Waterjet Cutting


  • History
  • Theory
  • Types
  • Equipment Used
  • Affects of Equipment Variation
  • Applications
  • Future Research
  • Limitations
  • Advantages
  • Links to Other Pages
  • References
  • Pictures are from Jet Edge Ultra-High Pressure WaterJet Systems
     
     




    History

    Waterjet cutting can be traced back to hydraulic mining of coal in the Soviet Union and New Zealand. Water was collected from streams and aimed to wash over a blasted rock face carrying away the loose coal and rock. Th is method of mining was redeveloped in South African gold mines to remove blasted rock from the work area into a collection drift or tunnel. In the California Gold Country between 1853-1886, pressurized water was first used to excavate soft gold rock from the mining surfaces. The pressurized water allowed the miner to stand further back from the face being washed. This was safer because there was less danger of being covered by a collapsing wall of blasted rock. By early 1900s this method of mining had re ached Prussia and Russia. In these two countries the pressurized water was used to wash blasted coal away.

    In the 1930s it was Russia that made the first attempt at actually cutting the rock with the pressurized water. A water cannon was used to generate a pressure of 7000 Bars.

    In the 1970s technology was developed in the USA that was capable of creating a 40,000 Bar pressure. Most of the waterjet mining growth after this involved combining a drill with the waterjet. In 1972 Professor Norman Franz of Michigan worked with McCartney Manufacturing Company to install the first industrial waterjet cutter. The equipment was installed in Alton Boxboard. Flow industries also began to market industrial waterjet cutting equipment. It was Flow Industries who added sand to a pressurized cleaning system to give metal a white finish. After this it was demonstrated that abrasive waterjet systems could cut through metal and ceramics. From here the waterjet cutting industry took off.

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    Theory

    Most waterjet cutting theories explain waterjet cutting as a form of micro erosion as described here. Waterjet cutting works by forcing a large volume of water through a small orifice in the nozzle. The constant volume of water traveling through a reduced cross sectional area causes the particles to rapidly accelerate. This accelerated stream leaving the nozzle impacts the material to be cut. The extreme pressure of the accelerated water particles contacts a small area of the work piece. In this small area the work piece develops small cracks due to stream impact. The waterjet washes away the material that "erodes" from the surface of the work piece. The crack caused by the waterjet impact is now exposed to the waterjet. The extreme pressure and impact of particles in the following stream cause the small crack to propagate until the material is cut through.

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    Type
    Waterjets:

    Waterjet cutting uses only a pressurized stream of water to cut through material. This type of cutting is limited to material with naturally occurring small cracks or softer material.

    Abrasive Waterjets:

    Slurry: An abrasive waterjet slurry system mixes the abrasive with the water jet early in the system. This is done before the water is pressurized. Slurry systems then accelerate the abrasive particles with the water throughout the system. This causes more wear on the internal parts than an entrainment system.

    Entrainment: An abrasive waterjet entrainment system mixes the abrasive with the waterjet in a mixing chamber just after the nozzle. In most systems being built today, a venturi effect is utilized to pull the abrasive into the waterjet. The abrasive pa rticles are accelerated into the stream and then with the stream out the orifice.

    Abrasive Water Suspension Jets:

    An abrasive water suspension jet system accelerates a suspension of abrasive in water through the system. This type of system appears to be more efficient than previously developed abrasive waterjet systems. *NOTE: Southwest Research Institute has patented a water/gel (SUPER-WATER (R)) abrasive system that cuts 0.006" wide. The intended use of this system is for micro machining.  SUPER-WATER (R) was developed by Berkeley Chemical Research, Inc., and has been found better then water in many applications from cutting to cleaning.  For more information on SUPER-WATER (R) please visit www.berkeleychemical.com.

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    Basic Equipment Used
    CNC guide machine
    PC based programmable controller or microprocessor based control
    Structural steel Base
    Servo drive system
    "X/Y" carriage
    Cantilever arm
    Motorized "Z" axis
    Catch tank
    Cutting table
    Work piece support grid/material
    Filtration system
    High pressure pumps
    Pressure intensifiers
    Abrasive material disposal/removal system
    Injector to draw abrasives into cutting stream
    Mixing chamber
    Cutting nozzle (varying orifice size)
    Abrasive removal system
    Chiller (optional)
    ****Components are subject to change depending on Customer requirements and machine manufacturers *******
    (Note: This is not an exhaustive list of parts used/needed)

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    Affects of Equipment Variation

    Nozzle Opening Shape:

    Size and Shape of the Orifice: Multiple Nozzles: Pressure Intensifiers:


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    Applications

    Due to the uniqueness of waterjet cutting, there are many applications where it is more useful and economical than standard machining processes. In this section, some of the major applications and uses for waterjet cutting will be discussed, and the reasons why this method works better.

    First of all, waterjet cutting is used mostly to cut lower strength materials such as wood, plastics, and aluminum. When abrasives are added, stronger materials such as steel, and even some tool steels can be cut, although the applications are somewhat limited. Listed below are different applications, and reasons why waterjet cutting is used for each one.

    Printed Circuit Boards: For circuit boards, waterjet cutting is mostly used to cut out smaller boards from a large piece of stock. This is a desired method, since it has a very small kerf, or cutting width, and does not waste a lot of material. Because the stream is so concentrated, it can also cut very close to the given tolerances for parts mounted on the circuit board without damaging them. Another benefit is that waterjet cutting does not produce the vibrations and forces on the board that a saw would, and thus components would be less likely to be damaged.

    Wire Stripping: Wire stripping is another application that can be used effectively in waterjet cutting. If no abrasives are used, the stream is powerful enough to remove any insulation from wires, without damaging the wires themselves. It is also much faster and efficient than using human power to strip wires.

    Food Preparation: The cutting of certain foods such as bread can also be easily done with waterjet cutting. Since the waterjet exerts such a small force on the food, it does not crush it, and with a small kerf width, very little is wasted.

    Tool Steel: For abrasive waterjet cutting, tool steels are one application, although a limited one. It can be very useful though because tool steel is generally very difficult to cut with conventional machining methods, and may cause an unwanted byproduct: heat. Abrasive waterjets, however, do not produce heat that could alter the structure of the material being cut, and thus the strength of the tool is retained.

    Wood Cutting: Woodworking is another application that abrasive waterjet machining can be used for. Since wood is a softer material compared to steel, almost all wood can be cut, and the abrasive particles sand the surface, leaving a smooth finish that doesnít require sanding.

    Cleaning Applications: You know cleaning

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    Future Research

    Since its development, waterjet machining has seen many improvements in its design. Many different types of abrasives, nozzles, flow rates, and jet positions have been experimented with to name a few. Here at Michigan Tech, one of the elements being researched is the type of abrasive used. Typically, garnet, which has a hardness of 8 on Mohs scale of hardness, is used because it is much harder than most materials and because it breaks in clean, sharp edges. Garnet is considered inexpensive when compared to abrasives like diamond, however, it still costs around $600 per ton of abrasive. Working with the Daimler-Chrysler Corporation, Michigan Tech has found a way to used crushed windshield glass as an acceptable replacement for garnet. Glass, which is made of silica and has a hardness of 6 of Mohs scale of hardness, is not as hard as garnet, however the cost of 1 ton of glass is about $50. As far as hardness is concerned, silica glass is still harder than most materials, and since it is crushed, the particles all have sharp edges that havenít been worn due to erosion that might occur in garnet, which has to be mined. The other benefit for using silica is that all the glass being used is scrap window glass that would have otherwise been sent to a landfill where it would be of no use.

    Several other improvements and experiments that are being worked on by other companies are:

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    Disadvantages to Waterjet Cutting

    Waterjet 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.

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    Advantages to Waterjet Cutting

    Waterjet cutting has many applications, and there are many reasons why waterjet cutting is preferable over other cutting methods. Listed below are several advantages, along with a brief explanation.

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    Links

    Berkeley Chemical Research, Inc. http://www.berkeleychemical.com

    http://www.omax.com/components_of_waterjet.html#Highpressurewaterpump

    http://wj.net/waterjet/WaterjetControl.html

    Website has FAQ, what is water jet cutting: http://wj.net/waterjet/index.html

    This sight has a nice picture on the front page of a CNC waterjet cutting machine: http://www.versaformcorp.com/waterjet.htm

    This shows a machine with 4 heads (abrasive) on it. Nice for alternatives page: http://www.geegraphite.com/wjframes.htm

    Six-Head machine Non-abrasive: http://www.geegraphite.com/wjframes.htm

    Concepts for Progress, Inc. www.con4prog.com/standard/mg2000.htm

    Omax Homepage www.omax.com/aboutabr.html

    Water Jet Cutting Systems www.usjetting.com/jetcut1.htm

    Waterjet Web Page www.waterjets.org

    WTI Homepage www.waterjet-tech.com

    OMAX Homepage www.omax.com

    Jet Edge Ultra-High Pressure Waterjet Systems www.jetedge.com

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    References

    Metals Handbook, 9th Edition. Volume 16, 1989, page 520-527

    "Interaction of abrasive water jet with cut material at high velocity impact- Development of an experimental correlation", A. Tazibt, N. Abriak, F. Parsy, European Journal of Mechanics, 1996, vol. 15, pg1037-1047

    Principles of Abrasive Water Jet Machining, Andreas W. Momber & Radovan Dovacevic, Springer-Verlag Berlin Heidelber, 1998, New York

    Sheet Metal Industries Vol67 1990

    "Slicing Through with Water Jet Technology", Matt Kalina. Welding Journal, Vol 78, No. 7. July 1999

    Waterjet Cutting: Technology and Industrial Applications, Richard K. Miller, SAEI Technical Publications, 1985, Madison, GA

    Waterjetting Technology, David A. Summers, Alden Press, 1995, Oxford UK

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