© Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens

Institute of Forming

Technology and Machines

Neue Entwicklungen beim Formhärten

New Press Hardening Developments

Speaker: Dr.-Ing. Sven Hübner

13. Werkstoff-Forum

HANNOVER MESSE 2013

Date: 09/04/2013

IFW, Universität Hannover Page 2 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Initial Situation: Blank Heating for Press Hardening

Source: Schwartz GmbH

• Length up to 40 m

• Investment up to 1.5 Mio. €

• Mostly used in continuous-running operation

• High energy consumption

• Thermal inert

• Only slow process control possible

• Undesired heating of periphery

• High maintenance expenditure

• Low required space

• Low investment

• No need for continuous operation

• Low energy consumption

• Effective fast process control possible

• Only heating of the blank

• Variable heating strategies

Continuous

Annealing

Furnace

Continuous

Annealing

Furnace Conductive Heating

IFW, Universität Hannover Page 3 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Heating Concept for Form Blanks

0 V

30 V

Rectangle blank:

Homogeneous voltage distribution

Homogeneous heating

Form blank:

Exact homogeneous voltage distribution

Principle is transferably for arbitrary blank geometries

1. Split in rectangularly and trapezoid zones

2. Additional staircase-shaped contacting

in trapezoid zones

3. Cooling of hotspots with compressed-air

Layout

30 V

0 V

30 V

0 V

0 V

30 V

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Transformer Contact and Switching Sequence of the Electrodes

2 3 1

zone T0 T2 T1

E2 + E7 staircase

E2 + E3 basis

E2 + E6 staircase

cycle

3

1 2 II

IV

III

I

E1 + E2 E3 + E4

start:

T = 20°C

T = 350°C

as above

VI

V

T = 650°C

as above

T = 950°C

sequence, exemplary

T = 350°C

T = 650°C

T = 950°C Programmable Logic Control (PLC):

a) Switching voltage at pneumatic valve -> pressing of electrodes

b) Waiting time (measuring by pressure switch) -> shifting time valve + kinematics + pressure buildup

c) Control signal to thyristor -> transformer on -> secondary current flow

IFW, Universität Hannover Page 5 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Connection Diagram thyristor

power stage

transfor-

mers

electrodes and

blank zones

pyro-

meter controller L1

L2

PC

P0

P1

P2

T0

T1

T2 thyristor-

controller 1

thyristor-

controller 0

thyristor-

controller 2

PLC

R0

R1

profi-

bus

PLC

pneumatic

valves

elektrodes

1-9

profibus-

joint

PC

8 bar

USt,0

L3

R2

Tist,0

Tist,1

Tist,2

RS232-

converter

Tist,0-2

Yist,0-2

Tsoll,0-2

OPC-server

Ymax,0-2

USt,0

USt,2

USt,1

USt,1

USt,2

out-

side

control

middle

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Pneumatic Diagram

E1 E2 E3 E4

E5 E6 E7

E8

2

1 3

4

5

V5

2

1 3

4

5

V6

2

1 3

4

5

V7

2

1 3

4

5

V8

2

1 3

4

5

V4

2

1 3

4

5

V3

2

1 3

4

5

V2

2

1 3

4

5

V1

8

bar

SPS

2 x ¾ "

100 l

2

1 3

4

5

V9

D3

D12

D13

D3

D13 D12

D1 D2

D4-11

D1 D2

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Cooling Water Diagram

flow

return

control box

plant

½ "

¾ "

transformers

ele

ctr

od

es

thy

ris

tore

s

T0 T2 T1

ele

ctr

od

es

ele

ctr

od

es

cu

rre

nt

bar

cu

rre

nt

bar

sid

e p

an

el

E1 E2 E3 E4

E5 E6

E7 E8

sid

e p

an

el

IFW, Universität Hannover Page 8 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Plant for Conductive Heating of Form Blanks pyrometer

blank

pneumatic cylinder

transformers profibus-

joint

cooling water

distribution

board

pneumatic valves and

distribution board

staircase electrode

(welding tongs)

frame

current strip

current bar

PC

control box

compressed-air-

storage

air regulator and distributor

compressed-air jet nozzle

electrode

technical data:

• 460 kVA – 50 % duty cycle

• primary: 400 V 1 kA

• secondary: 30 V 15 kA

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Heating Zone

blank

pneumatic cylinder electrode

thermal insulating blank ceramic deflection barricade

staircase electrode (welding tongs)

current strip

compressed-air jet nozzle

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Compressed-air Cooling

Intense cooling of lokal hotspots because of the large current density in the current discharge zone at

the staircase electrode

Low large-area cooling for balance effects

Temperature-resistant: stainless steel nozzle, seal: copper ring, stainless steel corrugated tube

Compressed-air storage 100 l plus ¾“ inlet pipe, valve V9, 12 air regulators and 4 backfitted manometers

• Intense cooling of lokal hotspots, two-sided of

all staircase electrodes

• Use of SILVENT laval jet nozzle: core jet with

surrounding protection jet

• Large-area jet for balance effects

• Current discharge zone (*)

• Head zone (**)

b1

b2

• One-sided, large-area jet

for cooling of the facile trapezoid zone

• b1 > b2 (trapeze)

*

*

**

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State of Phase Staircase Electrodes Middle Zone

Staircase electrodes must amplify the basic current and not counter them

Determination of the current with current measuring tongs (primary) and current measuring belt (secondary)

Displayed by an oscilloscope

oscilloscope / current measuring

tongs

current measuring belt

B = basic current

S = staircase

electrodes

R = resulting

current

B

S

R

B

S

R

B

S

R

S

Basic current and staircase electrodes

counter each other

Basic current and staircase electrodes

amplify each other

Basic current and both staircase

electrodes amplify each other

IFW, Universität Hannover Page 12 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

PC: Operating Interface Labview Software

calibration

heating sequence

start

display

set temperature

actual temperature

phase cut YIst

IFW, Universität Hannover Page 13 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Input Heating Sequence

number of heating steps

zone

time

max. phase cut

Ymax

set temperature

staircase electrodes

%-value

staircase electrodes

IFW, Universität Hannover Page 14 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Heating Curve Left Zone

2 3 1

set temperature: T = 930 °C

Ymax = 45 %

time = 22 s

IFW, Universität Hannover Page 15 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Video Heating Left Zone

2 3 1

set temperature: T = 930 °C

Ymax = 45 %

time= 22 s

IFW, Universität Hannover Page 16 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Heating Curve Right Zone

2 3 1

set temperature: T = 930 °C

Ymax = 70 %

time= 45 s

IFW, Universität Hannover Page 17 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Video Right Zone

2 3 1

set temperature: T = 930 °C

Ymax = 70 %

time= 45 s

IFW, Universität Hannover Page 18 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Heating Curve Middle Zone

2 3 1

set temperature: T = 930 °C

Ymax = 25 % bis 32 %

time= 113 s

IFW, Universität Hannover Page 19 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Video Middle Zone

2 3 1

set temperature: T = 930 °C

Ymax = 25 % bis 32 %

time= 113 s

IFW, Universität Hannover Page 20 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Heating Experiments

2 3 1

IFW, Universität Hannover Page 21 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Summary and Outlook

Summary

• Conductive heating of form blanks is possible against

different literature references

• Example: form blank of a B-pillar

• Blank heating in zones

• Elimination of hotspots and inhomogeneitys by compressed-air cooling

Outlook for an industrial application:

• Reduction of the heating time with stronger electrical power

supply of the plant

IFW, Universität Hannover Page 22 © Leibniz Universität Hannover, IFUM, Prof. Dr.-Ing. B.-A. Behrens Dr.-Ing. S. Hübner

Thank you for your attention!

Thanks also goes to the AiF and the EFB for founding the IGF-Project 16248 N.