1. A Study on Solid and Shell Material Model in Stamping Simulation
Elangovan P
Stamping Simulation Engineer
Valeo India Private Limited
Block - A, 4th Floor, TECCI Park
No. 176 Rajiv Gandhi Salai
Sozhanganallur
Chennai - 600 119, India
Keywords: FEA, Sheet Metal forming, Elements, Deep drawing, HyperForm
Abstract
Sheet metal stamping simulation will be carried to predict the part failure during product design stage and some times during process
too, mainly for stages definitions and optimized blank development. But this study will focus on how solid and shell material model is
used in stamping simulation and their impact on results and application. This study will focus on Deep drawing process which will be
carried out with Shell and Solid Elements. Active tool elements will be designed for this study. The expected contribution from this
study is when and where to use Shell and Solid Elements for the Stamping simulation using HyperForm.
Introduction
Deep drawing is a forming process to make cylindrical components. Now, days for all kind of forming
process up to maximum extent, we can optimize the process using FEA Simulation softwares. This will give
an advantage of reduction in product development cost and product development time. FEA Simulation
software’s are very helpful for the process people and R&D People. For Blank Optimization, Stages
definition and Press tonnage calculation. For R&D, they can work with different materials with different sheet
thickness to develop the robust design. In addition to that the marketing people can work on Quotation
purpose based on Blank development and Strip layout. Most of the Sheet metal simulation engineers will
work on Shell Elements because of its lesser sheet thickness and it requires lesser time for simulation.
Difference between Shell and Solid Elements
Shell Elements are used for lesser thickness and larger displacement problems. For shear strain forming
and higher thickness, we need to go for Solid elements. Shell elements can reduce the simulation hours.
Element type for Shell is Shell43-Three degrees of freedom in Rotation and Translation and for solid Solid45
(Elasto-Plastic Volume Element) which as three degrees of freedom with no degree of freedom in rotation.
These element types should be used appropriately for better results.
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2. Process Methodology
Figure 1.0: Typical Drawing process
A typical drawing process is shown in the fig.1.0 which explains how the drawing operation is performed in
real process. A blank is kept over the die and it is held by Blank holder and Bottom Shedder to control the
material flow. Punch will travel at a defined velocity to a certain depth. More material flow will leads to
wrinkling effect this is because of insufficient pressure given by Blank Holder during process. More Blank
holder pressure leads to thinning and even cracks. Draw quality steel to be used for this kind of application.
For Severe draw Extra Deep draw steel will be used. For, better drawability the r-plastic strain ratio is
important. r should be (r>1) and Work hardening exponent value should be n>0.20.
Figure 1.1: Component drawing
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3. For Shell Modeling
Figure 1.3: Shell Elements Simulation Results
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4. For Solid Modeling
Challenges
Stamping simulation using shell elements is common through out the industry because of its HyperForm
auto process, for using solid elements we did more iterations to run the simulation with the support of Altair
people (Material model, Number of layers, stamping velocity and contact) etc. Even then we could not
complete the calculation fully.
Figure 1.4: Tool and Blank Design
Figure 1.5: Solid Elements Simulation Results
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5. Shell element is extruded to 1mm sheet thickness with 5layers by applying type7 contact (surface to node
group). For shell element adaptive meshing is available, for solid it is not available. Hence, it is understood
for solids it will take additional time.
Plastic strain- Comparison between Shell and Solid Modeling
The above comparison is shown for progression depth of approximately 11mm. Since, the simulation hours
for solid elements is too high and even not completed after 20hours. But, for shell elements it has taken just
2.5hrs to complete it. The results are plotted in HyperView. Plastic Strains for solids can be viewed in
HyperView. Basically, HyperView plots are based on shell elements only. Hence, thinning and fld strain
plots are unable to predict. We are working on this to find the alternate solution.
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6. Results & Discussions
This study is to understand the difference between the solid and shell elements in stamping simulation. As
per sheet metal theory the failure prediction by Keeler-Goodwin will be based on sheet surface. Hence,
based, on Shell element model we can conclude the result. Flc strains are with in the limit. Hence, the
process is safe. Thinning reduction is around 16.4% which is acceptable. Regarding solid elements we need
to check for alternate solution in HyperView or enhance it for solid elements.
Benefits Summary
Formability study was carried out for different parameters like Blank holder pressure, Stamping velocity and
Contact definition the best tryout was explained in this paper. Since the forming process is carried out in
virtual environment using the FEA technology we can predict the formability of the component without
spending money on manual tryouts and corrections.
Future Plans
Even then, this study is not completed yet. But, we learned how to simulate using solid elements. Further
study is required to improve the solid elements in HyperForm. We are planned to work with Altair to define
the optimized material models, element types and number of layers for solid elements which can enhance
the capability of solid forming by reducing the running hours.
Conclusions
Formability study using shell and solid elements is performed in HyperForm. Results of Shell element are
presented. The use and development of Solid-shell finite elements for sheet forming simulation is a growing
topic on Computational Mechanics. We are expecting to work with Altair to define the solid stamping
simulation methodology which will reduce the running hours and as simple as shell autoprocess in
HyperForm.
ACKNOWLEDGEMENTS
I would like to thanks Management of Valeo India Private limited, Chennai for providing Altair’s HyperWorks
software and constant motivation. We are also thankful to Mr.Yogesh from Altair India for support and
guidance for preparation of the paper.
REFERENCES
1. Coupling Forming Simulation and Fatigue Life Prediction of Vehicle Components Daniel.B.Dallas, Littleton
2. David A. Smith, Die design hand book, Third Edition, SME, 1990
3. Altair User’s Guide
4. IDDRG
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