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,
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IE370Lecture17 - SHEET METALWORKING Cutting Operations...

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