Nov 13 Sheetmetal

Nov 13 Sheetmetal - ME 250 November 13, 2007 Sheet Metal...

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ME 250 November 13, 2007 Sheet Metal Working Course pack: All sections except 20.4 HW 9, Problem 3 (CES) Tolerance = 0.01 and NOT 0.1 Can manufacturing The typical aluminum can weighs less than half an ounce. Its thin walls withstand approx a pressure of 90 psi (exerted by the carbon dioxide in beer and soft drinks) Aluminum's shiny finish also facilitates decorative printing, important for a product that must grab the attention of consumers in a competitive market 100 billion aluminum beverage cans produced / year in the U.S. Why sheet metal parts? • High strength • Good dimensional accuracy • Good surface finish • Relatively low cost • Economical mass production for large quantities Sheet metalworking Cutting and forming operations performed on relatively thin sheets of metal Thickness of sheet metal = 0.4 mm to 6mm (1/64 in to 1/4 in) Operations usually performed as cold working (room temperature) Terminology Punch-and-die : the tooling to perform cutting, bending, and drawing Stamping press : the machine tool that performs most sheet metal operations Stampings : sheet metal products
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Sheet metal cutting Shearing to make large sheets into smaller ones Blanking to cut part perimeters out of sheet metal Punching to make holes in sheet metal Cutting action (Fig 20.1) Cutting sheet metal by shearing action Sheared edge (Fig 20.2) Appearance of the cut edge Blanking & punching (Fig 20.4) blanking punching Clearance Clean separation Æ meeting of fracture lines Good clearance Clearance (Fig 20.5) clearance too small clearance too large
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Clearance ca t = sheet metal thickness clearance Typical clearance: 4% – 8% of sheet metal thickness Clearance on die or punch? Q. Desired profile created by the die or the punch? Punch size determines hole size D h Assigning clearance (Fig 20.6) Die size determines blank size D b Assigning clearance For a round blank of diameter D b Clearance on punch diameter = D b –2c Blanking die diameter = D b For a round hole of diameter D h Hole punch diameter = D h Clearance on die diameter = D h For a round hole of diameter D h Hole punch diameter = D h Clearance on die diameter = D h + 2c Cutting forces Cutting force F is determined by F = StL where S = shear strength, MPa (lb/in 2 ) t = sheet metal thickness, mm (in.) L = length of cut edge, mm (in.) S = 0.7 X [ultimate tensile strength] Example problem Making a washer Problem
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This note was uploaded on 04/04/2008 for the course ME 250 taught by Professor Dutta during the Fall '07 term at University of Michigan.

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Nov 13 Sheetmetal - ME 250 November 13, 2007 Sheet Metal...

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