copyright © 2005, twi ltd world centre for materials joining technology flux cored arc welding twi...

Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

FLUX CORED ARC WELDING

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Flux cored arc welding

FCAW FCAW methodsmethods

With gas With gas shielding - shielding - “Outershiel“Outershiel

d”d”

Without gas Without gas shielding - shielding -

“Innershield“Innershield”(114)”(114)

With metal With metal powder - powder - “Metal “Metal core”core”

With active With active gas gas

shielding shielding (136)(136)

With inert With inert gas gas

shielding shielding (137)(137)


“Outershield” process


“Innershield” process


Structure of the cored wires

• provide form stability to the wire

• serves as current transfer during welding

Functions of metallic sheath:

Function of the filling powder:

• stabilise the arc• add alloy

elements• produce gaseous

shield• produce slag• add iron powder


Core elements and their function

• Aluminium Aluminium - deoxidize & denitrify- deoxidize & denitrify

• Calcium - provide shielding & form slagCalcium - provide shielding & form slag

• Carbon - increase hardness & strengthCarbon - increase hardness & strength

• Manganese - deoxidize & increase strengthManganese - deoxidize & increase strength

• Molybdenum - increase hardness & strengthMolybdenum - increase hardness & strength

• Nickel - improve hardness, strength, Nickel - improve hardness, strength, toughness toughness & corrosion resistance& corrosion resistance

• Potassium - stabilize the arc & form slagPotassium - stabilize the arc & form slag

• Silicon - deoxidize & form slagSilicon - deoxidize & form slag

• Sodium - stabilize arc & form slagSodium - stabilize arc & form slag

• Titanium - deoxidize, denitrify & form slagTitanium - deoxidize, denitrify & form slag


Types of cored wire

• not sensitive to not sensitive to moisture pick-upmoisture pick-up

• can be copper coated can be copper coated better current transferbetter current transfer

• thick sheath thick sheath good good form stability form stability 2 roll 2 roll drive feeding possibledrive feeding possible

• difficult to manufacturedifficult to manufacture

• good resistance good resistance to moisture to moisture pick-uppick-up

• can be copper can be copper coatedcoated

• thick sheaththick sheath• difficult to seal difficult to seal

the sheaththe sheath

Seamless cored wire

Butt joint cored wire

Overlapping cored wire

• sensitive to sensitive to moisture moisture pick-uppick-up

• cannot be cannot be copper copper coatedcoated

• thin sheaththin sheath• easy to easy to

manufacturmanufacturee


Cored wire manufacturing process

Str

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Th

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etal

Flu

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Clo

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Fo

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FCAW wire designation

Wire designation acc. BS EN 758:Wire designation acc. BS EN 758:

Standard Standard numbernumber

Tubular cored Tubular cored electrodeelectrode

Tensile Tensile propertiesproperties

Impact Impact propertiesproperties

Light alloy Light alloy additionsadditions

Type of electrode coreType of electrode core

Shielding gasShielding gas

Welding position Welding position (optional)(optional)

Diffusible hydrogen content Diffusible hydrogen content (optional)(optional)

EN 758 - T 46 3 1Ni B M 4 H5EN 758

T 46 3 1Ni MB 4 H5


FCAW wire designation

Wire designation acc. AWS A-5.20:Wire designation acc. AWS A-5.20:

Welding position (0 - F/H only; Welding position (0 - F/H only; 1- all positions)1- all positions)

Electrode usability (polarity, Electrode usability (polarity, shielding and KV); can range shielding and KV); can range from 1 to 14from 1 to 14

E 71 T-6 M J H8

Designates an electrodeDesignates an electrode

Minimum UTS of weld metal (ksi x Minimum UTS of weld metal (ksi x 10)10)Flux cored electrodeFlux cored electrode

E 71 T-6

Shielding gas for classificationShielding gas for classification

M

27J at -40°C requirement 27J at -40°C requirement (optional)(optional)

Diffusible hydrogen content Diffusible hydrogen content (optional); can be 4, 8 or 16(optional); can be 4, 8 or 16

J H8


FCAW - differences from MIG/MAG

• usually operates in usually operates in DCEP but some DCEP but some “Innershield” wires “Innershield” wires operates in DCENoperates in DCEN

• power sources need power sources need to be more powerful to be more powerful due to the higher due to the higher currentscurrents

• doesn't work in deep doesn't work in deep transfer modetransfer mode

• require knurled feed require knurled feed rollsrolls

• ““Innershield” Innershield” wires use a wires use a different type of different type of welding gun welding gun



350 Amps self shielded welding gun350 Amps self shielded welding gun

Courtesy of Lincoln Courtesy of Lincoln ElectricElectric

Contact tip

Thread protector

Conductor tube

Trigger

Handle

Hand shield

24V insulated switch lead

Welding gun cable

Close wound stainless steel spring wire liner (inside welding gun cable)



Self shielded Self shielded electrode nozzleelectrode nozzle


Travel Angle

75° 75°90°


Backhand (“drag”) technique

AdvantagesAdvantages• preferred method for flat or horizontal preferred method for flat or horizontal

positionposition• slower progression of the weldslower progression of the weld• deeper penetrationdeeper penetration• weld stays hot longer weld stays hot longer easy to remove easy to remove

dissolved gassesdissolved gasses

DisadvantagesDisadvantages• produce a higher weld profileproduce a higher weld profile• difficult to follow the weld jointdifficult to follow the weld joint• can lead to burn-through on thin sheet can lead to burn-through on thin sheet

platesplates


Forehand (“push”) technique

AdvantagesAdvantages• preferred method for vertical up or preferred method for vertical up or

overhead positionoverhead position• arc is directed towards the unwelded arc is directed towards the unwelded

joint joint preheat effect preheat effect• easy to follow the weld joint and control easy to follow the weld joint and control

the penetrationthe penetration

DisadvantagesDisadvantages• produce a low weld profile, with coarser produce a low weld profile, with coarser

ripplesripples• fast weld progression fast weld progression shallower depth shallower depth

of penetrationof penetration• the amount of spatter can increasethe amount of spatter can increase


FCAW advantages

• less sensitive to lack of fusionless sensitive to lack of fusion• requires smaller included angle compared to MMArequires smaller included angle compared to MMA• high productivityhigh productivity• all positionalall positional• smooth bead surface, less danger of undercutsmooth bead surface, less danger of undercut• basic types produce excellent toughness basic types produce excellent toughness

propertiesproperties• good control of the weld pool in positional good control of the weld pool in positional

welding especially with rutile wireswelding especially with rutile wires• seamless wires have no torsional strain seamless wires have no torsional strain twist twist

freefree• ease of varying the alloying constituentsease of varying the alloying constituents• no need for shielding gasno need for shielding gas


FCAW advantages

Deposition rate for carbon steel weldingDeposition rate for carbon steel welding


FCAW disadvantages

• limited to steels and Ni-base alloyslimited to steels and Ni-base alloys• slag covering must be removedslag covering must be removed• FCAW wire is more expensive on a weight FCAW wire is more expensive on a weight

basis than solid wires (exception: some basis than solid wires (exception: some high alloy steels)high alloy steels)

• for gas shielded process, the gaseous for gas shielded process, the gaseous shield may be affected by winds and draftsshield may be affected by winds and drafts

• more smoke and fumes are generated more smoke and fumes are generated compared with MIG/MAGcompared with MIG/MAG

• in case of Innershield wires, it might be in case of Innershield wires, it might be necessary to break the wire for restart necessary to break the wire for restart (due to the high amount of insulating slag (due to the high amount of insulating slag formed at the tip of the wire)formed at the tip of the wire)

copyright © 2005, twi ltd world centre for materials joining technology flux cored arc welding twi...

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