模具与数控专业英语.ppt

Unit Two Die Design Mold with CNC professional English 2.5 Bending Die Design Mold with CNC professional English Bending is of the most common forming operations. We merely have to look at the components in an automobile or an appliance-or at a paper clip or a file cabinet-to appreciate how many parts are shaped by bending. Bending is used not only to form flangesAndseamsAndand corrugations but also to impart stiffness to the part(by increasing its moment of inertia). Mold with CNC professional English The terminology used in bending is shown in Figure 2-12 .Note thatAndIn bendingAndthe outer fibers of the material are in tensionAndwhile the inner fibers are in compression. Because of the Poissons ratioAndthe width of the part(bend lengthAndL)in the outer region is smaller, and in the inner region it is larger than the original width. This phenomenon may easily be observed by bending a rectangular rubber eraser. Mold with CNC professional English Figure 2-12 Bending terminology Mold with CNC professional English 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 becomes smaller), the tensile strain at the outer fiber increases, and the material eventually cracks (Figure 2-13). Mold with CNC professional English Figure 2-13 Poisson effect Mold with CNC professional English The minimum bend radius for various materials is given in Table 2-2 and it is usually expressed in term of the thickness, such as 2T, 3T, 4T and so on. Mold with CNC professional English Table 2-2 Minimum Bend Radius for Various Materials at Room Temperature T-Thickness of material Mold with CNC professional English Bend allowance as shown in Figure 2-12 is the length of the neutral axis in the bend and is used to determine the blank length for