【正文】 is simple, and it is adaptable to a wide variety of shapes, furthermore, the process can be easily automated. Die materials for press brakes may range from hardwood (for lowstrength materials and small production runs) to carbides. For most applications, carbonsteel or grayiron dies are generally used.。to15176。to 5176。s ratio, the width of the part (bend length, L) in the outer region is smaller, and in the inner region is larger than the original width. This phenomenon may easily be observed by bending a rectangular rubber eraser. Minimum bend radii vary for different metals, generally, different annealed metals can be bent to a radius equal to the thickness of the metal without cracking or weakening. As R/T decreases (the ratio of the bend radius to the thickness bees smaller), the tensile strain at the outer fiber increases, and the material eventually cracks (Figure 5). Figure 4 Bending terminologyFigure5 Poisson effect The minimum bend radius for various materials is given in Table 1 and it is usually expressed in terms of the thickness. such as 2 T, 3 T, 4T.Table 1 Minimum bend radius for various materials at room temperatureMaterialConditionSoft HardAluminum alloys06TBeryllium copper04TBrass,lowleaded02TMagnesium 5T13TSteelsAustenitic stanless6TLowcarbon,lowalloy,HSLA4TTitanium3TTitanium alloys4TNote :T——thickness of material Bend allowance as shown in Figure 4 is the length of the neutral axis in the bend and is used to determine the blank length for a bent part. However, the position of the neutral axis depends on the radius and angle of bend (as described in texts on mechanics of materials).An approximate formula for the bend allowance, Lb is given byLb= α(R十kT) Where Lb——bend allowance, in (mm). α——bend angle, (radians) (deg). T——sheet thickness, in (mm). R——inside radius of bend, in (mm). k—— when R is less than 2T and when JR is more than 2T.Bend methods arc monly used in press tool. Metal sheet or strip, supported byV bock[Figure 6(a)],is forced by a wedgeshaped punch into the block. This method, termed V bending, produces a bend having an included angle which may be acute, obtuse, or 90176。附件2：外文原文Stamping Die DesignThe wide variety of sheet metal parts for both the automobile and electronic industries is produced by numerous forming processes that fall into the generic category of sheetmetal forming. Sheetmetal forming ( also called stamping or pressing )is often carried out in large facilities hundreds of yards long.It is hard to imagine the scope and cost of these facilities without visiting an automobile factory, standing next to the gigantic machines, feeling the floor vibrate, and watching heavy duty robotic manipulators move the parts from one machine to another. Certainly, a videotape or television special cannot convey the scale of today39。彎板機(jī)的模具材料可以是硬木（用于低強(qiáng)度材料與小批量生產(chǎn)），也可以是硬質(zhì)合金材料。彎板機(jī)使用一個(gè)用在機(jī)械或液壓饑上的長模具，適用于小批量生產(chǎn)。此種類型加工工序用于小批量生產(chǎn)或試樣零件。因此幾種液壓機(jī)驅(qū)動(dòng)很容易就被制成復(fù)雜成形與切斷加工（拉深、擠壓、切斷、模鍛等）的單一機(jī)械，并且所要求的運(yùn)動(dòng)可以容易地定位，彎扳機(jī)除了它的長床身之外基本是與開式壓力機(jī)棚同的，床身長度可為6～20英尺(～6米)或更長，它基本上是用在尺寸大的鈑金零件上的各種類型的彎曲加工成形，它也可以使用不同整套的刀具分別進(jìn)行淺沖孔、切口與成形（見圖11）。液壓機(jī)框架結(jié)構(gòu)的形式是非常類似于機(jī)械式力機(jī)。圖10 典型液壓機(jī)液壓機(jī)屬于壓力限定型的成形機(jī)械，液壓機(jī)的主要用途體現(xiàn)在沿滑塊路徑外力是必須保持恒定或處于精確攤制鋒成形技術(shù)領(lǐng)域中。液壓機(jī)主要是用于成形加工工序中，相比大多散機(jī)械式壓力機(jī)，它有一個(gè)比較長的工作周期。這裝置的設(shè)計(jì)是在沖壓行程的末端以很高壓力。三動(dòng)式壓力機(jī)應(yīng)用不是很廣泛。圖9 典型通用壓力機(jī)三動(dòng)式壓力機(jī)具有和雙動(dòng)式壓力機(jī)相同的內(nèi)、外滑塊。此種類型的壓力機(jī)有一個(gè)外滑塊（壓邊圈），并且有一個(gè)切斷的內(nèi)滑塊（沖頭夾緊器）。圖8 減少或消除回彈的方法從應(yīng)用角度來說，有許多類型的壓力機(jī)，諸如：閉式雙點(diǎn)偏心軸單動(dòng)機(jī)械壓力機(jī)，沖壓成形機(jī)，液壓成形壓力