Robust Welding Schedules Sheet Metal Welding Conference

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

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Robust Welding Schedules Sheet Metal Welding Conference

  1. 1. RYERSON
  2. 2. Outline Objective Introduction Experimental method (spot welding trials) Discussion of results (weld lobe data analysis) Conclusions RYERSON 2
  3. 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. RYERSON 3
  4. 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 RYERSON 4
  5. 5. RYERSON 5
  6. 6. Method - Equipment & Testing 5 CU RRENT 0 -5 TIME 1 Second = 60 Cycles Force Current Time Welding Pulse RYERSON 6
  7. 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 RYERSON 7
  8. 8. RYERSON 8
  9. 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 RYERSON 9
  10. 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 RYERSON 10
  11. 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 RYERSON 11
  12. 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 RYERSON 12
  13. 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 RYERSON 13
  14. 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 RYERSON 14
  15. 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) RYERSON 15
  16. 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 RYERSON 16
  17. 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 RYERSON 17
  18. 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 RYERSON 18
  19. 19. RYERSON 19
  20. 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 RYERSON 20
  21. 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 RYERSON 21
  22. 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) RYERSON 22
  23. 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 RYERSON 23
  24. 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 RYERSON 24
  25. 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 RYERSON 25
  26. 26. RYERSON 26
  27. 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 RYERSON 27
  28. 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 RYERSON 28
  29. 29. RYERSON 29
  30. 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 RYERSON 30
  31. 31. RYERSON 31
  32. 32. I gratefully acknowledge the financial support by (NSERC) and facilities provided by Dofasco Inc. Hamilton for conducting the present work RYERSON 32
  33. 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 RYERSON 33
  34. 34. RYERSON 34

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