seam welding. lesson objectives when you finish this lesson you will understand: the various forms...

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