Abstract:
An apparatus and method for characterizing gas flow through features fabricated in a hollow part. A pressurized gas is applied to an interior of the part, and this gas pressure flows outward through features fabricated in the part. At the same time, a stabilizing pressurized gas is applied to an exterior part skin; and the stabilizing gas has a controlled temperature differential from the gas applied to the part interior. An infrared signature of escaping gas and the surrounding part skin is analyzed by a classification method. Analysis of this infrared signature classifies the relative flow rate, size and position of the feature fabricated in the part.

Description:
FIELD OF THE INVENTION 
     The present invention relates to manufacturing gas turbine engine components and, more particularly, to inspecting complex cooling holes through a surface of a gas turbine engine component. 
     BACKGROUND OF THE INVENTION 
     During operation, gas turbine engines, whether used for flight or stationary power generation, develop extremely high temperature and high velocity gases in a combustor portion of the engine. These gases are ducted on blades of a turbine rotor to cause rotation of the rotor and are redirected by the stator vanes onto additional rotor blades to produce more work. Because of the high heat of the gases, it is desirable to cool the blades and vanes to prevent damage and, to extend the useful life of, these engine components. It is known in the art that a turbine component such as that shown in  FIG. 8  can be cooled by film cooling that is provided by a plurality of fabricated features, for example, cooling holes. 
     A commonly used method of cooling a turbine component  20  is to duct cooling air through internal passages and then vent the cooling air through a plurality of cooling holes  22 . This air cools internal surfaces of the component by convection and cools the components outer surfaces by film cooling. The cooling holes  22  are typically formed along a line generally parallel to, and a selected distance from, a trailing edge  24  of the component to provide a film of cooling air over a surface of the component when the cooling holes discharge air during engine operation. Other rows or arrays of cooling holes or vents may be formed in the blade and vane components of a rotor or stator of a turbine depending upon design constraints. 
     To facilitate the distribution of the cooling air substantially completely over the convex and concave surfaces of the blade airfoil or platform, as shown in  FIG. 9 , the upstream end of each cooling hole  22  has a generally cylindrical, inlet portion  26  that extends from a location  28  inside of a wall of the component  20 . At the location  28 , the cooling hole  22  then flares or diverges to provide a discharge portion  30  that terminates on an exterior surface  32  of the component  20  to be cooled by the air flow. The shape of the discharge end functions as a diffuser to reduce the velocity of the cooling airstreams being discharged from the cooling holes  22 . The lower velocity cooling airstreams are more inclined to cling to the surface  32  for improved cooling. High quality cooling holes  22  with diffusers  30  provide superior performance but are costly and difficult to manufacture. 
     After the cooling holes have been manufactured, it is necessary to inspect each of the holes to determine whether it exists and is properly formed as a complex hole. One method of inspection is a manual method in which an inspector is provided with a drawing of the desired hole pattern and a pin. The inspector first confirms that a hole exists at each location identified by the pattern; and then, the inspector inserts the pin through each of the holes to determine whether the hole is properly drilled as a through-hole. As can be appreciated, such an inspection process is highly repetitive, tedious and stressful for the inspector and, in addition, is expensive and inefficient for the manufacturer of the turbine component. 
     Other known hole inspection processes are automated and utilize a laser or a flow of fluid through the holes. The flowing fluid used most commonly is either air or water. In the case of air, the mass of air flowing through a feature can be measured. With water, a visual signal of a flow pattern is possible. These methods need a human visual check or physical measurement of a single feature to characterize its flow condition, All of these known methods are time-consuming and rely on human intervention to perform the characterization which leads to errors. 
     Thus, there is a need for an inspection apparatus and process that can automatically inspect and identify qualitative characteristics of complex cooling features in gas turbine components faster, more precisely and less expensively than known inspection apparatus and processes. 
     SUMMARY OF THE INVENTION 
     The present invention provides an inspection apparatus and process that accurately and quickly determine the flow characteristics of cooling features fabricated in gas turbine blades. With the inspection apparatus and process of the present invention, the flow characteristics are easy to interpret; and thus, the inspection apparatus and process are faster, more error-free and less expensive than known tactile and visual inspection processes. The inspection apparatus of the present invention provides an automatic process and thus, removes the chance of human error. Therefore, the inspection apparatus of the present invention is especially useful for inspecting a presence and quality of a large number of complex cooling holes in gas turbine component. 
     These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first exemplary embodiment of an automated inspection system for inspecting a complex feature fabricated in a part in accordance with the principles of the present invention. 
         FIG. 2  is an overall schematic diagram of the first exemplary embodiment shown in  FIG. 1 . 
         FIG. 2A  is a cross-sectional view of an exemplary embodiment of an annular gas discharge nozzle in accordance with the principles of the present invention. 
         FIG. 3  is a flowchart of an exemplary embodiment of a process for analyzing a raw infrared image using the embodiments of  FIGS. 1 ,  2  and  7 . 
         FIG. 4  is an exemplary representation of a point summing cross pattern used in a significant point algorithm with the process shown in  FIG. 3 . 
         FIG. 5  is a representation of eight-border coordinates used to determine a feature using the process of  FIG. 3 . 
         FIG. 6  is a representation of an image of infrared signatures for the group of features shown in  FIGS. 1 and 2  when processed according to the process shown in  FIG. 3 . 
         FIG. 7  is an overall schematic diagram of another exemplary embodiment of an automated inspection system for inspecting a complex feature fabricated in a part in accordance with the principles of the present invention. 
         FIG. 8  is a partial perspective view of an example of a known turbine component that utilizes rows of features or cooling holes that must be inspected using the embodiments of  FIGS. 1 ,  2 ,  3  and  6 . 
         FIG. 9  is a partial perspective and cross-sectional view of a cooling hole in the turbine component illustrated in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 and 2 , one example of a feature inspection system  38  is used to inspect fabricated features in a part, for example, air cooling holes  22  in a known turbine blade  20  as described with respect to  FIGS. 8 and 9 . The blade  20  is supported in a holding fixture  40 ; and a gas tight seal  42 , for example, a molded urethane seal, is formed around an inlet opening at a base  44  of the blade  20 . A robotic arm  46  is mounted in a cabinet  27  and is controlled by a programmable control  48  also mounted on the cabinet  27 . The robotic arm  46  is operable to position an infrared (IR) radiometer or camera  50  with respect to the blade  20 . In one exemplary embodiment, the robotic arm  46  is mounted upside-down above the blade  20 , so that the robotic arm  46  can be moved to different positions and orientations that permit the IR camera  50  to provide thermal images of all of the fabricated blade features  22  to be inspected. The robotic arm  46  may be one of several commercially available six-axes robot arms, for example, a six-axes robot arm commercially available from DENSO Robotics of Long Beach, Calif. The IR camera  50  is an uncooled IR detector array consisting of 76,800 micro bolometer elements arranged in a pattern that is 320 elements wide by 240 elements high. The IR camera  50  is capable of detecting electromagnetic energy in the range of 7.5-13 micrometers and may be one of several commercially available cameras such as those available from FLIR Systems, Inc. of Wilsonville, Oreg. 
     In a feature inspection cycle, the IR camera is positioned at a desired position and orientation with respect to the blade; and the control  48  commands a first valve  64  to open, which allows air from a source of pressurized air  66  to enter a heater  68 . The control  48  is also electrically connected to the heater  68  and a first temperature sensor  70  providing a first temperature feedback signal. The control  48  uses the first temperature feedback signal and a known PID control to operate the heater  68  and bring the air temperature to a range of about 70-315 degrees Fahrenheit. A first gas pressure regulator  72  is electrically connected to, and operable by, the control  48  to provide the air at a pressure in a range of about 0.05-3.0 pound(s) per square inch gauge (“PSIG”). This warmer air passes through a nozzle  76  and is applied over an area of a blade outer surface or skin  79  that surrounds the various features  22  being inspected. The nozzle  76  may simply be an open end of a tube positioned adjacent the camera lens  51  and directed toward one or more features being captured by the IR camera  50 . In an alternative exemplary embodiment shown in  FIG. 2A , the nozzle  76  may be an annular piece  94  ring sized to be mounted around an IR camera lens  51 . An annular gas passage  96  intersects a number of angled gas discharge passages  98  located circumferentially around the annular piece  94  and hence, the IR camera lens  51 . The gas discharge passages  98  may be angled to intersect a centerline  100  at generally a common point  102 , and thus, the discharge passages  98  are angled or directed toward the one or more features to be captured by the IR camera  50 . 
     Simultaneously with opening the first valve  64 , the control  48  commands a second valve  52  to open, which allows a helium gas from a source of helium gas  54  to enter a chiller  56 . The control  48  is also electrically connected to the chiller  56  and a second temperature sensor  58  providing a second temperature feedback signal. The control  48  uses the second temperature feedback signal and a known PID control to operate the chiller  56  and bring the air to a temperature in a range of about 25-70 degrees Fahrenheit. A second gas pressure regulator  60  is electrically connected to, and operable by, the control  48  to maintain the helium at a pressure in a range of about 0.1-35 PSIG. The chilled and pressurized helium gas is then applied through the fixture  40  and into an interior cavity through an opening at the base  44  of the blade  20  and allowed to escape through the various features  22  that are being inspected. 
     An initial pre-inspection cycle in a range of about 1-30 seconds is used to purge air from an interior of the blade  20 , and the blade  20  is brought to a desired temperature. A control memory  76  stores a hole inspection application program  92  that is operable to inspect the blade features  22  with the IR camera  50  and analyze detected temperatures to identify a feature present, partial feature present or an absence of a feature. The general process executed by the application program  92  is shown in  FIG. 3 . The control  48  first, at  300 , commands the robotic arm to move the IR camera  50  to a first position and orientation with respect to the blade  20 . The IR camera  50  is triggered by the control  48  to capture a raw image in an X-Y pattern. The X-Y pattern is a grid of  320  temperatures in the X-axis and  240  temperatures in the Y-axis, for total of 76,800 floating-point temperatures. In this exemplary embodiment, the IR camera  50  is operable to convert the X-Y temperature grid pattern to corresponding digital signals and store them in memory  78 . 
     The control  48  then, at  302 , commands a transfer of the temperature grid pattern from the IR camera  50  to the control memory  78 . Next, at  304 , the entire temperature grid pattern is first analyzed to locate a first region of interest. As will subsequently be described, a region of interest is one or more of the features  22  that have been previously identified in a setup cycle. Therefore, for each programmed IR camera position, one or more regions of interest are stored in the memory  78 ; and a region can be imposed on, or identified within, the stored X-Y temperature grid pattern. 
     Thereafter, at  306 , a “significant point” detection process begins within a chosen region of interest; and the significant point detection process is used to analyze each X-Y temperature point in the grid pattern of a region of interest. The analysis of each X-Y temperature point begins by summing a first X-Y temperature point with points directly next to it in a first cross pattern to determine an average temperature. A cross pattern size, that is, the number of points to be summed in the four directions from the first point, is determined by a selected target size setting of even numbers in a range of about 2-20 points. The cross pattern size is chosen during the setup cycle as will be described. An example of a point summing cross pattern is shown in  FIG. 4 . If the temperature point  23  being analyzed and the selected target size is two, then an average value of the temperature points  23 - 23   h  is determined using Equation 1 below. Equation 1 is a general mathematical expression or algorithm for determining an average temperature in the first cross pattern, and its result is used as a hole area temperature baseline. 
                     hole   _     =           ∑     i   =     n   -       t   s     2           i   =     n   +       t   s     2           ⁢           ⁢       X   i     ⁢     Y   n         +       ∑     i   =     n   -       t   s     2           i   =     n   +       t   s     2           ⁢           ⁢       X   n     ⁢     Y   i               2   ⁢     t   s       +   2               (     Eq   .           ⁢   1     )               
Where
         t s =target size setting   n=temperature array index       
     Next, as further shown in  FIG. 4 , X-Y temperature points in a second cross pattern beyond the first cross pattern are used in a similar fashion to determine temperature baseline of the surrounding skin area  79 . The skin area region represented by a second cross pattern size is also defined by a target size setting of even numbers in a range of about 2-20 points. Continuing with the above example in  FIG. 4 , for the temperature point  23 , if the selected target size is two, then an average value of the temperature points  25   a - 25   h  is determined using Equation 2 below. Equation 2 is a general mathematical expression or algorithm for determining an average temperature in the second cross pattern beyond the first cross pattern, and its result is used as a skin area temperature baseline. 
                     skin   _     =                 ∑     i   =     n   -     t   s           i   =     n   -       t   s     2     -   1         ⁢           ⁢       X   i     ⁢     Y   n         +       ∑     i   =     n   +       t   s     2     +   1         i   =     n   +     t   s           ⁢           ⁢       X   i     ⁢     Y   n         +                   ∑     i   =     n   -     t   s           i   =     n   -       t   s     2     -   1         ⁢           ⁢       X   n     ⁢     Y   i         +       ∑     i   =     n   +       t   s     2     +   1         i   =     n   +     t   s           ⁢           ⁢       X   n     ⁢     Y   i                   2   ⁢     t   s                 Eq   .           ⁢   2               
Where
         t s =target size setting   n=temperature array index       
     Thereafter, a difference between the average skin and hole temperatures is determined using Equation 3a below and compared to a selectable threshold setting in a range of about 0.01-10.
 
Δtemp=  skin −  hole   (Eq. 3a)
 
If the temperature difference between the average skin and hole temperatures is determined to be less than a selected temperature threshold or reference value, then the Xn-Yn temperature point being analyzed is considered not to be significant. In the example of  FIG. 4 , if the temperature difference using the temperature point  23  is less than the temperature threshold, the temperature point  23  is not considered to be associated with a blade feature  22 . The process then repeats the above analysis with the next X-Y temperature point in the X-Y temperature grid.
 
     However, if the average skin and hole temperatures of any X-Y temperature point is greater than the temperature threshold, that X-Y temperature point is considered to represent a temperature point associated with a feature and is stored in the memory  78  as a significant point in an array of significant points. The above process is repeated for all of the points in the region of interest, and the output of this algorithm is an array of significant points. The temperature threshold or reference temperature is determined during the setup process. 
     The control  48  is operable, at  308 , to identify the various features by detecting all significant points that share a common border. If a significant point is bordered by another significant point, these points are grouped to form a detected feature. The algorithm used for detection is an eight cell test as shown in  FIG. 5 . For a selected significant point, each of the coordinates for the eight bordering points is tested for its existence in the array of significant points. Bordering points that are found are deleted from the significant point array and stored along with an associated center point as a detected feature in a feature array in the memory  78 . This process continues until no further bordering points are found. Thus, each feature identified in the feature array is defined by a center point and eight bordering points. The control  48  repeats the above process until all significant points have been tested. 
     The center coordinates of each detected feature are determined by the control  48 , at  310 , using Equations 4 and 5 below. The X center point determined by Equation 4 and the Y center point determined by Equation 5 are each found by dividing a sum of all respective axis points by an area value and adding one as a bias. This area value, A, is used for classification of the feature. 
     
       
         
           
               
             
               
                 
                   
                     
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     Next, the control  48  determines, at  312 , a classification or qualitative characteristic of a detected feature using Equations 6 and 7 below. First, with Equation 6, a comparison of the detected feature area, A, is made with a stored selected partial limit size. If a feature area is greater than or equal to a selected partial limit size, which is in a range of about 1-50 points, the feature is classified as a through hole  82  shown in  FIG. 6 ; however, if the feature area is less than the partial limit size, the feature is classified as a partially blocked hole  84 . The partial limit size is selected during the setup cycle. Using Equation 7, blocked holes  80  are determined by calculating a difference between an expected number of holes and a total number of holes detected. Extra holes are indicated to by a negative result of Equation 7.
 
A=Σfeature_points  (Eq. 6)
 
 E =expected_features−no_features_found  (Eq. 7)
 
     Thereafter, the control  48 , at  314 , determines whether all detected features in the feature array have been classified. If not, the classification process described above is repeated until all features in the feature array have been classified. Next, the control  48  determines, at  316 , whether the current position and orientation of the IR camera is the last position and orientation. If not, the process of  FIG. 3  is repeated until the IR camera  50  has been moved to all of the positions and orientations stored in the memory  78  and thus inspecting and classifying all of the blade features  22 . 
     In order to establish desired positions and orientations for the IR camera  50  and determine values for many of the parameters used in executing the inspection cycle program  92  of  FIG. 3 , a setup cycle process is executed. In a first step of the setup cycle, the robotic arm  46  is moved to various preliminary positions around the blade  20  by an operator providing input commands to the control  48 . At each preliminary position, an IR setup image is taken and stored in the computer  48 ; and a sufficient number of preliminary positions are chosen, so that all of the blade features  22  to be inspected are in one or more setup images. Further, to provide the most reliable feature discrimination, at each of the preliminary positions, the IR camera  50  is oriented such that the centerline of the lens  51  is generally parallel to a centerline of the features or holes  22  to be inspected. However, the feature inspection systems and processes described herein are operable with other IR camera orientations. 
     Next, for convenience, often the setup images are transferred to a computer remote from the control  48  of the inspection system  38  in order to finish the setup process. Such a remote computer is loaded with the inspection cycle program of  FIG. 3  and is able to operate the inspection cycle program in a simulation mode. Further, the user is able to create a display of each of the setup images using a known program that converts the X-Y temperature point grid pattern of each image to a color or gray scale. Upon viewing each image, the user determines which, if any, features are best shown in that image. In that viewing process, the inspection cycle program of  FIG. 3  is executed using default values for setup selectable parameters, for example, the target size setting, the temperature array index, the temperature threshold, the partial limit size and other parameters. 
     The user is able to change the values of those parameters and observe how the result of the inspection cycle program changes in terms of being able to better discriminate, identify and classify one or more features of interest. The results of the inspection cycle program are displayed to the user in a manner similar to the view shown in  FIG. 6 . Thus, for example, during the simulation, the user can increase the target size setting to see if that impacts the resulting discrimination and classification. Further, the gas temperatures can be changed to increase the resulting temperature difference determined in Equation 3. Often the larger the temperature difference the better the discrimination and the faster the feature inspection process can be executed. However, gas temperatures that are too high or too low will affect feature discrimination, so there must a balance struck between a temperature difference and the gas temperatures. 
     If the user is not satisfied with the result of the simulation of the inspection cycle program, the setup image can be deleted; and the next setup image viewed. If the user is satisfied with the resulting feature classification of the inspection cycle program simulation, the user places a boundary around one or more of the features being observed, for example, the boundary  86  of  FIG. 6 . That boundary represents a region of interest in a setup image taken at a particular preliminary position and orientation. In any setup image, the user can create as many boundaries or regions of interest as there are holes; and each region of interest can include one or more holes or rows of holes. Further, that particular preliminary position and orientation is defined as a programmed position and orientation that are to be used during subsequent executions of the inspection cycle program either in a simulation mode or during a part inspection cycle or process. 
     The above process is repeated until all of the features  22  on the blade  20  have been inspected in a region of interest. If some features cannot be adequately defined, then more setup images must be taken; and the above process repeated for those features. At this point, the inspection cycle program  92  includes (1) all of the positions and orientations of the IR camera  50  that are necessary to inspect the desired blade features  22 , (2) all of the regions of interest  86  for a position and orientation, wherein each region of interest defines one or more of the blade features, and (3) values for all of the selectable parameters, for example, the target size setting, the temperature array index, the temperature threshold, the partial limit size and other parameters, which have been determined to provide the best feature discrimination. The inspection cycle program is then transferred to the control memory  78 , and an inspection cycle can be executed. 
     A pre-inspection cycle is used to normalize the temperature of the blade  20 . In the pre-inspection cycle, the control  48  opens the valves  64 ,  52  to initiate flows of air and helium. Temperature feedback signals from the temperature sensors  70 ,  58  are used by the control  48  to operate the respective heater  68  and chiller  56  to bring the air and helium to a desired temperature. Further, the flows of cooled helium through the blade  20  and heated air over the blade skin  79  for a period of time, for example, 1-30 seconds, normalizes the temperature of the blade, that is, the blade temperature reaches a sufficiently stable value to permit execution of the inspection process. 
     During the pre-inspection cycle, the control  48  also operates the pressure regulators  72  and  60  to establish desired pressures for the heated air and chilled helium respectively. The desired pressures are chosen during the setup cycle to optimize a discrimination and classification of features in the IR image during the inspection process. For example, if the air is too cold or the helium is too hot, feature discrimination and classification will be adversely affected. Further, once desired pressures of the air and helium are established that provide an acceptable feature discrimination and classification, changes in the ambient pressure around the blade  20  will adversely affect the feature discrimination and classification process. Therefore, during the pre-inspection cycle, a pressure sensor  90  provides the control  48  with a pressure signal representing the ambient pressure around the blade  20 . The control  48  then sets the desired air and helium pressures as respective multiple values of the ambient air pressure to establish a desired ratio of air and helium pressures. Further, as the ambient pressure changes during subsequent executions of the feature inspection program, the control  48  changes the respective multiple values to maintain the desired air and helium pressures in constant relationship with respect to the ambient air pressure. To determine the desired air and helium pressures, the robotic arm can be moved to different inspection programmed positions; and the IR camera images viewed. The air and helium pressures are then adjusted to obtain a desired quality of an IR image. 
     In an alternative exemplary embodiment shown in  FIG. 7 , the feature inspection apparatus is changed by inverting the locations of the chiller  56  and the heater  68 . With this embodiment, the control  48  operates the first pressure regulator  72  to supply air to the chiller  56  at a pressure in a range of about 0.05-3.0 PSIG. The chiller  56  cools the air to a temperature in a range of about 25-70 degrees. This cold air is applied through the nozzle  76  to an outer surface of the blade  20  around the various features being supplied the heated helium. At the same time, the control  48  operates the second pressure regulator  60  to supply the helium gas  54  to the heater  68  at a pressure in a range of about 0.1-35 PSIG. The heater  68  heats the helium gas to a temperature in a range of about 70-150 degrees, and the heated helium is applied to an interior cavity through an opening at the base  44  of the blade  20  and allowed to escape through the various features  22  to be inspected. After a period of time, the IR camera  50  is triggered to capture a temperature image; and the process previously described with respect to  FIG. 3  is repeated to identify and classify various features. However, it should be noted that the Equation 3b is different from Equation 3a as indicated below: 
     The feature inspection systems  38  of  FIGS. 1 ,  2  and  7  and method of  FIG. 3  are substantially automated, faster, more error-free and less expensive than known tactile and visual inspection methods. The feature inspection systems  38  of  FIGS. 1 ,  2  and  7  inject a gas through the internal passages of the blade  20 , which is less dense and lighter than ambient air, for example, helium. The lighter gas provides a more predictable and reliable gas flow through the small passages within the blade  20  and out the complex shaped features  22  that exit on the blade skin  79 . Further, the feature inspection systems  38  of  FIGS. 1 ,  2  and  7  provide a simultaneous heating of one gas, for example, air, and cooling of the other gas, for example, helium. The simultaneous heating and cooling improves the capability of the feature inspection systems  38  to discriminate and classify features using the process described with respect to  FIG. 3 . In addition, the feature inspection systems of  FIGS. 1 ,  2  and  7  continuously regulate the pressures of the gas with respect to ambient air pressure around the blade  20 . Such a pressure regulation further improves the capability of the feature inspection systems  38  to discriminate and classify the blade features  22 . Thus, the feature inspection systems  38  are especially useful for inspecting a large number of complex fabricated features, for example, cooling holes, in gas turbine component. 
     While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, while the hole inspection process described herein is directed to an application for inspecting features in a part, will be appreciated, the described hole inspection process can be used to inspect features on other parts, for example, fuel injectors, spray nozzles, combustors, stator blades, etc. 
     Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.