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7/30/2019 13 Deforming

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DEFORMINGElasti i i

Elastic-perfectl lastic

Rigid perfectl lastic

i i

e p

Stress strain behavior of ductile materials

c-plast c w th strain hardening

y p

y p

Rigid plast c w th strain hardening

Topics for todays lecture

~~~~ DFM

Process characteristics

~~

Force

~~ Stamping:

Shapes

Size

Deformation processes

Deforming process characteristics

Deforming physics

Common deforming processes

Material/continuum changes during processing

Machining = Local, concentrated

Deforming = Over large volume

Machining: ~10s - 100s of lbs

~10s - 100s of tons

Materials - Virtually all ductile materials

- Limited by strain/flow

- Limited by force/equipment

Advantages and disadvantages

~~

~~ )~~

~~

Friction

~~~

AdvantagesParallel 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

Important physics

Stress/strainAffect CQFR

Affect deforming force -> equipment & energy requirements

Affect on deforming force -> equipment & energy requirements

Why lubrication is needed and can help

Friction is not repeatable quality.

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Stress strain behavior of ductile materials

Elastic-plastic with strain hardening

Elastic-perfectly plastic

Rigid perfectly plastic

Rigid plastic with strain hardening

e p

12L14 Steel True Stress-Strain Behavior

0

100

200

300

400

500

600

0.00 0.01 0.02 0.03 0.04 0.05

Strain,mm

/mm

Stress,

MPa

0

10

20

30

40

50

60

70

80

Stress,kpsi

Youngs modulus190 GPa [27.4 Mpsi]

Tangent modulus0.41 GPa [0.06 Mpsi]

Intercept

Example: 12L14 Steel in Duratec

Forging force and frictionAxisymmetric upsetting

Purpose

~ Find Fz( )~ Sensitivity

Assumptions:

~ Tresca flow~ Constant friction coefficient~ Plastic deformation

Fz

h

2 R

Forging force and friction

( ) ( ) dhdrrdddrhdrdrpdrhdF rrrr +++==2

220

dFinner arc dFfriction top & bottom dFhoop dFouter arc

hh

p

dr

d zr == 22

Yzr =Eqxn: B - Tresca Yield Criterion

( ) = rRhYz

2exp

Eqxn: A Equilibrium in r direction


Affect of friction on contact pressure

-150000

-125000

-100000

-75000

-50000

-25000

0

0 0.05 0.1 0.15 0.2 0.25 0.3

Distance from center line [inches]

Contactpressure[psi]

mu = 0

mu = .1

mu = .2

mu = .5

Increasing

Y=75000 psih = inch

Forging force and friction cont.

( )

== 122exp2122

2

0 h

R

h

RY

R

hRdrrF

R

zz

( )

+=

h

RYRFz

3

21

2

Now use Taylors series expansion (3 terms) to approximate the exponen tial function

Expand about 0, makes this approximation valid for small values of 2 R/h

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0

2

4

6

8

10

0

[ ]

[

]

Common processesSheet metal

Forging

Affect of part size and friction on forging force

0.05 0.1 0.15 0.2 0.25

Part size inches

Forging

force

tons

mu = 0

mu = .1

mu = .2

mu = .5


Increasing

Y=75000 psi

h = inch

Extrusion

Rolling

ForgingBending and shearing

Rolling and extrusion Affect of grain size

~~ Hardness~~ For example (Ferrite)

grain

y

oyd

k+=

Properties affected by grain sizeStrength

Ductility

We desire smaller grains for better properties

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Recrystallization

/ /

DFM for deforming processes

Lubrication

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

Parting line and flash

Draft angle

Radii

Mechanics of spring back

SB

Example: Elastic spring back

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RRRR

o

o>

13 deforming

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