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毕业设计 外文文献翻译题 目（中文）冲压成型 （英文）Stamping becomes typ学生 皓 目录1.冲压成型STEPHENS2.材料特性MARK JAFEStamping becomes typThe confidence level in successfully forming a sheetmetal stamping increases as the simplicity of the parts 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 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 mode 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 FormThe most basic type of die used to shape material is the solid form die. This tool simply 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 “loose metal” is present on the stamping, caused by uncontrolled material flow, the part tends to be dimensionally and structurally unstable.Stretch FormForming 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 three 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 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 fed 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 then 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.DrawThe draw die has earned its name not from the mode of deformation, but from the fact that the 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-form 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,after 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 press 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 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 form 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 circumferentially 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 overcome 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. Compressionincreases 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 draw 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 material. 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 material 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. 冲压成型 译文：板料冲压成形成功机率着冲压件形状的复杂程度减少而增加,冲压成形的目的是生产具有一定尺寸,形状并有稳定一致应力状态,甚至无起皱无裂纹的冲压件.冲压有一种至多种成形方式用来成型所需形状,它们是弯曲,局部成形,拉深,局部成形用来成形,凹陷形状或凸包,拉深用来成形,啤酒罐之类的冲压件,随着冲压件的形状越来越复杂,多种成形方法将会被用到同一零件的成型中,事实上,有很多冲压件上同时有弯曲,局部成型,拉深模具成型的特征,通常有三种形式的模具,它们是自由成型,局部成形以与拉深形式.一 自由成形自由成形是用的最基本的一种成形材料的成形模具,这类模具只是简单地通过一个冲头在压力机下行过程中把材料“撞击”进入凹模中成形材料。得到的是由无控制材料流动导致的应罚状态的冲压件，由无约束材料流动产生的“松弛金属区”的出现，冲压件尺寸和形状上趋于不稳定。二 局部成形成形工序中用一压边圈来控制材料流动压边圈是置于模具上的一个多压装置，由带压边圈模具成形的冲压件可分为三部分，如图一，它们分别是产品表面（图中红色表示部分），压边圈（图中蓝色表示部分）以与连接这两部分的壁，在凸模一端壁与壁之间的角称作凸模过渡区。凸模模穴理论上是在壁与压边圈面的交叉处，凸模被置于凸模穴之中，而压边圈被放在凸模穴外凸模的周围，这种模具还有上面的装置将压边圈与凸模联接起来，片料或工序件放到指定位置后压力机下行，上模开始接触片料，压边圈在凸模周围的材料上压出一些锁紧台阶或筋，从防止成形过程中材料从压边圈流向凸模部分随压边圈不再发生作用，材料不断地变形直到成形为凸模下部成形部分形状，在压力机回程时，模具做与下行时相反的动作，最后已经成形的冲压件被从模具上移走，就完成了一冲局部成形。三 拉深拉深的得名并不是因为材料在成形中变形情况得来，而是因为在拉深过程中材料进入拉离压边圈表面，直入凸模下面尽管拉深变形产生在拉深模中，但很多局部成形，弯曲模在工作过程中也对板料进行不同程度的拉深变形。拉深模的工作机制，与局部成形模具非常类似，不同的是，在拉深模中，压边圈部分有特定的地方必须更加严格地控制材料流入凹模量，以防止起皱，拉深模中，控制材料流入是通过成形半月型的拉深筋来代替局部成形中的锁紧台阶，一般在直边部分设一至三条，以控制这部分的材料流入而在复杂边部分少设或不设拉深筋，当板料工序件放到模具相应位置后，拉深的第一个阶段是模具是板料以与压边圈的接触.毛坯上为考虑到拉深过程中毛坯圆周沿走私方向减少留有的法兰边,是所有材料中流动最俦的地方,随着压力机滑块继续下行,材料变形流过凹模圆角半径.板料开始形成与凸模一致的形状，在拉深的工序中，这部分很少发生变形。被除数压在凹模腔中的空气由于凸模以与制件的下降而从气孔中排出。四 凸模、凹模的圆角半径应为4-6倍料厚以防止裂纹与起皱。随着模具继续闭合，校形开始发生，弯过凹模圆角材料，变形成钣金件的直壁部分，压边圈下边 的材料被拉入凹模并弯过凹模圆部分，考虑到防止材料被拉裂，凹模圆角半径应为4-10个料厚。毛坯变形情况为周向压缩么向拉伸，这样被拉入凹模圆腔中的工序称为拉深，拉深过程有：摩擦压缩、拉伸。因此，拉深过程中，压力机必须提供足够大的压力，以克服拉深过程中的各种抗变形力，如：压边圈与毛坯间的静摩擦力，额外的力也是必须的，用来克服拉深过程中滑支摩擦力。克服由压边圈弯过凹模圆角在后面行程中校直成直壁材料的变形力。在毛坯被拉入凹模沉着凹模半径变弯，在接下来变形中校直的同时，压边圈部分毛坯被沿周向压缩。而且沿着圆周半径方向上压缩量随着半径增大而增大半径越大的地方，需压缩的面积也大，这样的结果是压边圈部分的材料变厚，而凸模部分的材料因为被拉深变薄。在有些拉深中，拉深变形使拉深壁变形成卷曲形或弓形。最薄的区域是冲压件直壁与圆角过渡部分，因为这部分在拉深过程中拉伸变形最久，受力最大，这里往往也是最容易拉裂的地方，因为这部分的加工硬化少于其它地方。拉深工序到压力机行程下死点结束，拉深工序结束后，压力机滑块上行，模具打开，奢力圈在弹性元件作用下，从凸模上卸下包附在凸模上的冲压件，冲头下面没有通气孔，当冲压件被压边圈推起时，空气可进入。冲压件离开凸模产生的真空部分如果不设通气孔，冲压件将很难脱出。 Material BehaviorAutoForge allows the material to be represented as 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 Youngs modulus (E), the Poissons ratio (S), and the initial yield stress (y). For a rigid-plastic 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 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 strains, is represented by Hookes 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 (Youngs modulus) of the material.E (modulus of elasticity) = (axial stress)/(axial strain) （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 Poissons ratio. Similarly, the shear modulus (modulus of rigidity) is defined as:G (shear modulus) = (shear stress)/(shear strain) (D.3)It can be shown that for an isotropic materialG = 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 material behavior can be completely defined by the two materialconstants E and n.Time-Independent Inelastic BehaviorIn 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 material, 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 shows 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) to 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 from 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. Figure 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 specimen 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 stress-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.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 slope2. Elastic perfectly-plastic material no workhardening3. Perfectly-plastic material no workhardening and no elastic response4. Piecewise linear representation multiple constant workhardening slopes5. Strain-softening material negative workhardening slopeIn addition to elastic material constants (Youngs modulus and Poissons 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 generally 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 ConditionsThe yield stress of a material is a measured 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 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 criteria.von Mises Yield ConditionAlthough 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. Figure D-6 shows the von Mises yield surface in three-dimensional deviatoric stress space.For an isotropic materialwhere s1, s2 and s3 are the principal stresses.s can also be expressed in terms of non principal stresses. Effects on Yield StressThis section describes MSC.Marc AutoForge capabilities 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 the 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 dependent 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 different 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 RulesIn a uniaxial test, the workhardening slope is defined as the slope of the stress-plastic strain curve. The workhardening 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 function 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 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 HARD statement.Isotropic HardeningThe 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-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 continuously loaded to point 2. Then, unloading from 2 to 3 following the elastic slope E (Youngs 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. 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 isotropic 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 RuleYield stress and workhardening rules are two experimentally 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 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.Constitutive RelationsThis 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.Let the workhardening coefficient H be expressed asLet the workhardening coefficient H be expressed as and the flow rule be expressed aswhere C is the elasticity matrix defined by Hookes law. After substitution of Equation D.11, this becomesContracting Equation D.13 by and recognizing thatwith use of Equation D.10 in place of the left-hand side,By rearrangementFinally, by substitution of this expression into Equation D.13, we obtainThe case of perfect plasticity, where H = 0,
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