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1、Unit 2 Die Design,Unit 2 Die Design,2.1 Lesson 3 Deformation Modes in Sheet Forming,The 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 “sheet-metal forming”. Sheet-metal forming（also
2、 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 manipu
3、lators move the parts from one machine to another,Certainly, a videotape or television special cannot convey the scale of todays automobile stamping lines. Another factor that one sees standing next to such lines is the number of different sheet-forming operations that automobile panels go through.
4、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, custom-made die.,Despite this wide variety of sub-processes, in each case the desired shapes are achieved by the modes of deformation known
5、 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 2-1 considers a simple forming process in which a cylindrical cup is produced from a circular blank.
6、,Drawing 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 constan
7、t. Modes of sheet forming are shown in Figure 2-2. Stretching is the term usually used to describe the deformation in which an element of sheet material is made to elongate in two perpendicular directions in the sheet plane. A special form of stretching, which is encountered in most forming operatio
8、ns, is plane strain stretching.,In this case, a sheet element is made to stretch in one direction only, with no change in dimension in the direction normal to the direction of elongation but a definite change in thickness, that is, thinning. Bending is the mode of deformation observed when the sheet
9、 material is made to go over a die or punch radius, thus suffering a change in orientation. The deformation is an example of plane strain elongation and contraction.,2.2 Lesson 4 Piercing Die Design New Words & Expressions,A complete press tool for cutting a hole or multi-holes in sheet material at
10、one stroke of the press, as classified and standardized by a large manufacturer as a single-station piercing die is shown in Figure 2-3. Any complete press tool, consisting of a pair（or a combination of pairs）of mating members for producing pressworked（stamped）parts, including all supporting and act
11、uating elements of the tool, is a die. Pressworking terminology commonly defines the female part of any complete press tool as a die.,The guide pins, or posts, are mounted in the lower shoe. The upper shoe contains bushings which slide on the guide pins. The assembly of the lower and upper shoes wit
12、h guide pins and bushings is a die set. Die sets in many sizes and designs are commercially available. The guide pins are shown in Figure 2-3. A punch holder mounted to the upper shoe holds two round punches (male members of the die) which are guided by bushings inserted in the stripper1. A sleeve,
13、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 too
14、l 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. Spring-loaded strip
15、pers hold the work material against the die block until the punches are withdrawn from the punched holes.,A workpiece to be pierced is commonly held and located in a nest (Figure 2-3) composed of flat plates shaped to encircle the outside part contours. Stock is positioned in dies by pins, blocks, o
16、r other types of stops for locating before the downstroke of the ram.,2.3 Lesson 5 Bending Die Design,Bending is one of the most common forming operations. We merely have to look at the components 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
