One of the widely used industrial cutting process described in brief for the beginners. Water jet cutting process is a industrial tool capable of cutting wide variety of materials using very high pressure of a mixture of water and abrasive material. They are often used during fabrication of machine parts.

1. Water Jet Cutting
Department of Metallurgical & Materials Engineering
Prepared by
Manish Gagan Swain,
Student, Master of Engineering - (Met. & Mats.) - Welding Technology

2. Introduction
Fundamentals
Applications
Advantages
Limitations
Equipment
Process Variables
Safe Practices
Reference

3. Introduction
Water jet cutting, also known as hydrodynamic machining
It cuts a wide variety of materials, both metals and non-metals,
using a high velocity water jet
Jet is formed by water forced by high pressure through an orifice in
a synthetic sapphire.
The orifice is approximately 0.1 mm to 0.6 mm (0.004 in. to 0.024
in.) in diameter; the high pressure ranges from 207 MPa to 414
MPa (30 000 psi to 60 000 psi).

4. Introduction
The velocity of the jet may vary from 520 meters per second (m/s)
to 914 m/s (1700 feet per second [ft/s] to 3000 ft/s).
When the jet of water is applied to the cut site at these speeds and
pressures it rapidly erodes the material and cutting action takes
place.
The typical range of nozzle-to-workpiece distance is 0.25 mm to 25 mm
(0.010 in. to 1.0 in.). Distances less than 6.4 mm (1/4 in.) are preferred.
The water stream, with a flow rate of 0.4 L/min to 19 L/min (0.1 gal/min to 5 gal/min) usually is manipulated by a robot
or gantry system, but small workpieces may be guided manually past a stationary water jet.

5. Introduction
Metals and other hard materials are cut by adding an abrasive in
powder form to the water stream, known as hydroabrasive
machining or abrasive-jet machining.
The abrasive particles (often garnet) are accelerated by the water
and accomplish most of the cutting. Higher flow rates of water are
required to accelerate the particles.

6. Introduction
If this process is properly applied, there is no thermal damage, thus eliminating deformation or
delamination of the workpieces. No dust is produced.
Materials are cut cleanly, without ragged edges (unless the travel
speed is too high), without heat, and generally faster than
bandsaw cutting.
A smooth, narrow (0.8-mm to 2.5-mm [0.030-in. to 0.100-in.]) kerf
is produced.
Note: Kerf is defined as the width of material that is removed by a
cutting process.

7. Fundamentals
The water used in water jet cutting first passes through a booster
pump to pressurize it to about 1300 kPa (190 psi) and to filter it.
Then an intensifier pump creates a water pressure of 207 MPa to
414 MPa (30 000 psi to 60 000 psi) with a flow rate of up to 13.3
L/min (3.5 gal/min]).
The stream is forced through a sapphire orifice and forms a water
jet. The velocity of the jet depends on the water pressure.

8. Fundamentals
Water jets can be made with jet diameters as small as 80 µm (0.003 in.). Abrasive jets generally are not
manufactured in smaller sizes than 0.23 mm (0.009 in.) in diameter.
For abrasive cutting, dry abrasives can be fed from a hopper into a
mixing chamber. There the water accelerates the particles to
supersonic velocities.
The high-speed slurry is focused and then exits the nozzle in a
stream 0.5 mm to 2.3 mm (0.020 in. to 0.090 in.) in diameter.

9. Fundamentals
Depending on the properties of the workpiece material, the actual
cutting is a result of erosion, shearing, or failure under rapidly
changing localized stress fields.
Water jet cutting does not produce thermal or mechanical
distortions. There is a slight work-hardening of metals at the cut
surface.
Downstream of the kerf, the water or water-abrasive stream is
collected in a tank or catcher.

10. Figure shows a water jet head cutting through 9.5-mm (3/8-in.) thick carbon steel.

11. Applications
In some cases, water jet cutting systems can cost-effectively replace three operations: the rough cutting,
milling, and deburring of contoured shapes.
Water jet cutting systems compete with processes such as
bandsaw and reciprocating knife cutting, flame cutting, plasma arc
cutting and laser beam cutting.
Water jet cutting systems can handle materials that would be
damaged by heat from thermal processes or that would adhere to
mechanical cutting tools and cause malfunction.

12. Applications
The extremely wide range of materials that may be cut are listed in
given table.
Although water jet cutting and abrasive jet machining often are
perceived as sheet material processing systems, thick metals and
other materials also can be cut.
Examples of cuts made to test the limits of the process involved
190 mm (7.5 in.) carbon steel, 75 mm (3 in.) 7075 T-6 aluminum,
64 mm (2.5 in.) 470-ply graphite/epoxy, and 250 mm (10 in.)
titanium.
Among the diverse industries that use the water jet cutting technology includes automotive, aerospace and defense;
manufacturers of building supplies, circuit boards, packaging, paper, glass, rubber products, and oil and gas equipment;
also fabrication shops, foundries, food processors, job shops, mines, shipyards, and steel service centers.

13. Figure: A Steel Circular Saw Blade Cut with Hydroabrasive
Machining

14. Figure: Abrasive Water Jet Stack Cutting of Various Metals
The versatility of water jet cutting process is
demonstrated by the simultaneous cuts through
carbon steel, brass, copper, aluminium and
stainless steel, as shown in Figure.

15. Given table shows cutting Speeds on
Various Materials with Abrasive Water Jet

16. Advantages
Two major advantages of water jet cutting are its wide range of
applications and the capability of making cuts without heat.
An abrasive jet is particularly good for cutting laminates of different
materials, including sandwiches of metals and nonmetals. no
predrilling is required
Multiple shapes can be nested and cut, depending on the limits of the
control system and the workpiece size.
Little or no deburring is required.
The process is easily adapted to robotic control.
Other than the orifice and the nozzle, there are no tools to wear out, although the robot mechanism and the
pumps may show signs of wear.

17. Advantages
Minimal lateral forces are generated, which allows simplified
fixture designs.
Tolerances depend on the equipment
and the workpiece material and
thickness, but can be as close as ±0.1
mm (0.004 in.) on dimensions and ±50
µm (0.002 in.) on positioning.
In basic water jet cutting, the kerf width usually is 0.13
mm (0.005 in.) or wider; in abrasive water jet cutting it
usually is 0.8 mm (0.032 in.) or wider.
The water jet tends to spread as it leaves the nozzle, so the kerf is wider
at the bottom than at the top. Kerf tapering can be reduced by adding
long-chain polymers, such as polyethylene oxide, to the water or by
reducing cutting speed.
Most abrasive and water jet cutting equipment can be
operated with computer numerical control (CNC) systems,
which are relatively easy to program.
Low maintenance is an advantage.

18. Limitations
The main limitation of the water jet cutting process is its relatively low
cutting speed.
Another limitation is that a device must be provided to collect the
exhaust liquid from the cutting stream..
Also, initial capital costs are high because of the pumps and pressure
chamber required to propel and direct the water jet
The material to be cut must be
softer than the abrasive used.
Very thin ductile metals are prone
to bending stress from an
abrasive jet and often show exit
burrs. Ceramics cut with a water
jet show a decrease in as-fired
strength.
Nozzles must be replaced every two to four hours (sometimes even
more frequently) in abrasive water jet systems.

19. Limitations
Optimally, the water supplied for the system should be deionized
water filtered to a particle size of 0.5 µm, to reduce maintenance, but
it is possible that other water treatment methods may be used, if the
water is relatively soft.
Proper disposal of waste water and slurry from the cutting operation
must be a part of the system.
Also, initial capital costs are high because of the pumps and pressure
chamber required to propel and direct the water jet
The fatigue life of abrasive water-jet-cut edges in critical applications, such as aerospace structures, can be lower than
that of a raw sheared edge if a coarse 60-grit abrasive particle is used. Decreasing the particle size to 150 grit increases
fatigue life 50% or more, but there is a corresponding decrease in cutting speed.

20. Equipment
The key pieces of equipment for a water jet or an abrasive water jet
system are the following:
1. A special high-pressure pump or intensifier to provide the
stream of water;
2. Plumbing and a tank, or catcher unit, to handle the water;
3. A gantry, robotic, or other delivery system to traverse and guide
the water jet;
4. The nozzle assembly unit that forms the jet; and
5. An abrasive particle delivery system.
CONSUMABLE MATERIALS
The sapphire orifice is the component of a cutting system that is subject to most wear. In abrasive systems, it is the
carbide nozzle. On pure water jet systems, a synthetic sapphire may last up to 200 hours. In abrasive systems, the
carbide abrasive nozzles last from two to four hours. Other consumables are water, abrasive particles, and electricity.
Abrasive particles are used at the approximate rate of 0.1 kg to 1.4 kg (0.25 lb to 3.0 lbs) per minute.

21. Figure: Typical Abrasive Water Jet Cutting System

22. Figure: Water Jet Cutting Machine Using a Four-Head Gantry System

23. Process Variables
Process variables:
1. Water jet pressure and diameter;
2. Size, type, and flow rate of the abrasive material;
3. Travel speed;
4. Angle of cutting; and
5. Number of passes.
Typical thicknesses cut by water jet cutting range
from 2.5 µm to 30 cm (0.0001 in. to 12 in). The
thickness and density of materials that can be
cut with a water jet can be increased by
increasing the pressure, increasing the jet
diameter, and lowering the travel speed.
The cutting speed of an abrasive jet can be
increased by increasing the flow rate of the
water or the size of the abrasive particles, or
both. The use of smaller sizes of abrasive
particles and slower cutting speeds will
improve the edge quality of the cuts.

24. Process Variables
Increasing the water pressure in abrasive jet cutting increases
the capability of the jet to cut thick plate up to 305 mm (12
in.) because of higher velocities of the particle. The optimum
pressure tends to remain in the range of 207 MPa to 310
MPa (30 000 psi to 45 000 psi), because higher pressures
result in increased equipment maintenance costs with only
slight process advantages.
Fine abrasive particles below 150 mesh are relatively ineffective; the most effective general purpose size
for cutting metals is 60 mesh or 80 mesh. For very hard ceramics, boron carbide abrasives sometimes are
used. High abrasive flow rates result in high cutting costs:

25. Safe Practices
As the water jet or abrasive jet easily could cut flesh or
bone, operator protection is mandatory. Maintenance
personnel must be trained in the safety aspects of
handling high-pressure equipment and water lines.
Pressure sensors should be in place to shut down the
system in case of tubing failure.
Noise generated during cutting typically is in the range
of 80 decibels (dB) to 95 dB, but may reach 120 dB.
Safety enclosures provided to protect the operator
from the cutting operation are designed to deaden
sound, but operators should use ear protection.

26. Reference:
AWS Handbook Volume 2: Welding
Processes- Ninth Edition

27. धन्यवादः
(Dhanyavaadaha)