Seam Welding

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Seam Welding
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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
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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
_at_ 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
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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

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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
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Sheet Thickness
0.7 mm
1.2 mm
2.0 mm
For Type A Pattern
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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
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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
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Nugget Formation in Pulsed Welds
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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?
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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 (HI2Rt)
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.
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Projection Seam Welds Experimental Procedure to
Maximize Current Density
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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
Seam Weld Quality Tests
Tensile Tests
Pillow Tests
Resistance Welder Manufacturers Association
Bulletin 21
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Typical data from Pillow Testing
6 x 6 inch Pillow
6 x 10 inch Pillow
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Douglas Process Standard DPS 10.800, McDonnell
Douglas Corp, 1996
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Homework
Seam Welding