spot welding, weld lobe, pulse welding, automotive fast paced welding.

1. RYERSON

2. Outline
Objective
Introduction
Experimental method (spot welding trials)
Discussion of results (weld lobe data analysis)
Conclusions
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3. Objective
Objective
Objective: Present work focuses on establishing
robust spot welding lobes for welding DP600 to itself
and to other grades. Nugget growth studies were
conducted to develop a suitable welding pulse which
can increase the lobe width.
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4. Introduction
Advanced high strength steels offer
affordable solutions with
weight reduction &
passenger safety
DP600 has excellent mechanical properties. Richer chemistry
can lead to narrower weld lobes
Material characterization data on formability, crash performance
and spot welding is still in progress
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5. RYERSON 5

6. Method - Equipment & Testing
5
CU RRENT
0
-5
TIME
1 Second = 60 Cycles
Force
Current
Time
Welding Pulse
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7. Materials
Develop robust spot welding process for given material
combinations
2.0 mm DP600 to 2.0 mm DP600 (Rocker to rocker)
2.0 mm DP600 to 2.0 mm 350 HSLA (Rocker to front rail)
These are the applications from a production vehicle (Vehicle)
All materials were 60G/60G hot dipped galvanized
8.0 mm diameter class-II Cu-Cr electrodes tips were used
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8. RYERSON 8

9. Single pulse
Single pulse welding cycle
7.00
6.00
Current (kA) / Force
5.00
4.00
3.00
(kN) 2.00
1.00
0.00
-10 -1.00
-2.00
-3.00
Current
force
-4.00
Time (Cycles)
For all welds squeeze time 35 cycles
Hold time 5 cycles
6 kN force
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10. Discussion of results
Weld lobe for DP600 (2.0/2.0 mm)
38
Lobe-1
34
w elding tim e
30
(c y c les )
933 A
26
22 600 A
18 567 A
14 Dmax= Electrode dia.
8.5 9.5 10.5 11.5 12.5 Dmin= 4 √t
welding current (kA)
Electrode force 20% higher than A/SP recommended
Acceptable lobe width for bare mild steel is 2000 Amps
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11. DP600: Challenges
welding time (cycles) Weld lobes for DP600 & BH 180 (2.0/2.0 mm)
28
DP600
26 BH Steel
24
22
20
18
16
14
9 10 11 12 13 14 15 16
welding current (kA)
DP600 can be spot welded at much lower welding current
At lower time DP600 shows narrower lobe width than low “C” steels
Lobe width increases with welding time
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12. Lobes for DP600
Weld lobe for DP600 (2.0/2.0 mm)
38
Lobe-1
2300 A Lobe-2
34 Lobe-3
welding time
30
(cycles)
26
22
18
567 A
14
8.5 9 9.5 10 10.5 11 11.5 12 12.5
welding current (kA)
Significant lobe width was achieved at higher welding time
No interfacial failures observed at any welding time
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13. Lobe for DP600
Weld lobe for DP600 (2.0/2.0 mm)
38
welding time(cycles)
34
Avg. nugget dia.
30 8.17 mm
26
Dmax= Electrode dia.= 8.0 mm
22
18 Avg. nugget dia.
6.88 mm
14
8.5 9 9.5 10 10.5 11 11.5 12 12.5
welding current (kA)
Lower welding time early expulsion
Higher welding time better control of nugget growth
For all lobes single pulse welding schedules were used
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14. Single pulse
Single pulse welding cycle
7.00
6.00
Current (kA) / Force
5.00
4.00
3.00
(kN)
2.00
1.00
0.00
-10 -1.00
-2.00
-3.00
Current
force
-4.00
Time (Cycles)
For all welds squeeze time 35 cycles
Hold time 5 cycles
Up/down-sloping, prepulsing, postpulsing schedules are being used
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15. Up Sloping and/or downsloping of the weld
current when used with truncated cone
electrodes can increase the lobe width of
materials which have “free Zn” layer
(Ref: Gedeon S.A. And Eager T.W. Metallurgical Trans. V. 17B pp.885)
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16. Up Sloping Pulse
Up Sloping cycle w elding pulse
8
Current / F orc e 6
4
2
0
-2
-5
-4
-6 Current
Current Intensity
Time (cycles) E.force
6 Up Sloping cycles
Current raised from 25% (I) to 50% (I)
Electrode force was constant throughout the pulse
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17. Up Sloping Lobe
Up Sloping & single pulse lobe for DP600
34
Upsloping
Single pulse
welding time (cycles)
30
26 Avg. nugget dia.
7.20 mm
22
18 Avg. nugget dia.
6.78 mm
14
8.5 9.5 10.5 11.5 12.5
welding current (kA)
Up Sloping schedule can weld at lower currents than single pulse
Up Sloping schedules could not achieve maximum nugget size
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18. Lobe widths for DP600 (2.0/2.0 mm)
2500 2300
Upsloping
Single
Lobe widths (Amps)
2000 1700
1500 1300
1000 767 750
733
567
500 317
0
18 22 26 30 34
Time (cycles)
Lobe width increase with the welding time
For all times Up Sloping pulse showed smaller lobes than single pulse
Higher welding time is not production feasible schedules
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20. Nugget growth mechanism
Electrode-1
12
welding current (kA)
10
8
Sheet-1 6
4
Sheet-2
2
0
10 Second 15 60 Cycles
5 10
= 20 25 30 35
welding time (Cycles)
Electrode-2
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21. Nugget growth in single pulse
(m m )/ w elding c urrent 12
Diameter
N ugget diam eter
10 current
8
6
4
2
0
0 5 10 15 20 25 30 35
welding time (cycles)
“Zn” removed after 13 cycles
Minimum nugget dia. formed at 21 cycles
Heat input in the last stage is fast
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22. Nugget growth in double pulse
W. Pulse
nugget growth (mm) /12 Diameter
welding current (kA)
10
8
6
4
2
0
0 10 20 30 40
welding time (cycles)
All “Zn” removed after 13 cycles
Intensity on 2nd pulse can be optimized
Robust current ranges can be achieved with double pulsing
(Ref: Militisky et al SAE-2003-01-0520)
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23. Designing of enhanced welding pulse
welding current (kA)
welding time (cycles)
Current intensity on the 2nd pulse =?
Enhanced pulse = 2 pulses with reduced current intensity on 2nd pulse
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24. Nugget growth with different welding pulse
9
8
Enhanced
nugget diameter (mm)
7
pulse
6
5
4
3 Double Pulse
2 100%-87.5%
1 100%-75%
0
15 25 35 45 55 65
welding time (cycles)
Enhanced pulse showed slower N. growth than single/double pulse
87.5% current intensity on 2nd pulse showed best results
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25. Lobe widths: enhanced pulse & single pulse (2.0 mm DP600)
2000 1800
1750
lobe width (Amps)
1500 1300
1250
1000
750
500
250
0
single pulse enhanced
pulse
Weld lobes at 26 cycles
Enhanced pulse showed wider lobe than single pulse
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27. Lobes for DP-HSLA welds (2.0/2.0 mm)
w eld in g tim e (cyc le s)
34.0
30.0
Enhanced pulse
26.0
22.0
18.0 Single pulse
14.0
10.20 11.20 12.20 13.20 14.20
welding current (kA)
Enhanced pulse with 87.5% intensity on the 2nd pulse was used
Enhanced pulse showed better lobe widths at higher time
Maximum nugget dia. achieved with single and enhanced pulse
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28. Lobe widths for DP-HSLA welds (2.0/2.0 mm)
3000 Single pulse 2587
Enhanced pulse 2233
2500
lobe width (amps)
2000 1667 1800
1633
1500 1233
1000
500
0
18 22 26 30
welding time (cycles)
Reference weld time for 2.0 mm mild steel is 22 cycles
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30. Conclusion
Lobe widths for DP600 can be improved by experimenting with weld
pulse design
Acceptable lobe width can be achieved using Enhanced Pulse for
welding DP-DP or DP-HSLA combinations
Larger nuggets can be achieved with Enhanced Pulse
Up-sloping schedule with 6 cycles did not improve lobe width
DP600 can be successfully welded at higher welding times
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31. RYERSON 31

32. I gratefully acknowledge the financial
support by (NSERC) and facilities
provided by Dofasco Inc. Hamilton for
conducting the present work
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33. Application Roof Crossmember
Body Side Member Roof
B-Pillar Inner
B-Pillar Rocker Outer Waist
Rear Reinf Reinf.
Kick-Up
Crossmember
Rocker Inner
Inner Kick-Up
Rocker to rocker Body Side Waist Crossmember Lower B-Pillar
Outer Reinf.
Rocker to front rail Reinf. Extension
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