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Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton Bulk Deformation - 1 ME 206 Manufacturing Processes 1

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Page 1: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Bulk Deformation - 1

ME 206Manufacturing Processes 1

Page 2: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

2

Outline

• What is bulk deformation?

• Cold vs hot working

• Forging introduction

• Forging analysis

• Forging defects

Page 3: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

3

What is bulk deformation?• Bulk deformation (or forming): processes

characterized by large amount of plastic deformation (large strains) carried out at elevated or room temperature

• Bulk plastic flow of material under uniaxial or multi-axial stresses dominated by compression

• Mass conserving processes à volume is constant

Page 4: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes &

Engineering

Instructor: Ramesh Singh Notes by Prof.

S.N. Melkote

4

Bulk Deformation Processes

• Examples include: forging, rolling, extrusion, rod

drawing etc.

Forging (heading)

Extrusion Rod Drawing

Rolling

Page 5: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

5

Cold vs Hot Working

• Many bulk deformation processes carried out at elevated temperatures

• Cold working: T < 0.3Tm– Usually a finishing step

• Warm working: T = 0.3~0.5Tm– Intermediate or final step

• Hot working: T > 0.5Tm– Initial step

Page 6: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes &

Engineering

Instructor: Ramesh Singh Notes by Prof.

S.N. Melkote

6

Cold Working

Advantages

– Better dimensional control

– Superior surface finish

– Strain hardening of surface layer can be

beneficial

Limitations

– Greater material strength à higher forces

– Stronger tooling required

– Lower ductility à small deformations

– Lower malleability à harder to shape material

– Anisotropic surface properties

Page 7: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes &

Engineering

Instructor: Ramesh Singh Notes by Prof.

S.N. Melkote

7

Hot Working

Advantages

– Lower yield strength à lower forces

– High ductility à larger strains possible

– Higher malleability à easy to shape metal

Limitations

– Easily forms oxide layers (scales) on surface àpoor surface finish

– Harder to control dimensions

Page 8: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

8

• Shape change via compressive forces• Types of forging processes

– Open die forging (upsetting)

– Closed or impression die forging

Forging

hi hf

flash

Page 9: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

9

• Carried out between flat dies• Parts weighing few lbs ~ 150 tons e.g. solid

shafts, spindles/rotors, rings, etc.• Often carried out in steps• Wide range of ferrous and non-ferrous metals

Open Die Forging

Stepped shaft Spindles

Source: http://www.forging.org

Page 10: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

10

• Carried out between shaped dies• Parts weighing few ounces ~ 25 tons e.g.

crankshafts,connecting rods, aircraft parts etc.• Most engineering metals: carbon steels,

stainless steels, aluminum, bronze, etc.

Closed Die Forging

Aircraft bulkhead Connecting rods

Source: http://www.forging.org

Page 11: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forgings

• Coins• Landing gear• Crank shafts• Turbine shafts

Page 12: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging presses

• Large machines– hold dies– form parts

Page 13: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Press types• Servo-hydraulic presses• Servo-electrical presses• Mechanical presses• Screw presses• Hammers

– gravity drop– power drop– counter blow (two rams)– high pressure gas

Page 14: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

50,000 ton press

Page 15: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forges

Schematic illustration of the principles of various forging machines. (a) Hydraulic press. (b) Mechanical press with an eccentric drive; the eccentric shaft can be replaced by a crankshaft to give the up-and-down motion to the ram. (continued)

Page 16: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forges

Schematic illustration of the principles of various forging machines. (c) Knuckle-joint press. (d) Screw press. (e) Gravity drop hammer.

Page 17: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging steps

• Prepare slug– saw– flame cut– shear

• Clean slug surfaces – shot blast– flame

Page 18: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging steps• For hot forging

– heat up and descale forging– make sure press is hot

• Lubricate– oil– soap– MoS2

– glass– graphite

Page 19: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Lubrication purposes

• Reduce friction• Reduce die wear• Thermally insulate part

– to keep it warm

Page 20: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging steps• Forge• Remove flash

– trim– machine

• Check dimensions• Post processing, if necessary

– heat treat– machine

Page 21: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Effect on grain structure

• Large grains are broken up.• Grains can be made to flow.

Page 22: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Dies• Final part shape determined by die

accuracy• Multiple parts can be made in one die• Progressive shaping can be done in one

die set• Need to be stronger than highest

forging stress

Page 23: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

23

• Simple stress analysis possible for open die forging process

• Analysis method called “slab” analysis• Applicable to plane strain compression with

low sliding friction

Forging Analysis

Source: http://www.forging.org

hi hf

Page 24: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Slab analysis assumptions• Entire forging is plastic

– no elasticity• Material is perfectly plastic

– strain hardening and strain rate effects later• Friction coefficient (µ) is constant

– all sliding, to start• Plane strain

– no z-direction deformation• In any thin slab, stresses are uniform• Three conditions exist: All sliding; Sliding-

sticking transition and Fully sticking

Page 25: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Open die forging analysis –rectangular part

F

F

h

w

dx

yx

unit depthinto figure

Page 26: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Expanding the dx slice on LHS

• p = die pressure• sx, dsx from material on

side• tfriction = friction force = µp

p

p

sx sx + dsx

tf

tf

Page 27: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Force balance in x-direction

p sx

k

dxh

d

dxhd

frictionx

frictionx

ts

ts

202

-=

=+

Mohr’s circle

(distortion energy (von Mises) criterion, plane strain)

flowflowx kp sss ×===+ 15.1322

N.B. all done on a perunit depth basis

Page 28: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Force balanceDifferentiating, and substituting into Mohr’s

circle equation

noting: tfriction = µp

pdxh

dpµ2

= dxhp

dp µ2=

( ) ( )

dxh

dpdxh

d

ddppdkd

frictionfrictionx

xx

÷÷ø

öççè

æ=\-=

-=\+=

tts

ss22

2

Page 29: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Sliding region

• Noting: @ x = 0, sx = 2k = 1.15 sflow

dxhp

dp xp

k

x

òò =02

Page 30: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging pressure – sliding region

( )

÷øö

çèæ××=

÷øö

çèæ=

=-

hx

p

hx

kp

hxkp

flowx

x

x

µs

µ

µ

2exp15.1

2exp2

22lnln

Sliding region result (0 < x < xk)

N.B done on a per unit depth basis

Increasing µ

X

÷÷ø

öççè

æ

f

y

Y15.1s

0

1

Page 31: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging pressure –approximation

• Taking the first two terms of a Taylor’s series expansion for the exponential about 0, for

÷øö

çèæ +=

hx

kpx µ212

1£x

yields

( ) å=

=+++++=n

k

kn

kx

nxxx

xx0

32

!!!3!21exp !

00

÷øö

çèæ +××=

hxp flowxµs 2115.1

Page 32: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Average forging pressure –all sliding approximation

• using the Taylor’s series approximation

2

22

2

21

2

22

2

0

22

0

2

0

whxx

w

dxhx

w

dxkp

kp

www

x

ave÷÷ø

öççè

æ+

=÷øö

çèæ +

==òò

µµ

N.B done on a per unit depth basis

÷øö

çèæ +=

hw

kpave

21

÷øö

çèæ +××=

hwp flowave 2

115.1 µs

Page 33: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging force –all sliding approximation

depthwhwF flowforging ××÷øö

çèæ +××=

2115.1 µs

depthwidthpF aveforging ××=

Page 34: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

ME 4210: Manufacturing Processes & Engineering

Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

34

Example Problem

A rectangular workpiece has the following original dimensions: w = 100 mm, h = 25 mm, and depth d= 20 mm and is being open die forged in plane strain. The true stress-true strain curve of the metal is given by MPa and the coefficient of friction is µ = 0.3. Calculate the forging force required to reduce the height by 20%. Use both the “exact” and the average pressure methods.

5.0400 tt es =

w

h

Page 35: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Slab - die interface• Sliding if tf < tflow

• Sticking if tf ³ tflow– can’t have a force on a material

greater than its flow (yield) stress– deformation occurs in a sub-layer just

within the material with stress tflow

slidingregion

stickingregion

Page 36: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Sliding / sticking transition• Transition will occur at xk

• using k = µp, in:

• hence:

µµ 21ln

21

=hxk

÷øö

çèæ=hx

kpx µ2exp2 ÷

øö

çèæ=hx

kk kµµ

2exp2

Page 37: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Sticking region

• Using p = k/ µ

pdxh

dpµ2

=

( )kxx xxhkpp

k-=-

2dx

hk

dpx

x

p

p k

x

kx

òò =2

dxkh

dpµ

µ2=

Page 38: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Sticking region

We know that • at x = xk, pxk

= k/µ

• and µµ 21ln

21

=hxk

Page 39: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging pressure - sticking region

hx

kpx +÷÷

ø

öççè

æ÷÷ø

öççè

æ-=

µµ 21ln1

21

2

Combining (for xk < x < w/2)

úúû

ù

êêë

é+÷÷ø

öççè

æ÷÷ø

öççè

æ-××=

hxp flowx µµ

s21ln1

2115.1

Page 40: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging pressure –all sticking approximation

• If xk << w, we can assume all sticking, and approximate the total forging force per unit depth (into the figure) by:

x=0 x=w/2

0

pedge

Dp

Page 41: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging pressure –all sticking approximation

kpedge 2=

÷øö

çèæ +××=

÷øö

çèæ +=\

hx

p

hx

kp

flowx

x

115.1

12

s

( )xhk

kpx22 =-dx

hk

dpxp

k

x

òò =02

2

Page 42: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Average forging pressure –all sticking approximation

22

2

1

22

2

2

0

22

0

2

0

w

hxx

w

dxhx

w

dxkp

kp

www

x

ave÷÷ø

öççè

æ+

=÷øö

çèæ +

==òò

÷øö

çèæ +=

hw

kpave

41

2

÷øö

çèæ +××=

hwp flowave 4

115.1 s

Page 43: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging force –all sticking approximation

depthwhwF flowforging ××÷øö

çèæ +××=

4115.1 s

depthwidthpF aveforging ××=

Page 44: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Sticking and sliding• If you have both sticking and sliding, and you

can’t approximate by one or the other,• Then you need to include both in your

pressure and average pressure calculations.

( ) ( )stickingaveslidingaveforging ApApF ×+×=

stickingslidingforging FFF +=

Page 45: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Material Models

nflow KY es ==

Strain hardening (cold – below recrystallization point)

Strain rate effect (hot – above recrystallization point)

( )mflow CY es !==

heightousinstantanevelocityplaten

hv

dtdh

h1ε ===!

Page 46: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-1• Lead 25 mm x 25 mm x 900 mm • sy = 6.89 MPa• hf = 6.25 mm, µ = 0.25• Show effect of friction on total forging force.• Use the slab method.• Assume it doesn’t get wider in 900 mm

direction.• Assume cold forging.

25

25

900

Page 47: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-2• At the end of forging:hf = 6.25 mm, wf = 100 (conservation of mass)

• Sliding / sticking transition

"347.025.02

1ln25.0225.021ln

21

=´´

=

=

k

k

x

hx

µµ

Page 48: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-3

• Sliding region:

( )xhx

pf

flowx

2exp1150

2exp15.1

×=

÷÷ø

öççè

æ××=

µs

Page 49: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-5

020004000600080001000012000

0 0.5 1 1.5 2 2.5 3 3.5 4

Distance from forging edge (in)

Forg

ing

pres

sure

(psi

)

P(sticking)P(sliding)

stickingsliding slidingfriction hill

xkxk

Page 50: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-6

• Friction hill– forging pressure must be large (8.7x) near the

center of the forging to “push” the outer material away against friction

Page 51: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-7

• Determine the forging force from:

• since we have plane strain

dApForce òò ×=

dxpdepthunitF x

xò=0

Page 52: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-8

• We must solve separately for the sliding and sticking regions

sticking

w

xx

sliding

x

xforging depthdxpdepthdxpFk

k

÷÷

ø

ö

çç

è

æ

÷÷ø

öççè

æ+÷

÷ø

öççè

æ÷÷ø

öççè

æ= òò .2.2

2/

0

Page 53: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-16or since the part is 36” deep:F(both) = 337 Tonnes

F(all sticking) = 363 tonnes

F(all sliding) = 496,800 lbs = 218 tonsCan we use exact solution for this???All sticking over-estimates actual value.

depthwhw

F flowforging ××÷øö

çèæ +××=

4115.1 s

depthwhw

F flowforging ××÷øö

çèæ +××=

2115.1 µs

Page 54: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging – Effect of friction• Effect of friction coefficient (µ) – all sticking

• Friction is very important

Friction coefficient Fmax (lbf/in depth) xk Stick/slide0 4600 2 slide

0.1 11365 2 slide0.2 19735 0.573 both

0.25 21331 0.347 both0.3 22182 0.213 both0.4 22868 0.070 both0.5 23000 0 stick

Page 55: Bulk Deformation -1ramesh/courses/ME206/Bulkdef1.pdf• Bulk deformation (or forming): processes characterized by large amount of plastic deformation (large strains) carried out at

Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-17Forging force vs. stroke – all sticking

0

5000

10000

15000

20000

25000

0 0.2 0.4 0.6 0.8Stroke (in)

Forg

ing

forc

e (lb

f/in

dept

h)

mu=0mu=0.1mu=0.2mu=0.25mu=0.3mu=0.4mu=0.5

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Prof. Ramesh Singh, Notes by Dr. Singh/ Dr. Colton

Forging - Ex. 1-19Maximum forging force vs. friction coefficient (µ)

all sticking

0

5000

1000015000

20000

25000

0 0.1 0.2 0.3 0.4 0.5 0.6Friction coefficient

Max

forg

ing

forc

e (lb

f/in

dept

h)

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57

Deformation WorkIn general, work done in bulk deformation processes has three

components

Total work, W = Wideal + Wfriction + Wredundant

Work of ideal plastic deformation, Wideal

= (area under true stress-true strain curve)(volume)

= (volume)

For a true stress-true strain curve :

÷÷ø

öççè

æò ttdt

ese

0

ntt Kes =

( ) ( ) tf

nt

ideal YnKW ee

volume1

volume1

=÷÷ø

öççè

æ+

=+

stress flow Avg. =fY

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58

Deformation Work

Friction between dies and workpiece causes inhomogeneous (non-uniform) deformation called barreling

Barreling Effect

Frictional Forces

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Deformation Work

Internal shearing of material requires redundant work to be expended

Ideal Deformation Redundant Deformation

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Redundant Zone

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Engineering

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S.N. Melkote

61

Closed/Impression Die Forging

• Analysis more complex due to large variation in

strains in different parts of workpiece

• Approximate approaches

– Divide forging into simple part shapes e.g. cylinders,

slabs etc. that can be analyzed separately

– Consider entire forging as a simplified shape

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Instructor: Ramesh Singh Notes by Prof. S.N. Melkote

62

Closed/Impression Die Forging

Steps in latter analysis approach• Step 1: calculate average height from volume V

and total projected area At of part (including flash area)

• Step 2:

LwV

AVht

avg ==

÷÷ø

öççè

æ==

avg

iavg h

hlnstrain avg.e

avgavg h

v== ratestrain avg.e!

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63

Closed/Impression Die Forging

• Step 3: calculate flow stress of material Yf for cold/hot working

• Step 4:

Kp = pressure multiplying factor= 3~5 for simple shapes without flash= 5~8 for simple shapes with flash= 8~12 for complex shapes with flash

tfpavg AYKF == load forging Avg.

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64

Other Analysis Methods

• Complex closed die forging simulated using finite element software

Source: http://nsmwww.eng.ohio-state.edu/html/f-flashlessforg.html

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65

Forging Defects

• Surface cracking due to tensile stresses

• Internal cracking in thick webs

Surface Crack

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Forging Defects

• Laps due to buckling of thin webs

• Cold shuts due to small radii fillets in die

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Summary

• What is bulk deformation?• Cold vs hot working• Forging analysis

– Slab analysis• Forging defects