Plasma arc machining

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Transcript Plasma arc machining

S.T.B.S College of Diploma Engineering,
Class: Mech-1051(B)
Prepared.BY:Thumar Sanket C.
TOPIC : Plasma arc machining
1.Working Principle of PAM
2.Process Details of PAM
3.Applications of PAM
4.Advantages of PAM Process
5.Disadvantages of PAM Process
1.Working Principle of PAM
In this process
gases are heated and
charged to plasma state.
Plasma state is the
superheated and
electrically ionized gases
at approximately 5000C⁰
These gases are
directed on the
workpiece in the form of
high velocity stream.
Working principle and
process details are
shown in Figure 5.
Figure 5 : Working Principle and
Process Details of PAM
2.Process Details of PAM
Details of PAM are described below.
Plasma Gun
Gases are used to create plasma like, nitrogen, argon,
hydrogen or mixture of these gases. The plasma gun consists of a
tungsten electrode fitted in the chamber. The electrode is given
negative polarity and nozzle of the gun is given positive polarity.
Supply of gases is maintained into the gun. A strong arc is established
between the two terminals anode and cathode. There is a collision
between molecules of gas and electrons of the established arc. As a
result of this collision gas molecules get ionized and heat is evolved.
This hot and ionized gas called plasma is directed to the workpiece
with high velocity. The established arc is controlled by the supply rate
of gases.
2.Process Details of PAM
Power Supply and Terminals
Power supply (DC) is used to develop two terminals in the
plasma gun. A tungsten electrode is inserted to the gun and made
cathode and nozzle of the gun is made anode. Heavy potential
difference is applied across the electrodes to develop plasma state of
Cooling Mechanism
As we know that hot gases continuously comes out of
nozzle so there are chances of its over heating. A water jacket
is used to surround the nozzle to avoid its overheating.
2.Process Details of PAM
There is no direct visible tool used in PAM. Focused
spray of hoot, plasma state gases works as a cutting tool.
Workpiece of different materials can be processed by PAM
process. These materials are aluminium, magnesium, stainless
steels and carbon and alloy steels. All those material which can
be processed by LBM can also be processed by PAM process.
3.Applications of PAM
The chief application of this process is profile cutting as
controlling movement of spray focus point is easy in case of
PAM process. This is also recommended for smaller machining
of difficult to machining materials.
4.Advantages of PAM Process
Advantages of PAM are given below :
(a) It gives faster production rate.
(b) Very hard and brittle metals can be machined.
(c) Small cavities can be machined with good
dimensional accuracy.
5.Disadvantages of PAM Process
(a) Its initial cost is very high.
(b) The process requires over safety precautions which
further enhance the initial cost of the setup.
(c) Some of the workpiece materials are very much prone
to metallurgical changes on excessive heating so this fact
imposes limitations to this process.
(d) It is uneconomical for bigger cavities to be machined.
Conventional Plasma Arc Cutting
In Conventional Plasma Arc Cutting, the arc is
constricted by a nozzle only; no shielding gas is added.
Generally, the cutting gas is tangentially injected the electrode.
The swirling action of the gas causes the cooler portions of the
gas to move radially outward, forming a protective boundary
layer on the inside of the nozzle bore. This helps prevent
damage to the nozzle and extends its life. Electrode life is also
improved. Since the arc attachment point (cathode) is forced to
move about and distribute its heat load more uniformly.
Conventional Plasma Arc Cutting
Air Plasma Arc Cutting
Air plasma arc cutting was introduced in early 1960s for
cutting mild steel. Oxygen in the air provides additional energy
from the exothermic reaction with molten steel, boosting cutting
speeds about 25 percent. Although this process can also be used
to cut stainless steel and aluminum, the cut surface will be
heavily oxidized and thus can be unacceptable for some
Air Plasma Arc Cutting
Dual-flow Plasma Arc Cutting
Dual-flow PAC is a slight modification of conventional PAC It
incorporates most of the features of conventional PAC but adds a
secondary shielding gas is secondary shielding gas around the nozzle.
The cutting gas is usually nitrogen the shielding gas is selected
according to the metal to be cut. Cutting speeds are slightly better
than those of conventional PAC on mild steel, but the cut quality is
not acceptable for some applications. Cutting speed and quality on
stainless steel and aluminum are essentially the same as with
conventional PAC.
Dual-flow Plasma Arc Cutting
Underwater Plasma Arc Cutting
Underwater PAC is suited to numerically(NC) shape cutting
and produces a noise level of 85dBA or less under normal operating
conditions. In comparison,conventional PAC typically produces
noise levels in the range of 105 to 115 dBA. Underwater cutting also
nearly eliminates ultraviolet radiation and fumes. Steel plate being
cut is supported on a cutting table with the top surface of the plate 2
to 3 inches underwater. Advice that locates the submerged top
surface of the metal is vital to the fully automated underwater PAC
process. Height control is maintained by a sensor that monitors arc
voltage. Cutting speed and quallity are comparable to those attained
with water injection PAC. Note that it is hazardous to cut aluminium
under water. Hydrogen generated by the process can be trapped
under the plate, creating the potential for explosion.
Underwater Plasma Arc Cutting
Plasma arc machining