冲压成型把手连接件级进模设计外文翻译

冲压成型-把手连接件级进模设计外文翻译 毕业设计 外文文献翻译题 目中文 冲压成型 英文 Stamping becomes typ 学生姓名 张皓 目录1冲压成型 作者 STEPHENS2材料特性 作者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 cansAs 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 The common types of dies that shape material are solid form stretch form and drawSolid FormThe most basic type of die used to shape material is the solid form die This tool simply displaces material via a solid punch 揷rashingthe material into a solid die steel on the press downstroke The result is a stamping with uncontrolled material flow lyin terms of strain distribution Since 搇oose metalis present on the stamping caused by uncontrolled material flow the part tends to be dimensionally and structurally unstableStretch FormForming operations that provide for material flow control do s o 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 dieDrawThe 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 has been 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 punchVery 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 ventsThe die radius should be between four and 10 times sheet thickness to prevent wrinkles and splitsStraightening 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 wallTo 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 thickerThe 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及拉深形式一 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及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及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及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倍料厚以防止裂纹及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 optionThe 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 materialE modulus of elasticity axial stress axial strain D1Experiments show that axial elongation is always accompanied by lateral contraction of the bar The ratio for a linear elastic material isv lateral contraction axial elongation D2 This is known as Poissons ratio Similarly the shear modulus modulus of rigidity is defined asG shear modulus shear stress shear strain D3 It can be shown that for an isotropic materialG E 2 1n D4 The stress-strain relationship for an isotropic linear elastic method is expressed asWhere is the Lame constant and G the shear modulus is expressed asThe material behavior can be completely defined by the two materialconstants E and 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 indicatedWithin the elastic region the stress-strain relationship is unique Therefore if the stress in the specimen is increased loading from zero point 0 to 1 point 1 and then decreased unloading to zero the strain in the specimen is also increased from zero to 1 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 2 and the total strain is 2 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 strainThe 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 below1 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 studiedYield 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 MSCMarc AutoForge uses the von Mises yield criteriavon 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 y equals the yield stress as measured in a uniaxial test Figure D-6 shows the von Mises yield surface in three-dimensional deviatoric stress spaceFor an isotropic materialwhere 1 2 and 3 are the principal stressescan also be expressed in terms of non principal stresses Effects on Yield StressThis section describes MSCMarc AutoForge capabilities with respect to the effect of temperature and strain rate MSCMarc 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 MSCMarc 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 yieldingWorkhardening 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 MSCMarc 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 statementIsotropic 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 y and stresses at points 2 and 4 are higher than y due to workhardening During unloading the stress state can remain elastic eg point 3 or it can reach to a subsequent reversed yield point eg point 5 The isotropic work-hardening rule states that the reverse yield occurs at current stress level in the reversed direction Let 4 be the stress level at point 4 Then the reverse yield can only take place at a stress level of -4 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 dp as a function of the current stress stateEquation D9 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 ruleIf the von Mises yield surface is used then the normal is equal to the deviatoric stressConstitutive 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 ruleLet 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 D11 this becomesContracting Equation D13 by and recognizing thatwith use of Equation D10 in place of the left-hand sideBy rearrangementFinally by substitution of this expression into Equation D13 we obtainThe case of perfect plasticity where H 0 causes no difficultyTemperature EffectsThis section discusses the effects of temperature-dependent plasticity on the constitutive relation Temperature effects are discussed using the isotropic hardening model and the von Mises yield condition The stress rate can be expressed in the formFor elastic-plastic behavior the moduli Lijkl areTh