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Finite element numerical simulation of deep drawing spinning with different passes

Abstract: by establishing a reasonable mechanical model and using the elastic-plastic finite element method, the numerical simulation of multi pass deep drawing spinning is carried out, and the stress-strain distribution laws under different passes are obtained. The difference between drawing spinning and deep drawing deformation is analyzed from the point of view of stress-strain distribution, and the deformation characteristics of multi-pass drawing spinning are revealed, which lays a foundation for further study on the forming limit and forming quality of multi-pass drawing spinning

key words: numerical simulation of pass deep drawing spinning stress and strain distribution

preface

deep drawing spinning is the most commonly used and representative forming technology in general spinning. At present, it is widely used in aviation, aerospace, military and civil processing technology fields. It usually refers to the processing process of using spinning tools to reduce the diameter of blanks (plates or prefabricated parts) and form rotating parts. Because it is similar to deep drawing, it is called deep drawing spinning for short [1]. Because the forming limit of one stretch spinning is very small, it is rarely used in actual production, and multi-pass spinning is widely used [2]. In the multi pass spinning process, different passes restrict and affect each other, and the deformation of each pass has a decisive impact on the final forming of the workpiece. Therefore, it is extremely necessary to explore the characteristics of deep spinning with different passes

in this paper, a reasonable mechanical model is established, and the elastic-plastic finite element method is used to simulate the deep drawing spinning of different passes, and the distribution law of stress and strain under different passes is obtained, and the difference between the deep drawing and spinning deformation is pointed out from the perspective of the distribution of stress and strain. Thus, the deformation characteristics of multi-channel stretch rotation are revealed

1 finite element model

1.1 basic assumption

multi pass stretch spinning greatly improves the forming limit in the process of stretch spinning compared with simple stretch spinning. However, the increase in the number of passes also increases the complexity of deformation, which brings great difficulties to the study of blank deformation under different passes. Therefore, this paper simplifies the multi-pass stretch spinning process and adopts some assumptions. Assumptions are as follows:

(1) since the final formed part is an axisymmetric part, the spinning process is simplified as an axisymmetric problem, which is solved by a 12 ton loader

(2) the contact pressure between the roller and the blank is evenly distributed, and the sheet metal is loaded simultaneously on the circumferential contact surface of each feeding step

(3) in addition to the axial and radial feed, the spinning wheel itself also rotates, and there is rolling friction between it and the blank, and lubricating oil is usually added in actual production to reduce friction. The relative rotational pressure of friction is negligible, so the friction effect is ignored here

1.2 mechanical model

during the spinning process, the feed rate of the spinning wheel per revolution of the blank is very small, so the local deformation of spinning can be regarded as a physical nonlinear problem of small deformation. According to the basic assumption, the axisymmetric center is fixed and constrained, and the plate under the core mold is clamped. Therefore, the thickness direction is constrained here, the outer edge of the plate is free, and the action of the rotary wheel on the blank is the surface distributed force. The model is shown in Figure 1

Figure 1 Schematic diagram of mechanical model

2 relevant process parameters

the main process parameters used in the numerical simulation are: the blank diameter is 180mm, the thickness is 1mm, the roller diameter is 140mm, the fillet radius is 6mm, the core die diameter is 80mm, and the feed ratio is 0.2mm/r

lf2m is selected as the blank, and the material performance parameters are elastic modulus of 71000mpa, hardening index of 0.16 and Poisson's ratio of 0.3

the roller track adopts the form of straight-line unidirectional pass pasting. In order to avoid interference between the spinning wheel and the core mold, the spinning point is selected as r=46mm

3 results and discussion

according to the above model, the four passes in multi-pass spinning are numerically simulated. Fig. 2 is the schematic diagram of four passes of tension and rotation deformation positions. Figure 3 shows the stress-strain distribution of multi-pass tension and rotation under four passes

Figure 2 Schematic diagram of each pass position of pull and spin

Figure 2 Schematic diagram of each pass position of pull and spin

from the stress distribution diagram, due to the use of pass mold sticking processing, with the increase of passes, the mold sticking part expands, and the core mold is attached. 5. Effective working space: 150 × one hundred and fifty × The stress near 240mm gradually decreases with the increase of passes; However, under the effect of material hardening, the maximum stress increases with the increase of passes, which also increases the yield stress of subsequent passes of plastic deformation and makes deformation difficult. Since the rotation point is selected at r=46mm, extreme values occur near the rotation point. In addition, from the perspective of the overall distribution of stress, there is a difference between the stress change of the initial pass and the later pass, which is mainly due to the difference in the shape change of different passes in the multi pass processing of flat slab blanks. The blank shape first changes from a flat plate to a cone, and then the center angle of the shell of each pass gradually decreases, and the shape is basically unchanged

as we all know, in the forming process of deep drawing cylindrical parts, the maximum radial tensile stress occurs at the circular angle of the punch (equivalent to the core die), and the maximum time is generally at the instantaneous outer edge radius of 0.9r0, that is, the initial stage of deep drawing. However, the tension and rotation are different. From the radial stress distribution figure 3 (a), it can be seen that the maximum radial stress occurs in the deformation area of the spinning wheel. Tensile cracking usually occurs in the wall. Another difference is that buckling and wrinkling may occur at the inner wall and outer flange when drawing conical parts. However, the tangential compressive stress of deep drawing spinning is only large at the outer edge (see Figure 3 (c)), and there is usually no wrinkling at the inner side. Therefore, drawing spinning has greater advantages than deep drawing forming

it can be seen from the strain distribution diagram that with the increase of passes, the outer diameter of the billet gradually shrinks and is close to the core mold. Therefore, it is listed as one of the 20 industrial bases (clusters) that the province focuses on. The radial and circumferential strains (Fig. 3 (D) and (f)) gradually increase, which is basically consistent with the deep drawing. However, due to the one-way linear path processing of the roller, the thickness strain (Fig. 3 (E)) changes sharply, the internal thickness decreases, and the thickness of the outer edge increases

4 conclusion

(1) a reasonable mechanical model is established in this paper, and the numerical simulation of multi pass stretch spinning forming is carried out, and the stress-strain distribution law under different passes is obtained. From the stress distribution diagram, it can be seen that the stress increases with the increase of passes, and the stress change of the previous pass is slightly different from that of the subsequent pass. From the strain distribution diagram, the strain increases with the increase of passes, and the changes between passes are basically the same

(2) comparing drawing spinning with deep drawing from the perspective of stress-strain distribution, it is concluded that drawing spinning has greater advantages than deep drawing

(3) the deformation characteristics of multi-pass stretch spinning are revealed from the perspective of stress-strain distribution, which lays a foundation for further study on the forming limit and forming quality of multi-pass stretch spinning

references

1 Japan plastic processing society Spinning forming technology Translated by Chen Jingzhi Beijing: China Machine Press, 1988, edited by wangzhongren Special plastic forming Beijing: China Machine Press, 1994

about the author: Liu Jianhua, female, born in 1972, is a doctoral student. The researchers, such as automatic experimental machine, large-scale structural experimental machine, environmental experimental machine such as upper and lower temperature constant temperature and humidity salt spray, electronic durability creep experimental machine, etc., are computer simulation of multi-pass ordinary spinning processing. (end)

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