沖壓成型-把手連接件級(jí)進(jìn)模設(shè)計(jì)外文翻譯 畢業(yè)設(shè)計(jì) 外文文獻(xiàn)翻譯題 目中文 沖壓成型 英文 Stamping becomes typ 學(xué)生姓名 張皓 目錄1沖壓成型 作者 STEPHENS2材料特性 作者M(jìn)ARK 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 沖壓成型 譯文板料沖壓成形成功機(jī)率著沖壓件形狀的復(fù)雜程度減少而增加沖壓成形的目的是生產(chǎn)具有一定尺寸形狀并有穩(wěn)定一致應(yīng)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狀越來越復(fù)雜多種成形方法將會(huì)被用到同一零件的成型中事實(shí)上有很多沖壓件上同時(shí)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及拉深形式一 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(gè)沖頭在壓力機(jī)下行過程中把材料撞擊進(jìn)入凹模中成形材料得到的是由無控制材料流動(dòng)導(dǎo)致的應(yīng)罰狀態(tài)的沖壓件由無約束材料流動(dòng)產(chǎn)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(dòng)壓邊圈是置于模具上的一個(gè)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(chǎn)品表面圖中紅色表示部分壓邊圈圖中藍(lán)色表示部分以及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(jī)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(tái)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(jī)回程時(shí)模具做與下行時(shí)相反的動(dòng)作最后已經(jīng)成形的沖壓件被從模具上移走就完成了一沖局部成形三 拉深拉深的得名并不是因?yàn)椴牧显诔尚沃凶冃吻闆r得來而是因?yàn)樵诶钸^程中材料進(jìn)入拉離壓邊圈表面直入凸模下面盡管拉深變形產(chǎn)生在拉深模中但很多局部成形彎曲模在工作過程中也對(duì)板料進(jìn)行不同程度的拉深變形拉深模的工作機(jī)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(yán)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(tái)階一般在直邊部分設(shè)一至三條以控制這部分的材料流入而在復(fù)雜邊部分少設(shè)或不設(shè)拉深筋當(dāng)板料工序件放到模具相應(yīng)位置后拉深的第一個(gè)階段是模具是板料以及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少留有的法蘭邊是所有材料中流動(dòng)最儔的地方隨著壓力機(jī)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及制件的下降而從氣孔中排出四 凸模凹模的圓角半徑應(yīng)為4-6倍料厚以防止裂紋及起皺隨著模具繼續(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(yīng)為4-10個(gè)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(jī)必須提供足夠大的壓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克服由壓邊圈彎過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(shí)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(jié)果是壓邊圈部分的材料變厚而凸模部分的材料因?yàn)楸焕钭儽≡谟行├钪欣钭冃问估畋谧冃纬删砬位蚬巫畋〉膮^(qū)域是沖壓件直壁與圓角過渡部分因?yàn)檫@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?yàn)檫@部分的加工硬化少于其它地方拉深工序到壓力機(jī)行程下死點(diǎn)結(jié)束拉深工序結(jié)束后壓力機(jī)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(dāng)沖壓件被壓邊圈推起時(shí)空氣可進(jìn)入沖壓件離開凸模產(chǎn)生的真空部分如果不設(shè)通氣孔沖壓件將很難脫出 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