Introduction to Materials Joining

1
Arc Welding Processes
2
Arc Welding Processes

• Learning Activities
• Read Handbook Pp 1-16,
• Look up Keywords
• View Slides
• Read Notes,
• Listen to
• lecture
• Do on-line workbook
• Do homework

• Lesson Objectives
• When you finish this lesson you will understand
• The similarities and difference between some of
  the various arc welding processes
• Flux and gas shielding methods
• Advantages and disadvantages of the arc welding
  processes
• Need to select between the processes

Keywords Welding Flux, Inert Shielding Gas,
Shielded Metal Arc Welding (SMAW), Gas Metal Arc
Welding (GMAW), Metal Transfer Mode, Flux Cored
Arc Welding FCAW), Submerged Arc Welding (SAW),
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Linnert, Welding Metallurgy, AWS, 1994
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Arc Welding Processes

• Welding processes that employ an electric arc are
  the most prevalent in industry
• Shielded Metal Arc Welding
• Gas Metal Arc Welding
• Flux Cored Arc Welding
• Submerged Arc Welding
• Gas Tungsten Arc Welding
• These processes are associated with molten metal

Electric Arc
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Linnert, Welding Metallurgy, AWS, 1994
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Protection of the Molten Weld Pool

• Molten metal reacts with the atmosphere
• Oxides and nitrides are formed
• Discontinuities such as porosity
• Poor weld metal properties
• All arc welding processes employ some means of
  shielding the molten weld pool from the air

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Welding Flux

• Three forms
• Granular
• Electrode wire coating
• Electrode core
• Fluxes melt to form a protective slag over the
  weld pool
• Other purposes
• Contain scavenger elements to purify weld metal
• Contain metal powder added to increase deposition
  rate
• Add alloy elements to weld metal
• Decompose to form a shielding gas

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Shielding Gas

• Shielding gas forms a protective atmosphere over
  the molten weld pool to prevent contamination
• Inert shielding gases, argon or helium, keep out
  oxygen, nitrogen, and other gases
• Active gases, such as oxygen and carbon dioxide,
  are sometimes added to improve variables such as
  arc stability and spatter reduction

Argon
Helium
Oxygen
Carbon Dioxide
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• What would happen if there was no flux on the
  wire to decompose into gas or no inert shielding
  gas was provided?
• What would the weld metal look like?

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Shielded Metal Arc Welding SMAW
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Shielded Metal Arc Welding (SMAW)
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SMAW Electrode Classification Example

• E7018
• E indicates electrode
• 70 indicates 70,000 psi tensile strength
• 1 indicates use for welding in all positions
• 8 indicates low hydrogen

E7018-A1-H8R
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• ANSI/AWS - 5.1 Specification for Covered Carbon
  Steel
• ANSI/AWS - 5.5 Specification for Low Alloy
  Steel
• ANSI/AWS - 5.4 Specification for Corrosion
  Resistant Steel

AWS Website http//www.aws.org
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Coating Materials -Partial List
Slipping Agents to Aid Extrusion Clay Talc
Glycerin Binding Agents Sodium Silicate
Asbestos Starch Sugar Alloying and
Deoxidizing Elements Si, Al, Ti, Mn, Ni, Cr
Arc Stabilizers Titania TiO2 Gas-Forming
Materials Wood Pulp Limestone
CaCO3 Slag-Forming Materials Alumina Al2O3
TiO2 SiO2 Fe3O4
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Linnert, Welding Metallurgy AWS, 1994
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Linnert, Welding Metallurgy AWS, 1994
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SMAW Advantages
Shielded Metal Arc Welding

• Easily implemented
• Inexpensive
• Flexible
• Not as sensitive to part fit-up variances

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Advantages

• Equipment relatively easy to use, inexpensive,
  portable
• Filler metal and means for protecting the weld
  puddle are provided by the covered electrode
• Less sensitive to drafts, dirty parts, poor
  fit-up
• Can be used on carbon steels, low alloy steels,
  stainless steels, cast irons, copper, nickel,
  aluminum

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Quality Issues
Shielded Metal Arc Welding

• Discontinuities associated with manual welding
  process that utilize flux for pool shielding
• Slag inclusions
• Lack of fusion
• Other possible effects on quality are porosity,
  and hydrogen cracking

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Limitations
Shileded Metal Arc Welding

• Low Deposition Rates
• Low Productivity
• Operator Dependent

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Other Limitations

• Heat of welding too high for lead, tin, zinc, and
  their alloys
• Inadequate weld pool shielding for reactive
  metals such as titanium, zirconium, tantalum,
  columbium

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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• Wood (cellulose) and limestone are added to the
  coating on SMAW Electrodes for gas shielding.
  What gases might be formed?
• How do these gases shield?

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Gas Metal Arc Welding
Gas Metal Arc Welding
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GMAW Modes of Metal Transfer
Gas Metal Arc Welding
Globular
Spray
Pulsed Spray
Short Circuiting
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GMAW Filler Metal Designations
Gas Metal Arc Welding

• ER - 70S - 6

Composition 6 high silicon
Electrode
Solid Electrode
Rod (can be used with GMAW)
Minimum ultimate tensile strength of the weld
metal
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AWS Specifications for GMAW Wire
AWS A5.18 - Carbon Steel Electrodes AWS A5.28 -
Low Alloy Steel Electrodes
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Shielding Gas
Gas Metal Arc Welding

• Shielding gas can affect
• Weld bead shape
• Arc heat, stability, and starting
• Surface tension
• Drop size
• Puddle flow
• Spatter

Ar
He
CO2
Ar-He
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GMAW Advantages
Gas Metal Arc Welding

• Deposition rates higher than SMAW
• Productivity higher than SMAW with no slag
  removal and continuous welding
• Easily automated

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Quality
Gas Metal Arc Welding

• Spatter
• Droplets of electrode material that land outside
  the weld fusion area and may or may not fuse to
  the base material
• Porosity
• Small volumes of entrapped gas in solidifying
  weld metal

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Limitations
Gas Metal Arc Welding

• Equipment is more expensive and complex than SMAW
• Process variants/metal transfer mechanisms make
  the process more complex and the process window
  more difficult to control
• Restricted access
• GMAW gun is larger than SMAW holder

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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• When comparing processes that have spray and
  globular metal transfer, which type of transfer
  mode do you thnk results in more spatter? Why?

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Flux Cored Arc Welding (FCAW)
Flux-Cored Arc Welding
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Linnert, Welding Metallurgy, AWS, 1994
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FCAW Electrode Classification
Flux-Cored Arc Welding

• E70 T - 1

Electrode
Type Gas, Usability and Performance
Minimum UTS 70,000 psi
Flux Cored /Tubular Electrode
Position
American Welding Society Specification AWS A5.20
and AWS A5.29.
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Linnert, Welding Metallurgy AWS, 1994
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Advantages
Flux-Cored Arc Welding

• High deposition rates
• Deeper penetration than SMAW
• High-quality
• Less pre-cleaning than GMAW
• Slag covering helps with larger out-of-position
  welds
• Self-shielded FCAW is draft tolerant.

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Limitations
Flux-Cored Arc Welding

• Slag must be removed
• More smoke and fumes than GMAW and SAW
• Spatter
• FCAW wire is more expensive
• Equipment is more expensive and complex than for
  SMAW

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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• What do you suppose would happen if the powder
  inside the core did not get compacted good?

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Submerged Arc Welding
Submerged Arc Welding
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SAW Flux / Filler Metal Compositions
Submerged Arc Welding

• F7A2-EM12K
• F indicates flux
• 70-95 ksi UTS, 58 ksi minimum yield strength, 22
  elongation
• A - as welded P - postweld heat treated
• 2 - minimum impact properties of 20 ft-lbs _at_ 20F
• E indicates electrode (EC - composite electrode)
• M - medium manganese per AWS Specifications
• 12 - 0.12 nominal carbon content in electrode
• K - produced from a heat of aluminum killed steel

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Advantages
Submerged Arc Welding

• High deposition rates
• No arc flash or glare
• Minimal smoke and fumes
• Flux and wire added separately - extra dimension
  of control
• Easily automated
• Joints can be prepared with narrow grooves
• Can be used to weld carbon steels, low alloy
  steels, stainless steels, chromium-molybdenum
  steels, nickel base alloys

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Limitations
Submerged Arc Welding

• Flux obstructs view of joint during welding
• Flux is subject to contamination Þ porosity
• Normally not suitable for thin material
• Restricted to the flat position for grooves -
  flat and horizontal for fillets
• Slag removal required
• Flux handling equipment

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Homework
Do Homework Assignment 2, Arc Welding Processes
from the Assignment Page of the WE300 Website.
Turn in next Class Period.