Arc Welding basics

1. Arc Welding process
By: Ajay Kumar
Email Id: ajay.kumar@utu.ac.in
Asst. Prof. Mech/Auto Department
CGPIT, UTU Bardoli

2. WELDING PROCESSES
 Best fastening(joining) method for metals.
 Welding is a process of joining two metal work-piece by heating them with or
without the application of pressure and filler material.
 Welding is used for making permanent joints.
 It is used in the manufacture of automobile bodies, aircraft frames, railway
wagons, machine frames etc.
 Filler material is used in welding for making welding strong and the composition
of filler material is same as the composition of parent metal (Work-piece)
Weldability:
Weldability of metal refers to the ability of material to be get welded.
Ex: The wood can not be welded but mild steel can be welded.

3. Classification of welding according to Heat source and
arrangement

4. Principle of Arc Welding
• A fusion welding process in which Bonding of metals is achieved by the heat from
an electric arc between an electrode and the work lie under arc welding process.
• Electric energy from the arc produces temperatures ~ 5500-6000 c , hot enough to
melt any metal.
• Most AW processes add filler metal to increase volume and strength of weld joint.

5. Arc Welding Process…….
• 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.
• A pool of molten metal is formed near electrode tip,
and as electrode is moved along joint, molten weld
pool solidifies.
Note: (Plasma is the region between electrode and work where
mostly flow of charged particles namely free electrons and
positive ions takes place. In this region, uniform voltage drop
takes place. Heat generated in this region has minor effect on
melting of the work piece and electrode.)

6. Arc Welding Process
Setup : Arc welding setup mainly involved:
 Power source
 Electrode (consumable or non-
consumable)
 Filler Rod
 Shielding arrangement (inert or non-
reactive gases)

7. Power source:
1. Alternating current (ac) machine
a) Transformer b) Motor or engine driven alternator
2. Direct current (dc) machine
a) Transformer with dc rectifier b) Motor or engine driven generator
1. Alternating current: Alternating current (AC) is an electric current which periodically reverses direction, in contrast
to direct current (DC) which flows only in one direction. Due to this reason polarity has no effect during welding using
ac power source but uniform heat is obtained on anode(+) and cathode(-).
2. DC power source : Direct current (DC) is the unidirectional flow of electric charge. A battery is a good example of a
DC power supply. Direct current may be obtained from an alternating current supply by using rectifier.
As in dc power source, polarity don’t have alternating nature thus during dc arc welding, workpiece and electrode
holder can be connected either positive or negative terminal.
On this basis dc electric source polarity can be classified in two ways,
a) Straight polarity and, b) Reverse polarity

8. Polarity in Arc Welding
Workpiece positive and electrode negative or DCEN Workpiece negative and electrode positive or DCEP

9. Difference Between Straight Polarity vs Reverse Polarity
Straight Polarity Reverse Polarity
Electrode and Workpiece In this Electrode is connected with
Negative terminal and Workpiece
with positive terminal.
In this Electrode is connected with
Positive terminal and Workpiece
with Negative terminal.
Electron Flow Electron flow from Electrode to
Workpiece
Electron flow from Workpiece to
Electrode
Heat 70% Heat is generated at w/p and
30% at electrode
70% Heat is generated at Electrode
and 30% at w/p
Applicable Used for thin plate welding Used for thick plate welding
Penetration Deeper Penetration Shallow Penetration
Deposition Rate Slow Deposition Rate Faster Deposition Rate

10. • Arc length
The distance from the tip of the electrode or wire to the work piece. Arc length
and arc voltage has linear relationship.
V = a + bL where, V = arc voltage, L = arc length & a and b are constant.
If L is very large, then I=0 and R = ∞, from V= IR, V also increases
Thus, by controlling the arc length welder can control the voltage.
• Arc Time – The time during which an arc is maintained.
• Arc Voltage– The voltage across the welding arc.
• Duty Cycle:The duty cycle gives you an idea of how hard and how long you can run a welding
machine before it overheats and shuts down. Duty cycle is the ratio of arcing time to the weld cycle time
multiplied by 100. Welding cycle time is either 5 minutes as per European standards or 10 minutes as per
American standard and accordingly power sources are designed.

11. Cycle time:
if f=50 Hz , cycle time = 1/f = 0.02 sec
to get the effective arc, Arc recovery time < cycle time/2

12. • Welding positions defined here for groove welds:
(a) flat, (b) horizontal, (c) vertical, and (d) overhead
Arc Welding Positions

13. Types of Arc Welding Electrodes
Consumable – consumed during welding process Acts as filler metal in arc
welding
Forms of consumable electrodes
• Welding rods (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
In both rod and wire forms, electrode is consumed by the arc and added to weld
joint as filler metal
Non-consumable – not consumed during welding process thus filler metal must
be added separately if it is added.
Ex: tungsten electrode in TIG welding.

14. Electrode nomenclature
• The American Welding Society (AWS) numbering system can tell a welder quite a bit
about a specific stick electrode including what application it works best in and how it
should be used to maximize performance.
• The prefix "E" designates an arc welding electrode. The first two digits of a 4-digit
number and the first three digits of 5-digit number indicate minimum tensile strength. For
example, E6010 is a 60,000 psi tensile strength electrode while E10018 designates a
100,000 psi tensile strength electrode.
E 60 1 10
Electrode Tensile Strength Position Type of Coating
and Current

15. Classification of Electrodes as per Indian Standard:
Structural steel electrodes were classified as per IS 814:1974 and this code was revised and
the revised code is IS 814:1991.
The corresponding code is given on each packet of electrode.
IS 815:1974
As per IS 815 electrodes are designated with letters and digits.
P X X X X X X S
Prefix (P) is either E or R which indicates solid extruded (E) or reinforced extruded (R) Electrode.
1 st digit – Indicates type of coating.
2 nd digit – Indicates weld positions in which electrode can be used.
3 rd digit – Indicates welding current conditions.
4 th and 5 th digit – Indicate UTS and YS of all weld metal.
6 th digit – Requirement of minimum % elongation and absorbed energy in charpy V- notch impact test of weld
metal.
Suffix (s) – P – Deep penetration electrode
H – Hydrogen controlled electrode
J, K and L – Amount of metal recovery in case of iron powder electrode
Suffix (s) are optional and may or may not be given if not applicable.

16. IS 814:1991
As per IS 814 electrodes are designated with letters and digits as given below:
E L X X X X S
• In this code E indicates extruded solid electrode, L is a letter to designate
type of coating,
• first digit indicates UTS and YS of deposited weld metal,
• second digit gives percentage elongation and impact values of weld metal
deposited,
• third digit gives welding positions in which electrode can be used and
• fourth digit gives the current conditions for the use of electrode.
• Suffix(s) are optional and indicate special characteristics of electrode such
as H1, H2, and H3 indicate hydrogen controlled electrodes with different
amount of diffusible hydrogen
• J, K, L indicate different amount of metal recovery in weld pool in case of
iron powder electrodes
• and X means radiographic weld quality.

18. Filler Material:
 Filler metal is additional metal used in the welding process to join the work pieces. It melts when
fed up in the welding arc and become the part of weld.
 Filler material is used to make the weld stronger and its composition is same as the parent metal.
 While welding, parent metal and the filler material make the molten pool by melting itself, and
when this molten pool solidifies , welding bead is created and welding is said to be done.

19. Arc Shielding
• At high temperatures in AW, metals are
chemically reactive to oxygen, nitrogen, and
hydrogen in air thus,
• 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, CO2 etc.
• And using Flux material.

20. Flux: Flux is a substance that prevents formation of oxides and other
contaminants in welding, or dissolves them and facilitates removal.
Flux Provides protective atmosphere for welding, Stabilizes arc and Reduces
spattering.
Role of common constituents added in flux of SMAW electrode is given below:

21. Difference between Arc Welding and Gas Welding:
S. No. Arc Welding Gas Welding
1. In the arc welding, electricity is used to generate
heat.
In gas welding, fuel gases like acetylene, hydrogen are
used to generate heat.
2. This welding generates higher temperature than gas
welding. The temperature is about 6000C.
This welding generates lower temperature than arc
welding. The temperature is about 3500C.
3. This welding generates stronger joint compare to gas
welding.
It gives weaker joint.
4. It gives poor surface finish. This welding gives good surface finish.
5. In arc welding, electrode is used. In gas welding gas torch is used.
6. The electrode is combined with the filler metal. A filler rod is used separately if required.
7. It can be used in welding alone. It can be used in welding, brazing and soldering.
8. There is risk of explosion due to high voltage. There is risk of explosion due to high pressure.
9. It is mostly used to joint similar material. It is mostly use to join both similar and different metals.
10. The heat is concentrated in arc welding. The heat is distributing according to the flame. There is
higher loss of energy.
11. It is more efficient. It is less efficient.
12. Speed of welding is high. Speed of welding is low.
13. The initial cost of arc welding is high. The setup cost of gas welding is low.

22. Advantages of arc welding over gas welding
• This welding generates higher temperature than gas welding. The temperature is
about 6000C.
• This welding generates stronger joint compare to gas welding.
• The heat is concentrated in arc welding.
• It is more efficient.
• Speed of welding is high.

23. Plasma Arc Welding (PAW)
• It is a fusion welding process wherein the coalescence is produced by heating the work
with a constricted arc established between a non consumable tungsten electrode and
work piece or between a non consumable electrode and constricted nozzle.
• The shielding of the weld pool is obtained by the hot ionized gas produced by passing
inert gas through the arc and constricted nozzle.
• Filler material may or may not be applied.
Principles of Operation:
• In the PAW process, the workpiece is cleaned and edges are prepared.
• An arc is established between a non consumable tungsten electrode and workpiece or
between a non consumable electrode and constricted nozzle.

24. • An inert gas is passed through the inner orifice surrounding the tungsten electrode
and subsequently the gas is ionized and conducts electricity.
• This state of ionized gas is known as plasma. The plasma arc is allowed to pass
through the constricted nozzle causing high energy and current density.
• Subsequently high concentrate heat and very high temperatures are reached.
• The low flow rate (0.25 to 5 l/min) of the orifice gas is maintained as excessive
flow rate may cause turbulence in the weld pool.
• However the orifice gas at this flow rate is insufficient to shield the weld pool
effectively. Therefore inert gas at higher flow rate (10-30 l/min) is required to pass
through outer gas nozzle surrounding the inner gas nozzle to protect the weld pool.