METHODS AND APPARATUS FOR TESTING A COMPONENT
BACKGROUND OF THE INVENTION
This invention relates generally to the testing of components, and more particularly to methods and apparatus for testing components having non-uniform surfaces
Eddy current (EC) inspection devices are used to detect abnormal mdications m a component under test such as, but not limited to, a gas turbine engine component At least one known EC inspection device is used to detect cracks, pings, dings, raised material, and/or other surface imperfections on a surface of the component, and/or to evaluate material properties of the component including the conductivity, density, and/or degrees of heat treatment of the component
During operation, known EC devices measure the interaction between an electromagnetic field generated by the EC device and the component being tested For example, known EC devices mclude a probe coil that generates a magnetic field. When the coil is positioned adjacent to a conductive component, an eddy current is generated on the surface of the component. A flaw on and/or near the surface of the component generates a disruption m the eddy current field which produces a secondary field that is received by the eddy current probe coil or by a sensor coil m the eddy current probe which converts the altered secondary magnetic field to an electrical signal that may be recorded on a strip chart recorder for example
At least one known EC device includes a relatively small coil that is typically 020 inches in diameter, that is used to detect surface flaws, surface contamination, material properties, and/or a surface roughness of the component being tested In use, a substantially constant pressure is applied to the probe as the coil moves along the surface of the component under test to facilitate maintaining an integrity of the signal generated by the EC device However, when the EC device is not oriented normal to the surface of the component being tested, a "lift-off effect" may be created
To facilitate reducing the lift-off-effect, at least one known EC device mcludes a dual-coil probe, e g a differential probe, having a parr of coils with an opposite polarity Each coil in the dual-coil probe generates an electrical signal when the probe contacts a surface of the component being tested When the dual coil probe passes over a smooth surface of the component being tested, the signals cancel each other
However, when the dual coil probe passes over a local physical abnormality on the surface, the probe generates a signal that is proportional to the size, depth, etc, of the physical abnormality
When a non-contmuous component surface feature is inspected, such as a feature on a rotating part, known differential probes may have difficulty resolving sharp curvatures, in such areas as corners and cusps During operation, when such probes encounter a corner or cusp, the differential probe device may become skewed to the surface of the component, such that a resulting lift-off effect may cause a loss of usable data Accordmgly, known EC devices may be less effective m generating an accurate response when the EC device is used to detect an abnormal condition on a component having complex geometries, and/or a component having irregular conditions, especially in components including sharp indexing or objects mat extend into the path of the probe such that the probe cannot consistently be placed normal to scan surface
BRIEF DESCRIPTION OF THE INVENTION
In one aspect, a method for inspecting a component is provided The method mcludes positioning an eddy current probe proximate to a surface of the component to generate a first position indication, positioning the eddy current probe proximate to the surface of the component to generate a second position indication that is different than the first position indication, and interpolating between the first and second position indications to determine a profile of a portion of the surface of the component
In another aspect, a differential eddy current probe for inspecting a component is provided The eddy current probe mcludes a body portion including an outer surface and having a width, and a length that is longer than the width, and a tip portion extending from the body portion, the tip portion including an end and an outer tip, the end extendmg between the body portion and the outer tip, the tip portion having a width and a length, the tip portion width gradually decreases from the tip portion end to the outer tip, the tip portion length gradually decreases from the tip portion end to the outer tip, and at least two differential coils mounted within said tip portion, each of said at least two coils composes a substantially cylindrical shape, at least a portion of each of said at least two coils is positioned adjacent to said tip portion outer tip for generating a magnetic field that is substantially perpendicular to a surface of the component being inspected
In a further aspect, an eddy current inspection system is provided The inspection system mcludes a differential eddy current probe and a computer coupled to the eddy current probe The computer is configured to position the eddy current probe proximate to a surface of a component to generate a first position indication, position the eddy current probe proximate to the component surface to generate a second position indication that is different than the first position indication, and interpolate between the first and second position indications to determine a profile of a portion of the component surface
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a front view of a known eddy current probe,
Figure 2 is a top view of the known eddy current probe shown in Figure 1,
Figure 3 is a front view of the known eddy current probe shown in Figure 1 illustrating a lift-off effect m an indexing direction,
Figure 4 is a front view of the known eddy current probe shown in Figure 1 and illustrating a lift-off effect in a scan direction;
Figure 5 is a schematic illustration of an exemplary gas turbine engine,
Figure 6 is a schematic diagram of an exemplary eddy current surface flaw detection system,
Figure 7 is a perspective view of an exemplary eddy current probe,
Figure 8 is a front view of the exemplary eddy current probe shown in Figure 7,
Figure 9 is a side view of the exemplary eddy current probe shown in Figure 7,
Figure 10 is a perspective view of the differential coils m the exemplary eddy current probe shown in Figure 7,
Figure 11 is a flowchart illustrating an exemplary method for perfonmng an eddy current inspection,
Figure 12 is a side view of an eddy current probe operating in a scan direction,
Figure 13 is a side view of an eddy current probe operating m an indexing direction,
Figure 14 illustrates the eddy .current probe shown in Figure 7 positioned normal to a surface of a component, and
Figures 15a and 15b illustrate a scanplan and C-scan images created by scanning a differential eddy current probe
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 is a front view of a known eddy current probe 500 Figure 2 is a top view of eddy current probe 500 shown in Figure 1 Figure 3 is a front view of eddy current probe 500 shown in Figure 1 illustrating a lift-off effect m an indexing direction Figure 4 is a front view of eddy current probe 500 shown in Figure 1 and illustrating a lift-off effect in a scan direction
Figure 5 is a schematic illustration of a gas turbine engme 10 including a fen assembly 12 and a core engme 13 including a high pressure compressor 14, and a combustor 16 Engme 10 also includes a high pressure turbine 18, a low pressure turbine 20, and a booster 22 Fan assembly 12 mcludes an array of fan blades 24 extending radially outward from a rotor disc 26 Engme 10 has an intake side 27 and an exhaust side 29 In one embodiment, the gas turbine engme is a CF6-50 available from General Electric Company, Cincinnati, Ohio Fan assembly 12 and turbine 20 are coupled by a first rotor shaft 31, and compressor 14 and turbine 18 are coupled by a second rotor shaft 33
During operation, air flows axially through fan assembly 12, m a direction that is substantially parallel to a central axis 34 extending through engme 10, and compressed an is supplied to high pressure compressor 14 The highly compressed air is delivered to combustor 16 Airflow (not shown in Figure 1) from combustor 16 drives turbines 18 and 20, and turbine 20 drives fan assembly 12 by way of shaft 31
Figure 6 is a schematic diagram of an exemplary eddy current surface flaw detection system 50 that can be used to inspect a component 52 such as, but not limited to, a gas turbine engme disk 54 which may be used with gas turbine engme 10 In the exemplary embodiment, disk 54 mcludes a plurality of dovetail posts 56 and a plurality of dovetail slots 58 defined between posts 56
Although the methods and apparatus herein are described with respect to posts 56 and dovetail slots 58, it should be appreciated that the methods and apparatus can be applied to a wide vanety of components For example, component 52 may be of any
operable shape, size, and configuration Examples of components may include, but are not lumted to, components of gas turbine engines such as seals, flanges, turbine blades, turbine vanes, and/or flanges The component may be fabricated of any operable base material such as, but not lumted to, mckel-base alloys, cobalt-base alloys, titanium-base alloys, iron-base alloys, and/or aluminum-base alloys More specifically, although the methods and apparatus herein are described with respect to aircraft engine parts, it should be appreciated that the methods and apparatus can be applied to a wide variety of components used within a steam turbine, a nuclear power plant, an automotive engine, or to inspect any mechanical components
In the exemplary embodiment, detection system 50 mcludes a probe assembly 60 and a data acquisition/control system 62 Probe assembly 60 mcludes an eddy current coil/probe 70 and a probe manipulator 72 Eddy current probe 70 and probe manipulator 72 are each electrically coupled to data acquisition/control system 62 such that control/data information can be transmitted to/from eddy current probe 70/probe manipulator 72 and data acquisition/control system 62 In an alternative embodiment, system SO also mcludes a turntable (not shown) configured to rotate component 52 around a central axis 74 during the inspection procedure
Data acquisition/control system 62 mcludes a computer interface 76, a computer 78, such as a personal computer with a memory 80, and a monitor 82 Computer 78 executes instructions stored in firmware (not shown) Computer 78 is programmed to perform functions described herein, and as used herein, the term computer is not limited to just those integrated circuits referred to m the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herem
Memory 80 is mtended to represent one or more volatile and/or nonvolatile storage facilities mat shall be familiar to those skilled m the art Examples of such storage facilities often used with computer 78 include, but are not limited to, sohd state memory (e g, random access memory (RAM), read-only memory (ROM), and flash memory), magnetic storage devices (e g , floppy disks and hard disks), and/or optical storage devices (e g , CD-ROM, CD-RW, and DVD) Memory 80 may be internal to or external to computer 78 Data acquisition/control system 62 also mcludes a recordmg device 84 such as, but not lumted to, a stnp chart recorder, a C-scan, and an electronic recorder that is electrically coupled to either computer 78 and/or eddy current probe 70
In use, component 52, such as disk 54, is mounted on a fixture (not shown) to secure disk 54 m place during inspection Eddy current probe 70 is coupled to probe manipulator 72 to position probe 70 within dovetail slots 58 to facilitate enabling substantially all of the interior of dovetail slots 58 to be scanned during inspection In the exemplary embodiment, probe manipulator 72 is a six-axis manipulator Eddy current probe 70 is electrically coupled to data acquisition/control system 62 by a data link 86 Eddy current probe 70 generates electrical signals in response to the eddy currents induced within the surface of dovetail slots 58 during scanmng of dovetail slots 58 by probe 70 Electrical signals generated by probe 70 are received by data acquisition/control system 62 over a data communications link 86 and are either stored in memory 80 or recorder 84 Computer 78 is also interconnected to probe manipulator 72 by a communications link 88 to facilitate controllimg the scanmng of disk 54 A keyboard (not shown) is electrically coupled to computer 78 to facilitate operator control of the inspection of disk 54 In the exemplary embodiment, a printer 40 may be provided to generate hard copies of the images generated by computer 78
Figure 7 is a perspective view of an exemplary eddy current probe 100 that may be used with eddy current surface flaw detection system 50 (shown in Figure 6) Figure 8 is a front view of eddy current probe 100 Figure 9 is a side view of eddy current probe 100 Figure 10 is a perspective view of a portion of eddy current probe 100 In the exemplary embodiment, eddy current probe 100 is a differential probe
Eddy current probe 100 mcludes a body portion 102 that mcludes an outer surface 104, a width 106, and a length 108 that is different than width 106 In the exemplary embodiment, body portion 102 is substantially rectangular shaped Eddy current probe 100 also mcludes a tip portion 110 that is coupled to body portion 102 In the exemplary embodiment, body portion 102 and tip portion 110 are integrally formed together such that body portion 102 and up portion 110 form a unitary eddy current probe 100
Tip portion 110 mcludes a tip body portion end 112 and a outer tip 114 Tip portion 110 has a width 116 and a length 118 that is greater than width 116 In the exemplary embodiment, width 116 gradually decreases from tip body portion end 112 to outer tip 114, and length 118 gradually decreases from tip body portion end 112 to outer tip 114
Tip portion 110 also mcludes an upper surface 120 that is coupled to body 102 In the exemplary embodiment, tip upper surface 120 includes a substantially rectangular
surface defined such that up portion width 116 is substantially similar to body portion width 106, and tip portion length 118 is substantially greater than body length 108 In the exemplary embodiment, tip width T16 and tip length 118 each gradually dimmish from tip upper surface 120 such that an apex 124 is formed at outer tip 114
Eddy current probe 100 also mcludes a first probe coil 130 and a second probe coil 132 mounted within tip portion 110 Probe coils 130 and 132 each mclude respective substantially flat outer surfaces 134 and 136 such that the outer surfaces of probe coils 130 and 132 are positioned coincident with the outer tip 114 In the exemplary embodiment probe coils 130 and 132 are differential coils When activated, coils 130 and 132 each generate a magnetic field that is substantially perpendicular to a surface of the component being scanned such as, but not limited to posts 56 and dovetail slots 58 More specifically, each coil 130, 132 in differential probe 100 generates an electrical signal when probe 100 contacts a surface of the component being tested When differential probe 100 passes over a smooth surface of the component being tested, the signals cancel each other However, when differential probe 100 passes over a local physical abnormality on the surface, differential probe 100 generates a signal that is proportional to me size, depth, etc, of the physical abnormality
Eddy current probe 100 has a length 118 that is longer than a gap defined between inspection areas in the scan direction, and a width 116 that is shorter in the indexing direction Coils 130 and 132 are positioned approximately in the center of tip portion 110 Accordingly, eddy current probe 100 mcludes an approximately spade-shaped tip portion 110 that enables gaps between inspection areas to be traversed without tip portion 110 falling into the gaps Moreover, and m the exemplary embodiment, the relatively round bottom of outer tip 114 facilitates coils 130 and 132 being fabricated with a radius of approximately 25 mils The relatively small size of eddy current probe 100 fecihtates probe 100 mamtaimng a substantially normal contact with relatively sharply contoured surfaces
Figure 11 is a flow chart illustrating an exemplary method 200 for inspecting a component having a surface that mcludes a local minima and a local maxima Figure 12 is a side view of an eddy current probe operating m a scan direction Figure 13 is a side view of an eddy current probe operating m an indexing direction
Method 200 mcludes positioning 202 an eddy current probe proximate to a surface of the component to generate a first position indication, positioning 204 the eddy current probe proximate to the surface of the component to generate a second position
indication that is different than the first position indication, and interpolating 206 the first and second position indications to determine a profile of a portion of the surface of the component
During operation, eddy current surface flaw detection system 50 is operated such that eddy current probe 100 is positioned on or near a surface 210 of component 52 to generate a first position indication 212 More specifically, eddy current probe 100 is positioned normal to surface (+/- 2 degrees) 210 until a signal is acquired from eddy current probe 100 as shown in Figure 14 Eddy current surface flaw detection system 50 is then operated such that eddy current probe 100 is positioned on or near surface 210 of component 52 to generate a second position indication 214 that is different than the first position indication 212 In the exemplary embodiment, eddy current probe 100 is positioned normal to component surface 210 at a plurality of positions 216 on component surface 210 and repositioned m the probe indexing direction to generate the plurality of position indications 216 Although the exemplary embodiment, illustrates four position indications 216, it should be realized that eddy current surface flaw detection system 50 may position eddy current probe 100 at any quantity of position indications without affecting the scope of the method descnbed herem
Plurality of position indications 216 are each sent to computer 78 for example for further processing More specifically, position indications 216 are utilized by computer 78 to determine a surface profile 218 of component 52 In operation, at least first position indication 212 and second position indication 214 are interpolated to generate a plurality of positions 220 between first and second position indications 212 and 214, respectively Plurality of positions 220 are then utilized with first and second position indications to determine a surface profile 218 of component 52 More specifically, m the exemplary embodiment, component 52 mcludes a relatively nonuniform extenor surface 210 Accordmgly, eddy current probe 100 is positioned at or near surface 210 at a plurality of points or positions 216 until a plurality of eddy current readings are generated Computer 78 receives the plurality of pomts or positions 216 and interpolates between each respective point/position 216 to generate a profile of component surface 210 In the exemplary embodiment, plurality of positions 216 includes at least one minima 222 and at least one maxima 224 More specifically, in the exemplary embodiment, component 52 mcludes a surface 210 that is substantially non-linear, I e contoured Accordmgly, eddy current probe 100 is positioned at a plurality of pomts or positions 216, mcludmg minima and maxima
positions 222 and 224 to facilitate ensuring the any local maxima or minima on the component surface is recorded and sent to computer 78 Computer 78 receives the plurality of points or positions 216 and interpolates between each respective point/position 216 to generate a profile of component surface 210 The component surface profile 218 is then utilized by computer 78 to generate a scan plan for component 52
In the exemplary embodiment, computer 78 receives the plurality of position indications and generates a scan plan 'Generating a scan plan includes generatmg a scan plan to facilitate directing eddy current probe 100 to scan an inspection area Scanplan as used herein is defined as a collection of Computer Numeric Control (CNC) commands that direct probe 100 to move along a predetermined line in the scan direction (shown in Figure 12) while acquiring a signal from eddy current probe 100 At the completion of each scan line, eddy current probe 100 is indexed to the next scan lme (shown in Figure 13) and eddy current probe 100 again is moved along a predetermined lme m the scan direction. More specifically, computer 78 mcludes the component profile mat is generated utilizing plurality of points or positions 216 and interpolating between each respective point/position 216 Therefore, computer 78 moves or indexes eddy current probe 100 along the profile 218 that is previously generated This process is continued until the scan plan is completed Figures 15a and 15b illustrate a scanplan usmg eddy current probe 100 wherem a scan lme of 360 degree circumferential rotation is illustrated.
In the exemplary embodiment, eddy current probe 100 requires contacting the surface of the component being inspected without unwanted lift-off, whereas at least one known eddy current probe has difficulty scanning a component that mcludes a highly contoured outer surface Designing a scan plan that is implemented usmg a known eddy current probe is relatively tome consuming smce the designer must incorporate expected occurrences of probe lift-off mto die scan plan prior to scanning the component Therefore generatmg a scanplan that utilizes a predetermined component surface profile facilitates maintaining the eddy current probe m a vertical position mat is substantially normal to a surface of the component being tested Accordingly, maintaining the eddy current probe substantially normal to the surface of the component being tested facilitates reducmg and/or eliminating the lift-off effect during the scanning procedure
In operation, couplmg an eddy current probe, such as probe 100, to an eddy current mspection system mcludes couplmg eddy current probe 100 to probe holder such as
probe manipulator 72 (shown in Figure 6) A rotation axis is then set to zero degrees before the scan starts The component 52 is then scanned using eddy current probe 100 based on the scan plan to generate a plurality of scan data Specifically, eddy current inspection system 50 is activated such that the component is scanned m the scaninng direction by turning the rotary axis while the probe stays at a fixed position Eddy current probe 100 then rides over any interrupted gaps on the component until the scan is completed m the scanmng direction At the next zero degree pomt of rotation, eddy current probe 100 is automatically moved or indexed to the next scan line in the indexing direction in accordance with the determined profile In the exemplary embodiment, the first scan lme begins at zero degrees, and each subsequent scan lme is registered to this pomt The. scan of the component proceeds until the scan plan is completed
The scan data is then analyzed to generate at least one image of the component being scanned mcludes collecting the signals, I e scan data, transmitted from eddy current probe 100 after the scan plan is completed, and combining the scan data mto at least one two-dimensional (2D) image for analysis In the exemplary embodiment, the 2D image mcludes a combination of the signals transmitted from eddy current probe 100 from both the inspection zones and those produced by the interrupted gaps between them In addition, the 2D image also includes a plurality of edge signals generated from both sides of the inspection zone For example, when eddy current probe 100 passes an edge of the component, I e from ah- to material, or vice versa, eddy current probe 100 generates a signal that is typically greater than a signal that is generated by the component material, and is therefore generally interpreted by eddy current probe 100 as a material abnormality To facilitate reducmg or minimizing the imaging effects of these signals, the 2D image is divided mto a plurality of sub-images mat have approximately the same shape The sub-images are then sent through a registration and subtraction process to minimize the unwanted signals from gaps and edges
In the exemplary embodiment, filters based on the charactenstic crack signatures of the tested component are then applied to the resultmg images to facilitate optimizing the segmentation of significant indications from any remaining noise In the exemplary embodiment, the matched filter is applied to the 2D image data, to facilitate detecting very small indications, down to approximately 10 mil m length
The eddy current inspection system described herein generates a scanplan, I e the motion control and data acquisition program for the inspection system, scans the
component according to the scanplan utilizing a differential eddy current probe, and analyzes the scan data Accordingly, the method and apparatus descnbed herein facilitate enabling interrupted features of a component to be inspected m a continuous fashion, thereby minimizing the amount of tune needed to acquire and process the data compared to known eddy current inspection systems, without having any adverse affects on the sensitivity of the inspection Moreover, the eddy current inspection system and probe descnbed herein facilitate inspecting a component that includes interrupted features because eddy current inspection system 50, differential probe 100 and image analysis provide and inspection that is relatively immune to surface contours and edges
The above-descnbed methods and apparatus provide a cost-effective and reliable means to facilitate reducing the amount tune needed to perform an eddy current inspection on a component under test Specifically, the method and apparatus descnbed herein facilitates reducing an inspection tune and improve an eddy current system performance by utilizing a continuous scan data acquisition method that eliminates the tune consuming raster scans typically used in single coils applications The eddy current probe descnbed herein includes a differential coil that is positioned to minimize sensitivity to onentation and can therefore, maintain consistent image quality and detectability.
Exemplary embodiments of digital eddy current inspection systems are descnbed above in detail The systems are not limited to the specific embodiments descnbed herein, but rather, components of each system may be utilized independently and separately from other components descnbed herem Each system component can also be used m combmation with other system components More specifically, although the methods and apparatus herem are descnbed with respect to aircraft engine parts, it should be appreciated that the methods and apparatus can also be applied to a wide vanety of components used within a steam turbme, a nuclear power plant, an automotive engine, or to inspect any mechanical component
While the invention has been descnbed in terms of vanous specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spint and scope of the claims.

WHAT IS CLAIMED IS:
1. A differential eddy current probe (100) for inspecting a component (52), said
eddy current probe comprising:
a body portion (102) comprising an outer surface (104) and having a width (106), and a length (108) mat is longer than said width;
a lip portion (110) extending from said body portion, said tip portion comprising an end (112) and an outer tip (114), said end extending between said body portion and said outer tip, said tip portion having a width (116) and a length (118), said tip portion width gradually decreases from said tip portion end to said outer tip, said tip portion length gradually decreases from said tip portion end to said outer tip; and
at least one differential pair of coils (130, 132) mounted within said tip portion, each of said at least one pair of coils comprises a substantially cylindrical shape, at least a portion of each of said at least one pair of coils is positioned adjacent to said tip portion outer tip for generating a magnetic field that is substantially perpendicular to a surface of the component being inspected.
2. An eddy current probe (100) in accordance with Claim 1 wherein said body portion (102) and said tip portion (110) are formed unitarily together.
3. An eddy current inspection system (50) comprising: a differential eddy current probe (100); and
a computer (78) coupled to said eddy current probe, said computer configured to
position (202) said eddy current probe proximate to a surface (210) of a component (52) to generate a first position indication (212);
position (204) said eddy current probe proximate to said component surface to generate a second position indication (214) that is different than said first position indication; and
interpolate (206) between said first and second position indications to determine a profile (218) of a portion of said component surface.
4. A system (50) in accordance with Claim 3 wherein said computer (78) is
further configured to:
position said eddy current probe (100) normal to said component surface (210) of the component (52) to generate said first position indication (212); and
position said eddy current probe normal to said component surface of the component to generate said second position indication (214).
5. A system (50) in accordance with Claim 3 wherein said computer (78) is further configured to interpolate between said first and second position indications (212, 214) to generate at least one position indication (216) that is between said first and second position indications.
6. A system (50) in accordance with Claim 3 wherein said computer (78) is further configured to generate a scan plan of said component using the determined profile (218).
7. A system (50) in accordance with Claim 3 wherein said computer (78) is further configured to:
move said eddy current probe (100) along a first scani line'in a scan direction; and
index said eddy current probe to a second scan line that is different than the first scan line such that said eddy current probe is maintained in a substantially normal alignment with said component surface (210) to generate a plurality of scan data.
8. A system (50) in accordance with Claim 7 wherein said computer (78) is further configured to index said eddy current probe (100) to a second scan line using the detennined profile (218).
9. A system (50) in accordance with Claim 7 wherein said computer (78) is further configured to analyze said scan data to generate at least one two-dimensional image of the component (52) being inspected.
10. A system (50) in accordance with Claim 9 wherein said computer (78) is further configured to:
select a filter based on said third image generated; and
filter said third image to generate a final image.