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
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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
ME Strategies & Planning / 20 October 2005 / Page 4
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
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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
ME Strategies & Planning / 20 October 2005 / Page 6
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
ME Strategies & Planning / 20 October 2005 / Page 8
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
ME Strategies & Planning / 20 October 2005 / Page 10
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°)
ME Strategies & Planning / 20 October 2005 / Page 12
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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ME Strategies & Planning / 20 October 2005 / Page 13
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
ME Strategies & Planning / 20 October 2005 / Page 14
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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ME Strategies & Planning / 20 October 2005 / Page 15
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
ME Strategies & Planning / 20 October 2005 / Page 16
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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Umformen I 4. LS-DYNA Anwenderforum, Bamberg 2005
C - I - 26
ME Strategies & Planning / 20 October 2005 / Page 17
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
© 2005 Copyright by DYNAmore GmbH
4. LS-DYNA Anwenderforum, Bamberg 2005 Umformen I
C - I - 27
© 2005 Copyright by DYNAmore GmbH
Umformen I 4. LS-DYNA Anwenderforum, Bamberg 2005
C - I - 28
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