【正文】 e 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。此種類型加工工序用于小批量生產(chǎn)或試樣零件。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。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）?！?176。在此情況下的彎曲力是材料強(qiáng)度的函數(shù)，此彎曲力的計(jì)算式為：P=KLST2/W式中：P——彎曲力，噸（對(duì)于米制使用單位，）； K——模具開啟系數(shù)：16倍材料厚度（16T），8倍材料厚度（8T）。然而，中性線（層）的位置是喲彎曲角度（正如在材料力學(xué)課本中所描述）來決定的。由于泊松比原因，在外部區(qū)域的零件（彎曲長度L）是小于原始寬度，處于內(nèi)部區(qū)域的則比原始寬度大。由于工件材料坯料或工件在沖制回程時(shí)與沖頭附連在一起，所以把材料從沖頭上剝離是必需的。導(dǎo)桿，或?qū)е?，是安裝在下模座上的。板料成形的原理如圖2所示。如果自己沒有去這些大公司訪問，沒有站在巨大的機(jī)器旁，沒有感受到地面的震顫，沒有看巨大型的機(jī)器人的手臂吧零件從一個(gè)機(jī)器移動(dòng)到另一個(gè)機(jī)器，那么廠區(qū)的范圍與價(jià)值真是難以想象的。板料成形（也稱為沖壓或壓力成形）經(jīng)常在廠區(qū)面積非常大的公司中進(jìn)行。一個(gè)凸緣板料上的單元體在半徑方向上被限定，而板厚保持幾乎不變。沖壓（術(shù)語）通常將完整壓制工具的凹模（母模）部分定義為模具。因?yàn)闆_頭的直徑是被沖孔的直徑所要求的，所以有一定間隙的凹模直徑是大于沖頭直徑的。圖4 彎曲術(shù)語彎曲中所用的術(shù)語，如圖4所示，應(yīng)該注意的是，在彎曲中材料的外纖維是處于拉應(yīng)力狀態(tài)，而材料的內(nèi)纖維則處于壓應(yīng)力狀態(tài)。彎曲容許范圍，是指彎曲中的中性線（層）的長度，用來確定彎曲零件的坯料長度。圖6 彎曲方式彎曲力的大小是可以通過對(duì)一根矩形橫梁的簡(jiǎn)單彎曲的工藝過程的確定來估算。一般而言，176。雙動(dòng)式壓力機(jī)是用于鈑金零件的拉深加工。此種壓力機(jī)利用一個(gè)曲柄（曲柄帶動(dòng)違節(jié)運(yùn)動(dòng)，連節(jié)是由兩個(gè)在上死點(diǎn)到下死點(diǎn)之間進(jìn)行擺動(dòng)的連桿組成，連桿擺動(dòng)時(shí)間很短）．在臨近沖程底部時(shí)慢速移動(dòng)的滑塊具有功率很大的短距離位移。這就可以使零件僅通過把復(fù)雜的零件分成幾個(gè)簡(jiǎn)單的加工工序?qū)崿F(xiàn)由復(fù)雜設(shè)計(jì)到精確制造的過程，且沒有使用昂貴的沖制刀具。s automobile stamping lines. Another factor that one sees standing next to such lines is the number of different sheetforming operations that automobile panels go through. Blanks are created by simple shearing, but from then on a wide variety of bending, drawing, stretching, cropping , and trimming takes place, each requiring a special, custommade die.Despite this wide variety of subprocesses, in each case the desired shapes are achieved by the modes of deformation known as drawing, stretching, and bending. The three modes can be illustrated by considering the deformation of small sheet elements subjected to various states of stress in the plane of the sheet. Figure 1 considers a simple forming process in which a cylindrical cup is produced from a circular blank.Figure 1 Sheet forming a simple cupDrawing is observed in the blank flange as it is being drawn horizontally through the die by the downward action of the punch. A sheet element in the flange is made to elongate in the radial direction and contract in the circumferential direction, the sheet thickness remaining approximately constant Modes of sheet fo