seam welding. lesson objectives when you finish this lesson you will understand: the various forms...
TRANSCRIPT
Seam Welding
Seam Welding
Lesson ObjectivesWhen you finish this lesson you will understand:• The various forms of seam welding• Nugget formation mechanisms• Quality testing of Seam Welds
Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line
workbook5. Homework
KeywordsRoll 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
Upper Electrode Wheel
Workpiece
Lower Electrode Wheel
Throat
Knurl or FrictionDrive Wheel
Roll Spot Weld
Overlapping SeamWeld
Continuous SeamWeld
[Reference: Welding Handbook, Volume 2, p.553, AWS]
Lap Seam Weld
Electrodes OverlappingWeldNuggets
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%)
Resistance Welder Manufacturers Association Bulletin # 23
6 on, 5 off (54%)
6 on, 5 off (54%)
75% 66% 60% 54% 50% 46% Heat
Effect of Cool Time (Heat %) on Nugget Properties
Resistance Welder Manufacturers Association Bulletin # 23
@ 6 Cycle Heat
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
Welding Speed
Resistance Welder Manufacturers Association Bulletin # 23
Seam Welding Multiple Thickness Sheets
Resistance Welder Manufacturers Association Bulletin # 23
Resistance Welder Manufacturers Association Bulletin # 23
Improper selection of Parameters Leads to Porosity in Weld
Mash Seam WeldSlightly LappedSheets 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
Resistance Welder Manufacturers Association Bulletin # 21
Effect of Electrode Force on Mash Seam Weld
Metal Finish Seam Weld
ChamferedElectrode
Broad, FlatElectrode
Flash
FinishSide
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
Resistance Welder Manufacturers Association Bulletin # 24
Recommended Sheet Positioning
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
Waddell, Mechanism of weld formation…,Welding and Metal Fabrication, Aug 1995
12
3 4Stage 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
12
3 4Stage 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
12
3 4Stage 3 Instability in current path, nugget approaching a steady state growth mode
Stage 1 Stage 2 Stage 3
Nugget Initiates Nugget MovesToward Exit
ApproachingSteady State
Waddell, Mechanism of weld formation…,Welding and Metal Fabrication, Aug 1995
12
3 4Stage 4 Steady State Growth of Nugget until either expulsion or current off time and new nugget formation
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
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
Waddell, Mechanism of weld formation…,Welding and Metal Fabrication, Aug 1995
2 m/min
6 m/min
16 m/min
Through SheetNugget Growth
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)
NuggetHAZ
Nugget
Nugget
HAZ
HAZ
Type A
Type B
Type C
EnterExit
Incr
ease
d S
pee
d
Increased Speed
Length of Heat Zone
Unstable Transition Pattern
Welding Speed
Hea
t Zon
e D
ista
nce
0.7 mm
1.2 mm
2.0 mm
Sheet Thickness
For Type A Pattern
Waddell, Mechanism of weld formation…,Welding and Metal Fabrication, Aug 1995
2 m/min
10 m/min
At High Speeds,Current Flow and Heat GenerationExtended to SheetSurface
Higher Speeds move from “A” to “C”
LongitudinalTransverse
EnterEnd
Exit End
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
Increased IndentationNugget Moves BackHeat Zone Increases
ContactArea
Nugget Formation in Pulsed Welds
ASM Handbook Vol6, 1993
ASM Handbook Vol6, 1993
Schematic of seam weld. Length of electrode footprint holds 3 welds
ASM Handbook Vol6, 1993
RSW Certification Training Class, Boeing
Irregular nuggets irregular pulses that does not give time for heat flow
Time
Dyn
amic
Res
ista
nce
Attorre, The influence of welding parameters on formation of solute bands…,Welding In the World, Vol37, 1996
Series of Overlapping Nuggets
ContinuousSeam Weld
Porter, Galvanizing and welding structural steel,Metal Construction, Nov 1983
Pulsed Current Continuous CurrentNo Cooling BetweenPulses in ContinuousTherefore Lower Current
Parameter (Lobe) Curves for Seam Weld
Gould, Resistance Seam Weldabilit,Report MR9112, EWI, 1991
Expulsion orOverheating
Minimum Condition for Continuous Weld
Speed Limited for Pulse or Continuous Current Options
What About Coated Sheets?
Uncoated SteelHot-Dipped Galvanized
AWS Welding Handbook , Vol 4, 1998
Resistance Seam Weldability of Low-CarbonSteel
Surface Eruption, Cu Contamination Cracking
Non-ContinuousSeam
Lower SpeedHigher Current
Peterson, “High Speed Seam Welding..”AWS Sheet Metal Welding Conf. VI, 1994
Weld
ExitEntry
High Speed
Expulsion
Coating
Coating Melts andExtrudes Out
Peterson, “High Speed Seam Welding..”AWS Sheet Metal Welding Conf. VI, 1994
Coated Steels have lower contact resistance delaying heating until coating is removed thusslower speeds are required to get coating out
Factors Limiting Travel Speed
Bulk ResistivityThe higher the bulk resistivity of the material, the higher the heating (H=I2Rt) and thus the higher the travel speed possible
Current DensityAs 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 MaterialsWhen 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.
ExpulsionWith 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
Tensile Tests
Pillow Tests
Seam WeldQuality Tests
Resistance Welder Manufacturers Association Bulletin # 21
6 x 6 inch Pillow6 x 10 inch Pillow
Typical data from Pillow Testing
Douglas Process Standard DPS 10.800,McDonnell Douglas Corp, 1996
Seam Welding