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BITS Pilani, Pilani Campus

Forging analysis

Outline

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Types of forgings

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Strip Forging

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Assumption forging forcefattains its maximum value at the end of the

operation

variation of stress field along y-axis is negligible

plane strain case

entire w/p is plastic in state during the process

constantis

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Let at any instant the thickness of the element is h and

width is 2l

Consider an element of width dx at a distance x from

origin.

Consider the equilibrium of the element in xdirection.

8/10/2019 MF F313 2014 L5 (1)

7/31BITS Pilani, Pilani Campus)3........(..........)/2(

02

)1(

)2....(..........

]2

,

2/)(

[

)1......(..........02

12

dxhdp

drdph

inputing

ddp

kp

criteriaMISESVONapply

p

areaplaneofcaseabeingit

stressesprincipalarepandxletnow

dxdh

x

x

x

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8/31BITS Pilani, Pilani Campus

zonestickingahavewelxtoxx

zonestickingnonslidingahavewexxtox

s

s

,

/,0

Now as we move along the x- axis from origin,

the friction stress are increasing and when

(say) it reaches a value equal to shear yield

stress and it remains constant then after. Inother words from

8/10/2019 MF F313 2014 L5 (1)


lxkep

ekpor

hxkpkc

kpxatequfrom

cfindto

chxpdp

dxhpdp

becomesequ

p

xxtoxZONESLIDINGFOR

hx

hx

s

0)4(..........2

2/

/2)2/ln(2ln

2),0(0)2(

/2/

)/2(

)3(

)0(

/21

/2

1

1

1

)6(]........./)([2

]/[2

2),4(sin

)/2(

)/2(

,

tan

)5.....(..........)/2(

],[

/2

)3(sin

/2

/22

/2

2

2

2

.2

haveweg,integratinandequ.aboveinkputing

hxxekp

hxekc

kepequgunow

xhkpc

cxhkp

ppxx

tcconsfindto

cxhkp

kpxhavexwe

hdxdp

equguagainZONESTICKINGFOR

s

hx

shxs

hxs

ss

ss

ss

ss

s

s

8/10/2019 MF F313 2014 L5 (1)

10/31BITS Pilani, Pilani Campuslxxhxkp

hxhk

hxhekp

getweequinxputing

hx

hxor

e

kekp

wegetequinthisputing

kpskpxdxFINDTO

s

hh

s

s

s

hx

hx

s

s

s

s

s

)7....(}]......../)2/1ln(1{2/1[2

)}]2/1ln(2/{/12/1[2

)}]2/1ln(2/{/1[2

),6(

)2/1ln(2/

)2/1ln(/2

2/1

2/

),4(

/,

2

)2/1ln()2/)(/2(

/2

]/2[

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]21[2

/

0

l

xs

xs

dxpdxpf

lengthunitforceforgingtotal

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DISC FORGING

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Let in a typical open die forging of a disc as shown infigure, thickness and force at the end of the operation

are h and F respectively:

Consider an elemental disc subtending an angle d at the

centre, between radii r and r + dr.Considering the radial equilibrium of strip,

For the cylindrical symmetry (Assumption)

Now neglecting the higher order term

0.22/sin.2..))(( drrddhdrhrdhddrrd rrr

r

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)1________(______________________________02.

02...

drhd

drrdhrdhrddhrd

r

rrr

)2(________________________________________3

6)()()(

,

Pr,,

2213

232

221

kp

getWe

k

eqinvaluesthesePuttingTherefore

StressesincipalarepandLet

r

n

r

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)3(________________________________________02

)1(

drhdp

eqinPut

dpd

or

n

r

zonestickingrr

zoneslidingRrr

ei

s

s

_______0

_______

..

placetakesslidingwhichbeyondradiustheisrLet s

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8/10/2019 MF F313 2014 L5 (1)


rhRh

sl

Rh

Rh

Rh

n

r

eekpor

ekrhpHence

ekCor

ekCor

CRhk

kp

eqfromTherefore

RrCf indTo

)/2()/2(

)/2(

)/2(

1

)/2(

1

1

1

.3

3ln)/2(ln,

3

)3/(

)/2()3ln(

3

)2(

,0,

Rrrekp srRh

sl

)4_______(____________________3 ))(/2(

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)5____(____________________)/2(,

)/2(

02

)3(,

,,

:

2CrhkpgIntegratin

drhkdpor

kdrhdp

eqinkPutting

palsokrrAt

ZoneStickingFor

n

ss

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)6___(____________________3))(/2(

3)/2()/2(

),5()/2(3

),4(

)/2(

)/2(

),5(

,

:

))(/2(

))(/2(

2

))(/2(

2

2

2

2

s

s

s

rRhs

rRhs

ns

rRh

ns

n

ss

ss

n

ss

ekrrhkp

ekrhkrhkp

getweeqinCPuttingrhkekC

eqaboveinvaluetheputandrrputtingbyeqFrom

rhkpCor

Crhkp

eqinPutting

pprrAt

CFindTo

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)6(,

)3/1ln()2/(

)3/1ln()2/(

)3/1ln())(/2(

3/1

3/

)4(

/

,

:

))(/2(

))(/2(

n

s

s

s

s

rRh

rRh

n

s

ss

s

eqinvaluerPutting

hRr

hrR

rRh

e

ekk

eqinthisPutting

kpor

pkrrAt

rFindTo

s

s

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drrpdrrp

drrpdrrpF

ForceForgingTotal

s

s

s

s

r R

r

r R

r

....2

.2..2.

:

0

12

0

12

R

r

rRhr

rRhr

R

r

rRhrr

s

s

s

s

ss

hrhkekrrRrhk

drrkerrkrRrhk

drrkedrrkdrrrRhk

)/2(1)4/.(32)3ln(1)2/(3/2/)/2(2

..32)2/)(3ln()2/(/(2)3/()2/()/2(2

..32.)3ln(1)/(2.))(/2(2

22))(/2(

0

22

))(/2(22

0

32

))(/2(

00

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Grain Flow Comparison

(a) casting, (b) machining, (c) forging

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Smith forging

Drop forging

Press forging

Upset forging

Swaging

Roll forging

Types of Forging

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Roll Forging

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Fillet radius

Draft

Flash gutter

Shrinkage allowance (hot forging)

Die Features

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Forging Defects

(a) Laps formed by web buckling during forging; web thickness should be increasedto avoid this problem.

(b) (b) Internal defects caused by oversized billet; die cavities are filled prematurely,

and the material at the center flows past the filled regions as the dies close.

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Thanks

MF F313 2014 L5 (1)

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