Arc Welding Process

Arc Welding Process

1. Unit: 3 Lecture: 35

. Dr. Jayanta Kr. Mahato
Welding Process: Arc Associate Professor

Welding Process A
Dept. Shobhit University, Meerut

2. Common Welding Joints

BUTT JOINT LAP JOINT T-JOINT

Lo)

T- joint Lap joint Corner joint

& Dr. Jayanta Kr. Mahato, Asst. Prof., Mechanical Engineering

3. Common Welding Joints

IN

KK

4. Common Welding Symbols
SS

TYPE OF WELD
GROOVE

beso | river
A |B lv

BASIC ARC AND GAS-WELD SYMBOLS

sLoT

ral x x Ï | |

BASIC RESISTANCE - WELD SYMBOLS

— E Ce ay

BEAD WELD FILLET WELD SLOT WELD SQUARE GROOVE
BEVEL GROOVE V-GROOVE WELO U-CROOVE MELO J-GROOVE WELD

ds

5. Butt Joint Edge Proportion & Weld Type

E E EG

Single Square Groove Single Bevel Groove Double Bevel Groove

6. Corner Joint Enga Proportion €. Weld Type

$3

=i il:

7. Arc Welding Process: What is an Electric Arc?

> An electric arc is a discharge of electric current across a

gap in a circuit

> It is sustained by an ionized column of gas (plasma)

through which the current flows

> To initiate the arc in AW, electrode is brought into contact
with work and then quickly separated from it by a short

distance

CURRENT
SLIDE
ne pe

ELECTRODE
HOLDER

CURRENT
SELECTOR

WORK RETURN /
GROUND LEAD GROUND

8. Flux

A substance that prevents formation of oxides and other
contaminants in welding, or dissolves them and

facilitates removal
Provides protective atmosphere for welding

Stabilizes arc
Reduces spattering

Q Flux Application Methods
Pouring granular flux onto welding operation
Stick electrode coated with flux material that melts during

welding to cover operation
Tubular electrodes in which flux is contained in the core and

released as electrode is consumed

&

9. Arc Shielding

1 At high temperatures in AW, metals are chemically reactive to
oxygen, nitrogen, and hydrogen in air
Mechanical properties of joint can be degraded by these
reactions

To protect operation, arc must be shielded from
surrounding air in AW processes

Arc shielding is accomplished by:
Shielding gases, e.g., argon, helium, CO,
Flux

Consumable electrode

Flux covering Bee
core wire

Evolved gas shield
Parent

‘Weld metal Slag material

re
Weld pool

10. Power Source in Arc Welding
| U SEE
ı Direct current (DC) vs. Alternating current (AC)
1 AC machines less expensive to purchase and operate, but
generally restricted to ferrous metals
1 DC equipment can be used on all metals and is
generally noted for better arc control

‘CURRENT

SLIDE
LIFTING re
HANDLE e ‘OR

Er

ELECTRODE
HOLDER

CURRENT
SELECTOR

WORK RETURN /
GROUND LEAD GROUND

‘CLAMP.

11. Arc Welding Equipment and Accessories

>In AC arc welding a step down BEER
transformer is used which
transforms AC supply from 440
Volts AC to 80-100 Volts AC.

> Well insulated electrode holder

>Wire cables and cable
connectors pr"

>Welding helmet and hand screen
or shield

Safety Goggles
Weld chipping hammer “A welding Equipments
Earthling Clamp Lal — = ©
Hand Gloves o AO
Apron and Sleeves

=,
Wire brush, chipping hammer ~~ ia 9

Electrode holder
(rand piece)

12. Arc Welding Process
o se

CURRENT

SLIDE
LIFTING
pee ff mae

150K

ELECTRODE
HOLDER

CURRENT
SELECTOR

WORK RETURN /
GROUND LEAD GROUND
Electrode holder

Electrode (consumable

or nonconsumable) Electrode cable

Welding machine
d Direction of travel «— |

Aro

Work

Molten weld metal Clamp Work cable

13. Arc Welding Process

>In this method, metal pieces to be
welded are heated locally to the
melting temperature by creating an
electric arc and then allowed to
solidify to form welded joint.
Additional metal for filling the weld
is provided by core wire of electrode
(As in metal arc welding) or by filler
rod (As in case of carbon arc
welding).

>For creating an arc low voltage
high ampere AC or DC current is
used.

>Filler material is used to supply
extra molten metal to fill the gap
between joints. Filler material has
similar composition and lower
melting point then the base material.

14. Arc Welding Process

>Flux is some time used to remove
the oxides formed during welding 3
process by combining with the
impurities and forming slag, which
floats on the molten metal. Molten
slag covers the weld and protects it
from oxidation.
> Polarity in DC Arc Welding: a
>The temperature of the arc is “ens
3700°C to 4000°C. In DC welding two
types of polarities are used.

> Straight Polarity: welding

electrode is kept negative and

work piece is kept positive.

> Reverse Polarity: In this work

piece is negative and electrode

is positive.

Consumable electrode

Flux covering i
Core wire

eee Parent
Weldpoo Materia

15. Manual Arc Welding and Arc Time
RI
1 Problems with manual welding:
1 Weld joint quality
1 Productivity
ı Arc Time = (time arc is on) divided by (hours worked)
1 Also called “arc-on time”
1 Manual welding arc time = 20%
1 Machine welding arc time ~ 50%

ELECTRODE
HOLDER

cuarenr
SELECTOR

&

16. AW Electrode
EEE

1 Consumable — consumed during welding process
Source of filler metal in arc welding
1 Nonconsumable — not consumed during welding

process
Filler metal must be added separately if it is added

Consumable Electrodes

1 Forms of consumable electrodes

Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch

or less in diameter and must be changed frequently

Weld wire can be continuously fed from spools with long

lengths of wire, avoiding frequent interruptions

1 In both rod and wire forms, electrode is consumed by
the arc and added to weld joint as filler metal

17. Consumable Electrode AW Processes

[U

ı Shielded Metal Arc Welding
ı Gas Metal Arc Welding
ı Flux-Cored Arc Welding

Covered electrode

— Flux coating

Direction
oe Core wire

r- Globules of molten
/ metal and slag

Solidified slag—,

1 Electrogas Welding

Weld metal

1 Submerged Arc Welding

Solid wire electrode
Current conductor

Flux cored are welding
(FCAW)

18. Nonconsumable Electrodes
a

ı Made of tungsten which resists melting

ı Gradually depleted during welding (vaporization is
principal mechanism)

ı Any filler metal must be supplied by a separate wire
fed into weld pool

Nonconsumable Electrodes AW Processes

1 Gas Tungsten Arc Welding

Shielding gas
1 Plasma Arc Welding

Contact tube

Tungsten electrode
(nonconsumable)

1 Carbon Arc Welding SSSR “FR

1 Stud Welding

(optional) Shielding gas

19. Advantages of Arc Welding Process

>Suitable for variety

of application and positions
> High metal deposition rate.
>Less training required for
welders and less
needed. supervision
>Equipment are easy to use and § orto rie
are less costly.
>Equipment are portable and can
be used in confined places.
>Auxiliary gas shield is not
required.
>Suitable for most commonly
used metals and alloys.

Mains supply

20. Disadvantages of Arc Welding Process

L

>Incorrect welding may §
result into low weld toughness

>Lack of fusion of metal if
weld parameters are incorrect

>Slag is to be removed after

every pass in multipass
welding.

21. Different Arc Welding Processes
RES

Process Known |Electrodes| Shielding | Operator | Popularity
as skill
required

Shielded SMAW |Rigid metal |Stick Low Diminishing
metal arc or stick coatings
welding
Gas metal arc |GMAW {Solid wire [CO,gas [Low Growing
welding or MIG
Flux core arc |FCAW {Hollow wire |Core Low Growing
welding or MIG materials
Gas tungsten |GTAW [Tungsten [Argon gas [High Steady
arc welding or TIG
Submerged |SAW Solid wire |Argon gas |High Steady
arc welding

22. Shielded Metal Arc Welding (SMAW)

sas A

Uses a consumable electrode consisting of a filler metal
rod coated with chemicals that provide flux and
shielding

Sometimes called "stick welding"

Power supply, connecting cables, and electrode holder.
Composition of filler metal usually close to base metal

| Coating: powdered cellulose mixed with oxides and
carbonates, and held together by a silicate binder

Welding stick is clamped in electrode holder connected to
power source

| Disadvantages of stick welding:
| Sticks must be periodically changed
| High current levels may melt coating prematurely

23. Shielded Metal Arc Welding (SMAW)

| =

Consumable electrode

Direction of travel

+. Electrode coating

Protective gas Slag
from electrode | fo
coating D AEPNEAARNSS

Solidified
weld metal

Base metal Molten weld metal

24. SMAW Applications

|
ı Used for steels, stainless steels, cast irons, and certain
nonferrous alloys

1 Not used or rarely used for aluminum and its alloys, copper

alloys, and titanium

Consumable electrode

Direction of travel

- Electrode coating
Protective gas

Sla
from electrode "E 9

coating } PONDS
Solidified

weld metal

&

25. Gas Metal Arc Welding (GMAW)

Uses a consumable bare metal wire as electrode with shielding
by flooding arc with a gas

| Wire is fed continuously and automatically from a spool through
the welding gun

I Shielding gases include argon and helium for aluminum
welding, and CO, for steel welding

Bare electrode wire plus shielding gases eliminate slag on weld
bead

| No need for manual grinding and cleaning of slag

short-circuit material transfor

Feed from spool

fille wire

\ 7 Shielding gas

Direction of travel
—_—

‘lobular material transfer

Solidified weld metal

ER parent 7 a
iy material shielding gas coverage
a Molten weld metal

26. GMAW Advantages over SMAW
ı Better arc time because of continuous wire electrode
1 Sticks must be periodically changed in SMAW
1 Better use of electrode filler metal than SMAW

1 End of stick cannot be used in SMAW
1 Higher deposition rates
1 Eliminates problem of slag removal
ı Can be readily automated

Feed from spool

\ NN Shielding gas

Electrode wire ———+|

Direction of travel
e
Nozzle ———+

Shielding gas

Solidified weld metal

Base metal Molten weld metal

27. Flux-Cored Arc Welding (FCAW)
RE
Adaptation of shielded metal arc welding, to overcome
limitations stick electrodes - two versions
1 Self-shielded FCAW - core includes compounds that produce shielding
gases
1 Gas-shielded FCAW - uses externally applied
shielding gases
ı Electrode is a continuous consumable tubing (in coils) containing
flux and other ingredients (e.g., alloying elements) in its core

Presence or absence of Freed fromepont
externally supplied
shielding gas Tubular electrode wire

oT . Flux core

distinguishes: (1) self- me
shielded - core provides
a À . . Shielding gas (optional)
ingredients for shielding, dee
(2) gas-shielded - uses
external shielding gases

&

Shielding gas

Nozzle (optional)
Direction of travel
<<

Solidified weld metal

Base metal Molten weld metal

28. Electrogas Welding (EGW)

Uses a continuous consumable electrode, flux-cored wire or bare
wire with externally supplied shielding gases, and molding
shoes to contain molten metal

ı When flux-cored electrode wire is used and no external gases are
supplied, then special case of self-shielded FCAW

ı When a bare electrode wire used with shielding gases from
external source, then special case of GMAW

Electrogas welding using flux-cored electrode wire: (a) front view
with molding shoe removed for clarity, and (b) side view showing
molding shoes on both sides

Flux-cored
electrode wire feed

Moving welding Molding shoe
head (upward) 7 (both sides)

> + Cooling water in
Base

pat Molten slag

Molten weld metal

Solidified weld metal ——— io

fa) (b)

29. Submerged Arc Welding (SAW)
RE
Uses a continuous, consumable bare wire electrode, with

arc shielding by a cover of granular flux
ı Electrode wire is fed automatically from a coil
1 Flux introduced into joint slightly ahead of arc by
gravity from a hopper
1 Completely submerges operation, preventing sparks,
spatter, and radiation

Consumable
electrode | Vacuum system for

from hopper

Granular flux
recovery of granular flux

— : Blanket of
Direction of travel granular flux
—

Slag (solidified flux)
Solidified weld metal

Molten weld metal

30. SAW Applications and Products

1 Steel fabrication of structural shapes (e.g., l-beams)

1 Seams for large diameter pipes, tanks, and pressure vessels
1 Welded components for heavy machinery

1 Most steels (except hi C steel)

1 Not good for nonferrous metals

Consumable
electrode Vacuum system for
recovery of granular flux

Granular flux
from |

Blanket of PS
granular flux

a, (solidified flux)

Molten flux Molten weld metal

31. Nonconsumable Electrode Processes

1 Gas Tungsten Arc Welding
1 Plasma Arc Welding

1 Carbon Arc Welding

1 Stud Welding

1)

32. Gas Tungsten Arc Welding (GTAW)
aa
Uses a nonconsumable tungsten electrode and an inert gas for arc
shielding
[| Melting point of tungsten = 3410BC (6170RF)
| A.k.a. Tungsten Inert Gas (TIG) welding
{| In Europe, called "WIG welding"
| Used with or without a filler metal
| When filler metal used, it is added to weld pool from separate rod

or wire
[ Applications: aluminum and stainless steel mostly
T
Pra] Direction of GTAW head
Argon or helium a Power
shielding gaa | Lls Shielding gas
Welding Contact Contact tube
direction tube Filler rod:
.— Power da Tungsten electrode
source| + Ñ (nonconsumable)
Fils Z Shlelding gas Electrical are E weld bead
rod € Arc
\
Copper shoe- +
Base metal Weldpool Weld deposit (optional) Sang gas

33. Advantages and Disadvantages of GTAW
Advantages: |

1 High quality welds for suitable applications

1 No spatter because no filler metal through arc

1 Little or no post-weld cleaning because no flux
Disadvantages:

1 Generally slower and more cosil

AW processes

Shielding gas
Contact tube

Tungsten electrode
{nonconsumable)

(optional) Shielding gas

34. Plasma Arc Welding (PAW)

Special form of GTAW in which a constricted plasma arc is
directed at weld area

1 Tungsten electrode is contained in a nozzle that focuses a high
velocity stream of inert gas (argon) into arc region to form a high
velocity, intensely hot plasma arc stream

1 Temperatures in PAW reach 28,000°C (50,000°F), due to
constriction of arc, producing a plasma jet of small diameter and

very high energy density
J Plasma gas

‘a Shielding gas

Tungsten electrode ————»

Direction of travel WW
.-—

Plasma stream

Solidified weld metal
Base metal

Molten weld metal

35. Advantages and Disadvantages of PAW
RR
Advantages:
1 Good arc stability and excellent weld quality
1 Better penetration control than other AW processes
1 High travel speeds
1 Can be used to weld almost any metals
Disadvantages:
1 High equipment cost
1 Larger torch size than other AW processes
1 Tends to restrict access in some joints

Plasma gas

Mm) a Shielding gas

Tungsten electrode

Direction of travel
aa ES,

Plasma stream

Base metal

&

Molten weld metal

36. ANY QUERY

“e
2