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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 学号 20073006139 指导教师 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 alloy LI Feng CHU Guan-nan LIU Xiao-jing (1. 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 with 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 were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle, 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 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, the 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 influence 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 of extrusion products 24. CHUNG et al 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 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 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, an extrusion die with guiding angle was designed to improve the metal flow 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 employed, 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 the 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 angle () 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 superimposed 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 was 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 were 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 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 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 the 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 homogeneously, 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 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 metal 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. 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 direction 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 employed, 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 of extrusion process, shrinkage cavity is a common defect. The comparison of the equivalent strain distribution 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 during 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 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 the 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 von-Mises yield criterion can be described by 15 where 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 with 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 corner 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 container.4.2 Types of deformation Lodes parameter 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. 10 represents tensile strain state, =0 represents plane strain state and 01 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 plastic 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 Division 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 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, 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 extrusion 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 state of the metal near the axis changes 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 remarkably, 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 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, NARAYANASAMY R, SRINIVASAN P. Design and development of streamlined extrusion dies: A Bezier curve approach J. Journal of Materials Processing Technology, 2005, 161(3): 375380. 2 DAMODARAN D, SHIVPURI R. Prediction and control of part distortion during the hot extrusion of titanium alloys J. Journal of Materials 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 fracture simulation during the extrusion processes J. Computer Methods in Applied Mechanics and Engineering, 2000, 186(1): 109120. 5 CHUNG S W, KIM W J, HIGASHI K. The effect of die geometry on the double shear extrusion by parametric FVM simulation J. Scripta Materialia, 2004, 51(11): 11171122. 6 ULYSSE 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, XIA J C, WANG X Y. Optimization of die profile for improving die life in the hot extrusion process J. Journal of Materials Processing Technology, 2003, 142(3): 659664. 9 FAZAL A, ARIF M. On the use of non-linear finite element analysis in deformation evaluation and development of design charts for 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. Journal of Materials ProcessingTechnology, 2003, 135(2/3): 189196. 11 LI Q, SMITH C J, HARRIS C, JOLLY M R. Finite element modelling investigations upon the influence of pocket die designs on metal flow in aluminium extrusion (Part II): Effect of pocket geometry configurations on metal flow J.Journal of Materials Processing Technology, 2003, 135(2/3): 197203. 12 LEE D J, KIM D J, KIM B M. New processes to prevent a flow defect in the combined forward-backward cold extrusion of a piston-pin J. Journal of MaterialsProcessing Technology, 2003, 139(1/3): 422427. 13 LI F， YUAN S J， HE Z B. Effect of guiding 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, 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) 铝合金压铸工艺过程中金属流动行为的变形分区 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70.8兆帕降至34.8兆帕。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 2.1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 2.2有限元模式DEFORMTM- 2D的是用来模拟挤压过程。由于对称的特点，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0.1秒;摩擦系数为0.3;等温挤压温度为435，挤压比为9.8。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 3.1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70.8（小）降至34.8（P2）MPa，沿径向方向的轴向应力分布的变化如（图4（a）。无导流角的径向应力分布如图4（b），从轴轴向应力状态为压应力，随着距离的增加表面变成拉应力。有导流角后，在模具出口径向应力变为压应力，径向应力和压应力几乎相等。n 3.2 最后阶段在挤压膨化过程的最后阶段，缩孔是一种常见的缺陷。在48毫米打孔的等效应变分布比较如图5所示 图4 轴向应力分布（a）和径向应力（b）图5 在挤压等效应变分布的最后阶段条件下的无导流角（a）和有导流角（b）。非均匀变形和流动过程中没有明显的挤压，如在图5（a）所示。在最后阶段的挤压缩孔中，与外面的金属相比，内部金属变形和流动加快。这将导致金属外面没有填补时间。有导流角后显示如图5（b），靠近轴之间的金属和在一个小模具更换底部平均应变的差异，以及在变形区金属流动均匀。n 4 形变分区从电网中的变形应力分布可以得到数值模拟软件，该软件可以方便的进行进一步分析后处理模块。n 4.1 形变方法的划分在一些地区的钢坯不能满足金属塑性变形和塑性变形的条件，在挤压时不能发生因摩擦。为方便起见，冯- Mises屈服准则可描述15 其中J2的是偏应力第二不变量，强度s是工件，这是一个恒定价值流的压力。J2的使用不变，应力场有无导流角的角度划分可以显示在图6。在标有阴影的区域发生塑性变形。图6刚性和塑性区没有导流角（a）和有导流角（b）。图6（a）表明，没有导流角，工件在容器的上部和容器的右下角的区域并未塑性变形。图6（b）所示，有导流角挤压时会有较大的塑性区，但没有死区。因此，可以认为，导流角增加了金属塑性变形的容器底部角落区域。n 4.2 变形的类型洛德的参数是用来表示定期压力的情况，因为它可以反映第二主应力的相对大小，而且也与应变状态类型相对-10表示拉伸应变状态，=0表示平面应变状态，01指压应变状态。也就是说，应变状态的类型和复杂程度可以由洛德的系数确定。通过洛德的系数分析，可以采取一些措施在改变压力的情况下，然后更改的塑性变形条件，提高钢坯的成形性能。以刚塑性分工为基础，该地区在塑料挤出过程中材料变形可利用洛德的系数视觉展示，如在图7所示的不同类型。图7部洛德的系数条件下，没有导流角（a）和有导流角（b）从图7（a）可以看出，如果没有导流角，洛德在附近的模具地区最系数为负，即在材料拉伸应变。所在地区的洛德系数为零属于平面应变，而在集装箱角落，洛德的系数为正，即应变压缩。主动摩擦挤压时，塑性区中的拉伸应变是无处不在的，如在图7（b）所示。因此，相对于无导流角的挤压，在容器中金属的流动更加均匀。n 5 实验在最后阶段的金属挤压流线的比较图8所示。流线在最后阶段的常规挤压不均匀。在挤压过程中它的弯曲角多在底模，这表明硬盘严重变形面积增加。在金属轴快流时轴附近的速度会大大不同，往往导致缩孔，在图8（a）所示。图8 金属流线在上一节最后阶段的挤压条件下的无导流角（a）和有导流角（b）从图8所示的流线（b）可以看出，在挤压与导角的最后阶段，部分金属流线均匀且几乎平行于轴。在模具底部金属流线稍微弯曲。相对于传统的挤压，在容器中金属的流动更加均匀。缩孔减少，产品质量明显提高。n 6 结论（1）当使用导流角时，附近的轴拉应力变化。对较高流动速度的金属轴其压应力，缩孔及轴向应力状态降低。（2）在模具出口使用导流角降低了轴向应力，流速不均匀性明显降低，由金属流动不均匀造成的扭曲现象减少。因此，表面引起的附加应力裂缝是可以避免的。（3）结果表明，在金属挤压与导流角的变形区，金属死区完全消失，在塑性变形区，改变了金属三种类型类型的变形均匀性，很大的提高了金属的流动性，提高了质量。参考文献： 1 PONALAGUSAMY R, NARAYANASAMY R, SRINIVASAN P. Design and development of streamlined extrusion dies: A Bezier c
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