UNCONVENTIONAL MACHINING PROCESS CLASSIFICATION-MECHANICAL ENERGY METHODS-ELECTRICAL ENERGY METHODS-CHEMICAL ENERGY METHODS-ELECTRO CHEMICAL ENERGY METHODS-THERMALENERGY METHODS.
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Non Traditional Machining is playing vital role in now a days in mechanical Industries so student it should be need sound knowledge in this particular subject due to impact of this subject i am prepare in this materials it is most useful for my students...
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By: Author-Prof.S.Sathishkumar
Advance machining processes are used where higher accuracy and surface finish is required. One of them, Abrasive jet machining is a non-traditional machining process in which a high-pressure air stream and abrasive particles impinge on a work surface through a nozzle. Abrasive jet machining (AJM) removes material through the action of a focused beam of abrasive jet directed at the workpiece the resulting erosion can be used for cutting, drilling and debarring etc. With the increase of needs for machining of ceramics, semiconductors, electronic devices and L.C.D., AJM has become a useful technique for micromachining. it is more useful in industries for precision work. Material removal rate during this process affected by different parameters like abrasive particle size, the velocity of abrasive flow rate, gas pressure, standoff distance etc.
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2. What is 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 .
3. components of abrasive jet
machining
Abrasive delivery system
Control system
Pump
Nozzle
Mixing tube
Motion system
4. 1.abrasive delivery system
Auto abrasive delivery system has the
capability of storing abrasive & delivery
the abrasive to the bucket . It’s works
auto programming system by help of
once measuring record & no adjustment
or fine tuning system . High sensitive
sensor gives extremely reliable &
repeatable .
5. 2.Control system
The control algorithm that computes exactly
how the feed rate should vary for a given
geometry in a given material to make a precise
part .
The algorithm actually
determines desired variation
in the feed rate & the tool
path to provide an extremely
smooth feed rate .
6. 3.pump
Crankshaft & intensifier pump are mainly use in
the abrasive jet machine .
The intensifier pump was the
only pump capable of reliably
creating pressures high .
Crankshaft pumps are more
efficient than intensifier pumps
because they do not require a power robbing
hydraulic system ultra high pressure & more
stroke per minute .
7. 4.nozzle
All abrasive jet systems use the same basic two
stage nozzle . First , water passes through a small
diameter jewel orifice to form a narrow jet .
The abrasive particles are
accelerated by the moving
stream of water & they pass
into a long hollow cylindrical
ceramic mixing tube.
Generally two type of nozzle
use , right angle head &
straight head .
9. 5. Mixing tube
The mixing tube is where the abrasive mixes with
the high pressure water .
The mixing tube should be
replaced when tolerances
drop below acceptable levels .
For maximum accuracy ,
replace the mixing tube
more frequently .
10. Water Jet and Abrasive Water Jet Machining
WJM - Pure
WJM - with stabilizer
AWJM – entrained – three phase –
abrasive, water and air
AWJM – suspended – two phase –
abrasive and water
o Direct pumping
o Indirect pumping
o Bypass pumping
11. 6.Motion system
In order to make precision parts , an abrasive
jet system must have a precision x-y table and
motion control system .
Tables fall into three general categories .
Floor-mounted gantry systems
Integrated table/gantry systems
Floor-mounted cantilever systems
12. working process
High pressure water starts at the pump , and is
delivered through special high pressure
plumbing to the nozzle .
At the nozzle , abrasive is introduced & as the
abrasive/water mixture exits , cutting is
performed .
Once the jet has exited the nozzle , the energy
is dissipated into the catch tank , which is
usually full of water & debris from previous
cut .
19. ajm features
There are main features
Obtainable tolerances
Material to machine
Material thickness
Accuracy of table
Stability of table
Control abrasive jet
of AJM
20. Machine aspects
Around curves
Inside corner
Feed rate
Acceleration
Nozzle focus
Speed cutting
Pump pressure
Hardness & thickness
Software controlling the
Power at the nozzle
motion
21. Types of abrasive materials
Different types of abrasive are used in
abrasive jet machining like garnet ,
aluminum oxide , olivine , silica sand ,
silicon carbide ,etc .
Virtually any material can be cut by
using abrasive jet machining method ,
i.e harder
materials like titanium to steel.
Abrasive particles must be hard ,high
toughness,
irregular in shape & edges should be
22. Advantages
Extremely fast setup & programming
No start hole required
There is only one tool
Low capital cost
Less vibration
No heat generated in work piece
Environmentally friendly
23. .
Advantages of AWJM
• Extremely fast set-up and programming
• Very little fixturing for most parts
• Machine virtually any 2D shape on any material
• Very low side forces during the machining
• Almost no heat generated on the part
• Machine thick plates
24. Disadvantages
Low metal removal rate
Due to stay cutting accuracy is affected
Abrasive powder cannot be reused
Tapper is also a problem
26. General Experimental conditions
Orifice – Sapphires – 0.1 to 0.3 mm
Focussing Tube – WC – 0.8 to 2.4 mm
Pressure – 2500 to 4000 bar
Abrasive – garnet and olivine - #125 to #60
Abrasive flow - 0.1 to 1.0 Kg/min
Stand off distance – 1 to 2 mm
Machine Impact Angle – 60o to 900
Traverse Speed – 100 mm/min to 5 m/min
Depth of Cut – 1 mm to 250 mm
27. Abrasive Jet Machining
Modelling of material removal
Material removal in AJM takes place due to brittle fracture of the
work material due to impact of high velocity abrasive particles.
Modelling has been done with the following assumptions:
(i) Abrasives are spherical in shape and rigid. The particles are
characterised by the mean grit diameter
(ii) The kinetic energy of the abrasives are fully utilised in
removing material
(iii) Brittle materials are considered to fail due to brittle fracture
and the fracture volume is considered to be hemispherical with
diameter equal to chordal length of the indentation
(iv) For ductile material, removal volume is assumed to be equal
to the indentation volume due to particulate impact.
28. Process Parameters and
Machining Characteristics
Abrasive : Material – Al2O3 / SiC / glass beads
Shape – irregular / spherical
Size – 10 ~ 50 μm
Mass flow rate – 2 ~ 20 gm/min
Carrier gas : Composition – Air, CO2, N2
Density – Air ~ 1.3 kg/m3
Velocity – 500 ~ 700 m/s
Pressure – 2 ~ 10 bar
Flow rate – 5 ~ 30 lpm
Abrasive Jet : Velocity – 100 ~ 300 m/s
Mixing ratio – mass flow ratio of abrasive to gas
Stand-off distance – 0.5 ~ 5 mm
Impingement Angle – 600 ~ 900
Nozzle : Material – WC
Diameter – (Internal) 0.2 ~ 0.8 mm
Life – 10 ~ 300 hours
31. Abrasive Jet Machining
In AJM, generally, the abrasive particles of around 50 μm grit size
would impinge on the work material at velocity of 200 m/s from a
nozzle of I.D. of 0.5 mm with a stand off distance of around 2 mm.
The kinetic energy of the abrasive particles would be sufficient to
provide material removal due to brittle fracture of the work piece or
even micro cutting by the abrasives.
32. Abrasive Jet Machining
In Abrasive Jet Machining (AJM), abrasive particles are made to impinge
on the work material at a high velocity. The high velocity abrasive particles
remove the material by micro-cutting action as well as brittle fracture of the
work material.
33. conclusion
The better performance , and the
applications represented above
statements confirm that
ABRASIVE JET MACHINING is
continue to expand .
The new software’s used to minimize
time and investments , there by making
it possible for more manufacturers of
precision parts to install AJM centers .