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Seam Welding. 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.

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slide2

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

introduction to resistance seam welding
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

lap seam weld
Lap Seam Weld

Overlapping

Weld

Nuggets

Electrodes

Travel

Front view Side View

[Reference: Welding Handbook, Volume 2, p.554, AWS]

slide5

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

slide6

Effect of Cool Time (Heat %) on Nugget Properties

@ 6 Cycle Heat

75% 66% 60% 54% 50% 46% Heat

6 on, 5 off (54%)

Resistance Welder Manufacturers Association Bulletin # 23

slide7

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

slide8

Welding Speed

Resistance Welder Manufacturers Association Bulletin # 23

slide9

Seam Welding Multiple Thickness Sheets

Resistance Welder Manufacturers Association Bulletin # 23

slide10

Improper selection of Parameters Leads to Porosity in Weld

Resistance Welder Manufacturers Association Bulletin # 23

mash seam weld
Mash Seam Weld

Slightly Lapped

Sheets

Wide, Flat

Electrodes

Weld Nuggets

Before welding After Welding

[Reference: Welding Handbook, Volume 2, p.554, AWS]

slide12

Effect of Sheet Overlap on Mash Lap Joint properties

Resistance Welder Manufacturers Association Bulletin # 21

slide13

Effect of Electrode Force on Mash Seam Weld

Resistance Welder Manufacturers Association Bulletin # 21

metal finish seam weld
Metal Finish Seam Weld

Finish

Side

Chamfered

Electrode

Flash

Broad, Flat

Electrode

Before Welding After Welding

[Reference: Welding Handbook, Volume 2, p.554, AWS]

slide15

Effect of Weld Current and Electrode Force on Finish Seam Welds

Resistance Welder Manufacturers Association Bulletin # 24

slide16

Effect of Current on Metal Finish Seam Weld

Resistance Welder Manufacturers Association Bulletin # 21

slide17

Recommended Sheet Positioning

Resistance Welder Manufacturers Association Bulletin # 24

slide23

Waddell, Mechanism of weld formation…,

Welding and Metal Fabrication, Aug 1995

slide24

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

slide25

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

slide26

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

slide27

Stage 1

Stage 2

Stage 3

Nugget Initiates

Nugget Moves

Toward Exit

Approaching

Steady State

slide28

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

slide29

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

slide30

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

slide31

Through Sheet

Nugget Growth

2 m/min

6 m/min

16 m/min

Waddell, Mechanism of weld formation…,

Welding and Metal Fabrication, Aug 1995

slide32

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
slide33

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

slide34

Sheet Thickness

0.7 mm

1.2 mm

2.0 mm

For Type A Pattern

slide35

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

slide36

Exit

End

Enter

End

Longitudinal

Transverse

Higher Speeds Result in Nugget Moving toward Exit End and Expulsion on Exit

slide37

Waddell, Mechanism of weld formation…,

Welding and Metal Fabrication, Aug 1995

slide38

Increased

Electrode

Force

Contact

Area

Nugget Moves Back

Heat Zone Increases

Increased Indentation

slide41

Schematic of seam weld.

Length of electrode footprint holds 3 welds

ASM Handbook Vol6, 1993

slide42

Irregular nuggets

irregular pulses that does not give time for heat flow

ASM Handbook Vol6, 1993

RSW Certification Training Class, Boeing

slide43

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

slide44

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

slide45

Speed Limited for

Pulse or Continuous

Current Options

Expulsion or

Overheating

Minimum Condition for

Continuous Weld

Gould, Resistance Seam Weldabilit,

Report MR9112, EWI, 1991

slide47

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

slide48

Entry

Exit

Expulsion

Weld

Coating

Coating Melts and

Extrudes Out

Peterson, “High Speed Seam Welding..”

AWS Sheet Metal Welding Conf. VI, 1994

High Speed

slide49

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

slide50

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.

slide51

Projection Seam Welds

Experimental Procedure to Maximize Current Density

slide52

Peterson, “High Speed Seam Welding..”

AWS Sheet Metal Welding Conf. VI, 1994

slide53

Peterson, “High Speed Seam Welding..”

AWS Sheet Metal Welding Conf. VI, 1994

slide54

Seam Weld

Quality Tests

Tensile Tests

Pillow Tests

Resistance Welder Manufacturers Association Bulletin # 21

slide55

Typical data from Pillow Testing

6 x 6 inch Pillow

6 x 10 inch Pillow

slide56

Douglas Process Standard DPS 10.800,

McDonnell Douglas Corp, 1996

slide57

Homework

Seam Welding