12-tig welding 2006

7/30/2019 12-TIG Welding 2006

1/42

CSWIP 3.1 Welding InspectionCSWIP 3.1 Welding Inspection

TWI Training & Examination Services

Course Reference WIS 5

Tungsten Inert GasTungsten Inert Gasoror

Gas Tungsten Arc WeldingGas Tungsten Arc Welding

7/30/2019 12-TIG Welding 2006

2/42

The TIG welding process was first developed in the USAThe TIG welding process was first developed in the USA

during the 2during the 2ndnd world war for the welding of aluminum alloysworld war for the welding of aluminum alloys

The process uses a non-consumable tungsten electrode The process requires a high level of welder skill

The process produces very high quality welds.

The TIG process is considered as a slow process compared toother arc welding processes

The arc may be initiated by a high frequency to avoid scratchstarting, which could cause contamination of the tungsten andweld

Tungsten Inert Gas Welding

7/30/2019 12-TIG Welding 2006

3/42

TIG - Principle of operation

7/30/2019 12-TIG Welding 2006

4/42

USA: GTAWUSA: GTAW

Gas ShieldGas Shield

ArcArc

Weld PoolWeld Pool

CeramicCeramicNozzleNozzle

TungstenTungstenElectrodeElectrode

Filler WireFiller Wire

Contact TubeContact Tube

Welding TorchWelding Torch Current ConductorCurrent Conductor

Shielding gasShielding gas


7/30/2019 12-TIG Welding 2006

5/42

Sizes/types vary depending on current/applicationTORCH

To deliver correct gas flow (velocity) depending on welding

position and joint configuration.

FLOWMETER

(graduated in ltr/min)

Correct type for application.(ar, he, ar/he mixture)

Argon/hydrogen for austenitic stainless steel

INERT GAS SUPPLY

(Cylinder & regulator)

Note that current actually flows from this leadRETURN LEAD

Flexible may carry current, gas, cooling water.TORCH HOSE

Transformers for AC aluminium alloys

Rectifiers for DC - steels

Transformer/rectifier for AC/DC

Inverters for AC/DC more portable - expensive

POWER SOURCE

440v 50Hz 3 phase or

240v single phase input

TIG power source

7/30/2019 12-TIG Welding 2006

6/42

InverterInverter

power sourcepower source

Power cablePower cable

FlowFlow--metermeter

Power controlPower control

panelpanel

Transformer/Transformer/

RectifierRectifier

Power controlPower control

panelpanel

Power returnPower return

cablecable

TorchTorch

assembliesassemblies

TungstenTungsten

electrodeselectrodes

Equipment for TIG

7/30/2019 12-TIG Welding 2006

7/42

Equipment for TIG

Power source control panel

Courtesy of Lincoln ElectricCourtesy of Lincoln Electric

ON/OFF switchON/OFF switch

AC balanceAC balance

Start/stop currentStart/stop current

Start methodStart method

AmmeterAmmeterRemoteRemote

controlcontrol

WeldingWelding

currentcurrent

Slope upSlope up

Slope downSlope down

PostflowPostflow

(Preflow)(Preflow)

BackgroundBackground

currentcurrent

Peak currentPeak current

Current typeCurrent type

& polarity& polarity

Pulse frequencyPulse frequency

2/4 stroke2/4 stroke

Pulse ON/OFFPulse ON/OFF

7/30/2019 12-TIG Welding 2006

8/42

ARC CHARACTERISTICS

VoltsVolts

AmpsAmps

OCVOCV

Constant Current/Amperage CharacteristicConstant Current/Amperage Characteristic

Large change in voltage =Large change in voltage =

Smaller change in amperageSmaller change in amperage

Welding VoltageWelding VoltageLarge arc gapLarge arc gap

Small arcSmall arc

gapgap

7/30/2019 12-TIG Welding 2006

9/42

TIG Torch

Torch types: Gas cooled: cheap, simple, large size, short life forcomponent parts

Water cooled: recommended over 150A, expensive, complex,small size, longer life for component parts

7/30/2019 12-TIG Welding 2006

10/42

TIG Torch

TorchTorch

bodybody

TungstenTungsten

electrodeelectrode

ElectrodeElectrode

colletcollet

TorchTorch

cap/tungstencap/tungstenhousinghousing

CeramicCeramic

nozzlenozzle

ColletColletholderholder

On/offOn/off

switchswitch

7/30/2019 12-TIG Welding 2006

11/42

TIG Torch

Gas lenses

reduces eddies in the gas flow

extends the length of the laminar flow

prevents contamination

highly recommended in case of reactivemetals (e.g. Ti, Al)

Stainless steelStainless steel

wire sievewire sieve

Thread forThread for

gas nozzlegas nozzle

Thread forThread fortorch bodytorch body

7/30/2019 12-TIG Welding 2006

12/42

Electrode tip for DCEN

Electrode tip preparedElectrode tip prepared

for low current weldingfor low current weldingElectrode tip prepared forElectrode tip prepared for

high current weldinghigh current welding

VertexVertex

angleangle

PenetrationPenetration

increaseincrease

IncreaseIncrease

Bead widthBead width

increaseincrease

DecreaseDecrease

22--2,5

times

2,5

times

elec

trodediameter

elec

trodediameter

7/30/2019 12-TIG Welding 2006

13/42

Electrode tip for AC

Electrode tip groundElectrode tip groundElectrode tip groundElectrode tip ground

and then conditionedand then conditioned

7/30/2019 12-TIG Welding 2006

14/42

Tungsten electrodesTungsten electrodes

The electrode diameter, type and vertex angle are all critical

factors considered as essential variables. The vertex angle is as

shown

Vetex angleVetex angle Note:Note: when welding

aluminium with AC current,the tungsten end ischamfered and forms a ballend when welding

DCDC --veve

Note:Note: too fine an angle willpromote melting of theelectrodes tip

ACAC

TIG Welding Variables

7/30/2019 12-TIG Welding 2006

15/42

Choosing the proper electrode

Polarity Influence cathodic cleaning effect

7/30/2019 12-TIG Welding 2006

16/42

Old types:Old types:

Thoriated: DC electrode -ve - steels and most metals

1% thoriated + tungsten for higher current values

2% thoriated for lower current values

Zirconiated: AC - aluminum alloys and magnesium

New types:New types:

Cerium: DC electrode -ve - steels and most metals

Lanthanum: AC - Aluminum alloys and magnesium

Tungsten ElectrodesTungsten Electrodes

7/30/2019 12-TIG Welding 2006

17/42

Tungsten electrode types

Pure tungsten electrodes:

colour code - green

no alloy additions

low current carrying capacity

maintains a clean balled end

can be used for AC welding of Al and Mg alloys

poor arc initiation and arc stability with AC compared with otherelectrode types

used on less critical applications

low cost

7/30/2019 12-TIG Welding 2006

18/42


Thoriated tungsten electrodes:

colour code - yellow/red/violet

20% higher current carrying capacity compared to pure tungstenelectrodes

longer life - greater resistance to contamination

thermionic - easy arc initiation, more stable arc

maintain a sharpened tip

recommended for DCEN, seldom used on AC (difficult to

maintain a balled tip)

This slightly radioactive

7/30/2019 12-TIG Welding 2006

19/42


Ceriated tungsten electrodes:

colour code - grey (orange acc. AWS A-5.12)

operate successfully with AC or DC

Ce not radioactive - replacement for thoriated types

7/30/2019 12-TIG Welding 2006

20/42


Lanthaniated tungsten electrodes:

colour code - black/gold/blue

operating characteristics similar with ceriated electrode

7/30/2019 12-TIG Welding 2006

21/42


Zirconiated tungsten electrodes:

colour code - brown/white

operating characteristics fall between those of pure andthoriated electrodes

retains a balled end during welding - good for AC welding

high resistance to contamination

preferred for radiographic quality welds

7/30/2019 12-TIG Welding 2006

22/42


UnstableUnstable

arcarcTungstenTungsten

inclusionsinclusions

WeldingWelding

currentcurrent

Electrode tipElectrode tipnot properlynot properly

heatedheated

ExcessiveExcessivemelting ormelting or

volatilisationvolatilisation

TooToo

lowlowTooToo

highhigh

Factors to be considered:Factors to be considered:


7/30/2019 12-TIG Welding 2006

23/42


Current type influence

++++

++

++++

++

++++

++

----

--

----

--

----

--

Electrode capacityElectrode capacity

Current type & polarityCurrent type & polarity

Heat balanceHeat balance

Oxide cleaning actionOxide cleaning action


DCENDCEN DCEPDCEPAC (balanced)AC (balanced)

70% at work70% at work

30% at electrode30% at electrode50% at work50% at work

50% at electrode50% at electrode35% at work35% at work

65% at electrode65% at electrode

Deep, narrowDeep, narrow MediumMedium Shallow, wideShallow, wide

NoNo YesYes -- every half cycleevery half cycle YesYes

ExcellentExcellent

(e.g. 3,2 mm/400A)(e.g. 3,2 mm/400A)GoodGood

(e.g. 3,2 mm/225A)(e.g. 3,2 mm/225A)PoorPoor

(e.g. 6,4 mm/120A)(e.g. 6,4 mm/120A)

7/30/2019 12-TIG Welding 2006

24/42

Shielding gas requirements

Preflow andpostflow

PreflowPreflow PostflowPostflow

Shielding gas flowShielding gas flow

Welding currentWelding current

Flow rateFlow rate

too lowtoo low

Flow rateFlow rate

too hightoo high

7/30/2019 12-TIG Welding 2006

25/42

Special shielding methods

Torch trailing shieldTorch trailing shield Welding in protective tentWelding in protective tent

7/30/2019 12-TIG Welding 2006

26/42

Special shielding methods

Pipe root run shieldingPipe root run shielding

7/30/2019 12-TIG Welding 2006

27/42

TIG torch set-up

Electrode extension

ElectrodeElectrode

extensionextension

StickoutStickout 22--3 times3 times

electrodeelectrode

diameterdiameter

ElectrodeElectrode

extensionextension

Low electronemission

Unstable arc

TooToo

smallsmall

OverheatingOverheating

TungstenTungsten

inclusionsinclusions

TooToo

largelarge

7/30/2019 12-TIG Welding 2006

28/42

TIG - arc initiation methods

simple method tungsten electrode is in contact

with the workpiece!

high initial arc current due to

the short circuit impractical to set arc length in

advance

electrode should tap the

workpiece - no scratch! ineffective in case of AC

used when a high quality is notessential

Arc initiationArc initiationmethodmethod

Lift arcLift arc HF startHF start

need a HF generator (spark-gap oscillator) that generates ahigh voltage AC output (radio

frequency) costly reliable method required on

both DC (for start) and AC (tore-ignite the arc)

can be used remotely

HF produce interference

requires superior insulation

7/30/2019 12-TIG Welding 2006

29/42

Types of current

can be DCEN or DCEP

DCEN gives deep penetration

requires special power source

low frequency - up to 20 pulses/sec(thermal pulsing)

better weld pool control

weld pool partially solidifies betweenpulses

Type ofType of

weldingwelding

currentcurrent

can be sine or square wave

requires a HF current (continuos orperiodical)

provide cleaning action

DCDC

ACAC

PulsedPulsed

currentcurrent

7/30/2019 12-TIG Welding 2006

30/42

Pulsed current

usually peak current is 2-10times background current

useful on metals sensitive to

high heat input

reduced distortions

in case of dissimilar

thicknesses equal penetrationcan be achieved

Time

Curr

ent(A)

Pulse

time

Cycle

time

Peak

current

Background

current

Average current

one set of variables can be used in all positions

used for bridging gaps in open root joints

require special power source

7/30/2019 12-TIG Welding 2006

31/42

TIG welding parameters

welding current penetration

arc voltage weld width

travel speed weld width + penetration

tilt angle

7/30/2019 12-TIG Welding 2006

32/42

VoltageVoltage

The voltage of the TIG welding process is variable only by the typeof gas being used, and changes in the arc length

CurrentCurrent

The current is adjusted proportionally to the tungsten electrodes

diameter being used. The higher the current the deeper thepenetration and fusion

PolarityPolarity

The polarity used for steels is always DC ve as most of the heat isconcentrated at the +ve pole, this is required to keep the tungstenelectrode at the cool end of the arc. When welding aluminium andits alloys AC current is used


7/30/2019 12-TIG Welding 2006

33/42

Gas type and flow rateGas type and flow rate

Generally two types of gases are used in TIG welding, argon andhelium, though nitrogen may be considered for welding copper andhydrogen may be added for the welding of austenitic stainless

steels.

The gas flow rate is also important.

Argon (Ar) InertArgon (Ar) Inert

Suitable for welding carbonsteel,stainless steel, aluminiumand magnesium

Lower cost, lower flow rates

More suitable for thinnermaterials and positionalwelding

Helium Argon mixesHelium Argon mixes

Suitable for welding carbon

steel, stainless steel,copper, aluminium andmagnesium

High cost, high flow rates

More suitable for thickermaterials and materials ofhigh thermal conductivity.


7/30/2019 12-TIG Welding 2006

34/42

1.1. PrePre--flow timer controlflow timer control

Adjusts the time the gas and

water valves are open

2.2. UpUp--Slope control (SlopeSlope control (Slope--In)In)

Prevents burn throughs and the

possibility of tungsten

inclusions

3.3. Output controlOutput control

Welding current control

4.4. DownDown--Slope control (SlopeSlope control (Slope--out)out)Crater fill and controls crater

pipe and the possibility of crater

cracks

5.5. PostPost--flow timer controlflow timer controlAdjusts the time the gas flows

after welding

1.1. 2.2. 3.3. 4.4. 5.5.


Ch k Wi h TIG W ldi

7/30/2019 12-TIG Welding 2006

35/42

The welding equipmentThe welding equipment

A visual check should be made to ensure the welding equipment isin good condition

The torch head assemblyThe torch head assembly

Check the diameter and specification of the tungsten electrode, therequired vertex angle and that a gas lens is fitted correctly. Check

the electrode stick-out length and that the ceramic is the correcttype and in good condition

Gas type and flow rateGas type and flow rate

Check the shielding gas is the correct type, or gas mixture and theflow rate is correct for the given joint design, welding position asstated in the WPS

Checks With TIG Welding

Ch k With TIG W ldi

7/30/2019 12-TIG Welding 2006

36/42

Current and polarityCurrent and polarity

Checks should be made to ensure that the type of current andpolarity are correctly set, and the range is within that given on the

procedure.

Other welding parametersOther welding parameters

Checks should be made to other parameters such as torch angle,

arc gap distance and travel speed.

SafetySafety

Check should be made on the current carrying capacity, or duty

cycle of the equipment and all electrical insulation is sound and inplace. Correct extraction systems should be in use to avoidexposure to toxic fume.

Checks With TIG Welding

Mechanised TIG

7/30/2019 12-TIG Welding 2006

37/42

Mechanised TIG

Cold wire no current is flowing

through the wire no

preheat simple equipment

special wire feeders canprovide continuos,intermittent or pulsedfeed

widely used on orbital

pipe welding and tube-to-tube sheetapplications

Mechanised TIG

7/30/2019 12-TIG Welding 2006

38/42

Mechanised TIG

Hot wire

current is flowing through thewire wire is resistance

heated nearly to its meltingtemperature when it is in

contact with the weld pool

higher welding speed thancold wire

high deposition rate normally used in flat position

wire is usually fed into theweld pool behind the arc

7/30/2019 12-TIG Welding 2006

39/42

Most welding defects with TIG are caused by a lack of welder skill,or incorrect setting of the equipment. i.e. current, torch

manipulation, welding speed, gas flow rate, etc. Tungsten inclusions (low skill or wrong vertex angle)

Surface porosity (loss of gas shield mainly on site)

Crater pipes (bad weld finish technique i.e. slope out)

Oxidation of S/S weld bead, or root by poor gas cover

Root concavity (excess purge pressure in pipe)

Lack of penetration/fusion (widely on root runs)

TIG typical defects


7/30/2019 12-TIG Welding 2006

40/42


Advantages

High quality

Good control

All positions

Lowest H2 process

Minimal cleaning

Autogenous welding

Can be automated

Disadvantages

High skill factor required

Low deposition rate

Small consumable range

High protection required

Complex equipment

Low productivity

High ozone levels +HF

7/30/2019 12-TIG Welding 2006

41/42

Any QuestionsAny Questions


7/30/2019 12-TIG Welding 2006

42/42

QU 1.QU 1. Give three reasons for the occurrence of tungstenGive three reasons for the occurrence of tungsteninclusionsinclusions

QU 2.QU 2. State the main welding parameters with the TIG weldingState the main welding parameters with the TIG weldingprocessprocess

QU 3.QU 3. Which electrode polarity is considered essential for theWhich electrode polarity is considered essential for thewelding of carbon steel? And give a brief description whywelding of carbon steel? And give a brief description why

QU 4.QU 4. Which electrode polarity is considered essential for theWhich electrode polarity is considered essential for thewelding of aluminium? And give a brief description whywelding of aluminium? And give a brief description why

QU 5.QU 5. State the tungsten electrode activators required to weldState the tungsten electrode activators required to weldcarbon steel and the light alloyscarbon steel and the light alloys

QU 6.QU 6. State the main advantages and disadvantage of the TIGState the main advantages and disadvantage of the TIGwelding processwelding process

QuestionsQuestions


12-tig welding 2006

Documents