The document discusses plasma arc machining (PAM). PAM uses a high-velocity jet of hot plasma to cut through electrically conductive materials. It is commonly used in fabrication shops for precision cutting of metals. PAM provides high-speed, precise cuts at a lower cost compared to other machining methods. The document then goes on to describe the process of generating plasma using high heat, and the mechanisms by which plasma removes metal through heating and melting. It also discusses the various torch designs and parameters that affect the performance of PAM.

1. PLASMA ARC MACHINING
Presented by
RAJKUMAR S W
1MS15MSE10
MTECH-MSE
25-Apr-16

2. 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.
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4. CONT…..
• Plasma cutting is often used in fabrication and welding shops,
automotive repair and restoration, industrial construction, salvage and
scrapping operations.
• Due to the high speed, precision cuts, combined with low cost of
operation, plasma cutting sees a widespread usage from large scale
industrial CNC applications down to small hobbyist shops.
Plasma -WHAT IS PLASMA?
 Gases when heated to elevated temperature, they turn into a
distinctly different type of matter which is called as plasma.
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5. 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.
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6. 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. 25-Apr-16

7. 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.
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8. PLASMA GENERATION
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10. MECHANISM OF METAL REMOVAL
 The metal removal in PAM is due to high temperature of gases.
 The heating of work piece is due to direct electron bombardment plus
convective heating of hot plasma.
 The heat produced is sufficient to raise the temperature above its
melting point.
 Approximately 45% of electrical power delivered to torch is used for
removal metal from work piece.
 PAM is used for cutting, spraying, & surfacing operations.
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11. PARAMETERS GOVERNING PAM
 Those associated with design and operation of torch.
 Those associated with physical configuration & setup.
 Environment in which work is performed.
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12. THE TORCH
The plasma is push out of the nozzle with a high velocity jet
Torch consist of non consumable cathode of 2% throiated tungsten.
Converging anode nozzle with a suitable orifice.
Two electrodes are separated by high carbonate resin .
Temperatures of plasma is 10000 degree celcius where as temperature of
oxyacetylene flame is 380 degree celcius.
Velocity of plasma jet is 500m/s.
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13. MODES OF OPERATION OF DC TORCH
 Non Transferred Arc Torch
 Transferred Arc Torch
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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.
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15. OPERATION OF TORCHES
 Torches can be operated in two modes.
• Laminar mode
• Turbulent mode
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16. LAMINAR MODE
 Long flame . . When low velocity or long flames are required, this mode of torch operation is used.
 Low gas flow rate . Low gas flow rates are maintained in long nozzles to obtain a laminar flame.
 Velocity of flame is with velocities 50m/s and length~ up to 900 mm can be achieved.
 This is used wherever the processed material is not to be sputtered out or when the disintegration of
molten drops into fine droplets is undesirable.
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17. TURBULENT MODE
 High velocity flame. When high velocity flames are required for material removal
by melt blasting or spraying,
 High gas flow rate.- high gas flow rates, which give rise to turbulent jets, are used.
 These flames are short in length and are cold outside the nozzle.
 Used for cutting, welding,& spraying.
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18. DESIGN OF DC PLASMA TORCHES
• The plasma torch is designed to obtain maximum thermal output.
• The increase in efficiency not only helps in achieving better heating of the gas but also in reducing electrode
losses and thereby increasing the life of electrode.
• The design also ensures that the erosion rates of the electrodes are kept to a minimum.
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19. PARAMETERS AFFECTING THE PERFORMANCE OF
TORCH
 Cathode size.
 Annode(nozzle) convergence.
 Nozzle orifice diameter.
 Orifice length.
 Electrode gap.
 Cooling of electrodes.
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20. CATHODE
The diameter & bluntness of cathode determines erosion rate.
Tapered rod with slightly blunt tips are used for non transferred application.
For cutting operation flat disk shaped electrode is used.
For welding operation blunt electrode is used.
For spraying and cutting 10mm diameter & cathode is used.
For welding 6mm diameter cathode is used.
Cathode is press fitted into water cooled copper holder & brazed.
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21. ANODE
 Anode nozzle has a convergence so as to match the cathode taper.
 Nozzle orifice is designed on the basis of the development of a stabilized plasma column.
 There are two zones of plasma
• Undeveloped zone
• Fully developed zone
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22. FULLY DEVELOPED ZONE
 In fully developed zone electrode loss is more
 Thus it is necessary to calculate
• Nozzle orifice diameter
• Nozzle orifice length
• Electrode gap
• Cooling of electrode
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23. NECESSARY FACTORS FOR CUTTING &SPRAYING
 For cutting operation
• Nozzle diameter is kept minimum
 For spraying operation
• Nozzle diameter is varied
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24. TYPES OF TORCH
1. Non transferred arc torch
2. Transferred arc torch
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25. NON TRANSFERRED ARC TORCH
 Turbulent mode flame torches
 Laminar mode flame torches
 High power torches
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26. TURBULENT MODE FLAME TORCHES
Flame obtained is
• short in length (about 15cm at 400amps in nitrogen)
• High velocity
• Uses rod type cathodes and nearly 25mm nozzle
• Throat lengths and orifice diameters can be varied over a wide range
• Used for spraying , insulator working and chemical synthesis.
• Has a characteristics “Shrek” or “hiss” sound.
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27. LAMINAR MODE FLAME TORCHES
• Such flames have low velocities, length as long as 1meter.
• Flame is emitted with soothing hum .
• The cathode diameters are small and the nozzle throats are large(upto 125mm)
• Used for spherodizing and melting ceramics.
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28. HIGH POWER TORCHES
• These torches are made for high temperature arc tunnels and are operated at very high currents(2000amps or
higher).
• To avoid electrode erosion , special magnetic confining fields are used at the nozzle.
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29. TRANSFERRED ARC TORCHES
1) Cutting torch
• Single flow torch
• Dual flow torch
• Multiport nozzle torch
• Oxygen plasma cutting torch
2) Welding torches
3) Micro or needle torches
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30. SINGLE FLOW TORCH
 Consists of disk shaped ,tapering cathode .
 Throat length of nozzle is 3mm to 5mm.
 High flow rates of gas.
 High velocity of flame.
 Suitable for cutting steels ,aluminium & copper.
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31. DUAL FLOW TORCH
 An additional gas flow surrounding the main
arc is provided.
 In carbon steel cutting, the dual gas flow steam
is of oxygen, so that the plasma cutting is
agumented by oxygen cutting to achieve very
high cutting speed.
 Gas flow shields workpiece.
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32. MULTIPORT NOZZLE TORCH
 The dual flow concept is used in a different form by
providing part of the plasma gas as shielding flow
through small ports surrounding the main orifice of the
nozzle.
 This flow constricts the arc and also shields the work
piece.
 It has the nozzle with multiport , the Gas flow shields the
gap.
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33. OXYGEN PLASMA CUTTING TORCH
 With zirconium as cathode , torches can be used with oxygen plasma for short duration electrode life.
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34. WELDING TORCHES
 Cathodes are of small diameter.
 Nozzles are longer.
 Torches operate at low velocity & minimum
turbulence so that the molten metal is not thrown
away.
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35. MICRO OR NEEDLE TORCHES
 These are similar to welding torches.
 Operates at low power rate (1kw).
 Used for welding , cutting of foils & wire
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36. GASES USED IN PAM
 Aluminium & magnesium can be cut with
nitrogen , nitrogen hydrogen mix or argon
hydrogen mix.
 Stainless steel (50mm thick) can be cut by
nitrogen hydrogen mix.
 Carbon steel can be cut with oxygen.
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37. THANK YOU
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38. 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.
• Sufficient literature on plasma arc welding is available but little information regarding plasma arc surfacing and
spraying exist.
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39. PLASMA ARC SURFACING
• Surfacing is defined as the deposition of filler metal on metal surface to obtain desired properties or
dimensions.
• It is usually employed to extend the life of a part which may otherwise have all the properties
necessary for an engineering application, or to replace metal which has worn out or corroded away.
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40. PLASMA ARC SPRAYING
• Spray coating is a process in which a surface of arbitrary thickness is obtained by spraying the previously
prepared surface of the base material with droplets of a molten material.
• Plasma spraying is a recent development in the filed of metalizing and has been gaining wider use as a method
for producing surface coating of refractory materials and for fabrication of free standing shapes.
• The utilization of plasma torches for spraying protective layers has brought about a rapid progress in coating
techniques.
• A higher operating temperature and the possible use of inert atmosphere are the main advantages derived from
this innovation
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41. SPRAY COATING WITH PLASMA
• The technique is similar to that of coating with oxy-fuel or electric arc metallizers.
• The process consists of two basic operations, the preparation of the surface to be coated and spraying proper.
• The surface preparation is of the parent material. The surface of the parent metal is cleaned by degreasing and
appropriately roughened by grit blasting.
• Degreasing in a hot alkaline bath of trichloetrylene is indispensable if a part has been contaminated with oil.
• In spraying with plasma guns, grit blasting will usually be sufficient because plasma produces coating with very
good adhesion.
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42. THANK YOU
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