Classification of Deformation Processes

Chapter 6. Bulk Deformation Processes

Processes

Sung-Hoon Ahn

School of Mechanical and Aerospace Engineering

Classification of Deformation Processes

ƒ Temperature

ƒ

Hot working(열간가공)Hot working(열간가공)

T > 0 . 6 T

ƒ

Warm working(온간가공)

ƒ

Cold working(냉간가공)

T

m

T > 0 . 6

T

m

T = 0 . 3 ~ 0 . 5 T

m

T < 0 . 3

ƒ Type of operation

ƒ

Primary working(1차가공) : solid piece of metal(금속괴) → slabs(슬래브), plates(후판) billets(빌랫)

plates(후판), billets(빌랫).

ƒ

Secondary working(2차가공) : products from primary working(1차가공품) → bolts(볼트), sheet metal parts(금속판재품), wire(선재).

ƒ Size and shape of the workpiece

ƒ

Bulk deformation(부피성형가공) : thickness or cross section of the work-( ) piece changes(forging(단조), rolling(압연), extrusion(압출), drawing(인발)).

ƒ

Sheet forming(판재성형가공) : generally shape changes, thickness changes are undesirable

are undesirable.

Forging (단조) (1) g g ( ) ( )

Bellows / Blower(풀무)

Anvil(모루)( )

Forging (단조) (2) g g ( ) ( )

ƒ Plastic deformation of the workpiece is carried out by compressive forces

forces.

ƒ Crankshafts, connecting rods, turbine disks, gears, wheels, bolt , g , , g , , heads, hand tools, etc.

ƒ The recrystallization temperature(재결정온도) for metals :

ƒ Basic categories of forging

5 . 0

~ / T

_m

T

ƒ Basic categories of forging

ƒ

Open die(자유단조)

ƒ

Impression die(형단조)

ƒ

Closed die(폐쇄단조)

Open-die forging (자유단조) g g ( )

ƒ Reducing the height of workpiece between two flat dies by compressing it.

compressing it.

Forces and work of deformation

height in

Reduction

h h

ln

% 100

0 1

0

0 1 0

⎟⎟⎞

⎜⎜⎛

−

− ×

=

h h

e h

h h h

ε

,

ln

,

1 1

1 0 1

0 1 0 1

−

=

−

=

⎟⎟⎠

⎜⎜⎝

=

=

h v h

e v

h e h

ε ε

&

&

Relative velocity

b h l

,

1 0 0 1

1

1 0

=

=

h

h A A

YA F

h

h between the plates

( )

^{( )}

) (

,

,

1 1

0

1

1

volume Work

volume Work

=

=

=

=

∫

Y A

Y F

K d

f

n

ε ε σ

ε

ε

σ

( )

1

) ( ) (

,

1 1

0

1 1

1

volume Work

= +

=

∫

n d K

K Y

Y A

Y F

n n f

ε ε

ε ε

ε

ε

1

n

+1

ε

(Y_f

: Flow stress, Y : Average flow stress)

^Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Methods of analysis - Slab method (1)

0 2

)

( σ

_x

+ d σ

_x

h + μσ

_y

dx − σ

_x

h = Horizontal forces :

2 0

=

+ dx

d

_x

μσ h

^y

σ ^ⓐ

U i di t ti it i f l t i

Y σ Y

σ − = 2 = ^′

: Average flow stress

Using distortion-energy criterion for plane strain

Methods of analysis - Slab method (2)

2 μσ

ⓐ

&

ⓑ

give

h y x

y y

Ce d dx

h dx d

/ 2 O.D.E

2

2 0

σ μ

σ μ

σ μσ

=

−

⎯

⎯ →

⎯

−

=

= +

y y

Ce h dx σ

σ ^→

specimen the

of edges at the

'

0

,

: conditions

Boundary x = a σ

_x

= ⎯ ⎯→ σ

_y

= Y

' '

/ ) ( 2

/ 2

e Y p

e Y C

h x a y

h a

=

=

=

σ ^μ

−

μ

1 '

] 1 [

'

'

^{2 ( )/}

Y a

e Y

Y

^{a x h}

y x

y

⎟ ⎞

⎜ ⎛ +

−

=

−

=

⁻

μ σ

σ ^μ

A ) )(

2 )(

(

1 '

width a

p F

Y h p

av av

=

⎟ ⎠

⎜ ⎝ +

≈ μ

pressure

Average

:

force Forging

:

Methods of analysis - Slab method (3)

Die pressure

Rectangular Specimen

Methods of analysis - others

ƒ Slip-line analysis(미끄럼선 해석)

ƒ Upper bound technique(상계해법)

ƒ Upper-bound technique(상계해법)

ƒ Finite element method(유한요소법)

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Impression-die/closed-die forging(형단조)(1) g g( )( )

ƒ Impression-die forging : the workpiece acquires the shape of the die cavities (impressions) while it is being upset between the closing dies.

( p ) g p g

ƒ

Flash(플래쉬) : significant role in the flow of material.

ƒ

Forces in impression-die forging : depending on its position, F=KpYfA.

ƒ

Land(랜드부) : controlling the forging load not to be excessive.

ratio L

h

Plane strain

) )(

)(

( K Y A

F = _{p f}

Impression-die/closed-die forging(형단조)(2) g g( )( )

ƒ Closed-die forging(폐쇄단조) : no flash is formed and the workpiece is completely surrounded by the dies.

Precision forging(정밀단조) flashless forging(밀폐단조) : the part formed is close to the final

ƒ

Precision forging(정밀단조), flashless forging(밀폐단조) : the part formed is close to the final dimensions, high forging load & capacity equipment needed.

ƒ

Isothermal forging(등온단조), hot-die forging(가열금형단조) : the dies are heated to the same temperature as the hot blank.

temperature as the hot blank.

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Closed-die forging (폐쇄단조) g g ( )

ƒ Orbital forging(궤도단조)

Miscellaneous forging operations (1)

ƒ Coining(코이닝)

ƒ an example of closed-die forging an example of closed die forging

ƒ minting of coins.

ƒ Heading(헤딩) – Fig 6.17

ƒ Piercing(천공) Fig 6 18

ƒ Piercing(천공) – Fig 6.18

ƒ Hubbing(허빙)

ƒ Cogging(코깅)

ƒ Fullering and edging(풀러링, 에징)

ƒ Role forging(압연단조)

ƒ Skew-rolling(강구전조작업)Skew rolling(강구전조작업)

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Miscellaneous forging operations (2)

Cogging Roll forging(Cross rolling)

Miscellaneous forging operations (3)

Steel balls by skew-rolling

Steel balls by y upsetting

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Defects in forging (1)

ƒ Caused by the material flow patterns in the die cavity.

ƒ Cold shut

ƒ Cold shut.

ƒ Grain flow pattern, end grain.

Buckling g

Over sized billet

Defects in forging (2)

Grain flow pattern Grain flow pattern

(단류선 영향)

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Die design (1)

ƒ The most important rule in die design : the workpiece material flow in the direction of least resistance.

ƒ Considerations

ƒ Strength and ductility of the workpiece material.

S i d

ƒ Strain rate and temperature.

ƒ Frictional characteristics.

ƒ Die distortion under high forging loads

loads.

ƒ Die design parameters

ƒ Flash clearance between the

ƒ Flash clearance between the dies : 3% of the max. thickness.

ƒ Length of the land : 5 times of the flash clearance.

flash clearance.

ƒ Proper radii for corners and fillets.

Die design (2)

ƒ Draft angles : Internal angles(7~10°) > External angles(3~5°)

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Forging equipment

ƒ Hydraulic presses(유압프레스)

ƒ Mechanical presses(기계프레스)Mechanical presses(기계프레스)

ƒ Screw presses(나사프레스) : for parts requiring precision(turbine blades) and control of ram speed.

H (해머) i l f h i d ki i

ƒ Hammers(해머) : potential energy of the ram is converted to kinetic energy.

ƒ Counterblow hammers(카운터블로해머)

Rolling (압연) g ( )

ƒ The process of reducing the thickness or changing the cross-section of a long workpiece by compressive forces applied through a set of rolls.p y p pp g

ƒ Plate(후판) : t ≥6mm / sheet (박판) : t ≤ 6mm

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Changes in the grain structure

W ht t t

Wrought structure

(단련 구조)

Mechanics of flat rolling

ƒ The velocity of strip must increase as it moves through the roll gap.

Slidi b t th ll d th t i d t

ƒ Sliding occurs between the roll and the strip due to the surface speed of the roll is constant.

ƒ Neutral point or no slip point(중립점)

L ft f t l i t k i l it ll l it

ƒ

Left of neutral point : workpiece velocity < roll velocity

ƒ

Right of neutral point : workpiece velocity > roll velocity

ƒ The frictional forces oppose each other at the neutral

point (F > F )

point. (F

friction_left

> F

friction_right

)

→ yielding a net frictional force to the right.

r r f

V V V −

= slip Forward

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Roll pressure distribution (1)

Roll pressure distribution (2)

) (

0 cos 2

sin 2

) )(

(

σ

φ φ μ σ

φ φ σ

σ

h d

pRd h

pRd dh

h

d

_{x x}

x

+ + − − ± =

_f

R h h

R h

h

φ

φ +

− +

= 2 ( 1 cos )

2

) 1 cos , sin

( , ) (

) 2 (

) cos (sin

) 2 (

φ φ

φ μ

φ φ σ

φ μ φ φ

σ

Q m

m d pR

h d

d pR h d

x

x

≈

≈

=

=

f f

f f

h C R h

R R

h Y

p

R h h

φ μ

φ

+

′ = +

=

−

ln

tan 2

ln

ln

¹

2

m

) (

] 2 ) [(

3 2

μ φ σ

m h pR

Y p d

Y Y p

f

f f x

′ =

−

= ′

=

−

^H

f

R R

R e Y h C

p

^μ

⎟ ⎞

⎜ ⎛

= ′

1 m

) (

2 1

) (

2

μ φ φ

μ φ φ

m m pR Y h

Y p d

d

d pR

f

f

=

⎥ ⎥

⎦

⎤

⎢ ⎢

⎣

⎡

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛ −

′ ′

=

Hi

f f

h e C R

h R h

H R

μ

φ

=

⎟ ⎟

⎜ ⎠

⎜

⎝

=

⁻

: zone entry In the

tan

2

¹

) (

2

1 φ μ

φ

φ d ^{Y h pR m}

d Y

p Y

p d h d

Y

_f

f f

f

f

⎞

⎛

′ =

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛ −

+ ′

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛

′ ′

⎦

⎣ ⎝ ⎠

h

f

) (H H o

f

e

o

h Y h

p = ′

^{μ −}

) 2 (

/ φ μ

φ m

h R Y

p Y

p d

d

f

f

=

′

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛

′

h

f

C = R : zone exit In the

h

H

Y

′ ^μ

f

f

e

Y h

p

= ^μ

Neutral point / front and back tension

=

=

₂^H_H ^{(H −2H )}

f

o

e

e e h

h

_{o n}

n

o μ

μ μ

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛ −

= 1 ln

2 1

f o o

n f

h H h

H h e

μ

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛ ⋅

=

^f

tan

^f

2

ⁿ

n

H R h R

φ h

h

_{( )}

)

( :

zone

Entry

^{H H}

o b f

e

o

h Y h

p = ′ − σ

^{μ −}

H f

f

e

h Y h

p ( σ )

^μ

:

zone

Exit = ′ −

f f

f

h

p ( )

′ )

(

slip roll cause to

required on

Back tensi 6.3

Exmple

Ho

f

e Y h

p σ

^μ

⎤

⎡ ⎜ ⎛ ⎟ ⎞

−

=₀

= ( )

^o

o f b f

h h e Y

p

_φ

σ

^μ

Defects in rolling

ƒ Surface defects

ƒ Structural defects

Structural defects

ƒ Residual stresses

ƒ In the case of small-diameter rolls or small reductions plastic deformation small reductions, plastic deformation occurs on the surfaces.

→ compressive stresses(surfaces), t il t (b lk)

tensile stresses(bulk).

ƒ In the case of large-diameter rolls or high reduction, plastic deformation

f th b lk i t th th

of the bulk is greater than the surfaces.

→ tensile stresses(surfaces), compressive stresses(bulk)

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Flat-rolling practice (평판 압연 작업) g ( )

ƒ Hot rolling : converts the coarse-grained, brittle and porous cast structure to wrought structure(finer grains and enhanced ductility) structure to wrought structure(finer grains and enhanced ductility).

ƒ Products of the first hot-rolling operation g p

ƒ

Bloom : square cross-section(정사각형), at least 150mm side, structural shapes by shape rolling(e.g. I-beam and railroad rails).

Slab : rectangular in cross section(직사각형) plates and sheet

ƒ

Slab : rectangular in cross-section(직사각형), plates and sheet.

ƒ

Billet : square cross-section(정사각형) smaller than bloom, various shapes (e.g. round rods(환봉강) and bars)

ƒ Rolling equipment

Small diameter rolls are preferable because the smaller the roll radius the

ƒ

Small-diameter rolls are preferable, because the smaller the roll radius the lower the roll force. However, small rolls deflect under roll forces and have to

Rolling equipment

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Miscellaneous rolling operations (1)

ƒ Shape rolling(형상압연) : H-section part, I-Beam and channels.

ƒ Ring rolling(링압연) : rings for rocket, turbines and gearwheel rims.g g( ) g g

ƒ Thread and gear rolling(나사 및 기어전조) : high production rates, great strength, improved fatigue life.

ƒ Rotary tube piercing(회전천공) : hot working process to make long thick walled

ƒ Rotary tube piercing(회전천공) : hot-working process to make long, thick-walled seamless tubing.

Miscellaneous rolling operations (2)

ƒ Ring rolling

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Miscellaneous rolling operations (3)

ƒ Thread and gear rolling

Miscellaneous rolling operations (4)

ƒ Rotary tube piercing

ƒ

Thick walled seamless tube

ƒ

Thick-walled seamless tube.

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Extrusion (압출) ( )

Direct extrusion(직접압출) : high friction between billet and wall

Indirect extrusion(간접압출) : no friction between billet and wall, die moves to the billet.

Mechanics of extrusion (1)

ratio, Extrusion

A R A

f

= o

ln ln

1 ln R

L L A

A

o f f

o ⎟⎟ =

⎠

⎜⎜ ⎞

⎝

= ⎛

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

= ⎛ ε

) )(

)(

( Work

1

u L A

Y u

o

= o

=

⎠

⎝

ε

Energy dissipated in plastic deformation per unit volume

) )(ln (

ln Work

R A Y

Y u p

L pA FL

o

o o o

⎟ =

⎟ ⎞

⎜ ⎜

= ⎛

=

=

=

) )(ln (

ln Y R

Y A u p

f

⎟ =

⎟

⎜ ⎠

⎜

= ⎝

=

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Mechanics of extrusion (2)

⎟⎟ −

⎜⎜ ⎞

⎛ +

= Y R

p tan [( ) 1 ] 1 α

_μ^cot_α

When friction is included

=

+

=

⎟⎟ ⎠

⎜⎜ ⎝ +

t t l

friction plastic

total

D pV P

P P

P

R Y

p

) 4 / (

] 1 )

[(

1

2

π

0

μ

=

=

f o o

friction

f o o

plastic

o total

D D Y

D V

P

D D Y

D V P

D pV P

) / ln(

) 2 / )(

2 / )(

(

] ) / )[ln(

)(

4 / (

) 4 / (

2 0

2 2

0

0

π π

π

=

=

=

_{o f o f}

R Y p

D D D

D Y

p

ln 7 1

] ) / [ln(

7 . 1 ) / ln(

41 . 3

/

²

⎟⎟ =

⎠

⎜⎜ ⎞

⎝

⎛

=

o

friction

D D kL

p

R Y p

) 4 (

ln 7 . 1

2

0

π

π

=

=

o o

friction

D Y L D k L

p 4 2

) ln (

: forces

Actual

p

=

Y a

+

b R

Defects in extrusion

ƒ Surface cracking(표면균열)

ƒ Too high extrusion temperature, friction, or extrusion speed.

ƒ Periodic sticking of the extruded product along the die land.

ƒ Extrusion defect(파이프결함)

ƒ Surface oxides and impurities drawn toward the center of the billet.

ƒ Reduced by modifying the flow pattern, machining the surface of the billet or using a dummy block.

ƒ Internal cracking(내부균열) : due to hydrostatic tensile stress at the center line Internal cracking(내부균열) : due to hydrostatic tensile stress at the center line.

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Drawing (인발) g ( )

ƒ The cross-sectional area of a bar or tube is reduced by pulling it through a converging die.

ƒ Rod and wire drawing are usually finishing process

ƒ Rod and wire drawing are usually finishing process.

⎟ ⎞

⎜ ⎛ A

o

Y l

=

⎟ ⎟

⎜ ⎠

⎜

= ⎝

n f o d

K Y ln A

ε σ

σ

= +

ⁿ

n Y K

1 ε

1

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

= ⎛

f o

f

A

A A Y

F ln

Defects in drawing

ƒ Similar to defects in extrusion.

ƒ Seams(솔기결함) : longitudinal scratches or folds in the material. ( ) g

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Swaging (스웨이징) (1) g g ( ) ( )

ƒ The metal flows in to the dies which apply compressive force pp y p or impact to the metal at room temperature.

ƒ Rotary swaging(회전 스웨이징) :

ƒ Rotary swaging(회전 스웨이징) : a solid rod or a tube is reduced in diameter by reciprocating radial mo ement of dies

radial movement of dies.

ƒ The Internal diameter and

thickness or shape of the tube

can be controlled with or without

mandrels(맨드릴).

Swaging (스웨이징) (2) g g ( ) ( )

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Case study (Space shuttle)

Solid rocket casing

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Forging processes for solid rocket casing