Forming characteristics of conical shell in the ho

2022-08-10
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The forming characteristics of deep drawing conical shell

Abstract: with the help of finite element analysis of the forming characteristics of single process deep drawing conical shell, the concept of deep drawing coefficient and its limit value is determined, and the calculation data is recommended

key words: single process deep drawing; Conical shell; Drawing coefficient; Calculation data

1. Preface

when drawing thin-walled conical shells in a single process, the metal deformation process has some characteristics, and it is difficult to evaluate the possibility of drawing. In addition, the ratio of blank diameter to conical shell diameter as the drawing coefficient and its limit value are not strictly defined. Moreover, the limit data of single process forming is lack of sufficient reasons. Therefore, when adjusting the process, it often leads to incorrect two-step forming, and the surface waviness, uneven distribution of wall thickness, and increased cost of parts. Jinan period cable copper strip tensile testing machine meets the standard gb/t 11091 (2) 005

II. Characteristics of single process deep drawing conical shell

in order to reveal the characteristics of single process deep drawing conical shell and evaluate its ultimate deformation, the finite element calculation system of thin shell forming is used

assuming that the forming of the conical shell is carried out with a punch with a spherical (Fig. 1a) or flat annular (Fig. 1b) working surface, the bus HM of the conical shell part that is not in contact with the punch is not a straight line during the whole process, but the curvature change along the bus HM assumes the shape shown in Fig. 2. The deformation characteristics of this part of conical shell mostly determine the limit possibility of the process and the quality of the workpiece obtained

figure 1

the deformation along the bus OK (see Figure 1) is unevenly distributed, and this unevenness will gradually increase during the process. Strain along thickness ε H is increasingly confined to the contact area between the conical shell and the punch, and its maximum point moves from point O to point H. Strain in local area at the determined loading (deformation) step ε H →∞, and then outside the local area ε h→0。 The shape of the conical shell on this loaded step is the limit shape

as the drawing coefficient K, take the ratio of the blank diameter D to the concave die diameter D. Its limit value K Pole = (d blank/D concave) pole will conform to the local strain zone ε h→∞。

under the real condition of drawing conical shell, the working surface of punch is different from the surface used in calculation. It has a conical segment connected with the spherical segment or annular segment in the HK point (Figure 2). The process of forming conical shell with this punch is different from the punch used in the calculation diagram of the final stage. At this time, point h moves towards point O and occupies the position of point HK. The HK point is the connection point between the arc radius r convex +s/2 and the straight line hkmk. It is obviously more difficult to calculate according to the two stage diagram. The test of this calculation scheme shows that the ultimate depth of the conical shell obtained will be 5% - 10% larger

figure 2

ensure the blank holder force of flange braking. When kostron selects a new material, it should be enough to overcome the formation of ripples outside the contact area of the conical shell, and it is not allowed to fully draw the flange under the blank holder at the end of forming. These requirements for the best braking of the flange under the blank holder must be observed in order to obtain high-quality workpiece edges. However, at present, there is no recommendation to select blank holder force when drawing conical shells in the references. In order to complete the above requirements, the blank holder force is changed in the calculation, that is, the circumferential stress outside the whole contact area is taken as a positive sign. In this way, the stability of the conical shell increases with the increase of its relative thickness. However, the dispersion between the calculated results and the experimental results is small in the range of relative thickness used

the calculation shows that the flange must have a large braking force under the blank holder when drawing the conical shell. In this way, the surface area of the conical shell should be significantly increased. This should be taken into account when determining the blank size

III. The recommended calculation data is to compare the calculation results with the experimental data. Some original parameters used in the calculation are the same as those used in the experiment

the blank material is 08F steel, and the plate thickness is 0.73mm. The hardening curve is approximately calculated according to the test results of the specimen under uniaxial tension with the following formula (the specimen is cut from the experimental sheet):

σ= 534(0.0102+ ε 0.237)

the average value of the anisotropy coefficient of the specimen cut at 0 °, 45 ° and 90 ° with the rolling axis is:

R = (R0 + 2r45 + r90)/4 = 1.25

friction coefficient value μ: In the contact area between conical shell and punch μ= 0.21, under the blank holder μ= 0.16。

Table 1 and table 2 respectively show the relationship data of d-concave/d-convex, r-concave/S0 and r-convex/S0 (S0 blank thickness) pairs that will not change the drawing degree K pole for several 10 years when drawing with spherical punch and ring punch. Table 1 Relationship between k-pole and r-concave/S0 and d-concave/d-convex during spherical punch drawing

Table 2 Relationship between k-pole and r-convex/S0 and d-concave/d-convex during ring punch drawing

Figure 3 shows the increment of conical shell surface area Δ The relationship curve between F (percentage of the original blank area) and D concave/D convex, R concave/S0 and R convex/S0 (k = k pole), 1, 2, 3, 4, 5 - R concave/S0 = R convex/S0 = 4.11, 6.85, 9.59, 12.33, 15.07, FIG. 3a and Fig. 3b are drawing with spherical punch and conical punch respectively

Figure 3 low industry concentration these problems

Figure 4 shows the relationship curve between the limit relative depth h/d concave and D concave/D convex, R concave/S0 and R convex/S0 (k = k pole). Figure 4A and figure 4B respectively show the drawing with spherical punch and ring punch. 1, 2, 3, 4, 5 are the same as Figure 3

figure 4

IV. conclusion

(1) with the help of finite element analysis of conical shell forming during single process deep drawing, the processibility of the process and the requirements to ensure the quality indicators required for the workpiece are determined

(2) the drawing coefficient must be the ratio of the blank diameter to the die diameter. Its limit value is closely related to the geometric parameters of the conical shell

references

[1] a Д.МАТВЕЕВ Etc Особенности формообразования при вытяжке Коницеских оболочек.К.Ш.П., 1997 (10): 16 ~ 18

[2] Du Dongfu, edited by Xun Wenxi Cold stamping die design Changsha: Hunan Science and Technology Press, 1985 forging technology, 1999, issue 2 (end)

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