tisza hot press forming v3 - university of miskolc · 2016. 8. 24. · 2014.07.10. 2 • hot press...

2014.07.10.

1

XXVIII. microCAD International Conference

Miskolc, 10‐11. April 2014.

Prof. Dr. Miklós Tisza Head of Department of Mechanical Technology

University of MiskolcInstitute of Materials Science & Technology

Department of Mechanical TechnologyMiskolc - Egyetemváros

HOT PRESS FORMING IN SHEET METAL FORMING

Dr. TM3

XXVIII. microCAD International ConferenceMiskolc, 10-11. April 2014.

Content• Introduction• Main tendencies in the automotive industry

• Challenges and driving forces in the automotive industry• Contradictory requirements and their effect on material and technological process

development

• Development tendencies in sheet metal forming• Steel developments • Application of conventional and high strength steels• Technological process developments

• Hot Press Forming – Press Hardening• Definition, fundamentals and main types of Hot Press Forming-Press Hardening Forming• Hot Press Steels (HPS) Materials and their mechanical properties• Application trends in the World of automobiles• Process characteristics

• Microstructure controlled press hardening• Tailor Welded Hot Forming Blanks

• Mass reduction potential of HPF

• Summary and Conclusions

2Dr. TM2

• Main driving forces

– Customers’ demand

– Global competition on the world market

• Customers’ requirements

– More economical

– Increased safety

– Higher comfort

• Legal requirements

– Increased environment protection

» Less harmful emissions

– Increased safety prescriptions

» more rigorous crash tests

Main tendencies in the automotive industry

• Meeting manifold requirements → mass reduction– Lower consumption

• Less harmful emissions • increased environmental

protection• more economical vehicles

• Contradictory requirements– Lower mass – thinner sheets

• but increased safety requirements

• more rigorous crash tests– solution: application of high

strength materials• unfavorable consequences:

reduction of formability


3Dr. TM6

• Main application field: car body elements (Body in White – BiW)

• Development tendencies are governed by the main requirements in car manufacturing – Low weight construction principles

– Higher strength together with suitable formability– Better crash performance

• Main material groups applied in car manufacturing– Conventional cold rolled (CR) steels– High Strength Steels (HSLA) and Advanced High Strength Steels (AHSS steels)– Non-ferrous metals and alloys

» Aluminium and its alloys» Magnesium and its alloys » Titanium and its alloys

– Non-metallic materials» Polymers» Ceramic materials» Composite (hybrid) materials (e.g. CFK)

Development tendencies in sheet materials


4Dr. TM7

Development trends in sheet materials

Micro-alloyed steels

Phosphorous alloyed steels

Dual-phase steels

Bake-hardening steels

1975 1980 1985 1990 1995 2000 2005

High strength steels

Isotropic steels

TRIP steels

SULC steels

22MnB5


5Dr. TM9

• Selected topics in sheet manufacturing

• Sheet hydroforming

– Laser forming

– Tailor Welded Blanks

– Hot forming

– Incremental sheet metal forming

– Superplastic forming

– New joining technologies

– Overall process control and monitoring

– Integrated product and process development

Process developments in sheet metal forming


6Dr. TM10

2014.07.10.

2

• Hot press forming (HPF) – also known as press hardening (PHF)

• a relatively new forming process

• recently developed particularly for the application of a special group of high strength steels in car body manufacturing in the automotive industry

• a unique metal forming processing technique

• the material is heated up to a sufficiently high temperature to provide austenitic microstructure

• then it is cooled down rapidly in the forming tool

• at certain cooling rate diffusionless martensitic phase transformation occurs leading to significant increase of the strength parameters

Hot Forming – Press hardening


7Dr. TM11

Short history of Hot Press Forming

• 1977: Invented and patented by Erland Lundström

• 1984: First applied in the automotive industry by the SAAB in the car series 9000

• 1999: First application of 22MnB5 Manganese-boron alloy in France

• 2005: The first published results on the application of Tailor Welded Blanks (TWB HWB)for hot forming

• 2008: The first application of galvanized Manganese-boron alloyed steel in car body making


8Dr. TM13

Hot Press Forming process cycle


9

723o C

Dr. TM15 Direct (a) and Indirect (b) process chain in Hot Press Forming


10Dr. TM16

Typical hot press formed parts in car body


11Dr. TM12

Areas of ultra-high strength steel application in thebody structure of a recent passenger car (Volkswagen Sharan)


12

2014.07.10.

3

Sh

are

PH

S(%

)

Trends in the usage of PHS in the automotive industry

16

14

12

10

8

6

4

2

0

• In most European cars PHS is applied in the body side structure.• In Asian cars PHS less frequently used and if so usually in the body side structure.• Some European carmakers use PHS as a strategic product for a wider range of parts.

ECB body benchmarking MY 2008-2011


13

Ms

tem

pera

ture

(°C

)

Har

dnes

s(H

V)

The martensitic steel family„adjustable strength by carbon content”

500

400

300

700

600

900

800

2000.00 0.10 0.500.20 0.30 0.40

Carbon content (wt.%)

400

350

300

500

450

550

Martensite hardness

M-start temperature

HV = 292 + 1156(%C)

30MnB5,C34

22MnB5

MS1200 – 1400

Ms = 561 – 474(%C) – 33(%Mn)

1900 MPa

1700 MPa

1500 MPa

1300 MPa


• Hardness (strength) of fully quenched martensite increases linearly with the carbon content.

• Start temperature of martensite transformation (Ms) decreases with the carbon content.

• At higher carbon contents hardness (strength) increase reduced by the content of retained austenite.

• At approximately 2200 MPatensile strength steel reaches its technical limit.

14

Material Properties of Typical Hot Press Steels (HPS)


Steel gradeMartensite

start, T oC

Critical cooling rate,

oC/s

Yield strength, MPa Tensile strength, MPa

as delivered

hot formed

as delivered hot formed

8MnCrB3 ‐ ‐ 447 751 520 882

20MnB5 450 30 505 967 637 1354

22MnB5 410 27 457 1010 608 1478

27MnCrB5 400 20 478 1097 638 1611

37MnB4 350 14 580 1378 810 2040

15Dr. TM14

t

Grade Cmax

Simax

Mnmax

Pmax

Smax

Cr+Momax

Timax

Bmax

22MnB5 0.25 0.40 1.40 0.025 0.010 0.50 0.05 0.005

The classic press hardening steel: 22MnB5 (EN 10083-3)


t8/5 < 1

t8/5

16

Tem

pera

ture

Temperature profile and microstructure developmentduring press hardening process

20 µm

20 µm303M0036 1000 : 1 3% ige HNO 3

Microstructure before press hardening Microstructure after press hardening

Alloying

F+ P M

Steel0605A03672 1000: 1Nital

Coating

Time

Transfer of plate

Die closure

Press hardening

Die opening (150-200°C)

5min 6s 12s

Heating to 880°C–950°C

bottleneck


17

T T

Microstructure controlled press hardening

Martensite

PearliteFerrite

Bainite

t

Ms

Martensite

PearliteFerrite

Bainite

Ms

Conventional PH process

Reheating in phase

Martensiticpress hardening

Reduced reheating temperature

Reheating in / phase

Dual-phasepress hardening

t

Reduced carbon content(good ductility, improved weldability)


18

2014.07.10.

4

T T

Microstructure controlled press hardening

Martensite

PearliteFerrite

Bainite

Martensite

PearliteFerrite

Bainite

t

Ms Ms

Cooling stop at elevated temperature

Reheating in phase

Bainiticpress hardening

Reduced reheating temperatureCooling stop at elevated temperature

Reheating in / phaseFerritic-bainiticpress hardening

t

Much reduced carbon content(good toughness, weldability)


19

Wei

ght

Weight reduction potential of press hardening steel

Estimated weight reduction

0

80

60

40

20

100

140

120

Mild Steel HSLAsteel

-5–10%-10–15%

-20–30% -20–40%

+ 15-25 %

Reference

DP-600 TRIP-800 Press hardening AluminumDP-800


20

Str

engt

h,M

Pa

DP

1000

22M

nB5

Elo

ngat

ion,

%

DP

800

400

200

0

800

600

18001600

1400

1200

1000

780 °C810 °C950 °C

YSTS

Press hardening in phases (22MnB5)

416

924

467

1037

1527

1029 9.5

13.8

7.3

10.4

5.2

2

0

6

4

16

14

12

10

8

780 °C810 °C950 °C

Au

A80

7

Reheating temperatureReheating temperature

Advantages of dual phase press hardening

• •

• •

Realization of dual phase microstructure with significantly improved elongationMechanical properties can be varied according to the reheating temperature

Energy saving through reduced furnace temperatureReduced thermal loads on the coating material


21

Tailored properties for side impact behavior

PH steelC: 0.22%

Laser seam

HSLAC: <0.10%

Defined deformation behaviour of B-pillar under sideimpact condition to minimize load on passenger by:

➡ Tailored blank (product approach)

➡ Tailored quenching (process approach)


22

Summary

• Press hardening technology has proven to be a good solution toproblems of forming ultra-high strength steels.

• Press hardening allows raising the strength level up to around2000 MPa enabling weight reduction of 20 to 30% without safetycompromise and cost increase.

• The key for further improvements lies in a combined approach byprocess and alloy design.

• Bainitic microstructures provide very interesting application potential inthe strength range of 700 to 1000 MPa.

• Nb microalloying provides a feasible solution to improve applicationproperties of all press hardening and air hardening steels.


23

Acknowledgement


This research work started in the framework of TÁMOP-4.2.1.B-10/2/KONV-2010-0001

and continued within the TÁMOP-4.2.2.A-11/1/KONV-2012-0029 project.

Both project are supported by the European Union and

co-financed by the European Social Fund. The financial support is gratefully acknowledged.

Thank you for your kind attention!

24

tisza hot press forming v3 - university of miskolc · 2016. 8. 24. · 2014.07.10. 2 • hot press...

Documents