Numerical Analysis of High Speed Roller Hemming Processes

Adam Opel AG

Numerical Analysis of HighSpeed Roller HemmingProcesses

Dr. Jens Baumgarten, ME Strategies & PlanningDr. Peter Plapper, ME BodyBamberg, October 20, 2005

ME Strategies & Planning / 20 October 2005 / Page 2

Adam Opel AG

Outline

• Introduction• Motivation• Target• Approach• Results• Conclusion and Outlook

© 2005 Copyright by DYNAmore GmbH

4. LS-DYNA Anwenderforum, Bamberg 2005 Umformen I

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Adam Opel AG

2-step 90°-roller hemming process

InnerOuter

Anvil

~90° ~45°

Roller

IntroductionRoller hemming process

Principle of roller hemming

• Flange is bent in a continuous processusing a robot-manipulated roller

• Incremental forming process

1 2


Adam Opel AG

IntroductionRoller hemming technology implementation

HighRüsselsheimAll closuresNextGenerationVectra

MediumTrollhättanHood, tailgateSaab 606

LowAntwerpDoors, a-pillarAstra RHT

LowTrollhättanDoors, hood,tailgate

Saab Cadillac

LowAzambujaTailgateCombo

HighBochumHoodZafira

MediumHeuliezDoors, hood,roof, tailgate

Tigra

CapacityPlantComponentsto be rollerhemmed

Model

GME‘s VisionGME‘s Vision


Umformen I 4. LS-DYNA Anwenderforum, Bamberg 2005

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Adam Opel AG

IntroductionHigh speed roller hemming technology

Complete system(robot and hemmingfixture for 3305 AstraHB3)

1300mm

Experimental straight-edge /straight-surface process forfundamental investigations

Modeled in this study

“Dynamic High SpeedRoller Hemming” tool withdriven rollers (patentpending)

Motor

Rollers

Facilitates hemmingspeeds of up to 1400 mm/s


Adam Opel AG

Motivation

Wrinkles

Pre-hem wrinkling• Wrinkles can occasionally be

not fully flattened out duringfinal-hemming

• Impairs the final part’squality in terms of surfaceand flushness conditions

One of the most significantproblems associated withroller hemming



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Adam Opel AG

Target

Current situation:• Literature/suppliers yield very limited data• In-depth theoretical analysis still to be performed

Provide tangible recommendations foroptimized process design to minimize pre-hemwrinkling

Understand underlyingphysical processes

Understand underlyingphysical processes

Systematically identifyinfluence of major

process parameters

Systematically identifyinfluence of major

process parameters


Adam Opel AG

ApproachSensitivity analysis by means of FEA

Investigated major process parameters

• Pre-hem roller lead angle β:β < 0°; β = 0°; β > 0° Translation

β = 0° β > 0°Translation

β < 0°Translation

• Pre-hem roller diameter d:d = 20mm; 40mm; 60mm

d

α > 0°

α < 0°

α = 0°

• Pre-hem roller taper angle α:

α > 0°; α = 0°; α < 0°

(α4 = -60°; α5 = -75°)

• ...



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Adam Opel AG

ApproachModel

8

10°

15

13,7

R 0,2Workpiece:• Length of „inner“ and „outer“ = 300mm• Sheet thickness „outer“ = 0.75mm• Sheet thickness „inner“ = 1.7mm• Material: mild steel

Anvil (rigid)

Final-hem roller*(rigid)vtrans = 2000mm/svrot = f (d)

Pre-hem roller*(rigid)

vtrans = 2000mm/svrot = f (d)

Inner(elastic-plastic)

Outer(elastic-plastic)

Pre-hem

Final-hem

*Geometries of pre- and final-hemroller vary in the course of the sensitivity study


Adam Opel AG

ApproachFEA details

Meshing guidelines for hem radius• 4 elements on 90° hem radius• Element size = 0.2mm• Aspect ratio = 1.0

Both hemming steps are simulated in a single run

Pre-hemming (explicit)

Final-hemming (explicit)

Analysis procedureNumerical parameters• LS-DYNA (Version 970, MPP, single precision)• Shell elements (type 16, full integration, 7 thru-

thickness integration points)• Material model 24: piecewise linear plasticity

Computing resources• p550 (IBM) with 4 Power5 CPUs, 4x4=16Gb

Memory• Expense: approx. 6,4 hours



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Adam Opel AG

ResultsPre-hem wrinkling

Wrinklingphenomena can bereproduced usingexplicit FEA

Evolution of stresses[MPa] in z-direction(tangential stresses) inhem flange during pre-hemming simulation(roller diameter =20mm; taper angle =0°; lead angle = 0°)


Adam Opel AG

ResultsPre-hem wrinkling

Stresses [MPa] in z-direction (tangentialstresses) in hem flange during pre-hemming simulation (roller diameter =20mm; taper angle = 0°; lead angle = 0°)

Outer

Inner

Pre-hem roller

Tangential tensile stresses of up to 440 MPa

Tangential compressivestresses of up to 320 MPa

Tangential compressive stresses likely to be cause of wrinkling

Motion

Local elongation of flange causes tangential compressive stresses



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Adam Opel AG

0

1

2

3

4

5

6

7

r2 r5 r8 r11 r14 r17 r20 r23 r26 r29

elon

gatio

n de

lta l

[mm

]

ResultsPre-hem Elongation of hem flange edge

Processparameters

000β [°]

000α [°]

604020d [mm]

l

l + Δl

Pre-hemming stage of roller

hemming

Local elongations sum up to substantialvalues of up to 5%

Large roller radii of curvature lead to lowelongation values


Adam Opel AG

ResultsPre-hem wrinkle depth

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300

z-coordinate [mm]

y-co

ordi

nate

[mm

]

Maximum wrinkle depth = 1.71mm

Minumum wrinkle depth = 0.15mm

z

y

Nodal coordinates ofhem flange edge



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Adam Opel AG

ResultsPre-hem wrinkle depth

0

0,2

0,4

0,6

0,8

1

1,2

1,4

r2 r5 r8 r11 r14 r17 r20 r23 r26 r29

wrin

kle

dept

h [m

m]

Processparameters

000β [°]

000α [°]

604020d [mm]

Occurrence of largewrinkle depths coincideswith large elongations ofhem flange edge

Elongation of flangecauses tangentialcompressive stresses =cause of wrinkling

Measures fit to reduceflange elongation lead tolower tendency towardswrinkling


Adam Opel AG

ResultsValidation

000β [°]

000α [°]

604020d [mm]

Processparameters Simulation accuracy calls for improvement

Good qualitative agreement

0

2

4

6

8

10

12

14

16

18

simulation experiment

mea

n pr

e-he

m w

rinkl

e w

idth

[mm

]

Wrinkle width

Process parameters investigated do notaffect wrinkle width

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

r5 r14 r23 r25 r26 r29

pre-

hem

wrin

kle

dept

h [m

m]

simulation

experiment



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Adam Opel AG

Conclusion and outlookConclusion• Straight-edge/straight-surface high speed roller hemming process

modeled using LS-DYNA• Pre-hem wrinkling phenomena reproduced• Good qualitative agreement simulation/experiment• Recommendations for an optimized process design developed and

validated

Outlook• Model curved-edge/curved-surface processes• Improve simulation accuracy• Model production process



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Numerical Analysis of High Speed Roller Hemming Processes

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