| The sheet cylindrical part,generally produced by the deep drawing,is a common stamping product.Due to the limitation of sheet ultimate drawing coefficient,the large diameter of the cylinder can not be formed by one deep drawing,and need to adopt multi-pass deep.However,during the drawing process,there will be plastic deformation uneven phenomenon of cylindrical parts because of the anisotropy of the sheet and the mold gap,fillet radius,blank holder force and lubrication and other technological factors,which results in making the mouth parts appear rugged ear.The emergence of the ear will not only increase the trimming process,the costs,but make the finished product rate low seriously.In this paper,the influence of non-uniform gap on the multi-pass drawing of the cylindrical part is studied by means of the Dynaform finite element simulation and multi-pass drawing tests.The research provides the basis for exploring the method of low production ear rate in industrial actual production.In this paper,the finite element theory of sheet metal drawing process is systematically expounded.Firstly,The Hill yield criterion and Barlat yield criterion are analyzed and compared.It is pointed out that Barlat yield criterion is more effective in simulating the plastic flow law of flange during the forming process.Then,the two most commonly used elements of Hughes_liu and Belytschko_Tsay and algorithms for implicit and explicit types are analyzed and compared.It is concluded that Belytschko_Tsay unit and explicit algorithm are most suitable for multi-pass drawing simulation,which are considered from the aspects of computational efficiency and precision.Finally,the two kinds of cold rolling steel(DC04 and DC05)of the six different programs of the second pass deep drawing are simulated by Dynaform finite element software.Simultaneously,the distribution of stress and strain under different schemes and the size of the ear rate are also analyzed.To begin,the first uniform gap and uneven gap two sets of drawing die,the second uniform gap and uneven gap two sets of drawing die are designed and each of them is equipped with six groups of multi-pass drawing plan.Deep drawing for the first time,the A-type uniform gap deepening is used to the program one,two and three,and the B-type uneven gap deep drawing is used to the scheme four,five and six.Deep drawing for the second time,the C-type evenly gap deepening is used to the program one and four,the D-type unevenly gap deepening is used to the program two and five.In addition,the 0 ° line on the cylindrical member is aligned with the D-type die 0 ° reference line after the first drawing.Scheme three and six use a D-type uneven gap drawing,and the 45 ° line on the cylindrical member is also aligned with the 0 ° reference line of the D-die.By comparing the first three groups of experiments,it is found that the use of non-uniform gap can reduce the second pass deepening of the system ear rate.Moreover,in the direction of the large should be arranged with large gaps,and in the direction of the small should be configured with small gaps,which can effectively reduce the system ear rate through the comparison of the four,five and six schemes.At the same time,it was found that the earning rate of the secondary drawing was lower than that of the one drawing,and the simulation results were in good agreement with the experimental results.This study shows that the use of Dynaform finite element can be a good prediction of multi-pass deep drawing of the ear and the use of reasonable uneven gap can effectively reduce the system ear rate.The method provides a theoretical basis for the subsequent realization of low ear or no ear drawing. |
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