IE370Lecture17

IE370Lecture17 - SHEET METALWORKING Cutting Operations...

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1 SHEET METALWORKING Cutting Operations Bending Operations Drawing Other Sheet Metal Forming Operations Dies and Presses for Sheet Metal Processes Sheet Metal Operations Not Performed on Presses Bending of Tube Stock Sheet Metalworking Defined Cutting and forming operations performed on relatively thin sheets of metal Thickness of sheet metal = 0.4 mm (1/64 in) to 6 mm (1/4 in) Thickness of plate stock > 6 mm Operations usually performed as cold working Sheet and Plate Metal Products Sheet and plate metal parts for consumer and industrial products such as - Automobiles and trucks - Airplanes - Railway cars and locomotives - Farm and construction equipment - Small and large appliances - Office furniture - Computers and office equipment Advantages of Sheet Metal Parts High strength Good dimensional accuracy Good surface finish Relatively low cost For large quantities, economical mass production operations are available
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2 Sheet Metalworking Terminology 1. “Punch-and-die” - Tooling to perform cutting, bending, and drawing 2. “Stamping press” - Machine tool that performs most sheet metal operations 3. “Stampings” - Sheet metal products Three Major Categories of Sheet Metal Processes 1. Cutting - Shearing to separate large sheets; or cut part perimeters or make holes in sheets 2. Bending - Straining sheet around a straight axis 3. Drawing - Forming of sheet into convex or concave shapes Figure 20.1 - Shearing of sheet metal between two cutting edges: (1) just before the punch contacts work Cutting Shearing between two sharp cutting edges Figure 20.1 - Shearing of sheet metal between two cutting edges: (2) punch begins to push into work, causing plastic deformation
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3 Figure 20.1 - Shearing of sheet metal between two cutting edges: (3) punch compresses and penetrates into work causing a smooth cut surface Figure 20.1 - Shearing of sheet metal between two cutting edges: (4) fracture is initiated at the opposing cutting edges which separates the sheet Shearing, Blanking, and Punching Three principal operations in pressworking that cut sheet metal: Shearing Blanking Punching Shearing Sheet metal cutting operation along a straight line between two cutting edges Typically used to cut large sheets into smaller sections for subsequent operations
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4 Figure 20.3 - Shearing operation: (a) side view of the shearing operation (b) front view of power shears equipped with inclined upper cutting blade Symbol v indicates motion Blanking and Punching Blanking - sheet metal cutting to separate piece from surrounding stock Cut piece is the desired part, called a blank Punching - sheet metal cutting similar to blanking except cut piece is scrap, called a slug Remaining stock is the desired part Figure 20.4 - (a) Blanking and (b) punching (piercing) Clearance in Sheet Metal Cutting Distance between the punch and die Typical values range between 4% and 8% of stock thickness - If too small, fracture lines pass each other, causing double burnishing and larger force - If too large, metal is pinched between cutting edges and excessive burr results
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