Seam Welding

1. Seam Welding

2. Seam Welding • Learning Activities • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Homework • Lesson Objectives • When you finish this lesson you will understand: • The various forms of seam welding • Nugget formation mechanisms • Quality testing of Seam Welds Keywords Roll Spot Weld, Overlapping Seam Weld, Continuous Seam Weld, Lap Seam Weld, Mash Seam Weld, Metal Finish Seam Weld, Butt Seam Weld, Foil Butt Seam Weld, Projection Seam Weld, Weld Current-Pulse Time, Welding Speed, Overlap Distance, Nugget Formation, Seam Weldability, Pillow Test

3. Introduction to Resistance Seam Welding Roll Spot Weld Upper Electrode Wheel Knurl or Friction Drive Wheel Overlapping Seam Weld Continuous Seam Weld Workpiece Throat [Reference: Welding Handbook, Volume 2, p.553, AWS] Lower Electrode Wheel

4. Lap Seam Weld Overlapping Weld Nuggets Electrodes Travel Front view Side View [Reference: Welding Handbook, Volume 2, p.554, AWS]

5. Effect of Weld Current and Pulse Timing 3 on, 2 off (60%) 6 on, 5 off (54%) 4 on, 3 off (57%) Resistance Welder Manufacturers Association Bulletin # 23

6. Effect of Cool Time (Heat %) on Nugget Properties @ 6 Cycle Heat 75% 66% 60% 54% 50% 46% Heat 6 on, 5 off (54%) Resistance Welder Manufacturers Association Bulletin # 23

7. Effect of Electrode Force Increased Electrode Force increases nugget penetration Increased Electrode Force causes increase in nugget width while reducing penetration, more electrode cooling Resistance Welder Manufacturers Association Bulletin # 23

8. Welding Speed Resistance Welder Manufacturers Association Bulletin # 23

9. Seam Welding Multiple Thickness Sheets Resistance Welder Manufacturers Association Bulletin # 23

10. Improper selection of Parameters Leads to Porosity in Weld Resistance Welder Manufacturers Association Bulletin # 23

11. Mash Seam Weld Slightly Lapped Sheets Wide, Flat Electrodes Weld Nuggets Before welding After Welding [Reference: Welding Handbook, Volume 2, p.554, AWS]

12. Effect of Sheet Overlap on Mash Lap Joint properties Resistance Welder Manufacturers Association Bulletin # 21

13. Effect of Electrode Force on Mash Seam Weld Resistance Welder Manufacturers Association Bulletin # 21

14. Metal Finish Seam Weld Finish Side Chamfered Electrode Flash Broad, Flat Electrode Before Welding After Welding [Reference: Welding Handbook, Volume 2, p.554, AWS]

15. Effect of Weld Current and Electrode Force on Finish Seam Welds Resistance Welder Manufacturers Association Bulletin # 24

16. Effect of Current on Metal Finish Seam Weld Resistance Welder Manufacturers Association Bulletin # 21

17. Recommended Sheet Positioning Resistance Welder Manufacturers Association Bulletin # 24

18. ASM Handbook Vol6, 1993

19. Porter, Galvanizing and welding structural steel, Metal Construction, Nov 1983

20. ASM Handbook Vol6, 1993

21. ASM Handbook Vol6, 1993

22. Nugget Formation in Continuous Seam Weld

23. Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

24. Stage 1 Takes 1 - 4 cycles, Increased resistance due to increased temp outweighs reduction in resistance due to better surface contact through asperity softening and surface oxide breakdown 2 1 3 4 Peak occurs earlier with thinner materials Resistance Curve for Establishment of Leading Edge of a Continuous Nugget Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

25. 2 Stage 2 Drop in resistance because of current shunting into the mushy and solid state bonded region 1 3 4 Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

26. Stage 3 Instability in current path, nugget approaching a steady state growth mode 2 1 3 4 Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

27. Stage 1 Stage 2 Stage 3 Nugget Initiates Nugget Moves Toward Exit Approaching Steady State

28. 2 Stage 4 Steady State Growth of Nugget until either expulsion or current off time and new nugget formation 1 3 4 Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

29. Particular Interest in Steady State Region Actual Data (effect of Speed) 2 m/min 4 m/mim Attorre, Heat Development in Resistance Seam Welding, Ironmaking and Steelmaking, 1996

30. At Lower Speeds At Higher Speed • Increased Current Ahead of nugget • Less Heat Extracted through Electrode • Larger thru Sheet Nugget Growth Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

31. Through Sheet Nugget Growth 2 m/min 6 m/min 16 m/min Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

32. Factors Promoting Thru Thickness Growth • High Welding Speeds • Increased Sheet Metal Thickness (less electrode cooling) • Increased Sheet Metal Resistivity • Increased Force (increased Electrode Arc Contact-Current Length) • Increased Current

33. Steady State Heat Flow Patterns (Examine HAZ in Front of Nugget Formation) Enter Exit Type A HAZ Nugget Length of Heat Zone Increased Speed Increased Speed Type B HAZ Nugget Unstable Transition Pattern Type C Nugget HAZ

34. Sheet Thickness 0.7 mm 1.2 mm 2.0 mm For Type A Pattern

35. 2 m/min 10 m/min At High Speeds, Current Flow and Heat Generation Extended to Sheet Surface Higher Speeds move from “A” to “C” Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

36. Exit End Enter End Longitudinal Transverse Higher Speeds Result in Nugget Moving toward Exit End and Expulsion on Exit

37. Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

38. Increased Electrode Force Contact Area Nugget Moves Back Heat Zone Increases Increased Indentation

39. Nugget Formation in Pulsed Welds

40. ASM Handbook Vol6, 1993

41. Schematic of seam weld. Length of electrode footprint holds 3 welds ASM Handbook Vol6, 1993

42. Irregular nuggets irregular pulses that does not give time for heat flow ASM Handbook Vol6, 1993 RSW Certification Training Class, Boeing

43. Series of Overlapping Nuggets Continuous Seam Weld Dynamic Resistance Time Attorre, The influence of welding parameters on formation of solute bands…, Welding In the World, Vol37, 1996

44. Parameter (Lobe) Curves for Seam Weld Pulsed Current Continuous Current No Cooling Between Pulses in Continuous Therefore Lower Current Porter, Galvanizing and welding structural steel, Metal Construction, Nov 1983

45. Speed Limited for Pulse or Continuous Current Options Expulsion or Overheating Minimum Condition for Continuous Weld Gould, Resistance Seam Weldabilit, Report MR9112, EWI, 1991

46. What About Coated Sheets?

47. Resistance Seam Weldability of Low-Carbon Steel Lower Speed Higher Current Surface Eruption, Cu Contamination Cracking Non-Continuous Seam Hot-Dipped Galvanized Uncoated Steel AWS Welding Handbook , Vol 4, 1998

48. Entry Exit Expulsion Weld Coating Coating Melts and Extrudes Out Peterson, “High Speed Seam Welding..” AWS Sheet Metal Welding Conf. VI, 1994 High Speed

49. Coated Steels have lower contact resistance delaying heating until coating is removed thus slower speeds are required to get coating out Peterson, “High Speed Seam Welding..” AWS Sheet Metal Welding Conf. VI, 1994

50. Factors Limiting Travel Speed Bulk Resistivity The higher the bulk resistivity of the material, the higher the heating (H=I2Rt) and thus the higher the travel speed possible Current Density As travel speed increases, more material is presented to the rolls per half cycle of current thus reaching a limit to the current density in the part Conductive Coating Materials When conductive coatings are present at the faying surface, they offer an increased shut path for current and thus also reduce current density. Welding takes place when these coatings are melted and extruded out of the weld zone. Expulsion With increased travel speed, complete nugget formation is delayed until the weld forms outside the pressure influence of the rolls (see next slide) and expulsion is easier.