DEFORMING

1. DEFORMING

2. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid plastic with strain hardening

3. Topics for today’s lecture Deformation processes ⊙Deforming process characteristics ⊙Deforming physics ⊙Common deforming processes ⊙DFM

4. Process characteristics Material/continuum changes during processing ⊙Machining = Local, concentrated ⊙Deforming = Over large volume Force ⊙ Machining: ~10s - 100s of lbs ⊙Stamping:~10s - 100s of tons Materials - Virtually all ductile materials Shapes - Limited by strain/flow Size - Limited by force/equipment

5. Advantages and disadvantages Advantages ⊙Parallel process: rapid bulk formation ⊙Overall material properties improved Disadvantages ⊙ Cost of equipment and dies ⊙ Limited flexibility in shapes and sizes (i.e. compared to machining ⊙ Accuracy ⊙ Repeatability

6. Important physics Stress/strain ⊙ Affect CQFR ⊙ Affect deforming force -> equipment & energy requirements Friction ⊙ Affect on deforming force -> equipment & energy requirements ⊙ Why lubrication is needed and can help ⊙ Friction is not repeatable… quality….

7. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid plastic with strain hardening

8. Example: 12L14 Steel in Duratec 12L14 Steel True Stress-Strain Behavior Intercept Tangent modulus 0.41 GPa [0.06 Mpsi] Stress, kpsi Stress, MPa Young’s modulus 190 GPa [27.4 Mpsi] Strain, mm /mm

9. Forging force and friction Axisymmetric upsetting Purpose ⊙ Find Fz(µ ) ⊙ Sensitivity Assumptions: ⊙ Tresca flow ⊙ Constant friction coefficient ⊙ Plastic deformation

10. Forging force and friction Eqxn: A – Equilibrium in r direction dFinner arc dF friction top & bottom dF hoop dFouter arc Eqxn: B -Tresca Yield Criterion

11. Forging force and friction Affect of friction on contact pressure Y=75000 psi h = ½ inch mu = 0 mu = .1 mu = .2 mu = .5 Contact pressure [psi] Increasing µ Distance from center line [inches]

12. Forging force and friction cont. Now use Taylor’s series expansion (3 terms) to approximate the exponential function Expand about 0, makes this approximation valid for small values of 2µR/h

13. Forging force and friction Y=75000 psi h = ½ inch Affect of part size and friction on forging force mu = 0 mu = .1 mu = .2 mu = .5 Forging force [tons] Increasing µ Part size [inches]

14. Common processes Sheet metal Forging Extrusion Rolling

15. Bending and shearing

16. Forging Blank Edging Blocking Finishing Trimming

17. Rolling and extrusion

18. Affect of grain size Properties affected by grain size ⊙ Strength ⊙ Hardness ⊙ Ductility ⊙ For example (Ferrite) We desire smaller grains for better properties

19. Recrystallization Recrystallization and Grain Growth in Brass Figure 7.21 Callister Cold- worked(33% CW) 3s at 580 C: initial recrystallization 4s at 580 C: partial replacement 8s at 580 C: completc recrystallization l5 min at 590 C: grain growth 10 min at 700 C: grain growth http://www.mmat.ubc.ca/other/courses/apsc278/lecture11.pdf

20. DFM for deforming processes Parting line and flash Draft angle Radii Lubrication

21. Mechanics of spring back Q: Why do we see spring back? A: Elastic recover of material

22. Example: Elastic spring back Example: Bending wire

23. Quantifying elastic spring back Elastic recovery of material leads to spring back ⊙Y = Yield stress E = Young’s Modulus t = thickness ⊙ ⊙With increase in Ri / t or Y OR decrease in E spring back increases Titanium Increasing Steel