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Ecological and economic reasons are forcing industry to improve efficiency and to save energy and resources by reducing product weight. In current product designs often insufficient geometric stiffness of the part prohibits exploiting the full potential of weight reduction offered by modern materials. Ideally adapting the geometry to the load profile by implementing appropriate structures often allows a wall thickness and weight reduction and improves the acoustic properties. To enable a target-oriented design, structures manufactured by working media and working energy based forming technologies were analysed.
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MATEC Web of Conferences 21, 11001 (2015)
DOI: 10.1051/matecconf/20152111001
Owned by the authors, published by EDP Sciences, 2015
Optimisation of component performance via structuring
Verena Psyk1,a , Petr Kurka1, Simon Kimme1, Markus Werner1, Dirk Landgrebe1, Andreas Ebert2,
and Mathias Schwarzendahl2
1Fraunhofer Institute for Machine Tools and Forming Technology, Reichenhainer Strasse 88,
09126 Chemnitz, Germany
2Westfalia Presstechnik GmbH & Co. KG, Gewerbering 26, 08451 Crimmitschau, Germany
Abstract. Ecological and economic reasons are forcing industry to improve efficiency
and to save energy and resources by reducing product weight. In current product designs
often insufficient geometric stiffness of the part prohibits exploiting the full potential
of weight reduction offered by modern materials. Ideally adapting the geometry to the
load profile by implementing appropriate structures often allows a wall thickness and
weight reduction and improves the acoustic properties. To enable a target-oriented design,
structures manufactured by working media and working energy based forming technologies
were analysed.
1. Introduction and motivation
Due to climate change and global warming, industry is being forced to take ecological aspects into
consideration when developing new products. Over the last 20 years, Europe’s transport sector has been
responsible for approximately 30% of Europe’s energy consumption making it a key player in climate
and resource aspects [1]. Decreasing the weight of a standard passenger car by about 100 kg can result in
fuel savings of about 300 to 800 litres over the vehicle’s lifetime and to a reduction of the CO2emission
by 9 grams per kilometre [2]. Therefore, especially for the automotive and transport industry – but also
for other industrial branches – lightweight design is a key issue for improving efficiency and accordingly
saving energy and resources. Developments as e.g. the multi-material concept implemented in the
Audi A3 [3] already succeeded in reducing vehicle weight, so that since 2000, a trend of decreasing
greenhouse gas emissions can be observed in Europe (compared to 1990) [1]. Nevertheless, according
to [4] almost all car manufacturers will miss the European carbon emission reduction targets for 2020,
so that further cutting of vehicle weight is indispensable.
In addition to the substitution of conventional materials by typical lightweight ones such as
aluminium and magnesium alloys, high-strength steels, and plastics, also the component design offers
enormous weight saving potential. When dimensioning a component, the material strength is a relevant
aspect, but often insufficient geometric stiffness of the part prohibits exploiting the full potential of wall
aCorresponding author:
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
MATEC Web of Conferences
Figure 1. Analysis and application oriented design of the structuring process.
thickness reduction offered by modern high-strength materials. If the component geometry is optimally
adapted to the load profile by implementing appropriate structures, a reduction in wall thickness is
possible. At the same time the acoustic properties can frequently be improved.
The optimum exploitation of these effects requires a sophisticated choice and design of the
structuring process. To enable an efficient and requirement dependant product and production planning,
the influence of different process parameters on the resulting properties of regular hexagonal comb
structures with different comb sizes and on the related part performance was systematically analysed
(compare Fig. 1). Working media and working energy based processes were applied for structuring a
square area of 220 ×220 mm.
The techniques regarded in the study feature technological and economic advantages compared to
conventional sheet metal forming processes (e.g. deep drawing). One of the most important technical
benefits is the improved formability of many materials due to the process specific load cases and
tribological systems. Significant cost savings are possible, because in the regarded processes only one
tool needs to be adapted to the specific structure, while the second active part of a conventional set of
tools is replaced by the working medium and in case of the working energy based electromagnetic
forming (EMF) by the tool coil, which can be flexibly applied for forming different structures.
Additionally, both technologies can be integrated into a conventional sheet metal forming process and
used for local structuring of deep drawn parts.
2. Working media based structuring
In working media based forming (also called hydroforming) a pressurised fluid, a viscous medium, or
an elastomer forms tubular [5] or sheet metal [6] workpieces against a solid tool. With regard to the
planned integration of the structuring process into a conventional sheet forming technology, the most
promising process variants are forming with an elastomer tool and hydro-mechanical deep drawing
with a membrane. One of the most important advantages is that compared to active hydroforming the
complexity of the equipment is relatively low. In forming with an elastomer, the punch consists of an
elastomer block enclosed by a steel frame to avoid undesired bulging. In hydro-mechanical deep drawing
the fluid basin is integrated in the forming press. In both cases the pressure is generated directly in the
tool due to the punch movement and the sheet workpiece is formed without necessitating an external
pressurisation unit. Moreover, these processes prevent direct contact of workpiece and fluid, so that
sealing effort is reduced and additional cleaning and drying is avoided [7]. In the study, structuring with
an elastomer tool was chosen for investigation and comparison to parts structured by EMF.
ICNFT 2015
Figure 2. a) Setup of structuring with an elastomer tool; b) Example of a structured part; c) Full shape forming die;
d) Forming die designed as partial structure.
2.1 Structuring with an elastomer tool
Structuring with an elastomer tool is a forming technology using an elastomer insert in the punch, which
shapes the sheet metal workpiece (see Fig. 2). The lower die is usually designed as a conventional steel
tool. The form defining surface can be realised either as a full shape solution as shown in Fig. 2c or as a
partial structure as shown Fig. 2d. In the first case the complete geometry of the structure including the
structure depth is defined by the die. In the second case, the die consists of 5 mm thick vertical division
walls between the individual combs allowing free forming of the comb domes according to the chosen
process parameters. This means especially that the structuring depth can by varied e.g. via the punch
stroke during forming with elastomer tools. The edges of the division walls were rounded with a radius
of 2.5 mm to avoid shearing of the workpiece, here.
In both cases the elastomer applies a pressure to the workpiece during closing of the tools which
causes the sheet to align to the lower die according to the structuring geometry. In doing so, flat as well
as slightly curved workpices and workpiece sections can be structured. Thereby, the application of an
elastomer punch offers several advantages compared to conventional deep drawing with a set of classical
full steel tools. The most important ones are that the elastomer insert applies the forming forces very
uniformly, thus decreasing the stress gradient in the workpiece and consequently reducing local sheet
thinning. The resulting strain distribution is more uniform compared to conventional deep drawing
and the maximum strain values are lower. Consequently, the forming area features more remaining
formability, which is related to higher energy absorption potential. This is of interest especially for
crash relevant components from the automotive and transport industry.
Compared to the flat initial material, the stiffening structures in the formed sheet shift the originally
low natural acoustic frequencies to higher values if the part is stimulated. As a result of this, the awkward
low frequency noise, which is typical for thin-walled parts, such as e.g. seat components or panels, is
significantly reduced. At the same time the structured material features damping properties so that less
structure-borne noise is emitted.
MATEC Web of Conferences
Figure 3. a) Tool coil for structuring by EMF; b) Position of turns and according magnetic pressure distribution
during forming sequences 1 and 2; c) Structured part after forming sequences 1 and 2.
The implementation of structures is not limited to regular geometries, but it is also possible to apply
arbitrary designs including bionic ones that are inspired e.g. by cobwebs or the wings of a dragonfly.
Depending on the structuring depth, especially the buckling strength can be significantly increased
compared to flat sheets and component sections. Based on the material choice, the sheet thickness,
and the geometry and size of the structuring elements, the bending stiffness can reach three-times the
value of a flat sheet. This innovative forming technology using an elastomer punch offers numerous
improvements considering the part properties, on the one hand, and can easily be implemented in
classical forming tools, on the other hand.
3. Structuring by electromagnetic forming
3.1 Principle and setup of structuring by EMF
EMF is a high-speed forming process using the energy density of pulsed magnetic fields to apply
Lorenz forces to workpieces made of electrically highly conductive materials as e.g. EN AW-5754,
which is regarded in these investigations. The physically correct volume forces can be mathematically
transferred to a so-called magnetic pressure, which is often more convenient for comparing the acting
loads in different processes. Depending on the geometry and the arrangement of tool coil and workpiece,
tubular parts can be compressed or expanded and forming of flat or preformed sheet metal components
is possible. A comprehensive review of the technology is presented in [8].
For the investigation of structuring by EMF, a tool coil with rectangular winding geometry was
designed, realised, and tested with partial structuring dies as exemplarily shown in Fig. 2d. The geometry
of the coil winding is shown in Fig. 3a. In principle, the pressure distribution applied for structuring
should be uniform, but in EMF only the areas of the workpiece close to the coil winding are pressurised,
so that the coil considered here features an unpressurised area in the centre as it is known from spirally
wound tool coils (see e.g. [8]). To overcome this deficit, the structuring was performed in two forming
sequences. After the first sequence, the workpiece was moved relative to the coil, so that the zone
initially positioned in the non-pressurised centre area of the coil was shifted to the pressurised area in the
second forming sequence (see Fig. 3b). As shown in Fig. 3c the workpiece features undeformed regions
after the first forming sequence, which are structured during the forming sequence 2. This sequential
forming approach can be used for stepwisely structuring even large flat sheets or flat sections of hollow
bodies (if accessible for the coil) with various shapes of the structuring elements using one and the same
ICNFT 2015
Figure 4. Influences on the structuring depth.
3.2 Properties of structures formed by EMF
To characterise the resulting structures, the structuring depth d– i.e. the depth of the comb domes (see
Fig. 4) – and the wall thickness distribution was measured. In Fig. 4 the structuring depth is correlated
to the maximum acting magnetic pressure, the initial sheet thickness, and the comb size.
As expected, for one and the same sheet thickness a higher pressure leads to deeper structures. The
comparison of different thicknesses shows that in case of low pressure (6.3 MPA) higher depths are
achieved for thinner sheets, while this trend is not so clear for higher pressures. This might be explained
as follows: At the beginning, the deformation is driven by the magnetic pressure and consequently,
thinner sheets are deformed more easily due to their lower inertia. After the first acceleration of the
sheet, the magnetic pressure collapses quickly and the deformation is continued due to inertia effects,
(see also [8]). During this process phase, the higher inertia of thicker sheets has more potential to proceed
the deformation. The total structuring depth is a result of both, the pressure driven and the inertia driven
deformation. Therefore, there is a pressure dependant sheet thickness leading to maximum deformation
(i.e. optimum efficiency of the energy transfer). A variation of the comb size shows that larger combs
feature lower resistance against forming (i.e. lower stiffness), so that deeper structures are achieved for
one and the same pressure.
Compared to the parts structured with an elastomer tool, specimens structured by EMF feature
a relatively high spreading of the individual comb depths even within one and the same part. This
is probably owed to the specific pressure distribution and to the sequential forming approach. The
qualitative wall-thickness distribution of parts structured by EMF and such structured with an elastomer
punch is similar, but in case of EMF localised thinning and cracking occurs at significantly higher
depths. Thus, EMF allows deeper structures compared to forming with elastomer tools, indicating an
extended material formability for this high velocity forming process, an effect that is well known from
previous publications as e.g. [9].
3.3 Performance of parts structured by EMF
To investigate the performance of the structured sheets, bending tests and measurements of the acoustic
frequency response were carried out. As a reference, also unstructured sheets (i.e. structuring depth
d=0 mm) were included in the measurement. The setup of the bending tests is shown in Fig. 5. The
force was applied in the centre cross section of the part at those positions where the bending punch
contacts a comb edge. Force-displacement-curves were recorded during bending. These curves initially
rise linearly, indicating an elastic deformation of the sheet before a further non-linear rise indicates
MATEC Web of Conferences
Figure 5. Geometric stiffness of specimens structured by EMF.
Figure 6. Acoustic properties of specimens structured by EMF.
plastic deformation. The slope of the linear section was chosen to describe the workpiece stiffness. As
shown in Fig. 5, this stiffness value is higher in case of higher sheet thicknesses and rises with increasing
structure depth. The influence of the comb size seems to be secondary compared to the structure depth.
The comparison shows that for the regarded specimens, the wall thickness can be reduced from 1.2mm
to 0.8 mm without losing stiffness if a structure of at least 6 mm depth is achieved. This leads to weight
savings of more than 30%.
For the measurement of the acoustic part properties, the structure was excited by noise coupled in
by a electro dynamic shaker. The frequency response function from exciting force to sound pressure
was measured in a defined distance from the structure. Special attention was paid to the influence of
the structuring on the first natural frequency (fn,1), the according frequency response H(fn,1 ), and the
frequency response at an exemplarily chosen frequency of 172 Hz H(f172). This frequency was selected
since it is the lowest first natural frequency of the regarded structured parts. The measurement results
clearly show that in general the structuring leads to a shifting of fn,1 to higher values, thus reducing
awkward, low frequency noise in practise (see Fig. 6). Higher structure depth leads to higher fn,1 but at
the same time H(fn,1) increases, too. With increasing comb size deeper structures are needed to achieve
the same level of fn,1, but this does not mean that higher pressure is required during EMF (compare
Fig. 4). Assuming the same structure geometry, thicker sheets cause higher values of fn,1. The values of
H(fn,1) are relatively similar for all regarded structures, whereas H(f172) shows clear dependencies. It
drops severely with increasing structure depth so that significant noise reduction in low frequency range
can be expected if conventional components are replaced by structured ones. Higher comb sizes again
necessitate deeper structures (but not necessarily higher pressures during EMF) to achieve a similar level
of H(f172). Higher sheet thickness also tends to result in lower H(f172).
ICNFT 2015
4. Summary and outlook
To provide fundamental knowledge for a target oriented design of structures, the influences of different
parameters on the resulting structure properties and the according part performance was investigated for
structuring using an elastomer punch and by EMF, respectively. The high weight saving potential (here
more than 30%) was exemplarily proved.
Future work will focus on developing a methodology using numerical simulation technologies,
which allows an efficient design of local structures and the according structuring process including
the selection of the most suitable forming technology, appropriate process parameters, and eligible
tool properties. It will enable dimensioning application and load oriented local structures in sheet
metal components leading to weight reduction and improved acoustic performance of the product.
Additionally, the integration of the structuring into a conventional forming operation will be regarded.
The published research results were partly achieved within the project “Lokal versteifte Leichtbaukomponenten”
(locally reinforced lightweight components), funded by the Sächsische Aufbaubank SAB with financial means of
the Europäischer Fonds für Regionale Entwicklung EFRE.
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[2] H. Helms, U. Lambrecht, et al. Energy savings by light-weighting. Final report for the International
Aluminium Institute, Institut für Energie- und Umweltforschung GmbH. Heidelberg (2003)
[3] AUDI AG (editor), Workshop Audi A3 (2012)
[4] T. Lawrence, Developing vehicles to meet carbon emissions reduction targets (2015),
[5] M. Koç, T. Altan, J. Mat. Proc. Tech. 108, 384–393 (2001)
[6] S.H. Zhang, Z.R. Wang, Y. Xu, Z.T. Wang, L.X. Zhou, J. Mat. Proc. Tech. 151, 237–241 (2004)
[7] M. Beckmann, F. Vollertsen, J. Mat. Proc. Tech. 174, 363–370 (2006)
[8] V. Psyk, D. Risch, B.L. Kinsey, A.E. Tekkaya, M. Kleiner, J. Mat. Proc. Tech. 211, 787–829 (2011)
[9] Golovashchenko, S., J. Mater. Eng. Perform. 16 (3), 314–320 (2007)
... For this reason, application examples of EMF have been limited to small and medium sized parts and part areas up to now. However, recent developments at the Fraunhofer IWU [39] and in China [40] focus on extending this process limit via enhancing the conventional EMF by a sequential -i.e. a stepwise -manufacturing approach. ...
... Analysis and application oriented design of the structuring process[39]. ...
... (a) Tool coil for structuring by EMF; (b) position of turns and according magnetic pressure distribution during forming sequences 1 and 2; (c) structured part after forming sequences 1 and 2[39]. ...
Full-text available
Ecological and economic reasons are forcing industry to improve efficiency and to save energy and resources. Especially for the automotive and transport industry – but also for all other industrial branches dealing with accelerated masses – lightweight design is a key issue for achieving this goal. In current product designs, insufficient geometric stiffness of the part often prohibits exploiting the full potential of weight reduction offered by modern materials. Ideally adapting the geometry to the load profile by implementing appropriate structures frequently allows wall thickness and weight reduction. At the same time, the acoustic properties can be improved in many cases, because the natural frequency of the modified structure is higher compared to a conventionally-designed structure, thus leading to a reduction of awkward low frequency noise (humming). To enable a target-oriented design, the influence of structures manufactured by elastomer tools and by electromagnetic forming (EMF) was analysed systematically. Knowledge about the influence of the structuring technology and the process parameters on the resulting structure properties and the part performance allows conclusions regarding the optimisation of the part functionality via a suitable selection and design of the process.
... Here, instead of a fluid medium an elastomer block enclosed by a steel frame is used for forming local details such as stiffening structures or design elements e.g. for part personalisation. The implementation of appropriate stiffening structures allows using a smaller wall thickness of the sheet and thus reducing weight while increasing the load capacitance [13]. The spectrum of possible structure geometries included regular patterns as shown in Fig. 5(a), but a requirement and load adapted structuring is much more likely irregular and shown in Fig. 5(b). ...
Full-text available
To reduce weight of a component and improve its performance, the part properties have to be adapted to the requirements, the load profile, and the function of the product. This leads to a continuously increasing complexity of the components necessitating innovative manufacturing strategies for producing the desired shapes from materials that are difficult to handle. Hydroforming offers high potential for fulfilling this demand, especially, if it is applied in deliberate process integrations, combinations, and chains that allow exploiting complementary advantages of all technologies involved. The paper presents four examples of such manufacturing strategies: magnetic pulse welding followed by tube hydroforming, deep drawing combined with injection moulding and hydroforming using the molten plastic, free bending or roll forming followed by hydroforming, and deep drawing with integrated media forming.
Deep drawing using pressurised membranes shows advantages when forming structured blanks. The forming accuracy of the production process MULTIBRAN was experimentally investigated by means of the forming of free form radii. The influencing parameters on the forming accuracy are: the pressure inside the membranes, membrane wall thickness, membrane material, sheet thickness, sheet material and the geometry of the cavity. An analytical approach for the calculation of the necessary pressure inside the membranes including the influencing variables was developed. With this equation the necessary pressure can be calculated within a spread range of 10%.
Electromagnetic forming is an impulse or high-speed forming technology using pulsed magnetic field to apply Lorentz’ forces to workpieces preferably made of a highly electrically conductive material without mechanical contact and without a working medium. Thus hollow profiles can be compressed or expanded and flat or three-dimensionally preformed sheet metal can be shaped and joined as well as cutting operations can be performed. Due to extremely high velocities and strain rates in comparison to conventional quasistatic processes, forming limits can be extended for several materials. In this article, the state of the art of electromagnetic forming is reviewed considering:•basic research work regarding the process principle, significant parameters on the acting loads, the resulting workpiece deformation, and their interactions, and the energy transfer during the process;•application-oriented research work and applications in the field of forming, joining, cutting, and process combinations including electromagnetic forming incorporated into conventional forming technologies.Moreover, research on the material behavior at the process specific high strain rates and on the equipment applied for electromagnetic forming is regarded. On the basis of this survey it is described why electromagnetic forming has not been widely initiated in industrial manufacturing processes up to now. Fields and topics where further research is required are identified and prospects for future industrial implementation of the process are given.
Pulsed electromagnetic forming is based on high-voltage discharge of capacitors through a coil. An intense transient magnetic field is generated in the coil and through interaction with the metal work-piece; pressure in the form of a magnetic pulse is built up to do the work. Data on formability of two aluminum alloys employed for exterior (6111-T4) and interior (5754) automotive body panels will be shown. Comparison of traditional Forming Limit Diagrams obtained by stretching of aluminum sheet with hemispherical punch to the results on formability, where hemispherical punch is replaced by a coil will be provided. It will be shown that material formability in high-rate forming conditions can significantly depend upon interaction with the forming die: electromagnetic forming into an open round window provides only slight improvement in formability, while forming in a V-shape die or into a conical die indicates a significant improvement. An important part of the electromagnetic forming technology is the design of the coil. The coil failure modes and measures preventing them are discussed.
In this paper, recent developments in sheet hydroforming technology are summarized, several key technical problems to be solved for the development of sheet hydroforming technology are analyzed, and varied sheet hydroforming technologies are discussed. Compound deformation by drawing and bulging is the main direction for the development of sheet hydroforming technology, in which it is advantageous to increase the feeding of materials, and the ratio of drawing deformation (drawing in of the blank flange) to bulging, enabling the forming limit of a sheet blank to be increased. It is also advantageous to increase the local deformation capacity for sheet hydroforming, to increase the range of application of the process. Press capacity is one of the important factors restraining the range of applications. As one of the flexible forming technologies that is still under development, it has much potential for innovative applications. Its applications have been increasing remarkably, recently in automotive companies. A breakthrough in the technology will be obtained by the development of novel equipment. A new sheet hydroforming technology using a movable die is proposed in this paper, which has been developed recently by the authors.
Tube hydroforming is used to describe the metal forming process whereby tubes are formed into complex shapes with a die cavity using internal pressure which is usually obtained by various means such as hydraulic, viscous medium, elastomers, polyurethanes and axial compressive forces simultaneously. Increasing use of hydroforming in automotive applications requires intensive research and development on all aspects of this new technology to satisfy an ever-increasing demand by the industry. A technological review of hydroforming process from its early years to very recent dates on various topics such as material, tribology, equipment, tooling are summarizes.
Energy savings by light-weighting. Final report for the International Aluminium Institute
  • H Helms
  • U Lambrecht
H. Helms, U. Lambrecht, et al. Energy savings by light-weighting. Final report for the International Aluminium Institute, Institut für Energie-und Umweltforschung GmbH. Heidelberg (2003)
Developing vehicles to meet carbon emissions reduction targets
  • T Lawrence
T. Lawrence, Developing vehicles to meet carbon emissions reduction targets (2015),
  • S Golovashchenko
Golovashchenko, S., J. Mater. Eng. Perform. 16 (3), 314-320 (2007)