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1、 畢業(yè)設計 外文文獻翻譯 題 目（中文）沖壓成型 （英文）Stamping becomes typ 學生 皓 目錄 1.沖壓成型STEPHENS 2.材料特性MARK JAFE Stamping becomes typ The confidence level in successfully forming a sheetmetal stamping increases as the simplicity of

2、 the part’s topography increases. The goal of forming with stamping technologies is to produce stampings with complex geometric surfaces that are dimensionally accurate and repeatable with a certain strain distribution, yet free from wrinkles and splits. Stampings have one or more forming modes that

3、 create the desired geometries. These modes are bending, stretch forming and drawing. Stretching the sheetmetal forms depressions or embossments. Drawing compresses material circumferentially to create stampings such as beer cans.As the surfaces of the stamping become more complex, more than one mod

4、e of forming will be required. In fact, many stampings have bend, stretch and draw features produced in the form die. Thecommon types of dies that shape materialare solid form, stretch form anddraw. Solid Form The most basic type of die used to shape material is the solid form die. This tool simpl

5、y displaces material via a solid punch “crashing” the material into a solid die steel on the press downstroke. The result is a stamping with uncontrolled material flow in terms of strain distribution. Since “l(fā)oose metal” is present on the stamping, caused by uncontrolled material flow, the part tend

6、s to be dimensionally and structurally unstable. Stretch Form Forming operations that provide for material flow control do so with a blankholder. The blankholder is a pressurized device that is guided and retained within the die set. Stampings formed with a blankholder may be described as having t

7、hree parts, shown in Fig. 1. They are the product surface(shown in red), blankholder surface (flat area shown in blue) and a wall that bridges the two together. The theoretical corner on the wall at the punch is called the punch break. The punch opening is the theoretical intersection at the bottom

8、of the draw wall with the blankholder. The male punch is housed inside the punch opening, whereas the blankholder is located around the punch outside the punch opening. These tools have a one-piece upper member that contacts both the blankholder and punch surfaces. A blank or strip of material is fe

9、d onto the blankholder and into location gauges. On the press downstroke, the upper die member contacts the sheet and forms a lock step or bead around the outside perimeter of the punch opening on the blankholder surface to prevent material flow off the blankholder into the punch. The blankholder th

10、en begins to collapse and material stretches and compresses until it takes the shape of the lower punch. The die actions reverse on the press upstroke, and the formed stamping is removed from the die. Draw The draw die has earned its name not from the mode of deformation, but from the fact that th

11、e material runs in or draws off the blankholder surface and into the punch. Although the draw mode of deformation is present in draw dies, some degree of the stretch forming and bending modes generally also are present. The architecture and operational sequence for draw dies is the same as stretch-f

12、orm dies with one exception. Material flow off the blankholder in draw dies needs to be restrained more in some areas than others to prevent wrinkling. This is achieved by forming halfmoon-shaped beads instead of lock steps or beads found in stretch-form dies.The first stage of drawing sheetmetal,af

13、ter the blank or strip stock hasbeen loaded into the die, is initial contact of the die steel with the blank and blankholder. The blank, round for cylindrical shells to allow for a circumferential reduction in diameter, is firmly gripped all around its perimeter prior to any material flow. As the pr

14、ess ram continues downward the sheetmetal bends over the die radius and around the punch radius. The sheetmetal begins to conform to the geometry of the punch.Very little movement or compression at the blank edge has occurred to this point in the drawing operation. Air trapped in the pockets on the

15、die steel is released on the press downstroke through air vents. The die radius should be between four and 10 times sheet thickness to prevent wrinkles and splits. Straightening of sheetmetal occurs next as the die continues to close. Material that was bent over the die radius is straightened to f

16、orm the draw wall. Material on the blankholder now is fed into the cavity and bent over the die radius to allow for straightening without fracture. The die radius should be between four and 10 times sheet thickness to prevent wrinkles and splits. The compressive feeding or pulling of the blank circu

17、mferentially toward the punch and die cavity is called drawing. The draw action involves friction, compression and tension. Enough force must be present in drawing to overcome the static friction between the blank and blankholder surfaces. Additional force is necessary during the drawing stage to ov

18、ercome sliding or dynamic friction and to bend and unbend the sheet from the blankholder surface to the draw wall. As the blank is drawn into the punch, the sheetmetal bends around the die radius and straightens at the draw wall. To allow for the flow of material, the blank is compressed. Compressi

19、on increases away from the die radius in the direction of material flow because there is more surface area of sheetmetal to be squeezed. Consequently, the material on the blankholder surface becomes thicker.The tension causes the draw wall to become thinner. In some cases, the tension causes the dr

20、aw wall to curl or bow outward. The thinnest area of the sheet is at the punch radius, and gradually tapers thicker from the shock line to the die radius. This is a probable failure site because the material on the punch has been work-hardened the least, making it weaker than the strain hardened mat

21、erial. The drawing stage continues until the press is at bottom dead center. With the operation now complete, the die opens and the blankholder travels upward to strip the drawn stamping off of the punch. Air vents provided in flat or female cavities of the punch allow air to travel under the materi

22、al as it is lifted by the blankholder. The stamping will have a tendency to turn inside out due to vacuum in the absenceof air vents. 沖壓成型 譯文： 板料沖壓成形成功機率著沖壓件形狀的復雜程度減少而增加,沖壓成形的目的是生產具有一定尺寸,形狀并有穩(wěn)定一致應力狀態(tài),甚至無起皺無裂紋的沖壓件. 沖壓有一種至多種成形方式用來成型所需形狀,它們是彎曲,局部成形,拉深,局部成形用來成形,凹陷形狀或凸包,拉深用來成形,啤酒罐之類的沖壓件,隨著沖壓件的形

23、狀越來越復雜,多種成形方法將會被用到同一零件的成型中,事實上,有很多沖壓件上同時有彎曲,局部成型,拉深模具成型的特征,通常有三種形式的模具,它們是自由成型,局部成形以與拉深形式. 一 自由成形 自由成形是用的最基本的一種成形材料的成形模具,這類模具只是簡單地通過一個沖頭在壓力機下行過程中把材料“撞擊”進入凹模中成形材料。得到的是由無控制材料流動導致的應罰狀態(tài)的沖壓件，由無約束材料流動產生的“松弛金屬區(qū)”的出現(xiàn)，沖壓件尺寸和形狀上趨于不穩(wěn)定。 二 局部成形 成形工序中用一壓邊圈來控制材料流動壓邊圈是置于模具上的一個多壓裝置，由帶壓邊圈模具成形的沖壓件可分為三部分，如圖一，它們分別是產

24、品表面（圖中紅色表示部分），壓邊圈（圖中藍色表示部分）以與連接這兩部分的壁，在凸模一端壁與壁之間的角稱作凸模過渡區(qū)。 凸模模穴理論上是在壁與壓邊圈面的交叉處，凸模被置于凸模穴之中，而壓邊圈被放在凸模穴外凸模的周圍，這種模具還有上面的裝置將壓邊圈與凸模聯(lián)接起來，片料或工序件放到指定位置后壓力機下行，上模開始接觸片料，壓邊圈在凸模周圍的材料上壓出一些鎖緊臺階或筋，從防止成形過程中材料從壓邊圈流向凸模部分隨壓邊圈不再發(fā)生作用，材料不斷地變形直到成形為凸模下部成形部分形狀，在壓力機回程時，模具做與下行時相反的動作，最后已經成形的沖壓件被從模具上移走，就完成了一沖局部成形。 三 拉深 拉深的得名并

25、不是因為材料在成形中變形情況得來，而是因為在拉深過程中材料進入拉離壓邊圈表面，直入凸模下面盡管拉深變形產生在拉深模中，但很多局部成形，彎曲模在工作過程中也對板料進行不同程度的拉深變形。 拉深模的工作機制，與局部成形模具非常類似，不同的是，在拉深模中，壓邊圈部分有特定的地方必須更加嚴格地控制材料流入凹模量，以防止起皺，拉深模中，控制材料流入是通過成形半月型的拉深筋來代替局部成形中的鎖緊臺階，一般在直邊部分設一至三條，以控制這部分的材料流入而在復雜邊部分少設或不設拉深筋，當板料工序件放到模具相應位置后，拉深的第一個階段是模具是板料以與壓邊圈的接觸. 毛坯上為考慮到拉深過程中毛坯圓周沿走私方向減

26、少留有的法蘭邊,是所有材料中流動最儔的地方,隨著壓力機滑塊繼續(xù)下行,材料變形流過凹模圓角半徑.板料開始形成與凸模一致的形狀，在拉深的工序中，這部分很少發(fā)生變形。被除數(shù)壓在凹模腔中的空氣由于凸模以與制件的下降而從氣孔中排出。 四 凸模、凹模的圓角半徑應為4-6倍料厚以防止裂紋與起皺。 隨著模具繼續(xù)閉合，校形開始發(fā)生，彎過凹模圓角材料，變形成鈑金件的直壁部分，壓邊圈下邊 的材料被拉入凹模并彎過凹模圓部分，考慮到防止材料被拉裂，凹模圓角半徑應為4-10個料厚。毛坯變形情況為周向壓縮么向拉伸，這樣被拉入凹模圓腔中的工序稱為拉深，拉深過程有：摩擦壓縮、拉伸。因此，拉深過程中，壓力機必須提供足夠大的壓

27、力，以克服拉深過程中的各種抗變形力，如：壓邊圈與毛坯間的靜摩擦力，額外的力也是必須的，用來克服拉深過程中滑支摩擦力?？朔蓧哼吶澾^凹模圓角在后面行程中校直成直壁材料的變形力。 在毛坯被拉入凹模沉著凹模半徑變彎，在接下來變形中校直的同時，壓邊圈部分毛坯被沿周向壓縮。而且沿著圓周半徑方向上壓縮量隨著半徑增大而增大——半徑越大的地方，需壓縮的面積也大，這樣的結果是壓邊圈部分的材料變厚，而凸模部分的材料因為被拉深變薄。在有些拉深中，拉深變形使拉深壁變形成卷曲形或弓形。最薄的區(qū)域是沖壓件直壁與圓角過渡部分，因為這部分在拉深過程中拉伸變形最久，受力最大，這里往往也是最容易拉裂的地方，因為這部分的加工硬

28、化少于其它地方。 拉深工序到壓力機行程下死點結束，拉深工序結束后，壓力機滑塊上行，模具打開，奢力圈在彈性元件作用下，從凸模上卸下包附在凸模上的沖壓件，沖頭下面沒有通氣孔，當沖壓件被壓邊圈推起時，空氣可進入。沖壓件離開凸模產生的真空部分如果不設通氣孔，沖壓件將很難脫出。 Material Behavior AutoForge allows the material to be represented as

29、 either an elastic-plastic material or as a rigid-plastic material. The material is assumed to be isotropic, hence, for the elastic-plastic model, a minimum of three material data points are required; the Young’s modulus (E), the Poisson’s ratio (S), and the initial yield stress (y). For a rigid-pla

30、stic material, only the yield stress is required. These data must be obtained from experiments or a material handbook. These values may vary with temperature in a coupled analysis. This is prescribed using the TABLES option. The flow stress of the material changes with deformation, so called strain

31、hardening or workhardening behavior and may be influenced by the rate of deformation. These behavior are also entered via the TABLES option. The linear elastic model is the model most commonly used to represent engineering materials. This model, which has a linear relationship between stresses and

32、strains, is represented by Hooke’s Law. Figure D-1 shows that stress is proportional to strain in a uniaxial tension test. The ratio of stress to strain is the familiar definition of modulus of elasticity (Young’s modulus) of the material. E (modulus of elasticity) = (axial stress)/(axial strain) （

33、D.1） Experiments show that axial elongation is always accompanied by lateral contraction of the bar. The ratio for a linear elastic material is: v = (lateral contraction)/(axial elongation) (D.2) This is known as Poisson’s ratio. Similarly, the shear modulus (modulus of rigidity) is defined as:

34、 G (shear modulus) = (shear stress)/(shear strain) (D.3) It can be shown that for an isotropic material G = E / 2 (1+n) (D.4) The stress-strain relationship for an isotropic linear elastic method is expressed as： Where is the Lame constant and G (the shear modulus) is expressed as： The m

35、aterial behavior can be completely defined by the two material constants E and n. Time-Independent Inelastic Behavior In uniaxial tension tests of most metals (and many other materials), the following phenomena can be observed. If the stress in the specimen is below the yield stress of the mate

36、rial, the material will behave elastically and the stress in the specimen will be proportional to the strain. If the stress in the specimen is greater than the yield stress, the material will no longer exhibit elastic behavior, and the stress-strain relationship will become nonlinear. Figure D-2 sho

37、ws a typical uniaxial stress-strain curve. Both the elastic and inelastic regions are indicated. Within the elastic region, the stress-strain relationship is unique. Therefore, if the stress in the specimen is increased (loading) from zero (point 0) to s1 (point 1), and then decreased (unloading) t

38、o zero, the strain in the specimen is also increased from zero to e1, and then returned to zero. The elastic strain is completely recovered upon the release of stress in the specimen. Figure D-3 illustrates this relationship. The loading-unloading situation in the inelastic region is different fro

39、m the elastic behavior. If the specimen is loaded beyond yield to point 2, where the stress in the specimen is s2 and the total strain is e2, upon release of the stress in the specimen the elastic strain, is completely recovered. However, the inelastic (plastic) strain remains in the specimen. Figur

40、e D-3 illustrates this relationship. Similarly, if the specimen is loaded to point 3 and then unloaded to zero stress state, the plastic strain remains in the specimen. It is obvious that is not equal to. We can conclude that in the inelastic region ? Plastic strain permanently remains in the speci

41、men upon removal of stress. ? The amount of plastic strain remaining in the specimen is dependent upon the stress level at which the unloading starts (path-dependent behavior). The uniaxial stress-strain curve is usually plotted for total quantities (total stress versus total strain). The total st

42、ress-strain curve shown in Figure D-2 can be replotted as a total stress versus plastic strain curve, as shown in Figure D-4. The slope of the total stress versus plastic strain curve is defined as the workhardening slope (H) of the material. The workhardening slope is a function of plastic strain.

43、 The stress-strain curve shown in Figure D-2 is directly plotted from experimental data. It can be simplified for the purpose of numerical modeling. A few simplifications are shown in Figure D-5 and are listed below: 1. Bilinear representation – constant workhardening slope 2. Elastic perfectly-pl

44、astic material – no workhardening 3. Perfectly-plastic material – no workhardening and no elastic response 4. Piecewise linear representation – multiple constant workhardening slopes 5. Strain-softening material – negative workhardening slope In addition to elastic material constants (Young’s mo

45、dulus and Poisson’s ratio), it is essential to be concerned with yield stress and workhardening slopes in dealing with inelastic (plastic) material behavior. These quantities vary with parameters such as temperature and strain rate, further complicating the analysis. Since the yield stress is genera

46、lly measured from uniaxial tests, and the stresses in real structures are usually multiaxial, the yield condition of a multiaxial stress state must be considered. The conditions of subsequent yield (workhardening rules) must also be studied. Yield Conditions The yield stress of a material is a mea

47、sured stress level that separates the elastic and inelastic behavior of the material. The magnitude of the yield stress is generally obtained from a uniaxial test. However, the stresses in a structure are usually multiaxial. A measurement of yielding for the multiaxial state of stress is called the

48、yield condition. Depending on how the multiaxial state of stress is represented, there can be many forms of yield conditions. For example, the yield condition can be dependent on all stress components, on shear components only, or on hydrostatic stress. MSC.Marc AutoForge uses the von Mises yield cr

49、iteria. von Mises Yield Condition Although many forms of yield conditions are available, the von Mises criterion is the most widely used. The von Mises criterion states that yield occurs when the effective (or equivalent) stress (sy) equals the yield stress (s) as measured in a uniaxial test. Figu

50、re D-6 shows the von Mises yield surface in three-dimensional deviatoric stress space. For an isotropic material where s1, s2 and s3 are the principal stresses. s can also be expressed in terms of non principal stresses. Effects on Yield Stress This section describes MSC.Marc AutoForge capabil

51、ities with respect to the effect of temperature and strain rate. MSC.Marc AutoForge allows you to input a temperature-dependent yield stress. To enter the yield stress at a reference temperature, use the model definition options ISOTROPIC. To enter variations of yield stress with temperatures, use t

52、he model definition options TEMPERATURE EFFECTS. Repeat the model definition options TEMPERATURE EFFECTS for each material, as necessary. The effect of temperatures on yielding is discussed further in “Constitutive Relations” on page D-13. MSC.Marc AutoForge allows you to enter a strain rate depende

53、nt yield stress, for use in dynamic and flow problems. To use the strain rate dependent yield stress in static analysis, enter a fictitious time using the TIME STEP option. The zero-strain-rate yield stress is given on the ISOTROPIC option. Repeat the model definition option STRAIN RATE for each dif

54、ferent material where strain rate data are necessary. Refer to “Constitutive Relations” on page D-13 for more information on the strain-rate effect on yielding. Workhardening Rules In a uniaxial test, the workhardening slope is defined as the slope of the stress-plastic strain curve. The workharde

55、ning slope relates the incremental stress to incremental plastic strain in the inelastic region and dictates the conditions of subsequent yielding. The isotropic workhardening model is used in MSC.Marc AutoForge. The uniaxial stress-plastic strain curve may be represented by a piecewise linear funct

56、ion through the WORK HARD option. As an alternative, you can specify workhardening through the user subroutine WKSLP. There are two methods to enter this information, using the WORK HARD option. In the first method, you must enter workhardening slopes for uniaxial stress data as a change in Cauchy

57、 or true stress per unit of logarithmic plastic strain (see Figure D-7) and the logarithmic plastic strain at which these slopes become effective (breakpoint). In the second method, you enter a table of yield stress, plastic strain points. This option is flagged by adding the word DATA to the WORK

58、 HARD statement. Isotropic Hardening The isotropic workhardening rule assumes that the center of the yield surface remains stationary in the stress space, but that the size (radius) of the yield surface expands, due to workhardening. The change of the von Mises yield surface is plotted in Figure D

59、-8(b). A review of the load path of a uniaxial test that involves both the loading and unloading of a specimen will assist in describing the isotropic workhardening rule. The specimen is first loaded from stress free (point 0) to initial yield at point 1, as shown in Figure D-8(a). It is then cont

60、inuously loaded to point 2. Then, unloading from 2 to 3 following the elastic slope E (Young’s modulus) and then elastic reloading from 3 to 2 takes place. Finally, the specimen is plastically loaded again from 2 to 4 and elastic unloaded from 4 to 5. Reverse plastic loading occurs between 5 and 6.

61、 It is obvious that the stress at 1 is equal to the initial yield stress sy and stresses at points 2 and 4 are higher than sy, due to workhardening. During unloading, the stress state can remain elastic (e.g., point 3) or it can reach to a subsequent (reversed) yield point (e.g., point 5). The isot

62、ropic work-hardening rule states that the reverse yield occurs at current stress level in the reversed direction. Let s4 be the stress level at point 4. Then, the reverse yield can only take place at a stress level of -s4 (point 5). Flow Rule Yield stress and workhardening rules are two experiment

63、ally related phenomena that characterize plastic material behavior. The flow rule is also essential in establishing the incremental stress-strain relations for plastic material. The flow rule describes the differential changes in the plastic strain components dep as a function of the current stress

64、state. Equation D.9 expresses the condition that the direction of inelastic straining is normal to the yield surface. This condition is called either the normality condition or the associated flow rule. If the von Mises yield surface is used, then the normal is equal to the deviatoric stress. C

65、onstitutive Relations This section presents the constitutive relation that describes the incremental stress-strain relation for an elastic-plastic material. The material behavior is governed by the incremental theory of plasticity, the von Mises yield criterion, and the isotropic hardening rule. L

66、et the workhardening coefficient H be expressed as Let the workhardening coefficient H be expressed as and the flow rule be expressed as where C is the elasticity matrix defined by Hooke’s law. After substitution of Equation D.11, this becomes Contracting Equation D.13 by and recognizing that with use of Equation D.10 in place of the left-hand side, By rearrangement Finally, by substitution of this expression into Equation D.13, we obtain The case of perfect plasticity, where H = 0,