DEFORMING
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DEFORMING. Stress strain behavior of ductile materials. σ. ε. Elastic-plastic with strain hardening Elastic-perfectly plastic Rigid perfectly plastic Rigid plastic with strain hardening. Topics for today’s lecture. Deformation processes. ⊙ Deforming process characteristics.

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Deforming

DEFORMING


Deforming

Stress strain behavior of ductile materials

σ

ε

Elastic-plastic with strain hardening

Elastic-perfectly plastic

Rigid perfectly plastic

Rigid plastic with strain hardening


Deforming

Topics for today’s lecture

Deformation processes

⊙Deforming process characteristics

⊙Deforming physics

⊙Common deforming processes

⊙DFM


Deforming

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


Deforming

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


Deforming

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….


Deforming

Stress strain behavior of ductile materials

σ

ε

Elastic-plastic with strain hardening

Elastic-perfectly plastic

Rigid perfectly plastic

Rigid plastic with strain hardening


Deforming

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


Deforming

Forging force and friction

Axisymmetric upsetting

Purpose

⊙ Find Fz(µ )

⊙ Sensitivity

Assumptions:

⊙ Tresca flow

⊙ Constant friction coefficient

⊙ Plastic deformation


Deforming

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


Deforming

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]


Deforming

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


Deforming

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]


Deforming

Common processes

Sheet metal

Forging

Extrusion

Rolling


Deforming

Bending and shearing


Deforming

Forging

Blank

Edging

Blocking

Finishing

Trimming


Deforming

Rolling and extrusion


Deforming

Affect of grain size

Properties affected by grain size

⊙ Strength

⊙ Hardness

⊙ Ductility

⊙ For example (Ferrite)

We desire smaller grains for better properties


Deforming

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


Deforming

DFM for deforming processes

Parting line and flash

Draft angle

Radii

Lubrication


Deforming

Mechanics of spring back

Q: Why do we see spring back?

A: Elastic recover of material


Deforming

Example: Elastic spring back

Example: Bending wire


Deforming

Quantifying elastic spring back

Elastic recovery of material leads to spring back

⊙Y = Yield stressE = Young’s Modulust = thickness

⊙With increase in Ri / t or Y OR decrease in E spring back increases

Titanium

Increasing

Steel


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