2c1 seam welding

8/13/2019 2c1 Seam Welding

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Seam Welding


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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
http://we019.eng.ohio-state.edu/wenc/wenc.cfmhttp://www-iwse.eng.ohio-state.edu/we602A/workbook.htm


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Introduction to Resistance Seam Welding

Upper Electrode Wheel

Workpiece

Lower Electrode Wheel

Throat

Knurl or Friction

Drive Wheel

Roll Spot Weld

Overlapping Seam

Weld

Continuous Seam

Weld

[Reference: Welding Handbook,Volume 2, p.553, AWS]


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Lap Seam Weld

Electrodes Overlapping

Weld

Nuggets

Travel

Front view Side View

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


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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%)


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6 on, 5 off (54%)

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

Effect of Cool Time (Heat %)

on Nugget Properties


@ 6 Cycle Heat


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Increased Electrode Force

increases nugget penetration

Increased Electrode Force causes

increase in nugget width whilereducing penetration, more

electrode cooling


Effect of Electrode Force


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Welding Speed



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Seam Welding Multiple Thickness Sheets



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Improper

selection of

Parameters

Leads to

Porosity in

Weld


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Mash Seam WeldSlightly Lapped

Sheets Wide, Flat

Electrodes

Weld Nuggets

Before welding After Welding



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Effect of Sheet Overlap on

Mash Lap Joint properties

Resistance Welder Manufacturers

Association Bulletin # 21


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Effect of Electrode Force

on Mash Seam Weld


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Metal Finish Seam WeldChamfered

Electrode

Broad, Flat

Electrode

Flash

Finish

Side

Before Welding After Welding



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Effect of Weld Current

and Electrode Force on

Finish Seam Welds



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Effect of Current on Metal

Finish Seam Weld




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Recommended

Sheet

Positioning


18/57ASM Handbook Vol6, 1993


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Porter, Galvanizing and welding structural steel,

Metal Construction, Nov 1983


20/57ASM Handbook Vol6, 1993


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ASM Handbook Vol6, 1993


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Nugget Formation in Continuous Seam Weld


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Waddell, Mechanism of weld formation,

Welding and Metal Fabrication, Aug 1995


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12

3 4Stage 1 Takes 1 - 4

cycles, Increased

resistance due to

increased temp

outweighs reduction in

resistance due to better

surface contact throughasperity softening and

surface oxide

breakdown

Peak occurs earlierwith thinner

materials

Resistance Curve for Establishment

of Leading Edge of a Continuous Nugget


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12

3 4Stage 2 Drop in

resistance because ofcurrent shunting into

the mushy and solid

state bonded region


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12

3 4

Stage 3 Instability in

current path, nugget

approaching a steadystate growth mode


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Stage 1Stage 2 Stage 3

Nugget Initiates Nugget Moves

Toward ExitApproaching

Steady State


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12

3 4Stage 4 Steady State

Growth of Nugget

until either expulsion

or current off time and

new nugget formation


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Actual Data(effect of Speed)

2 m/min

4 m/mim

Attorre, Heat Development in Resistance Seam Weld

Ironmaking and Steelmaking, 1996

Particular Interest in Steady State Region


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Increased Current

Ahead of nugget

Less Heat Extractedthrough Electrode

Larger thru Sheet

Nugget Growth

At Higher Speed

At Lower Speeds

Through Sheet


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2 m/min

6 m/min

16 m/min

Through Sheet

Nugget Growth


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S S


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Steady State Heat Flow Patterns(Examine HAZ in Front of Nugget Formation)

NuggetHAZ

Nugget

Nugget

HAZ

HAZ

Type A

Type B

Type C

EnterExit

Increased Speed

Length of Heat Zone

Unstable

Transition Pattern


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Welding Speed

HeatZo

neDistance 0.7 mm

1.2 mm

2.0 mm

Sheet Thickness

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


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LongitudinalTransverse

EnterEnd

Exit

End

Higher Speeds Result in Nugget Moving toward

Exit End and Expulsion on Exit


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Increased

Electrode

Force

Increased IndentationNugget Moves Back

Heat Zone Increases

Contact

Area


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Nugget Formation in Pulsed Welds


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Schematic of seam weld.

Length of electrode footprint holds 3 welds


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RSW Certification Training Class, Boeing

Irregular nuggets

irregular pulses that does not give time for heat flow


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Time

Dynam

icResistance

Attorre, The influence of welding parameters on formation of solute bands,

Welding In the World, Vol37, 1996

Series of Overlapping Nuggets

Continuous

Seam Weld

Parameter (Lobe) Curves for Seam Weld


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Porter, Galvanizing and welding structural steel,

Metal Construction, Nov 1983

Pulsed Current Continuous CurrentNo Cooling BetweenPulses in Continuous

Therefore Lower Current

( )


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What About Coated Sheets?

R i t S W ld bilit f L C b


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Uncoated SteelHot-Dipped Galvanized

AWS Welding Handbook , Vol 4, 1998

Resistance Seam Weldability of Low-Carbon

Steel

Surface Eruption, Cu Contamination Cracking

Non-Continuous

Seam

Lower Speed

Higher Current


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Peterson, High Speed Seam Welding..AWS Sheet Metal Welding Conf. VI, 1994

Weld

Exit Entry

High Speed

Expulsion

Coating

Coating Melts andExtrudes Out


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Coated Steels have lower contact resistance

delaying heating until coating is removed thus

slower speeds are required to get coating out


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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.


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Projection Seam WeldsExperimental Procedure to Maximize Current Density


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Peterson, High Speed Seam Welding..

AWS Sheet Metal Welding Conf. VI, 1994


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Tensile Tests

Pillow Tests

Seam Weld

Quality Tests



Typical data from Pillow Testing


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6 x 6 inch Pillow

6 x 10 inch Pillow

Typical data from Pillow Testing


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Douglas Process Standard DPS 10.800,McDonnell Douglas Corp, 1996


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Seam Welding

2c1 seam welding

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