02_rolling_bulk forming

Forming Technology

Bulk Forming

02_Rolling

2.215/16 L02 Rolling

Content

L02 – Rolling

IntroductionFlat-longitudinal rolling

FundamentalsKinematicsBite and deformation conditionsStress state

Product propertiesProcess variants


Content

L02 – Rolling





Roll gapRolling stock

Roll

Principles of longitudinal rolling

Upper roll

Lower roll

Rolling stock

Profile

Profile roll

The rolling stock is compressed within its thickness and it is

elongated in longitudinal direction

Flat rolling

Profile rolling

Roll design for longitudinal shapes

Process principle

Product


Classification of rolling processes accordingto DIN 8583

Tool kinematics: Longitudinal, cross and skew rolling

Tool geometry: Flat and profile rolling

Workpiece geometry: Solid and hollow body

Longitudinal rolling Cross rolling Skewed rolling


Rolling

Classification of rolling processes accordingto DIN 8583

Longtidunal rolling Cross rolling Skewed rolling

Source: Lange Vol. I – (DIN 8583)

Flat

-Lo

ngitu

dina

l ro

lling

Prof

ile-

Long

itudi

nal

rollin

g

Flat

-C

ross

rollin

g

Prof

ile-

Cro

ss ro

lling

Flat

-Sk

ewed

rollin

g

Prof

ile-

Skew

ed ro

lling

Flat

-Lon

gitu

dina

l rol

ling

of s

olid

pro

duct

s

Flat

-Lon

gitu

dina

l rol

ling

of h

ollo

w p

rodu

cts

Prof

ile-L

ongi

tudi

nal

rollin

g of

sol

id p

rodu

cts

Prof

ile-L

ongi

tudi

nal

rollin

g of

hol

low

pr

oduc

ts

Flat

-Cro

ss ro

lling

of s

olid

pro

duct

s

Flat

-Cro

ss ro

lling

of h

ollo

w p

rodu

cts

Prof

ile-C

ross

rollin

gof

sol

id p

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cts

Prof

ile-C

ross

rollin

gof

hol

low

pro

duct

s

Flat

-Ske

wed

rollin

gof

sol

id p

rodu

cts

Flat

-Ske

wed

rollin

gof

hol

low

pro

duct

s

Prof

ile-S

kew

ed ro

lling

of s

olid

pro

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s

Prof

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of h

ollo

w p

rodu

cts


Content

L02 – Rolling





Flat-longitudinal rolling

Source: Kopp

Thickness change Thickness reduction ∆h

∆h = h0 - h1

Relative thickness change εh:εh = (h1 - h0) / h0 = ∆h / h0

Compression ratio γ:γ = h1 / h0 (γ < 1)

Width change

Mean width

Spreading ratio β:β = b1 / b0 (β ≥ 1)

Reduction per pass ∆A∆A = A0 - A1

Equivalent strain (von Mises) (Plane strain)


Deformation zone of the flat-longitudinal rolling

α0: Rolling angle

x: Horizontal coordinate in roll gap (0 < x < ld)

ld: Compressed length (length of roll gap in rolling direction)

h(α), h(x) Local plate thickness in roll gap

hm Mid plate thickness hm = 0.5 (h0+h1)

ld / hm Roll gap ratio (also ld / h0)

Ad: Compressed area (projection of the contact area on xy-plane)

hrhhrld

4

2

rxhxh

rhh2

1

21

Source: Kopp

2.1015/16 L02 Rolling

Content

L02 – Rolling




7.1115/16 MMT 1 – Module 3-1 – Rolling

Velocity field for the flat-longitudinal rolling(Slab method)

with follows:

Volume constancy(for plane deformation):

Source: Lange, Kopp

Rolling stock velocityin roll gap

with:

rhx

v

rxh

hv

rxh

hvxvx

1

21

2

1

112

1

00

1dlx 0

rxhxh

2

1

xhhv

xhhvxvx

11

00

xvxhvhvh x 1100

2.1215/16 L02 Rolling

Velocity increase Example: Cold rolling-tandem mill

12 1

2

hv vh

Quadro mills

2.1315/16 L02 Rolling

Velocity field for the flat-longitudinal rolling (Slab method)

Increase of the rolling stock velocity in roll gap from v0 to v1

Components of rolling circumferential velocity in rolling direction remains nearlyconstant:

with 1cos uuux vvv )cos(

Source: Kopp

2.1415/16 L02 Rolling

Relationship between velocities of rolling stock and rolls

BSZ: Backward slip zoneFSZ: Forward slip zonevx: Rolling stock velocityvux: Rolling stock circumferential

velocity component in rollingdirection

At the so-called neutral point (x = xF) the rolling stock and the rollingcircumferential velocity are equal: vx = vux

Relative velocity before and after the neutral point:Backward slip zone: vrel = vx – vux < 0Forward slip zone: vrel = vx – vux > 0

Location of neutral point (volume constancy):Source: Kopp

1 1 1F dh vx lh r

2.1515/16 L02 Rolling

Content

L02 – Rolling




2.1615/16 L02 Rolling

Approximations:

with

follows: or:0

Bite and deformation conditions

Bite condition:

Deformation condition: Assumption: Normal and friction force acting in the middle of the roll gap (at α0/2)

For the deformation condition (analog to the bite condition):

rhrh

2max

0

421

2tan

→ Friction coefficients for bite and deformation condition can be different!

(max. possible thickness reduction)

Source: Kopp

rh

00tan

0

00

tansincos

NN FF

rh 2max

2.1715/16 L02 Rolling

Content

L02 – Rolling




2.1815/16 L02 Rolling

Calculation of rolling force and torque

Rolling force F

Rolling moment Md for a roll

Rolling power P

In which a = m ∙ ld and m ≈ 0.45

kw = mid σz (empirical value)wmwd khrbkAF

dMP 2

aFM d

dA zdAF

Estimation:

dl

zd dxxbM0

Estimation:

Source: Kopp

7.1915/16 MMT 1 – Module 3-1 – Rolling

Compression stress distribution in rolling gapduring flat rolling (measured)

Source: Hoff and Dahl

Along the rolling direction similar to the stress state according to SIEBEL:Strong increase up to neutral point, then droptoward the exit

Along the width b: largest stress is present in the middle because of prevented flow ofmaterial in the width direction

z

2.2015/16 L02 Rolling

Content

L02 – Rolling




2.2115/16 L02 Rolling

Quality failure: Crowning

Source: J. Ihlefeldt

Crowning: Plate is thicker in the central area than at the edge

Reasons:

Counteractive measures: Pre-stressing of the rolls and roll housing Working rolls supported by the back-up rolls Crowned grinding of rolls (camber) Specific cooling

2.2215/16 L02 Rolling

Measure 1: Pre-bending of work rolls

Positive pre-bending of working rolls counteracts thenegative bending from the band(bending up in the roll gap)

Positive bendingof the working rolls

Negative bendingof the working rolls

Positive bending

Negative bending

2.2315/16 L02 Rolling

Measure 2: Additional back up rolls

Additional support rolls prevent bending of the working rolls

Angetriebene WalzenNicht angetriebene Walzen

a) Duo-Gerüst b) Quarto-Umkehrgerüst c) 20-Rollen-Gerüsta) Two-high mill

(Duo)b) Four-high mill

(Quadro)c) 20-high mill

(Sendzimir design)

Driven rollsNon-driven rolls

2.2415/16 L02 Rolling

Consequences of a too weak roll crown

Source: Hosford & Caddel

2.2515/16 L02 Rolling

Consequences of a too strong roll crown

Source: Hosford & Caddel

2.2615/16 L02 Rolling

Videoclip: Hot rolled strip

Process flow:

Coiler

Block heating

Scale washer

Roughing train

Finishing train

Strip cooling

Cropping shear

Source: Institut für den wissenschaftlichen Film

2.2715/16 L02 Rolling

Influence of rolling temperature

Source: ThyssenKrupp, Worldsteel Association

Hot Rolling• Recrystallization• Low deformation energy• Surface scale• Low strength• Low residual stresses

Cold Rolling• No recrystallization• High deformation energy• High surface quality• Work hardening• Anisotropy• Residual stresses

Hot rolled: S235 – Re > 235 MPa; A = 25 %

100 µm

Cold rolled: DC06 – Rp 0,2 > 120 MPa; Rm > 270 MPa; r90 > 1,6

50 µm

Static Recrystallization

DynamicRecrystallization

Grain growth

2.2815/16 L02 Rolling

Content

L02 – Rolling




2.2915/16 L02 Rolling

Profile-longitudinal rolling: Hot rolling of steel profiles

Profile rolling Pass sequenceHot rolling process

Hot rolling of steel profiles generally with multiple calibers or passesAdapted pass sequence for the gradual forming of the rectangular cross-sectionto the final shapeRisk of high internal stresses at inapproriate pass sequence

2.3015/16 L02 Rolling

Profile-longitudinal rolling of tubes: Pilgrim step process

Pilgrim step process (Mannesmann process)

Production of thin-walled seamless tubesGradual forming by stretching the thicker tube wall over a mandrelConical calibrated rolls are operated contrary to the rolling directionUniform wall thickness and circularity of the tube is obtained by repeatedlyrolling over each tube region

Source: DIN 8583-2:2003-09

Pilger roll

Mandrel

Workpiece

2.3115/16 L02 Rolling

Profile-longitudinal rolling

Cold rolling of spline shafts of solid materialCold reduction of solid material

Cold rolling of thin-walled, cylindrical hollow parts

carrier flange

Disc carrier

Torsion bar

2.3215/16 L02 Rolling

Flat-cross rolling of hollow bodies: Ring rolling

Ring rotates between main roll and mandrel rollThickness and diameter of the ring are determined by theradial adjustment of the mandrel rollProduction of the outside circular contour by centering rollsSecond pair of rolls (axial rolls) for simultaneous rolling ofthe front faces of the ring

Source: E. Dittrich und J. Teutrine

2.3315/16 L02 Rolling

Skewed rolling – procedure I

Thread rolling is a continuousprocess

Skewed rolling of parts(ex. Bearing balls)

Source: Fritz and Schulze, DIN 8583-2:2003-09

Roll

Workpiece

2.3415/16 L02 Rolling

Skewed rolling – procedure IIVideo: Manufacturing of seamless pipe

Skewed rolling for piercingwith barrel rolls(Mannesmann process)

Source: Fritz and Schulze, DIN 8583-2:2003-09

Roll

Plug bar

Workpiece

Plug

2.3515/16 L02 Rolling

Automobile cross member(tailor rolled blank)

Flexible rolling „Tailor Rolling“

Source: RWTH Aachen

Product designed for various loading along the componentVariable profile thickness in longitudinal rolling direction

Product: Tailor Rolled Blanks

2.3615/16 L02 Rolling

Appendix: German for Production Engineers

English German English GermanRolling Walzen Back plane of

deformation zoneEinlaufebene

Rolling stock Walzgut Front plane of deformation zone

Auslaufebene

Roll gap Walzspalt Neutral point Fließscheide

Roll pass Walzstich Bite condition Greifbedingung

Roll stand Walzgerüst Crown / Camber Balligkeit / Bombierung

Rolling direction Walzrichtung Ring rolling Ringwalzen

Backward slip zone

Nacheilzone Working roll Arbeitswalze

Forward slip zone

Voreilzone Back-up roll Stützwalze

2.3715/16 L02 Rolling

Bibliography

Kopp, R.; Wiegels, H.:

Einführung in die Umformtechnik. Verlag Mainz, Aachen, 1999.ISBN 3-86073-821-6

Spur, G.; Stöferle, Th.:

Handbuch der Fertigungstechnik, Band 2/1 Umformen, Carl Hanser Verlag, 1983, ISBN 3-446-12533-7

Lange, K. Umformtechnik. Handbuch für Industrie und Wissenschaft: Band 2: Massivumformung. ISBN 3-5401-7709-4

Hosford, W.; Caddell, R.:

Metal Forming: Mechanics and Metallurgy, Cambridge University Press, 2007, ISBN 0-5218-8121-8

Fritz, A.H.; Schulze, G.

Fertigungstechnik. Springer, 2010, ISBN: 9-783-642-12878-3(Als E-book in der Universitätsbibliothek erhältlich)

Lenard, J.G. Primer on Flat Rolling, Elsevier, 2007, ISBN: 0-08-045319-8

Wagoner,R.H.; Chenot J.L.

Fundamentals of Metal Forming, 1996, ISBN-13: 978-0-471-57004-2

Ihlefeldt, J. Regelkonzept zur Planlageeoptimierung beim Kaltwalzen von Band, Diss., 1983, Universität Dortmund

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