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Bulk Deformation Processes

Bulk Deformation Processes . Operations that induce shape changes on the workpiece by plastic deformation under forces applied by various tools and dies Forging Rolling Extrusion Drawing. Open Die Forging – Upsetting. % Reduction in height=(h 0 -h 1 )/h 0 *100 e 1 =(h o -h 1 )/h 0

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Bulk Deformation Processes

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  1. Bulk Deformation Processes • Operations that induce shape changes on the workpiece by plastic deformation under forces applied by various tools and dies • Forging • Rolling • Extrusion • Drawing

  2. Open Die Forging – Upsetting • % Reduction in height=(h0-h1)/h0*100 • e1=(ho-h1)/h0 • True strain=E1=ln(h0/h1) • If v is the velocity between platens (dies): • e’1= -v/h0 • E’1= -v/h1 • True strain rate increases rapidly as height of the specimen approaches zero.

  3. Forging • Plastic deformation by compressive forces • Open-die forging • Impression-die forging • Closed-die forging

  4. Upsetting causes “barreling” • Frictional Force • Lower temperature of die surface • Non-uniform flow • Friction • 0.6 for hot • 0.1 for cold • Lubrication – hot dies reduces barreling

  5. Work of Deformation

  6. Specific Energy (energy/Volume)

  7. Total Work Expended • Work=(u)(volume) • Actual Energy is more that theoretical • Friction • Redundant Work • Utotal = Utheoretical + Ufriction • Efficiency=Uth./Utotal

  8. Method of Analysis We know from distortion energy criterion for plane stress:

  9. Solving two equations: at

  10. Paverage can be obtained using: • Yf=kEn • Upsetting force: • F=Pav*cross-section area • F=Pav*2a*width • This is true for any instantaneous h

  11. For cylindrical work r is the final radius after upsetting and h is the final value

  12. Problem • Diameter=6 inch • Height=4 inch • After upsetting=2 inch • Coeff. Of friction =0.2 • Material=Annealed Steel • Find Force

  13. For annealed steel (r2 from Volume conservation)

  14. Impression Die Forging • Workpiece takes the shape of the die cavity • Flashes are created radially outward • High Friction in the Flash

  15. Flash:Very high length:height ratioFlash cools faster than the bulk and hence resists deformation - This helps the billet to fill the cavity Complex Shapes have different strains and strain rates.Thus level of strength at different locations depends on values of ‘n’ strain hardening exponent, ‘m’ strain rate sensitivity of the material

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