TAILIEUCHUNG - 7Design for Machining7

x | 7 Design for Machining INTRODUCTION In machining material is removed from the workpiece until the desired shape is achieved. Clearly this a wasteful process and many engineers feel that a main objective should be to design components that do not require machining. Since most manufacturing machines are designed to remove metal by machining the view that machining should be avoided must be considered impracticable for the immediate future. However the trend toward the use of near net shape processes that conserve material is clearly increasing and when large-volume production is involved this approach should be foremost in the designer s mind. In this chapter we first introduce the common machining processes. Then we consider the ways in which the work material can be readily changed to the desired form by machining and the ways in which the surfaces of the component are finished. Finally an introduction to early cost estimating for designers is presented. All machine tools provide a means of i holding a cutting tool or abrasive wheel ii holding a workpiece and Hi providing relative motion between them in order to generate the required surfaces. MACHINING USING SINGLE-POINT CUTTING TOOLS Lathes are designed to rotate the workpiece and feed the cutting tool in the direction necessary to generate the required machined surface. 267 Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 268 Chapter 7 The workpiece is gripped in a chuck or collet or is mounted on a faceplate mounted on the end of the main spindle of the machine. The rotation of the workpiece is provided by an electric motor driving the main spindle through a series of gears. Cutting tools can be driven or fed parallel to or normal to the axis of rotation of the workpiece. Modem lathes are provided with computer control of all workpiece and tool motions. These are known as computer numerical control CNC lathes and the tools can be fed in any direction in the horizontal plane to generate a .

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