One of the most accurate industrial cutting blades is a thousandth of an inch supersonic jet of water carrying abrasive particles to a target surface. Water-jets cut simple or complex shapes from steel, glass, plastic, composites, paper, or fabric, without causing the thermal or mechanical distortions associated with mechanical saws. In the battle to reduce costs, engineering and manufacturing departments are constantly on the lookout for an edge. The water-jet process provides many unique capabilities and advantages that can prove very effective in the cost battle. Learning more about the water-jet technology will give you an opportunity to put these cost-cutting capabilities to work.

The water-jet has shown that it can do things that other technologies simply cannot. From cutting whisper thin details in stone, glass and metals; to rapid hole drilling of titanium; to cutting of food, to the killing of pathogens in beverages and dips, the water-jet has proven itself unique. Water-jets remove material without heat. In this cold cutting process, the supersonic water-jet stream performs a supersonic erosion process to "grind" away small grains of material. After this water-jet stream has been created, abrasive can be added to the stream to increase the power of the process many times.

The materials being machined by this process do not experience any hardening due to process because heat generated is very less. Also, since major cutting forces are directed in downward direction it can be used to machine materials with very small wall thickness. The depth of cut or thickness of part to be machined is a function of speed and best material machining is obtained for thickness less than 1inches.

History of water-jet cutting:

Dr. Norman Franz is regarded as the father of the water jet. He was the first person who studied the use of ultrahigh-pressure (UHP) water as a cutting tool. The term UHP is defined as more than 30,000 pounds per square inch (psi). Dr. Franz, a forestry engineer, wanted to find new ways to slice thick trees into lumber. In the late 1950's and early 1960’s, Franz first dropped heavy weights onto columns of water, forcing that water through a tiny orifice. He obtained short bursts of very high pressures (often many times higher than are currently in use), and was able to cut wood and other materials. His later studies involved more continuous streams of water, but he found it difficult to obtain high pressures continually. Also, component life was measured in minutes, not weeks or months as it is today.

Dr. Franz never made a production lumber cutter. Ironically, today woodcutting is a very minor application for UHP technology. But Franz proved that a focused beam of water at very high velocity had enormous cutting power—a power that could be utilized in applications beyond Dr. Franz’s wildest dreams.

Types of water-jet cutting: 

The two types of water jets are the pure water jet and the abrasive water-jet. Both have unique capabilities proven to benefit the industry.

Pure Water-jet

Pure water jet is the original water cutting method. The first commercial applications were in the early to mid 1970s, and involved the cutting of corrugated cardboard. The largest uses for pure water-jet cutting are disposable diapers, tissue paper, and automotive interiors. In the cases of tissue paper and disposable diapers the water jet process creates less moisture on the material than touching or breathing on it.

Pure water jet attributes:
Very thin stream (0.004” to 0.010” in diameter is the common range)
Extremely detailed geometry.

Little material loss due to cutting

Non-heat cutting.
Cut very thick.
Cut very thin.
Usually cuts very quickly.
Able to cut soft light materials (Fiberglass insulation up to 24” thick)
extremely low cutting forces.
Simple fixtures

Abrasive Water jets:

The abrasive water jet differs from the pure water jet in just a few ways. In pure water jet, the supersonic stream erodes the material. In the abrasive water jet, the water jet stream accelerates abrasive particles and those particles, and not the water, erode the material. The abrasive water jet is hundreds, if not thousands of times more powerful than a pure Water jet. Both the water jet and the abrasive water jet have their place. Where the pure water jet cuts soft materials, the abrasive water jet cuts hard materials, such as metals, stone, composites and ceramics. Abrasive water jets using standard parameters can cut materials with hardness up to and slightly beyond aluminum oxide ceramic (often called Alumina, AD 99.9).

Abrasive Water jet attributes:

Extremely versatile process.
No heat affected zones
No mechanical stresses.
Easy to program.

Thin stream (0.020 to 0.05 inch in diameter)
extremely detailed geometry.
Thin material cutting.
10 inch thick cutting.
Stack cutting.
Little material loss due to cutting.
Simple to fixture.
Low cutting forces (under 1 lb while cutting)
One jet setup for nearly all abrasive jet jobs
Easily switched from single to multihead use.
Quickly switch from pure water jet to abrasive water jet.

Reduced secondary operations
Little or no burr.

How does the process look?

Figure 1

The real inroads made by water-jet are in the aerospace, automotive, medical, defense and machining industries where water-jet cutting is being used to shape mild steel parts up to 12 inches thick, stainless steel parts of 10 inches and "carve" intricate parts for implants in titanium.

As pressure on manufacturers is maintained to produce faster, better, lighter and stronger products, new materials are constantly being developed. Many of these are considered composites, being made from a series of different materials laminated together. For example, a layer of titanium and aluminum separated with a honeycomb layer made from a pheonalic, an epoxy looking type of material with fibers weaving their way through the structure, are now common. The issue that quickly comes to mind is how to cut the laminated materials. Water-jet cutting in many cases does not see the difference between the materials in the various layers, enabling the materials to be cut quickly, efficiently and with precision. Water-jet cutting can best be described as an accelerated erosion process under control. Water is pressurized to 60,000 psi, forced through a small orifice normally 0.003 inch to 0.016 inch in diameter, after which abrasive is added to the stream and accelerated to 2,000 miles per hour. It is this fast traveling abrasive that does the cutting on hard materials. In soft materials, only water is used

There is no heat generated with water-jet cutting, hence the lack of any localized damage to the part as is associated with laser, plasma and oxy-fuel cutting. Tolerances as close as 0.005 inch can often be held comfortably, eliminating the need for any secondary machining or finishing. This often allows manufacturers to use water-jet cutting to complete a project in fewer steps, saving costs and reducing turnaround time.

  Figure 2.  Dual head water-jet cutting steel.

 Water-jet cutting is unique in that the stream does not know what it is about to cut through. It simply erodes its way through whatever is in its path. For this reason, water-jet cutting has become an extremely versatile process. Businesses operating water-jet systems are able to offer a diverse range of services, cutting virtually every material known on earth. A job shop that was limited to cutting steel with an oxy-fuel torch, with the addition of a water-jet could now offer services to businesses manufacturing wooden toys, signs, marble inlay floors for hotel and residential lobbies, custom glass designs, gaskets and complex parts in almost every steel, alloy and composite. From works of art, to intricate engineering parts in stainless, inconel and titanium, water-jet cutting is carving its way into the future.

Designing for water-jet cutting

Although water jet machines use many of the same principles as conventional machine shop tools such as lathes and milling machines, the details of the processes are quite different. This includes tolerances, surface finish, size of table, and expendable materials. As with any process, there are advantages and disadvantages. Look over the list below for both and see if water jet cutting can reduce your cost or do a job not possible any other way.

1. TOLERANCES: Most water jet machines have large tables and cut within +/- 0.020 accuracy. On small pieces with special care, accuracies of +/- 0.002 can be held. The accuracies apply to the top of the material. If the material is thick, the side is tapered so that the top is smaller than the bottom. This is caused by a reduction in cutting power of the jet stream as it passes down through the material. The amount of taper is affected by the feed rate of the machine.
2. REPEATABILITY: The repeatability of machines is on the order of +/- 0.002 in most cases. There is some variation due to the flow rate of the abrasive delivery to the head. Backlash in the positioning system also causes some error.
3. FINISH: The cut edge of the material appears similar to a sand blasted surface. Normal abrasive is 80 grit sizes. Jobs can be run with a 120 grit for a better finish at higher cost. As the cutting speed is increased, the bottom of the cut lags the top of the cut. This is seen in thicker parts and is called Rooster Tailing. Rooster tailing also leads to under cutting at inside corners as well as a tang at outside corners. The effect only occurs on the bottom side of the material with the topside appearing perfect.
4. ROOSTER TAIL REMOVAL: changing the speed within the cutting program can reduce the effects of rooster tailing. Since the effect is prominent only at corners, the machine can be programmed for a slow speed at corners and higher speed for straight cuts. The programming takes longer but on long runs it is better than cutting the entire part at a slow rate.
5. NESTING: Parts can be closely nested on a sheet to save material. Since the kerf or width of cut is only 0.04 inch, odd shaped parts can greatly benefit from nesting. A set of parts of different shapes but the same thickness can easily be nested and cut using the same program.
6. SPEED: The cutting speed and the depth of cut are  important to both customer and shop because it determines, to a large extent, the cost of the job. When there is a large variance in bid prices, it is probably because the low bidder quoted a fast cutting speed, which will produce a poor quality edge..
7. MATERIALS: The water jet process will cut any material softer than the garnet abrasive mixed into the water stream. All metals, plastics, composites, tile, marble, and granite can be cut. Thickness is limited only by the machine size. For some materials at certain thick nesses, other methods of cutting are less expensive. Choices of methods are in many cases obscured by other advantages such as superior finish, no hardening of the metal, no warping or distortion, small kerf, and ability to cut brittle material such as glass and stone without chipping.
8. SECONDARY OPERATIONS: In many cases, secondary finishing can be eliminated. In the case of marble, granite, and slate finished pieces cut to intricate shapes fit together without further effort to form artistic patterns for floor and wall use. With machine parts, intricate parts with slots, holes, and contours can be made to close tolerances and used as is or with minimum secondary operations such as counter boring, and bending.
9. TOOLING: Conventional machine tools require fixturing to keep the work from moving and deflecting under the pressure of the tool. The water jet process exerts no such pressure and therefore does not need positioning and clamping devices. A sheet of material can be placed on the table and parts cut from it without clamps. Small pieces may need to be held or positioned for cutting using simple stops on the table surface.
10. SMALL PARTS: Small parts can be cut and retained in the master plate by tabbing. With tabbing, the start and stop point of the cutting program leaves the part attached by a small bridge. The tab width is controlled so that it will support the part but can easily be broken and ground off. The tab is similar to the sprue in a plastic molded part.

Example from the shop floor:

Figure 4

The ability to hold parts tolerances to 0.005 inch while circumventing the issues of heat-affected zones, local hardening, and burring continues to launch new opportunities for water-jet cutting, according to Richel. Inc., a water-jet consulting firm based in Tallmadge, Ohio. The firm recently reported that water-jet cutting helped save time and costs for Miamisburg, Ohio-based CAM manufacturing, which produces high-tolerance parts for the aerospace and aircraft industries.

After retrofitting a used, water-only cutting system to a multiple-abrasive-head cutting system, CAM Manufacturing was able to achieve near net-shape cutting on a "fan" made of Hastalloy X, Richel reported. The fan, 0.75-inch thick, has an OD of 5.3 inches and an ID of 4.25 inches. The firm also eliminated some costly steps associated with traditional machining.

When the parts were manufactured on traditional machining centers, burring was severe. As a result, the entire part needed to be re-machined after all the teeth of the fan had been cut. But by using a simple, 2-axis water-jet with manual Z, CAM cut the teeth to tolerances of +0.015 inch. Use of the water-jet caused virtually no burring, thus eliminating the second machining phase of removing burrs. It also freed the milling machine, previously used to "hog out" the material, to be used only for final shaving of the teeth.

In addition, because the water-jet placed no stress on the thin support ring, it caused no distortion and eliminated the need to machine any part of the teeth, Richel reported. Use of the water-jet is said to have reduced total cost of machining from $272 on a 4-axis machining center, to $110 with the water-jet. Similarly, time of machining dropped from four hours and ten minutes, to two hours and five minutes.

Getting the most out of water-jet cutting                       (By using CAM software)

Figure 5

By analyzing the part’s geometry, the software can check all the parameters, like line length and angle of intersection between the present and the next line or arc. If the change in geometry exceeds any limitations specified in the CAM process, calculations by the software vary the speed, acceleration, deceleration, and offset of the kerf value, automatically. The CAM software then modifies the code posted to the controller to simulate the necessary changes in speed, enabling the tail of the water-jet stream to "catch up."

If there is no change in direction, but rather a straight line that extends into a tight radius, it is necessary to slow down on the radius if cut quality is maintained. The software is designed to evaluate every arc independently an allocate a different speed to each, depending on its radius and length. To ensure smooth transitions between the arcs, the software will generate code that decelerates into tighter arcs (smaller radii), enabling the water-jet stream to be at the correct speed before entering the arc. Acceleration of the stream would also apply when the situation is reversed.

Nesting and Material Utilization Are Keys to Cutting Costs:

Although ideally suited to small runs and custom work, adding multiple heads and CAD/CAM software customized for multiple head use transforms the water-jet into a high-production tool. Although there is an increase in consumable cost, the overhead cost remain constant, enabling two, three, or four parts to be cut in the same time frame required to cut one part. With a multiple-head water-jet, it is possible to compete with single-head lasers in thinner steels under certain conditions.

To set up the tool path for multiple head nesting, it should only be necessary to specify the number of water-jet cutting heads, the size of the sheet being used, and let the software do the rest. The program should calculate the optimum spacing of the heads to maximize material use and switch various heads on and off, either automatically or by informing the operator to do it manually, as required.

CAD/CAM software is now available that automatically tracks each sheet of material being cut, placing the material remaining in a remnant library. When a future part requires the same material, the library can be searched and the part nested in the appropriate remnant. It is also possible to create a sheet of any particular shape with parts nested into it, enabling scrap materials to be used economically. Nesting software also is capable of nesting parts within parts, ensuring that all available material is used.

There are occasions when straight lines are cut as common lines between parts. The lines need not be the same length, and the parts need not be the same shape. Good CAM software is able to nest and arrange the parts so that all lines that can be cut as common will be. It also is possible to specify the lead-ins for each cut to start in the previous kerf already cut, removing the need for piercing the material each time another part is cut. Time and cost savings of about 45% are achievable with common line cutting. A system with multiple cutting heads and a good CAD/CAM package can produce six times more work than a competitor without such a setup.

Addressing all the features specifically available for water-jet cutting as well as all other 2-D cutting such as laser, plasma, and oxy-fuel, would require a live demonstration. The software is becoming so powerful that in several instances all that are needed is a controller that can read and act on the code. Generating good code and maximum material utilization are the job of the "brains" behind any successful 2-D cutting operation. Good CAD/CAM software is now available that can make up for other, more human limitations.

Typical applications of water-jet cutting:

The spectrum of applications for water-jet cutting ranges from the delicate to the stalwart. FDA regulations allow the use of water-jet technology in cutting food items such as cakes, French fries, steak, poultry and fish. Water jets have proven themselves as both efficient and sanitary.

On the other extreme, abrasive water-jet systems (AWJ) bombard armor plating used in the assembly of M1 tanks and Bradley fighting vehicles. In between lies a wide spectrum of other applications. Artists, interior designers and shipbuilders are among the many who are embracing water-jet technology. Industries such as paper, textile, aeronautics and steel are routinely incorporating the technology into their manufacturing process.

Water-jet technology is performing old tasks in a new efficient manner. Complex and intricate designs and mosaics made of tile; stone and glass - often used in decorative surfaces and corporation logos - are now executed with the aid of a water-jet. Many of the projects would have been impossible to create without a water-jet because of the intricacy of the design and the fragile nature of the materials.

Water-jets are also helping ease the burden of rising medical costs. It’s a technology helping technology. To date, applications have been used with foam, GIO phenolic, steel, armor plating, urethane, titanium, kevlar, aluminum, linen phenolic, brass, neoprene, copper, glass, stainless steel, spectra, fiberglass, corrugated cardboard, acrylic, ceramic tile, wood, rubber, glass, marble and granite.

Table 1

Macro mechanisms of material removal

The geometry of the generated cutting front that is generally curved as shown in Figure and the topography of the generated surface are two major features of the macroscopic, abrasive water jet material-removal regime. Thus, insight into the character of at least the macroscopic, material-removal process is obtained from analysis of the surface structures of the abrasive water jet cut specimens. The next section discusses aspects of cutting front inspections.

Geometry of the cutting front generated during abrasive water-jet cutting (Univ. Hannover, IW)

Surface-Profile

Inspections Despite the surface topography, Figure shows surface profiles of an aluminum sample. From the first view, the most striking feature is the existence of two different regions. One region, covering the upper part of the specimen, shows a smooth surface; whereas, the second region, located in the lower part, exhibits some regularly appearing surface marks.

Process costs and major variables

The cost of abrasive jet machining can be segmented into various factors as listed below:-
1. Cost of mixing tube that generally ranges between $250-$350 lasting about 50-150 hrs.
2.Cost of abrasives that generally ranges between $0.15-$0.30 per pound and their consumption is between 0.5-2 lbs/min
3.Cost of electricity and water can generated as variables depending on the location of the unit.
4.Cost of operator would again be a function of expierence.
5.Cost of spare parts(?)

FORMULA FOR ESTIMATION OF COST BY ABRASIVE JET MACHINING

1. Cost of mixing tube =$a/hr
2. Cost of abrasives=$b /pound/hr
3. Cost of electricity=$c /hr
4. Cost of operator=$d/hr
5. Cost of spare parts would be a variable quantity.

Comparison of water-jet cutting with Co₂ Laser.

Fundamental process differences

Typical process applications and uses

Initial investment and average operating costs

Precision of process

Safety considerations and operating environment

Disadvantages to Water-jet Cutting

Water-jet cutting is a very useful machining process that can be readily substituted for many other cutting methods; however, it has some limitations to what it can cut. Listed below are these limitations, and a brief description of each.

·         One of the main disadvantages of water-jet cutting is that a limited number of materials can be cut economically. While it is possible to cut tool steels, and other hard materials, the cutting rate has to be greatly reduced, and the time to cut a part can be very long. Because of this, water-jet cutting can be very costly and outweigh the advantages.

·         Another disadvantage is that very thick parts cannot be cut with water-jet cutting and still hold dimensional accuracy. If the part is too thick, the jet may dissipate some, and cause it to cut on a diagonal, or to have a wider cut at the bottom of the part than the top. It can also cause a ruff wave pattern on the cut surface.

·         Taper is also a problem with water-jet cutting in very thick materials. Taper is when the jet exits the part at a different angle than it enters the part, and can cause dimensional inaccuracy. Decreasing the speed of the head may reduce this, although it can still be a problem.

Conclusion:

Water Jet competes favorably with
EDM when:

• Extreme accuracy is not required.
• Parts are not conductive.
• Burned edge is unacceptable.
• Additional machining is required.
• Cost is important.

Water Jet competes favorably with
LASER when:

• Material is over 1/4 inch thick.
• Parts are SS or exotic material.
• Parts are copper or brass.
• Parts are shiny.
• Burned edge unacceptable.
• Distortion unacceptable.
• Additional machining is required.

Water Jet competes favorably with
PLASMA when:

• Burned edge unacceptable.
• Distortion unacceptable.
• Intricate shape required.
• Nesting yield is important.
• Finnish is important.
• Closer tolerance required.
• Additional machining required.

Water Jet competes favorably with
MACHINE TOOLS when:

• Cutting large parts.
• Extreme accuracy not required.
• Part used as cut.
• Nesting yield important.
• Intricate shape required.
• Parts are hard on tools.
• Parts are brittle, hard, and soft.
• Run length is intermediate.
• Tooling is expensive.
• Frequent design changes.
•  
• Water Jet Cutting Related to Jet & Rock Properties

Abstract.

A continuous water jet is used to cut slots in seven rock types in an experiment, which

correlates jet and rock properties with jet performance. The jet, operating at pressures from 5,000 to 25,000 psi is traversed across the rock surface at speeds between 15 and 750 ft/min. The rock properties considered in the analysis are uniaxial compressive strength, Young's modulus, Shore hardness, Schmidt hammer value, Rock Impact Hardness Number and Rock Fracture Toughness. Regression analyses are performed on the results, based on the 7,180 measurement tests of the

depth of slot cut.

Experimental Design

Rock is not a homogeneous, isotropic material, and for this reason the experiment was

designed to yield a large amount of data so that variation in rock properties and jet penetration due to this variation should be kept as small as possible. Evidence from preliminary studies had shown that it is more effective to cut slots in the rock surface and remove the rock between the slots mechanically than it is to remove the rock by water

jets alone (. A reduction in specific energy of breakage from 300 joules/cm3 to 20 joules/cm3 was obtained in one test with Berea sandstone. Further, it had been found that a continuous traversing jet penetrated further into the rock in the same amount of time than either a pulsed jet or a stationary, continuous jet (Fig. 1) at the same pressure (14).

Figure 1. Penetration of a jet into red Woolton sandstone at a pressure of 8,000 psi. and a standoff istance of 2 inches.

The experiment was therefore designed to find the parameters controlling the slot depth cut by the et and the relative efficiency of cutting. The initial design was to vary the jet pressure, from 5000to 25,000 psi. the traverse speed of the jet nozzle over the rock surface, from 15 to 750 t/min, and the number of passes made by the nozzle over the same area of the rock surface from 1 to 16. Data from this experiment, carried out in Berea sandstone and Indiana limestone, indicated (Fig. 2) that the jet became increasingly inefficient with increasing pass number (15, 16). At the same time it is unlikely that, in any machine design, the jet will pass over the surface of the rock more than once between passes of the mechanical cutters. The design of the experiment was accordingly changed, and a fourth parameter, nozzle diameter, incorporated into the experiment. A single pass was made over the rock surface for the remaining tests.

Experimental Procedure.

Cubic samples of rock, measuring six inches along each side, were prepared from seven

rocks: four sandstones, one limestone, one marble and one granite (Table 1). Each sample to be tested was placed in the chuck of a lathe and clamped with the axis of rotation passing through the center of the specimen. The nozzle and the feed pipe from the supply-pump were attached to the horizontal feed carriage of the lathe (Fig. 3). The gearing of the lathe allowed the nozzle to be traversed across the rock surface at a constant feed rate per revolution of the chuck. A slotted steel plate was placed between the rock sample and the nozzle. The slots in the plate were cut to the same width as the distance moved by the nozzle in a single revolution of the chuck. The jet was therefore exposed to the rock surface for one revolution of the chuck as the nozzle moved over the

slot. Five slots were made at half inch intervals and spaced from the center of the axis of rotation. It had previously been determined that there was no interference between adjacent jet slots when separated by this distance (14).

Experimental Equipment

The distance between the nozzle and the rock surface was standardized at two inches.

Previous testing has shown that distance has little effect on jet performance in the range from two to four inches (17). A soluble oil was added to the water in order to lubricate the pump. Despite their known advantage (18, 19), no long chain polymers were added to the water. This was because the equipment included a recirculation system, and the polymer is known to age (20) and could be expected to denigrate after passing through the pump a number of times. This would have included an uncontrolled variable into the experiment. The result of each cutting run was to leave a concentric set of slots cut in the rock surface (Fig. 4). The traverse speed of the jet nozzle relative to the rock surface for each slot was a function of the slot radius and the rotational speed of the chuck. The depth of the slot was measured at our points around the periphery of the slot, and an average value obtained. This value was entered in the raw data file. The data was processed using the SPSS computer program (21) to determine the statistical coefficients between the dependent and independent variables and to derive regression equations.

From the analysis the jet velocity ratio was found to have the highest correlation with the depth of slot cut for all rock types. Analysis of the specific energy data indicated that the jet velocity ratio had the highest correlation coefficient for the sedimentary rock, but that the jet pressure had a higher correlation with specific energy for the crystalline rock. This would suggest a possible difference in the cutting mechanism of the jet in the two rock groups. Such a difference has been observed in the test specimens. Granular material is eroded by the jet, with the particles of the material remaining substantially intact. Crystalline rock suffers intra- and intercrystalline failure under water jet impact and the particles removed are fragments of the original crystalline structure. This conclusion was confirmed in subsidiary tests carried out on specimens of Missouri Granite and Georgia Granite. The slot depth was reduced with an increase in the nozzle traverse speed (Fig. 5), but the specific energy of rock removal was also decreased (Fig. 6). Thus, although less depth was achieved, a greater volume of rock was removed. The fact that the faster the nozzle is traversed, the more efficiently the jet cuts, makes it somewhat rare among cutting devices.

Figure 5. Depth of slot cut versus nozzle speed.

Rock Properties.

Six rock properties were measured for each rock tested (Table 1). Uniaxial compressive

strength and Young's modulus at 50% strength were measured using an LVDT strain jacket. The specific fracture energy, as defined by Cooley (11) was also calculated. Shore scelerescope and Schmidt hammer values were determined as non-destructive measurements of the rock hardness, and the Rock Impact Hardness Number (RIHN) was measured as a destructive hardness value. The Fracture Toughness (FT) of the rock was also measured.

Figure 6. Specific Energy of breakage versus nozzle traverse speed. (Buff sandstone).

Figure 7. Depth of slot cut versus nozzle diameter (Pink sandstone).

Figure 8. Specific energy of breakage versus nozzle diameter (Pink sandstone).

Concluding Remarks.

Three regression equations have been developed, based on experimental data, to describe the water jet cutting of rock. The equations are constructed as a combination of water jet and rock properties combined to predict the depth of the slot cut in the rock, and the specific energy of breakage of the rock. The third equation describes the properties which control a dimensionless measure of jet performance. The specific energy and dimensionless ratio equations had a multiple regression coefficient of around 0.9, indicating that it should be possible to predict jet performance with a previous knowledge of the rock and jet properties. The analysis did not, however, include any data on spallation. Because spallation has been found to occur consistently under certain test conditions, the results predicted in the equation are likely to give a high estimate of the energy required to cut rock.

References:

·         Introduction. (Author: HYVÖNEN M., KOSKINEN K.T  .

1.       Journal: T   Mechanical Engineering, May2001, Vol. 123 Issue 5, p48, 6p, 7c, 2bw

·         http://www.omax.com/waterjet_generalinfo.html

1.       (Date February 3^rd 2002)

·         Forming Parts with Waterjet   By Richard Ward (Job Shop Technology, March 1999)

·         Comparative analysis (http://www.teskolaser.com/top#top

·         (Date:March 14^th 2002)

·         CAM SOFTWARE AT THE HEART OF PRODUCTIVE CUTTING SYSTEMS (By: Richard Ward (Modern Application News, December 1998)

·         Case study (http://www.umr.edu/~rockmech/staff_faculty/faculty_papers/paper11.pdf)  (Date 12^th March 12, 2002)

§         Macro mechanism of material    http://www.seas.smu.edu/rcam/research/waterjet/MicroAna.html

§         Arola D, Ramulu M 1995 Abrasive waterjet machining of titanium alloy. In: Labus T J (ed) 1995 Proc. 8th Amer