The document discusses plasma arc machining (PAM), a material removal process where a high-velocity plasma jet melts and cuts through a workpiece. PAM can cut any electrically conductive material, operates at very high temperatures up to 30,000°C, and offers faster cutting speeds than oxy-fuel cutting. The key components of a PAM system include a power supply, gas supply, plasma torch, and methods to stabilize the plasma arc. Process parameters like gas type, stand-off distance, and cutting speed influence the performance and capabilities. PAM is useful for precision cutting of metals and difficult-to-cut alloys.

1. National Institute of Technology Warangal
PLASMA ARC MACHINING
PRESENTED BY
L SURESH KUMAR
MTECH
MANUFACTURING ENGINEERING

2. CONTENTS
 Introduction
 About plasma
 Generation of plasma
 Process
 Equipment
 Parameters influencing PAM performance
 Process capability
 Applications
 Advantages
 Disadvantages
 Referrences

3. INTRODUCTION
 Plasma arc machining is a material removal process.
 The material removal takes place by directing a high velocity jet of
high temperature (11,000-30,000℃) ionized gas on work piece.
 Narrow plasma jet melts the workpiece material in its path.
 With the high temperature involved, can be used for any material
those resistant to oxy-fuel gas cutting.

4. WHAT IS PLASMA...?
 Mixture of free electrons,positively charged
ions and neutral atoms.
 Obtained by heating gas at high temperature
so that it is partially ionized.
 The central zone of plasma reaches a
temperature of 15,000℃and it is completely
ionized.
 Heating of gas takes place in restricted
region of the nozzle duct, resulting
in high-velocity gas exit.

5. GENERATION OF PLASMA
heating the gas to high temp to ionize
the gas is popular method for generating
plasma.
this can be done by two methods....
1. By applying suitable electric field
across the gas column
2. By exposing gas column to radiation

6. When gases are heated the following can occur :
(i). elastic and inelstic collisns between the atoms
(ii). ionization of gases takes place resulting in
production of electrons and ions
(iii). electrons collide with atoms, create high temp and
thermal KE of atoms, further collision produce ions
and electrons. thus, new matter which is called
plasma is characterized by is ability to conduct
electricity due to presence of free charges is
produced.

7. PROCESS
 Gases are heated and charged to
plasma state.
 Plasma state is the
superheated and
electrically ionized gases
at approximately 5000℃
 These gases are
directed on the w/p in the
form of high velocity stream.
 gases Used H2,N2, O2 .
 plasma arc can be used for cutting,
welding, spraying, etc..,
fig. Schematic diagram of PAM

8. EQUIPMENT
Plasma arc machining consists of
1. Power supply (1000A, 200V DC)
2. Gas supply (1.4MPa)
3. Cooling water system
4. control console and plasma torch

9. POWER SUPPLY
 Uses DC power supply.
 The power supply should have saturation current, beyond which
the current should not rise even for short circuit.
 for easy ignition and maintenanceof arc,OCV must be higher
than load value.
 normally,DC motor-generator sets or trnsductor controlled
rectifier units with saturable core reactors are used.

10. GAS SUPPLY
 Any gas that should not attack the tungsten electrode or the work piece.
 The flowing pressure can be upto 1.4MPa results in plasma velocity of 100
m/s.
 higher the gas flow rate higher the momentum of the plasma jet.
 higher flow rate also helps to remove the molten mterial from the molting
zone.
 carbon alloy and cast steels are cut with mixture of N2 and H2 i the
compressed air.
 SS,Al, and other non ferrous alloys are cut with Ar, N2 and H2 .
 gas flow rates are 2 to 11 m3/hr and are controlled by using mass flow
controllers(MFCs)

11. PLASMA TORCH
 In PAM, electric arc constricts from nozzle, generates basic
plasma jet.
 Instead of diverging into open arc, The nozzle constricts arc
into a small cross section.
the plasma arc are classified as..,
1. Air plasma torch
2. Dual gas plasma torch
(plasma gas,shielding gas)
3. Oxyen injected plasma torch
4. Water injected plasma torch

12. IMAGES OF THE NOZZLE
Air plasma torch Dual gas plasma torch Water injected plasma torch

13. METHODS TO STABILIZE ARCS
 Plasma torches transform
electrical energy into thermal
energy in the form of the
plasma jet.
 it is important to stabilize the
electric arc which is burns in
constricted space and frcedd
away by gas or liquid.
 If liquid is used vapour is
surrounds the arc column.
 Acc. to stabilizing medium, therre
is gas or liquid stabilized plasma
torches.
i. Wall or sheath stabilization.
ii. vortex stabilization, and
iii. Liquid sabilized plasma
torches.

14. PARAMETERS INFLUENCING PAM
PERFORMANCE
Parameters associated with,
i. Design and operation of the torch.
ii. The physical configuration of the set-up
iii. The environment in whch work is performed.

15. PARAMETER ASSOCIATED WITH DESIGN AND
OPERATION OF THE TORCH
there are two modes of operation of dc plasma torches:
i. Non-transfered mode
ii. Transfered mode
Turbulent and Laminar mode

16. DESIGN ASPECT
 the plasma torch is designed for the maximum thermal output.
the following design parameters affect the performance of the torch.
1.cathode size
2.convergence of nozzle
3.nozzle orifice diameter
4.orifice length
5.electrode gap
6.cooling of electrode

17. GENERAL DESIGN CONSIDERATIONS
 large current require larger dia cathode,orifice length and electrode gap.
 while operating at larger arc voltages, it is preferable to increase the angle of
taper at the cathode tip.
 while operating at transferred arc anode,flat face cathode is used due to high
arc voltages.
 edges of constrictions are rounded off to avoid turbulence.
 non transferred arc modes use long throat lengths, while for transferred arc
mode, the min length is used.
 no water leakage into the plasma chamber from the cooling chamber is
allowed.
 oxygen or compounds of oxygen in the plasma gas are detremental to the
cathode.

18.  for successful utilization of PAM it is necessary to analyse the following process
parameters..,
Power supply Shielding Nozzle
(a) type: DC (a) type : CO2, H2O Ar,H2 (a) SOD: 6-30mm
(b) Voltage: 200V (b) pressure: 11bar (b) diameter:0.80-6.30mm
(c) Current: 50-1000A (c) flow rate: 50m3/hr (c) life: 2-5 hrs
(d) Power: 2-200KW (d) Material: Zr, Hf
Primary gas Cutting parameter
(a) Composition:N2:H2=90:10 (a) tool : plasma jet
(b) Pressure: 10bar (b) max velocity of plasma jet:500m/s
(c) Flow rate: 50 m3/min (c) max temperature: 16000-20000℃
(d) MRR: 150 cm3/min
(e) max plate thickness: 200mm
(f) cutting speed: 0.1 - 7.5 m/min.

19. PARAMETERS ASSOCAITED WITH TE PHYSICAL
CONFIGURATION OF THE SYSTEM
 In PAM, important vaiables are,
stand-off distance,angle, depth of cut, speed and feed of the work
towards the torch.
 the feed and depth is determined by material removed.
Stand - off distance is the distance between the nozzle and work piece.
the effect of SOD are
 minntain min SOD for better quality cuts since arc divergence is less
 increased power input is necessary when SOD distance is large.
 SOD can range from 6.5-76.2mm

20. CUTTING SPEED
 The speed depends on the thickness of the material to be machined.
 thick materials require lower speed than thin materials.
 the typical values of cutting speed are..,
Material Thickness Arc Current Cutting speed (mm/min)
plasma arc cutting speeds

21. parameters associated with environment in
which work is performed
 the protective atmosphere has created to reduce the oxidationof
exposed high temp machined surface
 the deflection of the arc should be kept min.
 the spread of the plasma column should be uniform on
impingement area.

22. Process capabilities
 carbon steel plates thicker than 50 mm can be cut 10 times faster than oxy-
fuel cutting.
 Accuracy of 0.8mm upto 35mm plates, 3mm upto 150mm plates.
 sharp radius upto 4 mm is possible but increases upto 38mm.
 MRR upto 150cm3/min is possible kerf angle 2° to 7° with the normal
cutting condition, 1° to 2° with special arrangement.
 smoother surface can be achieved compared to oxy-acetylene flame.
 Mg,Ti,Cu,Ni znd alloys of copper and nickel can be cut with PAM.
 It is used for profile cutting of many metals like mild steel, alloy steels, titanium
etc..,

23. Applications
 PAM can be used to make cuts in electrically conductive metals.
 PAM is used for cutting grooves in the hardened shaft.
 PAM is used for underwater cutting.
 plasma arc can be used for depositing filler material on the on the surface or
corroded or worn out part to obtain desired properties like corrosion
resistance,wear resistance, anti friction properties.
 PAM Is used for profile cutting stainless steel, Al, Ti, other non-ferrous
material.

24. Advantages
 used for cutting ferrous and non ferrous materials at high speeds.
 profile cutting of SST and titanium is posible.
 no contact between the tool and the work piece. hence simple work holding
devices are enough.
 cutting rate of all materials are high.
 equally effective regardless of hardness of material and other propertiesof
materials.
 can be automated easily.
 PAM can machine exotic metals at high rates.

25. Disadvantages
 Burr is often produced.
 Taper on the work piece may occur.
 process alters the surface metullurgically. it produces hard and uneven
surfaces.
 smoke and noise is produced duringthis process. hence eyes and nose
shielding is required.
 Sharp corners are difficult to make using PAM.
 the process produces HAZ. HAZ can cause premature failure of tHe
component.