robust spot welding schedules-17th feb - autosteel/media/files/autosteel/great designs in...
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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
Welding Time (Cycles)
Nnu
gget
Dia
(mm
)/ C
urre
nt
(kA
)
Welding PulseNuggeDiameter
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Designing of Enhanced Welding PulseDouble Pulse Different Intensity
Welding Time (Cycles)
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
Welding Time (Cycles)
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
Weld Lobe Width (Amps)
18 22 26 30
Welding Time (Cycles)
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
Weld Lobe Width (Amps)
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