TAILIEUCHUNG - 9Design for Sheet Metalworkingb

0 | 9 Design for Sheet Metalworking INTRODUCTION Parts are made from sheet metal in two fundamentally different ways. The first way involves the manufacture of dedicated dies which are used to shear pieces of required external shape called blanks from metal stock that is in strip form. The strip stock may be in discrete lengths that have been cut from purchased sheets or may be purchased as long lengths supplied in coil form. With this method of manufacture dies are also used to change the shape of the blanks by stretching compressing or bending and to add additional features through piercing operations. The dies are mounted on vertical presses into which the sheet metal stock may be manually loaded or automatically fed from coil. The alternative method of manufacture involves the use of computer numerically controlled CNC punching machines which are used to make arrays of sheet metal parts directly from individual sheets. These machines usually have a range of punches available in rotating turrets and are referred to as turret presses. The method of operation is to first produce all of the internal part features in positions governed by the spacing of parts on the sheet. The external contours of the parts are then produced through punching with curved or rectangular punches or by profile cutting. The latter operation is usually performed by plasma or laser cutting attachments affixed to the turret press. Parts produced on a turret press are essentially flat although internal features may protrude above the sheet surface. For this reason it is common practice to carry out secondary bending operations if required on separate presses. These are typically performed on wide shallow bed presses called press brakes onto which standard bending tools are mounted. 381 Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 382 Chapter 9 TABLE Standard . Sheet Metal Thickness Steels Aluminum alloys mm Copper alloys mm Titanium alloys mm Gage no. mm 28

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