WELDING
By hammering nuggets of gold or silver into rods,
forming the rods into circles or segments of a circle,and then
forging the ends together to form a continuous ring. This
earliest welding process is called forge welding.
Temporary joint was first –rivetted joint which is weight increased
Welding is permanent joint needed
in second world war
It is a process in which localized permanent joint can be produced by
with or w/out application 0f heat, or pressure.
ADVANTAGES
1. Permanent joint……..
2. Strength……….
3. Any position………….
4. Similar/Dissimilar……
.As we reqd
.We get exact mech strength of raw material in weld part also
.We can build in any shape by weld
.Same material also with other material
LIMITATIONS
1.
2.
3.
4.
Setup cost-….. Machine cost
Technician- ………
skill required
HAZ---------Mech property can be changed
Cracks………….
Defects To be avoided by taking preventive measures
WELDING………CLASSIFICATION……………
A
. . .SOLID STATE……Diffusion,U/Sonic,Forge,Friction,Explosive
B. LIQUID STATE……Based on heat production, There are three types
1.ARC……MMAW,Fcaw,SAW,Shielded Gas (TIG,MIG,PAW)
2. Resistance……………...Spot, Seam, Projection welds
3. Chemical Reaction………Gas welding, Thermit weld
C. SOLID/LIQUID STATE…………………….Soldering, Brazing.
Here Base metal is solid and filler metal is fused into liquid state
ARC welding
Welding circuit
 Open Circuit Voltage ---------60v to 110v
Always current is zero
 Closed Circuit Voltage -------18v to 55v (or) Arc Voltage
(Short circuit voltage)
Always current is as per setting
Voltage is increased by increasing the Arc length, Max 55v by
increasing the arc length (La=0.5d to 1.5d) where d is the dia of
electrode.
Arc is cutoff, if increased beyond 1.5d distance .
HOW THE ARC IS PRODUCED:
 Due to high potential Difference Electrons in cathode are pushed
to transfer towards bottom of electrode when electrode is –ve
charged.
 These Electrons break the air molecules and air decomposes into
+ve ions and –ve ions.ie called plasma stage(good conductor of
electricity).charged particles in air.To continue this arc arc length is
maintained.
 +ve ions melt faster than Electrons hence 2/3 of heat is at +ve side.
 As ac current is passed in circuit (DCSP+DCRP alternatively)
uniform heat generation is obtained.
METHOD OF STRIKING ARC:
TYPES OF POLARITIES IN DC MACHINE
Cathode is Negative charged having electrons of small mass hence getting 1/3 of heat
Anode is positive charge having positive ions of high mass hence getting 2/3 of heat
If we use consumable electrode we select DCRP (DCEP) for Non-Consumable electrode we select
DCSP (DCEN).
DCEN
DCEP
For high thickness of workpiece
For less thickness of workpiece
For high melting point material
For low3 melting point material
Metal deposition rate is less
Metal deposition rate is high—Kg/Hr
For Low speed application
For high speed application
ELECTRODE ANGLE
ARC BLOW: Specially occurred in DC welding M/C.
The clash of Magnetic field which was already present in work piece with
present Magnetic field of Short circuit within electrode and work piece…..Hence
arc always goes towards the Strength of Magnetic field at centre of work
piece….Hence Spatter occurs by deflecting the arc..
Arc blow can be controlled mainly by following 4 methods….
WELDING TECHNIQUES:.(ADVANCED WELDING TECHNIQUE).
Key point is to maintain constant Arc length. If arc length is changed the
Welding parameter is changed by Current. When Voltage(arc length) varies , Current
(Heat)also varies asper Ohms law.(V=IR)
1. Manual arc welding--Two motion (Speed and Feed) are controlled by man
2. Automatic arc welding--Both are controlled by machine.
3. Semi-automatic arc welding—one motion (speed) is controlled by man.
Type of welding Machines: Based on step-down Transformer.
1. Constant current…Drooping Characteristics…(Parabolic curve)Downward bend
curve have small changes in current….Due to hand shake arc length varies in
turn voltage varies…so this is suitable for manual weld.
2. Constant Voltage….small change in voltage will give high change in current…so
machine will keep arc length constant will not affect current….hence suitable
for Automatic machines
OTHER FEATURE OF WELDING M/C TO BE ASSESSED ON PURCHASE FOR USE:
1. Short circuit current…
Max current can be allowed at rated condition..Arc voltage is the function of
arc length
2.
(D)-Duty cycle…
Arc is ON w/out overheating the elements of welding machine…%of time=Arc
on time/(arc on time+Idle time)….I2D=constant…In india we follow 5 min i.e 3
min arc on, 2 min Idle will give 60% duty cycle.
TYPES OF JOINTS:
WELDING TERMS

Permitted Reinforcement of weld is T/10 where T is the thickness of
parent metal.
ARC LENGTH
LONG ARC
NORMAL ARC
CHARACTERISTICS OF ARC
SHORT ARC
WELDING POSITIONS FOR PLATE WELD
1F AND 1G
2F ANF 2G
3F AND 3G
4F AND 4G
WELDING POSITIONS FOR PIPE WELD
1G AND 2G POSITION
5G AND 6G POSITION
TACK WELD:
WELDING PROCESS
FUNCTIONS OF FLUX DURING WELDING
FLUX COATING MATERIAL TO PROTECT THE WELD STRENGTH:
DESIGNATION OF ELECTRODE: BIS( Bureau of Indian Standard)used only in India.
E122 413 P
E…..Extrusion..Type of manufacturing of Electrode
1….Type of flux coating…..1-High cellulose, 2-High Titanium(TiO )--Rutile
2…Position of Electrode….0-F,H,V-u+d,O
2
1-F,H,V-u+d
2- V-u+d
2…Polarity of Electrode…..1—DCSP (DCEN)..
2—DCSP—v90
413…Strength of Electrode….4—Tensile strength
1—Yield strength
3--% of Elongation
P….Specific Information ( Deep penetration)
DESIGNATION OF ELECTRODE: ASPER
ISO—International Organisation for Standardisation.
ER 4312HJX
E…Extrusion (Manufacture type)
R..Type of Flux used….A—Acidic, B—Basic, C—Cellulose, R—Rutile.
43..Mechanical properties of joint…4—Yield strength and Ultimate tensile strength
3--% of Elongation
12..Performance characteristics of coverings..
1—Welding position
2—Welding current and voltage settings
H..Special characteristics….H—Hydrogen controlled electrodes
J—Iron powdered electrodes-(110-129%)Deposition recovery
X—Radiographic quality of weld.
DESIGNATION OF ELECTRODE: ASPER
E6013
E………….Electrode.
60………..Tensile strength in 1000psi.
1………….Welding position in all position (1-3)
3………….Flux coating of Titania potassium(0-8)
AWS
WELD DEFECTS AND ITS CAUSES
CAUSES OF DEFECTS
UNDERCUT
1. HIGH CURRENT,
2. SHORT ARC,
3. TOO SPEED,
4. INCORRECT ANGLE OF ELECTRODE,
5. HIGH HEAT ON JOB
OVERLAP:
1. LESS CURRENT
2. SLOW SPEED,
3.LONG ARC,
4.OVER SIZE OF ELECTRODE
BLOW HOLE and POROSITY
1. DUST,OIL,GREASE ON JOB,
2. HIGH SULPHUR ON JOB
3. FAST COOLING OF WELD
4. EDGE PREPARATION NOT DONE
5. WETNESS ON METAL
SPATTERS
1. HIGH CURRENT,
2. LONG ARC,
3.WRONG POLARITY
4.ARC BLOW
5.FLUX DAMAGED ON ROD
EDGE OF PLATE MELTED OFF:(lap&coner)
1. OVERSIZE ELECTRODE
2. HIGH CURRENT
3. WRONG WEAVING OF ELECTRODE.
IMAGE OF DEFECTS
CRACKS
1. LOCALISED STRESS
2. FAST COOLING OF WELD
3. HIGH SULPHUR ON METAL
4. W/O PRE &POST HEAT OF METAL,
5. LESS DUCTILITY OF METAL,
6.WRONG SELECTION OF ELECTRODE,
7.WRONG TECHNIQUE USED.
INCOMPLETE PENETRATION
1.TOO SPEED,
2.KEY HOLE NOT MAINTAINED IN ROOTRUN,
3.LESS CURRENT,
4.OVERSIZE ELECTRODE,
5.ANGLE OF ELECTRODE INCORRECT,
6.INSUFFICIENT ROOT GAP.
SLAG INCLUSION
1.WRONG EDGE REPARATION,
2.DAMAGED ELECTRODE,
3.HIGH CURRENT,
4.LONG ARC,
5.WRONG WELD TECHNIQUE,
6. CHIPPING OF SLAG NOT DONE ON
SUBSEQUENT PASS
OVERSIZED WELD/EXCESSIVE REINFORCEMENT
1. OVER WELD NOT NEEDED FOR
ECONOMIC,TIME,PRODUCTION
PURPOSE.
2. INCREASED WEIGHT.
EXCESSIVE CONCAVE/INSUFFICIENT THROAT THICKNESS
1.UNDER SIZED ELECTRODE,
2.TOO SPEED WELDING,
3.WRONG WEAVING OF ELECTRODE,
4.NO CONSTANT SPEED.