The document provides an in-depth overview of plasma arc welding (PAW), detailing its introduction, equipment, modes of operation, and the effects of various parameters on weld quality. It describes two primary modes (melt-in and keyhole) and outlines the advantages and disadvantages of PAW, such as high-quality welds and greater heat input. Additionally, it highlights applications in small part welding and tool repair, emphasizing PAW's precision and control in various industrial settings.

1. Plasma Arc
Welding
BY
ABHISHEK ANAND THAKUR
Dept. of Mechanical Engineering
Tezpur University

2. Content
 Introduction
 Keywords
 Plasma arc welding
 Equipment
 How it works ?
 Types of PAW & modes of operation
 Effect of Various Parameter
 Advantage and Disadvantage
 Application

3. Introduction
 Introduced to welding industry in 1964
 Method of bringing better control to arc
welding process in lower current ranges
 PAW brought to industry by providing an
advanced level of control and accuracy to
produce high quality welds
 Provide long electrode life for high
production requirements
used in a variety of operations ranging from
high volume welding of strip metal

4. Keywords
 Plasma : A gas heated to a very high temperature
and ionized so that it becomes conductive.
 Pilot Arc : First arc between between electrode &
constricting nozzle.
 Keyhole : A welding technique in which a concentrated
heat source penetrates the WP forming a hole at the
leading edge of the molten weld metal
 Sinter : Integrate into a solid or porous mass by means
of heating.
 Weld bead geometry :

5. Plasma Arc Welding
Equipment
 Power Source : Open circuit
voltage of 80 volts
 Current – (50 – 300A )
 A dc welding current is required .
 A welding torch -Non
consumable tungsten electrode
 A cooling system : Water re-
circulator
 Plasma Welding Torch
 Plasma Gas : Argon
 Shielding Gas : Argon,
Argon/Hydrogen or Helium

6. How it works ?
The tungsten electrode has a negative polarity
and the work-piece a positive polarity. Electrons
flow to the WP.
 Plasma consists of electrons, ions and neutral
particles and have disorder violent movement.
 So molecule are partly dissociated and the
atoms ionized.
 On collision with WP surface they give their
energy to the WP and recombine.
 The jet deliver a narrow & constricted plasma
with a very high energy density.

7. o Arc is established between
electrode and WP.
o Arc is established between
electrode and nozzle.
o The WP is part of the electrical
circuit and heat is obtained
from the anode spot and the
plasma jet. Therefore, higher
amount of energy is transferred
to work.
o The WP is not part of the
electrical circuit and heat is
obtained from the plasma jet.
Therefore, less energy is
transferred to work.
o Higher penetration is obtained,
so thicker sheets can be
welded.
o Less penetration is obtained, so
thin sheets can be welded.
o Higher process efficiency. o Less process efficiency.
Two types of Plasma Arc Welding
Transferred plasma arc welding
process
Non-transferred plasma arc
welding process

8. Two Modes of operation in PAW
1. Melt – in mode : When energy is transferred to WP
from plasma arc the energy strike the surface and
immediately causes heating.
 It is due to the combination of conduction of heat
in the arc and conversion of kinetic energy.
 If the rate at which energy is being deposited
exceeds the rate at which heat is being conducted
away, the temperature will rise and cause melting
and produce a fusion weld. This mode of energy
deposition and weld production is called the melt-
in mode or the conduction mode
1. Melt – In mode 2. Keyhole mode

9. 2. Keyhole Mode : If the density of the energy coming
from the plasma arc is very high , such that the
deposition rate exceeds the rate at which it is lost by
conduction into the WP .
 In this case, the plasma arc can penetrate the molten
pool and form a small throughout hole in the weld pool,
refer as the keyhole.
 Moving the welding torch and the associated keyhole
will cause the flow of the molten metal surrounding the
keyhole to the rear region where it re-solidifies to form
a weld bead. This is the keyhole mode in PAW
 Keyhole mode produces larger penetration than the melt-in mode.

10. Effect of Various Factors on weld Quality
 Instability of the keyhole : It lead weld discontinuities
such as excessive penetration and incomplete penetration.
 Nozzle shape and size : Nozzle constrict the plasma jet
stream & focusing the heat on WP.
 Tungsten electrode set-back : Distance between the
end of the electrode and the nozzle exit & It has has a
significant effect on weld bead formation and arc
penetration.
 Composition and flow rate of the plasma gas : It
have strong effect on the behaviour of the weld pool ,
on the appearance of the weld, on the welding speed
and on the weld defects.

11.  Welding current : Weld joint will be best if a low
plasma gas flow rate and a high welding current are used.
 Welding speed : too high welding speed will result in
undercutting and incomplete penetration while inadequate
welding speed leads to excessive penetration so highest
possible welding speed is desirable economically .
 Distance from the nozzle to the workpiece : too
small height will lead to narrow weld and undercut while
too high one will affect the arc penetration and the welding
quality. Appropriate distance is 3–12 mm.
 Effect of plasma gas on the weld quality of plasma arc
welding is more important than that of shielding gas

12. Features of Plasma Arc Welding
 Protected electrode
 Low amperage welding capability (as low as 0.05 amp)
 Arc consistency & gentle arc starting.
 Minimal high frequency noise issues, HF only in pilot arc
start, not for each weld.
 Arc energy density reaches 3 times that of GTAW. Higher
weld speeds possible
 Weld times as short as 0.005 secs.
 Length of arc benefit due to arc shape and even heat
distribution
 Diameter of arc chosen via nozzle orifice

13. Advantages of Plasma Arc Welding
 Control and quality : Torch design allows for better
control of the arc.
 More Freedom During Manual Welds : Torch-to-
work distance from the plasma arc is less critical than GTAW.
So more freedom to observe and control the weld.
 Faster Travel Speeds: The higher heat concentration and
the plasma jet allow for higher travel speeds.
 Keyhole Effect : High temperature and high heat
concentration of plasma allow for the keyhole effect, which
provides complete penetration single pass welding of many
joints.
 Lesser angular distortion : Heat-affected zone is smaller
than with the GTAW So weld have more parallel sides,

14. Disadvantages of Plasma Arc Welding
 Greater heat input : It produces wider welds and heat-
affected zones than LBW and EBW This may result in
more distortion and loss of mechanical properties
 Complex and costly : High start up costs and . Plasma
welding equipment are very expensive.
 More specialized welding process : Training and
expertise required is also more intense.
 Gives out ultraviolet and infrared radiation.
 Operation produces a high noise of the order of 100dB
 Bulkiness of the torch : It makes manual welding
more difficult.

15. Application of Plasma Arc Welding
 Small Part Welding : PAW process can consistently
start an arc to the tip of wires or other small components
and make repeatable welds with very short weld time
periods.
such as needles, wires, light bulb filaments, thermocouples
 Sealed Components : Medical and electronic
components are sealed via this welding
 Tool Die & Mold Repair : Micro-plasma welding
processes are used for tool, die and mold repair.
 Tube Mill Welding : Output of the tube mill depends on
the arc welding speed and total time spent welding
 Long Strip Metal Welding