Abstract:
A suspended abrasive waterjet narrow kerf cutting method is reconfigured to simultaneously drill multiple, closely-spaced holes in a target, including holes in confined non line-of-sight locations. Working fluid nozzles can be located on a flat or non-flat tool surface and arranged in uniform or non-uniform patterns, in an angled or perpendicular orientation, and in parallel or non-parallel arrangements. Individual nozzles or nozzle groups can be easily changed to provide increased or diminished working diameters, allowing control over the hole sizes and resultant airflow thru the drilled workpiece.

Description:
TECHNICAL FIELD 
     The present invention is directed to hole drilling, and more particularly to a hole drilling system and method that uses high pressure liquid to drill holes in a part. 
     BACKGROUND OF THE INVENTION 
     Many manufacturing applications require hole drilling to form holes in a target product. Mechanical drilling systems are appropriate for forming relatively large holes, but are not suitable for drilling small diameter holes because mechanical drilling methods are unable to drill small holes cleanly within tight tolerances. 
     Laser systems have been used in hole drilling systems because they can be precisely focused and can drill even small diameter holes relatively cleanly. However, these processes are thermal processes and often cause metallurgical damage in the holes they drill, leaving recast material on the sides of the hole walls that are prone to cracking and failure if highly stressed. 
     U.S. Pat. No. 5,184,434 to Hollinger et al. (“the &#39;434 patent”) illustrates a cutting process using a small diameter jet of high pressure fluid containing abrasive particles to cut a target product. The &#39;434 patent teaches fully wetting the abrasive in the fluid and also teaches treating the abrasive/fluid mixture to prevent the abrasive from settling out of the fluid. By controlling the size of the orifice through which the jet is output, the kerf width of the cut formed by the jet can be quite narrow, allowing the jet to make very fine cuts. However, the &#39;434 patent focuses solely using the jet in a cutting process and does not address the special concerns of hole drilling in any way. As a result, currently known hole drilling systems still rely on mechanical or thermal processes or use a conventional abrasive waterjet hole drilling method using a high pressure waterjet orifice, a mixing chamber to entrain dry abrasive particles, and a focusing tube. The large physical dimensions of conventional waterjet system components severely limits the ability to drill holes in confined spaces and/or in closely-spaced hole patterns. 
     There is a desire for an improved hole drilling system and method that can drill holes in a target cleanly in closely-spaced patterns, with no thermal damage to the target, simultaneously and in non line-of-sight locations. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a hole drilling system and method that uses coherent abrasive suspension jets to drill holes in a target. Abrasive particles are suspended in a working fluid before the fluid is jetted toward the target by increasing the fluid viscosity before the abrasive material is added to the fluid. To achieve mixing of the water and abrasive prior to the forming of the jet, suitable polymeric materials are mixed with the working fluid water to achieve an increased fluid viscosity, ensuring that the jet that is outputted through the system is coherent rather than divergent to maintain high abrasive particle velocities to drill holes efficiently. Further, by keeping the jet coherent at high velocities, the invention can cleanly drill holes even if the desired holes have small diameters without creating any thermal damage in the hole. 
     One advantage of the process for hole drilling with a coherent abrasive suspension jet is the elimination of the dry abrasive mixing chamber and focusing tube used in conventional abrasive waterjet hole drilling systems. The coherent abrasive suspension jet utilizes a viscous or viscoelastic suspension that maintains the abrasive in an even distribution throughout the liquid so that it might easily be pumped and passed through the nozzle already mixed. This permits the use of very small and closely spaced orifices to simultaneously drill multiple holes, including shallow-angled holes in confined, non line-of-sight locations. 
     In one embodiment, the jet nozzles used in the inventive system are smaller and narrower than conventional abrasive jet nozzles because the pre-mixed abrasive and fluid does not require two separate conduits, one for the abrasive and one for the fluid, to conduct mixing within a chamber disposed just before the nozzle. As a result, multiple nozzles can be arranged closely together to drill multiple, closely-spaced holes simultaneously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating the general concepts of a system according to one embodiment of the invention; 
         FIGS. 2A ,  2 B and  2 C are representative diagrams of a jet head used in one embodiment of the present invention; 
         FIG. 3  is a diagram of the system shown in  FIG. 1  according to one embodiment of the invention; 
         FIG. 4  is a diagram of a system according to another embodiment of the invention; 
         FIGS. 5A and 5B  are representative diagrams of one example of a jet head that can be used in the inventive system. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic diagram illustrating various primary components of a drilling system  100  according to one embodiment of the invention. Generally, the system  100  sends an abrasive working fluid  104  through one or more jet heads  102  to a target  106 . The flow and pressure of the working fluid  104  is controlled by flow of a control fluid  174 , such as oil, hydraulic fluid, or water, through the system  100  via a series of valves. In the schematic shown in  FIG. 1 , an isolator  168  prevents the working fluid  104  from contacting the control fluid  174 . An air-driven intensifier pump  180  is used to control the pressure of the control fluid  174  and therefore the working fluid  104 . In one embodiment, the intensifier pump  180  is able to produce 10,000 psi of control fluid  174  at up to 6 gallons/minute with no compressible or inertial stored energy via control of a high-speed pneumatic servo valve SV. 
     The isolator  168  is charged by manipulation of various valves in the system  100 . In the illustrated schematic, for example, the isolator  168  may be charged by closing valves V 2  and V 3 , opening valves V 4  and V 5 , and then opening valve V 6  to cause the working fluid  104  to be pumped into the isolator  168  and displace the control fluid  174  to, for example, a tank through another valve V 4 . To send the working fluid  104  to the jet head  102  and begin drilling, valves V 2  and V 3  are opened and valves V 4  and V 5  are closed. 
     A pressure controller  380  may use various pressure/time profiles to control flow of the control fluid  174  at various pressures via controller software. More particularly, the steady state and dynamic response of the system  100  can be controlled by the controller  380 , a transducer XD, the pneumatic servo valve SV, and one or more pumps PF. A flowmeter FM may be used to measure the flow of the control fluid  174 . A needle valve V 1  or other valve sets the steady state and dynamic response of the system  100 . Note that the valve V 1  may be controlled to allow an abrupt fluid pressure drop at the end of a drilling cycle, if desired. 
     Various embodiments of the overall system shown in  FIG. 1  will now be described below in greater detail.  FIGS. 2A ,  2 B and  2 C are representative diagrams illustrating a jetting portion of a hole drilling system  100  according to one embodiment of the invention. Although  FIGS. 2A and 2B  illustrate a single nozzle, a given system can contain multiple nozzles, which will be explained in greater detail below. The device shown in  FIG. 2  is the jet head  102 , which directs a coherent jet of the working fluid  104  to the target  106 . The working fluid  104  is a water/abrasive suspension. As shown in  FIG. 2 , the jet head  102  structure includes a feed tube  108  that directs a flow of the working fluid  104  to a nozzle holder  110 . The nozzle holder  110  allows different nozzles to be connected to the system so that the same system  100  can be easily adapted to drill different-sized holes. The nozzle holder  110  may be machined from a standard hex socket stainless steel set screw (e.g., a standard 4–40 hex socket set screw) to form a threaded holder structure. 
     In one embodiment, the nozzle holder  110  retains a poly-crystalline diamond (PCD) nozzle  112 , which typically has an orifice opening in the range of 0.003 to 0.020 inches. A high pressure coherent abrasive suspension jet of working fluid  104  (e.g., 10,000 psi) forced through a poly-crystalline diamond nozzle  112  having an orifice diameter of, for example, 0.005 inches will produce a highly collimated jet stream of working fluid  104  that can drill a hole in the target  106 . Because the jet stream of working fluid  104  is designed to have abrasive particles suspended in it, as will be explained in greater detail below, no further collimation of the jet of working fluid  104  is needed. 
     The poly-crystalline diamond nozzle  112  may be drilled so that it has an entrance  114  having a wider diameter d that tapers inward toward a small orifice  116  diameter before tapering back outward slightly. The nozzle  112  dimensions are selected to accommodate this tapering. For example, the poly-crystalline diamond nozzle  112  diameter itself may be around 0.050 inches in diameter by 0.040 inches long, while the entrance  114  may have a diameter d of 0.025 inches that eventually tapers to an orifice diameter of 0.005 inches. This large taper reduces fluid turbulence as the fluid travels from the feed tube  108  into the nozzle  112 , producing a fluid stream with reduced divergence. 
     In one embodiment, the outer diameter of the nozzle  112  and the inner diameter of the nozzle holder  110  are dimensioned so that the nozzle  112  slip-fits into the nozzle holder  110 . A lip  118  extending from the inner diameter of the nozzle holder  110  holds the nozzle  112  in position. The poly-crystalline diamond nozzle  112  is sealed to the nozzle body  110  by brazing or other suitable means to seal against leakage from the high fluid pressure in the feed tube  108 . 
     As can be seen in  FIG. 2 , the structure of the jet head  102  can be kept simple because the fluid and the abrasive are already mixed before they even enter the inlet feed tube  108  of the jet head  102 , eliminating the need for separate fluid and abrasive tubes or any mixing chamber within the jet head. Pressures in the system  100  can typically range from 5,000 to 15,000 psi, but there are no upper or lower pressure limits and any pressure coupled with compatible abrasive grades and nozzle orifice diameters can be used in the system. Because the jet head  102  is so simple and does not require a focusing tube to direct the jet stream of working fluid  104 , the jet stream can drill holes with diameters as small as 0.003 inches cleanly and without any metallurgical damage to the material surrounding the hole. 
     The fluid forming the jet stream of working fluid  104  is a fluid having abrasive particles suspended in a carrier fluid without settling. This suspension allows the fluid to be pumped through the nozzle  112  and eliminate the need to add abrasive at a later stage or constantly stir or agitate a slurry of the abrasive. The fluid may formed by adding fluid additives to water to control the viscosity of the fluid; in one embodiment, the fluid is a solution of around 3.9 percent by volume to increase the fluid viscosity to more than 9,000 centipoises. The fluid may use a methyl cellulose/water mixture or other long-chain polymer/water mixture as the viscous medium within which to suspend the abrasive particles. A typical viscoelastic fluid is marketed by Berkeley Chemical Company under the brand name “Superwater” and is a methacrylamide/water mixture. The abrasive particles themselves may be any non-hygroscopic material, such as 50 micron particles of garnet. Other materials, such as alumina, silica, or silicon carbide, may also be used as the abrasive. The abrasive particles may be mixed with the high viscosity fluid at a concentration of around 53 grams/liter. The fluid additive and the abrasive particles may be added to water in separate stages using an orbital mixer to ensure optimum mixing. 
     The high viscosity of the fluid prevents settling of the abrasive particles within the solution and maintain the coherency of the abrasive suspension jet as it passes through the nozzle  112 . The fluid may also have some degree of viscoelasticity to provide fluid elasticity when it hits the target, thereby maintaining a collimated jet configuration even as it hits the target. Both viscous and viscoelastic fluids effectively ensure high abrasive particle velocities as they hit the target  106  as well as maintain a small jet stream of working fluid  104  cross-sectional diameter to ensure focused hole drilling. 
     With a coherent abrasive suspension jet, the abrasive particles are fully wetted by the water-based suspending medium and are surrounded by the water based continuum. Therefore, there is no possibility of air entrainment in the jet as in the case of the conventional jets with a dry abrasive feed or slurry feed. 
       FIG. 3  is a representative diagram illustrating the overall hole drilling system  100  in greater detail.  FIG. 3  shows one way in which the working fluid  104  is transported to the jet head  102  and expelled toward the target  106 . The working fluid  104  is retained in liquid suspension tank  150  and is forced to flow into the system by any appropriate fluid transportation method, such as using compressed air to displace the fluid from the suspension tank  150 , to send the fluid through a suspension tank outlet port  152  and a suspension tank conduit  154 . This flow out of the suspension tank  150  is regulated by a suspension charging valve  156 . When the suspension charging valve  156  is open, the working fluid  104  is forced to flow into a suspension charging conduit  158  through a conduit T connector  160 , then through a suspension port  164 , and then into a piston pressure vessel, such as a floating piston cylinder  166 . 
     In this example, the floating piston cylinder  166  is a dual chamber cylindrical vessel with the isolator  168  that divides a working fluid chamber  170  from an control fluid chamber  172 . The working fluid chamber  170  holds the fluid and the suspended abrasive particles, while the control fluid chamber  172  holds control fluid  174 , such as any hydraulic fluid or water. The isolator  168  may have an upper O-ring seal  176  and a lower O-ring seal  178  to ensure that no mixing occurs between the abrasive suspension working fluid  104  and the control fluid  174 . 
     The control fluid  174  is kept under high pressure by air pressure or any other method. In one embodiment, the control fluid  174  is kept under high pressure in the control fluid chamber  172  by an air driven intensifier pump  180  at a pressure of up to 55,000 psi. The control fluid  174  is sent though the intensifier pump  180  via an intensifier pump conduit  182  and through a check valve  184 . The control fluid  174  is made to flow through a conduit  186 , a conduit T-connector  188 , a conduit  190 , and finally through an intensifier port  192  into the control fluid chamber  172 . 
     When the suspension charging valve  156 , the intensifier check valve  184 , an open depressurization valve  194 , and a suspension outlet valve  196  are appropriately configured, the control fluid  174  may be expelled from the control fluid chamber  172 , through a port  192 , conduit  190 , and a depressurization conduit  198 , the open depressurization valve  194 , and finally through a depressurization outlet conduit  200 . 
     To discharge the working fluid  104  out of the working fluid chamber  170 , the suspension outlet valve  196  is opened to allow the working fluid  104  to jet out of the suspension port  164  through the suspension conduit  162  and the conduit T-connector  160 . The fluid then flows through the suspension conduit  162 , the open suspension outlet valve  196 , and finally through a suspension outlet conduit  204 . The suspension outlet conduit  204  carries the pressurized working fluid  104  to the nozzle holder  110  and finally through the nozzle  112  to form the pressurized fluid jet that is sent toward the target  106 . The jet is then directed toward a focused point on the target  106  until it breaks through the target, thereby forming a hole. 
     The system shown in  FIG. 3  requires the floating piston cylinder  166  to be initially charged to start working fluid  104  flow. This is conducted using the abrasive working fluid  104  by opening the suspension charging valve  156 , closing the suspension outlet valve  196 , opening the depressurization valve  194 , and closing the intensifier check valve  184 . In this valve configuration, a minimal amount of pressure applied to the working fluid  104  forces the working fluid  104  to flow out of the suspension tank  150  into the working fluid chamber  170  of the floating piston cylinder  166 . This forces the isolator  168  downward, increasing the volume of the working fluid chamber  170  and decreasing the volume of the control fluid chamber  172 . As a result, the depressurized control fluid  174  in the control fluid chamber  172  is forced out through the open depressurization valve  194  as described above. The control fluid  174  is then drained and removed from the system  100  via the depressurization outlet conduit  200 . 
     Once the floating piston cylinder  166  has been charged with the abrasive suspension working fluid  104 , a reverse discharge process may be conducted. To do this, the suspension charging valve  156  is closed, the suspension outlet valve  196  is opened, the depressurization valve  194  is closed, and the intensifier check valve  184  is opened. In this configuration, the control fluid  174  is forced by the intensifier pump  180  to flow through the intensifier check valve  184  into the control fluid chamber  172  as described above. The higher pressure of the control fluid  174  flowing into the control fluid chamber  172  forces the isolator  168  upward through the floating piston cylinder  166 , thereby decreasing the volume of the working fluid chamber  170 . The decreased working fluid chamber  170  volume forces pressurized suspended abrasive working fluid  104  out of the floating piston cylinder  166  through the suspension outlet valve  196  at the pressure of control fluid  174  as described above. From the outlet valve  196 , the pressurized working fluid  104  flows through the suspension outlet conduit  204  through the nozzle holder  110  and then through the nozzle  112  as a high-pressure jet toward the target  106 . 
     The target  106  may be disposed on a platform  250  that can be indexed to move as individual holes have been drilled through the target  106 . In one embodiment, a controller  252  controls movement of the platform  250  so that the target  106  is moved relative to the nozzle  112  each time a drilled hole is complete. This allows sequential drilling of multiple holes in the same target  106 . 
       FIG. 4  illustrates an alternative embodiment of the hole drilling system shown in  FIG. 3 . In this embodiment, a second, parallel floating piston cylinder  166   b  is included. The components of this parallel system are identical to those described in  FIG. 3  and the numbers associated with their identity are repeated in  FIG. 4  with sub-indications “a” and “b” for clarity. The embodiment shown in  FIG. 4  can maintain a constant jet of working fluid  104  while at the same time recharging the system. This is accomplished through various valve switching sequences, which will be explained in greater detail below. 
     In the embodiment shown in  FIG. 4 , it is assumed that the system  100  is in an initial state where a first cylinder  166   a  is charged and a second cylinder  166   b  is discharged. With the first intensifier check valve  184   a , the second depressurization valve  194   b , the second suspension charging valve  156   b , and the first suspension outlet valve  196   a  in an open position, and with the first depressurization valve  194   a , the second intensifier check valve  184   b , the second suspension outlet valve  196   b , and the first suspension charging valve  156   a  in a closed position, the first cylinder  166   a  is faced with intensifier pressure within its control fluid chamber  172   a  by way of the open first intensifier check valve  184   a . This forces the first isolator  168   a  upward, which in turn forces the jet of working fluid  104  in the first cylinder  166   a  out of the first working fluid chamber  170   a  by way of the first suspension outlet valve  196   a.    
     Simultaneously, the second cylinder  166   b  recharges as the jet of working fluid  104  in the second cylinder is allowed to flow through the second suspension charging valve  156   b  into the second working fluid chamber  170   b , forcing the second isolator  168   b  downward. The downward movement of the second isolator  168   b  forces the control fluid out of the second control fluid chamber  172   b  through the open second depressurization valve  194   b  and then to the second depressurization outlet conduit  200   b.    
     When the first cylinder  166   a  approaches a fully discharged state and the second cylinder  166   b  approaches a fully charged state, the second suspension charging valve  156   b  and the second depressurization valve  194   b  are closed. Closing these valves isolates the second cylinder  166   b  momentarily. The second intensifier check valve  184   b  is then opened, which pressurizes the second cylinder  166   b  by allowing it to see the control fluid via the open second intensifier check valve  184   b  into the second control fluid chamber  172   b . The second suspension outlet valve  196   b  is then opened, placing both the first cylinder  166   a  and the second cylinder  166   b  in a discharge state. While both the first and second cylinders  166   a ,  166   b  are discharging, the suspension outlet valve  196   a  is closed to discontinue the discharging of the first cylinder  166   a.    
     The first intensifier check valve  184   a  is then closed to isolate the first cylinder  166   a  and allow the first cylinder  166   a  to begin recharging. This process is initiated by opening the first depressurization valve  194   a , which allows the depressurization of the first control fluid chamber  172   a  and therefore allows the control fluid to flow out of the first control fluid chamber  172   a . At the same time, the first suspension charging valve  156   a  is opened to allow the working fluid  104  to flow into the first working fluid chamber  170   a . During the time the first cylinder  166   a  is recharging, the second cylinder  166   b  continues to discharge the fluid jet  104  through the nozzle  112 . 
     The same sequence of valve openings and closings occurs when the first cylinder  166   a  has been fully charged and the second cylinder  166   b  is nearing a full discharge state. This transition sequence of discharging and charging the first and second cylinders  166   a ,  166   b  can be carried on indefinitely as long as sufficient abrasive working fluid  104  is supplied from the suspension tank  150  and as long as control fluid  174  is supplied through the intensifier pump  180 . 
     Regardless of the specific system used to drill holes, the pressure of the working fluid  104  impinging the target can be adjusted if desired to prevent the jet from creating a ricochet pattern as the abrasive particles bounce off the target, creating a knife edge or otherwise unclean drilling pattern. To do this, the drilling process may start at a low pressure and gradually increase to a high, target pressure once the jet has engaged with the material by breaking past its surface. By varying the jet pressure in this manner, it is possible to create a clean hole without any defective cuts due to ricochet of the abrasive particles off of the target. Moreover, varying the jet pressure can control the configuration of the hole itself. 
     In one embodiment, if the inventive system is used to drill holes having a desired profile, a pressure controller  380  may control a time/pressure profile of the fluid while drilling an entry portion of a hole, then use a different time/pressure profile while drilling a middle portion of a hole and then using yet another time/pressure profile to shape the exit geometry of the hole. These differing time/pressure profiles allows the same nozzle  112  to drill a hole having slight variations in geometry. 
     Note that the pressure controller  380  can also control the time/pressure profile of the fluid to allow tapering of the working fluid  104  during the drilling cycle to generate non-circular, shaped holes in the target  106 . Alternatively, the orifice  116  of the nozzle  112  may be formed with non-circular, sectional areas to produce a working fluid  104  stream with a profile that can drill a hole with a desired shape. By controlling the time/pressure profile and/or the shape of the orifice  116 , it is also possible to drill holes having a non-uniform profile (e.g., a hole with different dimensions on either side of the target or a hole with varying dimensions along its length). Thus, the system provides a great deal of flexibility on hole shaping with minimal adjustment. 
       FIGS. 5A and 5B  illustrates an example of a multiple-conduit configuration that can drill multiple holes simultaneously. As noted above, the simple structure of the nozzle holder  110  and the nozzle  112  allows multiple nozzles  112  to be arranged close together to drill closely-spaced holes in the target  106 . Moreover, the small profile of the nozzle holder  110  and nozzle  112  allows the nozzles  112  to be arranged so that the holes are drilled at an angle in a selected pattern. The inventive system and method therefore allows multiple holes to be drilled simultaneously under limited clearances, even in non-line of sight locations and on curved surfaces, while preserving the highest possible metallurgical quality in the target  106  even if the target  106  has a coating (e.g., a thermal barrier coating). 
     As shown in the plan view of  FIG. 5A  and the section view of  FIG. 5B , the jet head  102  can be configured in the form of a block  400  having a plurality of conduits  402  that can accommodate multiple nozzle holders  110  and therefore multiple nozzles  112 . A cover  404  is held to the block  400  with screws or other fasteners  405 . The cover  404  has an opening  406  that accommodates the feed tube  108 . The block  400  has a milled plenum  408  that distributes fluid from the feed tube  108  to the nozzles  112  held in the conduits  402  by the nozzle holders  110 . This ensures that the fluid is expelled from the multiple nozzles  112  simultaneously to drill multiple holes. 
     In one embodiment, if threaded nozzle holders  110  are used, the diameters of the conduits  402  are the same as the tap drill diameter of the nozzle holders  110  so that the nozzle holders  110  can be screwed into and form a close fit within the conduits  402 . Using threaded nozzle holders  110  allows the nozzle holders  110  and the nozzles  112  to be easily removed and replaced. In the configuration shown in  FIGS. 5A and 5B , it is possible to place nozzles  112  having different diameters in the same block  400 , providing flexibility in the final drilling pattern. 
     Note that although the illustrated embodiment shows the conduits  402  generally parallel to each other, the conduits  402  can be disposed at any angle and any direction and may even intersect, depending on the desired hole drilling pattern. Moreover, the conduits  402  may be arranged at an angle with respect to the surface of the block  400 . In other words, the conduits  402  can be disposed in any orientation with respect to each other and with respect to the block surface depending on the desired hole configuration to be drilled. 
     In one example, the working fluid  104  used to drill multiple targets is a room temperature, water-based fluid having 50 micron abrasive particles of garnet suspended in the fluid at 52.8 grams per liter. In this example, a long molecular chain acrylic polymer is added at 3.9% by volume to increase the viscosity of the fluid and keep the abrasive particles suspended in the fluid. The jet head  102  contains multiple nozzles  112  that are arranged in a desired configuration. In the example shown in  FIGS. 5A and 5B , the orifices  116  are on the order of 0.005 inches in diameter and the bodies of the nozzles are on the order of 0.050 inches in diameter by 0.040 inches thick and brazed or otherwise attached into position within the nozzle body  110 , which are threaded into the conduits  402  at an angle of around 30 degrees. In one embodiment, the nozzles  112  are made of a poly-crystalline diamond material or other material with suitable wear resistance. The nozzles  112  may be staggered to form a desired hole pattern. During drilling, each nozzle  112  is fed by a 0.040 inch diameter conduit at a rate of approximately 1.0 cc/second to generate a plurality of parallel holes. Note that the orientation and relative positions of the nozzles  112  can be easily adjusted via any known manner to produce non-parallel holes on non-planar surfaces without departing from the scope of the invention. The plurality of fluid jets is positioned during the impinging step so that the plurality of the holes are separate from each other, with each of said plurality of holes defining a boundary, and said plurality of holes not being positioned within the boundary of another of said plurality of holes. 
     By drilling multiple holes at the same time, the inventive method and system can rapidly produce parts having a plurality of holes without sacrificing the quality of the holes and preserving the metallurgical characteristics of the material around the holes. Further, the inventive hole drilling system and method can cleanly drill through materials other than metal, including composites and ceramics, at rapid dates due to the high fluid pressure and the non-thermal grinding action of the abrasive particles. 
     It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.