Robust spot welding schedules-17th Feb - Autosteel/media/Files/Autosteel/Great Designs in Steel... · w w w . a u t o s t e e l . o r g RYERSON 3 Objective: Present work focuses on

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Robust Schedules for Spot Welding Zinc Coated Advanced High Strength Automotive Steels

Gajendra Tawade (Ryerson University) Gary Boudreau (Dofasco Inc. Canada)


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Outline

ObjectiveIntroductionExperimental Method (Spot Welding Trials)Discussion of Results (Weld Lobe Data Analysis)Summary and Conclusions


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Objective: Present work focuses on developing a robust spot welding process for welding DP600 to itself and to other grades. Different welding pulses and electrode tip designs were used to increase the lobe width

Objective


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Advanced high strength steels have been identified as an affordable solution to satisfy conflicting requirements like

Weight reduction &Passenger safety

Material characterization data on formability, crash performance and spot welding is still in progress

Introduction


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Introduction

DP600 has excellent mechanical properties. Richer chemistry makes it more difficult to weld

Hardenability elements can lead to narrower weld lobes

Focus of Current work is to increase lobe width


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Introduction

Mechanical properties of materials used

All materials are 60G/60G Hot Dipped Galvanized

0.25493031380.7 & 1.0EDDQ0.18334543502.0HSLA-350

0.2226.16263852.0DP600

nTE(%)UTS MPaYS MPaThickness (mm)Grade


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Experimental MethodExperimental Method


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Method -Equipment and Testing

ForceCurrentTime

1 Second = 60 Cycles

-5

-3

-1

1

3

5

0

TIME

CU

RR

ENT

Current


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Develop robust spot welding process for given material combinations2.0 mm DP600 to 2.0 mm DP600 2.0 mm DP600 to 2.0 mm 350 HSLA 2.0 mm DP600 to 0.7 mm EDDQ2.0 mm DP600 to 1.0 mm EDDQ

All materials were 60G/60G Hot Dipped Galvanized

These are the applications from a production vehicle

Method - Materials Tested


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Advantages of Robust Welding Schedules

DP600 generally have narrower lobes than conventional Low ‘C’ steelsThe present work was initiated to increase the lobe widthMinimum acceptable lobe width is 2000 Amps

Dmax= Electrode diaDmin= 4 √t

D

Weld Lobes for DP600 & BH 180 (2.0mm to 2.0mm)

14

16

18

20

22

24

26

28

9 10 11 12 13 14 15 16

Welding Current (kA)

Wel

ding

tim

e (C

ycle

s)

DP600BH Steel

Dmax

Dmin


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Discussion of ResultsExperiment No.1-DP600 to DP600 (2.0/2.0 mm)


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Weld Lobe for DP600 (2.0mm-2.0mm)

Sample preparation, electrode installation, stabilization & lobe tests conducted according to A/SP procedures20% higher Electrode Force for DP600All other welding parameters selected according to A/SP

14

18

22

26

30

9 10 11 12 13

Welding Current (kA)

Wel

ding

Tim

e (C

ycle

s)

Weld Lobe

567 A600 A

900 A


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Lobe Widths & Welding TimesLobe Widths & Welding Times

567767

1300

1700

2300

0

400

800

1200

1600

2000

2400

Weld Lobe Width (Amps)

18 22 26 30 34Welding Time (Cycles)

2.0mm DP600 welded to 2.0mm DP600

Weld Lobe

Acceptable lobe width=2000Amps

Reference weld time for 2.0 mm mild steel

Lobe width

with experiments


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Weld Lobe for DP600

Nature of the curve : wide at the top & narrow extended tail at the bottom

WELD LOBE DP-600 (2.0mm to 2.0mm)

14

18

22

26

30

34

38

8.5 9 9.5 10 10.5 11 11.5 12 12.5

Welding current (KA)

Wel

ding

tim

e (c

ycle

s)Weld Lobe

570 A767 A

1300A

1700 A

2300A


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Nugget Growth Studies for DP600


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Nugget Growth

Sheet-1

Sheet-2

Electrode-1

Electrode-2

1 Second = 60 Cycles

-5

-3

-1

1

3

5

0

TIME

CU

RR

ENT

Current


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Nugget Growth in Single PulseDP600 Welded to DP600 (2.0/2.0mm)

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35

Welding Time (Cycles)

Nug

get D

ia (m

m) /

Cur

rent

(k

A)

Nugget DiameterWelding pulse

Zinc removed after 13 cyclesRapid Nugget growth after 17 cyclesHeat input in the last stage is fast


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Nugget Growth in Double Pulse (DP600)

All Zinc removal after 13 CyclesNugget growth without zinc can be ensured at 20 cyclesNugget growth with double pulse is slower than single pulseCan this effect be enhanced with lower current intensity on 2nd pulse?

0

2

4

6

8

10

12

0 10 20 30 40


Nnu

gget

Dia

(mm

)/ C

urre

nt

(kA

)

Welding PulseNuggeDiameter


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Designing of Enhanced Welding PulseDouble Pulse Different Intensity


Wel

ding

Cur

rent

(kA

)

Welding Pulse

Experiments were conducted to find appropriate current intensity on the second pulse


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Nugget growth Vs welding time for different pulses

0123456789

0 10 20 30 40 50 60


Nug

get D

iam

eter

(mm

)

Single pulseDouble Pulse100%-87.5%100%-75%

Nugget Growth With Different Welding Pulses

Enhanced Pulse

Slope of linesSingle Pulse = 5.61Double Pulse = 5.41Enhanced Pulse = 3.82


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38% increase in the lobe width with proper welding pulse

1300 Amps

1800 Amps

0 350 700 1050 1400 1750 2100

Lobe width (Amps)

(2.0mm DP600 t0 2.0mm DP 600)

Lobe width

Enhanced Pulse

Single Pulse

No. of Pulses

1

2

Weld lobes at 26 cycles For same Welding parameters Enhanced pulse showed wider lobe than Single pulse


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Experiment No 2- HSLA to DP600 (2.0/2.0 mm)


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1633 1667

1233

1800

22332587

0

500

1000

1500

2000

2500

3000


18 22 26 30


Lobe Width 2.0mm HSLA-2.0mm DP600

Single Pulse Enhanced Pulse

Achievement of Acceptable Lobe Width

Acceptable Lobe Width

Reference weld time for 2.0mm Mild steel


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Heat Balance – Unequal Thickness


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Heat Balance – Tip Diameter

Electrode-2

6.0 MM

Electrode-18.0 MM

Sheet-12.0 MM

Sheet-2 EDDQ0.7 MM


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Results & DiscussionExperiment No-3 DP600 to EDDQ (2.0/0.7mm)


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Lobe Widths for DP600 to EDDQ (2.0/0.7 mm)

500

1233

1633

0

300

600

900

1200

1500

1800


12 16 20

Welding Time (Cycles)Single Pulse

Reference weld time for welding 0.7mm to 0.7 mm Mild steel is 11 cycles


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Results & DiscussionResults & DiscussionExperiment NoExperiment No--4 DP600 to EDDQ (2.0/1.0 mm)4 DP600 to EDDQ (2.0/1.0 mm)


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Lobe Widths for DP600 to EDDQ (2.0/1.0 mm)

825 850

1425

0200400600800

10001200140016001800

Lobe Widths (Amps)

13 17 21Welding Time (Cycles)Weld Lobe

Reference weld time for welding 1.0mm to 1.0mm Mild steel is 13 cycles

Experiments were conducted with Double pulse, enhanced pulse and triple pulse. Single pulse was found to be the most beneficial


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Summary


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Summary- Equal Thickness

2233 Amps

1800 Amps

Lobe with Enhanced Pulse at 26 cycles

1800 Amps

1300 Amps

Lobe with Single Pulse at 26 Cycles

24%DP600 to 350 HSLA

38%DP600 to DP600

% Increase in the Lobe Width

Material A welded to Material B (2.0mm)

Maximum lobe width for HSLA to DP (2.0/2.0 mm) combination was achieved with Enhanced Pulse = 2587 Amps


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Summary- Unequal Thickness

1425 Amps

1633 Amps

Maximum Lobe with Single Pulse

DP600 to EDDQ (2.0/1.0 mm)

DP600 to EDDQ (2.0/0.7 mm)

Material A welded to Material B

Single pulse found to be more beneficial than Double Pulse or Enhanced Pulse for welding unequal thickness combination


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Lobe width can be improved by experimenting with weld pulse designAcceptable lobe width can be achieved using Enhanced Welding Pulse for DP600 joints and DP-HSLA jointsWelding Process is stable with Enhanced Pulse Lobe data with unequal tip diameters are available for further discussions

Conclusion


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Future work

• Mechanical testing of joints with Single Pulse & Enhanced Pulse Design

• Designing of Enhanced pulse for unequal thickness combinations

• Welding unequal thickness combinations with equal diameter tips

• Metallographic study of welds


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Thank [email protected]

Documents

Robust spot welding schedules-17th Feb - Autosteel/media/Files/Autosteel/Great Designs in Steel... · w w w . a u t o s t e e l . o r g RYERSON 3 Objective: Present work focuses on