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Lehrstuhl für Umformtechnik und Gießereiwesen
Edge-fracture-tensile-test
Kantenrissprüfverfahren im Zugversuch
Dipl.-Ing. Martin Feistle
Technische Universität München, Institute of Metal Forming and Casting
Zwick GmbH & Co. KG | Ulm, Germany | 12th – 15th October 2015
2
Contents
Motivation and objective
State of the art
Edge-fracture-tensile-test
Experimental process setup
Design of experiments
Results
• Influence of the cutting strategy on the principal strain
• Cutting surface characteristics
Conclusion and Outlook
References
3
Motivation and objective
Challenges due to the formation of edge-cracks Reduced producibility
Increased component rework
Increased mechanical tool wear and damage
Re-design of tool
Increased risk of component failure
during the lifecycle
Change in sheet material and thickness
Objective
Identification of process- and material-adjusted shear-cutting parameters to reduce the risk of
the edge-crack formation and to increase the edge formability of high-strength steels
Collar forming experiment
Bulging ratio 1.4
Bulging ratio 1.7
HCT780X
HCT780X
Process-
optimization
2 mm
2 mm
Edge-cracks increase
auxiliary costs and
reduce the component reliability
4
State of the art
Shear cut edges of higher- and high-strength steels (especially dual phase steels) show a
high risk of edge-crack formation
The material‘s forming potential can not be utilized
Necessity to estimate the edge-crack sensitivity of a given material
Testing methods of edge-cracks
Friction based Collar forming experiment
Diabolo experiment
Hole-expansion test
ISO 16630
BMW-test
Frictionless Strip-tensile-test
Dog-bone-tensile-test
Half-a-dog-bone-tensile-test
Open-hole-tensile-test
Tensile-test with notched
specimen
Edge-fracture-tensile-test
Unidimensional
stress Strip-tensile-test
Dog-bone-tensile-test
Half-a-dog-bone-tensile-test
Edge-fractrue-tensile-test
Multidimensional
stress Hole-expansion test
BMW-test
Diabolo experiment
Diabolo experiment [7]
Hole-expansion test
ISO 16630 [5]shear-
cut
milled
edge-fractrue
tensile-test [12]strip-tensile-test open-hole-tensile-test BMW-test
shear-
cut
half-a-dog-bone
tensile-test [12]
milled
shear-
cut
5
Edge-fracture-tensile-test
Schematic draft of sample geometry
(a) Closed cutting line (b) Open cutting line
60
148
R25
60
148
R25
Cutting
CuttingCutting
Cutting
Milled edge
Locating hole
Shear cut edge
Punch outline
Edge-fracture-tensile-sample
Milled edge
Locating hole
Punch outline
Shear cut edge
Edge-fracture-tensile-sample
Development of a new testing
procedure
Evaluation of the edge-crack sensitivity
based on the tensile test according to
DIN EN ISO 6892-1 Frictionless procedure
Shear-cut surfaces are usually subjected
to uniaxial stress during the forming
process
Cost-efficient and simple manufacturing of
samples, use of
reference samples with milled
surfaces on both sides
edge-crack samples with one shear-
cut side
Logging of the logarithmic elongation
upon mechanical failure, local necking
and mechanical fracture possible
8
Experimental process chain for a closed cutting line
Sh
ea
rcu
te
dge M
illed
ed
ge
Max. strain ε1 [-]
0.231
0.200
0.180
0.160
0.140
0.120
0.100
0.080
0.0500.050
0.110
0.140
0.231
0.150
Measuring area of the
edge-fractrue-sample
Gas pressure
spring
Spring
Base plate
Die
Blank
holder
Punch
Locator
Gas valve
Top plate
Milled starting blank
Edge-crack-tensile-test shear cutting tool
One-side shear-cut edge-crack
tensile test samplesTensile test
Shear-cut sheet
metal
2D-deformation analysis Principal strain
Secondary strain
Sheet metal thinning
Tensile test samples with
spray pattern Aramis 4 M
Laser Extensometer Array HP
Zwick GmbH & Co. KG
9
Design of experiments
Process variation
edge-fracture-tensile-test
HCT980X, s0 = 1.5 mm
Process evaluationReference experiments
Samples milled on both sides
Cutting surfaces
Tactile surface measurement
Light microscope recording
Optical 2D-deformation analysis
Principal strain
Secondary strain
Sheet metal thinning
Die clearance (2 %, 5 %, 10 %, 15 %, 20 %)
Cutting outline (closed, open (2 mm, 4 mm scrap-width))
Shear cutting radius (sharp-edged, rounded)
Cutting process (one-, two-stage)
Blank holder pressure (20 bar – 140 bar)
High-speed pressBSTA 1600-181
Universal testing machineZwick Typ 1484 / DUPS-M
2D-deformation systemLaser Extensometer Array HP
Aramis 4 M
10
Design of experiments
Process variation
edge-fracture-tensile-test
HCT980X, s0 = 1.5 mm
Process evaluationReference experiments
Samples milled on both sides
Cutting surfaces
Tactile surface measurement
Light microscope recording
Optical 2D-deformation analysis
Principal strain
Secondary strain
Sheet metal thinning
Die clearance (2 %, 5 %, 10 %, 15 %, 20 %)
Cutting outline (closed, open (2 mm, 4 mm scrap-width))
Shear cutting radius (sharp-edged, rounded)
Cutting process (one-, two-stage)
Blank holder pressure (60 bar)
High-speed pressBSTA 1600-181
Universal testing machineZwick Typ 1484 / DUPS-M
2D-deformation systemLaser Extensometer Array HP
Aramis 4 M
13
Distribution of strain before mechanical failure as function of
the manufacturing technique
Distribution of the principal strain before
mechanical failure for milled samples
Milled
sample
edge
Milled
sample
edge
Edge-
crack
Distribution of the principal strain before
mechanical failure for one-side shear-cut samples
Milled
sample
edge
Shear-cut
sample
edge
Reference sample Edge-crack tensile sample
Metallographic microscope image
Mechanical failure due to edge-crack with
characteristic horizontal path
Aramis-Image principal strain Aramis-Image principal strain
Metallographic microscope image
Mechanical failure initiated by ductile
fracture in the sample‘s center
Position of ductile
fracture initiation at
later time
Position of edge
crack initiation at
later time
14
Results
Influence of the cutting strategy on the principal strain at lokal necking
0,000
0,050
0,100
0,150
0,200
0,250
prin
cip
al str
ain
[-]
specific die clearance [%]
milled 2 5 10 15 200.000
0.050
0.100
0.150
0.250
0.200
Closed cutting line
prin
cip
alstr
ain
[-]
-63 %
-31 %
HTC980X
Open and closed cutting line
Sharp edged cutting edges
Blank holder pressure 60 bar
One stage cutting process
Punching reduces the principal strain
Increase of the principal strain with an
increase in the die clearance at
u = 2 % - 20 %
Tool displacement reduces the principal
strain by up to 63 %
15
Results
Influence of the cutting strategy on the principal strain at lokal necking
0,000
0,050
0,100
0,150
0,200
0,250
prin
cip
al str
ain
[-]
specific die clearance [%]
milled 2 5 10 15 200.000
0.050
0.100
0.150
0.250
0.200
0,000
0,050
0,100
0,150
0,200
0,250
prin
cip
al str
ain
[-]
specific die clearance [%]
milled 2 5 10 15 200.000
0.050
0.100
0.150
0.250
0.200
Closed cutting line
Open cutting line, scrap-width 4 mm
Values for a closed
cutting outline
prin
cip
alstr
ain
[-]
prin
cip
alstr
ain
[-]
Punching reduces the principal strain
Increase of the principal strain with an
increase in the die clearance at
u = 2 % - 20 %
Tool displacement reduces the principal
strain by up to 63 %
Cutting off increases the principal strain
compared to the punching process
Increase of the principal strain is in
comparison to a punching process
dependant on the die clearance
-63 %
+50 %
-31 %
-23 %
HTC980X
Open and closed cutting line
Sharp edged cutting edges
Blank holder pressure 60 bar
One stage cutting process
18
Results
Cut-face parameters as function of the cutting parameters
hE
hB
hS
hG
hE: Total rollover height
hS: Clean-shear height
hB: Total fracture height
hG: Burr height
s0: Sheet thickness
β: Fracture angleβ
s0
According to VDI 2906-2 [18]
Measuring station – MarSurf PCV
19
Results
Cut-face parameters as function of the cutting parameters
0%
20%
40%
60%
80%
100%
u=
5 %
u=
5 %
u=
15
%
u=
15
%
closed line open line
scrap-width 4 mm
The cut surface parameters according to [18]
are influenced by the stiffness of the scrap
due to a change in stress during the cutting
process
Closed cutting line yields the highest values
for rollover and clean-shear height
Rollover height increases when using a
higher die clearance
hE
hB
hS
hG
hE: Total rollover height
hS: Clean-shear height
hB: Total fracture height
hG: Burr height
s0: Sheet thickness
β: Fracture angleβ
s0
According to VDI 2906-2 [18]
Measuring station – MarSurf PCV
hE
hB
hS
20
Conclusion and Outlook
Conclusion
The edge-fracture-tensile-test offers advantages which allow to evaluate the
edge-fracture-sensitivity• Frictionless procedure
• Cost-efficient and simple manufacturing of samples
• Modular tool desing allows easy variation of the shear-cutting parameters
• Cut-face is usually subjected to uniaxial strain
Higher residual formability can be maintained by using a • material specific die clearance and an
• open cutting line with small scrap-width
Advantages by using a Laser Extensometer Array HP
• No sample preparation
• No system calibration for each test series
• Easy heandling and flexible positioning of the measuring points
Outlook
Validation of the edge-fracture-tensile-test using standard edge-crack testing methods, e.g. Collar-forming experiment
Diabolo experiment
Open-Hole-Tensile-Test
21
Thank you for your attention!
Picture: TUM, Uli Benz
22
References
[1] Kleiner M, Geiger M, Klaus A. Manufacturing of Lightweight Components by Metal Forming. CIRP Annals – Manufacturing Technology, Volume 52, Issue 2, Elsevier
B.V., Amsterdam, Netherlands; 2003. p. 521-542.
[2] Lange K. Umformtechnik – Handbuch für Industrie und Wissenschaft. Band 3: Blechbearbeitung, 2. Auflage, Springer-Verlag, Berlin, Heidelberg; 1990.
[3] Doege E, Behrens BA. Handbuch Umformtechnik. 2. Auflage, Springer-Verlag, Berlin, Heidelberg; 2010.
[4] Kardes N, Altan T, Examining edge cracking in hole flanging AHSS. Stamping Journal FMA Publication, Rockford, IL, USA; 2008.
[5] N. N. Metallic materials - Sheet and strip - Hole expanding test. ISO 16630, ISO copyright office, Geneva, Switzerland; 2009.
[6] N. N. Flanged holes - Flange forming. VDI 3359, Association of Engineers, Beuth Verlag GmbH, Düsseldorf; 2013.
[7] Liewald M, Gall M. Experimental investigation of the influence of shear cutting parameters on the edge crack sensitivity of dual phase steels. IDDRG 2013
Conference, Zurich, Switzerland; 2013.
[8] Golovashchenko S, Ilinich A. Analysis of Trimming Processes for Stamped Body Panels. Source: http://www.autosteel.org/~/media/Files/Autosteel/Great%20
Designs%20in%20Steel/GDIS%202008/30%20-%20Analysis%20of%20Trimming%20Processes%20for%20Stamped%20Body%20Panels.pdf; 2008
[9] Dykeman J, Malcolm S, Huang G, Zhu H, Ramisetti N, Yan B, Chintamani J. Characterization of Edge Fracture in Various Types of Advanced High Strength Steel.
SAE 2011 World Congress & Exhibition, Technical Paper 2011-01-1058; 2011.
[10] Lee J, Ko Y, Huh H, Kim H, Park S. Evaluation of Hole Flangeability of Steel Sheet with respect to the Hole Processing Condition. Key Engineering Materials Vols.
340-341. Trans Tech Publications, Switzerland; 2007. p. 665-670.
[11] Konieczny A, Henderson T. On Formability Limitations in Stamping Involving Sheared Edge Stretching. SAE Paper No. 2007-01-0340, SAE International,
Warrendale, PA, USA; 2007. p. 41-50.
[12] Feistle M, Krinninger M, Pätzold I, Volk W. 60 Excellent Inventions in Metal Forming. In: Tekkaya AE, Homberg W, Brosius A. editors. Springer-Verlag, Germany;
2015
[13] N. N. Metallic materials - Tensile testing - Part 1: Method of test at room temperature (ISO/DIN 6892-1:2014). DIN EN ISO 6892-1, DIN German Institute for
Standardization, Beuth Verlag GmbH, Düsseldorf; 2014.
[14] Volk W, Hora P. New algorithm for a robust user-independent evaluation of beginning instability for the experimental FLC determination. International Journal of
Material Forming, Volume 4, Issue 3 Online, ISSN 1960-6214, Springer-Verlag France; 2010. P. 339-346
[15] Krauer J. Erweiterte Werkstoffmodelle zur Beschreibung des thermischen Umformverhaltens metastabiler Stähle. Dissertation, Technische Hochschule Zürich,
Switzerland; 2010
[16] N. N. Dörrenberg Edelstahl GmbH: Datenblatt Werkstoff-Nr.: 1.2379; 2004.
[17] N.N. Salzgitter Flachstahl GmbH: Werkstoffblatt Dualphasenstahl HCT980XD, Nummer 11-980, Ausgabe Nr. 03;2014
[18] N. N. Quality of cut faces of (sheet) metal parts after cutting, blanking, trimming or piercing; shearing, form of sheared edge und characteristic values. VDI 2906-2,
Association of Engineers, Beuth Verlag GmbH, Düsseldorf; 1994.
23
Dipl.-Ing. Martin Feistle
Tel.: +49 89 289 14554
Technische Universität München
Lehrstuhl für Umformtechnik und Gießereiwesen
Walther-Meißner-Straße 4
85748 Garching
Tel.: +49 89 289 13791
Lehrstuhlinhaber
Prof. Dr.-Ing. Wolfram Volk
www.utg.de