2. Syllabus
Abrasive Jet Machining
Working Principles
Water Jet Machining
Equipment used
Abrasive Water Jet Machining &
Process parameters
Ultrasonic Machining
MRR
Variation in techniques used
Applications
3. Abrasive Jet Machining
Working Principles – equipment used – Process
parameters – MRR-Variation in techniques used – Applications
4. Working Principle
A stream of abrasive grains (Al2O3 or SiC) is carried by high pressure gas
or air (compressed).
Impinges on the work surface at very high velocity through a nozzle of
0.3 to 0.5 mm diameter
Sand Blasting (SB) - a similar process
The major differences between are SB and AJM
smaller diameter abrasives
a more finely controlled delivery system
Material removal – by mechanical abrasion action of the high velocity
abrasive particles
7. Working
A gas (Nitrogen, CO2 or air) is supplied at 2 – 8 kg/cm2
Oxygen should never be used. (because, it causes violent chemical action with
the work piece chips or abrasive particles).
Gas passes through a mixing chamber after filtration and regulation.
In the mixing chamber, abrasive particles (10 – 40 µm) are present and
vibrated at 50 Hz.
Amplitude of vibration – to control the feed rate of abrasives.
(Gas + abrasives) - passed through a 0.45 mm diameter tungsten carbide
nozzle at a speed of 150 – 300 m/s.
The nozzle is directed over the area to be machined
8. Working
Aluminum oxide (Al2O3) and silicon carbide (SiC) powders are used for heavy
cleaning, cutting and deburring.
Magnesium carbonate is recommended for use in light cleaning and etching.
Sodium bicarbonate – fine cleaning and cutting of soft materials.
Commercial grade powders are not suitable – b’cos their sizes are not well
classified. Also, they may contain silica which can cause a health hazard.
Abrasive powders are not reused. B’cos, contaminations and worn grits will
reduce the machining rate (MRR).
The nozzle stand off distance is 0.81 mm
9. Process parameters VS Metal Removal Rate
Mass flow rate
Abrasive grain size
Gas pressure
Velocity of abrasive particles
Mixing Ratio
Nozzle tip clearance
11. Application
Drilling holes
Cutting slots
Cleaning hard surfaces
Deburring and polishing
Machining intricate shapes or holes in sensitive, brittle, thin, or difficultto-machine materials
Frosting glass and trimming of circuit boards, hybrid circuit resistors,
capacitors, silicon, and gallium
12. Advantage
The process is used for machining super alloys and refractory materials.
It is not reactive with any work piece material.
No tool changes are required.
Intricate parts of sharp corners can be machined
No initial hole is required for starting the operation as required by wire
EDM.
Material utilization is high.
It can machine thin materials
13. Disadvantage
The removal rate is slow.
The tapering effect may occur especially when drilling in metals.
The abrasive may get impeded in the work surface.
Suitable dust-collecting systems should be provided.
Soft materials can’t be machined by the process.
Silica dust may be a health hazard
14. Water Jet Machining
Working Principles – equipment used – Process
parameters – MRR-Variation in techniques used – Applications
15. Working Principle
Water is pumped at a sufficiently high pressure, 200-400 MPa (2000-4000 bar) using
intensifier technology.
An intensifier works on the simple principle of pressure amplification using hydraulic
cylinders of different cross-sections as used in “Jute Bell Presses”.
When water at such pressure is issued through a suitable orifice (generally of 0.2- 0.4
mm dia), the potential energy of water is converted into kinetic energy, yielding a high
velocity jet (1000 m/s).
17. 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 debris & impurities
19. Advantage
There are no bits or tools touching the material surface, thus there
is no tool replacement costs.
Ultrahigh-pressure Water-jets cut to accuracy's of +/-0.010".
Low level of mechanical stress (less than a pound) placed on the
work piece preventing damage and deformations.
20. Application
Used for cutting
Composites
Plastics
Fabrics
Rubber
wood products etc.
Also used in food processing industry
22. Introduction
WJM - suitable for cutting plastics, foods, rubber insulation, automotive carpeting and headliners, and
most textiles.
Harder materials such as glass, ceramics, concrete, and tough composites can be cut by adding
abrasives to the water jet.
Abrasive water jet machining (AWJM) – Developed in 1974 to clean metal prior to surface treatment
of the metal.
The addition of abrasives to the water jet enhanced MRR and produced cutting speeds between 51
and 460 mm/min.
Generally, AWJM cuts 10 times faster than the conventional machining methods of composite
materials.
Zheng et al. (2002) claimed that the abrasive water jet is hundreds of times more powerful than the
pure water jet.
23. WJM & AWJM
Different approaches and methodologies in WJM & AWJM
WJM – with stabilizer
AWJM – entrained – three phase (water + air + abrasives)
AWJM – suspended – two phase (water + abrasives)
Direct pumping
Indirect pumping
WJM – pure
Bypass pumping
In all the above variants, the basic methodology remains the same.
24. Basic Methodology
Water is pumped at a sufficiently high pressure, 200-400 MPa (2000 – 4000 bar).
“Intensifier” works on the principle of pressure amplification using hydraulic cylinders of two different
cross-sections.
When water at such a pressure is passed through a suitable orifice (nozzle having φ = 0.2 – 0.4 mm),
the potential energy of water is converted into kinetic energy.
This yields high velocity (~ 1000 m/s) jet of water.
Such a high velocity water jet can machine thin sheets/foils of aluminium, leather, textile, frozen foods,
etc.
WJM – commercially pure water (tap water) is used for machining.
25. Variants in WJM & AWJM
Problem in WJM – as the high velocity water jet is discharged from the orifice, the jet tends to entrain
atmospheric air and flares out – decreasing the machining ability.
Hence, stabilizers (long chain polymers) are added to water (WJM with stabilizer).
Stabilizers hinders the fragmentation of water jet.
In AWJM, abrasive particles are added to the water jet to enhance its cutting ability by many folds.
In entrained type AWJM, the abrasive particles are allowed to entrain in water jet to form abrasive
water jet wit sufficient velocity of as high as 800 m/s.
Such high velocity abrasive jet can machine almost any material.
28. WJM & AWJM - Materials
Steels & Non-ferrous alloys
Ti alloys, Ni- alloys
Polymers
Honeycombs
Metal Matrix Composite & Ceramic Matrix Composite
Concrete
Stone – Granite
Wood
Reinforced plastics
Metal Polymer Laminates
Glass Fibre Metal Laminates
29. Applications of WJM & AWJM
The cutting ability of WJM can be improved drastically by adding hard and sharp abrasive particles
into the water jet.
Thus, WJM is typically used to cut so called “softer” and “easy-to-machine” materials like thin sheets
and foils, non-ferrous metallic alloys, wood, textiles, honeycomb, polymers, frozen meat, leather etc.
But, the domain of “harder” and “difficult-to-machine” materials like thick plates of steels, aluminium
and other commercial materials, metal matrix and ceramic matrix composites, reinforced plastics,
layered composites, etc. are reserved for AWJM.
Other than cutting (machining) high pressure water jet also finds application in paint removal,
cleaning, surgery, peening to remove residual stress etc.
AWJM can as well be used besides cutting for pocket milling, turning, drilling, etc.
One of the strategic areas where “robotic AWJM” is finding critical application is dismantling of nuclear
plants.
30. WJM & AWJM - Advantages
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
Can machine thick plates
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31. AWJM - Elements
AWJM accelerates a jet of water (70 percent) and abrasive (30 percent) from 4.2 bar up to a velocity
of 30 m/s.
Silicon carbides, sand (SiO2), corundum, and glass beads of grain size 10 to 150 μm are often used
as abrasive materials.
Using such a method, burrs of 0.35 mm height and 0.02 mm width left in steel component after
grinding are removed by the erosive effect of the abrasives while water acts as an abrasive carrier.
The introduction of compressed air to the water jet enhances the deburring action.
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34. ULTRASONIC MACHINING (UM)
In UM the tip of the tool vibrates at low amplitude and at high frequency. This
vibration transmits a high velocity to fine abrasive grains between tool and the
surface of the work piece.
Material removed by erosion with abrasive particles.
The abrasive grains are usually boron carbides.
This technique is used to cut hard and brittle materials like ceramics, carbides,
glass, precious stones and hardened steel
35. Metal cutting as in this process abrasives contained in a slurry are driven at high
velocity against the work piece by a tool vibrating at low amplitude and high
frequency
Amplitude is kept of the order of 0.07 mm and frequency is maintained at
approximately 20,000 Hz.
The work piece material is removed in the form of extremely small chips
Abrasive slurry acts as a multipoint cutting tool and does the similar action as done by
a cutting edge
41. Feed Mechanism
Gravity feed Mechanism
Spring loaded Feed Mechanism
Pneumatic or Hydraulic Feed Mechanism
42. Application
The machining of hard and brittle materials like carbides glass, ceramics,
precious stones, titanium
It is used for tool making and punch and die making
It is widely used for several machining operations like turning, grinding,
trepanning and milling
43. Advantage
Its main advantage is the work piece after machining is free from any residual
stress as to concentrated force or heat is subject to it during the machining
process.
Extremely hard and brittle materials can be machined, their machining is very
difficult by conventional methods.
Very good dimensional accuracy and surface finish can be obtained.
Operational cost is low.
The process is environmental friendly as it is noiseless and no chemical and
heating is used
44. Limitation
Its metal removal rate (MRR) is very low and it can not be used for large
machining cavities.
Its initial setup cost and cost of tool is very high, frequency tool
replacement is required as tool wear takes place in this operation.
Not recommended for soft and ductile material due to their ductility.
Power consumption is quite high.
Slurry may have to be replaced frequently