2. Introduction
Manufacturing Technology I
Metal casting (Sand casting and other casting processes)
Materials Joining (Arc welding, TIG, EBW, PAW, etc.)
Bulk deformation (Metal Forming – Forging, Rolling, Extrusion)
Sheet metal processes (Shearing, bending, drawing, etc.)
Manufacturing of plastic materials (Injection molding, etc).
Manufacturing Technology II (Material removal process)
Metal Cutting or Mechanical Abrasion
Centre lathe and special purpose lathes
Shaper, Planer, Slotter, Milling, Drilling, Broaching, Gear cutting, etc.
Grinding, Honing, Lapping, etc.
CNC and DNC
3. Introduction – Contd.
3
Machining – produces finished products with high degree of accuracy.
Conventional machining
Utilizes cutting tools (harder than workpiece material).
Needs a contact between the tool and workpiece.
Needs a relative motion between the tool and workpiece.
Absence of any of these elements – makes the process a unconventional or
nontraditional one.
Big boon to modern manufacturing industries.
The need for higher productivity, accuracy and surface quality – led to
combination of two or more machining actions, called hybrid machining
processes.
4. History of Machining
4
In ancient days – hand tools (stones, bones or stick).
Later – hand tools of elementary metals (bronze or iron)
Till 17th Century – tools were either hand operated or driven mechanically by
very elementary methods.
Wagons, ships, furniture, etc. – were produced.
Introduction of water, steam and electricity – power driven machine tools
Caused a big revolution in 18th and 19th centuries.
1953 – Numerical control machine tools – enhanced the product productivity
and accuracy.
10. Need for Unconventional Machining
10
• Greatly improved thermal, mechanical and chemical properties of modern materials –
Not able to machine thru conventional methods. (Why???)
• Ceramics & Composites – high cost of machining and damage caused during machining
– big hurdles to use these materials.
• In addition to advanced materials, more complex shapes, low rigidity structures and
micro-machined components with tight tolerances and fine surface finish are often
needed.
• To meet these demands, new processes are developed.
• Play a considerable role in aircraft, automobile, tool, die and mold making industries.
11. Need for Unconventional Machining
11
• Very high hardness and strength of the material. (above 400 HB.)
• The work piece is too flexible or slender to support the cutting or grinding forces.
• The shape of the part is complex, such as internal and external profiles, or small
diameter holes.
• Surface finish or tolerance better than those obtainable conventional process.
• Temperature rise or residual stress in the work piece are undesirable.
13. Mechanical Based Processes
13
1. Working principles
2. Equipment used
3. Process parameters
4. MRR
5. Variation in techniques used
6. Applications
AJM
WJM
AWJM
USM
14. 14
Electrical Based Processes
1. Working principle
2. Equipment used
3. Process parameters
4. Surface finish & MRR
5. Electrode/Tool
6. Power & Control circuits
7. Tool wear
8. Dielectric
9. Flushing
10. Applications
Electrical
EDM
WEDM
15. 15
Chemical & Electrochemical Based
Processes
1. Working principles
2. Etchants & Maskants
3. Techniques of applying maskants
4. Process parameters
5. Surface finish & MRR
6. Electrical circuits in case of ECM
7. Applications
CHM
ECM
ECG
ECH
16. 16
Thermal Based Processes
1. Working principles
2. Equipment used
3. Types
4. Beam control techniques
5. Applications
LBM
PAM
EBM
17. Mechanical based Unconventional Processes
USM – thru mechanical abrasion
in a medium (solid abrasive
particles suspended in the
fluid)
WJM – Cutting by a jet of fluid
AWJM – Abrasives in fluid jet.
IJM – Ice particles in fluid jet.
Abrasives or ice – Enhances
cutting action.
17
18. Thermal based Unconventional Processes
Thru – melting & vaporizing
Many secondary phenomena –
surface cracking, heat
affected zone and striations.
Heat Source:
Plasma – EDM and PBM.
Photons – LBM
Electrons – EBM
Ions – IBM
Machining medium: different
for different processes.
18
19. Chemical & Electrochemical based
Unconventional Processes
CHM – uses Chemical dissolution
action in an etchant.
ECM – uses Electrochemical
dissolution action in an
electrolytic cell.
19
21. Ultrasonic Machining
• In ultrasonic machining (USM), also called ultrasonic grinding, high-frequency
vibrations delivered to a tool tip, embedded in an abrasive slurry, by a booster or
sonotrode, create accurate cavities of virtually any shape; that are, negatives of
the tool.
• Since this method is non-thermal, non-electrical, and non-chemical, it produces
virtually stress-free shapes even in hard and brittle work-pieces. Ultrasonic drilling
is most effective for hard and brittle materials; soft materials absorb too much
sound energy and make the process less efficient.
6/27/2015
22. Ultrasonic Machining
• Almost any hard and brittle material, including
aluminum oxides, silicon, silicon carbide, silicon nitride,
glass, quartz, sapphire, ferrite, fiber optics, etc., can be
ultrasonically machined.
• The tool does not exert any pressure on the work-piece
(drilling without drills), and is often made from a softer
material than the work-piece, say from brass, cold-rolled
steel, or stainless steel and wears only slightly.
• The roots of ultrasonic technology can be traced back to
research on the piezoelectric effect conducted by Pierre
Curie around 1880. He found that asymmetrical crystals
such as quartz and Rochelle salt (potassium sodium
titrate) generate an electric charge when mechanical
pressure is applied. Conversely, mechanical vibrations are
obtained by applying electrical oscillations to the same
crystals. Ultrasonic waves are sound waves of frequency
higher than 20,000 Hz.
6/27/2015
23. Ultrasonic Machining
• The tool, typically vibrating at a low
amplitude of 0.025 mm at a frequency of
20 to 100 kHz, is gradually fed into the
work-piece to form a cavity corresponding
to the tool shape.
• The vibration transmits a high velocity
force to fine abrasive grains between the
tool and the surface of the work-piece. In
the process material is removed by micro-
chipping or erosion with the abrasive
particles.
• The grains are in a water slurry which also
serves to remove debris from the cutting
area. The high-frequency power supply for
the magneto-strictive or piezoelectric
transducer stack that drives the tool is
typically rated between 0.1 and 40 kW.
6/27/2015
Channels and holes ultrasonically machined in a polycrystalline silicon wafer.
24. Ultrasonic Machining
• The abrasive particles (SiC, Al2O3 or BC d= 8~
500 µm) are suspended in water or oil.
• The particle size and the vibration amplitude
are ususally made about the same.
• The particle size determines the roughness or
surface finish and the speed of the cut.
• Material removal rates are quite low, usually
less than 50 mm3/min.
6/27/2015
Coin with grooving carried out with USM
25. Ultrasonic Machining
• The mechanical properties and fracture
behavior of the work-piece materials also
play a large role in both roughness and
cutting speed. For a given grit size of the
abrasive, the resulting surface roughness
depends on the ratio of the hardness (H)
to the modulus of elasticity (E). As this
ratio increases, the surface roughness
increases.
• Higher H/E ratios also lead to higher
removal rates: 4 mm3/min for carbide
and 11 mm3/min for glass.
6/27/2015
ultrasonic machining can be used to form intricate,
finely detailed graphite electrodes.
26. Ultrasonic Machining
• Machines cost up to $20,000, and production rates of about 2500
parts per machine per day are typical.
• If the machined part is a complex element (e.g., a fluidic element) of
a size > 1 cm2 and the best material to be used is an inert, hard
ceramic, this machining method might well be the most appropriate
6/27/2015
900 watt Sonic-mill, Ultrasonic Mill
27. Ultrasonic Machining
Advantages and disadvantages of ultrasonic machining.
6/27/2015
Advantages Disadvantages
Machining of any material regardless of conductivity Low material removal rate
Precision machining of brittle hard materials Toolwears fast
Does not produce electric, thermal or chemical defe cts at
the surfa ce
Machining area and depth are quite restricted
Can drill circular or non-circular holes in very hard
materials
Less stress because of its non-thermal nature
28. Abrasive Water-Jet Cutting
• A stream of fine grain abrasives mixed with air or suitable
carrier gas, at high pressure, is directed by means of a
nozzle on the work surface to be machined.
• The material removal is due to erosive action of a high
pressure jet.
• AJM differ from the conventional sand blasting process in
the way that the abrasive is much finer and effective control
over the process parameters and cutting. Used mainly to cut
hard and brittle materials, which are thin and sensitive to
heat.
31. Typical AJM Parameters
• Abrasive
– Aluminum oxide for Al and Brass.
– SiC for Stainless steel and Ceramic
– Bicarbonate of soda for Teflon
– Glass bed for polishing.
• Size
– 10-15 Micron
• Quantity
– 5-15 liter/min for fine work
– 10-30 liter/min for usual cuts.
– 50-100 liter/min for rough cuts.
32. Typical AJM Parameters
• Medium
– Dry air, CO2, N2
– Quantity: 30 liter/min
– Velocity: 150-300 m/min
– Pressure: 200-1300 KPa
• Nozzle
– Material: Tungsten carbide or saffire
– Stand of distance: 2.54-75 mm
– Diameter: 0.13-1.2 mm
– Operating Angle: 60° to vertical
33. Typical AJM Parameters
• Factors affecting MRR:
– Types of abrasive and abrasive grain size
– Flow rate
– Stand off distance
– Nozzle Pressure
34. • Advantages of AJM
• Low capital cost.
• Less vibration.
• Good for difficult to reach area.
• No heat is genera6ted in work piece.
• Ability to cut intricate holes of any hardness and brittleness in the
material.
• Ability to cut fragile, brittle hard and heat sensitive material without
damage
• Disadvantages of AJM:
• Low metal removal rate.
• Due to stay cutting accuracy is affected.
• Parivles is imbedding in work piece.
• Abrasive powder cannot be reused.
35. • Applications of AJM:
• For abrading and frosting glass, it is more economical than acid
etching and grinding.
• For doing hard suffuses safe removal of smears and ceramics
oxides on metals.
• Resistive coating etc from ports to delicate to withstand normal
scrapping.
• Delicate cleaning such as removal of smudges from antique
documents.
• Machining semiconductors such as germanium etc.
36. Water Jet Machining
• The water jet machining involves directing a high pressure (150-1000
MPa) high velocity (540-1400 m/s) water jet(faster than the speed of
sound) to the surface to be machined. The fluid flow rate is typically from
0.5 to 2.5 l/min
• The kinetic energy of water jet after striking the work surface is reduced
to zero.
• The bulk of kinetic energy of jet is converted into pressure energy.
• If the local pressure caused by the water jet exceeds the strength of the
surface being machined, the material from the surface gets eroded and
a cavity is thus formed.
• The water jet energy in this process is concentrated over a very small
area, giving rise to high energy density(1010
w/mm2
) High
38. Continue…
• Water is the most common fluid used, but additives such as alcohols, oil
products and glycerol are added when they can be dissolved in water to
improve the fluid characteristics.
• Typical work materials involve soft metals, paper, cloth, wood, leather,
rubber, plastics, and frozen food.
• If the work material is brittle it will fracture, if it is ductile, it will cut well:
• The orifice is often made of sapphire and its diameter rangesfrom 1.2
mm to 0.5 mm:
39. Water Jet Equipments
• It is consists of three main units
(i) A pump along with intensifier.
(ii)Cutting head comprising of nozzle and work table movement.
(iii) filter unit for debries,pout impurities.
• Advantages
- no heat produced
- cut can be started anywhere without the need for predrilled holes
- burr produced is minimum
- environmentally safe and friendly manufacturing.
Application – used for cutting composites, plastics, fabrics, rubber, wood products
etc. Also used in food processing industry.
40. Abrasive Water jet machining
• The rate of cutting in water jet machining, particularly while cutting
ductile material, is quite low. Cutting rate can be achieved by mixing
abrasive powder in the water to be used for machining.
• In Abrasive Water Jet Cutting, a narrow, focused, water jet is mixed with
abrasive particles.
• This jet is sprayed with very high pressures resulting in high velocities
that cut through all materials.
• The presence of abrasive particles in the water jet reduces cutting
forces and enables cutting of thick and hard materials (steel plates over
80-mm thick can be cut).
• The velocity of the stream is up to 90 m/s, about 2.5 times the speed of
sound.
41.
42. Continue..
• Abrasive Water Jet Cutting process was developed in 1960s to cut
materials that cannot stand high temperatures for stress distortion or
metallurgical reasons such as wood and composites, and
traditionally difficult-to-cut materials, e.g. ceramics, glass, stones,
titanium alloys
45. The fundamentals of
electrochemical surface treatment
• Electrochemical surface treatment is based on
anodic metal dissolution.
• Metal dissolution by a) active dissolution,
b)transpassive dissolution
• Dimensional resolution is mainly determined by
current and potential distribution around a
cathodic matrix
• Forced convection removes bubbles (by H2 and O2
evolution) and oxidic and hydroxidic debris e.g.
Fe(OH)3 and other oxidation-solvolysis products
47. Electrochemical shaping of metals
Active dissol. and
mass transfer
Transpassive dissol.
With fast sweep
Transpassive dissolution
with mechanical scraping
48. Some examples of electrochemical machining of hard
metals: Primary Current density distribution
49. Current density distributions
• Primary: neglects charge transfer kinetics
and influence of mass transfer.Decisive:
only distributions of pure Ohmic resistances
• Secondary: Adding charge transfer
resistances to purely Ohmic resistances
• Tertiary: Mainly determined by mass
transfer conditions
51. Addition of electrolyte resistances Rp and Rv add
to charge transfer resistance to give primary and
secondary current distributions
52. Even current density distribution
At rotating disc electrode under mass
transport limited condition ( limiting
current density) is a typical tertiary
c.d. distribution
53. Electropolishing
Mass transfer controlled transport of
dissolution products through a thin,
statistically fluctuating layer of debris
generates the polishing effect
Current densities amount from hundred
to several hundred mA cm-2
54. Electropolishing electrolytes
• Composition given in lecture manuscript
• Almost all contain phosphoric acid
• Almost all – exception electropolishing W –
are strongly acidic
• Some contain organic cosolvents
• Are obtained and optimized by trial and
error
55. Electrochemical machining electrolytes
• Are neutral (neither basic nor acidic) with the
exception of basic electrolyte for molybdenum
• Most of them contain sodium nitrates or
perchlorate
• Current densities amount to several A cm-2
• Copious exchange of electrolyte must be secured
to remove Joule`s heat and all debris
58. The surface of the workpeace which is farther
away charges more slowly than next to the tool
59. ح = l x ρ x Cspec
with l = length of current line
ρ = specific resistance of
electrolyte (approximately 10 Ω cm)
ζ is charging time; as potential changes
exponentially with time:
Φo – Φ = (Φo – Φ )t=(1-exp(-t/ )ح
60. Improve the resolution of anodic
dissolution from millimetres to
micrometres
Applying pulses in nanoseconds
instead of direct currents
61. Example from L.Cagnon, V. Kirchner, M. Kock, R. Schuster, G. Ertl,
Th. Gmelin and H. Kueck, Z. Phys. Chem. 217, (2003), 299 - 313
62. Example from M. Kock, V.
Kirchner and R. Schuster,
Electrochim. Acta 48, (2003)
3213 - 3219
63. The LIGA – Process for building
Micro-structures by x-ray-assisted masking
and cathodic metal deposition
• Resolution is determined by precision
of masks and their copy on photo-
resist – hence x-ray copying
64.
65. Summary
• With maximal cutting rates corresponding to
several A cm-2 electrochemical machining is too
slow to be generally applicable instead of
mechanical machining
• But ultrahard alloys can only be treated by
electrochemical machining which usually gives
also a good polishing finish
• Applying nanosecond pulses increases the
dimensional resolution, so that also micrometer
structures can be produced – it is still an open
question how to utilize these possibilities in
commercial processes.
67. EDM Operation
One of the most widely used non-traditional processes
Shape of a finished work surface produced by a shape of electrode
tool
Can be used only on electrically conducting work materials
Requires dielectric fluid, which creates a path for each discharge as
fluid becomes ionized in the gap.
Metal is melted/vaporized by the series of electrical discharges
Can be very precise and produces a very good surface finish
68. Work Materials in EDM
Work materials must be electrically conducting
Hardness and strength of work material are not
factors in EDM
Material removal rate depends on melting point of
work material
69. Module 4a 4
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
70. Special form of EDM uses small diameter wire as electrode to cut a
narrow kerf in work
Wire EDM
71. Operation of Wire EDM
Work is fed slowly past wire along desired cutting path.
CNC used for motion control.
While cutting, wire is continuously advanced between supply
spool and take-up spool to maintain a constant diameter.
Dielectric fluid is required.
Applied using nozzles directed at tool-work interface or
submerging work part
72. Wire EDM Applications
Ideal for stamping die components
Since kerf is so narrow, it is often possible to fabricate
punch and die in a single cut
Other tools and parts with intricate outline shapes,
such as lathe form tools, extrusion dies, and flat
templates
74. Laser-Beam Machining
Uses a concentrated beam of light to vaporize
part of the workpiece
Usually produces a rough surface with a heat-
affected zone
Can cut holes as small as .005 mm with
depth/diameter ratios of 50:1
75. Uses the light energy from a laser to remove material by
vaporization and ablation
Laser Beam Machining (LBM)
The punch
is a light
beam
78. Laser-Beam Machining
Example of a part cut by laser-beam machining
Splatter marks appear where the laser first cuts into the material
79. Laser-Beam Machining
Design Considerations:
- Non-reflective workpiece surfaces are
preferable
- Sharp corners are difficult to produce; deep
cuts produce tapers
- Consider the effects of high temperature on
the workpiece material
80. LBM Applications
Drilling, slitting, slotting, scribing, and marking
operations
Drilling small diameter holes - down to 0.025 mm (0.001
in)
Generally used on thin stock
Work materials: metals with high hardness and strength,
soft metals, ceramics, glass and glass epoxy, plastics,
rubber, cloth, and wood
81. Electron Beam Machining
Vaporizes material using electrons accelerated
to 50-80% the speed of light
Produces finer surface finish and narrower cut
width than other thermal cutting processes
Requires a vacuum; generates hazardous X rays
85. Objectives
• Define plasma arc cutting (PAC).
• Explain how a PAC cutter operates.
• Identify the parts of a PAC cutter.
• Explain advantages and disadvantages of the
PAC system.
• Identify materials that can be cut with the
PAC.
• Explain safety associated with using the
plasma arc cutter.
86. History
• The plasma-arc process had its origin almost 50 years ago,
during the height of World War II.
• Plasma cutting was accidentally discovered by an inventor
who was trying to develop a better welding process.
• In an effort to improve the joining of aircraft materials, a
method of welding was developed that used a protective
barrier of inert gas around an electric arc to protect the
weld from oxidation.
87. History
• It was discovered that by restricting the opening through which the
inert gas passed, the heat produced by the process was greatly
increased.
• At the same time, the smaller opening caused the flow of gas to speed
up dramatically, ultimately blowing out a channel in the work.
• The plasma-arc cutting process started seeing commercial use in the
first few years of the sixties.
• It was an extremely expensive process to undertake, and most cutting
was performed by large burning services.
89. Plasma
• Plasma has two meanings.
– The fluid portion of blood.
– A state of matter that is found in the region of an electrical
discharge (arc).
• Plasma created by an arc is an ionized gas that has both
electrons and positive ions whose charges are nearly equal
to each other.
• Plasma is present in any electrical discharge.
90. Plasma
• Plasma consists of charged particles that conduct the electrons across
the gap.
– Both the glow of a neon tube and the bright fluorescent light bulb are
examples of low-temperature plasmas.
• Plasma results when a gas is heated to a high enough temperature to
convert into positive and negative ions, neutral atoms, and negative
electrons.
– The temperature of an unrestricted arc is about 11,000°F
– The temperature created when the arc is concentrated to from a plasma is
about 23,000°F.
91. Machines
• Most, if not all, of the light portable plasma cutters are 110
volt machines.
– Suited primarily for cutting sheetmetal and other light work.
• The next level up are the 220 volt machines with 50 to 80
amp output current.
– These are portable from the standpoint that one person can put it
on a truck and take it to the job.
92. How PAC works
• Plasma cutters work by sending an electric arc through a gas that is passing
through a constricted opening.
– The gas can be shop air, nitrogen, argon, oxygen. etc.
• This elevates the temperature of the gas to the point that it enters a 4th state
of matter.
– Scientists call this additional state plasma. As the metal being cut is part of the
circuit, the electrical conductivity of the plasma causes the arc to transfer to the
work.
• The restricted opening (nozzle) the gas passes through causes it to squeeze by
at a high speed. This high speed gas cuts through the molten metal.
• The gas is also directed around the perimeter of the cutting area to shield the
cut.
93. How a Plasma Cutter works
• A complete plasma cutter consists of a
– power supply,
– a ground clamp,
– and a hand torch.
• The main function of the power supply is to convert the AC line voltage
into a user-adjustable regulated (continuous) DC current.
• The hand torch contains a trigger for controlling the cutting, and a
nozzle through which the compressed air blows. An electrode is also
mounted inside the hand torch, behind the nozzle.
95. Operation
• Initially, the electrode is in contact with
(touches) the nozzle.
• When the trigger is squeezed, DC current
flows through this contact.
• Next, compressed air starts trying to force its
way through the joint and out the nozzle.
96. Operation
• Air moves the electrode back and establishes a fixed gap between it
and the tip.
– The power supply automatically increases the voltage in order to maintain
a constant current through the joint - a current that is now going through
the air gap and turning the air into plasma.
• Finally, the regulated DC current is switched so that it no longer flows
through the nozzle but instead flows between the electrode and the
work piece. This current and airflow continues until cutting is halted.
97. Starting the Arc
• In many of today's better plasma cutters, a
pilot arc between the electrode and nozzle is
used to ionize the gas and initially generate
the plasma prior to the arc transfer.
• Other methods that have been used are
touching the torch tip to the work to create a
spark, and the use of a high-frequency starting
circuit.
98. PAC versus Oxy-Fuel
• In general, fabricators consider oxy-fuel to be superior to
plasma for cutting steel when thicknesses exceed about 1/2
inch.
• This is because of the slight bevel (4 to 6 degrees) in the cut
face that plasma produces. It is not noticeable in thinner
materials, but becomes more so as thicknesses increase.
Also, at thicknesses above 1/2 inch, plasma has no cutting
speed advantage over oxy-fuel.
99. PAC versus Oxy-Fuel
• If you are planning to cut non-ferrous metals such as
stainless or aluminum, which cannot be cut by oxy-fuel,
consider a 50 to 80 amp, 220 volt plasma cutter.
• Plasma cutting is by far the simplest and most economical
way to cut a variety of metal shapes accurately.
• Plasma cutters can cut much finer, faster, and more
automatically than oxy-acetylene torches.
101. Plasma Torch
• A device depending on its design, which
allows the creation and control of the plasma
for welding and cutting processes.
• Plasma torch supplies electrical energy to a
gas to change it into the high energy state of a
plasma
102. Torch Body
• Made of a special plastic that is resistant to
high temperatures, ultraviolet light, and
impact.
• Provides a good grip area and protects the
cable and hose connections to the head.
• Torch body is available in a variety of lengths
and sizes.
103. Torch head
• Torch head is attached to the torch body where the cables and hoses
attach to the electrode tip, nozzle tip, and nozzle.
• Torch and head may be connected at any angle such as 90°, 75°, 180°
(straight), or it can be flexible.
• Because of the heat in the head produced by the arc, some provisions
for cooling the head and its internal parts must be made.
– Cooling for low power torches may be either by air or water.
– High power torches must be liquid cooled.
• It is possible to replace just the torch head on most torches if it
becomes worn or damaged.
104. Power switch
• Manual power switch used to start and stop
the power source, gas, and cooling water.
• Thumb switch on the torch body most often
used.
• Foot control can be used.
105. Common Torch Parts
• Parts of the torch
– Electrode
– Tip nozzle insulator
– Nozzle tip
– Nozzle guide
• Nozzles and the metal parts
are usually made out of
copper, and they may be
plated.
• The plating of copper parts
will help stay spatter-free
longer.
107. Electrode tip
• Electrode tip is often made of copper electrode with a
tungsten tip attached.
• Use of copper/tungsten tip has improved the quality of
work they can produce.
• By using copper, the heat generated at the tip can be
conducted away faster.
• Keeping the tip as cool as possible lengthens the life of the
tip and allows for better quality cuts for a longer time.
• Old torches you must grind the tungsten electrode
108. Nozzle Insulator
• Located between the electrode tip and the
nozzle tip
• Provides the critical gap spacing and electrical
separation of the parts.
• The spacing between the electrode tip and
nozzle tip called the electrode setback is
critical to the proper operation.
109. Nozzle tip
• Has a small, cone-shaped, constricting orifice in the center.
• The electrode setback space, between the electrode tip and nozzle tip is
where the electric current forms the plasma.
• The preset close-fitting parts provide the restriction of the gas in the presence
of the electric current so the plasma can be generated.
• The diameter of the constricting orifice and electrode setback are major
factors in the operation of the torch.
• As the diameter of the orifice changes, the plasma jet action will be affected.
• When the setback distance is changed, the arc voltage and current flow will
change.
110. Nozzle
• Sometimes call the cup.
• Made of ceramic or any other high-
temperature resistant substance.
• Helps prevent the internal electrical parts
from accidental shorting and provides control
of the shielding gas or water injection if they
are used.
111. Water shroud
• Water shroud nozzle may be attached to some
torches.
• Water surrounding nozzle tip is used to
control the potential hazards of light, fumes,
noise, or other pollutants produced.
112. Power Requirements
• Requires a drooping arc voltage or constant current, direct
current, high-voltage, power supply.
• Drooping arc voltage allows for a rapid start of the plasma
arc at the high open circuit voltage and more controlled
plasma arc aas the voltage rapidly droops.
– Ranges from 50-200 volts closed circuit
– Ranges from 150-400 volts open circuit.
113. Amperages
• High voltage
• Amperage range from 10-200 amps.
• Some automated machines may have 1,000
ampere capacities.
• Higher the amperage capacity the faster and
thicker they will cut.
114. Cutting speeds
• High cutting speeds are possible
– Up to 300 inches per minute
– 25 feet a minute
– ¼ mile an hour
115. Metals to be cut
• Any material that is conductive can be cut using the PAC process.
• In a few applications nonconductive materials can be coated with conductive
material so that they can be cut.
• Most popular materials cut
– Car o steel up to 1”
– Stai less steel up to 4”
– Alu i u up to 6”
• Other metals commonly cut
– Copper
– Nickel-alloys
– High-strength, low alloy steels
– Clad materials
– Expanded metal
116. Starting Methods
• Two methods are used to establish a current
path through the gas
– High frequency alternating current
– Momentary shorting
117. High frequency alternating current
• Most common
• Uses a high frequency alternating current carried through the
conductor, the electrode and back from the nozzle tip.
• High frequency current will ionize the gas and allow it to carry the
initial current to establish a pilot arc.
• After the pilot arc has been started, the high frequency starting circuit
can be stopped.
• When the torch is brought close enough to the work, the primary arc
will follow the pilot arc across the gap, and the main plasma is started.
• Once the main plasma is started, the pilot arc power can be shut off.
118. Momentary shorting
• Requires the electrode tip and nozzle tip to be
momentarily shorted together.
• This is accomplished by automatically moving
them together and immediately separating
them again.
119. Safety
• Electrical shock
– Because the open circuit voltage is much higher for this process than for any other,
extra caution must be taken.
– The chance that a fatal shock could be received from this equipment is much
higher than from any other welding equipment.
• Moisture
– Often water is used with PAC torches to cool the torch, improve the cutting
characteristics, or as a part of a water table.
– A y ti e ater is used it’s ery i porta t that there e o leaks or splashes.
– The chance of electrical shock is greatly increased if there is no moisture on the
floors, cables, or equipment.
120. Safety
• Noise
– Because the plasma stream is passing through the nozzle orifice at a high speed, a loud sound
is produced.
– The sound level increases as the power level increases.
– High le els of sou d a ha e a u ulati e effe t o o e’s heari g.
• Light
– PAC produces light radiation in all three spectrums.
• Large quantity of visible light, if the eyes are unprotected, will cause night blindness.
• Most dangerous of the lights is ultraviolet. This light can cause burns to the skin and eyes.
• Infrared can be felt as heat, and it is not as much a hazard.
• Fumes
– PAC produces a large quantity of fumes that are potentially hazardous.
– A specific means for removing them from the work space should be in place.
121. Safety
• Gases
– Some of the plasma gas mixtures include
hydrogen.
– Hydrogen is a flammable gas.
– Make sure that the system is leak-proof.
• Sparks
– Danger of accidental fire is present.
– Use a fire watch person if excessive sparks are
present.
