1. FLD Creation for SS304 Using Experiments & It’s Validation Using
HyperForm 11.0
Ravi J Bhatt Mallika R Bhatt
Research Scholar Visiting Professor
Nirma University Dollyben Desai Institute of Computer
S G Highway Science
Ahmedabad-382 481, At & Post Amadpore
Gujarat, India Navsari-396 445, Gujarat, India
Abbreviations: FEA - Finite Element Analysis, FLD - Forming Limit Diagram, LDH - Limiting Dome
Height
Keywords: Computer Simulation, Forming Limit Diagram, Sheet Metal Forming
Abstract
Sheet metal forming is the process of converting flat sheet of metal into a part of desired shape without fracture or excessive
localized thinning. The application of sheet metal forming includes automotive industry, aerospace industry, household
equipment’s and many more. Forming Limit Diagram (FLD) is used during the design stage of any new sheet metal
component for tooling shape & optimizing variables. It is nothing but a combination of major & minor strain. In this study FLD
is obtained experimentally with Hemispherical Dome Test. Validation is carried out using computer simulation through
HYPERFORM, for the simulation a typical industrial component was chosen which had manufacturing complications &
material properties for that were obtained by Uniaxial Tensile Testing. The results of experimental & HYPERFORM are in
good agreement. It is favorable to use HYPERFORM, as it gives better results with reduction in lead time & cost. Eliminates
material wastage. Also improves quality and productivity. As an FEA tool HYPERFORM can give better idea for
manufacturing of complicated geometries.
Introduction
As new market requirements have becoming more persistence through introduction of new technologies for
improvements in performance trends, these FEM based software simulation has becoming more affordable
& reliable as they reduces lead time & cost. Here an attempt is made to determine FLD of SS304 using
experiments & validated with computer simulation through HYPERFORM. The forming limit of sheet metal is
defined to be the state at which a localized thinning of the sheet initiates during forming, ultimately leading to
a split in the sheet. The forming limit is conventionally described as a curve in a plot of major strain vs. minor
strain. Fig.1 shows the conventional forming limit diagram.
Figure 1: Forming Limit Diagram
Literature Review
FLD concept was first given by GENSAMER (1946) but concept was extended by KEELER (1964) and
GOODWIN (1968) and represents the criteria of deep drawing operation [1]. Many efforts have been made
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2. in area of forming process & forming limit diagram; Djavanroodi [2] Ti6Al4V titanium and Al6061- T6
aluminum alloy sheets, with the thickness of 1.08 mm and 0.8 mm respectively. The properties for these
materials obtained from uniaxial tensile testing based on ASTM E8 standard and anisotropic characteristics
(r-values) obtained according to ASTM-E517 standard. Sansot [3] have done experimental determination of
FLD for the SPCE 270 steel sheet, the limit dome height testing according to the American Society of
Testing Materials (ASTM) as published in ASTM E 2218-02 was carried out on an 80-ton hydraulic press
machine at room temperature. Damoulis [4] described The dynamic explicit FEM code was able to help the
authors to solve a practical example of the automotive industry aiming to plot of a FLD, the FLC and the
failure representation (tearing) of the pressed part critical points for a St1405 material.
Determination of FLD using Experiments
1) Uniaxial Tensile Testing
Uniaxial tensile testing has been performed on six different samples with different orientation
according to rolling direction viz. 0, 45 & 90 degrees. Fig. 2 shows tool setup for uniaxial tensile
testing and tensile properties have been obtained [5],[6],[7].
Figure 2: Universal Testing Machine & Testing Samples
Table I Evaluated Tensile Properties
Sample ID Rolling Yield Ultimate Strength Anisotropy Strain
Direction Strength Tensile Co-efficient Index r Hardening
(Degree) (MPa) Strength K (MPa) Exponent n
(MPa)
1 45 299 554 1055.12 0.9297 0.2340
1A 45 288 569 1100 0.9652 0.2431
2 90 364 619 1080.27 1.0511 0.1923
2A 90 282 569 1050.41 0.9945 0.2482
3 0 318 571 1070.93 1.0813 0.2201
3A 0 293 568 1062.38 1.2273 0.2389
Average 307.33 575 1069.85 1.0415 0.2294
2) Circular Grid Marking by Laser Engraving
In minor and major strain measurement circle plays important role. These circles commonly have
diameters of 2.5 mm (0.100 in.). They are measured across the diameter of the circle when the line
width is minimal. The width of samples ranging from 12 mm up to 180 mm & length of the samples
kept 180 mm constant. Here Fig.3 shows that the possible shape change in the grid pattern [8] &
grid marking has been done on samples (21 samples have been prepared) as according to Fig.4 by
using laser engraving machine shown in Fig.5.
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3. Figure 3: Possible Change in the Shape of Grid Pattern
Figure 4: Grid Marking on Samples Figure 5: Laser Engraving Machine
3) Solid Modeling of Experimental Setup
Limiting dome height test [8] had chosen for experimental work. The solid modeling of experimental
setup have been done using PRO-E a commercially available modeling software. The modeled
setup with punch, die, upper ring & lower ring is given in Fig.6.
Figure 6: Solid Modeling of Tool Setup
4) Experimental Determination of FLD
The experiments have been carried out on 150 tone capacity hydraulic press as shown in Fig. 7.
Hydraulic pressure applied until the sample gets failed. The failed samples are shown in Fig. 8. The
strain produced in each samples have been measured by using profile projector Fig. 9. Then after
according to major & minor strain FLD have been generated for SS304.
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4. Figure 7: Experimental Setup Figure 8: Failed Samples
Figure 9: Profile Projector
Determination of FLD using Computer Simulation through HyperForm 11.0
Here the typical component for computer simulation has been chosen, manufactured in two draws.
First draw & second draw is shown in Fig. 10 & Fig. 11 respectively. By using HyperForm 11.0 &
employing all material properties obtained from uniaxial tensile testing, FLD have been obtained for
first & second draw as shown in Fig.12 & Fig.13 respectively.
Figure 10: Manufacturing in First Draw Figure 11: Manufacturing in Second Draw
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5. Figure 12: Forming Limit Diagram of First Draw
Figure 13: Forming Limit Diagram of Second Draw
Results & Discussions
Comparison of FLD of SS304 found from experiments & computer simulation is given by Fig.14.
The difference between two FLD0 is found to be 12.5%.
Figure 14: Comparison of Experimental & HyperForm FLD
Benefits Summary
HyperForm can be used for arrival at FLD but the over estimation is to be compensated when going for new
product development from SS304. This eliminated material wastage for experiments. Reduced lead time of
manufacturing. Quality & Productivity is improved. Proper utilization of plant capacity has been achieved.
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6. Challenges
As this component had manufacturing complications & large dimensions so it was very difficult to go with
experiments using full size dimensions of component.
Future Plans
As the results obtained from experiments & HyperForm are in good agreement the study of different
parameters viz. lubrication, blank holding pressure, strain hardening exponent & strain rate will be carried
out for similar product.
Conclusions
Here an attempt is made to determine FLD using experiments & computer simulation and to study the
effects of various parameters on FLD. The following conclusions are drawn from the above study.
• With six samples of SS304 at different orientations to rolling direction have been prepared and
average 'n' value is found to be 0.2294 and corresponding K value is found to be 1454.81MPa.
• In order to determine FLD using computer simulation HyperForm 11.0 software was chosen. For
that, same material properties & process parameters were used. The computer simulation &
experimental FLC showed the same trend. However it is found that in each case, computer
simulation gives FLC value above that of experimental value by about 12.5%.
• This work will help industry to go directly with HyperForm for SS304 material for future product
development.
ACKNOWLEDGEMENTS
I, Ravi J Bhatt, would like to thank Mr. Shivraj Patil (Altair, Pune) to provide me valuable guidance to
understand HyperForm 11.0. Also I would like to express my sincere gratitude to Mr. T R Jain (MD, Shri
Navkar Metals) for providing me an opportunity to work under them.
REFERENCES
[1] Metal Working, “Sheet Metal Forming”, ASM Handbook, Volume 14B, (2006), U.S.A.
[2] Djavanroodi F., A. Derogar, “Experimental and numerical evaluation of forming limit diagram for Ti6Al4V titanium and Al6061-T6
aluminum alloys sheets”, Journal of Materials & Design, pp 4866-4875 (2010).
[3] Sansot P., U. Vitoon, J. Jittichai, S. Surasak, “Determination of Forming Limit Stress Diagram for Formability Prediction of SPCE
270 Steel Sheet”, Journal of Metals, Materials and Minerals, Volume 21, pp 19-21, (2011).
[4] Damoulis G. L., G. Edson, B. G. Ferreira , “Analysis of the Industrial Sheet Metal Forming Process using the Forming Limit
Diagram (FLD) through Computer Simulations as Integrated Tool in Car Body Development”, International Journal of Mechanical
Sciences, pp 210-217,(2002).
[5] ASTM Handbook, “Standard test methods and Definitions for Mechanical Testing of Sheet Product”, ASTM A370, (2011), U.S.A.
[6] ASTM Handbook, “Standard Test Method for Tensile Strain-Hardening Exponents (n -Values) of Metallic Sheet Materials”, ASTM
E646, (2007), U.S.A.
[7] ASTM Handbook, “Standard Test Method for Plastic Strain Ratio r for Sheet Metal”, ASTM E517, (2010), U.S.A.
[8] ASTM Handbook, “Standard Test Method for Determining Forming Limit Curves”, ASTM E2218, (2008), U.S.A.
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