Abstract and Figures

For ecological and economic reasons, the main goals in the automotive industry are the reduction of fuel consumption and the CO2 emissions of future car generations. On most cars with combustion engines produced today, the body accounts for one of the largest shares by weight, which has a leverage effect on the weight of the other vehicle components. Reducing the weight of the car body is thus very important for reducing climate-damaging CO2 emissions. Standard composites are highly advantageous in terms of their weight and mechanical properties but very cost-intensive due to the need for manual processing. A promising approach for the automated, large scale production of lightweight car structures with a high stiffness-to-weight ratio is the combination of high strength steel alloys and CFRP prepregs in a hybrid material – fiber metal laminate (FML) – which can be further processed by forming technologies such as deep drawing. FML consists of two sheet-metal top layers with a CFRP core. With this layer structure, the forming process can be simplified by comparison to the forming of standard composite material. The CFRP patches are chambered within the top layers and do not come into contact with the tool surfaces. The forming of fiber metal laminates is significantly more cost-efficient than the forming of standard composite materials. In current research being conducted by the Chair of Forming and Machining Technology (LUF) at the University of Paderborn, manufacturing processes are being developed for the production of high strength automotive structure components in fiber metal laminates. This paper presents the results of ongoing experimental and numerical research at the LUF into the forming of hybrid fiber metal laminates. The paper focuses on the dimensional accuracy of deep drawn FML-parts and the individual measures (tool, process and material design) necessary for achieving the desired part quality.
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Procedia Manufacturing 47 (2020) 36–42
2351-9789 © 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
10.1016/j.promfg.2020.04.118
10.1016/j.promfg.2020.04.118 2351-9789
© 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientic committee of the 23rd International Conference on Material Forming.
Available online at www.sciencedirect.com
ScienceDirect
Procedia Manufacturing 00 (2019) 000000
www.elsevier.com/locate/procedia
2351-9789 © 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
23rd International Conference on Material Forming (ESAFORM 2020)
Combined Curing and Forming of Fiber Metal Laminates
Thomas Heggemanna,*, Werner Homberga, Hüseyin Saplia
aChair of Forming and Machining Technology (LUF), Paderborn University, Warburger Str. 100, 33100 Paderborn, Germany
* Corresponding author. Tel.: +49-5251-60-5350; fax: +49-5251-60-5342. E-mail address: th@luf.uni-paderborn.de
Abstract
For ecological and economic reasons, the main goals in the automotive industry are the reduction of fuel consumption and the CO2 emissions of
future car generations. On most cars with combustion engines produced today, the body accounts for one of the largest shares by weight, which
has a leverage effect on the weight of the other vehicle components. Reducing the weight of the car body is thus very important for reducing
climate-damaging CO2 emissions. Standard composites are highly advantageous in terms of their weight and mechanical properties but very
cost-intensive due to the need for manual processing. A promising approach for the automated, large scale production of lightweight car structures
with a high stiffness-to-weight ratio is the combination of high strength steel alloys and CFRP prepregs in a hybrid material fiber metal laminate
(FML) which can be further processed by forming technologies such as deep drawing. FML consists of two sheet-metal top layers with a CFRP
core. With this layer structure, the forming process can be simplified by comparison to the forming of standard composite material. The CFRP
patches are chambered within the top layers and do not come into contact with the tool surfaces. The forming of fiber metal laminates is
significantly more cost-efficient than the forming of standard composite materials. In current research being conducted by the Chair of Forming
and Machining Technology (LUF) at the University of Paderborn, manufacturing processes are being developed for the production of high
strength automotive structure components in fiber metal laminates. This paper presents the results of ongoing experimental and numerical research
at the LUF into the forming of hybrid fiber metal laminates. The paper focuses on the dimensional accuracy of deep drawn FML-parts and the
individual measures (tool, process and material design) necessary for achieving the desired part quality.
© 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
Keywords: Hybrid Forming; Multi Material System; Sheet Metal, Carbon Fiber Reinforced Plastic (CFRP); Automotive Lightweight Design, Integrated
Forming, Advanced Fiber Placement, Deep Drawing, Fiber Metal Laminate
1. Introduction
In the context of scarcer fossil raw materials and rising fuel
prices, lightweight designs are increasingly entering the
automotive industry. One of the key objectives in the
development of future car generations is the reduction of fuel
consumption and, concomitantly, the reduction of pollutant and
CO2 emissions. A reduction in the vehicle weight leads to a
greater ratio of payload to deadweight and, in addition,
functions such as acceleration and driving dynamics are better
met. A lower mass results in lower acceleration, ascent, and
rolling resistances. Overall, this results in a lower energy
consumption and lower CO2 emissions. In a car, a mass saving
of 100 kg leads to a saving of 0.3-0.5 l of fuel per 100 km and
a reduction of 8.5 - 14 g of CO2 per km [1]. Accounting for up
to 20% of the total weight of a vehicle, the body offers great
potential for weight savings [2]. A common approach is the
substitution of high-density materials such as steel by lighter,
low density materials with a high strength, such as CFRP.
Significant weight advantages can be realized by using
composite materials [3,7]. However, the high material costs and
the necessity of employing manual manufacturing processes
limit the use of just composites to the high-priced car segment.
One promising approach is structural components in a multi
material design, such as hybrid parts made of high-strength
steel with local CFRP reinforcements. Such hybrid components
have cost advantages compared with exclusively CFRP
components and can be reinforced in a load-adapted manner.
The divergent physical and mechanical properties of steel and
CFRP, however, require the separate production of each part
Available online at www.sciencedirect.com
ScienceDirect
Procedia Manufacturing 00 (2019) 000000
www.elsevier.com/locate/procedia
2351-9789 © 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
23rd International Conference on Material Forming (ESAFORM 2020)
Combined Curing and Forming of Fiber Metal Laminates
Thomas Heggemanna,*, Werner Homberga, Hüseyin Saplia
aChair of Forming and Machining Technology (LUF), Paderborn University, Warburger Str. 100, 33100 Paderborn, Germany
* Corresponding author. Tel.: +49-5251-60-5350; fax: +49-5251-60-5342. E-mail address: th@luf.uni-paderborn.de
Abstract
For ecological and economic reasons, the main goals in the automotive industry are the reduction of fuel consumption and the CO2 emissions of
future car generations. On most cars with combustion engines produced today, the body accounts for one of the largest shares by weight, which
has a leverage effect on the weight of the other vehicle components. Reducing the weight of the car body is thus very important for reducing
climate-damaging CO2 emissions. Standard composites are highly advantageous in terms of their weight and mechanical properties but very
cost-intensive due to the need for manual processing. A promising approach for the automated, large scale production of lightweight car structures
with a high stiffness-to-weight ratio is the combination of high strength steel alloys and CFRP prepregs in a hybrid material fiber metal laminate
(FML) which can be further processed by forming technologies such as deep drawing. FML consists of two sheet-metal top layers with a CFRP
core. With this layer structure, the forming process can be simplified by comparison to the forming of standard composite material. The CFRP
patches are chambered within the top layers and do not come into contact with the tool surfaces. The forming of fiber metal laminates is
significantly more cost-efficient than the forming of standard composite materials. In current research being conducted by the Chair of Forming
and Machining Technology (LUF) at the University of Paderborn, manufacturing processes are being developed for the production of high
strength automotive structure components in fiber metal laminates. This paper presents the results of ongoing experimental and numerical research
at the LUF into the forming of hybrid fiber metal laminates. The paper focuses on the dimensional accuracy of deep drawn FML-parts and the
individual measures (tool, process and material design) necessary for achieving the desired part quality.
© 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
Keywords: Hybrid Forming; Multi Material System; Sheet Metal, Carbon Fiber Reinforced Plastic (CFRP); Automotive Lightweight Design, Integrated
Forming, Advanced Fiber Placement, Deep Drawing, Fiber Metal Laminate
1. Introduction
In the context of scarcer fossil raw materials and rising fuel
prices, lightweight designs are increasingly entering the
automotive industry. One of the key objectives in the
development of future car generations is the reduction of fuel
consumption and, concomitantly, the reduction of pollutant and
CO2 emissions. A reduction in the vehicle weight leads to a
greater ratio of payload to deadweight and, in addition,
functions such as acceleration and driving dynamics are better
met. A lower mass results in lower acceleration, ascent, and
rolling resistances. Overall, this results in a lower energy
consumption and lower CO2 emissions. In a car, a mass saving
of 100 kg leads to a saving of 0.3-0.5 l of fuel per 100 km and
a reduction of 8.5 - 14 g of CO2 per km [1]. Accounting for up
to 20% of the total weight of a vehicle, the body offers great
potential for weight savings [2]. A common approach is the
substitution of high-density materials such as steel by lighter,
low density materials with a high strength, such as CFRP.
Significant weight advantages can be realized by using
composite materials [3,7]. However, the high material costs and
the necessity of employing manual manufacturing processes
limit the use of just composites to the high-priced car segment.
One promising approach is structural components in a multi
material design, such as hybrid parts made of high-strength
steel with local CFRP reinforcements. Such hybrid components
have cost advantages compared with exclusively CFRP
components and can be reinforced in a load-adapted manner.
The divergent physical and mechanical properties of steel and
CFRP, however, require the separate production of each part
Available online at www.sciencedirect.com
ScienceDirect
Procedia Manufacturing 00 (2019) 000000
www.elsevier.com/locate/procedia
2351-9789 © 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
23rd International Conference on Material Forming (ESAFORM 2020)
Combined Curing and Forming of Fiber Metal Laminates
Thomas Heggemanna,*, Werner Homberga, Hüseyin Saplia
aChair of Forming and Machining Technology (LUF), Paderborn University, Warburger Str. 100, 33100 Paderborn, Germany
* Corresponding author. Tel.: +49-5251-60-5350; fax: +49-5251-60-5342. E-mail address: th@luf.uni-paderborn.de
Abstract
For ecological and economic reasons, the main goals in the automotive industry are the reduction of fuel consumption and the CO2 emissions of
future car generations. On most cars with combustion engines produced today, the body accounts for one of the largest shares by weight, which
has a leverage effect on the weight of the other vehicle components. Reducing the weight of the car body is thus very important for reducing
climate-damaging CO2 emissions. Standard composites are highly advantageous in terms of their weight and mechanical properties but very
cost-intensive due to the need for manual processing. A promising approach for the automated, large scale production of lightweight car structures
with a high stiffness-to-weight ratio is the combination of high strength steel alloys and CFRP prepregs in a hybrid material fiber metal laminate
(FML) which can be further processed by forming technologies such as deep drawing. FML consists of two sheet-metal top layers with a CFRP
core. With this layer structure, the forming process can be simplified by comparison to the forming of standard composite material. The CFRP
patches are chambered within the top layers and do not come into contact with the tool surfaces. The forming of fiber metal laminates is
significantly more cost-efficient than the forming of standard composite materials. In current research being conducted by the Chair of Forming
and Machining Technology (LUF) at the University of Paderborn, manufacturing processes are being developed for the production of high
strength automotive structure components in fiber metal laminates. This paper presents the results of ongoing experimental and numerical research
at the LUF into the forming of hybrid fiber metal laminates. The paper focuses on the dimensional accuracy of deep drawn FML-parts and the
individual measures (tool, process and material design) necessary for achieving the desired part quality.
© 2020 The Authors. Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license https://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming.
Keywords: Hybrid Forming; Multi Material System; Sheet Metal, Carbon Fiber Reinforced Plastic (CFRP); Automotive Lightweight Design, Integrated
Forming, Advanced Fiber Placement, Deep Drawing, Fiber Metal Laminate
1. Introduction
In the context of scarcer fossil raw materials and rising fuel
prices, lightweight designs are increasingly entering the
automotive industry. One of the key objectives in the
development of future car generations is the reduction of fuel
consumption and, concomitantly, the reduction of pollutant and
CO2 emissions. A reduction in the vehicle weight leads to a
greater ratio of payload to deadweight and, in addition,
functions such as acceleration and driving dynamics are better
met. A lower mass results in lower acceleration, ascent, and
rolling resistances. Overall, this results in a lower energy
consumption and lower CO2 emissions. In a car, a mass saving
of 100 kg leads to a saving of 0.3-0.5 l of fuel per 100 km and
a reduction of 8.5 - 14 g of CO2 per km [1]. Accounting for up
to 20% of the total weight of a vehicle, the body offers great
potential for weight savings [2]. A common approach is the
substitution of high-density materials such as steel by lighter,
low density materials with a high strength, such as CFRP.
Significant weight advantages can be realized by using
composite materials [3,7]. However, the high material costs and
the necessity of employing manual manufacturing processes
limit the use of just composites to the high-priced car segment.
One promising approach is structural components in a multi
material design, such as hybrid parts made of high-strength
steel with local CFRP reinforcements. Such hybrid components
have cost advantages compared with exclusively CFRP
components and can be reinforced in a load-adapted manner.
The divergent physical and mechanical properties of steel and
CFRP, however, require the separate production of each part
Thomas Heggemann et al. / Procedia Manufacturing 47 (2020) 36–42 37
2 Thomas Heggemann/ Procedia Manufacturing 00 (2019) 000000
with a subsequent bonding process. This results in long,
complex process chains and in relatively long process times,
which are predetermined by the curing times of conventional
structural adhesives. An alternative, promising approach for the
economic, automated mass production of lightweight structures
with a high stiffness-to-weight ratio is the combination of high-
strength steel alloys and CFRP prepregs in special hybrid
material fiber-metal laminate (FML), which can be further
processed by forming processes such as deep drawing. FML
consists of metal sheet top layers with a CFRP core. The CFRP
patches are chambered within the sheet metal layers and are not
in direct contact with the tool surfaces. Compared to the
forming of just composites, the forming process can be
simplified and the process chain gets shorter, which is
significantly more economic. Fiber metal laminates also have
the particular advantage that the mechanical properties of the
components produced can be adjusted by the number of CFRP
layers and the fiber orientation of the individual patches within
the layers.
Direct substitution of sheet metal parts with FML is not
possible due to the fact that the material behaviors of metal and
CFRP diverge. Hence an adequate material and process design
has to be investigated. The focus of the current research work
being carried out by the LUF is the development of an adequate
process and material design for the manufacture of structural
parts made of FML with enhanced mechanical properties and a
high shape and dimensional accuracy.
By contrast to composite materials, metals have
approximately isotropic mechanical properties and deform
through elastic and plastic flow. The plastic forming behavior
of metals depends in general on the stress rate, the load speed
and the temperature [5,6].
Composite materials such as CFRP consist of fiber and a
matrix material and have a high anisotropy and divergent
forming behavior. In respect of the fiber itself, the mechanical
properties in the fiber direction are highly dissimilar compared
to the transverse fiber direction [4].
Thermosetting matrix materials have to be cured from a
viscous resin until they attain their final strength. The curing
process is dependent on time, temperature and the prevailing
pressure.
Automotive body parts often have complex geometries with
unsteady drawing depths which are manufactured by forming
processes such as deep drawing. During the forming process,
combined pressure-tension stresses and tension-tension stresses
are induced in the main forming zone, which is the flange. The
tangential pressure stresses that occur lead to a wrinkling of the
flange during the deep drawing process. In order to prevent
wrinkling, tool elements such as blank holders induce normal
stresses at the surface of the flange. When the blank holder
force FBH exceeds a certain value, the tension forces that occur
lead to a thinning of the material and consequently to bottom
tears and cracks. [5,6]
Deep drawing of FML sheets with non-adapted rigid tools
leads to several typical defects: as long as the matrix material is
not cured, pressure stresses applied by normal forces, for
example, can lead to hydrostatic conditions within the FML
sheet, which forces the resin to flow into neighboring zones. [8,
9] As a result, the shape and dimensional accuracy of the FML
parts is affected negatively. Especially in radii areas of the
workpieces the wall thickness distributions are not
homogeneous due to the high contact pressures.
Regarding the forming behavior of CFRP patches, the main
deformation mechanisms are interlaminar layer slip, draping
(displacement in individual layers), and transversal flow and
resin percolation inside the prepreg. [10,11,12] As a result,
delamination, buckled and torn off rovings can be observed in
flange and frame areas.
2. Experimental Setup
Fig. 1. Schematic image of the semi-finished product and the combined
forming and curing process
Appropriate tests were designed and carried out at the LUF
for developing an advanced tool and process design and for
examining the forming behaviour of the FML sheets during the
deep drawing process and the resulting shape and dimensional
accuracy of the finished parts. The effects of the combined
tensile pressure stresses and bending stresses that occur on the
38 Thomas Heggemann et al. / Procedia Manufacturing 47 (2020) 36–42
Thomas Heggemann/ Procedia Manufacturing 00 (2019) 000000 3
semi-finished parts were investigated using a cup-design
specimen geometry.
Fig. 2. Schematic image of FML UD layer sequence
The FML specimens consisted of two circular top layer
sheet-metal blanks (HCT490X, s0 = 0.55 mm) with an initial
diameter of D0 = 180 mm and one to three layers of
unidirectional CFRP prepregs with 230 g/m2 fiber weight per
unit area and a resin content of 39%. The CFRP prepreg patches
also had an initial diameter of D0 = 180 mm.
Fig. 3. Schematic image of the CFRP patch geometry
For the experimental investigations, a temperature-stable
ETFE foil with a thickness of sF = 25µm was used in order to
minimize friction between the hybrid sheets and the active tool
surfaces and to stop the resin from contaminating the tools. The
tool setup consisted of a stamp, a blank holder and a die. All
the active tool elements can be heated with heating cartridges.
The stamp is cylindrical and has a diameter of dSt = 99 mm and
a radius of rSt = 10 mm. The cylindrical die has an inner
diameter of dD = 105 mm and a blanking radius of rD =10 mm.
The drawing depth used in the experiments was h = 38 mm.
The tools were mounted inside a high precision pillar guide
rack to achieve a high level of parallelism between the active
tool elements, and especially between the die and the blank
holder. The tool setup was mounted inside a hydraulic press.
For the experimental investigations, the FML sheets were
positioned inside the tool setup. The active tools were heated
to a temperature of TT = 140°C for the combined forming and
curing process.
Fig. 4. Schematic image of the FML design 1 and the layer sequence
After placing the hybrid sheets in the tool setup, the forming
procedure was started. A blank holder force of FBH,1 = 260 kN
was used for the forming operation. After the forming process,
the FML specimens were cured at a curing temperature of
TC = 140°C inside the tools for the curing time of
tC = 10 minutes. After the curing process, the parts were
extracted from the forming tools. To analyse the forming result
and to evaluate the quality achieved in the FML parts, the
Thomas Heggemann et al. / Procedia Manufacturing 47 (2020) 36–42 39
4 Thomas Heggemann/ Procedia Manufacturing 00 (2019) 000000
specimens were cut in the center and examined by optical and
tactile methods, such as microscopy.
Fig. 5. Schematic image of the patch design 2 and the layer sequence
Fig. 1 b) shows the process and the tool setup of the
combined forming und curing process. In a first step, the FML
sheet is applied to the die. In the next step, the forming process
is initiated. The punch force FP as well as the blank holder force
FBH, 1 will be set for this, and the semi-finished FML part is
formed through the punch into the die. The wrinkling of the
FML sheet during the process, caused by the tangential stresses
occurring at the flange, is suppressed by normal stresses
applied by the blank holder. After the forming process, the
hybrid part remains inside the tool until the matrix material is
cured to its full strength.
To investigate the influence of the number of CFRP layers
on the forming behaviour and on the resulting shape and
dimensional accuracy of the FML components, one to three
CFRP layers were used as the core. The semi-finished
component used for the first experiments thus consisted of two
top-layer circular sheet-metal blanks and one to three inner
layers of unidirectional CFRP prepregs as shown in Fig. 2. The
CFRP layer of the single layer FML sheet was arranged with a
fiber orientation of 0°. The second layer of CFRP inside the
two-layer FML was rotated by 90° compared to the first layer,
giving the FML sheet an orthotropic design. The third layer
inside the three-layer FML sheet was also rotated by 90°
compared to the second layer so that the layer sequence was
/90°/0°. To investigate the influence of the fiber orientation
on the forming behavior and on the resulting shape and
dimensional accuracy, in particular in the frame area of the
FML components, two different patch designs were used for
the experimental investigations. The basic geometry used for
this purpose is shown in Fig. 3. The circular unidirectional
CFRP patch had an outer radius of Ro = 90 mm, a defined fiber
direction (design 1: 0 °, see Fig. 4; design 2: 90 °, see Fig. 5)
and two circular recesses with the radii of Ri = 90 mm,
resulting in a width of bi = 89 mm at the thinnest point. The
recesses were filled by two biconvex UD prepreg patches with
radii of Ro = 90 mm and Ri = 90 mm and a fiber direction
rotated by 90 ° compared to the first patch. Thus, for a single
prepreg layer, a combined 0°/90° fiber orientation results. As a
result of the patch arrangement, the fibers arranged in the frame
and flange area of the FML sheet are subjected during the
forming process to tangential compressive stresses in the fiber
direction (design 2) or transversely to the fiber direction
(design 1).
3. Results
In order to determine the influence of the number of
unidirectional CFRP layers used on the resulting shape and
dimensional accuracy of the hybrid components, FML sheets
with one to three unidirectional CFRP layers were formed and
Fig. 6. Wrinkle height hwr inside the specimens dependent on the number of
CFRP Layers
40 Thomas Heggemann et al. / Procedia Manufacturing 47 (2020) 36–42
Thomas Heggemann/ Procedia Manufacturing 00 (2019) 000000 5
Fig. 7. Wrinkle height hwr inside the specimens, 1-Layer, dependent on the
patch design
cured inside the tool system developed. Fig. 6 illustrates the
relationship between the heights of the wrinkles hwr and the
measuring depth zmd inside the analysed specimens. Due to the
normal force FBH,1 applied by the blank holder, no wrinkles can
be determined at the top of the flange area. Thus, the first
measuring plane is in the feed zone and has a depth of
zmd = 2.5 mm from the top of the flange.
Fig. 8. Wrinkle height hwr inside the specimens, 2-Layer, dependent on the
patch design
The wrinkles measured in this depth have a height of
hwr = 0.42 mm for an FML sheet with a single-layer
unidirectional CFRP patch and sink steadily until a measuring
depth of zmd = 17 mm to a value of hwr = 0.15 mm. The height
of the wrinkles hwr then increases up to a measuring depth of
zmd = 22 mm to a value of hwr = 0.24 mm and decreases further
with an increasing measuring depth zmd, so that at a measuring
depth of about zmd = 27 mm wrinkle heights of about hwr = 0.05
mm can be detected.
In FML sheets with two unidirectional CFRP layers rotated
by 90 degrees in relation to each other, the average wrinkle
heights hwr in the feed zone and in the flange area are increased
by about 79 % compared to single-layer FML sheets. The
forming of three-layered FML sheets leads to even higher
values of the wrinkle heights hwr, especially in the upper frame
area. In conclusion, additional FML layers with unidirectional
fiber direction leads to a significant deterioration of the shape
and dimensional accuracy inside the FML components.
Fig. 9. Wrinkle height hwr inside the specimens, 3-Layer, dependent on the
patch design
In further investigations, the prepreg patch alignments as
shown in Fig. 4 and Fig. 5 were used to determine the influence
of the fiber orientations in the flange and frame area on the
resulting shape and dimensional accuracy of the FML
components. The measurement results of the wrinkle heights of
both single layered FML designs are shown in Fig. 7. For
reference, the gradients of the wrinkle height of the
unidirectional FML are marked gray. The orange-marked curve
represents the wrinkle heights of those specimens which tend
to absorb compressive forces transversely to the fiber direction
in the main forming zone and in the frame area during the
forming process (design 1, Fig. 4). The blue curve represents
those FML specimens that tend to absorb compressive forces
in the fiber direction (design 2, Fig. 5). For both designs, short
as well as long and continuous fibers result due to the patch
geometry. Design 1 shows a similar course of the wrinkle
height over the measuring depth compared to the reference but
this leads to a slight deterioration of the shape and dimensional
accuracy from a measuring depth deeper than zmd = 13 mm. A
fiber arrangement in which the patches tend to be loaded by
compressive stresses in the fiber direction in the edge region of
the sheets during the forming process (design 2) results in a
significant reduction in the wrinkle height. Thus, with this
design, the shape and dimensional accuracy is improved by up
to 95% compared to the reference. Due to the fiber orientation
and the shortened fiber length, the fibers can slip into each other
in the fiber direction. Additional flow channels for the resin are
Thomas Heggemann et al. / Procedia Manufacturing 47 (2020) 36–42 41
6 Thomas Heggemann/ Procedia Manufacturing 00 (2019) 000000
released so that the resin is distributed in the frame area.
The curves of the wrinkle heights of the two-layered FML
(unidirectional references are marked dark grey) and the
investigated patch designs (blue and orange) are shown in Fig.
8. The curves of the unidirectional reference and design 1
(orange) show a very similar course. A significant
improvement in the shape and dimensional accuracy over the
entire range of the feed zone and frame can be achieved when
using design 2 (blue). On average, an improvement of the shape
and dimensional accuracy of about 55% can be achieved with
this fiber arrangement.
Fig. 10. Microsectional view of the frame area at a measuring depth of
zmd = 17 mm for the investigated designs (3-layerer FML)
The curves of the wrinkle heights for the three-layered
unidirectional reference (black) and design 1 (orange) are
presented in Fig. 9. Wrinkle heights of between hwr = 0.60 mm
and hwr = 0.80 mm at depths of up to zmd = 20 mm can be
observed. Thus design 1 does not significantly improve the
shape and dimensional accuracy for this stacking sequence. A
significant improvement can be achieved by aligning the
patches according to design 2, in which the short and long
fibers in the forming zone and in the frame area can slip into
each other. Compared to design 1 this fiber alignment allows a
more homogeneous distribution of the resin. Fig. 10 shows the
micro sectional views of the frame areas at a measuring depth
of zmd = 17 mm of the three layered FML specimen. For the
UD FML and design 1, large pores can be detected inside the
wrinkles, as marked with the yellow arrows. The occurring
pore formation can be attributed to the resulting circumferential
fiber alignment when the cup geometry is formed. With design
2, the resin can be distributed homogeneous in circumferential
direction in the frame area, resulting in less and smaller pores
and lower wrinkle heights hwr. The flow resistance for the resin
in fiber direction is lower compared to the transversal flow
direction. Concequently with this patch arrangement a
significant improvement in the shape and dimensional accuracy
of 60% on average can be achieved.
4. Conclusion
In this study, experimental research has been conducted into
the development of the process and material design for the
manufacture of deep drawn parts made of FML sheets. The
main focus of these investigations was to determine the
influence of the number of CFRP layers and the fiber alignment
with the aim of improving the shape and dimensional accuracy
of the FML parts during the combined forming and curing
process. The wrinkle height of the inner metal sheets was
reduced by almost 64%, from hwr = 0.24 mm down to
hwr = 0.09 mm for FML cups with one layer of CFRP. For the
two- and three-layered FML components, the wrinkle heights
were reduced by 60%. Future work will investigate the transfer
of knowledge from this study to more complex geometries.
Acknowledgements
The authors gratefully acknowledge the financial support
from the European Regional Development Fund (ERDF) and
the state of North Rhine-Westphalia (NRW).
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Book
Dieses Lehr- und Übungsbuch umfasst die Grundlagen des konstruktiven Leichtbaus im Fahrzeug- und Maschinenbau. Dabei wurde besonderer Wert auf eine praxisorientierte Darstellung gelegt, um der Ingenieurausbildung an Hochschulen passgenau gerecht zu werden. Es führt methodisch in die Arbeitstechniken und konstruktiven Fragestellungen ein. Ziel des Buches ist es, besondere Prinzipien und Analogien herauszustellen, um dem Leser geeignete Problemlösungsansätze an die Hand zu geben. Auf Grund der vielen Übungsbeispiele ist es sehr gut zum Selbststudium geeignet. Viele Hinweise zur praktischen Umsetzung lassen es auch für den Ingenieur zu einem verlässlichen Ratgeber werden. Der Inhalt Analog zu den in der Praxis auftretenden Bearbeitungsschritten wurde das Themenspektrum wie folgt strukturiert: • Konstruktive Fragestellungen und deren Umsetzung • Dimensionierung • Kriterien für die Werkstoffauswahl • Elastomechanische Phänomene • Leichtbauparameter typischer Werkstoffe • Langzeitnutzung bei statischer und dynamischer Belastung • Gezielte Strukturoptimierung und Strukturzuverlässigkeit
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A finite element model for sheet forming of unidirectional continuous fibre-reinforced composite laminates, which incorporates large deformation contact elements for modelling tool contact and interply slip, is presented. The composite plies are assumed to behave as an ideal fibre-reinforced fluid, having the constraints of inextensibility in the fibre direction and material incompressibility. A finite element model has previously been developed which can simulate large deformations of an ideal fibre-reinforced fluid body in plane strain using a quasi-static approach. This model is extended in this paper to include interply effects and tool contact by using special contact finite elements. The potential of the model is illustrated using test case simulations.
Bewertung alternativer Fertigungslinien für Kfz-Pleuel -CFK-Verbund als Stahlsubstitution bietet Vorteile
  • W Eversheim
  • K Erkes
  • K Kirberg
Eversheim W, Erkes K, Kirberg K. Bewertung alternativer Fertigungslinien für Kfz-Pleuel -CFK-Verbund als Stahlsubstitution bietet Vorteile. In: Industrie-Anzeiger / Spezial. Produkt Report; 1986. Band 108. p. 18-21.
Zur fertigungsgerechten Auslegung von Faser-Kunststoff-Verbundbauteilen für den extremen Leichtbau auf Basis des variabelaxialen Fadenablageverfahrens Tailored Fiber Placement
  • A Spickenheuer
Spickenheuer A. Zur fertigungsgerechten Auslegung von Faser-Kunststoff-Verbundbauteilen für den extremen Leichtbau auf Basis des variabelaxialen Fadenablageverfahrens Tailored Fiber Placement. Dresden. Dissertation. 2013.
Engineering Plasticity. Vand Nostrand Reinhold Co. London. The International Journal of Production Research
  • W Johnson
  • P B Mellor
Johnson W, Mellor PB. Engineering Plasticity. Vand Nostrand Reinhold Co. London. The International Journal of Production Research. 1973.
Chassis lightweight design exemplified on a suspension strut -State of the art and potential
  • D Lutz
Lutz D. Chassis lightweight design exemplified on a suspension strut -State of the art and potential. In: 11th Aachen Colloquium Automobile and Engine Technology. Aachen 2002.
Manufacturing processes for combined forming of multi-material structures consisting of sheet metal and local CFRP reinforcements
  • H C Schmidt
  • U Damerow
  • C Lauter
  • B Gorny
  • F Hankeln
  • W Homberg
  • T Troester
  • H J Maier
  • R Mahnken
Schmidt HC, Damerow U, Lauter C, Gorny B, Hankeln F, Homberg W, Troester T, Maier HJ, Mahnken R. Manufacturing processes for combined forming of multi-material structures consisting of sheet metal and local CFRP reinforcements. In: Key Engineering Materials 2012. p. 295-300.
Combined Forming of Steel Blanks with Local CFRP Reinforcement
  • U Damerow
  • J Dau
  • W Homberg
Damerow U, Dau J, Homberg W. Combined Forming of Steel Blanks with Local CFRP Reinforcement. In: 10th International Conference on Technology of Plasticity, ICTP 2011. p. 441-446