Patent Publication Number: US-8530787-B2

Title: Flow tester for laser drilled holes

Description:
BACKGROUND 
     Laser drilling is a technique for forming holes in various materials, including hard to process materials such as aircraft grade castings. Laser drilling can be used to form very small holes, including holes that are created at an angle that may be otherwise very difficult to form. 
     Holes formed by laser drilling and other processes may be used to conduct gasses. For example, a turbine engine&#39;s turbine blades may have a series of holes through which cooling air may pass to form a cooled boundary layer around the blade. The flow of gasses through these holes can be a functional aspect of the blade that is difficult to measure. 
     SUMMARY 
     A flow tester may use a low impedance flow meter to test a hole at a predetermined Reynolds number. The flow tester may be mounted to a robot so that testing may be fully automated. For example, the flow tester may be incorporated into a laser drilling workcell and used to test flow characteristics of a test coupon or workpiece to calibrate or verify the laser settings. Another example may be used for testing flow characteristics of a finished workpiece. The flow tester may have a testing tip that is compliant to form a seal against a workpiece, and the testing tip may be able to seal against angled, curved, or other surfaces. The flow tester may be capable of testing individual holes or groups of holes and determining an effective cross sectional area for the hole at the predetermined Reynolds number. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is a diagram illustration of an embodiment showing a system for measuring flow. 
         FIG. 2  is a diagram illustration of an embodiment showing a probe tip and concentric positioning of the probe tip. 
         FIG. 3  is a diagram illustration of an embodiment showing a probe tip and non-concentric positioning of the probe tip. 
         FIG. 4  is a cross-sectional diagram illustration of an embodiment showing a testing probe. 
         FIG. 5  is a cross-sectional diagram illustration of an embodiment showing a testing probe with a compliant probe tip. 
         FIG. 6  is a cross-sectional diagram illustration of an embodiment showing the testing probe of  FIG. 5  with the compliant probe tip deformed against a base material. 
         FIG. 7  is a cross-sectional diagram illustration of an embodiment showing a testing probe with a first removable probe tip. 
         FIG. 8  is a cross-sectional diagram illustration of an embodiment showing a testing probe with a second removable probe tip. 
         FIG. 9  is a diagram illustration of an embodiment showing a probe tip and concentric positioning of the probe tip, where both the probe tip and hole to be measured are elliptical. 
     
    
    
     DETAILED DESCRIPTION 
     A flow tester may use a low impedance flow meter to measure the flow from individual holes. The workpiece being tested may be mounted on a plenum that is pressurized to a predetermined pressure. The effective area of individual holes or groups of holes may be calculated knowing the pressure and temperature of the plenum as well as the pressure measured at a hole exit, the mass flow and the atmospheric pressure. 
     The flow tester may perform measurements on workpieces at a predetermined Reynolds number. The Reynolds number is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces in fluid flow, and quantifies the relative importance of the two types of forces for given flow conditions. Measurements taken in different conditions but with similar Reynolds numbers are often very comparable. Such a technique may be used when a device is used in situations that are difficult to simulate. For example, flow at very high temperatures or pressures may be evaluated using flow at similar Reynolds numbers but with room temperature flow, for example. 
     The flow tester may be integrated with a robotic manipulator. The robotic manipulator may position a test probe over individual holes to create a seal against a workpiece and capture the flow from the hole. After the flow parameters are measured, the robotic manipulator may position the flow tester over another hole. 
     Such a system may be useful in testing items that have many small holes. An example may be a blade from a turbine engine, where pressurized cold air may be forced through a series of small holes to form a cold boundary layer of air over the blade. Such blades may be used in the combustor section of a turbine engine and may be subjected to extreme temperature and pressure. The flow tester may be used to perform quality tests of the blades, for example. 
     In another use, the flow tester may be used in conjunction with a laser drilling operation. The flow tester may be used to measure the performance of the laser drilling operation and may be used to provide feedback to change or modify settings for the laser drilling operation. The flow tester may be used to measure the flow from a test coupon for setting the drilling settings or used for testing drilled holes in a workpiece. 
     An effective cross sectional area may be computed for a hole using the parameters collected by the flow tester. A low impedance flow sensor may measure the mass flow rate of the hole, and other sensors may measure flow path inlet pressure, flow path exit pressure, atmospheric pressure, and flow path inlet temperature. 
     Throughout this specification, like reference numbers signify the same elements throughout the description of the figures. 
     When elements are referred to as being “connected” or “coupled,” the elements can be directly connected or coupled together or one or more intervening elements may also be present. In contrast, when elements are referred to as being “directly connected” or “directly coupled,” there are no intervening elements present. 
     The subject matter may be embodied as devices, systems, methods, and/or computer program products. Accordingly, some or all of the subject matter may be embodied in hardware and/or in software (including firmware, resident software, micro-code, state machines, gate arrays, etc.) Furthermore, the subject matter may take the form of a computer program product on a computer-usable or computer-readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 
     The computer-usable or computer-readable medium may be for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. By way of example, and not limitation, computer-readable media may comprise computer storage media and communication media. 
     Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and may be accessed by an instruction execution system. Note that the computer-usable or computer-readable medium can be paper or other suitable medium upon which the program is printed, as the program can be electronically captured via, for instance, optical scanning of the paper or other suitable medium, then compiled, interpreted, of otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. 
     Communication media typically embodies computer-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” can be defined as a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above-mentioned should also be included within the scope of computer-readable media. 
     When the subject matter is embodied in the general context of computer-executable instructions, the embodiment may comprise program modules, executed by one or more systems, computers, or other devices. Generally, program modules include routines, programs, objects, components, data structures, and the like, that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments. 
       FIG. 1  is a diagram of an embodiment  100 , showing a system measuring flow. Embodiment  100  may be one example of an embodiment where a robotic manipulator may be used to position a probe over individual holes for testing. 
     The diagram of  FIG. 1  illustrates functional components of a system. In some cases, the component may be a hardware component, a software component, or a combination of hardware and software. Some of the components may be application level software, while other components may be operating system level components. In some cases, the connection of one component to another may be a close connection where two or more components are operating on a single hardware platform. In other cases, the connections may be made over network connections spanning long distances. Each embodiment may use different hardware, software, and interconnection architectures to achieve the described functions. 
     Embodiment  100  is an example of a flow test system that may be used to measure flow from individual holes. A probe  102  may have a tip  104  that seals against a workpiece  106  to capture flow coming from one of the holes  108 . In some cases, the probe  102  may be used to capture flow from holes  112  that may be drilled in a test coupon  110 . 
     The workpiece  106  may be mounted in a fixture  112  that contains a plenum  114 . Similarly, the test coupon  110  may be mounted in a fixture that contains a plenum  116 . The respective plenums may be pressurized so that a gas flows from the holes  108  or  112  into the atmosphere. The probe  102  may be positioned over one or more holes to capture the air flowing from the plenum to the atmosphere. 
     A compressed gas source  118  may provide gas through a controllable pressure regulator  120  to pressurize the plenum  114  or  116 . In some cases, the compressed gas may be air, while other cases helium, nitrogen, argon, or other gas may be used. 
     The probe  102  may be any mechanism that may be used to seal against the workpiece  106  or test coupon  110  to receive gas that may be expelled through one or more of the holes  108  or  112 . The probe tip  104  may be a compliant mechanism that may seal around a hole. In many cases, the probe tip  104  may be sized so that a seal may be created around one hole without impinging on other holes. 
     In an embodiment that may test turbine blades, the hole sizing and spacing may be small. For example, a typical hole size may be 0.015-0.050 inches with spacing on the order of a 2 or 3 times the diameter of the hole. The holes may be arranged in a single line or in a pattern. Other embodiments may have larger or smaller holes and larger or smaller spacing, or place the holes in various configurations. 
     The holes may be perpendicular to the surface of a workpiece  106  or test coupon  110 . In some cases, a laser drilling system may be capable of creating a hole at an angle to the surface of the workpiece. For example, some laser drilling systems may be able to create holes that are at 30 degrees, 45 degrees, 60 degrees, or at other angles to perpendicular. 
     The probe  102  may be connected to a flow meter  122 . The flow meter  122  may be a low impedance flow meter, such as an inline flow meter, variable area flow meter, pitot tube flow meter, ultrasonic flow meter, or some other flow measurement device. 
     The probe  102  may have a tip  104  that may seal against the surface of a workpiece  106  or test coupon  110 . The tip  104  may have one or more compliant elements that may allow the tip  104  to seal against angled or curved surfaces. In some cases, the tip  104  may have a portion that deforms to form a seal. Examples of different embodiments are illustrated later in this specification. 
     A temperature sensor  124  and pressure sensor  126  may be used by a data analyzer  128  to calculate an effective area of a hole. In many embodiments, the measurement system may be fully automated, and the flow meter  122 , temperature sensor  124 , and pressure sensor  126  may each generate digital or analog output signals that may be received by the data analyzer  128  to calculate an effective area. In many cases, the data analyzer  128  may also control the controllable pressure regulator  120  to generate a desired pressure within the plenums  114  or  116 . 
     The temperature sensor  124  and pressure sensor  126  are illustrated as being connected to the fixture  112 . In embodiments where the holes  112  are to be tested in the test coupon  110 , similar temperature and pressure sensors may be connected to the plenum  116 . 
     The effective area of a hole may be calculated using the following formulae: 
     
       
         
           
             
               AE 
               hole 
             
             = 
             
               
                 mdot 
                 * 
                 
                   T 
                   3 
                   
                     ( 
                     
                       1 
                       / 
                       2 
                     
                     ) 
                   
                 
               
               
                 0.91886 
                 * 
                 
                   P 
                   3 
                 
                 * 
                 M 
                 * 
                 
                   
                     ( 
                     
                       1 
                       + 
                       
                         0.2 
                         * 
                         
                           M 
                           2 
                         
                       
                     
                     ) 
                   
                   
                     - 
                     3 
                   
                 
               
             
           
         
       
       
         
           
             M 
             = 
             
               
                 [ 
                 
                   
                     ( 
                     
                       
                         PR 
                         
                           ( 
                           
                             1 
                             / 
                             3.5 
                           
                           ) 
                         
                       
                       - 
                       1 
                     
                     ) 
                   
                   0.2 
                 
                 ] 
               
               
                 1 
                 / 
                 2 
               
             
           
         
       
       
         
           
             PR 
             = 
             
               
                 P 
                 3 
               
               
                 
                   P 
                   a 
                 
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                   P 
                   4 
                 
               
             
           
         
       
     
     where: 
     AE hole =Effective Area (in 2 ) 
     m dot=Mass Flow Rate (lbm/sec) 
     T3=Flow Path Inlet Temperature (deg F.) 
     M=Mach Number (unit less) 
     PR=Pressure Ratio (unit less) 
     Pa=Atmospheric Pressure (psia) 
     P4=Flow Path Exit Pressure (psia) 
     P3=Flow Path Inlet Pressure (psia) 
     The formulae above may be used to compute the effective area of a hole based using English units. Similar formulae may be used for SI units. 
     The temperature sensor  124  may be used to measure the T3 value. The P4 value may be measured using the flow meter  122 , and the P3 value may be measured using the pressure sensor  126  in the example of embodiment  100 . 
     In many embodiments, the flow meter  122 , temperature sensor  124 , and pressure sensor  126  may generate digital signals corresponding with the units above. In some cases, the data analyzer  128  may perform unit conversions to convert a received signal to a value corresponding with the desired units. 
     The test system may operate by causing a pressure within the plenum  114  to reach a predetermined level. The pressure may cause flow through the holes  108  to atmospheric pressure. The probe  102  may be placed over each of the holes in succession and while sealed to a hole, the various pressure and temperature measurements may be taken and used to calculate an effective area for the hole. Once the measurements are taken, the probe  102  may be repositioned over another hole and another set of measurements taken. This process may repeat for each of the holes  108 . 
     The test system may operate by determining a desired Reynolds number for the workpiece  106 . The Reynolds number may be calculated for the intended use for the workpiece, then a comparable Reynolds number flow may be calculated using the flow system of embodiment  100 . In some cases, the test flow may exhaust to atmospheric pressure and room temperature gas may be used. 
     In order to create a similar Reynolds number flow for testing, the pressure inside a plenum of a test fixture or test coupon holder may be set to a desired pressure. In some embodiments, a gas heating or cooling system may be used to respectively raise or lower the gas pressure inside the plenum to achieve a desired Reynolds number flow. 
     The Reynolds number may be affected by the compressed gas used in the test system. In some cases, air may be used as the compressed gas, but other gases may also be used. 
     The data analyzer  128  may operate in conjunction with a robot controller  130  that may cause the robot  132  to move the probe  102  into position. The robot controller  130  may generate tool paths and movement signals to cause the probe  102  to move from one hole location to another. 
     The data analyzer  128  and robot controller  130  may have a master/slave relationship. In some embodiments, the robot controller  130  may be configured to sequence the movement of the probe  102  and testing of the holes  108 . In such an embodiment, the robot controller  130  may position the probe  102 , then send a signal to the data analyzer  128 , which may cause the data analyzer  128  to perform the test. After performing the test, the data analyzer  128  may send a signal to the robot controller  130  to resume the sequence. In such an embodiment, the robot controller  130  may act as a master device while the data analyzer  128  may act as a slave device to the robot controller  130 . 
     In other embodiments, the data analyzer  128  may operate as a master device and the robot controller  130  may operate as a slave device. In such an embodiment, the data analyzer  128  may send a signal to the robot controller  130  to move to a designated location. Once the robot controller  130  is in position, the robot controller  130  may transmit a signal to the data analyzer  128  and the data analyzer  128  may perform the tests. In some such embodiments, the data analyzer  128  may contain a list of positions for each of the holes  108  and may transmit addresses or coordinates of those holes to the robot controller  130 . 
     The robot  132  may be any positioning device. The robot  132  as illustrated may be a robot arm that has several degrees of motion. The robot  132  may be capable of positioning the probe  102  in any position and at any angle within the robot&#39;s reach. In many such robots, the probe  102  may be positioned within a three dimensional space by defining a point and a vector within the three dimensional space. The point may define the position of the end of the tip  104 , and the vector may define the orientation of the probe  102  from the point. 
     In some embodiments, the robot  132  may have an interchangeable end effector  134 . An interchangeable end effector may be a mechanism by which the robot  132  may be able to change tools or end effectors quickly. In some embodiments, the robot  132  may be able to detach the probe  102  and use another end effector, then detach the other end effector and re-attach the probe  102 . In many such embodiments, the interchangeable end effector  134  may have connections for pressurized air and electronics, as well as sensor connections such as a connection to the flow meter  122 . In some embodiments, an end effector may include a flow meter  122  and may pass flow measurements to the data analyzer  128  through an electrical connection in the interchangeable end effector  134 . 
     A laser  136  may be incorporated into the robotic system for drilling the various holes  108  or  112 , and may be used in several different manners with the data analyzer  128  and other sensors. In some embodiments, a single robotic end effector may include a probe  102  and a laser  136 . In other embodiments, a robot may have two separate end effectors: a probe  102  and a laser  136 . In still other embodiments, a laser drilling machine may have a first robot that manipulates and positions a laser  136  while a second robot manipulates and positions a probe  102 . 
     In one embodiment, the laser  136  may be a component in a laser drilling system. The laser drilling system may have a laser controller  138  that operates the laser  136  using various laser drilling settings  140 . The data analyzer  128  and probe  102  may be used to configure the settings  140  by providing feedback on holes drilled by the laser  136 . 
     In such an embodiment, the laser  136  may be used to drill one or more holes. The probe  102  and data analyzer  128  may be used to measure the flow of the holes and to analyze the effective area of the holes. The data analyzer  128  may compare the measured results of the hole to expected results to determine if the settings  140  may be adjusted. The expected results may have a range of expected values so that when an expected value falls within the range, the settings may be left unchanged. In many such embodiments, the data analyzer  128  may measure the effective area of a hole and cause the settings  140  to be adjusted to make the hole larger or smaller to fit within the expected range of the effective area of the hole. 
     The system may first calibrate the laser settings  140  by using a test coupon  110 . The laser  136  may be used to drill several holes in the test coupon  110 , then the probe  102  may be used to measure each hole. Based on the measurements, the laser settings  140  may be adjusted. Some embodiments may perform the calibration routine again until the laser settings are producing expected results. In some cases, such setting adjustment routines may be performed iteratively until the settings converge on an acceptable set of values. 
     The laser settings  140  may be any adjustable values that may be used to cause the laser  136  to perform in a different manner. The adjustments may be, for example, power levels, focus settings, length of a percussive blast, number of percussive blasts, or other configurable settings. 
     When the laser  136  is used for drilling very small holes, the laser  136  may be positioned in a single location and the laser may be fired several times to produce a hole. Such a laser drilling system may be termed a percussive drilling mechanism. In such systems, the energy levels, timing, and duration of the percussive blasts may change the overall size of the holes. 
     The holes drilled by such a system may have rather irregular shapes. The manufacture of the holes involves successively blasting the workpiece with laser energy that may vaporize or blast the base material away. While the hole is generally round, the size of the hole may be difficult to measure using pin gages or other mechanical measuring system. In such cases, the embodiment  100  may be used to measure the holes using conditions that are similar to the end use of the workpiece and by calculating the effective area of the holes. By measuring in these conditions, the measurements better reflect the performance of the workpiece in terms of effective area of flow rather than pure dimensional measurements that may be obtained with conventional physical measurement techniques such as using pin gages, for example. 
     Such systems may be used to drill holes that may be otherwise difficult to manufacture. For example, turbine blades may be manufactured from very exotic and hard to machine materials. A conventional twist drill may dull or fail when used in such materials, especially for very small hole sizes. For holes drilled at an angle, the complexities may increase further. In some cases, laser drilling may be the only alternative for producing such holes. 
     When the laser  136  is used for drilling larger holes, the laser  136  may first break through the workpiece, then the laser  136  may be moved in a circular manner over the workpiece to create a hole. In such embodiments, the data analyzer  128  may be used to calculate the effective area of the hole. After comparing the effective area of the hole and any deviation from an expected effective area, the data analyzer  128  may cause the laser settings  140  or the robot path settings to change. In some embodiments, the data analyzer  128  may cause both of the laser settings  140  and the robot path to change. In such an embodiment, the robot path may be adjusted to make the effective area larger or smaller, while the laser settings  140  may be adjusted to remove more or less material. 
       FIG. 2  is a diagram of an embodiment  200 , showing a hole to be measured and the positioning of a probe tip to measure the hole. 
     The base material  202  is illustrated with a hole  204 . The probe tip  206  is illustrated as being centered or concentric with the hole  204 . In many cases, the concentric placement of the probe tip  206  may be the ideal condition when attempting to measure the flow from the hole  202 . 
     The shaded area of the probe tip  206  may illustrate the contact area for a probe tip against the base material  202  when the probe forms a seal against the base material  202 . 
     The base material  202  may be the material of a test coupon or workpiece. The hole  204  is illustrated as being circular. In some embodiments, the hole  204  may be irregularly shaped. 
       FIG. 3  is a diagram of an embodiment  300 , showing a hole to be measured and the positioning of a probe tip to measure the hole. Embodiment  300  is an example of an off-centered placement of the probe tip. 
     The base material  302  is illustrated with a hole  304 . The probe tip  306  is illustrated as being off centered or not concentric entered or concentric with the hole  304 . 
     In some cases, the probe tip  306  may be positioned off center with respect to the hole  304 . Such a situation may occur due to tolerances in the positioning of the probe tip, or due to tolerances in positioning the base material  302  or in drilling the base material  302 . 
       FIG. 4  is a cross sectional view of an embodiment  400  showing a testing probe. 
     The view of embodiment  400  is a schematic cross section that illustrates the functional components of a probe. Actual embodiments may have different sizes and proportions of the various components. Because the view shows some functional components, many details have been removed, including other parts, connection mechanisms, and the like. 
     The probe  402  is illustrated as having a probe tip  404  and a hose  406 . The probe  402  is also illustrated as having a hollow core that may conduct air or other fluid from a hole  412  through the hose  406 . The hose  406  may be connected to a flow meter. 
     The probe  402  has a probe tip  404  that may press against the base material  410  to form a seal at the interface  408 . The seal may pass the pressurized air or other fluid through the hose  406 . 
     In many embodiments, the probe tip  404  may affect a seal at the interface  408  when compressive force is applied to the probe  402 . In some cases, the probe tip  404  may deform or may contain deformable components so that a fluid-tight seal may be created to the base material  410 . 
       FIG. 5  is a cross sectional view of an embodiment  500  showing a testing probe with a deformable tip. 
     The view of embodiment  500  is a schematic cross section that illustrates the functional components of a probe. Actual embodiments may have different sizes and proportions of the various components. Because the view shows some functional components, many details have been removed, including other parts, connection mechanisms, and the like. 
     The probe  502  is illustrated as having a probe tip  504  and a hose  506 . Like embodiment  400 , the probe  502  is illustrated as having a hollow care that may conduct air or other fluid from a hole  512  through the hose  506 . The hose  506  may be connected to a flow meter. 
     The probe  502  has a probe tip  504  that may have a flared end  508 . The flared end  508  may be pressed against the base material  510  to form a seal that the interface  518 . 
       FIG. 6  is a cross sectional view of an embodiment  600  showing the probe of embodiment  500  pressed against the base material. 
     The view of embodiment  600  is a schematic cross section that illustrates the functional components of a probe. Actual embodiments may have different sizes and proportions of the various components. Because the view shows some functional components, many details have been removed, including other parts, connection mechanisms, and the like. 
     Embodiment  600  shows the probe  502  of embodiment  500  pressed against the base material  510 . When the probe  502  is pressed against the base material  510 , the flared end  508  may be deformed as illustrated. The deformation may be sufficient to seal the probe  502  against the base material  510 . 
     In the example of embodiments  500  and  600 , the probe tip  504  may be manufactured of a pliable material, such as polyurethane or other compliant plastic material. Such probe tips may be machined, cut, or formed into a shape with a flared end. In some designs, the probe tip  504  may be slid over the probe  502  and may be held together by an interference fit, which may also serve to seal the interface between the probe  502  and the probe tip  504 . 
       FIG. 7  is a cross sectional view of an embodiment  700  showing a probe with a replaceable tip. 
     The view of embodiment  700  is a schematic cross section that illustrates the functional components of a probe. Actual embodiments may have different sizes and proportions of the various components. Because the view shows some functional components, many details have been removed, including other parts, connection mechanisms, and the like. 
     A probe  702  is illustrated as having a probe tip  704  that may be connected to the probe  702  by a set of threads  706 . The probe tip  704  may form an interface  718  to a base material  714  with an O-ring  710 . The probe tip  704  may have a groove  712  to receive the O-ring  710 . 
     The probe  702  may form a seal around the hole  716  by compressing the O-ring  710  against the surface of the base material  714 . In many embodiments, the interface  718  may be created by a dry contact between the O-ring  710  and the base material  714 . Some embodiments may use vacuum grease or other material along the interface  718  to create or assist in creating a seal. 
     The probe tip  704  may be a removable and replaceable probe tip. Embodiment  800  illustrates a different probe tip configuration. 
     The probe tip  704  is illustrated as being connected to the probe  702  by a set of threads  706 . Such embodiments may be assembled by twisting the probe tip  704  onto the probe  702 . Other embodiments may have different engagement mechanisms, including a sliding fit, interference fit, or other mechanical engagement mechanisms. 
       FIG. 8  is a cross sectional view of an embodiment  800  showing a probe with a replaceable tip. Embodiment  800  may illustrate the probe of embodiment  700  with a different type of probe tip. 
     The view of embodiment  800  is a schematic cross section that illustrates the functional components of a probe. Actual embodiments may have different sizes and proportions of the various components. Because the view shows some functional components, many details have been removed, including other parts, connection mechanisms, and the like. 
     The probe  702  is illustrated as having a probe tip  804  that is curved or irregularly shaped. The probe tip  804  is illustrated as being connected to the probe  702  using the screw threads  706 . 
     The probe tip  804  is curved to match the approximate shape of the base material  810  in the region of the hole  812 . The probe tip  804  may have a groove  814  in which an O-ring  816  may be placed. 
     Embodiment  800  may create a seal between the O-ring  816  and the base material  810  when the probe  702  is pressed against the base material  810 . 
     The probe tip  804  may be used in cases where the base material  810  has a shape that cannot be sealed using a different type of probe tip. In many complex parts, the shape of the base material  810  may be a compound curve, for example. 
     Some embodiments may have several different probe tips that have special shapes, where each of the shapes may be used in specially contoured sections of a workpiece. In such embodiments, the probe tip  804  may be configured to be quickly and easily replaceable. Some robotic embodiments may have an automated mechanism for replacing the probe tips  804  to test different holes in a single workpiece. 
       FIG. 9  is a diagram of an embodiment  900 , showing a hole to be measured and the positioning of a probe tip to measure the hole. The hole and probe tip are illustrated as irregularly shaped. 
     The base material  902  is illustrated with a hole  904 . The probe tip  906  is illustrated as being centered or concentric with the hole  904 . 
     The illustration of embodiment  900  shows both the hole  904  and the probe tip  906  as being elliptical. Such a condition may occur when the hole  904  may be a circular hole drilled at an angle. The condition may also occur when the hole is cut as an elliptical shape. Laser cutting machines may be configured to cut an elliptical hole by moving the laser in an elliptical shaped path during the cutting process. 
     The elliptical shape illustrated in embodiment  900  may represent any shape of hole that may be tested. 
     Embodiment  900  illustrates a test probe that has a shape that closely resembles the shape of the hole being tested. Other embodiments may use any shaped probe to test any shaped hole, provided that the test probe form a seal around the periphery of the hole. 
     The foregoing description of the subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the subject matter to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments except insofar as limited by the prior art.