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2024-08-05 03:08本頁面
【正文】 the die) which are guided by bushings inserted in the stripper. A sleeve, or quill, encloses one punch to prevent its buckling under pressure from the ram of the press. After penetration of the work material, the two punches enter the die bushings for a slight distance.The female member, or die, consists of two die bushings inserted in the die block. Since this press tool punches holes to the diameters required, the diameters of the die bushings are larger than those of the punches by the amount of clearance.Since the work material stock or workpiece can cling to a punch on the upstroke, it may be necessary to strip the material from the punch. Springloaded strippers hold the work material against the die block until the punches are withdrawn from the punched holes. A workpiece to be pierced is monly held and located in a nest (Figure 23) posed of flat plates shaped to encircle the outside part contours. Stock is positioned in dies by pins, blocks, or other types of stops for locating before the downstroke of the ram.Bending is one of the most mon forming operations. We merely have to look at the ponents in an automobile or an applianceor at a paper clip or a file cabinetto appreciate how many parts are shaped by bending. Bending is used not only to form flanges, seams, and corrugations but also to impart stiffness to the part ( by increasing its moment of inertia ).The terminology used in bending is shown in Figure 4. Note that, in bending, the outer fibers of the material are in tension, while the inner fibers are in pression. Because of the Poisson39。.Friction between a springloaded knurled pin in the vee die and the part will prevent or reduce side creep of the part during its bending. Edge bending [Figure 6(b)] is cantilever loading of a beam. The bending punch forces the metal against the supporting die. The bend axis is parallel to the edge of the die. The workpiece is clamped to the die block by a springloaded pad before the punch contacts the workpiece to prevent its movement during downward travel of the punch.Figure 6 Bending methodsBending Force can be estimated by assuming the process of simple bending of a rectangular beam. The bending force in that case is a function of the strength of the material. The calculation of bending force is as follows:P=KLST2/W Where Pbending force, tons (for metric usage, multiply number of tons by to obtain kilonewtons).K——die opening factor: for a die opening of 16 times metal thickness, for an opening of 8 times metal thickness.L——length of part, in.S——ultimate tensile strength, tons per square in.W——width of V or U die, in.T——metal thickness, in.For U bending (channel bending) pressures will be approximately twice those required for V bending, edge bending requires about onehalf those needed for V bending.Springback in that all materials have a finite modulus of elasticity, plastic deformation is followed, when bending pressure on metal is removed, by some elastic recovery (see Figure 7). In bending, this recovery is called springback. Generally speaking, such a springback varies in sheet from 176。, depending upon finite modulus of elasticity, modes of bending, clearance of die and so on, but phosphor bronze may spring back from 10176。. Figure 7 Springback during bending Methods of reducing or eliminating springback in bending operations can be made according to the following operations, shown in Figure 8, and parts produced in bending die are also overbent through an angle
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