Transcript No Slide Title

Seam Welding
Seam Welding
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
Introduction to Resistance Seam Welding
Roll Spot Weld
Upper Electrode Wheel
Knurl or Friction
Drive Wheel
Overlapping Seam
Weld
Continuous Seam
Weld
Workpiece
Lower Electrode Wheel
Throat
[Reference: Welding Handbook,
Volume 2, p.553, AWS]
Lap Seam Weld
Overlapping
Weld
Nuggets
Electrodes
Travel
Front view
Side View
[Reference: Welding Handbook, Volume 2, p.554, AWS]
Effect of Weld Current and Pulse Timing
3 on, 2 off (60%)
4 on, 3 off (57%)
6 on, 5 off (54%)
Resistance Welder Manufacturers Association Bulletin # 23
Effect of Cool Time (Heat %)
on Nugget Properties
@ 6 Cycle Heat
75%
6 on, 5 off (54%)
66%
60%
54%
50%
46% Heat
Resistance Welder Manufacturers Association Bulletin # 23
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
Welding Speed
Resistance Welder Manufacturers Association Bulletin # 23
Seam Welding Multiple Thickness Sheets
Resistance Welder Manufacturers Association Bulletin # 23
Improper
selection of
Parameters
Leads to
Porosity in
Weld
Resistance Welder Manufacturers Association Bulletin # 23
Mash Seam Weld
Slightly Lapped
Sheets
Wide, Flat
Electrodes
Weld Nuggets
Before welding
After Welding
[Reference: Welding Handbook, Volume 2, p.554, AWS]
Effect of Sheet Overlap on
Mash Lap Joint properties
Resistance Welder Manufacturers
Association Bulletin # 21
Effect of Electrode Force
on Mash Seam Weld
Resistance Welder Manufacturers
Association Bulletin # 21
Metal Finish Seam Weld
Finish
Side
Chamfered
Electrode
Flash
Broad, Flat
Electrode
Before Welding
After Welding
[Reference: Welding Handbook, Volume 2, p.554, AWS]
Effect of Weld Current
and Electrode Force on
Finish Seam Welds
Resistance Welder Manufacturers Association Bulletin # 24
Effect of Current on Metal
Finish Seam Weld
Resistance Welder Manufacturers
Association Bulletin # 21
Recommended
Sheet
Positioning
Resistance Welder Manufacturers Association Bulletin # 24
ASM Handbook Vol6, 1993
Porter, Galvanizing and welding structural steel,
Metal Construction, Nov 1983
ASM Handbook Vol6, 1993
ASM Handbook Vol6, 1993
Nugget Formation in Continuous Seam Weld
Waddell, Mechanism of weld formation…,
Welding and Metal Fabrication, Aug 1995
1
2
3
4
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
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
1
2
3
4
Stage 2 Drop in
resistance because of
current shunting into
the mushy and solid
state bonded region
Waddell, Mechanism of weld formation…,
Welding and Metal Fabrication, Aug 1995
1
2
3
4
Stage 3 Instability in
current path, nugget
approaching a steady
state growth mode
Waddell, Mechanism of weld formation…,
Welding and Metal Fabrication, Aug 1995
Stage 1
Nugget Initiates
Stage 2
Nugget Moves
Toward Exit
Stage 3
Approaching
Steady State
1
2
3
4
Stage 4 Steady State
Growth of Nugget
until either expulsion
or current off time and
new nugget formation
Waddell, Mechanism of weld formation…,
Welding and Metal Fabrication, Aug 1995
Particular Interest in Steady State Region
Actual Data
(effect of Speed)
2 m/min
4 m/mim
Attorre, Heat Development in Resistance Seam Weldi
Ironmaking and Steelmaking, 1996
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
Through Sheet
Nugget Growth
2 m/min
6 m/min
16 m/min
Waddell, Mechanism of weld formation…,
Welding and Metal Fabrication, Aug 1995
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
Steady State Heat Flow Patterns
(Examine HAZ in Front of Nugget Formation)
Enter
Exit
Type A
HAZ
Nugget
Length of Heat Zone
Increased Speed
HAZ
Nugget
Type B
Unstable
Transition Pattern
Type C
Nugget
HAZ
Heat Zone Distance
Sheet Thickness
0.7 mm
1.2 mm
2.0 mm
For Type A Pattern
Welding Speed
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
Exit
End
Enter
End
Transverse
Longitudinal
Higher Speeds Result in Nugget Moving toward
Exit End and Expulsion on Exit
Waddell, Mechanism of weld formation…,
Welding and Metal Fabrication, Aug 1995
Increased
Electrode
Force
Contact
Area
Nugget Moves Back
Heat Zone Increases
Increased Indentation
Nugget Formation in Pulsed Welds
ASM Handbook Vol6, 1993
Schematic of seam weld.
Length of electrode footprint holds 3 welds
ASM Handbook Vol6, 1993
Irregular nuggets
irregular pulses that does not give time for heat flow
ASM Handbook Vol6, 1993
RSW Certification Training Class, Boeing
Dynamic Resistance
Series of Overlapping Nuggets
Continuous
Seam Weld
Time
Attorre, The influence of welding parameters on formation of solute bands…,
Welding In the World, Vol37, 1996
Parameter (Lobe) Curves for Seam Weld
Pulsed Current
No Cooling Between Continuous
Pulses in Continuous
Therefore Lower Current
Current
Porter, Galvanizing and welding structural steel,
Metal Construction, Nov 1983
Expulsion or
Overheating
Speed Limited for
Pulse or Continuous
Current Options
Minimum Condition for
Continuous Weld
Gould, Resistance Seam Weldabilit,
Report MR9112, EWI, 1991
What About Coated Sheets?
Resistance Seam Weldability of Low-Carbon
Steel
Lower Speed
Surface Eruption, Cu Contamination Cracking
Higher Current
Non-Continuous
Seam
Uncoated Steel
Hot-Dipped Galvanized
AWS Welding Handbook , Vol 4, 1998
Entry
Exit
Expulsion
Weld
Coating
Coating Melts and
Extrudes Out
High Speed
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
Peterson, “High Speed Seam Welding..”
AWS Sheet Metal Welding Conf. VI, 1994
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.
Projection Seam Welds
Experimental Procedure to Maximize Current Density
Peterson, “High Speed Seam Welding..”
AWS Sheet Metal Welding Conf. VI, 1994
Peterson, “High Speed Seam Welding..”
AWS Sheet Metal Welding Conf. VI, 1994
Seam Weld
Quality Tests
Tensile Tests
Pillow Tests
Resistance Welder Manufacturers
Association Bulletin # 21
Typical data from Pillow Testing
6 x 6 inch Pillow
6 x 10 inch Pillow
Douglas Process Standard DPS 10.800,
McDonnell Douglas Corp, 1996
Seam Welding