畢業(yè)設(shè)計論文外文文獻翻譯中英文對照鋁合金壓鑄工藝過程中金屬流動行為的變形分區(qū)

1、 畢業(yè)設(shè)計外文資料翻譯題目 鋁合金壓鑄工藝過程中金屬流動行為的變形分區(qū) 專業(yè) 機械設(shè)計制造及其自動化 班級 07q3 學生 學號 20073006139 指導教師 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

2、(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 di

3、e 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 µ were employed for the division of deformation area. the results show that when the metal is extruded with the guidin

4、g 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.

5、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

6、, 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

7、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

8、 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. fi

9、nite 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

10、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 m

11、etal 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

12、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 investig

13、ate 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. guidi

14、ng 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 sup

15、erimposed 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 b

16、illet 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 an

17、d 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 r

18、esults 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 indicate

19、s 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 emplo

20、ying 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 po

21、ckets 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

22、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

23、 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 prop

24、erties. 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 thera

25、dial 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

26、 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 strai

27、n 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 ob

28、vious 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 emp

29、loyed 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 mod

30、ule 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 convenienc

31、e, 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 region

32、s 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 t

33、he 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 corne

34、r of the container.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

35、 represents 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 chang

36、e 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

37、.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 eq

38、uals 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 gui

39、ding 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 i

40、n 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

41、 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 r

42、educed 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 disa

43、ppears, 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 ponalagusam

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53、 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) 鋁合金壓鑄工藝過程中金屬流動行為的變形分區(qū) 哈爾濱工業(yè)大學 材料科學與工程學院哈爾濱工業(yè)大學威海分校 船舶工程學院摘 要：為減少因傳統(tǒng)壓鑄過程中不均勻金屬流動引起的缺陷，設(shè)計發(fā)明了一款帶有導

54、角的沖模用于改善金屬流動行為。諸如偏應(yīng)力的第二不變量j2和羅德系數(shù)µ等特征量均用于變形分區(qū)。結(jié)果顯示，當使用導角對金屬進行壓鑄時，容器底部未形成任何金屬流動界面，死區(qū)完全消失，塑性變形區(qū)域中的金屬變形類型由三種張力變?yōu)橐环N張力，且變形和金屬流動的均勻性均得到極大改善。最后壓鑄階段的不均勻金屬流動得到了改善，從而減少了軸端的縮孔。距離軸最遠的點上的徑向應(yīng)力由張應(yīng)力轉(zhuǎn)變?yōu)榭箟簯?yīng)力和軸向應(yīng)力，壓強由70.8兆帕降至34.8兆帕。因此，由附加應(yīng)力引起的表面裂縫大大減小。關(guān)鍵詞 壓鑄工藝 流動缺陷 變形分區(qū)n 1簡介在擠壓過程中改善金屬流動是一個重要手段，可以提高成形性和消除缺陷1。許多因素可

55、能會影響到金屬的流動，其中模具結(jié)構(gòu)與金屬流動是密切相關(guān)的。模袋設(shè)計參數(shù)分析表明，不同的角度和模腔的偏移對金屬流動影響較大，而后者往往造成產(chǎn)品的擠壓彎曲24。chung等人5發(fā)現(xiàn)可以通過采用一個較小的錐形來降低應(yīng)變分布和雙剪切擠壓過程中死區(qū)產(chǎn)生的不均勻性。ulysse6發(fā)現(xiàn)，如果不糾正或適當調(diào)整模具軸承，該產(chǎn)品可能被扭曲和變形。有限元方法可用于模具7優(yōu)化設(shè)計，以及有效控制金屬流動的均勻性，金屬很容易被擠壓 8，擠壓力也可以大大降低9。許多對模具優(yōu)化設(shè)計的研究工作已經(jīng)完成，但其中大多數(shù)是為避免某些擠壓缺陷而設(shè)計的。通過采用有限元方法可以使復雜的模具結(jié)構(gòu)優(yōu)化，但很難將它應(yīng)用到實際生產(chǎn)10-12。對于

56、上述缺點，從擠壓模具的設(shè)計與導流角來看可以提高擠壓過程中金屬的流動性。 導流角是指傳統(tǒng)的模具13項圓角不同。雖然引入過渡角可以提高產(chǎn)品質(zhì)量，難以根本改善金屬的流動以及避免缺陷;經(jīng)過導流角之后，在擠壓變形區(qū)金屬具有兩次較低擠壓比，極大地改變了死在腔里的金屬流動，影響擠壓缺陷。因此，在這項工作中，數(shù)值模擬擠壓和無導流角會影響金屬流動的角度，還必須比較分析模擬與實驗的結(jié)果。n 2 模擬條件n 2.1模具結(jié)構(gòu) 直接熱擠壓被視為典范。有無導流角模具結(jié)構(gòu)如圖1所示。導流角（）可以在一定范圍內(nèi)變化，=0只沒有導流角的情況。n 2.2有限元模式deformtm- 2d的是用來模擬擠壓過程。由于對稱的特點，選擇

57、了如圖2所示的在軸對稱模型仿真。在徑向約束的對稱平面上，使正常的變形零疊加。圖1圖中模具結(jié)構(gòu)沒有導流角（a）和有導流角（b）圖2在擠壓工藝條件下有限元模型沒有導流角（a）和有導流角（b）在實驗中應(yīng)用7075鋁合金坯。坯料直徑為50毫米，高度50毫米。模擬實驗的幾何和材料參數(shù)均相同。在這項工作中，模擬進行擠壓過程，采用剛塑性有限元模型。沖床，容器和模具被視為剛體。該沖壓速度為2毫米/秒;的時間增量為0.1秒;摩擦系數(shù)為0.3;等溫擠壓溫度為435，擠壓比為9.8。分別進行的數(shù)值模擬為= 5，10，15，20，30。結(jié)果表明，擠壓負荷是在=1514最低。因此，選中=15的沖模。n 3金屬流動的模擬n 3.1穩(wěn)定階段從網(wǎng)格變形可以看出，在這個區(qū)域的電網(wǎng)在沖模腔內(nèi)為平行四邊形。這表明，變形和金屬流動很均勻。因此，很容易生成沒有死區(qū)的沖模腔。圖3顯示了在模具底部有和沒有導流角的流場可以看出，從圖3（a），如果沒有導流角，在模底有一個明顯的金屬流接口。沖模腔內(nèi)有部分金屬流動向內(nèi)部其他方向流動形成死區(qū)。有導流角的情