A. Mentella esaform 2010

13th ESAFORM Conference
on
MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Multi-material FEM approach for the
prediction of the behaviour of
draw-bended tubular profiles
Alessia Mentella Matteo Strano Martin Skrikerud
alessia.mentella@unicas.it matteo.strano@polimi.it msk@esi-group.com
UNIVERSITY of CASSINO POLITECNICO di MILANO ESI GROUP, Switzerland
Dept. of INDUSTRIAL ENGINEERING Dept. of MECHANICAL ENGINEERING
Cassino (FR), ITALY Milano (MI), ITALY

on
MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

OUTLINE
Introduction
• ConteSt
• Hollow section production

Rotary-draw bending of metallic profiles
• Process description
• Main quality indexes
• Process difficulty factor
• Multimaterial approach

Finite Element modelling
• OHS-D
• OHS-E
• RHS-D; SHS

Experimental validation and results

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Alessia Mentella - alessia.mentella@unicas.it

on
MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

INTRODUCTION
Contest
AUTOMOTIVE SPACEFRAME:
a connection of hollow bent parts
The behavior of thin-walled tubular
members during bending has
frequently been examined in
connection with structural applications

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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

INTRODUCTION
Hollow Section Production
EXTRUSION ROLL FORMING

Hollow
Section
WELDING LINE
• Different mechanical properties along the
cross section profile, although the material is
nominally the same.
• It is possible to identify zones with greater
values of hardness (e.g. near the welding line)
or with smaller initial thickness. HEAT AFFECTED ZONE
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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Rotary-draw bending
Process description
Method E Method A

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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Rotary-draw bending
Main quality indexes
ODZ − ODX
O% = ⋅100
OD
A0 − A
A% = ⋅100
A0

#Flex: number of curvature changes
in each cross section.

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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Rotary-draw bending
Main quality indexes
ODZ − ODX Bd − Bn Ad − An
O% = ⋅100 O% = +
OD Bn An
An , Bn : cross section nominal
dimentions in horizontal and
vertical direction, respectively.
Ad , Bd : cross section deformed
dimentions in horizontal and
vertical direction, after the
profile bending.
Circular hollow section Non-round section
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on
MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Rotary-draw bending
Bending Factor
OD
WF t0 OD 2 8 I NRS
BF = = = BFNRS =
DOB RM RM ⋅ t0 π RM 3 ⋅ t 0
OD
The factor is obtained by replacing OD at the
A. Mentella, M. Strano, R. Gemignani, S. Farina. Tube free
bending: a new index for the control of the cross section numerator with the moment of inertia of the cross
quality. In 9th AITeM Conf. 2009. section around the Z axis.
Round cross section: BFnew= BFNRS
OD t OD 2
BFnew = =
(RM OD ) RM 1.5 ⋅ t 0.5
3 Cross section distortion
LESS important
The thickness has a smaller effect on the BFNRS Cross section shape
process, than the mean bending radius. MORE DEGRADATED
Circular hollow section Non-round section
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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Rotary-draw bending
Multi-material approach

Measures
have been
performed
on the back,
undeformed
side of a
bent tube.

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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Rotary-draw bending
Multi-material approach
2 EXTRADOSS The material, in
The approach each part of the
consists of section, has
dividing the 1 WELDING LINE 3 STRETCHED different
profile surface ZONE mechanical
in 3 or 4 zones. properties and
2 INTRADOSS
different initial
thickness.

SHS RHS OHS

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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Finite Element Modelling
4-nodes shell elements with 5 integration Kinematic conditions and the constrains
points throughout the thickness
Tools Closing Bending
Lock: translation YZ, Rotational
Bending die, rotation XYZ; Kinematics: angular
Bending clamp,
Imposed velocity: velocity, axis
Clamp die
translation on X. direction Z.
Lock: translation YZ,
rotation XYZ; Lock: translation XZ,
Pressure-die
Imposed velocity: rotation XYZ;
translation on X.
CONTACT Lock: translation YZ,
• Non Linear Penalty Contact rotation XYZ;
• Coulomb friction model Wiper All locked
Imposed velocity:
Contact interface Friction Coefficient translation on X.
Lock: translation YZ,
Tube/Pressure and bend dies 0.50 Mandrel All locked
rotation XYZ;
Tube/Wiper die 0.12
Tube/Clamp dies 0.99
Tube/Mandrel (and balls) 0.08 σ(εp)=K(ε0+ εp)n
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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

D E
BFNRS Hard-way bending BFNRS
- +
Easy-way bending
It requires considerable
less bending moment

D

OHS-E bend OHS-D bend RHS-D bend SHS
An, Bn 36, 18 mm 18, 36 mm 30, 18 mm 30, 30 mm
t0 1.22 mm 1.3 mm 1.22 mm 2.015
RM 45 mm 75 mm 74 mm 74 mm
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OHS - Case and profile zones εo n K [MPa] t0 [mm]
D0 Single-material 0.0147 0.148 688 1.300
D1 Welding line 0.0418 0.122 774 1.304
D2 Intrados, extrados 0.0011 0.157 659 1.306
D3 Stretched zone 0.0011 0.157 659 1.245
E0 Single material 0.0356 0.1442 664 1.227
E1 Upper zone 0.0011 0.1574 641 1.236
E2 Intrados 0.0700 0.1400 585 1.184
E3 Extrados (welding) 0.0700 0.1220 790 1.220

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RHS εo n K[MPa] t0[mm] SHS εo n K[MPa] t0[mm]
Welding line 0.0010 0.1000 947.0 2.685 Intra - Extra 0.0010 0.125 739.0 1.943
Stretched line 0.0010 0.1185 899.0 2.486 Welding line 0.0030 0.106 896.0 2.246
Intrados - Extrados 0.0030 0.1185 899.0 2.341 Stretched line 0.0030 0.118 781.0 1.885
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MATERIAL FORMING
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Brescia, Italy

Experimental
Single material
3 Materials

Extrados

3 materials
Intrados
Experimental

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Brescia, Italy

Thickness distribution OHS-E
1,600

1,500
Extrados EXP.
Estradosso (saldatura)
1,400
medio reale
Thickness [mm]

1,300
Extrados FEM
Estradosso simulato 3m
1,200

1,100
Intrados EXP.
Intradosso medio reale
1,000

0,900
Intrados FEM
Intradosso simulato 3m
0,800

0,700

0,600
1 3 5 7 9 11 13 15 17 19

Curvilinear Abscissa [cm]

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EXP.
FEM

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MODEL Def. Indef. def/indef Difference EXP-FEM
Experimental Area [mm2] 440.073 536.878 81.969% 0.000%
OHS-D Perimeter [mm] 86.594 88.558 97.783% 0.000%
3 materials Area [mm2] 428.167 518.82 82.527% 0.558%
OHS-D Perimeter [mm] 86.402 88.456 97.678% 0.105%
Experimental Area [mm2] 481.7855 533.284 90.343% 0.000%
OHS-E Perimeter [mm] 83.9555 88.728 94.621% 0.000%
3 materials Area [mm2] 469.892 524.071 89.662% 0.681%
Single material Area [mm²] 469.279 524.071 89.545% 0.798%

Cross section distortion
O% A% #Flex BFNRS LESS important
OHS-D 24.93 20.25 2.5 0.27
OHS-E 8.25 8.74 2 0.75 BFNRS Cross section shape
MORE DEGRADATED
RHS-D 2.33 4.03 2 0.92
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MATERIAL FORMING
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Brescia, Italy

Further results
A% 25
OHS-D
A0 − A 20
A% = ⋅100
A0 15
OHS-E
10
SHS
5 RHS

0
0.0 0.4 BFNRS 0.8 1.2

8 I NRS
BFNRS =
π RM 3 ⋅ t 0
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MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Conclusion
1. A FEM model, able to take into account the differences in thickness
distribution and in mechanical properties along the profile cross
section, has been built and validated with the commercial code PAM-
TUBE.
2. Then, a quantitative indicator BFNRS of the process difficulty has been
developed, in order to represent, from a geometrical point of view,
the degree of severity of bending in terms of potential risk of shape
degradation of the bent profiles.
3. Finally, it is shown that the process difficulty factor BFNRS is well
correlated to both the aesthetical and functional quality indicators,
especially the ovalization O% and the reduction of area A% of the
deformed cross sections.
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on
MATERIAL FORMING
April 7-9, 2010
Brescia, Italy

Multi-material fem approach for the
prediction of the behaviour of draw-
bended tubular profiles
Alessia Mentella Matteo Strano Martin Skrikerud
alessia.mentella@unicas.it matteo.strano@polimi.it msk@esi-group.com

THANK YOU FOR YOUR ATTENTION!

A. Mentella esaform 2010

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A. Mentella esaform 2010