Patent Application
20090299687
The present invention relates to reverse engineering inspection techniques.
In order to reverse engineer a component, it is generally necessary to obtain detailed information about that component in order to establish parameters for newly-manufactured components. As used herein, the term “reverse engineering” is meant to encompass the production of both slavish copies of existing components as well as copies that may incorporate one or more changes or improvements over existing components (this latter process is sometimes called “re-engineering”). Simply proceeding through data acquisition without a systematic approach for data collection may produce data that is less helpful, or may even make data collection impossible.
Conventional inspection of gas turbine engine components typically proceeds with probing of one or more sample parts using a coordinate measuring machine (CMM) program, and a comparison of that probing data to a dimensioned drawing and a nominal data values. In other words, this conventional inspection of gas turbine engine components begins with a known set of engineering decisions, embodied in the dimensioned drawing and nominal data values, and CMM programming to obtain probing data proceeds on the basis of that known set of engineering decisions. This process is known in the art as actual-to-nominal best-fit inspection. In a reverse engineering context, however, a dimensioned drawing and a nominal model are typically not available. In the absence of a dimensioned drawing and nominal model to generate a CMM program, CMM operators need some guidance to be able to obtain data from existing parts to enable engineering decisions to be made as to the parameters established for newly-manufactured components.
A method of inspecting gas turbine engine rotor disks for reverse engineering includes establishing a plurality of datums for providing a local coordinate system, establishing rim face and primary rim slot data, manually verifying coordinate measuring machine probe indexing relative to probe locations on a rotor disk programming coordinate measuring machine probing of the primary rim slot as a function of the manually verified coordinate measuring machine probe indexing along a plurality of scan lines that are substantially parallel to each other, obtaining coordinate measuring machine probing data from coordinate measuring machine probing of a plurality of sample rotor disks, outputting dimension data as a function of average values of coordinate measuring machine probing data for the plurality of sample rotor disks, and outputting tolerance data as a function of dimension data value ranges for the plurality of sample rotor disks.
The present invention, in general, provides a method for inspecting a disk-like component for reverse engineering purposes. The present invention has particular applicability to reverse engineering rotor disks for gas turbine engines where nominal data and tolerances are unknown. As used herein, the term “reverse engineering” is meant to encompass the design and production of both slavish copies of existing components as well as copies that may incorporate one or more changes or improvements over existing components (this latter process is sometimes called “re-engineering”). The method of the present invention can include establishing a plurality of datums (e.g., three datums) for providing a local coordinate system, manually verifying measurement apparatus indexing relative to probe locations on a rotor disk and the local coordinate system to reduce a risk of invalid data collection due to invalid probe contact with that rotor disk, and then programming coordinate measuring machine (CMM) probing of the primary rim slot along a plurality of scan lines that are substantially parallel to each other. Probing data can be obtained from probing of a plurality of sample rotor disks with a CMM. Dimension data can be generated as a function of average values of CMM probing data for the plurality of sample rotor disks, and tolerance data can be generated as a function of dimension data value ranges for the plurality of sample rotor disks.
According to the present invention, a number of datums can be established for the disk 20 to enable the creation of a local coordinate system and the collection of reverse engineering data. A primary datum 38, which is a planar datum acting as an axial reference, is established for the disk 20 with the CMM system by suitable probing, which can be conducted manually. The primary datum 38 can be established at an outer face of one of the flanges 28 or 30 (the first flange 28 is used in the illustrated embodiment) using the CMM system.
A secondary datum 40, which acts as a radial or diameter reference, is also established for the disk 20 by suitable probing with the CMM system. As shown in the illustrated embodiment, the secondary datum 40 is defined within the plane of the primary datum 38, and with respect to the radial locations of the holes 36 in the first flange 28. More particularly, the secondary datum 40 can be established with respect to the locations of the centers of the holes 36, which can be calculated using software of the CMM system. In an alternative embodiment, the secondary datum 40 can be established with respect to an inner diameter surface of the bore 34 or a snap surface of the disk 20. This alternative manner for establishing the secondary datum 40 can be used, for example, with rotor disks that lack holes on a flange like those illustrated with the disk 20. In either embodiment, the CMM system is used to establish the secondary datum 40 about a center of origin 41 (or calculated center). The location of the center of origin 41, where a center axis A of the disk 20 intersects the plane of the primary datum 38, can be calculated using software of the CMM system after probing the holes 36, the bore 34, a snap surface, etc.
A tertiary datum 42, which acts as a clocking (or angular orientation) reference, is also established for the disk 20 with CMM system probing.
If the disk 20 has an odd number of evenly-spaced holes, the procedure illustrated in
In a still further alternative embodiment, the tertiary datum 42 can be established with respect to an offset hole among a set of otherwise equally spaced holes, which is a method sometimes used to provide a clocking reference point. In this embodiment, the tertiary datum can be established between the center of origin 41 and a center point of the offset hole.
Together the primary, secondary and tertiary datums 38, 40 and 42 can be used to establish a local coordinate system for inspection and reverse engineering purposes. Data collection with the CMM system can be referenced against the local coordinate system or any of the individual datums 38, 40 and 42.
Next, as shown in the perspective view of
An angular location θ of a primary slot 32P relative to the tertiary datum 42 is then determined, and CMM probing of the primary slot 32P is conducted at the P-plane 50.
As shown in
In an alternative embodiment shown in
In all embodiments, the probe 52 is used to probe at least two points 60 and 62 in the P-plane 50 at opposite sides of the primary slot 32P. Software of the CMM system can then be used to calculate a center point 64 of the primary slot 32P. The center point 64 of the primary slot 32P can be used to verify the angular location θ of the primary slot 32P relative to the tertiary datum 42. Furthermore, probing of the primary slot 32P can be used to verify location of the P-plane 50 (e.g., relative to the primary datum 38). Verification at this stage can include consultation with design engineers.
Next, where the disk 20 has equally spaced slots 32, angular spacing β between slots is determined, according to the formula: 360° divided by the total number of slots 32. It should be noted that slot location information derived from the angular spacing β can be provided in polar or Cartesian coordinates.
Additional probing data is collected for the primary slot 32P using the CMM system.
Once preliminary information about the disk 20 has been collected as described above, coordinate data establishing the precise configuration of the slits 32 can be collected. The preliminary data allows indexing of the probe 52 to be verified relative to the slots 32 (e.g., relative to the slash angle ω of the slots 32), in order to reduce a risk of invalid data collection.
Next, the primary datum 38 is established (step 102). Probing of at least three points, and preferably at least twelve points, at a face of the first flange 28 can be used to establish the primary datum 38. The secondary datum 40 is then established with respect to the primary datum 38 (step 104). In establishing the secondary datum 40 with holes 36, at least four points on an inner surface of at least two of the holes 36 are probed, or, where a flange-to-diameter ratio is greater than 2.0, at least eight points can be probed per hole 36. Where the bore 34 or a snap surface is used to establish the secondary datum 40, at least twelve points are probed at each of two axially spaced sections of an inner diameter surface. Subsequently, the tertiary datum 42 is established (step 106). Some alternative tertiary datum establishment procedures are described above. The three datums 38, 40 and 42 can be established according to the procedures described above. These datums 38, 40 and 42 allow a local coordinate system to be established through the inspection process.
The forward and aft rim faces 46 and 48 are then established (step 108), and the P-plane 50 (or midplane P) is established (step 110). The primary slot 32P in the rim 24 is then clocked, establishing angular location θ relative to the tertiary datum 42 (step 112). The angular spacing β of all of the equally spaced slots can then be calculated, for example, using the equation provided above (step 114). With the completion of steps 100-114, CMM probe 52 indexing can then be verified to reduce a risk of invalid data collection (e.g., shanking out). The primary slot is then probed to determine its first and second center points 64 and 70 (steps 118 and 120 respectively). With the first and second center points 64 and 70 determined, the slash angle ω and the conical angle of the slots 32 can then be determined (steps 122 and 124 respectively).
Probing in the foregoing steps can be performed manually. At step 126, indexing of the probe 52 can be verified and a more automated probing program can be established using conventional programming software of the CMM system for performing subsequent probing. Without data gathered with the non-programmed data acquisition procedures in the earlier steps described above, later CMM programming would present significant problems for an operator that has no dimensioned drawing or model against which a CMM program can be established. To the extent that such an operator could proceed, the risk of invalid data acquisition would be high, and, if non-programmed manual probing were continued, the inspection process would be highly time-consuming.
According to CMM programming, line scans 72, 74 and 76 of the primary slot 32P are performed (step 128). Also as part of step 128, lines scans 72, 74 and 76 of a plurality of the other slots 32 are performed. For example, line scans 72, 74 and 76 of eight or more, or 16 or more of the slots 32 are performed at equally spaced positions about the axis A of the disk 20. The line scans 72, 74 and 76 of all of the selected slots 32 are considered representative of all the slots. However, in alternative embodiments, all slots 32 of the disk 20 could be scanned. It should be noted that the particular slots selected, the number of slots selected, and the locations of the selected slots can vary as desired. Moreover, additional probing of the sample parts to obtain additional data can be performed, for instance, gathering data from locations other than at the slots 32.
Once all line scans for the disk 20 have been performed, other sample disks of the same type as the disk 20 can be positioned for scanning by the CMM system in the same manner as for the disk 20. In this way, the programmed line scans 72, 74 and 76 can be repeated using the CMM system program established for the disk 20 to obtain data from a number of different sample parts as part of step 128, for instance, gathering line scan data from seven or more additional sample disks. By obtaining data from multiple parts, possible tolerance variations, defects, or other that may arise on a part-by-part basis can be accounted for, and a risk of collected reverse engineering data varying significantly from the unknown original part design specifications is thereby reduced.
The resultant data set from scans of all sample parts is collected and stored. A nominal part form can be determined by averaging (e.g., finding an arithmetic mean) of the resultant data set (step 130). In addition, tolerance ranges can be established from the resultant data that compiles data subsets for individual parts in the sample set (step 132).
Part data can then be output for storage or display (step 134). The output data can include identification of the primary, secondary and tertiary datums 38, 40, and 42, respectively, and characteristics for reverse engineering such as profile, true position, run out and flatness relative to the three datums 38, 40 and 42. A “blueprint” model for reverse engineering can be generated from the output part data (step 136). The blueprint model is not limited to hard copies of relevant information, but, for example, can be a electronic model. The blueprint model can include desired dimensioned drawings, identification of relevant datums, tolerances and other manufacturing specifications, and any further information useful for reverse engineering purposes. For example, profile, true position, run out and flatness relative to the three datums 38, 40 and 42 can be provided on the blueprint model (step 138). Subsequently, reverse engineered parts can be manufactured according to the blueprint model.
It should be recognized that the present invention provides a systematic approach to inspection of rotor disks for gas turbine engines for reverse engineering purposes. Nominal values and tolerances of a part can be determined even when inspection of sample parts begins with that data being unknown. Moreover, initial probing and inspection steps according to the present invention can allow a CMM program to be developed while also reducing the risk of invalid data collection. Due to the relatively tight tolerances present on gas turbine engine disks, especially for slots in disk rims, high requirements and. demands are placed on reverse engineering methods, rendering some possible alternative techniques unsuitable. For instance, ATOS data alone generally lacks suitable precision in establishing nominal and tolerance data for disk slots.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For instance, particular steps for the present inspection method can vary according to the particular configuration of the part being inspected. Moreover, additional steps not mentioned can be performed, and undesired steps can be omitted for certain applications.
