metal flow and the filling of the inner ribs was studied,and influence of the structural parameters of the blank on the forming force and the defects was further mastered.The design method of the blank for roll-drawing forming was proposed.The roll-drawing forming process schemes of blanks with different specifications were formulated,and the aluminum alloy large-section thin-walled square box with inner high longitudinal ribs was produced.It provides theoretical basis and technical guidance for metal flow control and precision forming of roll-drawing forming of such square boxes.The theoretical calculation formula of roll-drawing force was derived by principal stress method.The variation of forming force and axial stress with roll-drawing ratio,thickness-width ratio and roll-drawing passes was revealed by numerical simulation.The mandrel force and roller force increase with the increase of the roll-drawing ratio or the decrease of the thicknesswidth ratio(the increase amplitude gradually decreases),and increase and decrease with the increase of the roll-drawing passes,respectively;and increase of roll-drawing passes makes the deformation of the box wall more uniform but also increases the maximum axial tensile stress in the dangerous area.Furthermore,the forming limit diagram was established by comparing the relationship between the maximum axial tensile stress and the safe tensile strength of the material under different parameters,which guides the selection of the forming parameters of the square box.To ensure the full filling of the inner high ribs in the square box,the design method of the blank for roll-drawing forming was proposed.The preforming scheme of the blank with inner and outer longitudinal ribs for roll-drawing forming has the best filling effect of the inner ribs,which is determined by numerical simulation analysis.Furthermore,the effects of the width ratio of inner and outer ribs,the compensation coefficient of outer ribs and the compensation scheme on metal flow and inner rib filling were studied.It is determined that the width ratio of inner and outer ribs is 1,the compensation coefficient of outer ribs is 1.2 and the integral compensation scheme of outer ribs has better forming effect of inner ribs.Based on the above results,the influence of the structural parameters of the outer ribs on the forming force and defects was analyzed by orthogonal experiments.In addition,the flash defect at the fillet of the square box blank was improved with the increase of the fillet radius,and the maximum force of the roll-drawing forming was gradually reduced with the increase of the bottom angle of the blank.The influence of the blank shape on the forming force and flash defect is mastered,the forming quality is improved,and the equipment tonnage and production cost are controlled.The influence of die and process parameters on forming force and forming quality was mastered by numerical simulation and response surface method.With the increase of roller radius,the mandrel force and roller force decrease and increase,respectively(gradually maintain stable).The increase of distance between rollers and roller radius is helpful to improve the deformation uniformity.In addition,the influence of roller groove parameters on the filling effect and forming force of inner ribs was analyzed,it is proved that the roller groove optimization scheme with equal coefficient compensation and equal width groove of outer ribs has the best forming effect of inner ribs.The roll-drawing forming process schemes of different specifications of square box blanks were formulated,and the vertical roll-drawing experiment of square box scaled parts and the horizontal roll-drawing experiment of large section square box were carried out.The 8 mm wall thickness,18 mm inner rib height and 46 mm inner rib width of 6061-aluminum alloy largesection thin-walled square box with 814×814×2000 mm specification was produced.It provides a theoretical basis and technical guidance for the metal flow control and precision forming of the square box of roll-drawing forming.The microstructure observation and mechanical properties test showed that the grains of the square box billet were significantly refined and the comprehensive mechanical properties were improved.