CA2090371A1

CA2090371A1 - Water jet mixing tubes used in water jet cutting devices and method of preparation thereof

Info

Publication number: CA2090371A1
Application number: CA002090371A
Authority: CA
Inventors: William Frank Banholzer; Thomas Richard Anthony; Robert Snee Gilmore; Paul Alfred Siemers; John Charles Mccloskey
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1992-03-27
Filing date: 1993-02-25
Publication date: 1993-09-28
Also published as: JPH068146A; ZA931795B; US5363556A; KR930019315A; EP0562764A1; IL105067A0

Abstract

RD-21,643 Improved Water Jet Mixing Tubes Used in Water Jet Cutting Devices and Method of Preparation Thereof Abstract of the Disclosure An improved two membered substantially crack-free water jet mixing tube of an abrasive water jet cutting device and a method of its preparation. The method comprises chemically vapor depositing diamond layer on a funnel shaped support member to form an inner member of the mixing tube, separating the inner member from the support member, depositing and then cooling an outer member on the outer side of the inner member to produce a compressive stress on the inner member that substantially prevents formation cracks on the inner member. The inner side of the inner member has a smooth bore having a microcrystalline structure and the outer member has a higher coefficient of thermal expansion than diamond.
The invention is also directed to a water jet cutting device that incorporates the aforementioned improved substantially crack-free water jet mixing tube.

Description

RD-21 ,643 Im~ro~/ed Wate~ Jet Mixir~ T~be~ d In Wate~ Jelt ~utting Devi~ and Me~hod ~7 Prepa~atiQn Ther~

ÇrQss R~fer~nce to Relate~ ~pplic~Qn~

Reference is made to commonly assigned, co-pending applications, serial number 07/713,499, filed on June 12, 1991, for An Improved Method for Prnducing 10 Articles by Chemical Vapor Deposition and The Articles Produced Therefrom and to serial number 07/a.64,81~, filed on January 16, 1990 for CVD Diamond Coated Annulus Components and Method of Their Fabrication, both of which are incorporated herein by reference.

Field of the Invention The present invention generally relates to improved cutting devices used for cutting materials by 20 hydro-machining and more particularly concerns a method of producing improved diamond water jet mixing tubes having improved crack resistance and high length to diameter (L/D) ratios.

Background of the Inv~ntion In recent years hydro-machining methods, including water jet cutting, have undergone significant advances. The reasons are obvious. A high pressure liquid 30 jet, such as a water jet, can cut through several types of materials quite easily and it can be even programmed, through a computer software, to cut intricate patterns.
Hydro-machining methods have been also used extensively in cutting patterns in various industries, such as the RD-21 ,6a,3 garmen~ industry, the corrugatedl carton manufacturing industry, aircraft industries, electronics industry, and so on. Additional list oF the application of hydro-machining is provided on page 91-95 of Wet ( rit! Abr~sive W~t~rjets, 5 American Machinist, October 1989, Penton Publishing, Inc., Cleveland, C)hio, pages 84-~7, incorporated herein by reference. For a general surnmary of various hydro-machining methods including water jet cutting methods, reference is made to the aforementioned special report on Wet Grit. A~rasive Watçrjets, and to Guha, J., High-Pressure waterjet C~ An IntrQduction, Ceramic Bulletin, Vol.
69, No.6, 1990, pages 1027-1029, both incorporated herein by reference.
One of the major difficulties encountered in the 15 hydro-machining technology is the short life span of the water jet mixing tubes used in the hydro-machining devices.
The presence of abrasive particles in the water jets used in the hydro-machining devices reduces the life span of these mixing tubes due to abrasion. However, the life span of 20 these mixing tubes can be significantly extended by producing them from diamond. Diamond is an allotrope of carbon exhibiting a crystallographic network comprising exclusively of covalently bonded, aliphatic Sp3 hybridized carbon atoms arranged tetrahedrally with a uniform 25 distance of 1.545 A between atoms and it is extremely hard, having a Mohs hardness of 10.
A method directed to improving the abrasion resistance of the annular interior surface of an annulus has been disclosed. Such a method comprises chemical vapor 30 depositing abrasion resistant materials, such as diamond on the annular interior surface, which is placed in compression by virtue of the difference in the coefficients of thermal expansion between the annulus material and the CVD
deposited diamond layer. However, the aforementioned RD-21 ,6a,3 ,~,, ~, ''.

method is not suitable to producing crack resi.stant articles having high L/D ratios (about 50) because it is difficult to chemically vapor deposit diamond along the annular interior surfaces of articles having high UID ratios. By way of 5 example, it is difficult to deposit diamond on ~he interior wall of an article of a funnel shape haviny a small diameter stem of about 0.500 millimeter outer diameter and having a long stem length of about 75 millimeters. The present invention is directed to addressing the problem of making such crack resistant funnel shaped articles having high L/D
ratios.

~atement Qf the Invention The present invention is directed to an improved method of producing a two membered substantially crack-15 free water jet mixing tube of an abrasive water jet cuttingdevice comprising, chemical vapor depositing a diamond layer on a support member to form an inner member of the tube, the inner member having a smooth inner side of diamond with a microcrystalline structure, separating the 20 inner member from the support member, depositing an outer member material having a higher coefficient of thermal expansion than diamond on an outer side of the inner member to form an outer member of the tube, and cooling the tube to contract the outer member for inducing 25 compressive stresses of sufficient strength on the inner member to substantially prevent formation of cracks in the inner member.
The present invention is also directed to an improved abrasive water jet cutting device comprising, a 30 water reservoir having an orifice positioned therein, means for producing a jet of water through the orifice, a funnel shaped two layered water jet mixing tube positioned in the RD-21 ,6~3 a, path of th~ jet of water, the mixing tube comprising a substantially crack-free inner member of diamond layer under compressive stress, the inner member having a smooth inner side with a microcrystalline structure, and an 5 outer member of a material having higher coefficient of thermal expansion than diamond, disposed on an outer side of the inner member, means for introducing abrasive particles along the funnel of the mixing tube, such that the abrasive particles are entrained in the jet of water exit out 10 of the mixing tube to form an abrasive water jet, and means for controlling the abrasive characteristics of the abrasive water jet.

BJief Description of the Dr~wings Figure 1 illustrates a cross sectional view of a 15 partial abrasive water jet assembly.
Figure 2 is a graph of the abrasive particle veloci~y against the stem length of a water jet mixing tube of the abrasive water jet assembly of Figure 1.
Figure 3 shows a compression wave and a 20 reflected tension wave transmitted through the wall of the water jet mixing tube of Figure 1 when an abrasive particle hits the inner wall surface.
Figure 4A shows the crack damage that results in a stand alone diamond layer of similar size and 2 5 characteristics as that of the water jet mixing tube of Figure 1, when the diamond layer is exposed to an abrasive water jet.
Figure 4B shows no crack damage to a two membered substrate having a diamond layer similar in 30 thickness and characteristics to the one in Figure 4A, except for the protection offered by the compressive force ~D-21 ,6~3 provided by an ou~r member, when the two membered substrate is exposed to the abrasive water jet.
Figure 5A shows in a cross sectional elevation, a water jet mixing tube of the preferred embodiment.
Figure 5B shows a cross sectional plan view of the water jet mixing tube of Figure 5A taken along section B-B in Figur0 5A.
Figure 6 is a magnifiecl view of Detail C of Figure 5B illustrating the crystalline structure of diamond of an inner member of the water jet mixing tube of Figure 5A.
Figure 7 shows an abrasive water jet device that utilizes the water jet rnixing tube of the preferred embodiment.
Detailed Description of the Prefçrred Embodiment Continuously flowing water gradually erodes the surfaces it contacts. That is how rivers and streams form paths that cut through mountains and valleys. Natures slow erosion process can be transformed into a high-speed cutting action by increasing the force provided by a jet of water. When water is compressed to ultra high pressure levels, such as about 37 MPa (about 20-60,000 psi) and released through a small opening about 0.01 to 0.02 millimeters (about O.Oû3 to 0.100 inches) in diameter, the expanding water stream attains a speed up to three times the velocity of sound. Such a focused jet of water, traveling at an estimated velocity of about 869 meters per second (1945 miles per hour) reieases sufficient kinetic energy to cut through most of even hard-to-cut materials, such as ceramics and hardened metals and their alloys.

RD-21 ,643 When the force produc~ed by the conversion of kinetic energy of the water jet as it impacts against the workpiece surface, exceeds the compressive strength of the material being cut, a cutting action takes place. Depending 5 on the properties of the workpiece material, the actual cutting is a result of surface erosion, shearing or failure under rapidly changing, localized stress fields. The aforedescribed cutting process produces insignificant thermal or mechanical distortion on the workpiece and it is almost dust free.
The capacity of the water jet to perform the cutting action by erosion is represented by its kinetic energy, Kinetic Energy (KE) = MV212, (1) where (M) is the mass of water molecules and (V) is the velocity of water in the water jet provided by, V = G/D2 (2) where G is the volumetric rate of water at constant pressure passing through an orifice of diameter D.
The effectiveness of the abrasive action of the 25 water jet can be significantly increased by adding fine abrasive particles to the water jet stream. Suspended particles in water jet stream move at the same high velocity as the water. Since the mass of the particles in the water jet is significantly higher than the water 30 molecules, the overall kinetic energy at the impingement of the water jet against the workpiece would be also significantly higher. Thus, the addition of abrasive particles in the water creates a ballistic effect. The particles bombard the workpiece surface, similar to small R[)-21 ,643 .
! .`

particulates, with energy levels that are several times higher than the water medium that carries them. The mass differential between water and abrasive particles creates a pulsed erosion procsss that is extremely effective on hard-to-cut materials. This process is sometimes referred to as abrasive water jet (AWJ) cutting and the particles entrained in the abrasive water jet accomplish almost 90%
of the cutting action.
Typical abrasive particles employed in the AWJ
cutting process are garnet, aluminum oxide, silicon nitride and diamond in mesh sizes that vary from about 36 to 150.
Garnets of mesh size about 80 to 100 are preferred. Typical AWJ nozzle diameters range from about 0.075 to 2.50 millimeters, preferably about 1.00 millimeter and the distance between the AWJ nozzle and the workpiece surface generally varies from about 0.05 to 1.50 millimeters. The AWJ process produces a very powerful cutting tool and its shearing action can cut metals and other hard materials, such as ceramics of over 150 millimeters in thickness.
However, the AWJ process suffers from a major drawback. The abrasive particles exiting through the AWJ
drastically abrade a water jet mixing tube of the AWJ in which, mixing and entrainment of the abrasive particles occurs. Conventional carbide water jet mixing tubes have to be replaced every two to four hours, sometimes even more fre~uently. However, the life of water jet mixing tubes can be significantly increased, i.e., up to about 20 to 100 hours by making them from diamond. Figure 1 shows a typical partial AWJ assembly arrangement, referred to by numeral 1, that illustrates the relevant components. A
liquid reservoir 11 2 contains a fluid, typically water, under a high pressure provided by pumping means 114 to produce a water jet 116 through an orifice 118. Water jet 116 is generally co-centrally positioned within the bore of a water RD-21,643 ~ ~ !
!~ `

jet mixing tube 120. Wa~er jet mixing tube 12U is generally provided with a funnel shape to allow easy flow of the abrasive particles 122 introduced into the funnel shape of mixing tube 120 through an abrasive particle delivery 5 system 124. Metering means (not shown) are provided to control the flow of abrasive particles 122 into the funnel of rnixing tube 120.
In operation, as the high pressure water jet 116 flows out of orifice 118 into the funnel shape of mixing 10 tube 120, a partial vacuum is created in the funnel, which in turn induces a flow of abrasive particles 122 forward to an exit end 121 of mixing tube 120. The aforementioned action also accomplishes mixing and entrainment of particles 122 to produce an AWJ stream 126, which is then used to cut a 15 workpiece 128.
To achieve an optimal cutting action, particles 122 must be fully entrained in AWJ stream 126 before they jet out of exit end 121 (also referred to as a stem end). In the beginning of the entrainment process, particles 122 are 20 stationary, while water jet 116 is at an extremely high velocity. As particles 122 enter water jet 116, they are bounced off the wall of the stem of mixing tube 120 and then rebounded back into water jet 116. Such a repetitious and violent process continues until particles 122 attain the 25 velocity of water jet 116 to form AWJ strearn 126. Thus, it is the presence of the stem wall of the funnel shaped mixing tube 120 which facilitates entrapment of particles 1~2.
Figure 2 graphically illustrates the 30 aforementioned process. Figure 2 is the graph of the abrasive particle velocity against the stem length of mixing tube 120 of Figure 1. (V) represents the velocity of water jet 116. It can be ascertained from the graph of Figure 2 that the velocity of particles 122 increases along the stem RD-21,6~3 .. ,, , ~ , .

g length of mixing tube 120 and as stated earlier, the stem wall is subjected to repetitious tensile loads until particles 120 achieve the velocity of water jet 116 to form AWJ stream 126. Thus, a significant portion of the stem 5 length of mixing tube 120 is exposed to the violent bouncing action of particles 122.
As stated earlier, even though the useful life of water jet mixing tube 120 can be extended by making it from diamond, the aforementioned bouncing action 10 significantly affects the life of even a diamond mixing tube, due to the cracks produced on the wall of mixing tube 120 by the bouncing action of particles 122. As shown in Figure 3, when an abrasive particle 302 hits an inner surface 304 of the stem wall 306 of mixing tube 120 of Figure 1, a compression wave 308 is created within stem wall 306. As compression wave 30~ strikes an outer surface 310 of wall 306, a tension wave 312 is reflected back into stem wall 306. ~t is well known, that diamond though quite strong in compression, is weak in tension. As a result, tension wave 20 312 produces cracks in stem wall 306. Thus, even though the mixing tube made of diamond has significantly higher life than the conventional sapphire tubes, it still suffers from damage due to the cracks produced by tension wave 312.
The present invention addresses the aforementioned crack problem experienced by the conventional diamond mixing tubes by providing them with an outer layer that produces compressive stress on the diamond mixing tubes. Figure 4A shows what happens to a diamond layer 402 when it was subjected to a tension wave created by an abrasive water jet 404. Within a short duration of less than 10 seconds, diamond layer 402 having a thickness of about 0.076 millimeters was cut through.
However, as shown in Figure 4B, when diamond layer 402 RD-21,6ar3 ....... ..

was backed up with an outer member 406, such as one of metal, diamond layer 402, under compression, became extremely strong and no ascertainable crack damage from the tension wave generated by the bouncing action of the 5 abrasive particles from water jet ~04 was detected. It should be noted that the aforementioned test was more severe than the normal vector forces acting upon the inner walls of the stem of water jet mixing tube 120 of Figure 1.
Turning now to Figures 5A and 5B, a preferred 10 embodiment comprising a two membered substantially crack free water jet rnixing tube generally indicated by numeral 5, is shown. Mixing tube 5 comprises an inner member 502 of diamond. An inner side 506 of inner member 502 is provided with a smooth surface, preferably having 15 surface roughness of less than about 10 microns. Detail C
of Figure 5B, shown in Figure 6, provides a magnified view of inner side 506. Inner side 506 is provided with a dense generally equiaxed microcrystalline grain structure 508.
The grain size of diamond microcrystals along inner side 20 506 varies from about 1/10 to about 2 microns. Such a grain structure is typically formed during the deposition of a CVD diamond layer on a substrate surface. Such a dense and smooth surface is very helpful in not only reducing frictional drag on AWJ stream 126, shown in Figure 1, but 25 also in reducing the crack damage to inner side 506. As the deposition of the CVD diamond layer continues, a radially oriented columnar grain structure 510 (in a c110> direction) generally follows microcrystalline grain structure 508. A
detailed discussion of Miller indices describing crystal 30 planes of atoms differentiating between c010>, <110> and <111> orientations, shown on pages 65-69 of Elements of Material Science, Second Edition t1964) by Lawrence H.
VanVlack of Addison Wisley Publishing Co., Reading, Massachusetts is incorporated herein by reference. The RD-21,643 grains of columnar grain s~ructure 510 Ya~y from about 100 to about 300 microns. An outer side 512 of inner member 502 is significantly rougher than inner side 506.
inner member 502 is preferably funnel shaped and its stern length, excluding the funnel shaped portion, varies from about 60 millimeters to about 90 millimeters, preferably about 75 millimeters. The bore of the stem end of inner member 502 varies from about 0.10 millimeter to about 5.00 millimeters, preferably about 1.00 millimeter.
The UD ratio defined as a ratio of the stem length to the inner diameter of the inner member 502 is about a,5 to 55, preferably about 50. The diameter of the funnel of inner member 502 varies from about 1.0 millimeter to about 15.0 millimeters, preferably about 4.5 millimeters and the funnel angle varies from about 10 to about 45. The wall thickness of inner member 502 is more than about 0.3 mm.
However, it is understood, in view of the graph of Figure 2, that one skilled in the art would vary all the aforementioned dimensions according to the abrasive particle size, the water jet velocity and other operational variables of AWJ stream 126 in Figure 1 and it is also construed that the present invention is not restricted to inner member 502 having the aforementioned dimensions.
It is contemplated that one skilled in the art would also utilize some other funnel shapes, such a funnel having a cylindrical projection for increasing the quantity of abrasive particles stored within the funnel shape or a funnel having a polygonal shape, such as a hexagonal shape, and a rectangular stem.
3c An outer member 504 is disposed on outer side 512 of inner member 502 and it is made of a material having a higher coefficient of thermal expansion than that of diamond. Inner member 502 is under compression provided by outer member 504. The compressive forces on R D-21, 6~3 inner member 502 prevent cracking of inner side 50~ when it is repeatedly impacted by the bouncing ac~ion of abrasiYe particles 122 present in AWJ stream 126, shown in Figure 1. I~Aaterials suitable for ou~er member 50a, are ~ungsten, 5 titanium, tunysten carbide, molybdenum, rhenium, niobium, tantalum, nickel, zirconium, hafnium, vanadium, chromium, brass, zinc, copper, tin, aluminum or alloys thereof. It should be unders~ood ~hat actual material used for producing outer member 504 will depend upon the process, 10 described hereinafter, by which outer member 504 is deposited on outer side 512 of inner member 502. An outer side 514 of outer member 504 may be shaped to conform to a desired shape by the machining methods, such as turning, milling and the like. Alternatively, outer side 514 may be 15 provided with a desired shape along with holding rneans such as ribs, threads, fillets, screw mounting holes and the like, to fit a standardized receptacle of a conventional AWJ
cutti ng device .
Two-membered substantially crack-free water 20 jet rnixing tube 5 of Figures 5A and 5B is produced by chemical vapor deposition of diamond of inner rnember 502 on a hollow support member, generally made of tungsten, molybdenum, rhenium, niobium, tantalum, zirconium, hafnium, nickel, vanadium, chromium or titanium, 25 preferably molybdenum. The support member is provided with a desired shape, such as a funnel shape. The support member (not shown in Figures 5A and 5B) is then separated from inner member 502, preferably by etching it away in an etch bath. The etch bath is preferably ultrasonically 30 agitated to dislodge bubbles formed on the support member walls during the etching action. The details of the aforementioned process of forming inner member 502 on the support member and the separation of the support member from inner member 502 are disclosed in a commonly R~-21,6~3 assigned co-pending applica~ion, serial numbe7 07/713,499, filed on June 12, 1991, incorporat~sd herein by reference.
Outer member 504 is preferably plasma deposited on outer side 512 of inner member 502. A
5 conventional low pressure radio frequency plasma spray rnethod is most preFerred. Details of such a process are disclosed in the commonly assigned U.S. patents No.

4,786,566, 4,978,585, 4,981,643 and 5,042,710 and a commonly assigned application, serial number 07/524,527, 10 filed on May 19, 1990, all incorporated herein by reference.
The materials for outer member 504, such as tungsten, tungsten carbide, molybdenum, rhenium, niobium, tantalum, zirconium, hafnium, nickel, vanadium, chromium, titanium or the alloys thereof may be employed in the 15 aforementioned plasma deposition process. Titanium is preferred. The thickness of outer member 504 should be sufficient to provide constant and sustained compressive pressure on inner member 502 and the thickness of outer member 504 can be calculated from a formula, Thickness of outer member 504 Youngs Modulus ~Ed) of diamond Thickness of inner member 502 Youngs Modulus (Em) of outer (diamond)member 504 material Once outer member 504 is formed on inner member 502, by the aforementioned process, and as outer member 504 cools down it produces a compressive stress on inner member 502 that prevents cracking of inner side 30 506 of inner member 502 when inner side 506 is repeatedly subjected to impaction by abrasive particles 122 presen~ in the AWJ stream 126 of Figure 1.
in another embodiment of the present invention, outer member 504 may be deposited on inner member 502 by 35 electroforming an electrolessly deposited first metal layer, RD-21 ,6a,3 p ~ -followed by an electrolytically deposited second metal layer. The electroforming process is adjusted to produce compressive stresses on inner member 502. The aforementioned electroforming process has been disclosed 5 in a commonly assigned co-pending patent application, serial number 07/713,499 filed on June 12, 1991, incorporated herein by reference. The first metal layer may be of copper, nickel or silver. Nickel is preferred. The second metal layer may be made of copper or nickel. Copper 10 is preferred.
In yet another embodimen~ of the present invention, outer member 504 may be deposited on inner member 502 by casting a metal or a metal alloy around inner member 502. Conventional casting methods, such as 15 monolithic and shell investment casting, high pressure die casting, low pressure casting and centrifugally filled molding are suitable for use in the present invention. The metal or the metal alloy should be a non-carbide forming, low melting point metal. By using such a low melting point 20 metal, any hot tearing of the metal during the cooling is avoided. Hot tearing is defined as a cracking or splitting of a molten metal layer during its cooling on a strong and unyielding surface, such as of diamond. A suitable material for casting of outer member 504 is nickel, brass, copper, 25 aluminum, zinc or tin. Brass is preferred.
The conventional casting process comprises fabricating an investment casting mold in which, inner member 502 is used as a central core of the mold. The infiltration of the molten outer member material along 30 inner side 506 of Figure 6 is prevented, for example, by filling inner member 502 with a thermally stable material, such as a ceramic powder. Alternatively, an elongated member, such as a wire matched to the inner diameter of mixing tube 5, may be placed inside mixing tube 5. Such a ~D-21 ,6~3 .~ " , wire could also be used as a fixture to precisely place inner member 502 within the cavity o~ the casting mold. As stated earlier, outer rnember 50~ rnade by the aforementioned casting process may be provided with a 5 d0sir0d shape having provisions, such as screw mounting holes, lugs, stops and the like, to facili~ate the placement of mixing tube 5 in the AWJ cutting device. The invention also contemplates providing the aforestated investment mold with multiple cavities for increasing the rate of 10 production of water jet mixing tube 5.
The p~resent invention is also directed to an abrasive water jet cutting device, shown in Figure 7, utilizing previously described funnel shaped two membered water jet mixing tube 5. Figure 7 shows a water line 702 15 that supplies, preferably a deionized water, to a booster pump 704. The water, under pressure, may be optionally pumped through a water filtration apparatus 706 to reduce the contaminant level in said water to preferably about 0.45 to about 0.50 ~m particle size. By keeping the contaminant 20 level in said water low, the clogging of mixing tube 5 of Figure 5A as well as orifice 118 of Figure 1 is prevented.
The heart of cutting device 7 is a high pressure intensifier pump and accumulator 708. High pressure pump 708 boosts the water pressure to ultra high pressures of about 20,000 25 to 60,000 psi at a flow rate of about 5 gallons per minute.
Typically, high pressure pump 708 is a hydraulically driven, reciprocating plunger type pump. Intensifier pump 708 is based on the principle that, in a hydraulic system, a large piston acting on a smaller piston increases the pressure on 30 the smaller piston in inverse proportion to the respective piston areas. The intensifier pump ratios typically range from about 10:1 to 20:1. The water, under high pressure, is then delivered to the accumulator portion of high pressure pump 708. The accumulator portion of pump 708 evens out RD-2-l ,6~3 , the variations in water pressure to less ~han about ~ 5%, thereby ensuring a eonstant press,ure flow of water at a uniform flow rate. The high pressure wa~er is d01ivered through swiveled high pressure pipes 710 to an abrasive jet 5 cutting head 712 mounted on a X Y-Z axis gantry robot motion control system 720. Gantry system 720 provides head 712 with a three axis movement. An abrasive jet assembly 714 is attached to head 712 and abrasive particles from a hopper 716 are delivered through a metering valve 718 into je~ assembly 71~. A workpiece 722 is located on the table of device 7 under robot gantry system 720. The partial abrasive water jet assembly 1 of Figure 1 incorporated with water jet mixing tube 5 of Figures 5A and 5B, is part of jet assembly 714 and it is 15 mounted inside assembly 720. The abrasive characteristics of abrasive jet 126, shown in Figure 1, are controlled preferably through a computer controlled panel 724. A
water collection tank 726 is generally provided under the table of device 7 to catch the waste water and the spent 20 abrasive particles.
The present invention also contemplates a water jet cutting device in which, the workpiece is provided with a motion in accordance with a predetermined program while the AWJ cutting head remains stationary.

Example 1 The process in the example set forth below was carried out by the steps described above.
A diamond inner member of a water jet mixing tube 30 was prepared by a conventional low pressure chemical vapor deposition. The outer side of the diamond inner member had 1/8 inch diameter and a stem length of 1.5 inches. The inner member had a bore of 0.040 inches.

RD-21 ,6~3 molybdenum wire was slipped through the bore of ~he inner member to hold the diamond inner member during the plasma spray deposition of ~itanium on the outer sid0 of the inner member. The wire was attached to a rotation and translation mechanism of a conventional low pressure RF
plasrna spray device. To prevent a reaction of the titanium alloy with the wire holding ~ixture, the molybdenum wire and the wire holding fixture were coated with a ceria stabilized zirconia deposit applied by using an air plasma spray process.
The plasma spray chamber of the plasma spray device was evacuated to a pressure of 21 microns of mercury, filled with argon to a residual pressure of 250 Torr and then the outer side o~ the inner member was RF plasma deposited with a layer of titanium alloy (Ti-6AI-4V (composition in weight percent)).
The plasma spray conditions are given below:

Gun/Substrate Conditions:

Gun to Substrate Distance: 35.5 centimeters Powder: Ti-6AI-4V
StrGke Length: 20.3 centimeters Powder Size: -80+140 mesh Rotation Rate: 130 rpm Tank Pressure: 250 Torr Plate Voltage: 6.1 kiloVolts Deposition Time: 13 minutes Plate Current: 8.5 amperes Powder Feed Rate: 31 grams/min.
Input Power: 51.9 kw 3c Grid Current: 1.0 amperes ~!~m~ Gun Gas Flows:
Argon Swirl Flow: 16 liters per minute R D-2 I, 643 Argon ~adial Flow: 97 litars per minute Heliurn Radial Flow: 7a~ liters per minute Helium Powder F low: 4.5 liters per minute Exampl~ 2 The procedure of Exarnple 1 was repeated on a diamond inner member having a stem length of 3 inches. The rough outer surface of the plasma deposited outer member was 10 sanded to smooth out the surface.

~x~m~e ~

A diamond inner member of 3 inches in length was 15 plugged at each end with an aluminum oxide (Al2O3) core pin to prevent infiltration of molten metal during the casting process on the inner side of the inner member. Gypsm bonded silica investment casting plaster was used to cement the core pins to the inner side. The aforementioned assembly was used as a core 20 of a mold made from gypsm bonded silica investment casting plaster having a cavity of the desired shape. The mold and the core were gradually heated from 148 C to 537 C and then down to 260 C for 14 hours to remove moisture from the core and the mold cavity. A molten metal at 500 C, comprising 8.4%
25 aluminum, 1.0% copper, 0.02% magnesium and balance of zinc, all in weight percentages, was poured into the mold cavity maintained at 260 C. After the cure time of one hour, the inner member having the outer cast thereon was removed from the mold and the core pins were separated from the assembly to 30 form the mixing tube.

Claims

1. A method of producing a two membered substantially crack-free water jet mixing tube of an abrasive water jet cutting device comprising:
chemical vapor depositing a diamond layer on a support member to form an inner member of said tube, said inner member having a smooth inner side of diamond with a microcrystalline structure;
separating said inner member from said support member;
depositing an outer member material having a higher coefficient of thermal expansion than diamond on an outer side of said inner member to form an outer member of said tube; and cooling said tube to contract said outer member for inducing compressive stresses of sufficient strength on said inner member to substantially prevent formation of cracks in said inner member.

2. The method according to claim 1 wherein said step of separating said support member from said inner member comprises etching away said support member in an etch bath.

3. The method according to claim 1 wherein said step of depositing said outer member further comprises RF
plasma spray depositing said outer member material on said outer side of said inner member.

4. The method according to claim 3 wherein said outer member material is selected from the group consisting of tungsten, tungsten carbide, molybdenum, rhenium, niobium, tantalum, zirconium, hafnium, nickel, vanadium, chromium and titanium.

5. The method according to claim 1 wherein said step of depositing said outer member further comprises RD-21,643 electroforming said outer member material on said outer side of said inner member.

6. The method according to claim 5 wherein said step of electroforming further comprises:
electrolessly depositing a first metal layer on said outer side of said inner member; and electrolytically depositing a second metal layer on said first metal layer.

7. The method according to claim 6 wherein said first metal layer is nickel and said second metal layer is copper.

8. The method according to claim 1 wherein said step of depositing said outer member further comprises casting an outer member material around said inner member placed in a mold.

9. The method according to claim 8 wherein said outer member material is brass, aluminum, copper, zinc or tin.

10. The method according to claim 1 wherein said support member is a funnel shaped hollow mandrel.

11. A method of producing a two membered substantially crack-free water jet mixing tube of an abrasive water jet cutting device comprising:
chemical vapor depositing a diamond layer on a funnel shaped hollow support member to form an inner member of said tube, said inner member having a smooth inner side of diamond with a microcrystalline structure;
etching away said support member from said inner member;
casting an outer member material having a higher coefficient of thermal expansion than diamond on an outer side of said inner member to form an outer member of said tube; and RD-21,643 cooling said tube to contract said outer member for inducing compressive stresses of sufficient strength on said inner member to substantially prevent formation of cracks in said inner member.

12. A two layered water jet mixing tube of an abrasive water jet cutting device comprising:
a substantially crack-free inner member of diamond layer under compressive stress, said inner member having a smooth inner side with a microcrystalline structure; and an outer member of a material having higher coefficient of thermal expansion than diamond disposed on an outer side of said inner member.

13. The mixing tube according to claim 12 wherein said material of said outer is selected from the group consisting of tungsten, tungsten carbide, molybdenum, rhenium, niobium, tantalum, zirconium, hafnium, nickel, vanadium, chromium, brass, copper, zinc, aluminum and titanium.

14. The mixing tube according to claim 13 wherein said mixing tube has a funnel shape.

15. The mixing tube according to claim 14 wherein said funnel shaped mixing tube has a circular funnel of about 1.0 to 15.0 millimeters in diameter, a cylindrical stem having about 0.10 to 5.00 millimeters of inner diameter and a L/D ratio of about 45 to 55.

16. An improved abrasive water jet cutting device comprising:
a water reservoir having an orifice positioned therein;
means for producing a jet of water through said orifice;
a funnel shaped two layered water jet mixing tube positioned in the path of said jet of water, said mixing RD-21 ,643 tube comprising a substantially crack-free inner member of diamond layer under compressive stress, said inner member having a smooth inner side with a microcrystalline structure, and an outer member of a material having higher coefficient of thermal expansion than diamond, disposed on an outer side of said inner member;
means for introducing abrasive particles along said funnel of said mixing tube, such that said abrasive particles entrained in said jet of water exit out of said mixing tube to form an abrasive water jet; and means for controlling the abrasive characteristics of said abrasive water jet.

17. The invention as defined in any of the preceding claims including any further features of novelty disclosed.