It is the presentation on Plasma arc welding for the Mechanical Dept students from Khalid Rasheed NFC-IET Multan, Pakistan.

1. 25-Apr-16

2. PLASMA ARC WELDING
Presented by
Khalid Rasheed
2k14-me-20
Shafqatullah
2k14-me-07

3. INTRODUCTION
Plasma are initially employed to cut metals that are
difficult to machine by conventional methods.
Later, plasma arc has been sucessfully used for
spraying ,surfacing & welding metals like aluminium,
stainless steel, titanium , brass and copper though
other conductive metals may be cut as well.
Plasma cutting is a process that cuts through
electrically conductive materials by means of an
accelerated jet of hot plasma.

4. THE 4TH STATE OF MATTER
• The first three states of matter are
solid, liquid and gas. For the most
commonly known substance, water,
these states are ice, water and
steam. If you add heat energy, the
ice will change from a solid to a
liquid, and if more heat is added, it
will change to a gas (steam). When
substantial heat is added to a gas, it
will change from gas to plasma, the
fourth state of matter.

5. PLASMA
• Plasma is an electrically conductive
gas. The ionization of gases causes
the creation of free electrons and
positive ions among the gas atoms.
When this occurs, the gas becomes
electrically conductive with current
carrying capabilities. Thus, it
becomes a plasma.

6. REASONS OF PLASMA STATE
This change takes place when gases are heated to
very high temperature
The number of collisions between the atoms, either
elastic or inelastic increases.
The gas ionises ,so that a portion of atoms are
stripped off from outer electrons
The electrons thus produced, in turn colloids with
atoms, so that there thermal kinetic energy
increases, and a light is emitted from them ,thus
producing more number of atoms and electrons.

7. GENERATION OF PLASMA
 First of all the gases are heated to very high temperature of about 16000 degree
Celsius so as to generate plasma
 This can be achieved by applying a suitable electric field across the gas column.
 The gases are then heated by an applied electric field.
 An igniter supplies the initial electrons ,which accelerated before colliding &
ionizing.
 The free electrons get accelerated & causes ionisation & heating of gases.
 This process continues till the steady state is obtained.
 The actual heating takes place when atoms recombines into molecules.

8. PLASMA (CUTTING) GAS
SELECTION
• Plasma gas is also called the cutting gas. This is
the gas that is ionized in the plasma process
and exits through the nozzle orifice. Examples
of plasma gas are:
• 1.Air 2.Oxygen 3.Nitrogen 4.Argon-Hydrogen

9. SHIELD GAS SELECTION
• The shield is the secondary gas in the plasma process. It surrounds the arc and
is used to help constrict the arc and cool torch. It creates and protects the
cutting environment which among other things affects the edge quality.
Examples of shielding gas are:
 Air
CO2
Oxygen-Nitrogen
Air-Methane
Nitrogen Methane

10. PRINCIPLE
In this case, the high velocity electrons of are collide
with the gas molecules & metal to form ionisation
of beam.
The plasma gas is forced through nozzle duct & is
made to direct on the work piece to be machined.
Much of the heating takes place in duct at about
1600 degree celcius & metal removal is due to
electron bombardment & hot plasma.

11. MECHANISM OF PLASMA ARC CUTTING
Accurate cuts can be made in stainless steel and non-
ferrous metals such as aluminum by plasma arc
cutting.
The cuts are made by a high temperature, high
velocity gas jet generated by constricting an arc
between a tungsten electrode and the component.
The heat from the arc melts the metal and the gas jet
removes the molten metal from the cut.

12. CONTINUED
The arc operates in an inert inner shield, whilst an outer shield provides
protection for the cut surface.
Argon, helium, nitrogen and mixtures of these gases are used for both the
inner and outer shields.
Plasma arc cutting is characterized by fast cutting speeds and is mainly used in
mechanized systems.
The cutting is accompanied by a high noise level which can be reduced by
operating the torch under water.

13. MODES OF OPERATION OF DC TORCH
 Non Transferred Arc Torch
 Transferred Arc Torch
25-Apr-16

14. Non Transferred Arc Torch
 The DC power source is connected directly across
cathode & anode (nozzle), so that the cathode and
nozzle carry same current.
 Plasma is in the form of flame.
 Useful for spraying ceramic working & chemical
synthesis.
 The hottest portion does not appear outside the
nozzle.
 The electrothermal efficiency is about 65% for sheat
stabilized torches and 75% for vortex stabilized
torches .
Transferred Arc Torch
 Cathode is connected to negative terminal & anode is connected to
positive terminal of DC power source through a suitable resistor to
limit the current through the nozzle to about 50 amp.
 Here arc is struck between tool &work piece.
 Once this arc is struck , the pilot flame circuit is disconnected.
 Useful for welding , cutting and hard surfacing of metals.
 Argon or nitrogen can be used during the operation.
 Electrothermal efficiency is increased to 85-90% , the only loss
being at the cathode and the unconnected nozzle.

15. Advantages of PAM Process
 It gives faster production rate.
 Very hard and brittle metals can be machined.
 Small cavities can be machined with good dimensional accuracy.
Disadvantages of PAM Process
 Its initial cost is very high.
 It is uneconomical for bigger cavities to be machined.
 Inert gas consumption is high.

16. APPLICATIONS OF PLASMA JETS
• Plasma arc process for cutting aluminum and other nonferrous materials was first
introduced in 1955.
• Due to the remarkable results, the process has now been widely accepted by
industries for varied applications.
• The major areas of industrial production where plasma jets have successfully been
employed are:
• Welding of material like titanium, stainless steel, etc. which are other-wise difficult
to weld.
• Plasma arc surfacing.
• Plasma arc spraying.