lecture_19_-_bulk_deformation_processes_-_ch_19

# lecture_19_-_bulk_deformation_processes_-_ch_19 - ME 350...

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BULK DEFORMATION PROCESSES IN METALWORKING 1. Rolling 2. Forging 3. Extrusion 4. Drawing ME 350 – Lecture 19 – Chapter 19

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Material Behavior in Metal Forming Plastic region of stress-strain curve is primary interest because material is plastically deformed The flow curve In plastic region : n f Y K σ ε = = where K = strength coefficient; and n = strain hardening exponent Stress and strain in flow curve are true stress and true strain… mostly in their absolute values
Flow Stress Instantaneous flow stress: n f Y K ε = _ 1 n f K Y n = + True Stress True Strain Fracture Average flow stress: _ f Y f Y

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Diagram of Flat Rolling Draft = thickness reduction: Conservation of Volume: f o t t d - = f f f o o o L w t L w t = f f f o o o v w t v w t =
Diagram of Flat Rolling There is a point on the roll where the work velocity equals the roll velocity , this is the . Friction is in on either side of this point. Forward slip: where, Maximum draft: Roll force: R d 2 max μ = r r f v v v s - = ) ( f o f f contact f t t R w Y wL Y F - = = min / rev N DN v r = = π friction of t coefficien - - =

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Rolling Issues: With Hot rolling, material properties are isotropic , but dimensional tolerances are not as tight, and scale (surface oxidation) occurs. In hot working the material can be considered perfectly plastic, n = and Y f = To reduce the power required to roll: 1. Change temperature: 2. Change roller radius: 3. Change rolling speed:
Shape Rolling Work is deformed into a contoured cross section rather than flat (rectangular) Accomplished by passing work through rolls that have the reverse of desired shape Products include: Construction shapes such as I‑beams, L‑beams, and U‑channels Rails for railroad tracks Round and square bars and rods

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Thread Rolling Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies Performed by cold working in thread rolling machines Advantages over thread cutting (machining): production rates: material utilization: threads strength:
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## lecture_19_-_bulk_deformation_processes_-_ch_19 - ME 350...

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