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Chapter 1
1.1Introduction:-
A water jet cutter, also known as a water jet or water jet, is an industrial tool capable
of cutting a wide variety of materials using a very high-pressure jet of water, or a
mixture of water and an abrasive substance. The term abrasive jet refers specifically to
the use of a mixture of water and abrasive to cut hard materials such as metal or granite,
while the terms pure water jet and water-only cutting refer to water jet cutting without
the use of added abrasives, often used for softer materials such as wood or rubber.
Water jet cutting is often used during fabrication of machine parts. It is the preferred
method when the materials being cut are sensitive to the high temperatures generated
by other methods. Water jet cutting is used in various industries,
including mining and aerospace, for cutting, shaping, and reaming.
Fig1.1:- Water jet cutter
2
Cutting steel, concrete, glass and marble with water - sounds a bit far-fetched doesn’t
it? Way back in the 1950s, a forestry engineer by the name of Norman Franz started
fiddling around with a high-pressure water stream to cut lumber. His aim was to
streamline the process and reduce the strain on traditional cutting equipment such as
saw blades, which easily became blunt and needed replacing. From these humble
beginnings an idea was born, and over the next couple of decades, water cutting became
an unparalleled method for cutting materials of all types, shapes and sizes.
FIG1.2:- nozzle
The end product? A water jet cutter – a machine capable of slicing metal and other
materials such as granite and marble with unbelievable accuracy. It does this by using
a jet of water at high velocity and pressure, sometimes mixed with an abrasive
substance, depending on the material that is being cut. Water jet cutters are usually used
to cut materials such as rubber, foam, plastics, leather, composites, stone, tiles, metals,
food and paper. However, they can’t cut tempered glass, diamonds and certain ceramics
3
Fig1.3:- water jet cutter operation.
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CHAPTER 2
2.2 HISTORY:-
While using high-pressure water for erosion dates back as far as the mid-
1800s with hydraulic mining, it was not until the 1930s that narrow jets of water started
to appear as an industrial cutting device. In 1933, the Paper Patents Company in
Wisconsin developed a paper metering, cutting, and reeling machine that used a
diagonally moving water jet nozzle to cut a horizontally moving sheet of continuous
paper.[2] These early applications were at a low pressure and restricted to soft materials
like paper.
Water jet technology evolved in the post-war era as researchers around the world
searched for new methods of efficient cutting systems. In 1956, Carl Johnson of Durox
International in Luxembourg developed a method for cutting plastic shapes using a thin
stream high-pressure water jet, but those materials, like paper, were soft materials.[3] In
1958, Billie Schwacha of North American Aviation developed a system using ultra-
high-pressure liquid to cut hard materials.[4] This system used a 100,000 psi (690 MPa)
pump to deliver a hypersonic liquid jet that could cut high strength alloys such as PH15-
7-MO stainless steel. Used as a honeycomb laminate on the Mach 3 North American
XB-70 Valkyrie, this cutting method resulted in delaminating at high speed, requiring
changes to the manufacturing process.[5]
While not effective for the XB-70 project, the concept was valid and further research
continued to evolve water jet cutting. In 1962, Philip Rice of Union Carbide explored
using a pulsing water jet at up to 50,000 psi (345 MPa) to cut metals, stone, and other
materials.[6] Research by S.J. Leach and G.L. Walker in the mid-1960s expanded on
traditional coal water jet cutting to determine ideal nozzle shape for high-pressure water
jet cutting of stone,[7] and Norman Franz in the late 1960s focused on water jet cutting
of soft materials by dissolving long chain polymers in the water to improve the
cohesiveness of the jet stream.[8]
5
In the early 1970s, the desire to improve the durability of the water jet nozzle led Ray
Chadwick, Michael Kurko, and Joseph Corriveau of the Bendix Corporation to come
up with the idea of using corundum crystal to form a water jet orifice,[9] while Norman
Franz expanded on this and created a water jet nozzle with an orifice as small as
0.002 inches (0.05 mm) that operated at pressures up to 70,000 psi (483 MPa).[10] John
Olsen, along with George Hurlburt and Louis Kapcsandy at Flow Research (later Flow
Industries), further improved the commercial potential of the water jet by showing that
treating the water beforehand could increase the operational life of the nozzle.[11]
Fig 2.1 old model of water jet system
2.2.1 1800:-
Hydraulic mining had its precursor in the practice of ground sluicing, a
development of which is also known as "hushing", in which surface streams of water
were diverted so as to erode gold-bearing gravels. This was originally used in the
Roman empire in the first centuries AD and BC, and expanded throughout the empire
wherever alluvial deposits occurred[2] The Romans used ground sluicing to remove
overburden and the gold-bearing debris in Las Medullas of Spain,
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and Dolaucothi in Britain. The method was also used in Elizabethan
England & Wales (or rarel for developing lead, tin and copper mines.1
Water was used on a large scale by Roman engineers in the first centuries BC and AD
when the Roman empire was expanding rapidly in Europe. Using a process later known
as hushing, the Romans stored a large volume of water in a reservoir immediately above
the area to be mined; the water was then quickly released. The resulting wave of water
removed overburden and exposed bedrock. Gold veins in the bedrock were then worked
using a number of techniques, and water power was used again to remove debris. The
remains at Las Medullas and in surrounding areas show badland scenery on a gigantic
scale owing to hydraulic king of the rich alluvial gold deposits. Las Medullas is now
a UNESCO World Heritage site. The site shows the remains of at least seven
large aqueducts of up to 30 miles in length feeding large supplies of water into the site.
The gold-mining operations were described in vivid terms by Pliny the Elder in
his Naturalist Historia published in the first century AD. Pliny was a procurator
in Hispania Terraconensis in the 70's and must have witnessed for himself the
operations. The use of hushing has been confirmed by field survey
and archaeology at Dolaucothi in South Wales, the only known Roman gold mine
in Britain.
The modern form of hydraulic mining, using jets of water directed under very high
pressure through hoses and nozzles at gold-bearing upland paleo gravels, was first used
by Edward Matteson near Nevada City, California in 1853 during the California Gold
Rush.[3] Matteson used canvas hose which was later replaced with crinoline hose by the
1860s.[4] In California, hydraulic mining often brought water from higher locations for
long distances to holding ponds several hundred feet above the area to be mined.
California hydraulic mining exploited gravel deposits, making it a form of placer
mining.
Early placer miners in California discovered that the more gravel they could process,
the more gold they were likely to find. Instead of working with pans, sluice boxes, long
toms, and rockers, miners collaborated to find ways to process larger quantities of
gravel more rapidly. Hydraulic mining became the largest-scale, and most devastating,
form of placer mining. Water was redirected into an ever-narrowing channel, through
a large canvas hose, and out through a giant iron nozzle, called a "monitor." The
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extremely high pressure stream was used to wash entire hillsides through enormous
sluices.
By the early 1860s, while hydraulic mining was at its height, small-scale placer mining
had largely exhausted the rich surface placers, and the mining industry turned to hard
rock (called quartz mining in California) or hydraulic mining, which required larger
organizations and much more capital. By the mid-1880s, it is estimated that 11 million
ounces of gold (worth approximately US$7.5 billion at mid-2006 prices) had been
recovered by hydraulic mining in the California Gold Rush.
2.2.2 1850:-
High-pressure vessels and pumps became affordable and reliable with the advent of
steam power. By the mid-1850s, steam locomotives were common and the first efficient
steam-driven fire engine was operational.[12] By the turn of the century, high-pressure
reliability improved, with locomotive research leading to a six fold increase in boiler
pressure, some reaching 1600 psi (11 MPa). Most high-pressure pumps at this time,
though, operated around 500–800 psi (3–6 MPa).
8
High-pressure systems were further shaped by the aviation, automotive, and oil
industries. Aircraft manufacturers such as Boeing developed seals for hydraulically
boosted control systems in the 1940s,[13] while automotive designers followed similar
research for hydraulic suspension systems.[14] Higher pressures in hydraulic systems in
the oil industry also led to the development of advanced seals and packing to prevent
leaks.[15]
These advances in seal technology, plus the rise of plastics in the post-war years, led to
the development of the first reliable high-pressure pump. The invention of Marlex by
Robert Banks and John Paul Hogan of the Phillips Petroleum company required a
catalyst to be injected into the polyethylene.[16] McCartney Manufacturing Company in
Baxter Springs, Kansas, began manufacturing these high-pressure pumps in 1960 for
the polyethylene industry.[17] Flow Industries in Kent, Washington set the groundwork
for commercial viability of water jets with John Olsen’s development of the high-
pressure fluid intensifier in 1973,[18] a design that was further refined in 1976.[19] Flow
Industries then combined the high-pressure pump research with their water jet nozzle
research and brought water jet cutting into the manufacturing world.
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2.2.3 1935:-
While cutting with water is possible for soft materials, the addition of an abrasive turned
the water jet into a modern machining tool for all materials. This began in 1935 when
the idea of adding an abrasive to the water stream was developed by Elmo Smith for
the liquid abrasive blasting.[20] Smith’s design was further refined by Leslie Terrell of
the Hydro blast Corporation in 1937, resulting in a nozzle design that created a mix of
high-pressure water and abrasive for the purpose of wet blasting.[21] Producing a
commercially viable abrasive water jet nozzle for precision cutting came next by
Dr. Mohamed Hashish who invented and led an engineering research team at Flow
Industries to develop the modern abrasive water jet cutting technology.[22] Dr. Hashish,
who also coined the new term "Abrasive Water jet" AWJ, and his team continued to
develop and improve the AWJ technology and its hardware for many applications
which is now in over 50 industries worldwide. A most critical development was
creating a durable mixing tube that could withstand the power of the high-pressure
AWJ, and it was Boride Products (now Kennametal) development of their ROCTEC
line of ceramic tungsten carbide composite tubes that significantly increased the
operational life of the AWJ nozzle.[23] Current work on AWJ nozzles is on micro
abrasive water jet so cutting with jets smaller than 0.015 inch in diameter can be
commercialized
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2.2.4 1990:-
As water jet cutting moved into traditional manufacturing shops, controlling the cutter
reliably and accurately was essential. Early water jet cutting systems adapted traditional
systems such as mechanical pantographs and CNC systems based on John Parsons’
1952 NC milling machine and running G-code.[24] Challenges inherent to water jet
technology revealed the inadequacies of traditional G-Code, as accuracy depends on
varying the speed of the nozzle as it approaches corners and details.[25] Creating motion
control systems to incorporate those variables became a major innovation for leading
water jet manufacturers in the early 1990s, with Dr John Olsen of OMAX Corporation
developing systems to precisely position the water jet nozzle[26] while accurately
specifying the speed at every point along the path,[27] and also utilizing common PCs
as a controller. The largest water jet manufacturer, Flow International (a spinoff of Flow
Industries), recognized the benefits of that system and licensed the OMAX software,
with the result that the vast majority of water jet cutting machines worldwide are simple
to use, fast, and accurate.[28]
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CHAPTER 3
3.1 Working:-
At its most basic, water flows from a pump, through plumbing and out a cutting head.
It is simple to explain, operate and maintain. The process, however, incorporates
extremely complex materials technology and design.
To generate and control water at pressures of 87,000 psi requires science and
technology not taught in universities. At these pressures a slight leak can cause
permanent erosion damage to components if not properly designed.
Thankfully, the water jet manufacturers take care of the complex materials technology
and cutting-edge engineering. The user need only be knowledgeable in the basic water
jet operation.
Flow machines are designed to operate as both pure and abrasive water jets. A pure
water jet is used to cut soft materials, and within just 2 minutes the very same water jet
can be transformed into an abrasive water jet to cut hard materials. With any type, the
water must first be pressurized.
Fig 3.1 horizontal water jet cutter
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3.1.1 High pressure water jet cutting:-
Water is pressurized to very high pressures, in excess of 50,000 psi. This pressurization
is accomplished with the use of pumps of various designs, discussed next in this chapter.
The high pressure water is transported through a series of stainless steel tubes to a
cutting head. Depending upon the material being cut, the cutting head can be either a
"pure water cutting head" or an "abrasive cutting head."
In the cutting head, the high pressure water is forced through a small diameter
orifice. The diameter of this orifice is anywhere from 0.004" to 0.020". This step
converts the pressure of the water jet stream into speed. We go from potential energy
to kinetic energy. Coming out of the orifice, the water jet stream is moving at 2200
mph or faster. Higher pressure results in higher speed. Smaller diameter orifices yield
a faster water jet stream, but also a stream with less kinetic energy since there is not as
much water available to accelerate abrasive grains to full speed.
In a pure water cutting head, the water immediately exits the cutting head after passing
through the orifice. The speed and power of the water jet stream is enough to cut soft
or thin materials like foam, rubber, soft wood, plastics, carpet, food, car headliners,
circuit boards and more.
In an abrasive cutting head, a very hard abrasive, typically garnet, is fed into the water
jet stream. The abrasive particles are accelerated to near the speed of the water jet
stream. This gives the abrasive particles much power. The abrasive water jet stream
now travels down through an abrasive nozzle, or mixing tube, approximately 3 inches
long with an inner diameter of between .030" and 0.050". The mixture of water and
abrasive exits the abrasive nozzle and will cut hard materials like metals, stone, acrylic,
ceramic, composites, phenolic and porcelain.
A CNC control will move the cutting head in up to 6 axes of motion to cut the targeted
work piece.
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3.2 Types of pumps:-
3.2.1 Intensifier
Intensifier pumps are called intensifiers because they use the concept of pressure
intensification or amplification to generate the desired water pressure.
If you apply pressure to one side of a cylinder and the other side of the cylinder is the
same surface area, the pressure on the other side will be the same. If the surface area of
the smaller side is half, then the pressure on that side will be doubled. Generally with
intensifier pumps there is a 20 times difference between the large surface area (where
the oil pressure is applied) and the small surface area (where the water pressure is
generated). The following picture shows this concep
Ultimately, there must be a restriction in the flow of water in order for the pressure to
be generated. This restriction is generated by the orifice in the cutting head. Pressure
is maintained until the orifice diameter exceeds the limits for water output of the pump.
For very small diameter orifices, in order to maintain pressure, the pump only needs to
cycle very slowly to maintain pressure. As the orifice gets larger, the pump must work
faster to maintain pressure and water flow. If the orifice gets too large, the pump tries
to cycle too fast for the design specification. An "over stroke" situation is sensed by the
control and the pump is stopped with an error message.
If there are leaks in the water circuit between the pump and the cutting head, this can
also result in a pump "over stroke" situation. The leaks effectively rob water available
to go to the cutting head. The same as putting in too large of an orifice, the pump runs
faster to maintain pressure until it reaches its limit.
Typically, intensifiers stroke at around 50 - 60 strokes per minute when working at full
capacity
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fig 3.2 Intensifier pump
3.2.2 Direct Drive
A direct drive pump works like a car’s engine. A motor turns a crankshaft attached to
3 or more offset pistons. As the crankshaft turns, the pistons reciprocate in their
respective cylinders, creating pressure in the water. Pressure and flow rate are
determined by how fast the motor turns the crankshaft. Direct drive pumps cycle much
faster than intensifiers, on the order of 1750 revolutions per minute. Direct drive pumps
generally are found in lower pressure applications (i.e. 55,000 pounds per square inch
and under). Maintenance on the direct drive pump tends to take longer than an
intensifier pump. Direct drive pumps can only run more than one cutting head only if
all cutting heads are cutting the same part at the same time. With an intensifier pump,
you could have cutting heads on multiple machines, cutting different parts, cycling the
various cutting heads on and off in any sequence. The intensifier pump will need to
only vary its stroke rate accordingly to maintain flow and pressure.
15
Fig 3.3 direct drive pump
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3.3 Principles of water jet cutting
There are two types of water jet cutting processes; pure water cutting, in which the
cutting is performed using only an ultra-high pressure jet of clean water, and abrasive
water jet cutting in which an abrasive (typically garnet) is introduced into the high
pressure stream.
Pure water cutting can be employed to profile a huge variety of materials, these will
typically be 'soft' materials such as gaskets, rubber, foam & plastics. Filtered tap water
is fed into an intensifier pump where it is pressurised to (typically) 60,000psi. This
ultra-high pressure water is forced through a tiny (0.15mm) orifice jewel which is
normally manufactured from sapphire. This has the effect of focusing the beam of water
into a fine, accurate stream travelling at speeds of up to 900m/sec, capable of accurate
cutting of a wide range of soft materials.
In order to cut 'harder' materials or any material containing glass or metal, then abrasive
water jet cutting would be employed. The principles of abrasive water jet cutting are
similar to pure water jet cutting, but once the stream has passed through the orifice it
enters a carbide nozzle. Within this nozzle is a mixing chamber within which a partial
vacuum is created as the water passes through. Garnet is introduced under gravity into
the nozzle and the partial vacuum within the mixing chamber has the effect of dragging
the abrasive into the water stream to create a highly abrasive cutting jet. Abrasive
cutting would typically be used on materials such as stainless steel, aluminium, stone,
ceramics & composite materials.
Fig3.4 mouthpiece of jet
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In both processes the head is controlled by a CNC controller, this offering great
accuracy and repeatability. The CNCcontroller is programmed by first drawing the part
to be manufactured using proprietary software, and then converting this drawing into a
G code format – CNC language.
Fig 3.5 vertical water jet
Water jet cutting is a cold grinding or cutting process. It combines the advantages of
laser – precision – with those of water: water jet cutting is thermoneutral. In addition to
laser cutting, water jet cutting is becoming increasingly important in Switzerland and
Germany. No thermal stresses occur with water jet cutting. The microstructure of the
material and the material strength remain. There are no cures, distortions, dripping slag,
melting or toxic gases.
In all processes, the cutting heads with the focusing nozzles are integrated in a guiding
machine (robot, 2D or 3D portal). The controlled CNC axes enable 2D, 2.5D or 3D
cutting processes. These processes can cut almost all materials – hard like steel and
glass, but also fragile and extremely soft materials – without stress forces. Water jet
cutting has three principles: the pure water jet principle “WJ”, the abrasive water jet
principle “AW” and the suspension jet principle, which is still at development stage.
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3.3.1 Water jet cutting with pure water:-
With pure water jet cutting “WJ”, a pure water jet with a diameter of 0.1 mm cuts the
material at up to three times the speed of sound (at speeds of up to 200 m/min). These
materials include textiles, elastomers, fibers, thin plastics, food, paper, cardboard,
leather, thermoplastic materials or food. The water is pressurized to 1,000–6,000 bar
(standard approximately 3,800 bar). After flowing through a high-pressure needle
valve, the water enters a 200 mm long and 3 mm in diameter wide collimation tube
(calming section). It is then pressurized by a water nozzle or a dynamic pressure nozzle
and accelerated. The jet speed varies according to geometry and pressure. The small
diameter of the water nozzle produces a very high local energy density, which remains
constant on a relatively long section in the direction of the water jet and cuts cleanly
and accurately when hitting the material.
Fig3.6 half section view of water jet
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3.3.2 Water jet cutting with abrasives:-
With abrasive water jet cutting, compact and hard materials such as metals (including
steel), hard stone, glass (including bullet-proof glass) and ceramic are separated. Before
the concentrated jet of water hits the material, a cutting material of the finest grain size
(abrasive) is added in the required dose in a mixing chamber, which ensures micro
cutting. The water serves as an accelerator for the abrasive particles and hits the material
with an impact speed of 800 m/s, thereby removing it with precision. Until the water
jet is produced, abrasive water jet cutting is identical to pure water jet cutting. The
difference is that the pure water jet is no longer used just for cutting, but as a carrier
material for the abrasive particles. The pure water jet flows into a mixing chamber, into
which the abrasive particles are then introduced. At the end of the mixing chamber is
the focusing tube, in which the abrasive grains in the water jet are accelerated and
confined to a specific cross-section.
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3.3.3 Water jet cutting with suspension jet
With the suspension jet principle or water abrasive suspension jet cutting, a pre-
prepared mixture of abrasive particles and water is discharged under high pressure from
a cutting nozzle. However, the abrasive agent is not added at the nozzle but is
pressurized under the exclusion of air. Therefore, a water-abrasive mixture (a
suspension) is expelled from the cutting nozzle under high pressure. This enables higher
cutting performance, allows greater thicknesses and almost all materials to be cut.
However, there is a delay in the start and stop of the cutting operation, since the abrasive
feed cannot be switched on and off as rapidly as in injection cutting. This is one
disadvantage when high-precision cutting is required. The wear on the valves and
nozzles is also much larger and attainable pressures are smaller. Therefore, this
principle is only seldom used on an industrial scale.
Fig 3.7 suspension jet
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3.4 PARTS OF WATER JET CUTTER:-
3.4.1. Electric motor and hydraulic pump
The electric motor and hydraulic pump (number 1 in picture above) create the oil
pressure needed for the oil side of the intensifier. This assembly is normally in the lower
portion of the pump cabinet. The electric motor and pump are rated in HP (or kW for
metric). Typical pump sizes are 30 HP, 50 HP, 75 HP, 100 HP and 150 HP As discussed
in the previous chapter, each pump will have an associated water output volume
(gallons per minute) and pressure (psi).
Again it is important to remember that HP is not necessarily an indication of pressure.
A 150 HP pump doesn’t necessarily create more pressure than a 50 HP pump.
Horsepower is more directly related to water output, since more HP will be needed to
create enough power to move the piston/plunger assembly in the intensifier at the
required stroke rate.
Fig3.8 Intensifier pump cabinet (150 HP)
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3.4.2. Directional control valves
One of the most important considerations in any fluid power system is control. If control
components are not properly selected, the entire system does not function as required.
In fluid power, controlling elements are called valves. There are three types of valves:
1. Directional control valves (DCVs): They determine the path through which a fluid
transverses a given circuit. Pressure control valves: They protect the system against
overpressure, which may occur due to a sudden surge as valves open or close or due to
an increase in fluid demand. 2. Flow control valves: Shock absorbers are hydraulic
devices designed to smooth out pressure surges and to dampen hydraulic shock. In
addition, the fluid flow rate must be controlled in various lines of a hydraulic circuit.
For example, the control of actuator speeds can be accomplished through use of flow
control valves. Non-compensated flow control valves are used where precise speed
control is not required because the flow rate varies with pressure drop across a flow
control valve. It is important to know the primary function and operation of various
types of control components not only for good functioning of a system, but also for
discovering innovative methods to improve the fluid power system for a given
application. 1.2Directional Control Valves A valve is a device that receives an external
signal (mechanical, fluid pilot signal, electrical or electronics) to release, stop or
redirect the fluid that flows through it. The function of a DCV is to control the direction
of fluid flow in any hydraulic system. A DCV does this by changing the position of
internal movable parts. To be more specific, a DCV is mainly required for the following
purposes:  To start, stop, accelerate, decelerate and change the direction of motion of
a hydraulic actuator.  To permit the free flow from the pump to the reservoir at low
pressure when the pump’s delivery is not needed into the system.  To vent the relief
valve by either electrical or mechanical control.  To isolate certain branch of a circuit.
2 Any valve contains ports that are external openings through which a fluid can enter
and exit via connecting pipelines. The number of ports on a DCV is identified using the
term “way.” Thus, a valve with four ports is a four-way valve A DCV consists of a
valve body or valve housing and a valve mechanism usually mounted on a sub-plate.
The ports of a sub-plate are threaded to hold the tube fittings which connect the valve
to the fluid conductor lines. The valve mechanism directs the fluid to selected output
23
ports or stops the fluid from passing through the valve. DCVs can be classified based
on fluid path, design characteristics, control methods and construction
Fig 3.9 Directional Control Valve
3.4.3. Intensifier
The intensifier proper (3 in Figures 4 and 2) consists of the hydraulic cylinder (4), high
pressure cylinders (7), and check valves (8) and end caps (9). Not visible from the
outside are the piston and plunger.
Fig 3.10 Intensifier
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3.4.4. Hydraulic cylinder
The hydraulic cylinder (4 in Figures 2 and 5) houses the piston and is the area where
the hydraulic oil does its work. The directional control valves control the flow of oil
into and out of each side of the hydraulic cylinder.
At each end of the hydraulic cylinder is an end plate that is used to connect the hydraulic
cylinder to the high pressure cylinder. The two end plates for the hydraulic cylinder are
connected and pulled tightly in place with 4 tie rods and bolts.
Fig 3.11 Hydraulic cylinder
3.4.5. Piston
The piston (number 5 in Figures 2 and 6) is the larger diameter cylindrical part located
within the hydraulic cylinder (4 in Figures 2 and 5). The piston effectively splits the
hydraulic cylinder into a left side and a right side. Oil cannot pass from one side to the
other past the piston. It must exit and enter the hydraulic cylinder through the hoses
attached to the directional control valve. The hydraulic oil pressure is exerted onto
either side of the piston in an alternating fashion so that a back-and-forth movement of
the piston and plunger assembly is generated.
25
Fig 3.12 Piston (5) and plunger (6) assembly
3.4.6. Plunger
The plungers (6 in Figure 7) are the two smaller diameter shafts that are connected to
each side of the piston. The attachment point is inside of the hydraulic cylinder. The
other ends of the plungers extend into the left and right high pressure cylinders. Seals
are placed around the plunger shaft to keep oil from seeping into the water side of the
pump, and vice versa. The plungers are made out of either stainless steel, or, more
recently, ceramic. Ceramic is used because of its ability to handle heat and high
pressure with little thermal expansion.
Fig 3.13 Ceramic plunger
26
3.4.7. High pressure cylinder
The two high pressure cylinders (7 in Figures 8 and 2) are where the water is
pressurized. They are usually referred to as "left hand side" and "right hand side." The
high pressure cylinders are machined out of very thick stainless steel and treated in
order to withstand the extreme pressures they are put under on a continual, cyclical
basis.
Fig 3.14 High pressure cylinder (7)
3.4.8. Check valve
There is one check valve (number 8 in Figures 10 and 8) at the end of each high pressure
cylinder at the end opposite from the hydraulic cylinder. The check valve allows fresh
water to enter the high pressure cylinder and high pressure water to exit the intensifier.
The check valve is designed to only let water flow in one direction. Fresh water comes
in though channels machined in the sides and exits through one or more holes in the
face of the valve. Various seals, poppets and springs are used to maintain this water
flow. Over several hundred hours these components will wear, allowing pressurized
water to flow out the water inlet path, or allowing pressurized water to seep back into
the high pressure cylinder. The symptoms and diagnosis of these various situations will
be discussed later in the "Maintenance" chapter.
27
Fig 3.15 View of upper portion of intensifier cabinet
Fig 3.16 Check Valve Body cross-section
28
3.4.9. End Cap
The end cap (number 9 in Figures 11 and 2) is either a cylindrical or square item. The
cylindrical version screws onto the output end of the high pressure cylinder. The square
type is held in place with tie rods and bolts. The end cap has a hole in the center for the
check valve and outlet body. It will also have a connection point for the incoming fresh
water. The water flows through holes machined through the cap to line up with inlet
holes in the check valve
Fig 3.17 fillets caps
29
3.4.10. High pressure tubing
High pressure 304 or 316 stainless steel tubing (number 10 in Figure 11) is attached to
the outlet of each check valve. Common outer diameters are 0.25", 0.313", 0.375" and
0.563". Inner diameters range from 0.062" to 0.312". There is usually a flexible
protective covering around the tube.
The high pressure tubing from the left hand high pressure cylinder will join together at
some point with the high pressure tubing from the right hand cylinder. The high
pressure tubing carries the pressurized water to the pressure attenuator. Additional high
pressure tubing will channel the high pressure water to the cutting head.
The length, number of bends and other obstructions to flow (e.g. hand valves) in the
high pressure tubing path must be taken into consideration when designing a high
pressure water jet system. Pressure will drop with each bend in the tubing. Also, as the
distance between the pump and the cutting head increases, internal friction of the water
as it drags against the inner walls will generate heat resulting in a loss of water pressure.
This topic will be discussed in more detail in the Chapter 5 "Pressure Drop in Tubing."
3.4.11. Pressure attenuator
The pressure attenuator (number 11 in Figures 13 and 2) smoothest out variations in
pressure after the high pressure water has exited the intensifier. With each reversal of
cycle of the intensifier, there is a slight delay in the increase of water pressure in the
opposite high pressure cylinder. This delay is due to: 1) reversal of motion where
instantaneous velocity at the end of the stroke equals zero, and 2) mechanical delays of
reversal. All of these factors can result in a drop in water pressure. Some manufacturers
do use proprietary technology to reduce this pressure drop, which we suggest you
investigate when selecting a pump. Generally, if a 50 HP pump can sustain a 0.014"
orifice at 60,000 psi continuous operating pressure, the implication is that this hydraulic
pressure drop challenge will have been addressed.
Figure 14 shows the pressure fluctuations in the high pressure water line prior to the
pressure accumulator. This shows a pressure change from high to low of almost 22,000
psi. So, for a 60,000 psi system, the high pressure water would be going from 60,000
psi to 40,000 psi after every stroke of the intensifier.
30
If this pressure fluctuation were not smoothed out by the pressure attenuator, cutting
results at the work piece would be undesirable. There would be a significant line in the
part with every stroke of the intensifier. Recall that any change in pressure results in a
change in speed of the water jet stream at the cutting head. This change in speed changes
the speed at which the abrasive particles are moving and, therefore, the amount of force
they will impact on the work piece. Lower pressure leads to less speed of the water
which leads to less force of the abrasive which leads to slower cutting, or rougher edge
quality.
Fortunately the pressure attenuator smoothest out these pressure spikes so that the water
at the cutting head maintains a steady pressure, speed and cutting power
Fig3.18 Pressure Attenuator
Fig3.19 Pressure fluctuation prior to accumulator
31
3.4.12. Inlet water
Prior to entering the pump cabinet, water may have to be treated to get the water within
the water jet manufacturer’s specifications. Within the pump cabinet, usually in the
lower portion, the water will typically go through one or more final filters just prior to
entering the intensifier (number 12 in Figures 15 and 2).
The inlet water must be able to maintain a specified flow rate and pressure to ensure
that the intensifier receives enough water. Incoming water must also meet certain
requirements with respect to Total Dissolved Solids (TDS), pH, organic matter,
temperature, etc. Poor water quality will result in drastically reduced high pressure
component life (i.e. anything the high pressure water comes in contact with). Different
pump manufacturers require different inlet water pressures, with some needing as little
as 30 psi, and others mandating a water pressure booster pump to maintain 100 psi.
Water quality will be discussed in more detail in the chapter 4 "Water QUILITY
Fig 3.20 water inlet system
32
3.5 Controls and PLC
The controls and PLC (not pictured) control the valves in the hydraulic circuit to
determine the pressure and flow of the hydraulic oil to and from the intensifier. Various
sensor and proximity switches can also be integrated into the controls to monitor the
entire pump to verify things like stroke rate, oil temperature and pressure, inlet water
pressure and flow rate and more. This capability makes working with and
troubleshooting the modern day intensifier much easier.
3.5.1 On-Off Valve
The pneumatic On-Off valve controls the flow of water to the cutting head. The On-Off
valve at the cutting is "normally closed." That is, when there is no compressed air
supplied to the On-Off valve, a needle fits tightly against a seat to stop any high pressure
water from getting to the cutting head. When compressed air is supplied to the On-Off
valve (i.e. "tool on" command from the control), the needle is forced up from its seating
location and the high pressure water can flow through the orifice to the cutting head.
In, or near, the high pressure pump cabinet is another On-Off valve that works in
tandem with the On-Off valve at the cutting head. The On-Off valve in the pump is
typically called the Safety Relief valve. This Safety Relief valve in the pump is
"normally open." This valve will stay open when there is no air supplied to it. When
the On-Off valve at the cutting head closes ("tool off" command by control or no power
to the system), the Safety Relief valve in the pump will open, relieving all water
pressure from the high pressure tubing. When the "tool on" command is issued by the
control, the Safety Relief valve closes so that all high pressure water will go to the
cutting head. Note, not all manufacturers of new pumps have the Safety Relief valve as
standard. We strongly suggest you ask your pump manufacturer if they supply this
standard, and when it is activated. Again, some pump manufacturers will only activate
the Safety Valve when an E-Stop is pressed; when the pump stops, high pressure lines
are still pressurized.
Both of these On-Off valves must be in good working order to protect against accidental
high pressure water discharge at the cutting head that could severely injure someone
working on or near the cutting head or any of the high pressure lines. Periodic
replacement of the needle, seat and associated parts is required to maintain these valves.
33
Fig 3.21 on/off valve
34
3.6 Abrasive feeding system
3.6.1 Pressurized Bulk hopper:-
Abrasive is transported via tubing and pressure from a large bulk hopper located near
the water jet cutting system to a mini-hopper near the cutting head. Bulk hoppers will
normally hold anywhere from several hundred pounds of abrasive to 2200 pounds. If
you are cutting with one head and 1.4 pounds per minute of abrasive, then you are
consuming about 84 pounds per hour. An 1100 pound hopper would last about 13 hours
of operation. This would mean that the machine could run for well over a shift before
it needed to be refilled. Most water jets are provided with approximately 600 pound
hoppers, which would equate to about 7 hours of operation. So, at least once during an
8 hour shift the hopper would need to be reloaded. The costs associated with the
additional downtime over the course of a year should be evaluated.
Fig 3.22 bulk hopper
3.6.2 Mini-hopper
A mini-hopper is typically mounted near and above the cutting head. Most of these
mini-hoppers allow for a gravity feed of abrasive down to the cutting head. Many mini-
hoppers control the amount of abrasive that can go down to the cutting head with the
use of a slide with different size holes in it. The operator can change the position of the
slide to change the amount of abrasive to the cutting head.
A recent advance in technology is remote CNC-control of the amount of abrasive
released from the mini-hopper. Having this capability allows for optimum feeding of
35
abrasive to the cutting head in relation to the water pressure at the pump for the
following desirable capabilities:
 Piercing of fragile materials like glass or stone. Typically a lower
water pressure will be used with a smaller amount of abrasive
 Changing abrasive amount for different abrasive nozzle sizes to
optimize part cost. This can be done automatically if the mini hopper
is set up to do this.
Fig 3.23 abrasive material feeding
36
CHAPTER 4
4.1 WATER QUALITY:-
4.1.1 Overview
This chapter will discuss water quality requirements for high pressure water jet cutting
and why it is crucial to maintain proper water quality.
Note: See "Recommendation for water treatment" at the end of this chapter for a
potential solution to everything you are about to read in this chapter about water
treatment.
4.1.2 Water specifications
Every manufacturer has specific requirements for water quality. Check with the
manufacturer to get the specifications for your particular machine.
The water supplied to the intensifier is critical to water jet cutting due to its direct
influence on the service life of the equipment components such as check valves, seals
and orifices. A high concentration of Total Dissolved Solids (TDS) causes accelerated
wear of any components that come in contact with the high pressure water because of
the increased abrasiveness of the water from the TDS.
As part of the installation planning, a water quality analysis should be performed by a
commercial company that specializes in water conditioning equipment. The minimum
information that should be supplied by this analysis is TDS, silica content and pH value.
Companies like Culligan can perform these tests, or you can search "water quality
testing" on the internet.
Inlet water should be treated for either the removal of hardness of the reduction of TDS.
Water softening is an ion exchange process that removes scale forming minerals such
as calcium. TDS reduction can be accomplished with either deionization (DI) or reverse
osmosis equipment. Generally, DI or RO provides better component life than water
softening.
37
A water purification supplier should be consulted to supply the most suitable equipment
for special conditions. It might be a good idea to ask any company that you are
considering using if they have supplied systems for any other high pressure water jet
cutting systems and check their references.
The best treatment process for a specific application is a function of the original water
quality and the desired service life of the affected components. Sixty to 70 ppm of TDS
is optimum. Any water treatment producing TDS content of less than 0.5 part per
million (ppm) should be avoided since the aggressiveness of such purified water will
damage pump components.
38
4.2 Water treatment guidelines
Criteria Values Recommended
Treatment
Total Dissolved
Solids (TDS)
Low TDS (<100
ppm)
Moderate TDS (100
- 200 ppm)
High TDS (>200
ppm)
Good water, requires only
softening
Can be treated by
softening, DI or RO
Poor water, should be
treated with RO or DI
Silica Content High content (>15
ppm)
Dual Bed Strong Base DI
pH Value Treated water must
have a value of 6 - 8
39
4.3 Suspended solids
In addition to the treatment described above, the water must be filtered for the removal
of suspended solids. Different manufacturers supply differently sized final filters for
this purpose, typically down to 0.45 nominal. See "Recommendation for water
treatment" at the end of this chapter for an alternative to this.
Water supply
The initial water supply should be at least 5 gallons per minute at 40 pounds per square
inch. The water may be boosted by a small pump to the 80 psi required by most
intensifiers. Some intensifiers do not require pressure boosters, requiring only 30 psi
for the incoming water. This removes a potential failure point from the system.
Hydraulic Oil Cooling
Intensifier pumps have hydraulic oil that must be cooled. Typically there are three
options:
1. Water-Cooled through a heat exchanger
2. Air-Over-Oil Cooler
3. Closed-Loop Chiller
4.
4.3.1 Heat exchanger - For water cooled pumps
1. A heat exchanger is primarily used for cooling the hydraulic fluid of the
intensifier pump. Typically the hydraulic oil temperature must be kept below
120° F (49° C). The heat exchanger will require a consistent water flow of 0 to
8 gpm (0 to 30 liters per minute) at an inlet temperature not exceeding 70° F in
order to keep the hydraulic fluid at the proper temperature. Actual volume of
water will depend on the pump selected. As many pumps are thermostatically
controlled, when the pump is cool, it may be that no water is required.
2. This cooling water must go to drain. The cost of this water must be balanced
against the costs of the other two cooling options (air-over-oil and chiller),
which would not have any water going down the drain.
3. Public utility water is usually acceptable for cooling purposes. In situations
where the water contains heavy mineral deposits, the exchanger tubes may
40
eventually become restricted by particle buildup. If this is a chronic problem,
pre-filtration and/or water softening may be necessary.
4. Depending upon plant setup, ambient temperature can also be a factor in cooling
the hydraulic fluid. Additional cooling may be required if the intensifier and/or
heat exchanger is confined to a small, high-temperature space.
Fig 4.1 heat exchanger
41
4.3.2. Air-Over-Oil Cooler
Some pumps will use an oil-air cooler to remove heat from the hydraulic oil, so no heat
exchanger is required. In the summer, the unit can be vented outside the building to
remove the heat from the building. In the winter it can be vented inside the building to
help out with heating the building.
Fig 4.2 oil cooler
4.3.3. Chiller
A chiller can be used to re-circulate the cooling water that is used by the intensifier's
heat exchanger. It cools the water and then sends it through the heat exchanger again,
creating a closed loop. A chiller is most effective in worth considering in a few
situations in particular:
 Warmer climates where the efficiency of the heat exchanger may be reduce
 Facilities that cannot send any water to a drain,
 Parts of the country where there is a water shortage, or if the cost of water is high,
because a 50 HP pump can use up to 5 gpm for cooling the hydraulics.
42
The chiller will only reuse the cooling water; you will still be putting approximately 1
gpm with a 50 hp pump of fresh water through the cutting head, which will not be
reused with the chiller.
Incoming water for the intensifier should also be maintained at 70° F (21° C) or cooler
for best high pressure seal life. If this temperature cannot be maintained, then the chiller
can also be used for this water.
Fig 4.3 chiller
Water circuit options
Water circuit options
Following are 4 different scenarios for the water flow through a water jet cutting
system.
43
Option 1 - Heat exchanger in pump, all water runs to a drain.
fig 4.4 Heat exchanger in pump, all water runs to a drain.
Option 2 - Air-Over-Oil cooler
fig 4.5 Air-Over-Oil cooler
44
Option 3 - Chiller and heat exchanger. Water for heat exchanger re-circulates; used
water from cutting runs to drain.
Fig4.6 water from cutting runs to drain.
Option 4 - Heat exchanger, chiller and WRS-3000 water recycling unit. No water to
drain. Only water required is make-up water to replace evaporation and spillage.
45
4.4 Recommendation for water treatment
WARD Jet has found that the use of a good quality water softener in conjunction with
a 0.2 absolute final filter to be successful for treatment of water for the intensifier. This
setup can be used as long as the water from the cutting tank is not being recycled for
use through the intensifier. In the worst case, if seal life does not seem to be living up
to expectations, then a DI or RO system can be installed
46
4.4.1 Benefits of Water jet Cutting
As one of the fastest growing machine tool industries, water jet cutting has proven to
save time and money on countless applications such as metal cutting and stone cutting.
See the advantages of water jet cutting and view our photo album of different uses for
the tool. Whether it's cutting sheet metal, titanium, granite, marble, or steel - water jet
might be the answer for you.
Benefits of Water jet Cutting
Let's Take a Look... Water jet cutting is best described as an accelerated erosion
process that we are controlling. For this reason, water jet can cut or erode through
virtually any material known, making it one of the most versatile machines available.
As one of the fastest growing machine tool industries, water jet cutting has proven to
save time and money on countless applications. Please take a look at the advantages
below to see if water jet could be for you.
Tolerances
Tolerances tighter than +/- 0.005" are achievable,
especially in thinner materials such as 1" stainless
steel. However, high tolerances come with a price,
sometimes up to 500% higher than if the same part
had been specified with a tolerance of +/- 0.015". By
being more flexible with tolerances, prices will plummet as cutting speeds increase.
Water jet cutting has the ability to vary tolerances in different locations on a part,
ensuring the best pricing and quality.
Thickness And Kerf
Materials ranging from 10" stainless steel to 0.010"
acrylics can be cut by water jet, making it a very
versatile tool. Stacking of very thin materials to
increase productivity is possible. Kerf ranges from
0.020" to 0.050".
47
Taper and Edge Finish
Taper and edge finish are directly related to cut speed.
The greater the speed, the more taper and the coarser the
edge finish. As the water jet slows down, taper can be
eliminated and the finish of about 120 achieved. Again,
slower means an increase in time...and price. For a finer
edge finish, use a finer abrasive.
No Heat Affected Zone (HAZ)
Water jet cutting is a natural erosion process involving no
chemicals or heat. Because of this, warping and distortion
typically associated with laser, plasma and oxy-fuel cutting
is eliminated, therefore minimizing the need for secondary
processing.
Nesting And Common Line Cutting
Unlike laser, plasma and oxy-fuel cutting, water jet
lends itself to common line cutting. WARDJet offers
optional state-of-the-art nesting software, allowing you
to nest multiple shapes together and cut them with
multiple heads. Tracking of remnants and nesting into
these odd shapes later, helps save precious material and can contribute toward reducing
your operating costs.
Cutting Speeds
The speed at which the water jet can cut through material will vary based on a variety
of parameters. In the charts below you can see that the orifice/nozzle combination you
select will have an influence on your cut speed. Generally when cutting with a single
48
head and a 50 hp pump the chart with the 14/40 orifice/nozzle combination is the closest
guide for cut speed. When cutting with two heads and a 50 hp pump use the chart with
the 10/30 orifice/nozzle combination to indicate the cutting speed of each head.
After selecting the correct chart find the material and the thickness that you will be
cutting. This will then give you an idea of your straight line cutting speed based on the
quality of edge finish and tolerance you need for your parts. These cutting speeds are
only a guide to estimate cutting speeds achievable. We recommend that test cutting is
done to determine actual feed rates on different materials and thicknesses.
4.5 Water jet in Any Industry
The versatility of the water jet allows it to be used in nearly every industry. There are
many different materials that the water jet can cut. Some of them have unique
characteristics that require special attention when cutting. As you can see in the chart
below each material you cut will have some unique characteristics that have to be taken
into account.
The information below explains some of the cutting techniques we've used when cutting
these materials. We recognize that there are many materials not listed so if you have a
specific question about your material feel free to contact us at (330) 677-9100.
49
4.5.1Alloys
Inconel, Hastalloy, Wasp alloy, Titanium, Aluminum, Stainless etc. No heat effected
zone or change in the molecular structure occurs in the alloy material. There is no
distortion as seen with typical heat cutting methods. Generally, cutting with water jet
costs less than traditional machining or cutting methods. In many cases, no secondary
removal of slag or damaged material is necessary, and minimal to no burring is seen.
4.5.2Steels
Water jet is not always the most cost effective method to cut steels. As a rule, if the
finished product is presently being cut using laser, plasma or oxyfuel, and no secondary
work is needed to the part after being cut, it is unlikely water jet will be an economical
solution. However, as soon as any secondary work, closer tolerances or removal of the
Heat Affected Zone (HAZ) is needed, water jet is probably the solution. With the use
of the WARD (Water jet Abrasive Recycling Dispenser) companies are able to reduce
their operating cost substantially, reducing the gap between laser and water jet cutting.
In many cases, water jet now costs less than laser!
50
4.5.3Laminates
Water jet, in most cases, does not see any difference between laminated materials - e.g.
acrylic, aluminum, stainless and honeycomb section all laminated as one. Many aircraft
parts consist of laminated materials where water jet is the only solution.
4.5.4Composites
many composites are very difficult to machine as the cutting tool tips 'gum' up and
quickly becomes inefficient. Water jet has no gumming at all and can leave a good clean
surface requiring no additional work.
4.5.5Plastics/Acrylics
It is possible to not only cut these materials effortlessly, but also drill start holes using
specialized low-pressure options available with certain systems.
51
4.5.6Rubber
Depending on the durometer value, rubber can be cut with water only or with abrasive.
Tests will quickly reveal what the best option is for your application.
4.5.7Gaskets
By using water jet for cutting gaskets, it is possible to automatically nest various sized
and shaped gaskets on one sheet effortlessly. There is no longer any need for stacks of
dies. Software will keep track of all remnant sheets allowing off cuts to be put back into
inventory and used for smaller parts. Specialized software is available to track materials
through the entire process.
52
4.5.8Fiberglass
When cutting materials that are typically associated with hazardous fine airborne
materials, water jet is an ideal solution. Particles and materials removed are transported
by the water away from the surface into the tank, reducing this risk and hazard.
4.5.9Glass
Intricate cutting and shaping of glass is easy with water jet. The water jet can generally
drill all its own start holes, making it a highly versatile tool. Glass from 1/32" to 10"
thick can be cut, even when laminated in multiple layers.
53
CHAPTER 4
CONCLUSION:-
As a conclusion, the experiment that have been carried out were successful, even though
the data collected are a little bit difference compared to the theoretical value. The
difference between the theoretical value and the actual value may mainly due to human
and servicing factors such as parallax error. This error occur during observer captured
the value of the water level. Besides that, error may occur during adjusting the level
gauge to point at the white line on the side of the weight pan. Other than that, it also
maybe because of the water valve. This error may occur because the water valve was
not completely close during collecting the water. This may affect the time taken for the
water to be collected. There are a lot of possibilities for the experiment will having an
error. Therefore, the recommendation to overcome the error is ensure that the position
of the observer’s eye must be 90° perpendicular to the reading or the position. Then,
ensure that the apparatus functioning perfectly in order to get an accurate result.
54
REFERENCE
1.http://www.cee.mtu.edu/~dwatkins/ce3600_labs/impact_of_jet.pdf
2. http://www.eng.ucy.ac.cy/EFM/Manual/HM%2015008/HM15008E-ln.pdf
3.http://staff.fit.ac.cy/eng.fm/classes/amee202/Fluids%20Lab%20Impact%20of%20a
%20Jet.pdf
4. WIKIPEDIA
5. http://www.wardjet.com/water jet-university
55
56
57
58

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Project report on water jet system

  • 1. 1 Chapter 1 1.1Introduction:- A water jet cutter, also known as a water jet or water jet, is an industrial tool capable of cutting a wide variety of materials using a very high-pressure jet of water, or a mixture of water and an abrasive substance. The term abrasive jet refers specifically to the use of a mixture of water and abrasive to cut hard materials such as metal or granite, while the terms pure water jet and water-only cutting refer to water jet cutting without the use of added abrasives, often used for softer materials such as wood or rubber. Water jet cutting is often used during fabrication of machine parts. It is the preferred method when the materials being cut are sensitive to the high temperatures generated by other methods. Water jet cutting is used in various industries, including mining and aerospace, for cutting, shaping, and reaming. Fig1.1:- Water jet cutter
  • 2. 2 Cutting steel, concrete, glass and marble with water - sounds a bit far-fetched doesn’t it? Way back in the 1950s, a forestry engineer by the name of Norman Franz started fiddling around with a high-pressure water stream to cut lumber. His aim was to streamline the process and reduce the strain on traditional cutting equipment such as saw blades, which easily became blunt and needed replacing. From these humble beginnings an idea was born, and over the next couple of decades, water cutting became an unparalleled method for cutting materials of all types, shapes and sizes. FIG1.2:- nozzle The end product? A water jet cutter – a machine capable of slicing metal and other materials such as granite and marble with unbelievable accuracy. It does this by using a jet of water at high velocity and pressure, sometimes mixed with an abrasive substance, depending on the material that is being cut. Water jet cutters are usually used to cut materials such as rubber, foam, plastics, leather, composites, stone, tiles, metals, food and paper. However, they can’t cut tempered glass, diamonds and certain ceramics
  • 3. 3 Fig1.3:- water jet cutter operation.
  • 4. 4 CHAPTER 2 2.2 HISTORY:- While using high-pressure water for erosion dates back as far as the mid- 1800s with hydraulic mining, it was not until the 1930s that narrow jets of water started to appear as an industrial cutting device. In 1933, the Paper Patents Company in Wisconsin developed a paper metering, cutting, and reeling machine that used a diagonally moving water jet nozzle to cut a horizontally moving sheet of continuous paper.[2] These early applications were at a low pressure and restricted to soft materials like paper. Water jet technology evolved in the post-war era as researchers around the world searched for new methods of efficient cutting systems. In 1956, Carl Johnson of Durox International in Luxembourg developed a method for cutting plastic shapes using a thin stream high-pressure water jet, but those materials, like paper, were soft materials.[3] In 1958, Billie Schwacha of North American Aviation developed a system using ultra- high-pressure liquid to cut hard materials.[4] This system used a 100,000 psi (690 MPa) pump to deliver a hypersonic liquid jet that could cut high strength alloys such as PH15- 7-MO stainless steel. Used as a honeycomb laminate on the Mach 3 North American XB-70 Valkyrie, this cutting method resulted in delaminating at high speed, requiring changes to the manufacturing process.[5] While not effective for the XB-70 project, the concept was valid and further research continued to evolve water jet cutting. In 1962, Philip Rice of Union Carbide explored using a pulsing water jet at up to 50,000 psi (345 MPa) to cut metals, stone, and other materials.[6] Research by S.J. Leach and G.L. Walker in the mid-1960s expanded on traditional coal water jet cutting to determine ideal nozzle shape for high-pressure water jet cutting of stone,[7] and Norman Franz in the late 1960s focused on water jet cutting of soft materials by dissolving long chain polymers in the water to improve the cohesiveness of the jet stream.[8]
  • 5. 5 In the early 1970s, the desire to improve the durability of the water jet nozzle led Ray Chadwick, Michael Kurko, and Joseph Corriveau of the Bendix Corporation to come up with the idea of using corundum crystal to form a water jet orifice,[9] while Norman Franz expanded on this and created a water jet nozzle with an orifice as small as 0.002 inches (0.05 mm) that operated at pressures up to 70,000 psi (483 MPa).[10] John Olsen, along with George Hurlburt and Louis Kapcsandy at Flow Research (later Flow Industries), further improved the commercial potential of the water jet by showing that treating the water beforehand could increase the operational life of the nozzle.[11] Fig 2.1 old model of water jet system 2.2.1 1800:- Hydraulic mining had its precursor in the practice of ground sluicing, a development of which is also known as "hushing", in which surface streams of water were diverted so as to erode gold-bearing gravels. This was originally used in the Roman empire in the first centuries AD and BC, and expanded throughout the empire wherever alluvial deposits occurred[2] The Romans used ground sluicing to remove overburden and the gold-bearing debris in Las Medullas of Spain,
  • 6. 6 and Dolaucothi in Britain. The method was also used in Elizabethan England & Wales (or rarel for developing lead, tin and copper mines.1 Water was used on a large scale by Roman engineers in the first centuries BC and AD when the Roman empire was expanding rapidly in Europe. Using a process later known as hushing, the Romans stored a large volume of water in a reservoir immediately above the area to be mined; the water was then quickly released. The resulting wave of water removed overburden and exposed bedrock. Gold veins in the bedrock were then worked using a number of techniques, and water power was used again to remove debris. The remains at Las Medullas and in surrounding areas show badland scenery on a gigantic scale owing to hydraulic king of the rich alluvial gold deposits. Las Medullas is now a UNESCO World Heritage site. The site shows the remains of at least seven large aqueducts of up to 30 miles in length feeding large supplies of water into the site. The gold-mining operations were described in vivid terms by Pliny the Elder in his Naturalist Historia published in the first century AD. Pliny was a procurator in Hispania Terraconensis in the 70's and must have witnessed for himself the operations. The use of hushing has been confirmed by field survey and archaeology at Dolaucothi in South Wales, the only known Roman gold mine in Britain. The modern form of hydraulic mining, using jets of water directed under very high pressure through hoses and nozzles at gold-bearing upland paleo gravels, was first used by Edward Matteson near Nevada City, California in 1853 during the California Gold Rush.[3] Matteson used canvas hose which was later replaced with crinoline hose by the 1860s.[4] In California, hydraulic mining often brought water from higher locations for long distances to holding ponds several hundred feet above the area to be mined. California hydraulic mining exploited gravel deposits, making it a form of placer mining. Early placer miners in California discovered that the more gravel they could process, the more gold they were likely to find. Instead of working with pans, sluice boxes, long toms, and rockers, miners collaborated to find ways to process larger quantities of gravel more rapidly. Hydraulic mining became the largest-scale, and most devastating, form of placer mining. Water was redirected into an ever-narrowing channel, through a large canvas hose, and out through a giant iron nozzle, called a "monitor." The
  • 7. 7 extremely high pressure stream was used to wash entire hillsides through enormous sluices. By the early 1860s, while hydraulic mining was at its height, small-scale placer mining had largely exhausted the rich surface placers, and the mining industry turned to hard rock (called quartz mining in California) or hydraulic mining, which required larger organizations and much more capital. By the mid-1880s, it is estimated that 11 million ounces of gold (worth approximately US$7.5 billion at mid-2006 prices) had been recovered by hydraulic mining in the California Gold Rush. 2.2.2 1850:- High-pressure vessels and pumps became affordable and reliable with the advent of steam power. By the mid-1850s, steam locomotives were common and the first efficient steam-driven fire engine was operational.[12] By the turn of the century, high-pressure reliability improved, with locomotive research leading to a six fold increase in boiler pressure, some reaching 1600 psi (11 MPa). Most high-pressure pumps at this time, though, operated around 500–800 psi (3–6 MPa).
  • 8. 8 High-pressure systems were further shaped by the aviation, automotive, and oil industries. Aircraft manufacturers such as Boeing developed seals for hydraulically boosted control systems in the 1940s,[13] while automotive designers followed similar research for hydraulic suspension systems.[14] Higher pressures in hydraulic systems in the oil industry also led to the development of advanced seals and packing to prevent leaks.[15] These advances in seal technology, plus the rise of plastics in the post-war years, led to the development of the first reliable high-pressure pump. The invention of Marlex by Robert Banks and John Paul Hogan of the Phillips Petroleum company required a catalyst to be injected into the polyethylene.[16] McCartney Manufacturing Company in Baxter Springs, Kansas, began manufacturing these high-pressure pumps in 1960 for the polyethylene industry.[17] Flow Industries in Kent, Washington set the groundwork for commercial viability of water jets with John Olsen’s development of the high- pressure fluid intensifier in 1973,[18] a design that was further refined in 1976.[19] Flow Industries then combined the high-pressure pump research with their water jet nozzle research and brought water jet cutting into the manufacturing world.
  • 9. 9 2.2.3 1935:- While cutting with water is possible for soft materials, the addition of an abrasive turned the water jet into a modern machining tool for all materials. This began in 1935 when the idea of adding an abrasive to the water stream was developed by Elmo Smith for the liquid abrasive blasting.[20] Smith’s design was further refined by Leslie Terrell of the Hydro blast Corporation in 1937, resulting in a nozzle design that created a mix of high-pressure water and abrasive for the purpose of wet blasting.[21] Producing a commercially viable abrasive water jet nozzle for precision cutting came next by Dr. Mohamed Hashish who invented and led an engineering research team at Flow Industries to develop the modern abrasive water jet cutting technology.[22] Dr. Hashish, who also coined the new term "Abrasive Water jet" AWJ, and his team continued to develop and improve the AWJ technology and its hardware for many applications which is now in over 50 industries worldwide. A most critical development was creating a durable mixing tube that could withstand the power of the high-pressure AWJ, and it was Boride Products (now Kennametal) development of their ROCTEC line of ceramic tungsten carbide composite tubes that significantly increased the operational life of the AWJ nozzle.[23] Current work on AWJ nozzles is on micro abrasive water jet so cutting with jets smaller than 0.015 inch in diameter can be commercialized
  • 10. 10 2.2.4 1990:- As water jet cutting moved into traditional manufacturing shops, controlling the cutter reliably and accurately was essential. Early water jet cutting systems adapted traditional systems such as mechanical pantographs and CNC systems based on John Parsons’ 1952 NC milling machine and running G-code.[24] Challenges inherent to water jet technology revealed the inadequacies of traditional G-Code, as accuracy depends on varying the speed of the nozzle as it approaches corners and details.[25] Creating motion control systems to incorporate those variables became a major innovation for leading water jet manufacturers in the early 1990s, with Dr John Olsen of OMAX Corporation developing systems to precisely position the water jet nozzle[26] while accurately specifying the speed at every point along the path,[27] and also utilizing common PCs as a controller. The largest water jet manufacturer, Flow International (a spinoff of Flow Industries), recognized the benefits of that system and licensed the OMAX software, with the result that the vast majority of water jet cutting machines worldwide are simple to use, fast, and accurate.[28]
  • 11. 11 CHAPTER 3 3.1 Working:- At its most basic, water flows from a pump, through plumbing and out a cutting head. It is simple to explain, operate and maintain. The process, however, incorporates extremely complex materials technology and design. To generate and control water at pressures of 87,000 psi requires science and technology not taught in universities. At these pressures a slight leak can cause permanent erosion damage to components if not properly designed. Thankfully, the water jet manufacturers take care of the complex materials technology and cutting-edge engineering. The user need only be knowledgeable in the basic water jet operation. Flow machines are designed to operate as both pure and abrasive water jets. A pure water jet is used to cut soft materials, and within just 2 minutes the very same water jet can be transformed into an abrasive water jet to cut hard materials. With any type, the water must first be pressurized. Fig 3.1 horizontal water jet cutter
  • 12. 12 3.1.1 High pressure water jet cutting:- Water is pressurized to very high pressures, in excess of 50,000 psi. This pressurization is accomplished with the use of pumps of various designs, discussed next in this chapter. The high pressure water is transported through a series of stainless steel tubes to a cutting head. Depending upon the material being cut, the cutting head can be either a "pure water cutting head" or an "abrasive cutting head." In the cutting head, the high pressure water is forced through a small diameter orifice. The diameter of this orifice is anywhere from 0.004" to 0.020". This step converts the pressure of the water jet stream into speed. We go from potential energy to kinetic energy. Coming out of the orifice, the water jet stream is moving at 2200 mph or faster. Higher pressure results in higher speed. Smaller diameter orifices yield a faster water jet stream, but also a stream with less kinetic energy since there is not as much water available to accelerate abrasive grains to full speed. In a pure water cutting head, the water immediately exits the cutting head after passing through the orifice. The speed and power of the water jet stream is enough to cut soft or thin materials like foam, rubber, soft wood, plastics, carpet, food, car headliners, circuit boards and more. In an abrasive cutting head, a very hard abrasive, typically garnet, is fed into the water jet stream. The abrasive particles are accelerated to near the speed of the water jet stream. This gives the abrasive particles much power. The abrasive water jet stream now travels down through an abrasive nozzle, or mixing tube, approximately 3 inches long with an inner diameter of between .030" and 0.050". The mixture of water and abrasive exits the abrasive nozzle and will cut hard materials like metals, stone, acrylic, ceramic, composites, phenolic and porcelain. A CNC control will move the cutting head in up to 6 axes of motion to cut the targeted work piece.
  • 13. 13 3.2 Types of pumps:- 3.2.1 Intensifier Intensifier pumps are called intensifiers because they use the concept of pressure intensification or amplification to generate the desired water pressure. If you apply pressure to one side of a cylinder and the other side of the cylinder is the same surface area, the pressure on the other side will be the same. If the surface area of the smaller side is half, then the pressure on that side will be doubled. Generally with intensifier pumps there is a 20 times difference between the large surface area (where the oil pressure is applied) and the small surface area (where the water pressure is generated). The following picture shows this concep Ultimately, there must be a restriction in the flow of water in order for the pressure to be generated. This restriction is generated by the orifice in the cutting head. Pressure is maintained until the orifice diameter exceeds the limits for water output of the pump. For very small diameter orifices, in order to maintain pressure, the pump only needs to cycle very slowly to maintain pressure. As the orifice gets larger, the pump must work faster to maintain pressure and water flow. If the orifice gets too large, the pump tries to cycle too fast for the design specification. An "over stroke" situation is sensed by the control and the pump is stopped with an error message. If there are leaks in the water circuit between the pump and the cutting head, this can also result in a pump "over stroke" situation. The leaks effectively rob water available to go to the cutting head. The same as putting in too large of an orifice, the pump runs faster to maintain pressure until it reaches its limit. Typically, intensifiers stroke at around 50 - 60 strokes per minute when working at full capacity
  • 14. 14 fig 3.2 Intensifier pump 3.2.2 Direct Drive A direct drive pump works like a car’s engine. A motor turns a crankshaft attached to 3 or more offset pistons. As the crankshaft turns, the pistons reciprocate in their respective cylinders, creating pressure in the water. Pressure and flow rate are determined by how fast the motor turns the crankshaft. Direct drive pumps cycle much faster than intensifiers, on the order of 1750 revolutions per minute. Direct drive pumps generally are found in lower pressure applications (i.e. 55,000 pounds per square inch and under). Maintenance on the direct drive pump tends to take longer than an intensifier pump. Direct drive pumps can only run more than one cutting head only if all cutting heads are cutting the same part at the same time. With an intensifier pump, you could have cutting heads on multiple machines, cutting different parts, cycling the various cutting heads on and off in any sequence. The intensifier pump will need to only vary its stroke rate accordingly to maintain flow and pressure.
  • 15. 15 Fig 3.3 direct drive pump
  • 16. 16 3.3 Principles of water jet cutting There are two types of water jet cutting processes; pure water cutting, in which the cutting is performed using only an ultra-high pressure jet of clean water, and abrasive water jet cutting in which an abrasive (typically garnet) is introduced into the high pressure stream. Pure water cutting can be employed to profile a huge variety of materials, these will typically be 'soft' materials such as gaskets, rubber, foam & plastics. Filtered tap water is fed into an intensifier pump where it is pressurised to (typically) 60,000psi. This ultra-high pressure water is forced through a tiny (0.15mm) orifice jewel which is normally manufactured from sapphire. This has the effect of focusing the beam of water into a fine, accurate stream travelling at speeds of up to 900m/sec, capable of accurate cutting of a wide range of soft materials. In order to cut 'harder' materials or any material containing glass or metal, then abrasive water jet cutting would be employed. The principles of abrasive water jet cutting are similar to pure water jet cutting, but once the stream has passed through the orifice it enters a carbide nozzle. Within this nozzle is a mixing chamber within which a partial vacuum is created as the water passes through. Garnet is introduced under gravity into the nozzle and the partial vacuum within the mixing chamber has the effect of dragging the abrasive into the water stream to create a highly abrasive cutting jet. Abrasive cutting would typically be used on materials such as stainless steel, aluminium, stone, ceramics & composite materials. Fig3.4 mouthpiece of jet
  • 17. 17 In both processes the head is controlled by a CNC controller, this offering great accuracy and repeatability. The CNCcontroller is programmed by first drawing the part to be manufactured using proprietary software, and then converting this drawing into a G code format – CNC language. Fig 3.5 vertical water jet Water jet cutting is a cold grinding or cutting process. It combines the advantages of laser – precision – with those of water: water jet cutting is thermoneutral. In addition to laser cutting, water jet cutting is becoming increasingly important in Switzerland and Germany. No thermal stresses occur with water jet cutting. The microstructure of the material and the material strength remain. There are no cures, distortions, dripping slag, melting or toxic gases. In all processes, the cutting heads with the focusing nozzles are integrated in a guiding machine (robot, 2D or 3D portal). The controlled CNC axes enable 2D, 2.5D or 3D cutting processes. These processes can cut almost all materials – hard like steel and glass, but also fragile and extremely soft materials – without stress forces. Water jet cutting has three principles: the pure water jet principle “WJ”, the abrasive water jet principle “AW” and the suspension jet principle, which is still at development stage.
  • 18. 18 3.3.1 Water jet cutting with pure water:- With pure water jet cutting “WJ”, a pure water jet with a diameter of 0.1 mm cuts the material at up to three times the speed of sound (at speeds of up to 200 m/min). These materials include textiles, elastomers, fibers, thin plastics, food, paper, cardboard, leather, thermoplastic materials or food. The water is pressurized to 1,000–6,000 bar (standard approximately 3,800 bar). After flowing through a high-pressure needle valve, the water enters a 200 mm long and 3 mm in diameter wide collimation tube (calming section). It is then pressurized by a water nozzle or a dynamic pressure nozzle and accelerated. The jet speed varies according to geometry and pressure. The small diameter of the water nozzle produces a very high local energy density, which remains constant on a relatively long section in the direction of the water jet and cuts cleanly and accurately when hitting the material. Fig3.6 half section view of water jet
  • 19. 19 3.3.2 Water jet cutting with abrasives:- With abrasive water jet cutting, compact and hard materials such as metals (including steel), hard stone, glass (including bullet-proof glass) and ceramic are separated. Before the concentrated jet of water hits the material, a cutting material of the finest grain size (abrasive) is added in the required dose in a mixing chamber, which ensures micro cutting. The water serves as an accelerator for the abrasive particles and hits the material with an impact speed of 800 m/s, thereby removing it with precision. Until the water jet is produced, abrasive water jet cutting is identical to pure water jet cutting. The difference is that the pure water jet is no longer used just for cutting, but as a carrier material for the abrasive particles. The pure water jet flows into a mixing chamber, into which the abrasive particles are then introduced. At the end of the mixing chamber is the focusing tube, in which the abrasive grains in the water jet are accelerated and confined to a specific cross-section.
  • 20. 20 3.3.3 Water jet cutting with suspension jet With the suspension jet principle or water abrasive suspension jet cutting, a pre- prepared mixture of abrasive particles and water is discharged under high pressure from a cutting nozzle. However, the abrasive agent is not added at the nozzle but is pressurized under the exclusion of air. Therefore, a water-abrasive mixture (a suspension) is expelled from the cutting nozzle under high pressure. This enables higher cutting performance, allows greater thicknesses and almost all materials to be cut. However, there is a delay in the start and stop of the cutting operation, since the abrasive feed cannot be switched on and off as rapidly as in injection cutting. This is one disadvantage when high-precision cutting is required. The wear on the valves and nozzles is also much larger and attainable pressures are smaller. Therefore, this principle is only seldom used on an industrial scale. Fig 3.7 suspension jet
  • 21. 21 3.4 PARTS OF WATER JET CUTTER:- 3.4.1. Electric motor and hydraulic pump The electric motor and hydraulic pump (number 1 in picture above) create the oil pressure needed for the oil side of the intensifier. This assembly is normally in the lower portion of the pump cabinet. The electric motor and pump are rated in HP (or kW for metric). Typical pump sizes are 30 HP, 50 HP, 75 HP, 100 HP and 150 HP As discussed in the previous chapter, each pump will have an associated water output volume (gallons per minute) and pressure (psi). Again it is important to remember that HP is not necessarily an indication of pressure. A 150 HP pump doesn’t necessarily create more pressure than a 50 HP pump. Horsepower is more directly related to water output, since more HP will be needed to create enough power to move the piston/plunger assembly in the intensifier at the required stroke rate. Fig3.8 Intensifier pump cabinet (150 HP)
  • 22. 22 3.4.2. Directional control valves One of the most important considerations in any fluid power system is control. If control components are not properly selected, the entire system does not function as required. In fluid power, controlling elements are called valves. There are three types of valves: 1. Directional control valves (DCVs): They determine the path through which a fluid transverses a given circuit. Pressure control valves: They protect the system against overpressure, which may occur due to a sudden surge as valves open or close or due to an increase in fluid demand. 2. Flow control valves: Shock absorbers are hydraulic devices designed to smooth out pressure surges and to dampen hydraulic shock. In addition, the fluid flow rate must be controlled in various lines of a hydraulic circuit. For example, the control of actuator speeds can be accomplished through use of flow control valves. Non-compensated flow control valves are used where precise speed control is not required because the flow rate varies with pressure drop across a flow control valve. It is important to know the primary function and operation of various types of control components not only for good functioning of a system, but also for discovering innovative methods to improve the fluid power system for a given application. 1.2Directional Control Valves A valve is a device that receives an external signal (mechanical, fluid pilot signal, electrical or electronics) to release, stop or redirect the fluid that flows through it. The function of a DCV is to control the direction of fluid flow in any hydraulic system. A DCV does this by changing the position of internal movable parts. To be more specific, a DCV is mainly required for the following purposes:  To start, stop, accelerate, decelerate and change the direction of motion of a hydraulic actuator.  To permit the free flow from the pump to the reservoir at low pressure when the pump’s delivery is not needed into the system.  To vent the relief valve by either electrical or mechanical control.  To isolate certain branch of a circuit. 2 Any valve contains ports that are external openings through which a fluid can enter and exit via connecting pipelines. The number of ports on a DCV is identified using the term “way.” Thus, a valve with four ports is a four-way valve A DCV consists of a valve body or valve housing and a valve mechanism usually mounted on a sub-plate. The ports of a sub-plate are threaded to hold the tube fittings which connect the valve to the fluid conductor lines. The valve mechanism directs the fluid to selected output
  • 23. 23 ports or stops the fluid from passing through the valve. DCVs can be classified based on fluid path, design characteristics, control methods and construction Fig 3.9 Directional Control Valve 3.4.3. Intensifier The intensifier proper (3 in Figures 4 and 2) consists of the hydraulic cylinder (4), high pressure cylinders (7), and check valves (8) and end caps (9). Not visible from the outside are the piston and plunger. Fig 3.10 Intensifier
  • 24. 24 3.4.4. Hydraulic cylinder The hydraulic cylinder (4 in Figures 2 and 5) houses the piston and is the area where the hydraulic oil does its work. The directional control valves control the flow of oil into and out of each side of the hydraulic cylinder. At each end of the hydraulic cylinder is an end plate that is used to connect the hydraulic cylinder to the high pressure cylinder. The two end plates for the hydraulic cylinder are connected and pulled tightly in place with 4 tie rods and bolts. Fig 3.11 Hydraulic cylinder 3.4.5. Piston The piston (number 5 in Figures 2 and 6) is the larger diameter cylindrical part located within the hydraulic cylinder (4 in Figures 2 and 5). The piston effectively splits the hydraulic cylinder into a left side and a right side. Oil cannot pass from one side to the other past the piston. It must exit and enter the hydraulic cylinder through the hoses attached to the directional control valve. The hydraulic oil pressure is exerted onto either side of the piston in an alternating fashion so that a back-and-forth movement of the piston and plunger assembly is generated.
  • 25. 25 Fig 3.12 Piston (5) and plunger (6) assembly 3.4.6. Plunger The plungers (6 in Figure 7) are the two smaller diameter shafts that are connected to each side of the piston. The attachment point is inside of the hydraulic cylinder. The other ends of the plungers extend into the left and right high pressure cylinders. Seals are placed around the plunger shaft to keep oil from seeping into the water side of the pump, and vice versa. The plungers are made out of either stainless steel, or, more recently, ceramic. Ceramic is used because of its ability to handle heat and high pressure with little thermal expansion. Fig 3.13 Ceramic plunger
  • 26. 26 3.4.7. High pressure cylinder The two high pressure cylinders (7 in Figures 8 and 2) are where the water is pressurized. They are usually referred to as "left hand side" and "right hand side." The high pressure cylinders are machined out of very thick stainless steel and treated in order to withstand the extreme pressures they are put under on a continual, cyclical basis. Fig 3.14 High pressure cylinder (7) 3.4.8. Check valve There is one check valve (number 8 in Figures 10 and 8) at the end of each high pressure cylinder at the end opposite from the hydraulic cylinder. The check valve allows fresh water to enter the high pressure cylinder and high pressure water to exit the intensifier. The check valve is designed to only let water flow in one direction. Fresh water comes in though channels machined in the sides and exits through one or more holes in the face of the valve. Various seals, poppets and springs are used to maintain this water flow. Over several hundred hours these components will wear, allowing pressurized water to flow out the water inlet path, or allowing pressurized water to seep back into the high pressure cylinder. The symptoms and diagnosis of these various situations will be discussed later in the "Maintenance" chapter.
  • 27. 27 Fig 3.15 View of upper portion of intensifier cabinet Fig 3.16 Check Valve Body cross-section
  • 28. 28 3.4.9. End Cap The end cap (number 9 in Figures 11 and 2) is either a cylindrical or square item. The cylindrical version screws onto the output end of the high pressure cylinder. The square type is held in place with tie rods and bolts. The end cap has a hole in the center for the check valve and outlet body. It will also have a connection point for the incoming fresh water. The water flows through holes machined through the cap to line up with inlet holes in the check valve Fig 3.17 fillets caps
  • 29. 29 3.4.10. High pressure tubing High pressure 304 or 316 stainless steel tubing (number 10 in Figure 11) is attached to the outlet of each check valve. Common outer diameters are 0.25", 0.313", 0.375" and 0.563". Inner diameters range from 0.062" to 0.312". There is usually a flexible protective covering around the tube. The high pressure tubing from the left hand high pressure cylinder will join together at some point with the high pressure tubing from the right hand cylinder. The high pressure tubing carries the pressurized water to the pressure attenuator. Additional high pressure tubing will channel the high pressure water to the cutting head. The length, number of bends and other obstructions to flow (e.g. hand valves) in the high pressure tubing path must be taken into consideration when designing a high pressure water jet system. Pressure will drop with each bend in the tubing. Also, as the distance between the pump and the cutting head increases, internal friction of the water as it drags against the inner walls will generate heat resulting in a loss of water pressure. This topic will be discussed in more detail in the Chapter 5 "Pressure Drop in Tubing." 3.4.11. Pressure attenuator The pressure attenuator (number 11 in Figures 13 and 2) smoothest out variations in pressure after the high pressure water has exited the intensifier. With each reversal of cycle of the intensifier, there is a slight delay in the increase of water pressure in the opposite high pressure cylinder. This delay is due to: 1) reversal of motion where instantaneous velocity at the end of the stroke equals zero, and 2) mechanical delays of reversal. All of these factors can result in a drop in water pressure. Some manufacturers do use proprietary technology to reduce this pressure drop, which we suggest you investigate when selecting a pump. Generally, if a 50 HP pump can sustain a 0.014" orifice at 60,000 psi continuous operating pressure, the implication is that this hydraulic pressure drop challenge will have been addressed. Figure 14 shows the pressure fluctuations in the high pressure water line prior to the pressure accumulator. This shows a pressure change from high to low of almost 22,000 psi. So, for a 60,000 psi system, the high pressure water would be going from 60,000 psi to 40,000 psi after every stroke of the intensifier.
  • 30. 30 If this pressure fluctuation were not smoothed out by the pressure attenuator, cutting results at the work piece would be undesirable. There would be a significant line in the part with every stroke of the intensifier. Recall that any change in pressure results in a change in speed of the water jet stream at the cutting head. This change in speed changes the speed at which the abrasive particles are moving and, therefore, the amount of force they will impact on the work piece. Lower pressure leads to less speed of the water which leads to less force of the abrasive which leads to slower cutting, or rougher edge quality. Fortunately the pressure attenuator smoothest out these pressure spikes so that the water at the cutting head maintains a steady pressure, speed and cutting power Fig3.18 Pressure Attenuator Fig3.19 Pressure fluctuation prior to accumulator
  • 31. 31 3.4.12. Inlet water Prior to entering the pump cabinet, water may have to be treated to get the water within the water jet manufacturer’s specifications. Within the pump cabinet, usually in the lower portion, the water will typically go through one or more final filters just prior to entering the intensifier (number 12 in Figures 15 and 2). The inlet water must be able to maintain a specified flow rate and pressure to ensure that the intensifier receives enough water. Incoming water must also meet certain requirements with respect to Total Dissolved Solids (TDS), pH, organic matter, temperature, etc. Poor water quality will result in drastically reduced high pressure component life (i.e. anything the high pressure water comes in contact with). Different pump manufacturers require different inlet water pressures, with some needing as little as 30 psi, and others mandating a water pressure booster pump to maintain 100 psi. Water quality will be discussed in more detail in the chapter 4 "Water QUILITY Fig 3.20 water inlet system
  • 32. 32 3.5 Controls and PLC The controls and PLC (not pictured) control the valves in the hydraulic circuit to determine the pressure and flow of the hydraulic oil to and from the intensifier. Various sensor and proximity switches can also be integrated into the controls to monitor the entire pump to verify things like stroke rate, oil temperature and pressure, inlet water pressure and flow rate and more. This capability makes working with and troubleshooting the modern day intensifier much easier. 3.5.1 On-Off Valve The pneumatic On-Off valve controls the flow of water to the cutting head. The On-Off valve at the cutting is "normally closed." That is, when there is no compressed air supplied to the On-Off valve, a needle fits tightly against a seat to stop any high pressure water from getting to the cutting head. When compressed air is supplied to the On-Off valve (i.e. "tool on" command from the control), the needle is forced up from its seating location and the high pressure water can flow through the orifice to the cutting head. In, or near, the high pressure pump cabinet is another On-Off valve that works in tandem with the On-Off valve at the cutting head. The On-Off valve in the pump is typically called the Safety Relief valve. This Safety Relief valve in the pump is "normally open." This valve will stay open when there is no air supplied to it. When the On-Off valve at the cutting head closes ("tool off" command by control or no power to the system), the Safety Relief valve in the pump will open, relieving all water pressure from the high pressure tubing. When the "tool on" command is issued by the control, the Safety Relief valve closes so that all high pressure water will go to the cutting head. Note, not all manufacturers of new pumps have the Safety Relief valve as standard. We strongly suggest you ask your pump manufacturer if they supply this standard, and when it is activated. Again, some pump manufacturers will only activate the Safety Valve when an E-Stop is pressed; when the pump stops, high pressure lines are still pressurized. Both of these On-Off valves must be in good working order to protect against accidental high pressure water discharge at the cutting head that could severely injure someone working on or near the cutting head or any of the high pressure lines. Periodic replacement of the needle, seat and associated parts is required to maintain these valves.
  • 34. 34 3.6 Abrasive feeding system 3.6.1 Pressurized Bulk hopper:- Abrasive is transported via tubing and pressure from a large bulk hopper located near the water jet cutting system to a mini-hopper near the cutting head. Bulk hoppers will normally hold anywhere from several hundred pounds of abrasive to 2200 pounds. If you are cutting with one head and 1.4 pounds per minute of abrasive, then you are consuming about 84 pounds per hour. An 1100 pound hopper would last about 13 hours of operation. This would mean that the machine could run for well over a shift before it needed to be refilled. Most water jets are provided with approximately 600 pound hoppers, which would equate to about 7 hours of operation. So, at least once during an 8 hour shift the hopper would need to be reloaded. The costs associated with the additional downtime over the course of a year should be evaluated. Fig 3.22 bulk hopper 3.6.2 Mini-hopper A mini-hopper is typically mounted near and above the cutting head. Most of these mini-hoppers allow for a gravity feed of abrasive down to the cutting head. Many mini- hoppers control the amount of abrasive that can go down to the cutting head with the use of a slide with different size holes in it. The operator can change the position of the slide to change the amount of abrasive to the cutting head. A recent advance in technology is remote CNC-control of the amount of abrasive released from the mini-hopper. Having this capability allows for optimum feeding of
  • 35. 35 abrasive to the cutting head in relation to the water pressure at the pump for the following desirable capabilities:  Piercing of fragile materials like glass or stone. Typically a lower water pressure will be used with a smaller amount of abrasive  Changing abrasive amount for different abrasive nozzle sizes to optimize part cost. This can be done automatically if the mini hopper is set up to do this. Fig 3.23 abrasive material feeding
  • 36. 36 CHAPTER 4 4.1 WATER QUALITY:- 4.1.1 Overview This chapter will discuss water quality requirements for high pressure water jet cutting and why it is crucial to maintain proper water quality. Note: See "Recommendation for water treatment" at the end of this chapter for a potential solution to everything you are about to read in this chapter about water treatment. 4.1.2 Water specifications Every manufacturer has specific requirements for water quality. Check with the manufacturer to get the specifications for your particular machine. The water supplied to the intensifier is critical to water jet cutting due to its direct influence on the service life of the equipment components such as check valves, seals and orifices. A high concentration of Total Dissolved Solids (TDS) causes accelerated wear of any components that come in contact with the high pressure water because of the increased abrasiveness of the water from the TDS. As part of the installation planning, a water quality analysis should be performed by a commercial company that specializes in water conditioning equipment. The minimum information that should be supplied by this analysis is TDS, silica content and pH value. Companies like Culligan can perform these tests, or you can search "water quality testing" on the internet. Inlet water should be treated for either the removal of hardness of the reduction of TDS. Water softening is an ion exchange process that removes scale forming minerals such as calcium. TDS reduction can be accomplished with either deionization (DI) or reverse osmosis equipment. Generally, DI or RO provides better component life than water softening.
  • 37. 37 A water purification supplier should be consulted to supply the most suitable equipment for special conditions. It might be a good idea to ask any company that you are considering using if they have supplied systems for any other high pressure water jet cutting systems and check their references. The best treatment process for a specific application is a function of the original water quality and the desired service life of the affected components. Sixty to 70 ppm of TDS is optimum. Any water treatment producing TDS content of less than 0.5 part per million (ppm) should be avoided since the aggressiveness of such purified water will damage pump components.
  • 38. 38 4.2 Water treatment guidelines Criteria Values Recommended Treatment Total Dissolved Solids (TDS) Low TDS (<100 ppm) Moderate TDS (100 - 200 ppm) High TDS (>200 ppm) Good water, requires only softening Can be treated by softening, DI or RO Poor water, should be treated with RO or DI Silica Content High content (>15 ppm) Dual Bed Strong Base DI pH Value Treated water must have a value of 6 - 8
  • 39. 39 4.3 Suspended solids In addition to the treatment described above, the water must be filtered for the removal of suspended solids. Different manufacturers supply differently sized final filters for this purpose, typically down to 0.45 nominal. See "Recommendation for water treatment" at the end of this chapter for an alternative to this. Water supply The initial water supply should be at least 5 gallons per minute at 40 pounds per square inch. The water may be boosted by a small pump to the 80 psi required by most intensifiers. Some intensifiers do not require pressure boosters, requiring only 30 psi for the incoming water. This removes a potential failure point from the system. Hydraulic Oil Cooling Intensifier pumps have hydraulic oil that must be cooled. Typically there are three options: 1. Water-Cooled through a heat exchanger 2. Air-Over-Oil Cooler 3. Closed-Loop Chiller 4. 4.3.1 Heat exchanger - For water cooled pumps 1. A heat exchanger is primarily used for cooling the hydraulic fluid of the intensifier pump. Typically the hydraulic oil temperature must be kept below 120° F (49° C). The heat exchanger will require a consistent water flow of 0 to 8 gpm (0 to 30 liters per minute) at an inlet temperature not exceeding 70° F in order to keep the hydraulic fluid at the proper temperature. Actual volume of water will depend on the pump selected. As many pumps are thermostatically controlled, when the pump is cool, it may be that no water is required. 2. This cooling water must go to drain. The cost of this water must be balanced against the costs of the other two cooling options (air-over-oil and chiller), which would not have any water going down the drain. 3. Public utility water is usually acceptable for cooling purposes. In situations where the water contains heavy mineral deposits, the exchanger tubes may
  • 40. 40 eventually become restricted by particle buildup. If this is a chronic problem, pre-filtration and/or water softening may be necessary. 4. Depending upon plant setup, ambient temperature can also be a factor in cooling the hydraulic fluid. Additional cooling may be required if the intensifier and/or heat exchanger is confined to a small, high-temperature space. Fig 4.1 heat exchanger
  • 41. 41 4.3.2. Air-Over-Oil Cooler Some pumps will use an oil-air cooler to remove heat from the hydraulic oil, so no heat exchanger is required. In the summer, the unit can be vented outside the building to remove the heat from the building. In the winter it can be vented inside the building to help out with heating the building. Fig 4.2 oil cooler 4.3.3. Chiller A chiller can be used to re-circulate the cooling water that is used by the intensifier's heat exchanger. It cools the water and then sends it through the heat exchanger again, creating a closed loop. A chiller is most effective in worth considering in a few situations in particular:  Warmer climates where the efficiency of the heat exchanger may be reduce  Facilities that cannot send any water to a drain,  Parts of the country where there is a water shortage, or if the cost of water is high, because a 50 HP pump can use up to 5 gpm for cooling the hydraulics.
  • 42. 42 The chiller will only reuse the cooling water; you will still be putting approximately 1 gpm with a 50 hp pump of fresh water through the cutting head, which will not be reused with the chiller. Incoming water for the intensifier should also be maintained at 70° F (21° C) or cooler for best high pressure seal life. If this temperature cannot be maintained, then the chiller can also be used for this water. Fig 4.3 chiller Water circuit options Water circuit options Following are 4 different scenarios for the water flow through a water jet cutting system.
  • 43. 43 Option 1 - Heat exchanger in pump, all water runs to a drain. fig 4.4 Heat exchanger in pump, all water runs to a drain. Option 2 - Air-Over-Oil cooler fig 4.5 Air-Over-Oil cooler
  • 44. 44 Option 3 - Chiller and heat exchanger. Water for heat exchanger re-circulates; used water from cutting runs to drain. Fig4.6 water from cutting runs to drain. Option 4 - Heat exchanger, chiller and WRS-3000 water recycling unit. No water to drain. Only water required is make-up water to replace evaporation and spillage.
  • 45. 45 4.4 Recommendation for water treatment WARD Jet has found that the use of a good quality water softener in conjunction with a 0.2 absolute final filter to be successful for treatment of water for the intensifier. This setup can be used as long as the water from the cutting tank is not being recycled for use through the intensifier. In the worst case, if seal life does not seem to be living up to expectations, then a DI or RO system can be installed
  • 46. 46 4.4.1 Benefits of Water jet Cutting As one of the fastest growing machine tool industries, water jet cutting has proven to save time and money on countless applications such as metal cutting and stone cutting. See the advantages of water jet cutting and view our photo album of different uses for the tool. Whether it's cutting sheet metal, titanium, granite, marble, or steel - water jet might be the answer for you. Benefits of Water jet Cutting Let's Take a Look... Water jet cutting is best described as an accelerated erosion process that we are controlling. For this reason, water jet can cut or erode through virtually any material known, making it one of the most versatile machines available. As one of the fastest growing machine tool industries, water jet cutting has proven to save time and money on countless applications. Please take a look at the advantages below to see if water jet could be for you. Tolerances Tolerances tighter than +/- 0.005" are achievable, especially in thinner materials such as 1" stainless steel. However, high tolerances come with a price, sometimes up to 500% higher than if the same part had been specified with a tolerance of +/- 0.015". By being more flexible with tolerances, prices will plummet as cutting speeds increase. Water jet cutting has the ability to vary tolerances in different locations on a part, ensuring the best pricing and quality. Thickness And Kerf Materials ranging from 10" stainless steel to 0.010" acrylics can be cut by water jet, making it a very versatile tool. Stacking of very thin materials to increase productivity is possible. Kerf ranges from 0.020" to 0.050".
  • 47. 47 Taper and Edge Finish Taper and edge finish are directly related to cut speed. The greater the speed, the more taper and the coarser the edge finish. As the water jet slows down, taper can be eliminated and the finish of about 120 achieved. Again, slower means an increase in time...and price. For a finer edge finish, use a finer abrasive. No Heat Affected Zone (HAZ) Water jet cutting is a natural erosion process involving no chemicals or heat. Because of this, warping and distortion typically associated with laser, plasma and oxy-fuel cutting is eliminated, therefore minimizing the need for secondary processing. Nesting And Common Line Cutting Unlike laser, plasma and oxy-fuel cutting, water jet lends itself to common line cutting. WARDJet offers optional state-of-the-art nesting software, allowing you to nest multiple shapes together and cut them with multiple heads. Tracking of remnants and nesting into these odd shapes later, helps save precious material and can contribute toward reducing your operating costs. Cutting Speeds The speed at which the water jet can cut through material will vary based on a variety of parameters. In the charts below you can see that the orifice/nozzle combination you select will have an influence on your cut speed. Generally when cutting with a single
  • 48. 48 head and a 50 hp pump the chart with the 14/40 orifice/nozzle combination is the closest guide for cut speed. When cutting with two heads and a 50 hp pump use the chart with the 10/30 orifice/nozzle combination to indicate the cutting speed of each head. After selecting the correct chart find the material and the thickness that you will be cutting. This will then give you an idea of your straight line cutting speed based on the quality of edge finish and tolerance you need for your parts. These cutting speeds are only a guide to estimate cutting speeds achievable. We recommend that test cutting is done to determine actual feed rates on different materials and thicknesses. 4.5 Water jet in Any Industry The versatility of the water jet allows it to be used in nearly every industry. There are many different materials that the water jet can cut. Some of them have unique characteristics that require special attention when cutting. As you can see in the chart below each material you cut will have some unique characteristics that have to be taken into account. The information below explains some of the cutting techniques we've used when cutting these materials. We recognize that there are many materials not listed so if you have a specific question about your material feel free to contact us at (330) 677-9100.
  • 49. 49 4.5.1Alloys Inconel, Hastalloy, Wasp alloy, Titanium, Aluminum, Stainless etc. No heat effected zone or change in the molecular structure occurs in the alloy material. There is no distortion as seen with typical heat cutting methods. Generally, cutting with water jet costs less than traditional machining or cutting methods. In many cases, no secondary removal of slag or damaged material is necessary, and minimal to no burring is seen. 4.5.2Steels Water jet is not always the most cost effective method to cut steels. As a rule, if the finished product is presently being cut using laser, plasma or oxyfuel, and no secondary work is needed to the part after being cut, it is unlikely water jet will be an economical solution. However, as soon as any secondary work, closer tolerances or removal of the Heat Affected Zone (HAZ) is needed, water jet is probably the solution. With the use of the WARD (Water jet Abrasive Recycling Dispenser) companies are able to reduce their operating cost substantially, reducing the gap between laser and water jet cutting. In many cases, water jet now costs less than laser!
  • 50. 50 4.5.3Laminates Water jet, in most cases, does not see any difference between laminated materials - e.g. acrylic, aluminum, stainless and honeycomb section all laminated as one. Many aircraft parts consist of laminated materials where water jet is the only solution. 4.5.4Composites many composites are very difficult to machine as the cutting tool tips 'gum' up and quickly becomes inefficient. Water jet has no gumming at all and can leave a good clean surface requiring no additional work. 4.5.5Plastics/Acrylics It is possible to not only cut these materials effortlessly, but also drill start holes using specialized low-pressure options available with certain systems.
  • 51. 51 4.5.6Rubber Depending on the durometer value, rubber can be cut with water only or with abrasive. Tests will quickly reveal what the best option is for your application. 4.5.7Gaskets By using water jet for cutting gaskets, it is possible to automatically nest various sized and shaped gaskets on one sheet effortlessly. There is no longer any need for stacks of dies. Software will keep track of all remnant sheets allowing off cuts to be put back into inventory and used for smaller parts. Specialized software is available to track materials through the entire process.
  • 52. 52 4.5.8Fiberglass When cutting materials that are typically associated with hazardous fine airborne materials, water jet is an ideal solution. Particles and materials removed are transported by the water away from the surface into the tank, reducing this risk and hazard. 4.5.9Glass Intricate cutting and shaping of glass is easy with water jet. The water jet can generally drill all its own start holes, making it a highly versatile tool. Glass from 1/32" to 10" thick can be cut, even when laminated in multiple layers.
  • 53. 53 CHAPTER 4 CONCLUSION:- As a conclusion, the experiment that have been carried out were successful, even though the data collected are a little bit difference compared to the theoretical value. The difference between the theoretical value and the actual value may mainly due to human and servicing factors such as parallax error. This error occur during observer captured the value of the water level. Besides that, error may occur during adjusting the level gauge to point at the white line on the side of the weight pan. Other than that, it also maybe because of the water valve. This error may occur because the water valve was not completely close during collecting the water. This may affect the time taken for the water to be collected. There are a lot of possibilities for the experiment will having an error. Therefore, the recommendation to overcome the error is ensure that the position of the observer’s eye must be 90° perpendicular to the reading or the position. Then, ensure that the apparatus functioning perfectly in order to get an accurate result.
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