Edge-fracture-tensile-test Kantenrissprüfverfahren im Zugversuch · DIN EN ISO 6892-1 Frictionless procedure Shear-cut surfaces are usually subjected to uniaxial stress during the

$Page 1: Edge-fracture-tensile-test Kantenrissprüfverfahren im Zugversuch · DIN EN ISO 6892-1 Frictionless procedure Shear-cut surfaces are usually subjected to uniaxial stress during the$
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


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


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


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


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


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


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


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

[-]


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

[-]


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

[email protected]

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

[email protected]

www.utg.de

Documents

Edge-fracture-tensile-test Kantenrissprüfverfahren im Zugversuch · DIN EN ISO 6892-1 Frictionless procedure Shear-cut surfaces are usually subjected to uniaxial stress during the