模具设计与制造专业英语黄义俊_统一模板(模具)Unit2课件教学.pptVIP

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 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 manipulators move the parts from one machine to another． Certainly, a videotape or television special cannot convey the scale of today’s 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. 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 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. 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 constant. Modes of sheet forming are shown in Figure 2-2. Stretching is the term usually used to describe the deformation in which an e