【模具与数控专业英语】教学内容2105.pptVIP

* Unit Two Die Design 模具与数控专业英语 2.5 Bending Die Design 模具与数控专业英语 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 flanges，seams，and corrugations but also to impart stiffness to the part（by increasing its moment of inertia）． 模具与数控专业英语 The terminology used in bending is shown in Figure 2-12 ．Note that，In bending，the outer fibers of the material are in tension，while the inner fibers are in compression． Because of the Poisson’s ratio，the width of the part（bend length，L）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. 模具与数控专业英语 Figure 2-12 Bending terminology 模具与数控专业英语 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). 模具与数控专业英语 Figure 2-13 Poisson effect 模具与数控专业英语 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. 模具与数控专业英语 Table 2-2 Minimum Bend Radius for Various Materials at Room Temperature T—thickness of material 模具与数控专业英语 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 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 by