m.i.g-m.a.g. welding m2 u10

8/10/2019 m.i.g-m.a.g. Welding m2 u10

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Trade of Metal Fabrication

Module 2: Thermal Processes

Unit 10: M.I.G/M.A.G. eldin!

Phase 2


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Trade of Metal Fabrication Phase 2

Module 2 Unit 10

Table of Contents

List of Figures.....................................................................................................................6

List of Tables......................................................................................................................7

ocu!ent "elease #istor$................................................................................................%

Module 2 Ther!al Processes.........................................................................................&

Unit 10 " M.I.G/M.A.G. eldin!....................................................................................#

$earnin! %utcome:......................................................................................................#

&e' $earnin! Points:...................................................................................................#

Trainin! (esources:...................................................................................................10

&e' $earnin! Points )ode:........................................................................................10

Metal 'rc (as)*hielded +M'(*, -elding....................................................................11

Introduction....................................................................................................................11

The Process....................................................................................................................12

Metal Transfer in MAG* eldin!.................................................................................1+

,lectrode ire *i-e...................................................................................................1

)ontact Tis and o--les..........................................................................................1

eldin! *eed...........................................................................................................1

ire ,tension...........................................................................................................1

(ases.................................................................................................................................17,conomic )onsiderations..............................................................................................1

C2 -elding of Mild *teel.............................................................................................1&

Metal Transfer For!s......................................................................................................20

Tac3 eld......................................................................................................................24

Metal)'rc (as *hielded -elding...................................................................................2/

Ancillar' ,5uiment......................................................................................................26

,lectrode ire (eel Assembl'..................................................................................26,lectrode ire 7ri8e Unit.........................................................................................26

9ori-ontal/ertical Position..........................................................................................2

%en *5uare ;utt


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T


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Unit 10


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Module 2 Unit 10

List of Figures

Fi!ure 1 > 7ia!ram of eldin! o--le and Gas *hield for Metal Arc Gas>*hielded

?MAG*@ eldin!.......................................................................................................10

Fi!ure 2 > MAG* eldin! Gun and eldin! Torch..........................................................11

Fi!ure 4 > Air>)ooled eldin! Torch................................................................................11

Fi!ure + > ;asic *et>U for MAG* eldin!.....................................................................12

Fi!ure 6 > MAG* eldin! a T>Fillet Test Piece................................................................12

Fi!ure > The Three T'es of Metal Transfer used in MAG* eldin!...........................1+

Fi!ure = > Metal Transfer Forms........................................................................................1#

Fi!ure > T'ical MIG/MAG eldin! Positions and Tac3 eld.....................................22

Fi!ure # > )lose>u of eldin! of a ;utt T *ra' Transfer..................................................................................42

Fi!ure 11 > *afet' Precautions...........................................................................................46

Fi!ure 12 > Poer *ource..................................................................................................4=

Fi!ure 14 > *chematic 7ia!ramB Pulse>Transfer................................................................4#

Fi!ure 1+ > $i!ht>7ut' *an>ec3 Torch.........................................................................+0

Fi!ure 16 " ire Feed Unit...............................................................................................+1

Fi!ure 1 > )omonents of Gas *hielded Metal Arc eldin! Process.............................+#

Fi!ure 1= > MIG/MAG eldin!........................................................................................60

Fi!ure 1 > Pie and Tube *ot eldin!...................................................................................................62

Unit 10 6


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Module 2 Unit 10

List of Tables

Table 1 > )ontact Ti Positions for MAG* eldin!.........................................................16

Table 2 > MIG and MAG Processes...................................................................................1=

Table 4 > Prearation for eldin! of *G )ast Irons..........................................................1

Table + > eld 7efects and Their )auses..........................................................................20

Table 6 > T'ical )onditions for MIG/MAG eldin! *heet.............................................+

Table > Gases for MIG/MAG eldin!...........................................................................+=

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ocu!ent "elease #istor$

ate 9ersion Co!!ents

02/11/0 First draft

06/12/0 Imlemented edits from

&enn'.

14/12/14 *%$A* transfer

Unit 10 %


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Module 2 Unit 10

Module 2 Ther!al Processes

Unit 10 M.4.(5M.'.(. -elding

uration 1 #ours

Learning utco!e:

;' the end of this unit each arentice ill be able to:

$ist the alicationsB characteristics and ha-ards associated ith

M.I.G/M.A.G.Cs eldin!

7escribe the three methods of filler metal transfers

*afel' set u and oerate Metal Acti8e Gas shielded e5uiment and eld

;utt and fillet eld in the flat osition

;e$ Learning Points:

Sk Rk Assembly of M.I.G. welding equipment.

Sc Rk M Regulation of gas flow and types of shielding

used and their applications.

Sk Rk Regulation of current settings.

Sk Rk Wire feed regulation speeds.

Sk Rk Maintenance and care of plant (water

cooled/air cooled).

Sk Rk Rk M.I.G./M.A.G. principles, techniques and

applications.

M Rk Wire filler sizes and tip sizes.

Rk Sc Applications and characteristics of the

M.I.G./M.A.G. process.

H Rk Safety standards and procedures safe work

area, P.P.E.

Sc Rk M.I.G./M.A.G. penetration of weld.

Rk Properties and strength of M.I.G./M.A.G. weld.

Rk History and development of the process.

P Organisation of work area safe work

environment P.P.E.

Unit 10 &


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Module 2 Unit 10

Training "esources:

Fabrication or3sho facilities

Metal inert !as eldin! lant/shieldin! !as and e5uiment

*afet' clothin! and e5uiment

9andouts

%8erheard transarencies

Trainin! 8ideos

Manufacturers data sheets

;e$ Learning Points Code:

M D Maths 7D 7rain! (& D (elated &noled!e *c D *cience

P D Personal *3ills *3 D *3ill 9 D 9a-ards

Unit 10 10


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Module 2 Unit 10

Metal 'rc (as)*hielded +M'(*, -elding

4ntroduction

These semi>automatic and automatic rocesses ha8e found increasin! use in recent 'ears.

The' ha8e relaced the use of o'acet'lene and manual metal arc rocesses on certain

t'es of fabrication.

The rocess is 3non b' different namesB such as MIG ?metallic inert !as@B )% 2eldin!

?hen a carbon dioide !as shield is emlo'ed@B metal acti8e !as eldin! andB in the

U*AB !as metal>arc eldin!. In the U&B the most idel' acceted name is MAG* ?metal

arc !as>shielded eldin!@ because this term co8ers shieldin! !ases other than inert !asesB

and also !as mitures.

Figure 1 ) iagra! of -elding automaticB it is suitable for full automation on certain

t'es of or3 and is used 5uite idel' in robot form.

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The Process

A continuous consumable ire electrode is fed throu!h a eldin! !un fitted ith a

concentric !as no--le. The arc is struc3 beteen the or3iece and the ireB hich acts

as both electrode and filler. The arc and the eld ool are shielded from atmosheric

contamination b' assin! a suitable !as throu!h the no--le to form a rotecti8e shield

around the eldin! area ?Fi!ure 1to Fi!ure 4@.

Figure 2 ) M'(* -elding (un and -elding Torch

*ome !uns can ha8e an outer no--le attachment for fume etraction. This has to be

carefull' set so as not to disturb the !as shield.

For non>ferrous metalsB ure ar!on is usuall' used as the !as shield. %ther !ases can be

usedB such as helium or ?for coer@ nitro!en. For ferrous metalsB the !ases used include

carbon dioideB ar!on and o'!enB ar!on and )%2.

Figure ) 'ir)Cooled -elding Torch

The arc is self>adEustin!B hich means that an' 8ariation in the arc len!th made b' the

elder roduces a chan!e in the burn>off rate of the electrodeB and the arc raidl' returns

to its ori!inal len!th.

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Fi!ure +shos the basic set>u for MAG* eldin!.

Figure / ) >asic *et)U3 for M'(* -elding

Figure ) M'(* -elding a T)Fillet Test Piece

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Figure 6 ) The Three T$3es of Metal Transfer used in M'(* -elding

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?lectrode -ire *i=e

Generall' sea3in!B the smaller>diameter ires ill !i8e !reater current densit'B resultin!

in a fast burn>off rate and a tendenc' to !i8e deeer>enetration elds.

Modern MAG* eldin! machines ha8e an automatic inductanceB but older machines ma'

need a manual settin!. The inductance is used for di transfer eldin!. Increasin! theinductance for a !i8en oen>circuit 8olta!e roduces a hotter arcB hich results in 5uieter

eldin! conditions ith less satter and a smoother eld finish. 7ecreasin! the

inductance roduces a cooler arc that !i8es out a distincti8e crac3lin! sound and a eld

surface ith a more ronounced rile.

%n machines that re5uire manual adEustmentB hi!h inductance ill be needed for thic3er

materials and lo inductance for thin sheet.

Contact Ti3s and mm

2. For sra' transfer: 1>40 mm

4. For flu>cored ire: 40>+6 mm

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(ases

*ince )%2and o'!en are not inert !asesB the title metallic inert !as is not true hen

either of these !ases is mied ith ar!on or )%2is used on its on. The title metallic

acti8e !as ?MAG@ is sometimes used in these cases.

Argon + 1% or 2% oxygen.The addition of o'!en as a small ercenta!e to ar!on !i8es

hi!her arc temeratures and the o'!en acts as a ettin! a!ent to the molten oolB

ma3in! it more fluid and stabilisin! the arc.

Helium is nearly always found in mixed gases. ;ecause of the !reater arc temeratureB

miin! it ith ar!onB o'!en or )%2controls the ool temeratureB increases ettin! and

stabilises the arc. The hi!her the helium content the hi!her the arc 8olta!e and the !reater

the heat outut. It is used in !as mitures for aluminiumB nic3elB curo>nic3elsB etc.B andis articularl' alicable to stainless steels ith the helium>ar!on>o'!en or )%2

mitures. 9elium>ar!on mitures are also used for the eldin! of # nic3el steels.

Carbon dioxide. Pure )%2is the cheaest of the shieldin! !ases and can be used as a

shield for eldin! steel u to 0.+ ) and lo>allo' steel. ;ecause there is some

dissociation of the )%2in the arc resultin! in carbon monoide and o'!en bein!

formedB the filler ire is trile deoidised to re8ent orosit'B and this adds somehat to

its cost and results in some small areas of sla! bein! resent in the finished eld. The

drolet rate is less than that ith ure ar!onB the arc 8olta!e dro is hi!herB and the

threshold 8alue for sra' transfer much hi!her than ith ar!on. The forces on the droletsbein! transferred across the arc are less balanced than ith ar!on>o'!en so that the arc

is not as smooth and there is some satterB the arc conditions bein! more critical than ith

ar!on>o'!en.

Gas flo rate can !reatl' affect the 5ualit' of the eld. Too lo a flo rate !i8es

inade5uate !as shieldin! and leads to the inclusion of oides and nitridesB hile too hi!h

a rate can introduce a turbulent flo of the )%2hich occurs at a loer rate than ith

ar!on. This affects the efficienc' of the shield and leads to a orosit' in the eld. The

aim should be to achie8e an e8en non>turbulent flo and for this reason satter should

not be alloed to accumulate on the no--leB hich should be directed as nearl' asossible at #0H to the eldB a!ain to a8oid turbulence.

The torch an!le isB in racticeB about =0>0H to the line of tra8el consistent ith !ood

8isibilit' and the no--le is held about 10>1 mm from the or3. If the torch is held too

closeB ecess satter build>u necessitates fre5uent cleanin!B and in dee U or

rearation the an!le can be increased to obtain better access. ea8in! is !enerall' 3et

as lo as con8enient to reser8e the efficienc' of the !as shield and reduce the tendenc'

to orosit'. ide eld beads can be made u of narroer strin!er runsB and tilted fillets

comared ith 9 fillets !i8e e5ual le! len!th more easil'B ith better rofile.

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Module 2 Unit 10

Mild steel sheetB butt eldsB )%2shieldin!B flatB 0. mm diameter ire ?aroimate

8alues@.

Thic@ness

+!!,

(a3

+!!,

-ire feed

+!5!inute,

'rc

+Aolts,

Current

+',

1 0 2.>4. 1>1= 6>0

1.2 0 4.2>+.0 1>1# =0>6

1. 0.6 +.0>>+. 1#>20 6>#6

2.0 0. 6.>=.0 1#>20 110>>126

2.6 0. =.0>>.+ 20>>21 126>1+0

4.0 1.6 =.0>>.+ 20>>21 126>1+0

?cono!ic Considerations

Althou!h filler ire for the )%2rocessB to!ether ith the cost of the shieldin! !asB is

more eensi8e than con8entional electrodesB other factors !reatl' affect the economic

8iabilit' of the rocess. The deosition rate !o8erns the eldin! seed hich in turn

!o8erns the labour char!e on a !i8en fabrication.

The deosition rate of the filler metal is a direct function of the eldin! current.

Table 2 ) M4( and M'( Processes

Metal arc !as shielded rocess. (ecommended !ases and !as mitures for 8arious metalsand allo's.

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Module 2 Unit 10

C2-elding of Mild *teel

There are four controls to enable otimum eldin! conditions to be achie8ed: ?1@ ire

feed seed hich also controls the eldin! currentB ?2@ 8olta!eB ?4@ !as flo.

For a !i8en ire diameter the ire feed rate must be abo8e a certain minimum 8alue toobtain a drolet transfer rate of abo8e about 20 er secondB belo hich transfer is

unsatisfactor'. ith increasin! ire feed rate the drolet transfer rate and hence the burn>

off increases and the uer limit is usuall' determined b' the caacit' of the ire feed

unit.

As stated beforeB the short>circuitin! arc is !enerall' used for eldin! thinner sectionsB

ositional eldin!B tac3in! and on thic3nesses u to .6 mm. In ositional eldin! the

root run ma' be made donards ith no ea8e and subse5uent runs uard. The loer

heat outut of this t'e of arc reduces distortion on fabrications in thinner sections.

Table ) Pre3aration for -elding of *( Cast 4rons

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Module 2 Unit 10

Metal Transfer For!s

Figure 7 ) Metal Transfer For!s

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Module 2 Unit 10

Fault Cause

Porosit'

)rac3in!

Undercuttin!

$ac3 of enetration

$ac3 of fusion

*la! inclusions

*atter " on or3

on no--le

in eld

Irre!ular eld shae

Insufficient *iB Mn in ire

Insufficient )%2shieldin!

Flo rate

because of Fro-en 8alue

)lo!!ed no--le

7rau!hts

7irt' or3 " !reaseB aintB scaleB rust

?i@ eld bead too small

?ii@ eld too deeB !reater than 1:2:1

?iii@ 9i!h sulhurB lo man!aneseB

slo coolin! rateTra8el seed too hi!h

;ac3in! bar !roo8e too dee

)urrent too lo for seed

Torch an!le too lo

)urrent too lo " settin! ron!

ire feed fluctuatin!

,lectrode etension too !reat


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Module 2 Unit 10

Tac@ -eld

A tac3 is a relati8el' small temorar' MIG/MAG eld that is used instead of a clam or

a self>tain! screB to tac3 and hold the anel in lace hile roceedin! to ma3e a

ermanent eld ?Fi!ure @. $i3e the clam or self>tain! screB the tac3 eld is ala's

and onl' a temorar' de8ice. The len!th of the tac3 eld is determined b' the thic3ness

of the metal anel to be elded and is aroimatel' a len!th of 16 to 40 times the

thic3ness of the metal anel. Tac3 elds must be done accuratel'B as the' are 8er'

imortant in maintainin! roer ali!nment.

Figure % ) T$3ical M4(5M'( -elding Positions and Tac@ -eld

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Module 2 Unit 10

Metal)'rc (as *hielded -elding

This eldin! rocess is a method of eldin! hereb' an electric arc is maintained

beteen a continuousl' fed consumable ire electrode. The rotecti8e !as shieldB the

ire and coolin! ater hen necessar' are fed throu!h a fleible hose connected to thetorch or !un at one end and the control unit at the other. This control unit usuall' houses

electronic sitches hich sto and start the ire feedB the shieldin! !as flo and the

coolin! aterB in addition to current and 8olta!e control. A contactor sitch usuall' on

the !un causes the ire to feed throu!h the coer contact ti in the end of the !un and so

allo the arc to be struc3.

It is imortant to note that the ire ti ill onl' arc durin! the time the ire is feedin!

outB and increasin! the ire seed causes an increase in current. The electrode is fed at a

constant seed hen selected at the control unitB but as stated abo8e this seed ma' be

8aried to increase or decrease the current.

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Module 2 Unit 10

'ncillar$ ?Bui3!ent

In addition to the oer source the

e5uiment is as illustrated:

?lectrode -ire "eel 'sse!bl$

The electrode ire reel or coll is mounted on

to a sindle or sider hubB either hori-ontall'

or 8erticall' as re5uired.

The hub is free to rotate as the ire is dran

off b' the ire dri8e unit.

An adEustable bra3in! de8ice is incororated

in the assembl' to re8ent o8errun of the

electrode ire hen the motor of the ire

dri8e unit is stoed.

?lectrode -ire riAe Unit

This ma' either be a ush or a ull t'e or

combined.

In the ush t'e the mechanism consists of

to or more feed rolls here the !ri or

ressure can be adEusted.

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#ori=ontal59ertical Position

3en *Buare >utt oint Pulse Transfer

,amle Procedure ,P=#

1. 7irect the electrode ire at the !a beteen the sheets to form a ear>shaed

melted area ?3e'hole@.

2. AdEust the rate of uards tra8el so as to maintain the 3e'hole ahead of the eld

ool ith a eld run built u abo8e the sheet surfaces behind the eld ool.

Visual Examination

A neat eld rofile ith a uniform ?but not ecessi8e@ enetration bead should beachie8ed.

Figure & ) Close)u3 of -elding of a >utt oint

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3en *Buare >utt oint i3 Transfer

Example Procedure EP80

1. ,stablish the arc at the to end of the Eoint.

2. The electrode ire should be ointed uards at an an!le of 6H>=6H.

4. 7irect the electrode ire at the !a beteen the sheets and adEust the rate of

donards tra8el to ensure e8en deosition and control of enetration.

Visual Examination

As in ,P0.

Material 6 mm or mm mild steel.

Pre3aration ?a@ s5uare ed!e.

?b@ be8el to 40H on each late.

o root face.

?lectrode ?a@ 0. mm

?b@ 1.2 mm

Feed "ate ?a@ 100>110 in./min.

?b@ 120>140 in./min.

Current ?a@ #0>100 ameres

?b@ 120>1+0 ameres

.C. 9oltage ?a@ 1#>20 8olts

?b@ 22>2+ 8olts

'rc 9oltage ?a@ 1=>1 8olts

?b@ 1#>21 8olts

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Module 2 Unit 10

Example ProcedureEP14

1. ,stablish the arc at the ri!ht>hand end of the Eoint.

2. 9old the torch so that the electrode ire is at ri!ht an!les to the sheets.

4. AdEust rate of tra8el to secure fusion ithout o8er>enetration.

Material 4 mm M* late

Pre3aration s5uare ed!e.

?lectrode 0. mm

Feed "ate 140>1+0 in./min.

Carbon io8ide 26>40 ft.J/hr.

Current #0>100 ameres

.C. 9oltage 1#>20 8olts

'rc 9oltage 1=>1 8olts

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Flat Position

Corner oint *3ra$ Transfer


1. ,stablish the arc on the tac3 eld at the ri!ht>hand end of the Eoint.

2. As soon as ool of molten metal is formed to full deth of Eoint>rearation

mo8e the !un ro!ressi8el' leftards.

4. Point the electrode at the root of the Eoint at an an!le of =6H>6H.

+. AdEust the rate of tra8el so that the deosit fills the Eoint.

6. )omlete the eld b' fusin! into the tac3 eld at the left>hand end of the

Eoint.

Visual Examination

A satisfactor' eld ill sho that the deosited metal has filled the Eoint ithout

ecessi8e meltin! aa' of the to ed!es of the fusion faces.

There should be si!ns of enetration to the root on the re8erse side of the Eoint ithout

burn>throu!h.

The abo8e also alies to ,P4 and ,P+.

Material 4/1K ?6.0 mm@ aluminium

allo'B 2 offB min. +L ?10.0 cm@

L ?20.0 cm@

Pre3aration s5uare ed!e

'sse!bl$ Tac3 eld both ends to !i8e

included an!le of #0HB no !a.

Place on bench ith Eoint>

rearation uer>most and

line of Eoint arallel ith front

of bench.

?lectrode 1/1K ?1. mm@

Feed "ate 220>2+0 in./min.

'rgon 46>+0 ft.J/hr.

Current 1#0>216 ameres

'rc 9oltage 2+ 8olts

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Module 2 Unit 10

Corner oint Pulse Transfer


Material 1+ s..!. ?2.0 mm@aluminium allo'B 2 offB

min. +L ?10.0 cm@ L

?16.0 cm@


'sse!bl$ as for ,P2


Feed "ate 0>#0 in./min.


Current 6>=6 ameres

Pea@ 9oltage 44>4+ 8olts

'rc 9oltage 1=>1 8olts

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Module 2 Unit 10

Close *Buare >utt oint *3ra$ Transfer


1. ,stablish the arc on the tac3 eld at the ri!ht>hand end of the Eoint.

2. hen fusion has been obtained to the full deth of the late commence the

leftards ro!ression.

4. The electrode should be ointed at an an!le of =6H>6H ithout ea8in!.

+. AdEust the rate of tra8el so that the deosited metal is built u Eust roud of the

late surface and burn>throu!h is a8oided.

Visual Examination

The eld face should be of e8en idthB free from undercut at the toes. The rofile should

be sli!htl' con8e.

There should be full enetration ith a sli!ht enetration bead shoin! on the re8erseside of the Eoint.

Material 4/1L ?6.0 mm@ aluminium

allo'B 2 offB min. +L ?10.0

cm@ L ?16.0 cm@


'sse!bl$ Tac3 eld ith three tac3sBno !a. The use of a

stainless steel !roo8ed

bac3in! bar is

recommended.


Feed "ate 2+0>2#0 in./min.


Current 200>246 ameres

'rc 9oltage 26>2 8olts

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3en *Buare >utt oint i3 Transfer



2. AdEust the rate of leftards tra8el to secure fusion of the saced ed!es of the

arent metal hile a8oidin! burn>throu!h.

Visual Examination

As for ,P=.

Material ,ither ?a@ 1 s..!. ?1.6

mm@ or ?b@ 4/1L ?6.0 mm@

mild steelB 2 offB min. +L

?10.0 cm@ L ?20.0 cm@

Pre3aration s5uare ed!e and 1/1L !a

'sse!bl$ Tac3 eld ith three tac3s

?lectrode ?a@ 1/42K ?0. mm@

?b@ 4/+K ?1.2 mm@

Feed "ate ?a@ 140>1+0 in./min.

?b@ 100>110 in./min.



?b@ 110>120 ameres


?b@ 21>22 8olts


?b@ 1#>20 8olts

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T oint *3ra$ Transfer


1. The electrode should be ainted directl' at the root of the Eoint and at an an!le

of =6H>6H.

2. A 8er' sli!ht forard and bac3ard recirocatin! motion of the eldin! !unill hel to smooth out the eld and !i8e !ood fusion at the toes.

Visual Examination

,amine the eld to chec3 an' oeratin! faults. (eeatB eldin! the other side of the

Eoint after ma3in! an' necessar' corrections to e5uiment settin!sB tra8el seed or

electrode an!le.

A satisfactor' eld should be e8enl' disosed in the EointB of uniform le! len!th and free

from undercut at the toes.

The abo8e also alies to ,P.

Figure 10 ) T oint ) *3ra$ Transfer

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Module 2 Unit 10

T oint i3 Transfer



2. As soon as fusion is established commence the leftards mo8ement.

4. AdEust the rate of tra8el to deosit a fillet eld ha8in! a le! len!th of about

4/42L ?2.6 mm@.

+. The electrode should be held ithout ea8in! at an an!le of 6H>=6H and

ainted directl' at the root.

Material ,ither ?a@ 1 s..!. ?1.6

mm@ or ?b@ 4/1L ?6.0 mm@

mild steelB 2 offB min. +L

?10.0 cm@ L ?20.0 cm@

Pre3aration s5uare ed!e and 1/1L !a

'sse!bl$ As for ,P6

?lectrode ?a@ 1/42K ?0. mm@

?b@ 4/+K ?1.2 mm@

Feed "ate ?a@ 140>1+0 in./min.

?b@ 100>110 in./min.



?b@ 110>120 ameres


?b@ 1#>20 8olts


?b@ 21>22 8olts

Unit 10 /


35/61


Module 2 Unit 10

*hielding (as

4!3ortant

CDL4lue ith blac@

band

'rgon)Carbon

io8ide >lue ith green

band

'LT?"ferrous metals.

'rgon)8$gen Mi8tures

The addition of small 5uantities of

o'!en to ar!on ma3es it more suitable

for use hen eldin! steels.

1. About 1 of o'!en is added hen

used for eldin! stainless steels and

u to 6 hen used for eldin!

mild steel b' sra'>transfer

techni5ue.

2. For ulse transfer techni5ueB ar!on

mied ith u to 2 of o'!en and

u to 6 of carbon dioide ith

small ercenta!es of other !asesB is

used for eldin! steels.

'rgon)Carbon io8ide Mi8tures

7i and sra' transfer eldin!

techni5ues are ossible ith a mied

shieldin! !as of 0 ar!on and 20

carbon dioide. The sra' transfer can

be further imro8ed b' the inclusion of

u to 2 of o'!en.

(as Mi8tures

These mitures are sulied in steel

c'linders. Alternati8el' searate !ases

ma' be mied in the roortions

re5uired b' the use of a !as mier.

Carbon io8ide

)arbon dioide is used as a shieldin! !as

for mild steel eldin!B and is cheaer

than ar!on>rich !ases. It is more suitable

for di transfer at lo currents but can

be used at hi!h currents for a form of

sra' or free fli!ht transfer. There are

to t'es of internal fittin!s to the

c'linders one hich allos !asB hich

mi!ht contain moistureB to be eEected on

oenin! the 8al8eB and the other called

the s'hon>t'e hich onl' allosli5uid carbon dioide to be eEected.

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Module 2 Unit 10

*afet$ Precautions +T.'.(.*. and M.'.(.*.,

The safet' recautions to be obser8ed ith these rocesses are similar for other metal arc

rocesses ith certain modifications.

In confined saces !as shieldsB if alloed to escaeB ma' dislace o'!en and causesuffocation. 7e!reasin! a!ents such as trichloroeth'lene and carbon tetrachloride

decomose around the arc to form oisonous comounds. $ocal fume etraction should

be used hen emlo'in! 8er' hi!h current densities or flu core electrode ireB and filter

breathin! ads to re8ent inhalin! oide dust. )orrect !rades of screen !lass should be

used as ultra 8iolet li!ht is !reater hen eldin! aluminium ith an ar!on shield

comared ith other rocesses. (emember to chal3 9%T on materials after eldin!B

eseciall' aluminium. Use li!ht !lo8es hen T.A.G.*. eldin! to a8oid burnin! throu!h

radiation and 9.F. burns beteen the fin!ers. Ade5uate rotecti8e clothin! should ala's

be orn.

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Module 2 Unit 10

Poer *ources

Transformer>rectifiers are normall' used for metal>arc !as shielded eldin!. A.).

e5uiment is suitable for eldin! ith !as shielded flu cored electrodes. Motor

!enerator oer sources of suitable desi!n ma' be used in certain circumstances.

Three forms of metal transfer across the arc are in common use. Poer sources are

a8ailable hich ma3e it ossible to select the aroriate circuit arran!ement for each

t'e of transfer.

7irect current usin! either a rectifier or !enerator is used in the M.A.G.*. eldin! s'stem

ith the olarit' of the electrode bein! ositi8e. The oer source characteristic is a

KflatK oer source as shon at Fi!ure 12for a constant otential machine.

Figure 12 ) Poer *ource

Modes of Metal Transfer

The mode of metal transfer from the ti of the electrode to late ma' be influenced b'

current densit'B t'e of arent metal and electrodeB !as shieldB etc. The to basic modes

are di and sra' transfer.

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Module 2 Unit 10

*3ra$ Transfer

For this t'e of transfer a oer source !i8in!

an outut of about +00 ameres ith an oen>

circuit 8olta!e ithin the ran!e 26>60 8olts

ma' be used.

ith hi!h current densit'B and articularl'

hen usin! an aluminium or aluminium allo'

electrode ireB the metal transfer is in the

form of tin' dros hen usin! ar!on

shieldin!.

*ra' transfer can be used for aluminium in

an' ositionB ith aroriate reduction in

eldin! current.

This mode of transfer can onl' be used

satisfactoril' on other metals hen eldin! inthe flat osition.

,8enB hen usin! the smallest diameter ireB

the minimum current is in the order of 10

ameres.

For eldin! in osition or for the eldin! of

thin materials di or ulsed transfer is used.

i3 Transfer

For this t'e of transfer a oer source !i8in!

an outut of about 200 ameres ith oen

circuit 8olta!e tain!s from 16>40 8olts is

aroriate. Inductance control must be

incororated. hen the arc len!th is short ?i.e.

arc 8olta!e is lo@ the end of the electrode

ire touches the eld ool and the current

rises.

If the rate at hich the current rises is

controlledB the end of the electrode is melted

off and flos into the eld ool. This is

3non as 7i Transfer and is onl' alicable

to materials ha8in! a relati8el' hi!h electrical

resistanceB e.!. steel.

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Module 2 Unit 10

Pulse Transfer

For this t'e of transfer the hi!h current ulses

ma' be obtained from a sin!le hase rectifier

connected to a rectifier oer source as used for

di transfer.

ith ulse transfer the eldin! current

alternates beteen hi!h and lo le8els. A hi!h

current densit' detaches drolets of metal and a

lo current densit' maintains the arc. ;' this

means a form of controlled sra' transfer is

obtained at lo current 8alues.

T'ical oeratin! ran!es are shon for *ra'B

7i and Pulse Transfer for 4/+K ?1.26 mm@ dia.

Mild steel ire.

Figure 1 ) *che!atic iagra!E Pulse)Transfer

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Module 2 Unit 10

T$3es of M.'.(.*. Transfer

There are se8eral t'es of torch but the' ma' be di8ided into the !as>cooled and ater>

cooled t'es. The dri8e ma' be b' electric motor ith the ire sool on the hand>held

!unB b' air motorB or siml' b' a ire>feed ush !un. A !as>cooled li!ht>dut' san>nec3

torch is shon in Fi!. 1#.6.

Figure 1/ ) Light)ut$ *an)


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Module 2 Unit 10

3erating the ?Bui3!ent

Controls

All e5uiment ill ha8e the folloin! controls:

1. olta!e control > !o8erns arc len!th.

2. ire feed control > !o8erns eldin! current.

,5uiment desi!ned secificall' for 7i Transfer eldin! ill ha8e an additional

control:

4. Inductance control. This !o8erns the rate of rise of current durin! short circuit and

therefore it controls the fre5uenc' of short>circuitin! and the eld rofile. It is

also used to re!ulate the amount of satter.

,5uiment desi!ned for Pulse Transfer ill ha8e additional controls:

+. Pulse hei!ht control. This re!ulates the maimum 8olta!e of each ulse.6. Pulse fre5uenc' control. This ma' be fitted on some oer sources.

Figure 1 -ire Feed Unit.

*'F?TD

o not touch electrode ire hen the current is sitched on.

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Module 2 Unit 10

(eneral 4nstructions

The folloin! !eneral instructionsB hich are not reeated in the tetB al' to metal>arc

!as shielded eldin!. Ala's:

1. )oml' ith the rescribed safet' recautions and fire re8ention

rocedure.

2. )hec3 that the return lead is firml' connected to bench and oer source.

4. )hec3 that all connections to ire feed and/or control unit are in !ood

order.

+. )hec3 that !as and ater hoses are not N3in3edC or otherise obstructed.

6. )hec3 that oer source is sitched on.

. )hec3 that the !as c'linder 8al8e is oen and hen usin! carbon dioide

from s'hon c'linder that the heater>8aoriser is sitched on.

=. )hec3 that the re!ulator ressure is set to 40 lb./in.O.

. )hec3 that correct si-e contact tube/ti is fitted to !un/torch.

#. )hec3 that correct si-e !as no--le is fitted.

10. )hec3 that the electrode ire etension and the relati8e ositions of the

eit ends of the contact tube and !as no--le are correct.

11. )hec3 that the Nburn>offC control ?if fitted@ is adEusted so that the electrode

ire etension is correct after brea3in! the arc.

12. )hec3 that the !as flo is correctl' set ?hile ur!in! the air from the

fleible tube assembl'@.

14. )hec3 that the ater sul' is turned on if usin! a ater>cooled !un.

In addition to the !eneral instructions !i8en abo8e others al' deendin! uon the t'e

of e5uiment and the eldin! techni5ue to be emlo'ed.

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Module 2 Unit 10

*3ra$ Transfer

1. hen fittedB the inductance control should be set at minimum.

2. *et oen circuit 8olta!e about 6 > abo8e the recommended oeratin! 8olta!e.

4. *elect the correct diameter and t'e of ire and set the ire feed seed control to

the recommended 8alue.

+. hen eldin! commences adEust the ire feed seed control to !i8e correct

currentB i.e. correct heat inut.

6. AdEust 8olta!e to correct 8alue as indicated the correct eld rofile:

arro eldB hi!h ecess metal > raise 8olta!e.

ideB flat eld > loer 8olta!e.

?arnin!: on some oer sources the current must be sitched off before

adEustin! 8olta!e@.

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'da3table 'ddition for M4( -elding

*elf)*hielded Flu8 Cored -ire

*elf>shielded flu cored ires are used ithout an additional !as shield and can be

usefull' emlo'ed in outdoor or other on site drau!ht' situations here a c'linder>

sulied !as shield ould be difficult to establish.

The core of these ires contains odered metal to!ether ith !as>formin! comounds

and deoidisers and cleaners. The !as shield formed rotects the molten metal throu!h

the arc and sla!>formin! comounds form a sla! o8er the metal durin! coolin!B

rotectin! it durin! solidification. To hel re8ent absortion of nitro!en from the

atmoshere b' the eld oolB additions of elements are made to the flu and electrode

ire to effecti8el' reduce the soluble nitro!en.

This rocess can be used semi> or full' automaticall' and is articularl' useful for on>site

or3.

*$nergetic -elding

*ets are no also a8ailable ith ro!rammable oer sources. Usin! 3non 5uantities

such as ameresB secondsB metres er minute feedB the eldin! ro!ram is di8ided into a

chosen number of sections and the eldin! arameters as indicated re8iousl' are used to

ro!ram the comuter hich controls the eldin! source. The ro!ram can be stored in

the comuter memor' of u to sa' 60 numbered eldin! ro!rams or it can be stored on

a searate ma!netic data card for eternal stora!e or use on another unit. ;' ressin! the

correct numbers on the 3e'board of the unit an' ro!rams can be selected and the chosenro!ram be!insB controllin! eldin! currentB shieldin! and bac3in! !asB !as re>floB

ire feed seedB arc len!thB ulsed eldin! current and sloe controlB etc. All safet'

controls are fitted and chan!es in the eldin! ro!ram can be made ithout affectin!

other data.

M4( -elding of 'lu!iniu!

hile most eldin! e5uiment is sulied rimaril' for the eldin! of ferrous metalsB

some can also be used for the eldin! of aluminium. ,5uiment ith lo amera!es is

reall' not suitableB althou!h it can be used for short eriods of eldin!. The lar!er>amera!e machines ?10 A and o8er@ are better e5uied to handle aluminium. The ire

si-es used are 1.0 mm and 1.2 mm for the lar!er machines for eldin! thic3er

aluminium. The torch contact ti must be of the correct si-e for the ire to be used. hen

eldin! ith aluminium ire a Teflon liner must be used in order to re8ent the

aluminium from stic3in! and dama!e occurrin! to the ire itself. AlsoB ure ar!on must

be used as the shieldin! !as oin! to its total inert characteristicsB and not ar!on mies or

carbon dioide.

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Module 2 Unit 10

(ases for M4(5M'( -elding

)arbonB carbon>man!anese and hi!h stren!th lo allo' steels

)%2is used to eld these steels. The choice deends on the comosition of the steel and

the oeratin! re5uirements.

General !uidelines:

Penetration increases ith the addition of helium. Penetration also increases

ith hi!her carbon dioide contents.

)arbon dioide can be useful for fillet elds in thic3late.

*atter increases ith increase in carbon dioide content.

*teel hich contains chromium needs secial consideration.

There is a dan!er that carbon dioide in the !as ill react ith the chromium to

form a carbide.

This renders the chromium in the steel less effecti8e.

The amount of carbon dioide hich can be tolerated deends on the chromium

content.

Table ) T$3ical Conditions for M4(5M'( -elding *heet

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Module 2 Unit 10

Table 6 ) (ases for M4(5M'( -elding

Unit 10 /&


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Module 2 Unit 10

(as *hielded Metal 'rc -elding

Metal 4nert (as +M4(,E Metal 'ctiAe (as +M'(, including C2and

Mi8ed (as Processes

The MIG semi>automatic and automatic rocesses are increasin! in use and are

dislacin! some of the more traditional o'>acet'lene and MMA uses.

For reair or3 on thin sheet as in the motor tradeB semi>automatic MIG usin! ar!on>)02

mitures has dislaced the traditional o'>acet'lene methods because of the reduced heat

inut and narroer 9AB thus reducin! distortion. For lar!er fabrication or3B

mechanical handlin! e5uiment ith automatic MIG eldin! leads has re8olutionised the

fabrication industr'B hile the ad8ent or robotsB hich are ro!ram controlled and use a

full' automated MIG eldin! head ith self>contained ire feedB ma3e less demands on

the s3illed elder.

Ar!on could not be used alone as a shieldin! !as for mildB lo>allo' and stainless steel

because of arc instabilit' but no sohisticated !as mitures of ar!onB heliumB )%2and

o'!en ha8e !reatl' increased the use of the rocess.

The rocess has 8er' man' alications and should be studied b' the student as one of

the maEor rocesses of the future.

It is con8enient to considerB under this headin!B those alications hich in8ol8e

shieldin! the arc ith ar!onB helium and carbon dioide ?)02@ and mitures of ar!on ith

o'!en and/or )%2and heliumB since the oer source and e5uiment are essentiall'

similar ecet for the !as sul'. These rocesses fall ithin the headin! MIG/MAG.

The rocess is suitable for eldin! aluminiumB ma!nesium allo'sB lain and lo>allo'

steelsB stainless and heat>resistant steelsB coer and bron-eB the 8ariation bein! filler ire

and t'e of !as shieldin! the arc.

The consumable electrode of bare ire is carried on a sool and is fed to a manuall'

oerated or full' automatic !un throu!h an outer fleible cable b' motor>dri8en rollers of

an adEustable seedB and rate of burn>off of the electrode ire must be balanced b' the

rate of ire feed. ire feed rate determines the current used.

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Module 2 Unit 10

Figure 16 ) Co!3onents of (as *hielded Metal 'rc -elding Process

Unit 10 1


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Module 2 Unit 10

M4(5M'( -elding

)ontrol of the an!le beteen the !un and the surface of the sheet is critical in MIG/MAG

eldin!.

Figure 17 ) M4(5M'( -elding

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Module 2 Unit 10

Pi3e and Tube oints

There are three main t'es of elded Eoint used in ieor3.

butt

branch

flan!e

Figure 1% ) Pi3e and Tube oints

If ossibleB durin! eldin! the ie should be rotated so that the eld is made in thehori-ontal osition > use sra'B di or ulse transfer for MIG/ MAG. If the eld must be

made in a fied osition and chan!es from flat to 8ertical to o8erhead as the eld

ro!resses round the Eoint > use di or ulse transfer for MIG/MAG.

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Module 2 Unit 10

*elf 'ssess!ent

Questions on ;ac3!round otes " Module 2.Unit 10

1. hat does the abbre8iation MIG / MAG eldin! stand forR

2. ;riefl' elain Pulse and 7i Transfer in relation to MIG / MAG eldin!.

. ame to Gases suitable for MIG eldin!.

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Module 2 Unit 10

/. $ist three *afet' Precautions hen MIG eldin!.

. In a coule of lines briefl' elain the MIG eldin! of Aluminium.

Unit 10 6


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Module 2 Unit 10

.

*uitable (ases for M4( -elding:

4nert (as:

'rgon)8$gen

Mi8tures:

'rgon)Carbon io8ide

Mi8tures:

(as !i8tures:

Carbon io8ide:

Ar!on of eldin! !rade urit' is used as the

shieldin! !as hen eldin! non>ferrous metals.

The addition of small 5uantities of %'!en to Ar!on

ma3e it more suitable for use hen eldin! steels.

7i and sra' transfer eldin! techni5ues are ossible

ith a mied shieldin! !as of 0 ar!on and 20 carbon

dioide. The sra' transfer can be further imro8ed b' the

inclusion of u to 2 of o'!en.

These mitures are sulied in steel c'linders.

Alternati8el' searate !ases ma' be mied in the

roortions re5uired b' the use of a !as mier.

)arbon dioide is used as a shieldin! !as for mild steel

eldin!B and is cheaer than ar!on>rich !ases. It is more

suitable for di transfer at lo currents but can be used at

hi!h currents for a form of sra' or Nfree fli!htC transfer.

There are to t'es of internal fittin!s to the c'linders

one hich allos !asB hich mi!ht contain moistureB to be

eEected on oenin! the 8al8eB and the other called the

sihon>t'e hich onl' allos li5uid carbon dioide.

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Module 2 Unit 10

/.

*afet$ Precautions:

Use effecti8e rotecti8e e5uiment and necessar' rotecti8e

clothin!.

9a8e full control of the torch/!un and hold it stead'. )oncentrate

on the eldin! oeration.

*uort the fleible hose assembl' so that dra! on the torch/!un

is reduced.

9old the torch/!un ith sufficient !ri at the oint of balance

to !i8e controlB otherise it ill cause muscle fati!ue.

arn an' b'standers hen about to stri3e the arc.

,nsure that an' ortable screens re5uired are in osition.

&ee the eldin! screen in front of the e'es until the arc is bro3en.

Follo closin! don rocedure at the end of the or3 eriod or

hen there is a lon! interrution.

Unit 10 &


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Module 2 Unit 10

.

M4( -elding of 'lu!iniu!:

hile most eldin! e5uiment is sulied rimaril' for eldin!

of ferrous metalsB some can also be used for the eldin! of aluminium.

,5uiment ith lo amera!es is not reall' suitable B althou!h it can

be used for short eriods of eldin!. The lar!er amera!e machines

?10 A and o8er@ are better e5uied to handle aluminium. The ire

si-es used are 1.0mm and 1.2mm for the lar!er machines for eldin!

thic3er aluminium. The torch contact ti must be of the correct si-e

for the ire to be used. hen eldin! ith aluminium ire a Teflon

liner must be used in order to re8ent the aluminium stic3in! and

dama!e occurrin! to the ire itself. AlsoB ure ar!on must be used as the

shieldin! !as oin! to its total inert characteristicsB and not ar!on mies

or carbon dioide.

Unit 10 60


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Module 2 Unit 10

4nde8

A

Adatable Addition for MIG eldin!B +6

*elf>*hielded Flu )ored ireB +6*'ner!etic eldin!B +6

Ancillar' ,5uiment

,lectrode ire 7ri8e UnitB 2+

,lectrode ire (eel Assembl'B 2+

C

)%2 eldin! of Mild *teelB 1

)osts and TrendsB ++

F

Flat Position

)lose *5uare ;utt *ra' TransferB 40

)orner Pulse TransferB 2#

)orner *ra' TransferB 2

%en *5uare ;utt 7i TransferB 41

T 7i TransferB 44T *ra' TransferB 42

G

Gas *hielded Metal Arc eldin!B +Metal Inert Gas ?MIG@B Metal Acti8e Gas ?MAG@

includin! )%2 and Mied Gas ProcessesB +

GasesB 1,conomic )onsiderationsB 1=

Gases for MIG/MAG eldin!B +

H

9ori-ontal/ertical Position

%en *5uare ;utt 7i TransferB 2

%en *5uare ;utt Pulse TransferB 26

M

Metal Arc Gas>*hielded ?MAG*@ eldin!B 10

IntroductionB 10

Metal Transfer in MAG* eldin!B 14The ProcessB 11

Metal Transfer FormsB 1#

Tac3 eldB 22

Metal Transfer in MAG* eldin!

)ontact Tis and o--lesB 16

,lectrode ire *i-eB 16eldin! *eedB 16

ire ,tensionB 16

Metal>Arc Gas *hielded eldin!B 24Ancillar' ,5uimentB 2+

Flat PositionB 2

9ori-ontal/ertical PositionB 26

Modes of Metal TransferB 4=

%eratin! the ,5uimentB +1

Poer *ourcesB 4=*afet' PrecautionsB 46

*hieldin! GasB 4+

T'es of M.A.G.*. TransferB +0

MIG eldin! of AluminiumB +6

MIG/MAG eldin!B 60

Modes of Metal Transfer7i TransferB 4

Pulse TransferB 4#

*ra' TransferB 4

O

%eratin! the ,5uiment

)ontrolsB +1

General InstructionsB +2

*ra' TransferB +4

P

Pie and Tube

m.i.g-m.a.g. welding m2 u10

Documents