Module -3

FORGING
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INTRODUCTION
Forging

 F org i n g i s a de f or m a t i on pr oce s s i n g of ma t eria ls

t h r o u g h compressive s t r e s s .
 I t is carried out either hot or cold. hot forging is done at
t e m p e r a t u r e s above r e c r y s t a l l i z a t i o n t e m p e r a t u r e s , t y pi ca l l y 0.6
t m , or above, where tm is m e l t i n g t e m p e r a t u r e .
 Warm forging is done in the t e m p e r a t u re r a n g e : 0.3 t m to
0.5 tm.
 The melting point of steel ranges from 2500-2800°F or
 1371-1540°C
 C o l d forging advantages
 Good sur face f i n i s h , h i g h s t r e n g t h and gr eat er accuracy.
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 Forging
INTRODUCTION
 H ot f org i n g requ i re s l ower l oa ds , beca u s e f l ow s t res s gets
reduced a t h i gh e r t e m p e ra t u re s .
 S t ra i n ra t es i n h ot wor k i n g m a y be h i g h –0. 5 to 500 s - 1.
 S t ra i n s i n h ot f or g i n g a re a l s o h i g h – t ru e s t ra i n s of 2
to 4. are common.
 Ap p l i c a t i o n s of forging bolts, d i s k s , g e a r s , t u rbi n e d i s k ,
c ra n k s h a f t , con ne ct i n g rod, va lve bodies, s m a l l components
for hyd ra u l i c c i rc u i t s .
 Fo r g i n g a dva n t a g e s .
 C l o s e r d i m e n s i o n a l a ccura ci e s
 require very l i t t l e m a c h i n i n g a f te r fo rg i n g … . .
 M a t e r i a l s av i n g is the re s u l t .
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 Forging
INTRODUCTION
Forging advantages .
Higher strength,
greater productivity,
favorable grain orientation,
high degree of surface finish are other merits
.
However, complex die making is costly.

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 Forging
TYPES OF FORGING:
 I n forg i n g t h e m a t eri a l is deform ed
a pplyi n g ei t h er impact load or gradual load.

 Based on the type of loading ,

 hammer forging
 Press forging.

 H a m m er forg i n g i nvolves i m pa ct l oa d,
 press forging involves gradual loads.

 Practical examples?
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 classified as ……..
• Based on the nature of material flow and
constraint on flow by the die/punch
– open die forging,
– impression die forging and
– flash less forging.

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 Forging
TYPES OF FORGING:
 O pen di e for g i n g : i n t h i s , t h e wor k pi ece i s com pre s s e d
between two p l a t e n s .
 The meaning of PLATEN is a flat plate; especially : one that exerts or
receives pressure (as in a printing press)
 There is no c o n s t ra i n t to m a t e r i a l flow in l a t e ra l di re ct i on .
 U p s e t t i n g is a n open die forging in which the bi lle t is subjected
to l a t e ra l flow by the f l a t die a n d p u n c h .
 B a r re l i n g :
 D u e to f r i ct i on t h e m a t er i a l f l ow a cr os s t h e t h i ck n es s i s non
u n i fo r m .
 M a t e r i a l a dj a cen t to t h e di e g et s re s t ra i n e d f rom
f lowi ng, wh e re a s , the m a t e r i a l a t center flows freely.
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 Upsetting/Heading
Decreases the length and increases the diameter of the
workpiece; often used to form heads on nails, bolts, etc.
 Forging
TY PE S O F F O RG IN G :

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 Forging
TYPES OF FORGING:
Impression die forging both die a n d p un c h h ave
i m p re s si o n s , s h a pe s which are i m p a r te d onto the work piece.
there is more con st ra i n e d flow in t h i s process.
 Moreover, the excess m e t a l flows out of the cavity,
forming f l a s h .

Flashless forging – in t h i s the work piece is

to t a l ly con st ra i n e d to move w i t h i n die cavity.
 No excess m a t e r i a l a n d hence no f l a s h forms.
 F l a s h l e s s forging involves h i g h level of accuracy.
 D e s i g n of shape of die cavit y, f i n i sh e d product volume are
i m p o r ta n t
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 Forging

TYPES OF FORGING:
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 Open Die Forging
Compresses the work between flat or nearly flat
dies
Fullering: Material
flows out of the
area of
concentration
and both sides,
making the
point of impact
thinner using a
convex
shaped die.

Edging: The
material flows
into the die area
from both sides
using die of
concave shape

Cogging : Process is
used in order to
work material into
the correct
thickness and
increasing length
 Forging
TYPES OF FORGING:
OPEN DIE FORGING:

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Open Die Forging
 Forging
TYPES OF FORGING:
OPEN DIE FORGING:
 F u l l e r i n g a n d e d gin g ope rations are done to reduce the cross
section u s i n g convex sha pe d or concave sha pe d dies.
 M a t e r i a l gets d is t r i b u t e d a n d hence gets elongate d an d
reduction in t h i ck n es s h a p p e n s .
 C o g g i n g operation involves sequence of compressions on ca st
ing ot s to reduce t h i c k n e s s a n d l e n g t h e n t h e m into blooms or
billets.
 F l a t or contoured dies are use d .

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 Open Die Forging
Advantages
Simple,
inexpensive dies;
wide range of sizes;
good strength

Limitations
Simple shapes only;
difficult to hold close tolerances;
machining necessary;
low production rate;
poor utilization of material;
high skill required
 Closed Die Forging
Also called impression-die forging; compresses the
material into the shape of the die cavity
Imprrssion Die Forging
TRIMMING…. Closed Die VS Fleshless Forgiving
 Closed Die Forging
Advantages
1. Good utilization of material;
2. better properties than open die forging;
3. good dimensional accuracy;
4. high production rate;
5. good reproducibility (Concept of Accurate &/ Precise
data set)

Limitations
High die cost for small quantities;
machining often necessary
 Roll Forging
Uses grooved rolls to reduce thickness and increase
length of round or flat bars
Roll Forging
Roll Forging
Roll Forging
 Forging
TYPES OF FORGING:
OPEN DIE FORGING:
 I n ope n di e f org i n g a cy l i n dr i ca l bi l l et i s s u bj e ct ed to
u p s e t t i n g between a pa i r of f l a t dies or p l a t e n s .
 U n der f r i ct i on l e s s h om og en e ou s de for m a t i on , t h e h ei g h t of
the cylinder is reduced a n d its d i a m e te r is i n c re a s e d .
 F or g i n g of s h a f t s , di s k s , r i n g s e t c a re pe r for m e d u s i n g open
die forging t e c h n i q u e .
 S qu a r e ca s t i n g ot s a re con v e r t ed i n t o r ou n d s h a pe by t h i s
process.
 O pen di e for g i n g i s cl a s s i f i ed i n t o t h ree m a i n t y pe s ,
n a me ly, cog g i n g , f u l l e r i n g a n d e dgi n g

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 Forging
TYPES OF FORGING:
CLOSED DIE FORGING:
 I t is also known as impression die forging .

 I mpre ssi on s are made in a pa i r of dies.

 The s e i m pre s si on s are t ra ns fe r re d to the work piece d u r i n g
d e fo r m a t i o n . a s m a l l gap between the dies ca lle d f l a s h g u t te r
 I t is provided so t h a t t he excess metal can flow into the
g u t te r a n d form a f l a s h .
Flash has got a very important role during
deformation.
 D u e to h i g h l e n g th to t h i c k n e s s ratio of the flash gutte r,
friction in the gap is very h i g h .
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 Forgi
TYPES OF FORGING:
ng
C lose d D i e Fo r g i n g :
 D u e to t h i s the m a te r i a l in the f l a s h gap is subjected to
h i g h pres s ure.
1 ) T h ere i s h i g h r es i s t a n ce to f l ow. t h i s
in turn prom ot es effective filling
of the die cavit y.
2 ) I n h ot f org i n g , t h e f l a s h cool s f a s t er a s
a re s u l t of i t being s m a l l e r in si ze .
 T h i s en h a n ces t h e res i s t a n ce of t h e f l a s h m a t er i a l to
deformation re s i s t a n c e .
 A s a re s ul t of t h i s , the b u l k of work piece is forced to deform and
fi ll the die cav i t y more e f fect ively – even i n t r i c a te parts of the
die c av i t y is f i lled
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TYPES OF FORGING:
Forging
C l o s e d D i e Fo r g i n g :

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 Forging
TY PE S O F F O RG IN G

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 Forging
TYPES OF FORGING:
2. EDGING
 E n d s of the bar are shaped to re q u i re m e n t u s i n g e dgi n
dies.
 Swaging
 C r os s s ect i on a l a rea of t h e b a r i s r edu ce d u s i n g con ca v dies.
S wa g i n g

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 Forging
TYPES OF FORGING:
ROLL FORGING
 I n t h i s proce s s , t h e ba r s t ock i s re du ced i n cros s - s e ct i on or
un dergoes c h a n g e in cross-section when it is pa sse d t hro u gh a
pa i r of grooved rolls made of die s te e l .
 T h i s pr oces s s er ves a s t h e i n i t i a l proces s i n g s t e p for
forging of part s such
 as connecting rod, c ra n k s h a f t etc.

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 Forging
TYPES OF FORGING:
ROLL FORGING
 A pa r t i cu l a r t y pe of rol l forg i n g ca l l ed s k ew rol l i n g i s
used for m a k i n g sphe ri ca l b a l l s for ba ll b e a r i n g s .

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Swaging
 Swaging

Uses
Hammerin
g
dies to
Decrease
the
diameter
of the part
 Forging
F O RG I N G D E F E C T S
 T h e di f f ere n t t y pe s of d ef ect s , occu r r i n g i n t h e for g i n g
operations are as follows:
 1. I n comple te die f i l l i n g .
 2. D i e m i s a l i g n m e n t .
 3. Fo r g i n g l a p s .
 4. I n com pl et e for g i n g pen et ra t i on - s h ou l d f or g e on t h e
press.
 5. M i c ro s t r u c t u ra l di f ferences re s u l t i n g in pronounced
property va r i a t i o n .
 6. H ot s h or t n e s s , du e to h i g h s u l ph u r con cen t ra t i on i n
steel a n d n i c ke l .
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 Forging
 F O RG IN G DE F E C TS
 7. Pitted surface, due to oxide scales occurring at high
temperature stick on the dies.
 8. Buckling , in upsetting forging, due to high compressive
stress.
 9. Surface cracking, due to temperature differential between surface
and center, or excessive working of the surface at too low
temperature.
 10. Micro cracking, due to residual stress

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 Forging
 F O RG IN G DE F E C TS
7

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 Forging
 F O RG IN G DE F E C TS
7

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 Forging
 F O RG IN G DE F E C TS
7

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Hot Forged Parts
Cold Forged Parts
Precision Forging
Cargo ship engine crankshaft
 Forging
 TYPES OF FORGING MACHINE
 Work restricted m a c h i n e s (energy or load limited)
 Hammers
 G r a v i t y Drop H a m m e r s
 Power H a m m e r s
 Counterblow H a m m e r s
 Fr i c t i o n Screw P re sse s
 H y d r a u l i c P re sse s
 S t ro ke L i m i t e d ( restricted) Machines – Mechanical
P re sse s
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 Forging
TYPES OF FORGING MACHINE
 MECHANICAL PRESSES DIFFERENT TYPES OF DROP HAMMERS

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 Forgi
TYPES OF FORGING MACHINE
ng
 M e c h a n i c a l board h a m m e r it is a stroke m a c h i n e . re st ri cte d
Re p e a t e d ly the board (weight) is rolls an d is ra i s ed by
dropped on the die.
 R a t i n g i s i n t er m s of wei g h t of t h e ra m a n d en e rg y
delivered.

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 Forging
Types of Fo r g i n g M a c h i n e
 S t e a m h a m m e r (power ha m me r ) ra n g e : 5 K N to 200 K N I t
use s s t e a m in a piston a n d cylinder a r ra n g e m e n t . I t h a s
gre a te r forging capacity.
 it can produce forgings ra n g i n g from a few kgs to
seve ra l ton n e s.
 P re ferre d in closed die fo rg i n g .

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 Forging
TYPES OF FORGING MACHINE
.

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 Forging
TYPES OF FORGING MACHINE
 HYDRAULIC PRESS
 I t is a load re st ri cte d m a c h i n e . I t h a s more of sque e zi n g
action t h a n h a m m e r i n g a c t i o n .
 H en ce di e s ca n b e s m a l l er a n d h a ve l on g er l i fe t h a n wi t h
a hammer.

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 Forging
TYPES OF FORGING MACHINE
Fe a t u r e s of H y d r a u l i c P re ss
 F u l l press load is ava i l a b l e d u r i n g the f u l l stroke of the
ra m .
 R a m vel oci t y ca n be con t r ol l ed a n d va r i ed d u r i n g t h e
st roke .
 I t i s a s l ow s pee d m a ch i n e a n d h en ce h a s l on g e r con t a ct t i me
a n d hence h i g h e r die t e m p e ra t u re s .
 T he slow sque e zi n g action give s close tole ra nce on
fo r g i n g s .
 I n i t i a l cost is h i gh e r compared to h a m m e r s .

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 Forging
TYPES OF FORGING MACHINE
 M e c h a n i c a l press wit h an eccentric drive; the eccentric s h a f t
can be replace d by a c r a n k s h a f t to give the up - and -down
motion to the ra m .

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 Forging
 TYPES OF FORGING MACHINE

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 Forging
TYPES OF FORGING MACHINE

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 Forging
TYPES OF FORGING MACHINE

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 Forging
 TYPES OF FORGING MACHINE
 FORGING HAMMERS •
 G ra v i t y d rop h a m m er s – D rop f or g i n g wi t h a f re e fa l l i n g ra m;
 E n e r g y based on product of ram’s we i ght a n d drop
h e i g h t ram wei ght s of 180-4500 kg (400-10000 lbs)
 Power drop h a m m e r s – downstroke is a c ce le ra te d by s t e a m , air,
or hyd ra u l i c pre ssure ra m we i gh t s of 225- 22500 k g

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 Forging
 TYPES OF FORGING MACHINE
 COUNTERBLOW HAMMERS – TWO RAMS THAT APPROACH EACH OTHER
HORIZONTALLY OR VERTICALLY ( PART MAY BE ROTATED BETWEEN
SUCCESSIVE BLOWS); OPERATE AT HIGH SPEEDS WITH LESS VIBRATIONS
TRANSMITTED – VERY LARGE CAPACITY POSSIBLE HIGH ENERGY RATE
MACHINES – RAM ACCELERATED BY AN INERT GAS AT HIGH PRESSURE;
VERY HIGH SPEEDS BUT PROBLEMS WITH MAINTENANCE, DIE
BREAKAGE, AND SAFETY

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 Forging
 TYPES OF FORGING MACHINE

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 Forgi
ng
 TYPES OF FORGING MACHINE

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 Forging
 TYPES OF FORGING MACHINE

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 Forging
TYPES OF FORGING MACHINE
 Friction screw presses screw presses – flywheel driven, energy
limited (if dies do not completely close, cycle repeats) •
 Small production runs, high precision • 1.4-280 MN (160-
31500 tons).

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 Force Analysis in Forging

UPSETTING OF RECTANGULAR PLATE - ANALYSIS

 C o n s i d e r a r e c t a n g u l a r bill et of h e i g h t ho , width (x axis) ‘2a” and
u n i t depth (z a xi s) .
 L e t t hi s bil let be subjected to pl ane s t r a i n u p s e t t i n g . pl ane s t r a i n
condition here me a n s there is no nor mal and shear s t r a i n along
the z direction – depth di r ection .
 The s l a b unde rgoes s t r a i n only al ong the y a x i s - h e i g h t
direction a nd a l ong the x direction – width di r ection .
 We can m a k e a force bal ance on a s m a l l e l e m e n t a l strip of width
dx , h e i g h t h and u n i t dept h, as shown

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 Force Analysis in Forging
Upsetting

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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS
 Assume that the lateral stress σx is uniform along the height
of the element

 Stresses acting on a small elemental billet of thickness dx and unit

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depth
 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS
Assumptions:
 Compressive stresses are positive.
 Sliding Columbic friction
 Coefficient of friction is low
 The height of the billet is small so that the forging pressure is
constant over the height of the billet.
 Assume that σx and σy are principal stresses

 Here σy is the forging stress necessary at any height h of the billet

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 Force Analysis in Forging
 U p s e t t i n g of r e c t a n g u l a r p l a t e - a n a lys i s
 A s s u m i n g the di me n si on of the bi lle t p e r p e n d i c u l a r to the
pla n e of the paper

 We h ave to e l i m i n a t e because there are two u n k n o w n s in

the above e q u a t i o n . For e l i m i n a t i n g we can a p p ly the von M i s e s
yield criterion for pla n e s t ra i n
 According to t h i s cri te rion, we have :

Note: Y’ is plane strain yield strength of the

material
 Y = u n i a x i a l yield stress
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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

Where L = 2a width of the billet

From the above equation we find that as L/h increases, the forging pressure
increases –resistance to compressive deformation increases.

This fact is utilized in closed die forging where the deformation resistance of flash,
being high [due to high L/h] the die filling is effective.

Note: Y’ is plane strain yield strength of the material

If the material is work hardening type of material, we have to replace Y’ with Y’f
which is the flow stress of the material
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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

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 Force Analysis in Forging
UPSET TING OF RECTANGULAR PLATE-ANALYSIS STICKING FRICTION

 Fr i ct i on a l s h e a r s t res s –μ p
i n cr ea s e s t owa r ds t h e a x i s as the
forging pressure p i n c re a s e s .
 h owev er, t h e m a x i m u m f r i ct i on a l s h ea r
s t r e s s ca n n ot
exceed the s he a r yield s t r e n g t h of the
material.
 wh en t h e l i m i t i n g con di t i on of τ = k , we ca n
sa y s t i ck i n g exi st s a t the i n t e r f a c e .
ge ne r al l y,
 we ca n r el a t e t h e f r i ct i on s h ea r s t r e s s wi t h
s h ea r y i el d s t r e n g t h by the
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relation.
 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

Note: Y’ is plane strain yield strength of the

material

Note:
Y’ is plane strain
yield strength of the
material

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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS
E x a m p l e : A r e c t a n g u l a r block of h e i g h t 40 m m , wi dt h 100 mm an d
depth 30 mm is subjected to upset forging under s l i d i ng friction
condition, with a friction coefficient of 0.2. the ma t e r i a l of the billet
h a s flow stress expressed as: .
Y = 300Ɛ 𝑛 c a l c u l a t e the forging load requi red a t the h e i g h t reduction
of 30%, a s s u m i n g pl ane s t r a i n compression .

S o l u t i o n : due to pl ane s t r a i n a s s u m p t i o n , the depth side of the

block r e m a i n s wit hout d e f o r ma t i o n . we can use the solution obtained
for plane s t r a i n compression . the aver age forging pressure is given
by:

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 Force Analysis in Forging
UPSETTING OF RECTANGULAR PLATE-ANALYSIS

G ive n : ao = 50 m m , ho = 40 m m ,
h f = (1-0. 3)h o = 28 m m , dept h = w = 30 m m .

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 Force Analysis in Forging
To find width after the deformation, we can use volume constancy
2 a 0 h 0 =2ah
a 0 h 0 =ah
50*40 = a*28
a= 71.42 mm

True strain = Ɛ=ln[ ℎ 0 ] = ln[ 40/28]=0.357

ℎ𝑓
Average flow stress = K Ɛ n /(n+1)
Where k is the strength coefficient
We also know the flow stress =σ=Y = KƐ n
n is the strain hardening component.

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 Forging
G i ven t h a t f l ow s t res s va r i a t i on a s
Y = 300Ɛ 0 . 2
Comparing the equation
Flow stress = Y=σ = K Ɛ n
K= 300 n=0.2
So Average flow stress = K Ɛ n /(n+1) = 300(0.357) 0 . 2 /( .2+1)
Average flow stress = 203.4 Mpa
Average forging pressure =
Flow stress = Y=σ = K Ɛ n = 244.14
= 244.14 *(Ɛ) n
= 244.14 * (0.357) 0 . 2
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= 199.41
Average forging pressure =
Forging
= 199.41
µ=.2
a= 71.42
h= 28
So average forging pressure = 353.59 59 Mpa
Average forging load = 353.59 x 71.43 x 30 = 757. 7KN

2/16/2025
Thank you