Abrasive jet Machining (Non Traditional Machining)

1. Module 2
Dr TSN, JSSATEB

2. Abrasive Jet Machining
 It is the material removal process where the
material is removed by high velocity stream of
air/gas or water and abrasive mixture .
 An abrasive is small, hard particle having sharp
edges and an irregular shape .
 High velocity jet is aimed at a surface under
controller condition
Dr TSN, JSSATEB

3. Cont…
 This stream is directed by means of a suitably
designed nozzle on to the work surface to be
machined.
 Metal removal occurs due to erosion caused by
the abrasive particles impacting the work
surface at high speed.
Dr TSN, JSSATEB

4. Principle
“ When a stream of abrasive particles carried in a
gas medium from nozzle is made to impinge on
the work surface at a high velocity, material can
be removed from the workpiece”
Metal removal occurs due to erosion caused by the
abrasive particle imparting the work surface at
high speed.
Dr TSN, JSSATEB

5. Process
• Jet of abrasive particles is carried by carrier gas or
air. The high velocity stream of abrasives is
generated by converting pressure energy of carrier
gas or air to its Kinetic energy and hence high
velocity jet.
• Nozzles directs abrasive jet in a controlled manner
onto work material. The high velocity abrasive
particles remove the material by micro-cutting
action as well as brittle fracture of the work
material.
Dr TSN, JSSATEB

6. Cont…
Dr TSN, JSSATEB

7. Cont…
• Process of removal of material by impact erosion
through the action of concentrated high velocity
stream of grit abrasives entrained in high velocity
gas stream.
• In AJM, generally,
abrasive particles size of around 50 microns grit
size
 velocity of 200 m/s
nozzle of ID 0.5mm
stand off distance of around 2mm.
Dr TSN, JSSATEB

8. Equipment
Dr TSN, JSSATEB

9. AJM
Dr TSN, JSSATEB

10. Equipment
Abrasive jet Machining consists of
1. Gas propulsion system
2. Abrasive feeder
3. Machining Chamber
4. Abrasives
5. AJM Nozzle
Dr TSN, JSSATEB

11. Gas Propulsion System
• Supplies clean and dry air.
• Air, Nitrogen and carbon dioxide to propel the abrasive
particles.
• Gas may be supplied either from a compressor or a
cylinder.
• In case of a compressor, air filter cum drier should be
used to avoid water or oil contamination of abrasive
powder. Dr TSN, JSSATEB

12. Cont…
• Gas should be non-toxic, cheap, easily available.
• It should not excessively spread when discharged from
nozzle into atmosphere.
• The propellant consumption is of order of 0.008 m3/min
at a nozzle pressure of 5 bar and
• Abrasive flow rate varies from 2 to 4 gm/min for fine
machining and 10 to 20 gm/min for cutting operation.
Dr TSN, JSSATEB

13. Abrasive Feeder
• Required quantity of abrasive particles is supplied
by abrasive feeder.
• The filleted propellant is fed into the mixing
chamber where in abrasive particles are fed
through a sieve.
• The sieve is made to vibrate at 50-60 Hz and
mixing ratio is controlled by the amplitude of
vibration of sieve.
Dr TSN, JSSATEB

14. Cont…
• The particles are propelled by carrier gas in a mixing
chamber.
• Air abrasive mixture moves further to nozzle.
• The nozzle imparts high velocity to mixture which is
directed at work piece surface.
Dr TSN, JSSATEB

15. Machining chamber
• It is well closed so that concentration of abrasive
particles around the working chamber does not reach to
the harmful limits.
• Machining chamber is equipped with vacuum dust
collector.
• Special consideration should be given to dust collection
system if the toxic material are being machined.
Dr TSN, JSSATEB

16. Abrasives
• Aluminum oxide (Al2O3) Silicon carbide (SiC) Glass
beads, crushed glass and sodium bicarbonate are some
of abrasives used in AJM.
• Selection of abrasives depends on MRR , type of work
material , machining accuracy.
Dr TSN, JSSATEB

17. AJM nozzle
• AJM nozzle is usually made of tungsten carbide or
sapphire which has resistance to wear.
• The nozzle is made of either circular or rectangular
cross section and head can be straight, or at a right
angle.
Dr TSN, JSSATEB

18. Cont…
• It is so designed that loss of pressure due to the bends,
friction etc is minimum possible.
• With increase in wear of a nozzle, the divergence of jet
stream increases resulting in more stray cutting and
high inaccuracy.
Dr TSN, JSSATEB

19. Dr TSN, JSSATEB

20. Dr TSN, JSSATEB

21. Process Parameter/ Variables in AJM
• Carrier Gas,
• Type of abrasive,
• Size of abrasive grain,
• Abrasive Flow rate and velocity ,
• Mean number of Abrasive particles per unit
volume of the carrier gas,
• Work material,
• Stand Off Distance (SOD)
Dr TSN, JSSATEB

22. Carrier Gas
• Composition – Air, CO2, N2
• Density – 1.3 kg/m3
• Velocity - 500 to 700 m/s
• Pressure - 2 to 10 bar
• Flow rate - 5 to 30 microns
Dr TSN, JSSATEB

23. Cont…
• Carrier gas, to be used in AJM, must not flare (flash)
excessively when discharged from the nozzle into
the atmosphere.
• Further, the gas should be nontoxic, cheap, easily
available and capable of being dried and cleaned
without difficulty.
• The gases that can be used are air, carbon dioxide or
nitrogen.
Dr TSN, JSSATEB

24. Cont…
• Air is most widely used owing to easy availability
and little cost.
• All abrasive powders supplied by the manufacturers
can be run with clean air, provided air filters have
been installed in the air lines.
Dr TSN, JSSATEB

25. Type of abrasive
• Material – Al2O3 SiC Glass beads Crushed glass
Sodium bi carbonate
• Shape – irregular/regular
• Size – 10 to 50 microns
• Mass flow – 2-20 gm/min
Dr TSN, JSSATEB

26. Cont…
• The choice of abrasive depends on the type of
machining operation, for example, roughing,
finishing, etc.,
• Work material and cost.
• The abrasive should have a sharp and irregular
shape and be fine enough to remain suspended in the
carrier gas and should also have excellent flow
characteristics. Dr TSN, JSSATEB

27. Cont…
• The abrasives used for cutting are aluminum oxide
and silicon carbide, whereas sodium bicarbonate,
dolomite, glass beads. Etc. are used for cleaning,
etching, deburring and polishing.
• Re use of abrasives is not recommended because
contamination clogs the orifice of the nozzle.
Dr TSN, JSSATEB

28. Grain Size
• Finer grains are less irregular in shape, and hence,
possess lesser cutting ability.
• Moreover, finer grains tend to stick together and
choke the nozzle.
• The most favorable grain sizes range from 10 to 50
microns.
• Coarse are recommended for cutting, whereas finer
grains are useful in polishing, deburring, etc.
• For the erosion of glass by silicon carbide (grain size
25 microns), the minimum jet velocity has been
found to be around 150 m/s.
Dr TSN, JSSATEB

29. Grain size
Dr TSN, JSSATEB

30. Dr TSN, JSSATEB

31. Abrasive flow rate and Velocity
• Increase in the flow rate of abrasive, increases the
metal removal rate Because more abrasive particle
are available for cutting.
• When the flow rate exceeds 14 gm/ min, the abrasive
velocity decreases, thereby reducing the metal
removal rate.
Dr TSN, JSSATEB

32. Cont...
• For the erosion of the worksurface by the abrasives,
the minimum jet velocity is found to be 150m/sec.
• The jet velocity is a function of the nozzle pressure,
nozzle design, abrasive grain size, and the mean
number of abrasives per unit volume of the carrier
gas.
Dr TSN, JSSATEB

33. Stand Off Distance (SOD)/ Nozzle Tip Distance(NTD)
• Stand Off Distance is defined as the distance
between the face of the nozzle and the surface of
the work
• A large SOD results in flaring of jet which leads to
poor accuracy.
• It is clear from figure that MRR increase with nozzle
tip distance or Stand off distance up to certain
distance and then decreases.
Dr TSN, JSSATEB

34. Cont...
• Penetration rate also increases with SOD and then
decreases.
• Decrease in SOD improves accuracy, decreases per
width, and reduces taper in machined groove.
• However light operation like cleaning, frosting etc
are conducted with large SOD.(say 12.5 to 75mm)
Dr TSN, JSSATEB

35. Dr TSN, JSSATEB

36. Dr TSN, JSSATEB

37. Mean number of Abrasive particles per unit
volume of the carrier gas,
• The mean number of abrasive particle per unit volume
of the carrier gas ca be obtained by mixing ration M
• A large value of M should result in higher rate of
metal removal.
Dr TSN, JSSATEB

38. Cont....
• Large abrasive flow rate has been found to adversely
influence jet velocity and some times even clog the
nozzle
• For given condition there is an optimum value of M that
gives maximum metal removal rate.
Dr TSN, JSSATEB

39. Nozzle Design
• Since abrasive particle leave the nozzle at a very high
velocity, it is subjected to abrasion wear, to overcome
this effect, wear resistant materials like tungsten
carbide, sapphire etc. are used to manufacture the
nozzle.
• The nozzle should be carefully designed so that the
pressure loss due to bends, friction etc.. is minimum.
• Nozzles may be either circular or rectangular in cross
section with suitable dimensions.
Dr TSN, JSSATEB

40. Process capability / Characteristics of AJM
• Metal Removal Rate (MRR)
• Accuracy
• Surface Finish
Dr TSN, JSSATEB

41. cont...
1. Material removal rate – 0.015 cm3/min
2. Narrow slots – 0.12 to 0.25mm ± 0.12mm
3 Surface finish -0.25 micron to 1.25 micron
4 Sharp radius up to 0.2mm is possible
5. Steel up to 1.5mm ,Glass up to 6.3mm is possible to cut
6. Machining of thin sectioned hard and brittle materials is possible.
Dr TSN, JSSATEB

42. Material Removal Rate (MRR)
• It is clear from the figure that at a particular pressure
MRR increase with increase of abrasive flow rate and is
influenced by size of abrasive particles. But after
reaching optimum value, MRR decreases with further
increase of abrasive flow rate.
• This is owing to the fact that Mass flow rate of gas
decreases with increase of abrasive flow rate and hence
mixing ratio increases causing a decrease in material
removal rate because of decreasing energy available for
erosion.
Dr TSN, JSSATEB

43. Cont…
Dr TSN, JSSATEB

44. Effect of Mixing ratio on MRR
Dr TSN, JSSATEB

45. Cont...
• Increased mass flow rate of abrasive will result in a
decreased velocity of fluid and will thereby decreases
the available energy for erosion and ultimately
theMRR.
Dr TSN, JSSATEB

46. Effect of Nozzle pressure on MRR
Dr TSN, JSSATEB

47. Cont...
• The abrasive flow rate can be increased by increasing
the flow rate of the carrier gas.
• This is only possible by increasing the internal gas
pressure as shown in the figure.
• As the internal gas pressure increases abrasive mass
flow rate increase and thus MRR increases.
Dr TSN, JSSATEB

48. Cont...
• As a matter of fact, the material removal rate will
increase with the increase in gas pressure.
• The abrasive must impinge on the work surface with
minimum velocity for machining glass by SIC particle
is found to be around 150m/s.
Dr TSN, JSSATEB

49. Dr TSN, JSSATEB

50. Applications
• Abrasive water jet cutting is highly used in aerospace,
automotive and electronics industries.
• In aerospace industries, parts such as titanium bodies
for military aircrafts, engine components (aluminium,
titanium, heat resistant alloys), aluminium body parts
and interior cabin parts are made using abrasive water
jet cutting.
Dr TSN, JSSATEB

51. Cont…
• In automotive industries, parts like interior trim (head
liners, trunk liners, door panels) and fibre glass body
components and bumpers are made by this process.
• Similarly, in electronics industries, circuit boards and
cable stripping are made by abrasive water jet cutting.
Dr TSN, JSSATEB

52. Cont…
• Used for machining of brittle and heat sensitive
materials like glass, quartz, semiconductor materials
like mica etc..
• Used in drilling holes, cutting slots, deburring,
trimming and removing oxides and other surface films
on the workpiece.
• Used in laboratories to prepare surfaces for strain
gauge applications.
• Removing glue and paint from paintings and leather
objects Dr TSN, JSSATEB

53. Advantages
• In most of the cases, no secondary finishing is
required
• No cutter induced distortion
• Low cutting forces on workpieces
• Limited tooling requirements
• No cutting burr
• Typical finish 125-250 microns
• Smaller kerf size reduces material wastages
• No heat affected zone
• Localizes structural changes
• No cutter induced metal contamination
Dr TSN, JSSATEB

54. Limitation
• Cannot drill flat bottom
• Cannot cut materials that degrades quickly with
moisture
• Surface finish degrades at higher cut speeds which
are frequently used for rough cutting.
• The major disadvantages of abrasive water jet
cutting are high capital cost and high
• Noise levels during operation.
Dr TSN, JSSATEB

55. Water Jet Machining (WJM)
• Using a jet of water to cut a sheet of metal
may sound impossible, but it is actually based
on a principle we learn early in our lives.
• A simple example of this when a finger is put
over part of a tap, the stream of water flows
with higher pressure so that it washes away
mud far more effectively, giving a jet cleaning
item.
Dr TSN, JSSATEB

56. Dr TSN, JSSATEB

57. Cont…
• If the jet of water is directed at a target in such a way
that, on striking the surface, the high velocity flow is
virtually stopped, then most of the kinetic energy of
the water in converted into pressure energy.
• In other words, liquid jet cutting removes material
primarily by the mechanical action of a high
velocity stream impinging on a small area. Whereby
its pressure exceeds the flow pressure of the material
being cut. Dr TSN, JSSATEB

58. Cont…
• The system used was a pulsed jet with velocity up to 500
m/s.
• The effect of varying stand off distances at pressure up to
92 MN/m2 were reported for jets with and without polymer
additive.
• Cutting capability at pressure up to 10,000 atm was
reported for a wide variety of target materials, including
wood, lead, rubber, aluminum, copper and steel.
Dr TSN, JSSATEB

59. Principle Of WJM
“ when a jet of water at a very high pressure and velocity
is made to strike the surface of the workpiece, the
kinetic energy of the jet is transformed into mechanical
work”
The material from the workpiece is rapidly removed by
the erosive force of the jet water.
Jet of water is not capable enough to cut thick metal, the
principle can be utilized to cut and slit soft and thin
workpiece materials
Dr TSN, JSSATEB

60. Equipment
A pressure source (pump) and a nozzle to form the jet
are the fundamental items in any jet cutting system.
• Other accessories include tubing and their fittings
and valves.
• Pressure generator system
• Tubing
• Nozzle
• Valve
• Cather
Dr TSN, JSSATEB

61. Pressure Generator system
It consists of the a pump, electric motor, intensifier and
accumulator and control valve.
• The pressure generator system delivers a constant and
continuous flow of high pressure water at the
prescribed pressure.
• Positive displacement pump or intensifier can be used
to supply high presure water jet
• A positive displacement pumps are suitable for low
and intermediate pressure up to 280 Mpa, and it is not
reliable for high pressure
Dr TSN, JSSATEB

62. Intensifier
• Intensifier increases the pressure of the water to high
level
• Intensifier usually consists of two cylinders with
different inner diameters.
• It makes use of the relatively low pressure oil to
generate extremely high pressure water ( up to
400Mpa) using piston and cylinder.
• the high pressure water is then fed into the
accumulator
Dr TSN, JSSATEB

63. Accumulator
• It is a pressure vessel (Reservoir)
• Which stores the high pressure water supplied by
intensifier
• This storage is required because energy is not
required continuously
• During the idle period energy is stored in the
accumulator and given out during cutting
operation
Dr TSN, JSSATEB

64. Valves
• Valves : most high pressure valves are of the needle
type.
• The main flow passage is controlled by a cone
shape on the end of the needle fixed into a seat.
• A gland seal is usually required to eliminate leaks
along the stem.
Dr TSN, JSSATEB

65. Pump
• Pump : pressurizing a liquid to the 1500-4000
MN/m2 range is usually accomplished either by
directed mechanical drive applied to a small
diameter plunger or by an intensifier
• where an intermediate pressure fluid drives a large
area piston, which in turn, drive a small diameter
ram which pumps the cutting fluid.
Dr TSN, JSSATEB

66. Tubing
• Tubing : high pressure tubing used to transport
fluid from one system component to another is
thick walled, with the ratio of the outside to inside
diameter at least 5 and sometimes as high as 10.
• The tubing may be made from a solid stainless steel
wall or a composite wall with stainless steel inside
and carbon steel as a jacket.
Dr TSN, JSSATEB

67. Tube- Fittings
• A metal to metal line contact is the usual technique
for achieving a fluid seal in high pressure tube
fittings, accomplished by drawing a cone shape
into a rounded socket.
• The cone may be machined directly onto the
tubing or a cone shaped insert may be used.
• At the highest pressures, the replaceable cone
design is the most workable.
Dr TSN, JSSATEB

68. Nozzles
• Nozzles meant to convert the high pressure liquid to
a high velocity jet present severe challenge to the
designer.
• For minimum erosion, the nozzle material should be
extremely hard.
• Yet to allow the formation of a smooth contour, the
material should be ductile and easily machinable.
Dr TSN, JSSATEB

69. WJM Operation
• The water and polymer are mixed properly and the
mixture is sent to the intensifier where its pressure is
raised.
• The hydraulic intensifier increases the intensity of the
pressure of water and supplies it to a hydraulic
accumulator since the energy is not required
continuously.
• During the idle periods, energy is stored in the
accumulator and given out during cutting.
Dr TSN, JSSATEB

70. Cont…
• The high pressure water coming from the accumulator
is controlled by a control panel from where it goes to
the nozzle after passing through the stop-start valve.
• The jet stream coming out of the nozzle cuts the work
piece and then collected in a drain system.
Dr TSN, JSSATEB

71. Process Parameters of WJM
Following are the critical parameters that affect on the
MRR
• Pressure of water
• Nozzle diameter
• Stand Off Distance (SOD)
Dr TSN, JSSATEB

72. Pressure of water
• Higher the velocity of the jet of water, the better is the
cutting action by it.
• Pressure of the water at the nozzle inlet should be high in
order to obtain a high velocity jet at the nozzle exit.
• As the pressure increases the cost and maintenance of the
equipment also increases.
• Maximum pressure of 400 Mpa is suitable for most of the
metal cutting operation
Dr TSN, JSSATEB

73. Nozzle Diameter
• Nozzle with an exit diameter of 0.05-0.35 mm gives
a coherent jet length of up to 3-4 cm
• Higher value of nozzle exit diameter gives a good
MRR
Dr TSN, JSSATEB

74. Stand Off Distance (SOD)
• Nozzle to workpiece SOD is less than 25mm
• SOD is considered as a fixed parameter and varies
in different situations
• SOD is depends on
– Type of metal
– Thickness
– Shape
– Diameter of Jet
– MRR
Dr TSN, JSSATEB

75. Advantages of WJM
1. No toxic gases or liquids are used in water jet
machining. ie. the process is a dust free process.
2. No heat produced. No heat affected zones or
mechanical stresses left on the cut surface.
3. The process gives a clean and sharp cut.
4. Fine surface finish can be obtained.
5. Soft materials up to 250mm thick can be easily
machined.
Dr TSN, JSSATEB

76. Cont…
6. Health hazards associated while cutting materials
like asbestos and fiberglass are minimized.
5. Cut can be started anywhere without the need for
pre-drilled holes
6. Burr produced is minimum
7. Environmentally safe and friendly manufacturing.
Dr TSN, JSSATEB

77. Limitations of WJM
1. Equipment is quite expensive.
2. Inefficient for thick metals.
3. Water which is re-circulated, should be filtered
accurately, otherwise results in cracks and damage to
the nozzle tip.
4. High pressure and noise of the Jet of water
necessitates safety equipments.
Dr TSN, JSSATEB

78. Cont…
5. Slight changes in water chemistry can significantly
affect the erosion resistance of some of the
components.
6. Not well suited for hard, non porous materials.
7. Brittle materials may crack.
8. Contaminated water must be treated before disposal.
Dr TSN, JSSATEB

79. Applications
• It is used from cutting thin details in stone, glass,
and metals, to rapid hole drilling of titanium.
• Used for cutting composites, plastics, fabrics,
rubber, wood products etc.
• Also used in food processing industry.
Dr TSN, JSSATEB

80. Cont…
• Used to cut non metallic materials like glass epoxy,
Graphite, Boron, Fiber reinforced plastics, leather.
• Used in aircraft industries for profile cutting of fiber
reinforce plastic .
• In mining and quarrying work , in tunnel profiles
prior to drilling and blasting
• Cutting PCB for electronic applications
Dr TSN, JSSATEB