Nov8-Forging - ME 250 Nov 8, 2007 Metal Forming Which...

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ME 250 Nov 8, 2007 Metal Forming Which Manufacturing Method? Casting Machining Forging Each process has advantages and limitations relative to part complexity, material properties, dimensional accuracy, surface finish and cost Metal Forming Forming includes a large group of manufacturing processes in which plastic deformation is used to change the shape of the metal workpiece. Deformation results from the use of a tool, called a die, which applies stresses that exceed the yield strength of the metal, which then deforms to take the shape determined by the geometry of the die Stresses applied are usually compressive. However, some processes bend the metal and some apply shear stresses Desirable properties of the metal include low yield strength and high ductility Stress-Strain Curve in Compression Typical engineering stress-strain curve in a compression test Plastic region in Log-Log Plot the relationship between true stress and true strain in the plastic region is n K ε σ = K = strength coefficient n = strain hardening exponent true stress increases continuously in the plastic region until necking Æ metal becomes stronger as strain increases Æ strain hardening Metal Forming Formed parts ¾ Structural beams ¾ Railroad ¾ Pipes ¾ Nails ¾ Kitchen sinks Equipment types ¾ Mechanical presses ¾ Hydraulic devices ¾ Flywheel driven devices
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Metal Forming Processes • Bulk deformation processes Å • Sheet-metal forming processes Bulk deformation process – Stresses metals to plastically deform to a desired shape – Can be done cold, warm, or hot – Very little or no waste – Near net or net shape parts Bulk Deformation Processes •Forging Å 19.3, 19.3.1-19.3.3 •Extrusion Å 19.5, 19.5.1-19.5.3 •Rolling •Drawing Forging – Deform the metal between two dies to conform to the die shape, using impact or gradual pressure (sometime under high temp.) – Compression strengthen parts – Usually “flash” is formed; needs subsequent machining Deformation of the workpiece is carried out by compressive forces Applications ¾ Crankshafts ¾ Connecting rods ¾ Gears ¾ Hand tools ¾ Bolt heads Forging The process may be ¾ Cold working T < 0.3T m ¾ Warm working 0.3 T m < T < 0.5T m ¾ Hot working T > 0.5T m Forging Basic categories of forging ¾ Open-die forging ¾ Closed-die forging aka Impression-die forging
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Forging types (Fig 19.10) open-die forging flashless forging impression-die forging Open-Die Forging Simplest form ¾ Involves placing a solid cylindrical workpiece between two flat dies and applying pressure through the dies Flow of metal is not confined Die surfaces may have a conical or curved shape Open-Die Forging Similar to compression test when workpart has cylindrical cross section and is compressed along its axis – Deformation operation reduces height and increases diameter of work – Common names include upsetting or upset forging (1) start of process with workpiece at its original length and diameter, (2) partial compression, and (3) final size.
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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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Nov8-Forging - ME 250 Nov 8, 2007 Metal Forming Which...

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