毕业设计外文翻译修改后

1、毕业设计外文资料翻译题目 铝合金压铸工艺过程中金属流动行为的变形分区专业 机械设计制造及其自动化班级 07Q3学生 张群学号 20073006139指导教师陈秀生二一一年三 月 十七 日J. Cent. South Univ. Technol. (2009) 16: 07380742 DOI: 10.1007/s1177100901223 Deformation division of metal flow behavior during extrusion process of 7075 aluminum alloyLI Feng CHU Guan-nan LIU Xiao-jing(1.

2、College of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150040, China; 2. College of Shipping, Harbin Institute of Technology at Weihai, Weihai 264209, China)Abstract: To reduce defects caused by non-homogeneous metal flow in conventional extrusion, a die wi

3、th guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J2 and Lodes coefficient µ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding an

4、gle, no metal flow interface forms at the containers bottom, the dead zone completely disappears, the deformation types of the metal in the plastic deformation area change from three types to one type of tension, and the homogeneity of the deformation as well as metal flow are greatly improved. The

5、non-homogeneous metal flow at the final stage of extrusion is improved, reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress, and decreased from 70.8 to 34.8 MPa. Therefore, th

6、e surface cracks caused by additional stress are greatly reduced.Key words: extrusion process; flow defect; deformation division1 Introduction The improvement of the metal flow during extrusion processes is an important means to increase the formability and eliminate defects 1. Many factors may infl

7、uence the metal flow, among which the die structure is closely related to the metal flow.Analysis of die pocket design parameters shows that different pocket angles and pocket offsets will influence the metal flow greatly, and the latter tends to cause the bending ofextrusion products 24. CHUNG et a

8、l 5 discovered that the inhomogeneity of the strain distribution and generation of dead zone during double shear extrusion could be decreased by applying a smaller taper. ULYSSE 6 found that if the die bearing was not corrected or tuned appropriately, the product might be twisted and warped. Finite

9、element method can be used for the optimum design of the die 7,and the homogeneity of the metal flow can be controlled effectively; the metal can beextruded easily 8, and the extrusion force can be decreased greatly 9.Many researches on the optimum design of the die have been done, but most of them

10、are designed for avoiding a certain extrusion defect. It is complicated tooptimize the die structure by employing the finite element method, and even difficult to apply it to practical production 1012. For the above shortcomings, anextrusion die with guiding angle was designed to improve the metal f

11、low during extrusion process. The guiding angle is different from the entry round corner of the conventional die 13. Although a wider entry round corner can be employed to improve the product quality, it cannot basically improve the metal flow and avoid the defects; after the guiding angle is employ

12、ed, the metal in the deforming area is extruded twice with a lower extrusion ratio, which greatly changes the metal flow at the die pocket and influences the extrusion defects. Therefore, in this work, numerical simulation of extruding with and without guiding angle was carried out to investigate th

13、e influence of guiding angle on metal flow, and comparison analysis between simulation and experiment results was also conducted. 2 Simulation conditions 2.1 Die structure The direct hot extrusion was taken as example. The die structures with and without guiding angle are shown in Fig.1. Guiding ang

14、le () can change in a certain range, and =0 means without guiding angle. 2.2 Finite element model DEFORMTM2D was used to simulate the extrusion process. Because of the symmetrical characteristics,axisymmetric model was selected in the simulation, as shown in Fig.2. The radial constrain is superimpos

15、ed on the symmetry plane to make the normal deformation zero. Fig.1 Schematic drawings of die structure under conditions of without (a) and with (b) guiding angle ()Fig.2 Finite element model of extrusion process under conditions of without (a) and with (b) guiding angle Aluminum alloy 7075 billet w

16、as used in the experiments. The billet was 50 mm in diameter and 50 mm in height. The geometrical and material parameters were the same in both the simulation and experiment. In this work, the extrusion process was simulated by using rigid-plastic finite element model. The punch, container and die w

17、ere considered as rigid bodies. The speed of the punch was 2 mm/s; the time increment was 0.1 s; the friction coefficient was 0.3; the isothermal extrusion temperature was 435 , and the extrusion ratio was 9.8. Numerical simulation was carried out at =5, 10, 15, 20 and 30, respectively. The results

18、showed that extrusion load was the minimum at =15 14. Therefore, the die with =15 was selected. 3 Simulation of metal flow 3.1 Steady stage It can be seen from the deformation of the grids that, grids in this area mostly flow towards the die pocket in the form of parallelogram, which indicates that

19、the deformation and flow of the metal are homogeneous. Therefore, it is easy for the metal to flow out the die pockets without the formation of dead zone.Fig.3 shows the velocity field with and without the guiding angle at the bottom of the die. It can be seen from Fig.3(a) that without employing th

20、e guiding angle, there is an obvious metal flow interface at the bottom of the die. A part of metal flows towards the die pocket, the other flows inward, and the dead zone is formed. After employing the guiding angle, as shown in Fig.3(b), the metal near the container flows towards the die pockets h

21、omogeneously, and no velocity interface is formed in the plastic deformation zone. The metal flows towards the die pockets radially without large angle turning, which will not only decrease the flow line turbulence, dead zone and overlap, but also improve the extrusion product quality.Fig.3 Velocity

22、 field at bottom of die under conditions ofwithout (a) and with (b) guiding angle Comparison of the axial stress on the die exit section with and without the guiding angle is shown in Fig.4. The stress states of the axis and surface are compressive stress and tensile stress respectively when the met

23、al is extruded without the guiding angle. With the increase of the distance from axis, the axial stress transforms from compressive stress to tensile stress. The compressive stress and tensile stress are approximately equal, which will result in non-homogeneity of the microstructure and properties.

24、The additional stress increases rapidly and leads to the surface cracks when the lubrication condition is not very good. After the guiding angle is employed, the axial tensile stress of the surface point decreases from 70.8 (P1) to 34.8 (P2) MPa, and the axial stress distribution along theradial dir

25、ection changes a little (Fig.4(a). The radial stress distribution is shown in Fig.4(b), without employing guiding angle, the stress state of axial points is compressive stress and that of the surface points is tensile stress that increases with the distance from axis. After the guiding angle is empl

26、oyed, the radial stress at the die exit becomes compressive stress, and the radial stress and compressive stress are almost equal.3.2 Final stage When lower billet is extruded at the final stage ofextrusion process, shrinkage cavity is a common defect. The comparison of the equivalent strain distrib

27、ution at the feeding of the punch of 48 mm is shown in Fig.5. Fig.4 Distribution of axial stress (a) and radial stress (b) Fig.5 Equivalent strain distribution at final stage of extrusion under conditions of without (a) and with (b) guiding angleThe inhomogeneous deformation and flow are obvious dur

28、ing the extrusion without the guiding angle, as shown in Fig.5(a). Compared with the outside metal, the inner metal deforms and flows faster, which causes that the outside metal cannot fill in time and the shrinkage cavity forms at the last stage of extrusion. After the guiding angle is employed as

29、shown in Fig.5(b), the mean strain difference between the metal near the axis and at the bottom of the die changes a little, and the metal flow in the deformation zone is homogeneous.4 Deformation division The stress distribution in the deformed grids can be obtained by the post-process module of th

30、e numerical simulation software, which is convenient for further analysis. 4.1 Method of deformation division In extrusion, the metal in some regions of a billet cannot satisfy the plastic deformation condition and the plastic deformation cannot occur due to the friction. For the convenience, the vo

31、n-Mises yield criterion can be described by 15where J2 is the second invariant of the deviator stress, and S is the flow stress of the work piece, which is a constant value. Using invariant J2, the division of stress field without or with the guiding angle can be shown in Fig.6. The regions marked w

32、ith shadow represent the areas where the plastic deformation occurs. Fig.6 Division of rigid and plastic regions under conditions of without (a) and with (b) guiding angle Fig.6(a) shows that without the guiding angle, the region of the workpiece in the upper part of the container and in the lower c

33、orner of the container does not deform plastically. In the extrusion with the guiding angle, as shown in Fig.6(b), the plastic region is larger, and there is no dead zone. So it can be assumed that the guiding angle increases the area of plastic deformation of the metal at the bottom corner of the c

34、ontainer.4.2 Types of deformation Lodes parameter µ is used to represent the stress situation regularly since it can reflect the relative magnitude of the second principal stress, and it is also relative with the type of strain state. 1µ0 represents tensile strain state, µ=0 represent

35、s plane strain state and 0µ1 represents compressive strain state. That is, the type of strain state and the degree of complicacy can be determined by Lodes coefficient. Through the analysis of Lodes coefficient, some measures can be taken to change the stress situation, and then change the plas

36、tic deformation condition to improve the forming property of the billet. Based on the rigid-plastic division, the strain of the material in the plastic area during extrusion process can be classified into different types using the visual display of Lodes coefficient, as shown in Fig.7. Fig.7 Divisio

37、n of Lodes coefficient under conditions of without (a) and with (b) guiding angle It can be seen from Fig.7(a) that without the guiding angle, Lodes coefficient in most of the region near the die is negative, i.e. the strain in the material is tensile. The region where Lodes coefficient equals zero

38、belongs to plane strain; while at the corner of the container, Lodes coefficient is positive, i.e. the strain is compressive. In the extrusion with active friction, the strain in the plastic region is everywhere tensile, as shown in Fig.7(b). So, compared with the extrusion without the guiding angle

39、, the metal flow in the container is more homogeneous. 5 Experimental Comparison of the metal flow line at the final stage of extrusion is shown in Fig.8. Flow line in the container is inhomogeneous at the last stage of conventional extrusion. It bends more seriously at bottom die corner in the extr

40、usion process, which indicates that the hard deforming area increases. Flow velocity near the container and axis is greatly different, and the metal at axis flows faster, which tends to cause the shrinkage cavity, as shown in Fig.8(a).6 Conclusions (1) When the guiding angle is used, axial stress st

41、ate of the metal near the axischanges from tensile stress to compressive stress, and the shrinkage cavity caused by the higher flow velocity of the axial metal is reduced. (2) The axial stress at the die exit is decreased by using the guiding angle, the inhomogeneity of flow velocity is reduced rema

42、rkably, and the twisting caused by the inhomogeneous metal flow is decreased. Therefore, the surface cracks caused by additional stress are avoided. (3) The results indicate that when the metal extruded with the guiding angle by deformation division, the dead zone of metal completely disappears, the

43、 deformation type of the metal in the plastic deformation area changes from three types to a type of tension, and the homogeneity of the deformation as well as metal flow are greatly improved, which is helpful for extruding and promoting the quality of extrudates. References 1 PONALAGUSAMY R, NARAYA

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45、terials Processing Technology, 2004, 150(1/2): 7075. 3 DENG Xiao-min, SUN Hong-jian, LI Sheng-zhi, FANG Mu-yun, CAO Jie. Friction and friction coefficient for aluminium alloyextrusion J. The Chinese Journal of Nonferrous Metals, 2003, 13(3): 599605. (in Chinese) 4 HAMBLI R, BADIE L D. Damage and fra

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47、SE P. Extrusion die design for flow balance using FE and optimization methods J. International Journal of Mechanical Sciences, 2002, 44(2): 319341. 7 HOSSEIN R D, MOSTAFA K. Simulation of “L” section extrusion using upper bound method J. Journal of Materials and Design, 2004, 25(6): 535540. 8 ZOU L,

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49、extrusion processes J. Finite Elements in Analysis and Design, 2003, 39(10): 10071020. 10 LI Q, SMITH C J, HARRIS C, JOLLY M R. Finite element investigations upon the influence of pocket die designs on metal flow in aluminium extrusion (Part I): Effect of pocket angle and volume on metal flow J. Jou

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52、uiding angle on metal flow and defects in extrusion deformation J. Journal of Materials Science and Technology, 2007, 15(1): 1518. (in Chinese) 14 ZOU Liang. Study on the function of impeding angle in extrusion die J. Journal of Plastic Engineering, 2006, 13(2): 6769. (in Chinese) 15 HU W L, HE Z B,

53、 FANG Y. Uniform principle on stress, strain and yield locus for analyzing metal forming processes J. Journal of Materials Processing Technology, 2004, 151(1/3): 2732. (Edited by CHEN Wei-ping) 中南大学学报. (2009) 16: 07380742铝合金压铸工艺过程中金属流动行为的变形分区李峰 初冠南 刘晓晶哈尔滨工业大学 材料科学与工程学院哈尔滨工业大学威海分校 船舶工程学院摘要：为减少因传统压铸过程

54、中不均匀金属流动引起的缺陷，设计发明了一款带有导角的冲模用于改善金属流动行为。诸如偏应力的第二不变量J2和罗德系数µ等特征量均用于变形分区。结果显示，当使用导角对金属进行压铸时，容器底部未形成任何金属流动界面，死区完全消失，塑性变形区域中的金属变形类型由三种张力变为一种张力，且变形和金属流动的均匀性均得到极大改善。最后压铸阶段的不均匀金属流动得到了改善，从而减少了轴端的缩孔。距离轴最远的点上的径向应力由张应力转变为抗压应力和轴向应力，压强由兆帕降至兆帕。因此，由附加应力引起的表面裂缝大大减小。关键词压铸工艺流动缺陷变形分区n 1简介在挤压过程中改善金属流动是一个重要手段，可以提高成形

55、性和消除缺陷1。许多因素可能会影响到金属的流动，其中模具结构与金属流动是密切相关的。模袋设计参数分析表明，不同的角度和模腔的偏移对金属流动影响较大，而后者往往造成产品的挤压弯曲24。CHUNG等人5发现可以通过采用一个较小的锥形来降低应变分布和双剪切挤压过程中死区产生的不均匀性。ULYSSE6发现，如果不纠正或适当调整模具轴承，该产品可能被扭曲和变形。有限元方法可用于模具7优化设计，以及有效控制金属流动的均匀性，金属很容易被挤压 8，挤压力也可以大大降低9。许多对模具优化设计的研究工作已经完成，但其中大多数是为避免某些挤压缺陷而设计的。通过采用有限元方法可以使复杂的模具结构优化，但很难将它应用

56、到实际生产10-12。对于上述缺点，从挤压模具的设计与导流角来看可以提高挤压过程中金属的流动性。导流角是指传统的模具13项圆角不同。虽然引入过渡角可以提高产品质量，难以根本改善金属的流动以及避免缺陷;经过导流角之后，在挤压变形区金属具有两次较低挤压比，极大地改变了死在腔里的金属流动，影响挤压缺陷。因此，在这项工作中，数值模拟挤压和无导流角会影响金属流动的角度，还必须比较分析模拟与实验的结果。n 2 模拟条件n 模具结构直接热挤压被视为典范。有无导流角模具结构如图1所示。导流角（）可以在一定范围内变化，=0只没有导流角的情况。n 有限元模式DEFORMTM- 2D的是用来模拟挤压过程。由于对称的

57、特点，选择了如图2所示的在轴对称模型仿真。在径向约束的对称平面上，使正常的变形零叠加。图1图中模具结构没有导流角（a）和有导流角（b）图2在挤压工艺条件下有限元模型没有导流角（a）和有导流角（b）在实验中应用7075铝合金坯。坯料直径为50毫米，高度50毫米。模拟实验的几何和材料参数均相同。在这项工作中，模拟进行挤压过程，采用刚塑性有限元模型。冲床，容器和模具被视为刚体。该冲压速度为2毫米/秒;的时间增量为秒;摩擦系数为0.3;等温挤压温度为435，挤压比为。分别进行的数值模拟为= 5，10，15，20，30。结果表明，挤压负荷是在=1514最低。因此，选中=15的冲模。n 3金属流动的模拟n

58、 稳定阶段从网格变形可以看出，在这个区域的电网在冲模腔内为平行四边形。这表明，变形和金属流动很均匀。因此，很容易生成没有死区的冲模腔。图3显示了在模具底部有和没有导流角的流场可以看出，从图3（a），如果没有导流角，在模底有一个明显的金属流接口。冲模腔内有部分金属流动向内部其他方向流动形成死区。有导流角的情况如图3（b）所示，冲模腔内的金属流向均匀，在塑性变形区形成没有速度的接口。金属的放射状流动没有大角度转向，这不但会降低湍流流线，死区和重叠，而且提高挤出模具腔的产品质量。图3中在模具的底部的流场无导流角（a）有导流角（b）关于出境断面有无导流角的轴向应力对比如图4所示。轴和表面的压应力和拉应力分别是金属在有无导流角的情况下的挤压产生的。随着从轴的距离的增加，轴向应力由压应力转变为拉应力。压应力和拉应力大致相等，这将导致微观结构和性能的非均匀性。润滑条件不是很好时额外的压力急剧增大，并导致表面裂缝。有导流角后，轴向拉应力从（小）降至（P2）MPa，沿径向方向的轴向应力分布的变化如（图4（a）。无导流角的径向应