deforming. stress strain behavior of ductile materials σ ε elastic-plastic with strain hardening...

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DEFORMING

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Page 1: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

DEFORMING

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

Stress strain behavior of ductile materialsσ

ε

Elastic-plastic with strain hardening

Elastic-perfectly plastic

Rigid perfectly plastic

Rigid plastic with strain hardening

Page 3: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Topics for today’s lecture

Deformation processes

⊙ Deforming process characteristics

⊙ Deforming physics

⊙ Common deforming processes

⊙ DFM

Page 4: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Process characteristicsMaterial/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

Page 5: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

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

Page 6: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

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….

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

Stress strain behavior of ductile materialsσ

ε

Elastic-plastic with strain hardening

Elastic-perfectly plastic

Rigid perfectly plastic

Rigid plastic with strain hardening

Page 8: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Example: 12L14 Steel in Duratec

12L14 Steel True Stress-Strain Behavior

Intercept

Tangent modulus 0.41 GPa [0.06 Mpsi]

Young’s modulus190 GPa [27.4 Mpsi]

Strain, mm /mm

Str

es

s,

MP

aS

tres

s, k

ps

i

Page 9: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Forging force and frictionAxisymmetric upsetting

Purpose

⊙ Find Fz(µ )

⊙ Sensitivity

Assumptions:

⊙ Tresca flow

⊙ Constant friction coefficient

⊙ Plastic deformation

Page 10: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

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

Page 11: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Forging force and friction

Y=75000 psi h = ½ inch

Affect of friction on contact pressure

Distance from center line [inches]

Co

nta

ct p

ress

ure

[p

si]

Increasing µ

mu = 0

mu = .1

mu = .2

mu = .5

Page 12: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

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 2µ R/h

Page 13: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Forging force and friction

Affect of part size and friction on forging force

Fo

rgin

g f

orc

e [t

on

s]

Part size [inches]

mu = 0 mu = .1 mu = .2 mu = .5

Increasing µ

Y=75000 psi h = ½ inch

Page 14: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Common processesSheet metal

Forging

Extrusion

Rolling

Page 15: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Bending and shearing

Page 16: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Forging

Blank

Edging

Blocking

Finishing

Trimming

Page 17: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Rolling and extrusion

Page 18: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Affect of grain size

Properties affected by grain size

⊙ Strength

⊙ Hardness

⊙ Ductility

⊙ For example (Ferrite)

We desire smaller grains for better properties

Page 19: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

RecrystallizationRecrystallization and Grain Growth in Brass

Figure 7.21 Callister

http://www.mmat.ubc.ca/other/courses/apsc278/lecture11.pdf

8s at 580 C: completcrecrystallization

3s at 580 C: initialrecrystallization

4s at 580 C: partial replacementCold- worked(33% CW)

l5 min at 590 C: graingrowth

10 min at 700 C: grain growth

Page 20: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

DFM for deforming processes

Parting line and flash

Draft angle

Radii

Lubrication

Page 21: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Mechanics of spring backQ: Why do we see spring back?

A: Elastic recover of material

Page 22: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

Example: Elastic spring backExample: Bending wire

Page 23: DEFORMING. Stress strain behavior of ductile materials σ ε Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid

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

SteelIncreasing