Sheet Metal Forming Using Additively Manufactured Polymer Tools

Abstract

Due to various trends, such as e-mobility, a long-term change in the automotive value creation structure is foreseeable. Shorter development cycles demand early prototypes and cause more changes. Currently, there is no cost-effective production process for originally deep drawn sheet metal parts in series quality at small production volumes. In this paper, the application of additively manufactured functional elements in deep drawing tools is investigated. Besides the first concept of such tools, first experimental test series are described and analyzed.

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Procedia CIRP 00 (2017) 000–000
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2212-8271 © 2017 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the scientific committee of the 28th C IRP Design Conference 2018.
28th CIRP Design Conference, May 2018, Nantes, France
A new methodology to analyze the functional and physical architecture of
existing products for an assembly oriented product family identification
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: paul.stief@ensam.eu
Abstract
In today’s business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of
agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production
systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to
analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and
nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production
system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster
these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable
assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and
a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the
similarity between product families by providing design support to both, production system planners and product designers. An illustrative
example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of
thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.
© 2017 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
Keywords: Assembly; Design method; Family identification
1. Introduction
Due to the fast development in the domain of
communication and an ongoing trend of digitization and
digitalization, manufacturing enterprises are facing important
challenges in today’s market environments: a continuing
tendency towards reduction of product development times and
shortened product lifecycles. In addition, there is an increasing
demand of customization, being at the same time in a global
competition with competitors all over the world. This trend,
which is inducing the development from macro to micro
markets, results in diminished lot sizes due to augmenting
product varieties (high-volume to low-volume production) [1].
To cope with this augmenting variety as well as to be able to
identify possible optimization potentials in the existing
production system, it is important to have a precise knowledge
of the product range and characteristics manufactured and/or
assembled in this system. In this context, the main challenge in
modelling and analysis is now not only to cope with single
products, a limited product range or existing product families,
but also to be able to analyze and to compare products to define
new product families. It can be observed that classical existing
product families are regrouped in function of clients or features.
However, assembly oriented product families are hardly to find.
On the product family level, products differ mainly in two
main characteristics: (i) the number of components and (ii) the
type of components (e.g. mechanical, electrical, electronical).
Classical methodologies considering mainly single products
or solitary, already existing product families analyze the
product structure on a physical level (components level) which
causes difficulties regarding an efficient definition and
comparison of different product families. Addressing this
Procedia CIRP 93 (2020) 20–25
2212-8271 © 2020 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 53rd CIRP Conference on Manufacturing Systems
10.1016/j.procir.2020.04.013
© 2020 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientic committee of the 53rd CIRP Conference on Manufacturing Systems
53rd CIRP Conference on Manufacturing Systems
Available online at www.sciencedirect.com
ScienceDirect
Procedia CIRP 53 (2019) 000–000
www.elsevier.com/locate/procedia
2212-8271 © 2019 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 53rd CIRP Conference on Manufacturing Systems
53rd CIRP Conference on Manufacturing Systems
Sheet Metal Forming Using Additively Manufactured Polymer Tools
Günther Schuha, Georg Bergweilera, Philipp Bickendorfa,*, Falko Fiedlera, Can Colaga
aLaboratory for Machine Tools and Production Engineering (WZL), Campus-Boulevard 30, 52074 Aachen, Germany
*Corresponding author. Tel.: +49 16094922447. E-mail address: p.bickendorf@wzl.rwth-aachen.de
Abstract
Due to various trends, such as e-mobility, a long-term change in the automotive value creation structure is foreseeable. Shorter development
cycles demand early prototypes and cause more changes. Currently, there is no cost-effective production process for originally deep drawn sheet
metal parts in series quality at small production volumes. In this paper, the application of additively manufactured functional elements in deep
drawing tools is investigated. Besides the first concept of such tools, first experimental test series are described and analyzed.
© 2019 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 53rd CIRP Conference on Manufacturing Systems
Keywords: Sheet metal forming, Forming tools, Additive tooling, Additive manufacturing, 3D printing, Deep drawing, Rapid tooling, Rapid prototyping,
Production technology, Flexibility, Body shop, Prototype tooling, Press shop, Tool shop
1. Introduction
The increasing pressure to innovate, shorter-product life
cycles, an increasing product variety as well as lower
production volumes are just some of the current and future
challenges facing the automotive industry [1]. The demand for
individualization and the parallel production of different
powertrain concepts, such as ICEV, HEV and BEV, is met with
the customized mass production, which challenges the
production technology.
Most of a conventional car body’s metal sheet parts are deep
drawn. Deep drawing is characterized by low unit costs for
mass production, high investments as well as tooling costs.
Because of the requirements regarding wear resistance and
form stability, deep drawing tools are mainly made of tooling
steel or cast iron [2]. High (plant) investments of several
million € in a press line lead to a high weighting of these costs
for small series production, especially compared to the low
material costs of deep drawn parts [3].
Currently, there is no suitable production technology for
economic small series production of deep drawn parts [4].
Existing production technologies which are economical for
small series are often not able to meet functional as well as
quality requirements of a mass production, e.g. in terms of
surface quality and repeatable dimensional accuracy [3]. This
paper investigates the suitability of additively manufactured
polymer tools by experimental test series as well as simulations
and evaluates this new technology.
2. Literature review
2.1. Deep drawing
As one of the most important sheet metal forming processes
in the automotive industry, deep drawing is established in both
mass and in small series production. By a mechanical action
of punch, a sheet metal blank is radially drawn into a forming
die (cf. fig. 1). By deep drawing, complex part geometries can
be achieved. The technology is common for box-shaped, cup-
shaped or hollow-shaped parts with a limited drawing ratio. If
the depth of the drawn part exceeds its diameter, a forming
process can be called deep drawing. In the following, deep
drawing is understood to be tensile pressure forming of a sheet
metal blank into a hollow body open on one side. [5]
Available online at www.sciencedirect.com
ScienceDirect
Procedia CIRP 53 (2019) 000–000
www.elsevier.com/locate/procedia
2212-8271 © 2019 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 53rd CIRP Conference on Manufacturing Systems
53rd CIRP Conference on Manufacturing Systems
Sheet Metal Forming Using Additively Manufactured Polymer Tools
Günther Schuha, Georg Bergweilera, Philipp Bickendorfa,*, Falko Fiedlera, Can Colaga
aLaboratory for Machine Tools and Production Engineering (WZL), Campus-Boulevard 30, 52074 Aachen, Germany
*Corresponding author. Tel.: +49 16094922447. E-mail address: p.bickendorf@wzl.rwth-aachen.de
Abstract
Due to various trends, such as e-mobility, a long-term change in the automotive value creation structure is foreseeable. Shorter development
cycles demand early prototypes and cause more changes. Currently, there is no cost-effective production process for originally deep drawn sheet
metal parts in series quality at small production volumes. In this paper, the application of additively manufactured functional elements in deep
drawing tools is investigated. Besides the first concept of such tools, first experimental test series are described and analyzed.
© 2019 The Authors. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-review under responsibility of the scientific committee of the 53rd CIRP Conference on Manufacturing Systems
Keywords: Sheet metal forming, Forming tools, Additive tooling, Additive manufacturing, 3D printing, Deep drawing, Rapid tooling, Rapid prototyping,
Production technology, Flexibility, Body shop, Prototype tooling, Press shop, Tool shop
1. Introduction
The increasing pressure to innovate, shorter-product life
cycles, an increasing product variety as well as lower
production volumes are just some of the current and future
challenges facing the automotive industry [1]. The demand for
individualization and the parallel production of different
powertrain concepts, such as ICEV, HEV and BEV, is met with
the customized mass production, which challenges the
production technology.
Most of a conventional car body’s metal sheet parts are deep
drawn. Deep drawing is characterized by low unit costs for
mass production, high investments as well as tooling costs.
Because of the requirements regarding wear resistance and
form stability, deep drawing tools are mainly made of tooling
steel or cast iron [2]. High (plant) investments of several
million € in a press line lead to a high weighting of these costs
for small series production, especially compared to the low
material costs of deep drawn parts [3].
Currently, there is no suitable production technology for
economic small series production of deep drawn parts [4].
Existing production technologies which are economical for
small series are often not able to meet functional as well as
quality requirements of a mass production, e.g. in terms of
surface quality and repeatable dimensional accuracy [3]. This
paper investigates the suitability of additively manufactured
polymer tools by experimental test series as well as simulations
and evaluates this new technology.
2. Literature review
2.1. Deep drawing
As one of the most important sheet metal forming processes
in the automotive industry, deep drawing is established in both
mass and in small series production. By a mechanical action
of punch, a sheet metal blank is radially drawn into a forming
die (cf. fig. 1). By deep drawing, complex part geometries can
be achieved. The technology is common for box-shaped, cup-
shaped or hollow-shaped parts with a limited drawing ratio. If
the depth of the drawn part exceeds its diameter, a forming
process can be called deep drawing. In the following, deep
drawing is understood to be tensile pressure forming of a sheet
metal blank into a hollow body open on one side. [5]

Günther Schuh et al. / Procedia CIRP 93 (2020) 20–25 21
2 Author name / Procedia CIRP 00 (2019) 000–000
Figures 1 a) and b) illustrate one process variant of deep
drawing process with a rigid punch (cf. DIN 8584-3). First, the
blank holder forces are applied in order to prevent wrinkles.
Subsequently, the punch forces are applied to form the metal
part. By deep drawing, the workpiece is formed by combined
tensile and compressive forces [6]. The workpiece is drawn by
forces applied by dies to its final shape. The marked areas of
the blank downside (cf. fig. 1 b)) show the most tensile
stressed/ thinned out areas due to tensile stress on the
workpiece during the process. The workpiece is thinned out
locally due to plastic material flow into the cavity of the die. If
the tensile strength exceeds the strength of the workpiece
material, fractures occur. The marked areas of the blank
downside in figure 1 b) show the most compressed areas during
the process. If the compressive forces exceeds the buckling
resistance of the workpiece, wrinkles occur. These most
common failure forms are shown in figures 1 c) and d) [7].
Wrinkles (cf. fig. 1 c)) are caused by excessive compressive
stress, which leads to local buckling. As a thinner material
tends to buckle easily, the use of blank holder is crucial by the
forming process of such materials [8]. Figure d) shows a
fracture, which mostly occur at the highest stressed areas such
as punch corner and the flange/ cup-wall interface. The
preliminary tests for the determination of the formability of
sheet metal parts can be conducted by cupping test according
to ERICHSEN (cf. Chapter 3.1) [9].
The automotive production consists of highly-automated
press lines, in which the quantity of the single presses varies
depending on the complexity and size of the part. The total
machine costs of a big sized, semi-complex press line for
automotive side panels is calculated by BIRKERT ET AL.
between approx. 7-9 M. €/a depending on the art of the press
drive (mechanical, hydraulic or servo drive) as well as the
transfer systems [10].
The serial deep drawing tools are produced out of grey cast
iron with variable material quality depending on the
requirements. Grey cast iron tools are finished to its final shape
by milling. The usage of fully hardened and coated steel onsets
at highly stressed areas, such as punch corners (cf. fig. 1 c)) is
common [10]. The casted tools with local coatings or hardened
onsets are highly cost intensive, so that there are various
prototype tooling materials and technologies [4].
The aim of a pilot series production in the automotive
industry is the early detection of production problems and
worker qualification for mass production [11]. To receive
reliable information about the deep drawing process and part
quality, the production methods in this stage should be close to
mass production conditions. At this stage, the production
should take place at the serial press lines and the tool
geometries as well as their wear mechanisms should be as close
to serial conditions as possible.
The use of materials with different hardness than serial tools
affects i.a. the tool wear, especially at the highly stressed areas,
since the abrasion volume of the material depends on the local
hardness of the softer body of the contacted materials [12].
Abrasion leads to a larger corner radius within the tool, which
effects the wrinkling behavior of formed metal parts [13].
Wrinkling causes a high pressure at its contact area with the die
and increases the abrasion. Therefore, the wrinkling might
increase with each drawing cycle, as the size of the die defect
grows [13]. The tribological behavior of die-sheet metal
combinations can be determined by experiments or
simulations. At present, the ARCHARD model is a widespread
simulation method to predict die wear. For the experimental
wear prediction, tests, such as pin-on-plate, pin-on-disc, and
scratch tests are established [14]. According to this model, the
wear volume is inversely proportional to the hardness of the die
[15]. As a consequence, tool materials different from the mass
production cannot deliver reliable information on deep drawing
processes in pilot production lines as defined before. The short
cycle times in pilot series production can also increase the tool
temperature substantially after several forming operations.
Because of low thermal conductivity of polymers, which
changes the friction behavior between sheet metal and tool, this
affects polymer prototyping tools even more than conventional
pilot series tools.
This should be examined in course of multicycle simulations
or experiments as well before the usage of such tool materials
for prototyping applications. Another important factor, which
affects the part quality and dimensional accuracy differences
between serial and prototype tools is the tool deflection or
elastic-plastic deformation of the tool due to press forces [10].
2.2. Research approaches
[16] demonstrated the production of 101 parts (tailgate lock
reinforcement) in two sheet metal materials (0.8 mm DC04, 0.8
mm S355MC) with deep drawing tools made by FFF (Fused
Filament Fabrication) polymer additive manufacturing to
evaluate dimensional conformance. For that, existing near-
contour tool elements are printed in polycarbonate and
mounted on the upper and lower tables of a conventional
hydraulic press. Every 10th part, the tool halves as well as the
respective part are measured optically. In the case of DC04, the
experiment showed good dimensional accuracy over the entire
quantity range. Parts made of S355MC showed the limits of the
material properties of the polycarbonate tool material. FFF
deep drawing tools are dimensionally stable up to 50 parts
made of S355MC. For designing such a polymer tool, new
design guidelines need to be taken into account to design a
fully-functional tool in the 1st shot, e.g. spring back of formed
sheet metal, compression behavior of the tools due to pressure
load, flow properties of polymers and tribological mechanisms
of action. Therefore, [16] proved that FFF polymer additive
Figure 1:
Deep drawing process and common failure types

22 Günther Schuh et al. / Procedia CIRP 93 (2020) 20–25
Author name / Procedia CIRP 00 (2019) 000–000 3
tooling is an economical approach with significant cost and
lead time savings compared to conventional tool production.
[17] developed the usage of polymer based additive forming
tools as a research approach to react to shortened development
cycles and increasing individualization. As the deep drawing
tools represent a bottleneck regarding production volume,
flexibility and a high risk regarding to change implementation
in the development process, this approach has been studied.
This study shows, that the FFF manufactured tools fulfil the
technical requirements for small series (20 parts) and are
56 - 63 % (depending on external or in-house manufacturing)
cheaper than conventional metal tools made with 42CrMo4.
The in-house manufacturing of forming tools has the potential
to reduce the tooling times to only one day, which is an
enormous advantage compared to the conventional value chain,
in which the tools are ordered from external suppliers due to
needed costly machinery technique and know-how. [18]
evaluates the technical and economic potential of FFF polymer
additive manufacturing as a tool of a holistic flexibilization of
automotive body shop process chain. [18] uses FFF
manufactured forming and bending tools and hybrid welding
jigs in order to reduce time and cost consumption. A hybrid jig
consists of an intelligent combination of standardized metal
elements and part specific FFF manufactured elements. This
paper shows that this approach has a cost saving potential up to
55 % compared to full metal tools as well as jigs, reduces the
reaction times for the spontaneous changes during the product
development process and is relevant in practice.
[19] and [20] investigated the tribological and wear
behavior, mechanical properties and load behavior of polymer
forming tools. [19] uses casted Polyurethane (PUR) tools and
proofs that this tool material shows, especially in contact with
coated sheet metals, an extraordinary well friction behavior.
However, there are some design restrictions for example
regarding to min. drawing radii or workpiece thickness, as the
wear rate increases with the surface pressure. According to
[19], the better friction behavior of polymer forming tools
might increase the max. drawing ratio without fractures, as the
better friction behavior allows a better material flow. [20] uses
epoxy resin infiltrated Layer Object Manufactured (LOM)
paper. The resin infiltration increases the compressive strength
of the tool significantly. The friction behavior of tool and
workpiece has also been analyzed by [20] with strip drawing
test. According to [20] the coefficient of friction (COF)
between steel sheet metal and LOM impregnated paper
(LOMim) is close to the coefficient with grey cast iron or steel
tools. However, the test conducted for aluminum sheet metal
and LOMim combination reveal a much higher COF.
Consequently, the expected friction ratio for this material
combination is higher. [20] manufactures 20 body part
prototypes with different sheet metals with varying strength.
The results show, that this tooling technique enables the
forming of soft deep drawing steels, such as DC04, even with
2 mm thickness. Apart from the design restrictions in order to
prevent highly shear or compressive stressed areas, another
problem observed by the process is the ejection of the formed
parts, as the part might clamp between the tools as a result of
the elastic tool deformation. In order to avoid this problem,
ejector pins can be placed in the tool.
[4] reviews the recent developments of tooling technologies
and analyzes the potential benefits resulting from this
development regarding the qualification as a new tooling
technology for small series production. E.g., the tooling
technology LOMim presented in the previous chapter causes a
comparatively high stair stepping effect due to thicker layers.
Therefore, the resulting surface quality of formed parts by such
tools is low and not suitable for exterior parts. However, a new
method with LOM manufacturing with profiled edge
lamination might solve this issue.
[4] evaluated seven additive and non-additive prototype
tooling technologies suitable for the small series production of
sheet metal parts such as Resin Casting, Arc Spraying,
Hydroforming. Multi-Point Forming, Incremental Sheet
Forming, Laminated Object Manufacturing, Powder-Based
Additive Manufacturing and FFF [4]. Subsequently, the review
paper defines their technical and economical limits regarding
to quantities formed by such tools. Automotive pilot series
production requires about 100 prototypes with a specific set of
quality criteria. According to this paper, tooling technologies,
such as Arc Spraying, Multi-Point Forming, LOM and FFF are
suitable for this lot size. Considering other important factors,
such as possibility to in-house tooling, low machine cost and
high dimensional accuracy of formed parts, FFF is the most
suitable technology for the manufacturing of deep drawing
tools under certain restrictions regarding the product flexibility
[18].
3. Studies
3.1. Cupping test
In the following, a cupping test according to ER ICHSEN (DIN
EN ISO 20582) with a test specimen out of 3D printed PLA
material will be described. In general, the cupping test is used
to determine the ductility of sheet metal materials by pressing
a spherically ended punch into the tested sheet metal which is
clamped between a die and a punch holder, until a registered
drop in force confirms a crack in the sheet metal [21].
Therefore, the normed spherically ended punch and the 3D
printed PLA (cf. red marks in fig. 2) sphere can be compared
in terms of the drawing capability.
The spherical punch geometry has been manufactured by an
Ultimaker 2 with PLA. The shrinkage as a result of the cooling
process of the polymer material has been considered for the
dimensioning of the punch. Then the punch has been mounted
on a BUP2000 Machine and 1 mm DC01 sheet metal strips
have been formed.
In [9], cupping test experiments has been conducted with a
standard metal punch for various deep drawing sheet metal
Figure
2:
Experimental setup for the Erichsen cupping test according to
Z
WICK
R
OELL
G
ROUP
and [9]

Günther Schuh et al. / Procedia CIRP 93 (2020) 20–25 23
4 Author name / Procedia CIRP 00 (2019) 000–000
strips (0.8 mm DC01; 0.8 mm DC04; 1 mm DC04). According
to [9], the measured height of the bulged specimen (H) varies
between 9.60 and 11.13 mm depending on the sheet thickness.
Table 1: Cupping test with different automotive steels
Material
Re [MPa]
Thickness [mm]
H [mm]
DC01
140 - 280
1.0
9.7
CR3
140 - 210
0.7
9.4
CR240LA
240 - 320
1.0
8.8
The preliminary experiments with PLA punch have proven
that for DC01 similar drawing depths are possible (cf. table 1).
Other automotive steels with a higher yield strength value Re
like CR240LA or CR3 were formable without any significant
wear or plastic deformation of the punch.
The following research is focused on optimizing the tool
design regarding production time (min. infill density, infill
pattern) and define geometrical restrictions regarding to
drawing radius and wear reduction.
3.2. Optimizing tool design regarding compressive strength
The main focus of this study was to predict tool failure of
the internal structure of additively manufactured forming tools
made by FFF during the load of a deep drawing process. With
the aim of improving the manufacturing parameters to ensure
higher compressive strength for mentioned forming tools, an
optimal infill pattern was selected and supplemented by
additional elements. Infill patterns describe which pattern is
used to build up the layers in a FFF printing process (e.g.
honeycomb pattern). The first step was to identify a set of
capable printing parameters and to develop an optimized
internal structure. Subsequently, the results were applied to an
illustrative demonstrator which was used to determine the
limits of depictability by means of deep drawing. In this
context, many 3D printed samples were manufactured in the
form of a cylinder. For this purpose, mainly the Ultimaker S5
3D printer and conventional Polylactide (PLA) material was
used. Subsequently, these cylinders were crushed by a
Zwick&Roell Z250 testing machine to determine the
compressive strength. A total of eight different infill patterns,
which were provided by the slicing software Ultimaker Cura,
were examined within a three-staged Design of experiments
setup. The results revealed that the Triangle and the Tri-
Hexagonal patterns had the highest compressive strength.
Henceforth, all further experiments were carried out with a
fixed parameter set (i.a. sample length, printing speed and
extrusion temperature) and the Triangle infill pattern as default.
The internal structure was defined as a combination of 3D
printed infill patterns and 3D printed geometries or integrated
standard elements. To further improve the properties of the
internal structure, additional elements have been developed.
Figure 3 shows the two most important additional elements
additional layers and screw elements.
Material consumption was held constant for all samples to
ensure a qualitative assessment of the results. The screw
elements approach (cf. fig. 3) made it possible to install steel
screws into the samples. The idea is to strengthen the internal
structure by means of rigid and cheap standard elements like
screws. Table 2 shows an increase of the max. bearable load
from 36.95 to 49.28 kN (increase of 33.4 %) with the
implementation of screw elements.
Table 2: Comparison of max. load sustained
Max. load sustained [kN]
Cubic infill pattern
21.45
Triangle infill pattern
36.95
Triangle infill pattern with
screw elements
49.28
Furthermore, additional layers helped the samples to
withstand the max. load for a longer period. Additional layers
are two plates with a height of 2 mm, which are printed from
solid material in contrast to the infill pattern. Figure 4 shows
the impact of additional layers on the force-strain-chart.
The validation of the
results from the infill
pattern study and the
additional elements were
carried out on a
demonstrator. The
demonstrator had a
forming geometry in the
shape of an elk’s head
and showed a complex
design with different sized geometries in its antlers. This
geometry was subsequently formed in various kinds of sheet
metal samples reaching from 0.5 mm to 1.5 mm in thickness.
The additively manufactured forming tools were loaded a total
of 19 times with an average load of 54.74 kN and did not show
any failures in the internal structure. Whereas the forming
geometry showed significant deformation up to the point of
lowering the imaging accuracy. Figure 5 shows the forming
tool and the tool deformation of the elk’s head.
Therefore, it becomes apparent that the initial problem has
been improved and the internal structure has been optimized
regarding the load path of deep drawing. A suitable infill
pattern was determined and the additional elements
strengthened the internal structure to such an extent that it could
withstand significantly higher loads. In this specific case,
antlers with a diameter less than 3 mm (cf. fig. 5) showed limits
regarding repeatable forming accuracy as the reproduction of
such filigree structures after several deep drawing processes is
Figure
3: Additional elements tested
Screw elements Additional layers
Figure
5: Impact of additional layers
0
10000
20000
30000
40000
0 10 20 30 40
Forc e [ N]
Compress ion [%]
0
10000
20000
30000
40000
0 10 20 30 40
Forc e [ N]
Compress ion [%]
Witho ut
addit ional layers
With additional layers
Figure 4: Forming deformation and geometrical setup
Ø 6.5
[mm]
Ø 4
Ø 2
Ø 1
Ø 1.5
Ø 3
Ø 5.5

24 Günther Schuh et al. / Procedia CIRP 93 (2020) 20–25
Author name / Procedia CIRP 00 (2019) 000–000 5
to be assessed as poor. This raises questions as to how far tips
have to be rounded off and which curvatures at the edges result
from the deep drawing process. The continuing task is therefore
the determination of guidelines for forming geometries of
additively manufactured forming tools, since PLA material
shows significant deformation in places of high loads.
3.3. Simulation of deep drawing cup geometries
In this experiment, the formability of a more complex
geometry with a 3D printed PLA tool has been investigated
both simulative and experimental. The two-sided punch model
(cf. fig. 6) has been chosen, because the ‘crater rim’ shaped area
of the upper die and its counterpart in the lower die present a
highly stressed area. In this area, the sheet metal part is loaded
with high tensile stress during the forming process, as it has
been drawn by tensile stresses from both sides, which leads to
a high shear stress on the die surface due to tribological
interaction of both parts. Furthermore, this area must withstand
a high pressure due to its small surface without significant
plastic deformation or fracture to assure the dimensional
accuracy of the sheet metal parts.
The preliminary examination for the optimal parameters
such as corner radius or die clearance has been conducted by
FEM-Simulations with ABAQUS. For the numerical analysis
of material interaction, an explicit solver has been chosen, since
this is more suitable regarding time consumption of dynamic
and nonlinear problems [22, 23]. To reduce the simulation time
further without sacrificing the simulation accuracy, the
adaptive meshing method has been used [24]. The most
relevant areas of the workpiece and die has been meshed with
a high density, while the less formed areas are meshed with less
density (cf. fig. 6). As the prediction of the die deformation is
a primary aim of the simulation, a dynamic simulation has been
conducted, which means both dies and the workpiece are
formable and no part has been considered as 100 % rigid. The
left graphic of figure 7 shows the simulation conducted for a
part formed with a rigid die out of tooling steel and the right
graphic shows the result with a dynamic die with the material
data sheet of PLA. Due to the springback effect of formed parts
and high elasticity of polymer dies, the simulation on the right
is more realistic.
The die clearance is a function of the sheet metal thickness
and an important parameter for the dimensional accuracy of the
formed sheet metal part. It also has a great effect on the drawing
forces, which the die must withstand. The simulation has been
conducted without the consideration of special properties of
additively manufactured parts such as anisotropies depending
on the build orientation or infill density and the dies are
considered as isotropic PLA materials. The interaction between
die and sheet metal part has been analyzed, since the die is not
rigid and deformed elastic-plastically significantly depending
on the process and geometry parameter.
Thereby, unsuitable die clearances have been detected
without time and cost consuming experiments. Fig. 8 ((1), left)
shows a simulation result with a small clearance of 2 mm for
the forming operation of 1 mm DC01 steel and fig. 8 ((2), right)
is the simulation of the same geometry by a larger clearance of
3 mm, which is more suitable to prevent die failure. In ((1) b)
and c), the initial states of bulge part and the outer circle can be
seen. Fig. a) and d) show the deformation (edge collapse of the
bulge part and edge wear of the outer circle) due to high
forming forces as a result of a small clearance. The increased
clearance of the dies reduces the necessary forming forces and
as a consequence, the dies are less weared or deformed.
For the experimental validation of the suitability of the
above presented simulation, the die geometry with a clearance
of 3 mm has been chosen and manufactured by an Ultimaker 2
FFF-printer. The optimal printing parameters regarding high
compressive strength have been determined based on the
Design of experiments presented in chapter 3.1 of this work.
First, the surface of the manufactured die has been scanned
by a Nikon MCAx ModelMaker handheld scanner after the 1st,
2nd, 8th, 13th and 23rd forming operation. The results show that
the die is deformed remarkably after the 1st forming operation
at the most stressed areas. The area and degree of deformation
is consistent with the simulative results above (cf. fig. 8 and 9).
The aim of the experiments is on the one hand the
comparison of the real die deformation with the simulative
results. On the other hand, it is the evaluation of multi-cycle
effects on the die deformation, since this simulation only
delivers the deformation after the 1st forming operation and
does not contain information about mid- or long-term wear.
Figure 9 presents the comparison of the optical measurement
after the 1st and 23rd forming operation. As seen, after the 1st
deformation of die and compression of the additively produced
Figure 6: Geometry and load simulation results for the die models
Upper die Lo wer d ie
Figure 7:
Load simulation results of formed part with rigid and
dynamic dies
Rigid d ie
Dyn amic d ie
Figure
8: Load simulation results of small (2 mm, left) and
big (3 mm, right) die clearance
(a)
(b) & (c) In itial Stag e
Inner & outercirc le
Bulge part
(1)
2 mm clearance
(2)
3mm clearance
(b)(c)
(d)(a)(d)
(c) (b)
(a) & (d) A fter simu lat io n
Die clearance

Günther Schuh et al. / Procedia CIRP 93 (2020) 20–25 25
6 Author name / Procedia CIRP 00 (2019) 000–000
layers, die deformation and wear is only on a minor level.
However, in the red marked area, a deformation of + 0.5 mm
(cf. scale on the right of fig. 9) can be seen. This might be a
result of adhesive wear of the die, as during the forming
process, PLA can be drawn with the material from the upper
parts of the outer circle. This minor change might also have
been measured, as some dust and coating material (zinc) of the
sheet metal part is collected at this area.
A good approximation for wear and deformation prediction
by process simulation with FFF-manufactured forming tools is
possible. The die deformation after the 1st forming operation is
remarkable high, so the dimensional accuracy of die and
formed parts must be measured after this operation. The die
wear due to the following 22nd forming operations is
insignificant, but the future research must be done with an
extended amount of experiments, as the automotive pilot series
production includes mostly 100 parts or more, for which the
suitability of the dies has been investigated.
4. Conclusion and future work
The cupping test confirms that 3D printed PLA tools are
sufficiently stable for sheet metals and provide similarly good
results as metallic tools in terms of formability. PLA material
shows good frictional properties. In addition, the simulation of
deep drawing cup geometries demonstrates that FEM
simulations of deep drawing can substitute a physical
experiment to investigate the forming accuracy. Nevertheless,
the simulation is limited in the representability of damage
mechanisms compared to experiments. Finally, results of
optimizing the tool design regarding compressive strength
demonstrates that the load capacity of the inner structure can
be significantly improved beyond the limits of the base material
by using additional elements. Furthermore, the limits of
forming accuracy were revealed.
Future research should continue to focus on the optimization
of manufacturing parameters to increase the material efficiency
and thus the productivity of the FFF process. In addition,
detailed knowledge of the deformation of the tools during a
small series production is required to maintain imaging
accuracies over several production cycles. One approach is to
increase the efficiency of the FEM simulation. In particular, a
reduction of the computing time is required to achieve more
reliable results.
Acknowledgements
I wish to acknowledge the Federal Ministry of Economics
and Technology (BMWi) for funding the project LeSS
(Lightweight Steel Spaceframe) in the context of which this
research was conducted.
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Figure 9: Die deformation after 1st and 23rd drawing operation [in mm]
Afte r 1
st
forming operation Afte r 23
rd
formin g operation