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Simulation – Partnership Solutions
Wim Slagter, The Netherlands
Michael Winter, Germany
MSC.Software Corporation, the established provider of simulation software and
services employs more than 1400 people in 22 countries. One of its main goals is to
make simulation software that helps engineers with developing better and cheaper
forgings faster. To achieve this goal of providing simulation solutions for industrial
practice, close collaboration with both forging companies and institutes has clearly
proven to be essential.
The current paper presents an overview of technology partnerships in simulation
between MSC.Software and leading forging companies/institutes. Various partnerships
were established around the world so far. They were focused on all kind of subjects
ranging from user interfaces and computational techniques to specific forging
technology such as metallurgy, defects (i.e., cracking, laps) and press kinematics.
Recently, a new partnership on ring rolling has been established. Results of those
partnerships will be presented.
1 Introduction
MSC.Software Corporation (NYSE: MNS) is the world's leading developer of simulation
software for engineering applications. Spanning more than three decades, this
leadership is built on a foundation of engineering expertise, technology partnership,
and customer support. With reported revenue of $236 million in 2001, it currently
employs more than 1400 people in 22 countries.
While MSC has dramatically improved and expanded its forging-simulation solutions to
customers around the world, no single company has the resources to develop and
maintain every aspect of such solutions. That's why MSC has established partnerships
with other leading companies and institutes. MSC works closely with a select group of
companies/institutes to integrate leading technologies, and products into a forgingsimulation solution that is tailored to forger's specific needs.
The current paper presents an overview of technology partnerships in simulation
between MSC and those companies and institutes.
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2 Technology Partnerships
2.1 Finite Volume Technology
With the development of numerical analysis techniques, the finite element method was
introduced in the early 1980's as a viable alternative to physical manufacturing. The
finite element method has been extensively researched through several research
groups but after 20 years it was still not being readily implemented in the industry [1] for
3-D forging simulation. Although MSC has been developing finite-element packages for
more than 3 decades, the lesson could be learned that a completely different approach
might be useful to pursue.
With the above challenge in mind, MSC started performing 3-D forging simulations with
a finite volume method. Unlike a traditional finite element mesh that distorts while
attempting to follow the deformation of material, the finite volume mesh is a fixed frame
of reference and material simply flows through the mesh. A Japanese National Forging
project was established in 1996 in which this method was investigated on a large set of
industrial forging processes. An example is shown below in Figure 1.
Figure 1 : Dual connecting rod simulated with finite volume method in 1997.
Although the finite volume method was the only method that could successfully solve
them all, new developments were required to make this approach industrially
acceptable. A technology partnership was set up with Sumitomo Heavy Industries such
that industry needs could be directly translated into new software development of
MSC.SuperForge. For example, special emphasis was put on developing algorithms
for simulating 3-D forging processes within an industrially acceptable time. Although
CPU time is relevant, it became quite clear that elapsed (clock) time is much more
important. Running a job in a relatively short CPU time but with necessary manual
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(read: user) interventions due to premature termination of the analysis is of course
unacceptable. A forging design department is always under high time pressure and
labor time is very costly. Therefore, special project tasks were devoted to robustness of
the finite volume method. For example, a special contact algorithm has been
developed, in which contact conditions are kinematically enforced between the die and
the work piece. The non-iterative nature of this contact algorithm makes it very unlikely
that the analysis will fail due to difficulties with contact. In addition, it completely avoids
penetrations common to penalty-based contact algorithms. Penetrations are, of course,
unacceptable because its accumulation in time might yield significant loss of material.
Finally, convergence is always guaranteed. This represents a significant advantage
over the penalty-based contact algorithms that try to choose the "right" penalty
coefficients. Especially in strongly nonlinear problems many iterations are often
necessary with either changed penalty coefficients or increased convergence
tolerances.
Finally, cooperation with the University of Michigan [2] and the Center for Mathematics
& Computer Science [3] was established to develop a new method for free surface
handling. Since a finite volume solver simply tracks the material volume fraction
(FMAT) per finite volume element, the orientation and exact position of the free surface
are not adequately defined. In addition, FMAT methods tend to be diffusive and do not
preserve material shape accurately. From this collaboration work, MSC concluded that
the free surface should be explicitly defined in the finite volume method. In this way, the
advantages of the finite element and the finite volume approach could be combined:
natural representation of the free surface and that of gross 3-D material deformation,
respectively. The foundation for advances in 3-D forging process modeling was hereby
considerably improved.
2.2 Forging-Specific GUI
In 1998, MSC and Hitachi Zosen Information Systems Co. (HZS) signed a long-term
partnership agreement to jointly develop a forging-specific graphical user interface
(GUI) for MSC.SuperForge. HZS has a 30% market share in CAD/CAM activities in
Japan. With HZS’ experience and understanding of forging processes, users, and
needs of the forging industry the GUI could be significantly extended and improved to
meet customers’ needs and requests.
Whereas it was not uncommon to spend days developing an accurate 3-D model, the
current GUI enables a significant reduction in elapsed time required to develop a model
(Figure 2). Fast and efficient exchange of CAD data becomes possible by means of
Standard Triangulation Language (STL) file transfer. This technique originating from
rapid prototyping is now fully eliminating the need for manually meshing of work piece
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and dies in case of forging simulations. Every CAD package supports STL. In contrast
to finite element methods, finite volume methods do allow very fine STL models to
capture all intricate die details.
Figure 2 : Graphical User Interface.
In addition, joint developments in GUI with HZS were towards using forging
terminology from the forge shop. For example, the motion of a crank press can be
represented through simply defining the actual press characteristics (i.e., stroke,
revolution speed and rod length). Besides press characteristics, material properties can
be stored in a database such that reuse of these data is easily possible. Apart from
flow lines and particle tracking, other GUI features such as automatic detection of laps
and lubricant pockets were being developed.
Finally, developments in GUI were focused on ease of use. Forging designers don’t
want to be bothered with meshing or other typical finite element terminology. An
advanced technique like Resolution Enhancement Technology enables new
developments of "meshless" forging simulations: since the finite volume mesh and the
(initial) material surface mesh are very simple, it is automatically generated and
completely hidden from the user. The forging designer can carry out parameter studies
in which they vary process parameters by drag-and-drop in the GUI. To perform a die
stress analysis, the finite element mesh is automatically generated and its boundary
conditions can be defined by graphical picking on the constraining planes of the die.
Consequently, the finite element solver of MSC.SuperForm (the successor to
MSC.AutoForge) will be spawned through the GUI of MSC.SuperForge.
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2.3 Microstructure
It is well known that metal flow in a forging process is not only affected by strain, strain
rate and temperature. Metal flow is also affected by micro-structural changes. However,
the latter has often been neglected in simulations. In principle, the numerical analysis is
often performed without a sufficient metallurgical background.
Although the number of forging simulations accounting for micro-structural changes
increases [4,5,6], most of them did not account for the full coupling of the three fields
(metallic structures, temperature and stress/strain), and all of them were limited to
simple shapes (two-dimensional models). Although the influence of the strain rate is
obviously important (i.e., decreasing martensite with increasing strain rate), most
published work was limited to the low strain rate range (~10-3 s-1).
To overcome the above limitations, MSC has been collaborated with a well-known
university in this field - the Kyoto University. The austenitic stainless steel SUS304 was
chosen for the project because of its obvious practical importance and notable microstructural phenomena that occur during the forging process. By means of the finite
volume method, an approach based on the metallo-thermo-mechanics [7] to simulate
metallic structure, temperature and stress/strain in the forging process associated with
strain-induced phase transformation has been developed. In addition it has been
extended to large 3-D deformation, and implemented into MSC.SuperForge. Special
attention has been paid to the effects of strain rate on structural change and
mechanical behavior (Figure 3).
(a) High strain rate
(b) Low strain rate
Figure 3 : Martensite distributions due to forging.
2.4 Ductile Damage
Forging simulation tools are able to predict material flow, die loads, distribution of
stresses, strains and temperature. In the last decade, more attention has been paid to
the prediction of damage. Tens of different damage models have been developed but
none of them were general enough to solve all forging problems, corresponding to the
different loading conditions (as discussed in [8-11]). In particular, it appears that all
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these models overvalue the dependence on the triaxiality parameter, while the fitting of
a reliable model should not depend on the loading conditions, but only on the material
used.
Therefore, a research project [12] was conducted at the University of Federal Armed
Forces in Hamburg (and funded by the German Research Council DFG) to develop a
new damage model that is generally applicable. It is a phenomenological model,
combining the mechanism of failure with considerations of the dissipated fracture
energy. In collaboration with both MSC and Femutec it has been implemented in
MSC.SuperForge and MSC.SuperForm (see Figure 4).
Drel
Figure 4 : Damage prediction of a hexagon socket screw.
This damage model requires material input parameters that can be measured in
relatively simple tension and compression tests. With this model of damage evolution
one is capable of predicting critical areas in forging simulations and has therefore a
basis for the optimization of the production sequence by varying this sequence until a
minimization of the damage criteria has reached.
2.5 Press Kinematics
In 2001, MSC and LASCO Umformtechnik GmbH signed a technology partnership
agreement. With more than 135 years of experience in mechanical engineering,
LASCO is recognized today as a manufacturer of the most advanced machines and
equipment for bulk and sheet metal forming. With LASCO’s experience and
understanding of forging machines, and needs of the forging industry the press
kinematics in MSC.SuperForge could be further optimized. For example, the
implementation of an energy/force relationship as shown in Figure 5 may significantly
improve the results of a simulation involving a screw press. LASCO presses &
hammers are standard available in the machine database of this program.
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100
Slip point
SPR
50
Net energy [%]
Blow efficiency [%]
1
2
FN : Nominal press force
FD : Continuously useable press force
F : Impact force
Pr
3
0
0
Force [%]
50
F
N
80
F
D
1 Spring energy
2 Slipping clutch energy
3 Forming energy
100
F
Pr
Figure 5 : Relationship energy/force of LASCO screw press - type SPR.
The energy requirements of the work piece and the forming power are essential factors
in determining the size of a screw press. For LASCO, simulation is considered as an
additional advisory tool to decide what energy-level press is required to form a part of
their customer or prospect. In addition, some hammer operators tend to use full power
at all times. This overloads the press, and may lead to premature die failure. By means
of simulation, LASCO can clearly show the benefits of using blows with less power.
Finally, LASCO will proceed with developing Knowledge Based Engineering
techniques but now closely linked with simulation. This enables concept design
geometry to be assessed rapidly for manufacturing feasibility.
2.6 Technology Transfer
In 1998, OTTO FUCHS Metallwerke – a technology and market leader in the non-steel
forging industry – joined MSC in a technology partnership. In view of OTTO FUCHS’
large variety of both forged parts (automotive & aerospace) and non-ferrous alloys (Al-,
Ti-, Mg-, Cu- & Ni-alloys) as well as their very high quality requirements (security parts,
Figure 6), their expertise appeared to be the key to bring simulation on a high industrial
level. The objective of this partnership was to advance the application of 3-D simulation
technology in the forging industry by working together to implement MSC.SuperForge
into the business and product development process. In order to achieve that objective,
a variety of new program functionality has been implemented. To increase throughput
of simulation projects, improvement of ease of use can be considered as one of the
most important development activities. Besides ongoing projects on micro-structural
analysis, new activities will be started in the field of extrusion and roll-forging simulation
as well as simulation-data management.
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Figure 6 : Example of simulated hinge fitting (Courtesy of OTTO FUCHS).
2.7 Precision Forging
In 1999, a technology partnership was set up with the Institute for Integrated
Production Hanover (IPH). IPH develops precision-forging technology that is based on
near-net shape technology. By means of this partnership, a win-win situation for each
partner could be created. On the one hand, simulation could provide IPH more costeffective means to investigate a large variety of process parameters. On the other
hand, MSC could gain more knowledge of the precision forging process.
IPH was able to set up a systematic database of process parameters for some
precision-forged products [13]. These parameters may affect the extent of die filling, the
holding force on upper & lower dies, the contact pressure on upper & lower punches,
as well as the deformation and temperature of the tools. IPH applies the more precise
process parameters for precision-forged parts such as connecting rods and
crankshafts (see Figure 7).
Figure 7 : Simulation example of precision-forged parts (Courtesy of IPH).
2.8 Ring Rolling
In 1999, together with the MSC-MARC merger, a technology partnership with
FEMUTEC Ingenieurgesellschaft mbH was formed. FEMUTEC is MSC’s competence
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center on metal forming in the German language area, and responsible for pre sales
support, customer support, and training for both MSC.SuperForm and
MSC.SuperForge. FEMUTEC is collaborating with MSC on several R&D projects for
both products. One of those is focused on the ring rolling process.
Years ago it was stated that ring rolling processes were not able to simulate. The main
reason was the problem of extremely long simulation (CPU) time due to tremendous
number of finite elements. Pilot studies at the very beginning of the research work in
1999 showed unacceptable CPU times of more than 8 weeks.
Therefore, the first approach was the simulation of a partial ring segment (Figure 8).
Due to the fact that a fully thermal-coupled analysis is necessary to accurately examine
the behavior of the ring during rolling, it is clear that this approach has an important
disadvantage: the part of the ring which is not within the forming area (outside the rolls)
and therefore not simulated, will get wrong thermal properties. This leads to
mismatching estimation of roller forces and moments, as well as inaccurate shapes.
Figure 8: Simulation of a ring rolling process.
The second approach was the simulation of the entire ring but using much less finite
elements. While meshing a profiled ring commonly needs 50-80K elements, a new
template technique based on MSC.SuperForm’s HexMesher was being developed that
enables a ring consisting of only circa 10K elements. In conjunction with implementing
an analytical surface description of the rolls, the CPU time could be reduced to 3-4
days. More optimization of numerical algorithms will be carried out in the near future.
The latest developments almost allow the economical simulation of complex ring rolling
processes in an industrial environment. The results were of good quality accounting for
all physical effects in the complete process chain (Figure 9).
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Figure 9: Forged and trimmed pre shape.
Nevertheless some more R&D work is necessary to bring the ring rolling simulation to
the process designers and the forgers in the shop floor – similar to what has been
achieved in the die forging area. Therefore, a new R&D consortium of companies was
initiated in the beginning of 2002. Members of this group are MSC.Software as the
software vendor, FEMUTEC GmbH as the software development partner, SMS
Eumuco GmbH as the machine vendor, and Karl Diederichs Dirostahl and Press- und
Schmiedewerk GmbH as industrial partners.
Objective of this R&D work is to develop a tool which allows forgers in the shop floor as
well as the process designers to get more insight in possible rolling defects, ways to
reduce tolerances, extent of shrinking, flatness and ovality, as well as magnitude of
forces and moments. Figure 10 shows a simulation example of a profiled ring rolling
process. The outcome of this collaborative project work is also likely to be valuable for
simulation of axial and radial roll forging processes.
Figure 10: Example of a profiled ring rolling process.
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3 Conclusions
Simulation of forging processes appears to be one of the most exciting and challenging
subjects. Since it involves a variety of disciplines ranging from metallography,
mechanics, mathematics, numerical methods, technology and applications, it is
undoubtedly of significance to collaborate with both metal-forming institutes and forging
companies - each having its own core competence to make forging simulation a
commodity.
Because technology moves at a rapid pace and forger needs continue to grow, MSC is
always carefully evaluating new potential partners.
4 References
1. Bramley A; Forging Modelling. Proc. of the 9th Intern. Cold Forging Congress, pp
165-168, 1995.
2. Aalburg C, Van Leer B; Experiments in minimizing numerical diffusion across a
material boundary, University of Michigan, 1996.
3. Koren B; Computational forging in the Eulerian formulation at MacNeal-Schwendler
(E.D.C.) B.V., Technical Report, Center for Mathematics and Computer Science,
Amsterdam, 1996.
4. Kawai N, Saiki H and Hirate H; Improvement of the Stretchability of 18-8 StainlessSteel Sheets due to Strain Induced Transformation. J. Japan Soc. Tech. Plasticity
17: pp 899-906, 1976.
5. Shinigawa K, Nishikawa H, Ishikawa T and Hosoi Y; Deformation-Induced
Martensitic Transformation in Type 304 Stainless Steel during Cold Upsetting. Iron
and Steel 3: pp 156-162, 1990.
6. Cortes R, Tsuta J.A; Flow Stress and Phase Transformation Analysis in the
Austenitic Stainless Steel under Cold Working – Part 3, Analyses for SUS 301,
SUS 304, SUS 310 Steels and Experiments on Forward and Backward Extrusions.
Memoirs of the Faculty of Engineering, Hiroshima University 11(3): pp 35-52, 1993.
7. Ding P; Research on Metallo-thermo-mechanical Simulation of Forging Processes,
Ph.D. Thesis, Kyoto University, 2001.
8. Dahl W and Pawelski O; Umformtechnik, Plastomechanik und Werkstoffkunde,
Verlag Stahleisen mbH, Duesseldorf, 1993.
9. Groche P; “Bruchkriterien fuer die Blechumformung”, Ph.D. thesis, Universitaet
Hannover, Fortschr.-Ber. VDI Reihe 2, Vol. 229, VDI-Verlag Duesseldorf, 1991.
10. Landgrebe D; “Bestimmung der Formaenderungsgrenzen durch duktiles Werkstoffversagen bei Kaltumformverfahren mit Hilfe der FEM”, Ph.D. thesis, Universitaet
der Bundeswehr Hamburg, 1999.
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11. Seidenfuss M; “Untersuchungen zur Beschreibung des Versagensverhaltens mit
Hilfe von Schaedigungsmodellen am Beispiel des Werkstoffes 20 MnMoNi5”,
Techn.-wiss. Ber. MPA Stuttgart, Universitaet Stuttgart, 1992.
12. Behrens A, Landgrebe D and Just H; Prediction of cracks in multistage cold forging
operations by finite-element-simulations with integrated damage criteria. Proc. of
the 8th Intern. Conf. on Metal Forming, Krakau, Polen, pp 245-252, 2000.
13. Altmann HC, Slagter WJ; Quality of simulation packages for flashless hot forging
operations, Simulation of Materials Processing: Theory, Methods and Applications,
Proc. of NUMIFORM 2001, 363-368.
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