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Seam Welding. Lesson Objectives When you finish this lesson you will understand: The various forms of seam welding Nugget formation mechanisms Quality.

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Presentation on theme: "Seam Welding. Lesson Objectives When you finish this lesson you will understand: The various forms of seam welding Nugget formation mechanisms Quality."— Presentation transcript:

1 Seam Welding

2 Lesson Objectives When you finish this lesson you will understand: The various forms of seam welding Nugget formation mechanisms Quality testing of Seam Welds Learning Activities 1.View Slides; 2.Read Notes, 3.Listen to lecture 4.Do on-line workbook 5.Homework 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 Upper Electrode Wheel Workpiece Lower Electrode Wheel Throat Knurl or Friction Drive Wheel Roll Spot Weld Overlapping Seam Weld Continuous Seam Weld [Reference: Welding Handbook, Volume 2, p.553, AWS]

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

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

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

7 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 Effect of Electrode Force

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

11 Mash Seam Weld Slightly Lapped Sheets Wide, Flat Electrodes Weld Nuggets Before weldingAfter 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

14 Metal Finish Seam Weld Chamfered Electrode Broad, Flat Electrode Flash Finish Side Before WeldingAfter 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 Resistance Welder Manufacturers Association Bulletin # 24 Recommended Sheet Positioning

18 ASM Handbook Vol6, 1993

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

20 ASM Handbook Vol6, 1993

21

22 Nugget Formation in Continuous Seam Weld

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

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

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

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

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

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

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

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

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

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) Nugget HAZ Nugget HAZ Type A Type B Type C Enter Exit Increased Speed Length of Heat Zone Unstable Transition Pattern

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

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

36 Longitudinal Transverse Enter End Exit End 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 Increased Indentation Nugget Moves Back Heat Zone Increases Contact Area

39 Nugget Formation in Pulsed Welds

40 ASM Handbook Vol6, 1993

41 Schematic of seam weld. Length of electrode footprint holds 3 welds

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

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

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

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

46 What About Coated Sheets?

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

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

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

50 Factors Limiting Travel Speed Bulk Resistivity The higher the bulk resistivity of the material, the higher the heating (H=I 2 Rt) 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.

51 Projection Seam Welds Experimental Procedure to Maximize Current Density

52 Peterson, High Speed Seam Welding.. AWS Sheet Metal Welding Conf. VI, 1994

53 Peterson, High Speed Seam Welding.. AWS Sheet Metal Welding Conf. VI, 1994

54 Tensile Tests Pillow Tests Seam Weld Quality Tests Resistance Welder Manufacturers Association Bulletin # 21

55 6 x 6 inch Pillow 6 x 10 inch Pillow Typical data from Pillow Testing

56 Douglas Process Standard DPS , McDonnell Douglas Corp, 1996

57 Seam Welding


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