Research On Stamping Performance And Servo Forming Process Of 6061 Aluminum Alloy Sheet

With the development of automobile lightweight technology,the application of aluminum alloy sheet in automobile cover parts and structural parts is expanding,and the aluminum alloy sheet has low forming performance at room temperature,and wrinkles and cracks are easily generated during drawing.The forming process of raising the drawing drawing limit by hot drawing increases the industrial production cost and reduces the drawing forming efficiency.The method for controlling the drawing speed of the sheet to increase the drawing limit of the sheet at normal temperature has the advantages of simple regulation mode and strong process applicability,and can effectively improve the drawing forming limit of the aluminum sheet under the single temperature at room temperature and reducing the deep drawing defects,It not only improves the forming efficiency of the drawn parts,but also reduces the production cost of the enterprise.,it is of great value to promote the practical production and application of aluminum alloy sheets in automobiles.Based on the basic process parameters affecting the stamping performance of 6061 aluminum alloy sheet,this paper research the influence of blank holder force,concave corner radius,lubrication coefficient and drawing speed on the deep drawing performance under constant speed of sheet metal.Based on the research on the influence of parameters on the drawing performance of the sheet metal,combined with the controllable characteristics of the forming speed of the servo press,the influence of the shifting mode of the press on the drawing forming limit and forming quality of the sheet is studied,and the aluminum alloy sheet is obtained.The variation of forming properties under different servo drawing process curves.The main research contents and results are as follows:1)The study of hydraulic constant speed drawing at room temperature of sheet metal shows that the mechanism of plastic properties of the main sheet is different in the speed range of0~200mm/min,when the speed range is 0~60mm/min the main factor is friction and work hardening;when the speed range is 60~200mm/min,the temperature effect is the main factor.Combined with Dynaform simulation sheet drawing process at 200~1000mm/min,the simulation results show that when the drawing speed is more than 300mm/min,the equivalent strain rate at the rounded corner of the deep drawing cup increases sharply and the strain rate increases.The tensile stress is generated at a large angle,and the drawing forming limit of the sheet is lowered.2)According to the plastic forming theory,in the process of deep drawing of the unformed sheet fillet,the outer boundary belongs to the free boundary and is in an unconstrained state.If the external force constraint is properly added,the material drawing forming limit can be significantly improved.Based on this,the rubber-coated unformed sheet is rounded in the drawing process on the side of the die,and the other part in contact with the mold is laminated by a polytetrafluoroethylene film to form a sheet.The ultimate deep drawing diameter in oil lubrication is increased from 97.5mm to 115mm,and the ultimate drawing ratio is increased by about 17%.3)The servo intermittent drawing mode has an important influence on the rounding reduction rate of the cup.The single-factor(intermittent position,intermittent time,intermittent number)servo forming drawing is studied.The results show that the intermittent position is drawn on the sheet.The deepening and the thinning rate of the rounded corners of the cup are greatly affected during the forming process.During the drawing process,the maximum thinning occurs at the intersection of the crank angle of 130~?(the sheet flange radius is 0.9R).The amplitude is intermittently stopped after this position,and the flange radius of the cup member enters the maximum tensile stress interval of(0.7R~0.9R).At this time,the rounded portion has a large thinning,and the intermittent effect is not effectively,so the appropriate intermittent position should be before the 0.9R position,the flange radius of the drawn cup is in the range of 0.9R~0.95R.The appropriate interval time in the batch process is 2 s.The excessively long interval time has little effect on the sheet deep drawing change,and the intermittent number has little effect on the sheet forming properties.4)Based on the one-way variable-speed tensile test,the effect of velocity variation on the plasticity of the material is studied.The results show that the low-speed deceleration mode of the early high-speed and late-stage is beneficial to the plastic flow of the material compared with the speed-increasing and constant-speed modes.The effect of different loading modes on the deep drawing performance of aluminum alloy sheets at room temperature was studied by servo press.The results show that the deceleration mode in the servo shifting mode is the thinning rate of the rounded corner during the deep drawing of the cup.The suppression effect is better than the acceleration mode;in the oscillating deep drawing mode,the re-contact with the separation of the punch and the sheet will produce a vibration shock,which will increase the unevenness of the fillet of the cup,thereby reducing the drawing forming limit of the sheet..5)Based on the study of the deep drawing forming performance of the sheet under the hydraulic constant speed mode,servo shifting and intermittent mode,the new servo shift intermittent drawing process is designed by the advantage of the composite shifting mode and the intermittent mode to improve the sheet forming performance.Compared with the crank mode,the intermittent mode and the shifting mode,the drawing mode of the sheet is increased by 2%,the thinning rate of the rounded corner of the cup is reduced by 10.6%,and the fillet of the cup is at the mouth of the cup.The thickness difference is reduced from 0.57mm in the constant crank angular velocity mode to 0.35mm in the servo shift intermittent mode,the thickness uniformity of the cup is improved,and the deep drawing forming property and forming quality of the sheet are improved.According to the analysis of EBSD and XRD,the number of small-angle grain boundaries,the number of large crystal grains and the residual stress of the rounded part of the cup in the servo shift mode are smaller than the shift mode,which means that it can be introduced in the shift mode.The intermittent intermittent drawing process obtained by the intermittent effect can reduce the structural defects and residual stress during the drawing process of the sheet,and the plasticity of the sheet during the deep drawing deformation is improved,so that the drawing forming limit of the sheet is improved.