Research On Theory And Technology Of Deep Drawing Based On Radial Segmental Blank Holder For Sheet Metal

The technology of sheet metal forming is more widely applied in various industrial fields which is mainly automobile manufacturing,a large number of new process sheets have been widely utilized,it is very important to improve the existing forming processes and develop new technologies to promote the progress of forming manufacturing technology.Deep drawing is one of the basic deformation methods of sheet metal forming,blank holding force and its control method are important factors affecting the forming process.Blank holder force control technology is the common key technology of sheet metal stamping forming and forming equipment,it is positive significance to further reveal the wrinkling mechanism and develop new forming technology by studying relevant problems.In this work,aiming at the deep drawing of axisymmetric parts and square boxes,the distribution law of stress and strain,critical blank holding force,different blank holding techniques to restrain wrinkling and improve forming effect were studied.It mainly includes that the integral direct parameter solution method is applied to obtain the stress-strain distribution law of axisymmetric forming of sheet metal;the deep drawing process of cylindrical parts with radial segmental blank-holder and curved die.The composite segmental blank-holder technology of square boxes is studied deeply,and the suitable loading method is used to realize the composite segmental blank-holder independently.Meantime,the influence of deformation condition on wrinkling,rupture and forming limit are analyzed.Firstly,with the conditions of thin plate theory,plane stress and proportional loading,the solution process of the stress-strain distribution of cylindrical,conical and general axisymmetric surface parts is analyzed by method of direct integral solution.The results of stress-strain distribution of axisymmetric deep drawing of arbitrary surface parts are calculated.The experiment is used to verify the theoretical calculation results,which are consistent with the experimental results.Based on thin plate theory and incremental theory,the differential equation of equivalent strain increment is obtained for formation of general axisymmetric curved surface parts under less assumptions.The step-by-step direct integral parameter solution is given according to taylor series expansion and integral definition.The stress and strain of deep drawing in cylindrical parts are calculated,and the theoretical calculation results are closer to the experimental results.Secondly,the deep drawing of axisymmetric cylindrical parts is studied,the critical blank-holder force and mathematical expressions of wrinkle model are analyzed,The drawing process of cylindrical parts with conical die and radial segmental blank-holder are studied,the metal sheets of 08 Al,AA5754 and AA6061 are taken as research objects,the forming process is analyzed by experiments and FEA(finite element analysis),when the dies with different cone angles are combined with the radial segmental blank-holder technology.The experimental results show that under suitable process conditions,the drawing coefficients are 0.373,0.410 and 0.431 respectively.It is showed that the new process can effectively improve the forming limit of cylindrical parts by theoretical analysis,FEA and experiment.Thirdly,critical blank-holder force of the square boxes is calculated and the mathematical expression of wrinkle model is analyzed.According to the thickness distribution law of flange area,the segment location of radial segmental blank-holder is determined.ST12 sheet with a diameter of 223 mm is selected,and the drawing process of square box shaped parts under the condition of radial segmental blank-holder is simulated.The influence of main factors in the forming process is analyzed..Furthermore,the forming process of square boxes with radial segmental blank-holder technique has be analyzed by experimental research.It is showed that the new process can effectively improve the forming limit and restrain FEA and experiment.Finally,the FEA and experiments are carried out to verify the wrinkling with local constraints in the flange region of cylindrical parts and square boxes,the wrinkling mechanism is also analyzed.It is pointed out that the wrinkling of sheet metal is not only related to the stress state,but also related to the constraint conditions in the forming process.The effectiveness of the method is further demonstrated.Focus on the problems of square boxes in deep drawing process,the composite segmental blank-holder technology is proposed,which is combined by radial segmental blank-holder technology and circumferential segmental blank-holder technology.The distribution rate in each segment is determined by the orthogonal test and FEA.It is showed that the square boxes in which the minimum thickness is 0.513 mm can be formed in constant blank-holder force by SPCC steel plate with 1.0 mm thickness and the diameter of 221 mm by FEA.In the same addition,the square box is obtain that the diameter is 253 mm and the minimum thickness is 0.493 mm are formed in parabolic variable blank-holder force successfully.It was manufactured the experimental die which can apply composite segmental blank-holder technology with normal and variable blank-holder forces for square boxes.In this way,the composite segmental blank-holder technology was accomplished in deep drawing process.Experiment results are gained under the condition of composite segmental blank-holder technology,it is showed that the maximum diameter of mild steel sheet is 213 mm and 231 mm respectively in constant blank-holder force and variable blank-holder force of low carbon steel sheet(SPCC with 1 mm thickness)by composite segmental blank-holder technology.It is showed that the cylindrical parts with radial blank-holder technology and square boxes with composite segmental blank-holder technology,which can effectively prevent the wrinkling in the flange region,the drawing limit of sheet metal and work-pieces surface quality are increased to a certain extent by studying the forming theory and deep drawing technology of axisymmetric parts and square boxes.