GTAW and Power Sources

8/16/2019 GTAW and Power Sources

1/18

GTAW Welding


2/18

GTAW

•Also referred to as “TIG” Welding

•Uses a shield gas, a non-consumable tungsten

electrode and a hand fed filler rod

•Excellent for welding thin metals, ielinewelding and exotic metals

•!ighl" s#illed labor needed for this rocess


3/18

Gas Tungsten-Arc

WeldingThe gas tungsten-arc welding process, formerly knownas TIG (for tungsten inert gas) welding.

Equipment for gas tungsten-arc weldingoperations. Source !merican "elding#ociety.


4/18

Comparison of Laser-Beam and

Tungsten-Arc Welding$igure %&.'omparison of thesi*e of weld +eads in(a) electron-+eam orlaser-+eam weldingto that in (+)conentional(tungsten-arc)

welding. Source!merican "elding#ociety, Welding Handbook (th ed.),''.


5/18

General Characteristics of

Fusion Welding ProcessesTABLE 27.1

Joining process Operation Advantage

Skill level

required

Welding

position

Current

type Distortion*

Cost of

equipment

Shielded metal-arc Manual Portable and

flexible

High All ac, dc 1 to 2 Low

Submerged arc Automatic High

deposition

Low to

medium

Flat and

horizontal

ac, dc 1 to 2 Medium

Gas metal-arc Semiautomatic

or automatic

Most metals Low to

high

All dc 2 to 3 Medium to

high

Gas tungsten-arc Manual or

automatic

Most metals Low to

high

All ac, dc 2 to 3 Medium

Flux-cored arc Semiautomatic

or automatic

High

deposition

Low to

high

All dc 1 to 3 Medium

Oxyfuel Manual Portable and

flexible

High All — 2 to 4 Low

Electron-beam,

Laser-beam

Semiautomatic

or automatic

Most metals Medium

to high

All — 3 to 5 High

* 1, highest; 5, lowest.


6/18


7/18


8/18

The GTAW (TIG) Process

Temperatures of up to /0,1112 $3 ',4%2 .

The torch contri+utes only heat to the work piece.

Advantagesweld more kinds of metals and metal alloys

stainless steel, nickel alloys such as 5onel and Inconel,

titanium, aluminum, magnesium, copper, +rass, +ron*e, andeen gold.

dissimilar metals


9/18

Concentrated Arc pin point control of heat input to the work piece resulting in a

narrow heat-affected *one.

adantage when welding metals with high heat conductiity

such as aluminum and copper.

No Slag- welder6s ision of the molten weld pool.

The finished weld will not hae slag to remoe +etween

passes.


10/18

No Sparks or Spatterno transfer of metal across the arc.

no sparks produced if the material +eing welded is free of

contaminants.

GTAW Disadvantages

low filler metal deposition rate.hand-eye coordination necessaryThe arc +righter than those produced +y #5!" and G5!".


11/18


12/18


13/18

Polarity

Direct Crrent !lectrode Negative (DC!N)

practically all metals.

appro7imately &18 of the heat will +e concentrated into the

workpiece.

deep penetration

The electrode receies a smaller portion of the heat energy than

when using !lternating urrent (!) or 9irect urrent Electrode

:ositie polarity (9E:).

This accounts for the higher current carrying capacity of a

gien si*e tungsten electrode with 9E; than with 9E: or !.


14/18


15/18

Direct Crrent !lectrode Positive (DC!P)"

!ppro7imately &18 of the heat will +e concentrated at the

positie side of the arc.

electrode receies the greatest amount of heat and +ecomes ery

hot, the electrode must +e ery large een when low amperages are

used, to preent oerheating and possi+le melting.

shallow penetration.

disadantage - magnetic forces the arc will sometimes wander

from side to side when making a fillet weld when two pieces ofmetal are at a close angle to one another.


16/18

DC!P

cleaning done continuously while the welding

o7ide can +e remoed +y the welding arc

positiely charged gas ions strike the work piece with sufficient

force to +reak up and chip away the +rittle aluminum o7ide


17/18

Why G#AW ses $ostly DC!P

sta+le arc, smooth metal transfer, relatiely low spatter,

good weld +ead characteristics and deep penetration for a

wide range of welding currents.

9E;

The molten droplet si*e tends to increase and the droplet

transfer +ecomes irregular, there+y increasing large grainspatter.


18/18

S#AW is the $ost versatile %elding process in ter$s o& polarity

The $a'ority o& covered electrodes se either AC or DC!P

So$e electrodes" speci&ically !*+, (.-/)" !*+0 (.-+1) and !1*/2(3!4D!-

2,5) o&&er good per&or$ance %ith AC" DC!P or DC!N

In contrast" high celllose type electrodes sch as !*+* (64.!-*+*)" !1*+*-P+

(64.!-1*+*S)" and !7*+*-P+ (64.!-7*+*S) &or pipe %elding are designed &or

se %ith DC!P only &or s$oother droplet trans&er

8o% car9on type Cr-#o electrodes sch as !1*+:-./8 (C#.-0:) and !7*+:-.,8

(C#.-+*:) are also designed &or se %ith DC!P only" &or 9etter per&or$ance

So$e speci&ic electrodes sch as 8.-7*;8 &or high strength steels and N.-+S &or

lo% te$peratre steels are reco$$ended to se AC only in order to garantee

strict re

GTAW and Power Sources

Documents

Transcript of GTAW and Power Sources