Method of repairing a firtree feature with wire electrical discharge machining

Methods of repairing a part having a firtree-shaped feature requiring rework are disclosed. An embodiment of the method includes receiving the part having the firtree-shaped feature requiring rework. The part is installed in a machine configured for wire electrical discharge machining (EDM). A location of the firtree-shaped feature relative to a datum of the machine is then determined. Wire EDM is performed on the firtree-shaped feature.

TECHNICAL FIELD

The present disclosure relates generally to turbine components, and more particularly to manufacturing turbine components having firtree-shaped features.

BACKGROUND

Gas turbine engines typically include one or more bladed rotors. A bladed rotor can include blades that are mounted to a disc by the engagement of firtree-shaped fixing slots formed in the disc with respective firtree-shaped roots of the blades. Forming the slots in the discs can be done by machining such as broaching, electrical discharge machining (EDM) or milling for example. Forming the slots can be time consuming, require relatively high accuracy and can result in relatively expensive parts.

SUMMARY

In one aspect, the disclosure describes a method for repairing a part having a firtree-shaped feature requiring rework defined in the part. The method comprises:receiving the part having the firtree-shaped feature requiring rework;installing the part in a machine configured for wire electrical discharge machining (EDM);locating the firtree-shaped feature relative to a datum of the machine; andperforming wire EDM on the firtree-shaped feature.

In another aspect, the disclosure describes a method of manufacturing a disc of a bladed rotor. The method comprises:using a machine configured for wire electrical discharge machining (EDM), machining a firtree-shaped slot in a disc-shaped workpiece using wire EDM, the firtree-shaped slot extending radially inwardly from a periphery of the workpiece;removing the workpiece from the machine;after a portion of the firtree-shaped slot requiring rework has been identified, installing the workpiece in the same or another machine configured for wire EDM;locating the firtree-shaped slot relative to a datum of the same or the other machine; andperforming wire EDM on the portion of the firtree-shaped slot requiring rework.

DETAILED DESCRIPTION

The present disclosure relates to using wire EDM for manufacturing and/or repairing a part having a firtree-shaped feature. In various embodiments, aspects of the present disclosure may be particularly useful for reworking firtree-shaped slots in bladed (e.g., turbine or compressor) discs or firtree-shaped roots of blades of such bladed rotors.

Part(s) of turbine discs may be machined by wire EDM to form cavities (sometimes called “fixing slots”) each having a “firtree” shape. The firtree-shaped slots may receive correspondingly shaped roots of the turbine blades therein for securely mounting the blades to the disc. Similarly, part(s) of turbine blades may be machined by wire EDM to form roots having a “firtree” shape. In some situations, the wire EDM process can leave imperfections on surfaces of a firtree-shaped feature during the process of cutting the firtree-shaped feature on the part. In some embodiments, the methods disclosed herein can permit the location or relocation of such firtree-shaped features in a machine configured for wire EDM in order to facilitate reworking of the applicable surfaces to correct the imperfection(s).

In some embodiments, the methods described herein may permit parts having such imperfections to be reworked in order to completely or sufficiently remove such imperfections using wire EDM and also keep the firtree-shaped feature within acceptable dimensional tolerances. In some embodiments, the methods described herein may permit some parts having imperfections to be salvaged thereby reducing scrap costs.

Aspects of various embodiments are described through reference to the drawings.

FIG. 1illustrates a gas turbine engine10of a type provided for use in subsonic flight, generally comprising, in serial flow communication, a fan12through which ambient air is propelled, a multistage compressor14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases.FIG. 1illustrates a turbofan turbine engine as an example, however it is understood that the present disclosure may be equally applicable to bladed rotors that are found in other types of turbine engines.

Engine10may include one or more bladed rotors where blades are mounted to a disc via cooperating firtree-shaped features. For example, turbine section18of the gas turbine engine10may include one or more such bladed rotors (e.g., turbine discs). Compressor14may include one or more such bladed rotors (e.g., compressor discs).

FIG. 2Adepicts a perspective view of an exemplary machine20configured for wire EDM having a disc-shaped workpiece40installed on a pivotable surface (e.g., rotary table). A front elevation view of part of the exemplary machine20is depicted inFIG. 2B. In some embodiments, the workpiece40may be secured to the rotary table using suitable clamps and/or bolts. In some embodiments, the workpiece40may be installed on the rotary table so that a center of rotation C (seeFIG. 3A) of the workpiece40during use substantially coincides with the center of rotation (axis24) of the rotary table. The disc-shaped workpiece40may be part of a turbine disc or other bladed disc. Machine20may include a computer numerical control (CNC) multi-axis motion system. Machine20may include one or more linear axes and/or one or more rotary axes. Machine20may include one or more data processors (referred hereinafter in the singular) and one or more computer-readable memories (referred hereinafter in the singular) storing machine-readable instructions executable by the data processor and configured to cause the data processor to generate one or more outputs for causing the execution of steps of the methods described herein. The data processor, memory and machine-readable instructions may be incorporated in a CNC controller38of machine20.

The disc-shaped workpiece40shown has a plurality of firtree-shaped slots42distributed around the disc-shaped workpiece40and extending radially inwardly from a periphery of the workpiece40. The disc-shaped workpiece40may be rotatable about a first axis22and a second axis24when mounted into the machine20. In some embodiments, the pivotable surface of the machine20may be powered by suitable drive means (e.g., electric servo motor) to rotate (i.e., tilt) the disc-shaped workpiece40about the first axis22in response to a command by the CNC controller38of the machine20. The disc-shaped workpiece40may be positioned on a turntable that is also powered by suitable drive means (e.g., electric servo motor). The turntable may be configured to rotate about the second axis24in response to a command by the CNC controller38.

The machine20comprises a wire electrode26that may extend between an upper nozzle28and a lower nozzle30. The upper nozzle28may be movable along a U-axis, V-axis and Z-axis, as depicted. The lower nozzle30may be movable along a Y-axis and X-axis. The machine20may also comprise a Coordinate Measuring Machine (CMM) touch probe32used for locating features of the workpiece40. The CMM touch probe32may be movable along the U-axis, V-axis and Z-axis. The CMM touch probe32may alternatively be movable along a different set of axes.

In some embodiments, the disc-shaped workpiece40may be rotated about the first axis22and/or the second axis24to position a firtree-shaped slot42in a position relative to the wire electrode26that is suitable for conducting wire EDM using the wire electrode26. A position and orientation of the firtree-shaped slot42may be determined relative to a datum such as an origin (i.e., “zero” point) such as point C or an axis of a reference coordinate system of the machine20. Based on measurements acquired via touch probe32or other measurement equipment (e.g., dial indicator, laser scanner, etc.), the CNC controller38of the machine20may be used to position/orient the workpiece40to place the firtree-shaped slot42to a position and orientation suitable for conducting wire EDM using wire electrode26. In some embodiments, the process of moving and orienting firtree-shaped slot42may be automated based on measurements acquired via touch probe32for example and/or position(s) acquired by electrical touching using the wire electrode26as described further below. The instructions may be configured to cause the CNC controller38to determine if a rotation of the disc-shaped workpiece40about the first axis22and/or the second axis24is necessary based on the position and orientation of the firtree-shaped slot42. If a rotation of the disc-shaped workpiece40about the first axis22and/or the second axis24is necessary or desired for ease of access and/or wire EDM, the CNC controller38may be configured to determine the amount of rotation required and configured to issue a command to the appropriate drive means to facilitate the rotation of the workpiece40.

The CNC controller38may also be configured to cause relative motion between the disc-shaped workpiece40and the wire electrode26along one or more cutting paths (tool paths) defined by a CNC program for example. The wire electrode26, upper nozzle28and lower nozzle30may be displaced along the cutting path(s). It is understood that machines having other arrangements or other number of axes may be suitable for causing relative movement between the wire electrode26and the workpiece40to perform wire EDM.

FIG. 3Adepicts a cross-sectional view of an exemplary firtree-shaped slot42containing an imperfection46that may be rectified by reworking using wire EDM. The imperfection46may be a linear mark (i.e. cavity, bump) and/or a deviation in surface roughness. In some embodiments, the firtree-shaped slot42may have a plurality of such imperfections46. The methods are described in relation to slot42which is a cavity formed on a periphery of disc-shaped workpiece40but it is understood that aspects of the methods described herein are also applicable for reworking other firtree-shaped features such as roots of (e.g., turbine, compressor) blades for example. The firtree-shaped slot42may have a two-dimensional firtree profile44having alternating bilateral projections48A-48D and bilateral grooves49A and49B on two sides opposite the radial axis (RA) extending from the center of rotation C of the workpiece40and passing through a point of convergence52in a live rim region54of firtree-shaped slot42. The center of rotation C may be a center of rotation of the bladed rotor including workpiece40during use. The point of convergence52may be a radially-inner extremity of the firtree-shaped slot42relative to the center of rotation C. The two sides of the firtree-shaped slot42may define the live rim region54. As depicted in the embodiment ofFIG. 3A, the live rim region54may be a curved (e.g., bulbous) portion and may include an intended point of entry53A of a repair path to an intended point of exit53B of the repair path (e.g., seeFIG. 7) and that passes through the point of convergence52. In some embodiments, firtree-shaped slot42may be substantially symmetrical and the radial line RA may be an axis of symmetry of the firtree-shaped slot42. In some situations, the radial axis RA may extend through a centroid G of the firtree-shaped slot42. However, it is understood that the methods described herein also apply to firtree-shaped slots that are asymmetric.

FIG. 3Bdepicts a perspective view of the exemplary firtree-slot42. The point of convergence52shown inFIG. 3Amay be located at an intersection between the radial axis RA and an inner surface62of the firtree-shaped slot42. As depicted inFIG. 3B, the firtree-shaped slot42has the two-dimensional firtree profile44and a thickness T. In some embodiments the firtree-shaped slot42may have a uniform two-dimensional firtree profile44across the thickness44. However, it is understood that the methods described herein can also be used to perform rework on firtree-shaped features that have a profile that is non-uniform (e.g., tapered) across the thickness T.

Imperfections46on the firtree-shaped slot42may be detected through visual inspection by an operator or by using suitable metrology equipment. Examples of imperfections46include bumps, recesses, linear indications, cracks and unacceptable surface finish that may be present on the inner surface62of the firtree-shaped slot42. The formation of imperfections46on the firtree-shaped slots42may occur during the process of machining the firtree-shaped slot42in the workpiece40or subsequently. Suitable processes used to machine the firtree-shaped slot42in the workpiece40may be wire EDM, broaching, milling or other material removal process(es). In some situations, the imperfection46may be caused as a result of an irregularity in one or more processes used for machining the firtree-shaped slot42or may caused due to damage.

The imperfection46on the firtree-shaped slot42may be repaired by reworking the firtree-shaped slot42or part(s) thereof using wire EDM. The firtree-shaped slot42has a tolerance band B that is magnified inFIG. 3Afor illustrative purposes. The tolerance band B should be respected during the rework so that firtree-shaped slot42may meet dimensional specifications and be salvaged. It is understood that types of imperfections46repairable using the methods disclosed herein have to allow the reworked firtree-shaped slot42to meet applicable specifications (e.g., be within the tolerance band B) in order to be salvaged and put into operation.

Prior to reworking the firtree-shaped slot42using wire EDM, a position and an orientation of the firtree-shaped slot42may be established relative to a datum such as a reference coordinate system of the machine. The reference coordinate system may have an origin at a physical reference on the machine20or on the workpiece40(e.g., center of workpiece40such as point C shown inFIG. 3A). The physical reference can be related to or correspond to a software reference (origin) of a CNC program so that a tool path of the wire electrode26may be executed at a proper location on the workpiece40. In some embodiments, the position and orientation of the firtree-shaped slot42may be adjusted to be at a specific position and orientation relative to the reference coordinate system of the machine20. In some embodiments, the position of the firtree-shaped slot42may be adjusted in stages. Starting from the installed location of the firtree-shaped slot42, the positon of the firtree-shaped slot42may be adjusted in a stepwise manner until the firtree-shaped slot42is at a specific position and orientation relative to the reference coordinate system that allows reworking using the wire electrode26. For example, a relatively coarse positioning of firtree-shaped profile42can initially be done manually and fine tuned to desired tolerance using the method(s) described herein.

In some embodiments, an orientation of a surface62of the firtree-shaped slot42located along a thickness T (seeFIG. 3B) of the firtree-shaped slot42is determined relative to the Z-axis for example. As depicted in the exemplary embodiment of the firtree-shaped slot42inFIG. 3B, the orientation of the surface62of the firtree-shaped slot42is determined along the thickness T of the firtree-shaped slot42at a location of projection48B, which may be the radially outermost projection of the firtree-shaped slot42. The orientation of the surface62may be determined by determining the location of two points P1and P2on the surface62and at different elevations along the thickness T. The orientation of the line P1-P2defined by points P1and P2may be used to locate the orientation of surface62relative to the Z-axis. In some embodiments, the location of line P1-P2may be selected to be substantially at a crest of the projection48B. The locations of points P1and P2may be digitized using the CMM probe32or a dial indicator64as depicted inFIG. 4. The dial indicator64may be moved from the first point P1along the crest of the projection48B to the second point P2or vice versa. The relative movement between the indicator64and the workpiece40may be controlled manually by an operator or it may be controlled by the CNC controller38. In some embodiments, based on the coordinates of the two points P1and P2, the surface62may be substantially aligned with the Z-axis for example. If the deviation from the Z-axis is above a certain threshold, a correction in the angle A (seeFIG. 2A) may be determined to substantially align line P1-P2with the Z-axis. In some embodiments, the threshold is 0.0001″ (0.0025 mm) or may be selected based on the tolerance band B. The correction in the angle A may be computed using the formula:

CompensationA⁡(°)=arctan⁡(ErrorAZ),Formula⁢⁢1
where ErrorAis a lateral deviation in the X-Y plane between points P1and P2, Z is the vertical distance along the Z-axis between the points P1and P2and Compensations is an angular displacement of the tilt A-axis required to bring the line P1-P2in substantial alignment with the Z-axis. The formula 1 above may be used in an iterative manner until the ErrorAis below the specified threshold. The workpiece40may then be rotated (i.e. tilted) by the calculated compensation angle about the axis22. The rotation may be facilitated by the drive means (e.g., electric servo motor) to align the surface62substantially along the Z-axis.

Although the measurement is shown to be taken at the projection48B of the firtree-shaped slot42for convenience and ease of access, it is understood that other locations inside the firtree-shaped slot42may be used to determine the orientation of the surface62along the thickness T of the firtree-shaped slot42. In some embodiments, an accuracy of the measurement may be higher when taken at a radially outer projection as opposed to another radially inner location. The selected location for the measurement may depend on a size of the workpiece40.

A position of the radial axis RA of the firtree-shaped slot42along the Y-axis may also be determined for example. To determine the position of the radial axis RA, one or more midpoints of the firtree-shaped slot42may be determined between each side of the firtree-shaped slot42. The wire electrode26may be used to determine the one or more midpoints by way of electrical touching. Electrical touching may involve using the wire electrode26to approach the workpiece40and detect a presence of the workpiece40when the wire electrode26approaches the workpiece40and current starts to flow (i.e., sparking) between the wire electrode26and the workpiece40. At that moment, the machine20may store a position of the wire electrode26at which the workpiece40is detected. Suitable settings (e.g., voltage, current) may be selected for electrical touching based on characteristics of the workpiece40. For instance, a roughness, cleanliness and material conductivity of the workpiece40may be considered when determining the settings to be used for electrical touching in order to minimize linear marks on the workpiece40. The depth of such linear marks may be higher when a higher current is supplied to the wire electrode26. In addition, the higher the current supplied to the wire electrode26during electrical touching, the lower a precision may be for detecting the presence of the workpiece40. In some embodiments, the current supplied to the wire electrode26may be set to maximize the precision and minimize a depth of an associated linear mark.

In some embodiments, the wire electrode26first may be positioned in a preferred area of the firtree-shaped slot42such as the live rim region54where the midpoints are desired to be determined. As depicted inFIG. 3A, the wire electrode26may be positioned between the imperfection46and an intended point of entry53A/exit53B of a repair in the live rim region54of the firtree-shaped slot42. The workpiece40having the firtree-shaped slot42may then be completely immersed in a dielectric fluid, which cools the wire EDM process and helps dispose of material removed from the workpiece40during wire EDM. The wire electrode26may then be used to touch-off opposite sides of firtree-shaped slot42using electrical touching in order to determine the location of the midpoint(s) firtree-shaped slot42. In order to determine a first midpoint of the firtree-shaped slot42, the wire electrode26configured for electrical touching may be used to determine a position of points56A and56B on the surface62. Points56A and56B may be within the live rim region54of the firtree-shaped slot42and be located on opposite sides of the radial axis RA of the firtree-shaped slot42. The wire electrode26may be moved from point56A to point56B or vice versa to determine the positions of the wire electrode26at each point56A and56B. The movement of the wire electrode26may be done manually by an operator (e.g., by jogging Y-axis movement in relatively small increments) or such movement may carried out automatically by the CNC controller38. The distance between points56A and56B may then be determined.

Using the measurements of points56A and56B, a first midpoint56C between the points56A and56B may be computed. The first midpoint56C may coincide with the radial axis RA of the firtree-shaped slot42.

Using the position of the first midpoint56C, an amount of deviation of the first midpoint56C in the Y-axis relative to the X-axis (Y=0) may be determined. If the error along the Y-axis is above a certain threshold, a correction in the angle of the rotary W-axis (axis24) may be determined. In some embodiments, the threshold is 0.0001″ (0.0025 mm) or may be selected based on the tolerance band (B). The correction in the angle W may be computed using the formula:

Compensationw⁡(°)=arctan⁡(ErrorYX)Formula⁢⁢2
where ErrorYis a deviation along the Y-axis of the position of midpoint56C from Y=0, X is a distance along the X axis between the center of rotation of the workpiece40and the midpoint56C and CompensationWis an angular displacement of the rotary W-axis required to bring the midpoint56C in substantial alignment with the X-axis. The workpiece40may then be rotated by the calculated compensation angle about the rotary axis24. The rotation may be facilitated by the turn table to align the midpoint56C substantially on the X-axis. The use of formula 2 may also serve to align the radial axis RA of the firtree-shaped slot42substantially along the X-axis.

To validate that the radial axis RA resides on the X-axis, a second midpoint57C of the firtree-shaped slot42may be determined between points57A and57B using the process described above at a second position along the X-axis. In some embodiments, a plurality of midpoints may be computed to determine that the radial axis RA of the firtree-shaped slot42resides on the X-axis. The formula 2 above may be used in an iterative manner until the Error is below the specified threshold. In some embodiments, an average of several midpoints56C,57C may be used for the purpose of improving accuracy of the alignment of the firtree-shaped slot42with the X-axis.

Although points56A,56B,57A and57B are disposed in live rim region54and used to compute midpoints56C,57C of the firtree-shaped slot42, it is understood that points at other locations could be used to compute one or more midpoints elsewhere along the radial axis RA of the firtree-shaped slot42. In the depicted embodiment, one or more rework cutting paths51(shown inFIG. 7) may be used to rework a portion of the firtree-shaped slot42. Specifically, the one or more rework cutting paths51may be used to rework a portion of the firtree-shaped slot42proximate the live rim region54and accordingly, it may be desirable to use electrical touching and compute the one or more midpoints in the portion of the firtree-shaped slot42that is being reworked. However, in some embodiments, the rework cutting paths51may be configured to machine an entirety of the firtree-shaped slot42. In these cases, a different set of points to compute different midpoints along the radial axis RA of the firtree-shaped slot42may be used. In some embodiments, a dimensional accuracy of a midpoint determined at a radially outer location within the firtree-shaped slot42may be higher than a midpoint determined at a radially inner location.

FIG. 5depicts an exemplary user interface65of a CNC software application running on CNC controller38of machine20. The position of wire electrode26to a machine coordinate system and a coincident part coordinate system is shown in table66. The user interface65may facilitate the location of one or more midpoints56C and57C by way of semi-automation. An operator or the CNC controller38may be prompted to move the wire electrode26to a start location and click on an “Activate” button on the user interface65in order to launch automatic jogging movements and electric touching at opposed points56A and56B and the computation of the midpoints56C. The rotary compensation movement of the W-axis based on formula 2 above may also be carried out automatically by CNC controller38in order to orient the radial axis RA along the X-axis for example.

In reference toFIG. 3A, in some embodiments, a location of the intersection between the surface62of the firtree-shaped slot42and the radial axis RA may be determine in order to locate the firtree-shaped slot along the X-axis. The wire26and electrical touching may again be used to locate the point of convergence52located at the bottom of the firtree-shaped slot42. The point of convergence52may be located by positioning the wire26at the previously computed midpoint56C for example and moving (e.g., jogging) the wire26radially inwardly along the radial axis RA until the point of convergence52on the surface62is located by way of electrical touching.

In some embodiments, the lower nozzle30of the machine20may be adjusted relative to the upper nozzle28of the machine20or vice versa to vary the orientation of the wire26. Such relative positioning between the upper nozzle28and the lower nozzle30may be used to orient the wire parallel to the Z-axis or to place the wire at another orientation that is oblique to the Z-axis if required depending on the geometry of the firtree-shaped slot42. The orientation of the wire26may be adjusted as a function of the perpendicularity of the workpiece40to the Z-axis.

FIG. 6depicts another exemplary user interface68of a CNC software application running on CNC controller38of the machine20. The position of wire electrode26to a machine coordinate system and a substantially coincident part coordinate system is shown in table69A. The user interface68may have a “vertical alignment” button69C which may be pressed to launch an automated procedure to orient the wire26to be parallel with the Z-axis if necessary.

To orient the wire electrode26to be parallel with the Z-axis, the procedure may determine a corresponding positional offset between the upper nozzle28and the lower nozzle30. Based on the determined offset, the wire electrode26may be adjusted to orient the wire electrode26to be parallel with the Z-axis in preparation for machining the workpiece40. In some embodiments, the procedure to orient the wire electrode26to be parallel with the Z-axis may involve using a tool having a thin eyelet. The wire electrode26may be positioned to extend through an opening of the eyelet. The lower nozzle30may be fixed in the X and Y axis in the center of the eyelet while the upper nozzle28may be positioned just above the eyelet and moved along the U and V axis to a plurality of positions to find its center within the eyelet using electrical touching. Then, the upper nozzle28may be moved upward to a higher Z position and then moved again along the U and V axes in order to find the center of the eyelet again. Other suitable approaches to establish a desired orientation of the wire electrode26may be used. Table69B indicates a lateral offset and a height between the upper nozzle28and the lower nozzle30. Table69B also indicates an angle of the wire26relative to the Z-axis.

In some embodiments, the orientation of the wire electrode26may be adjusted as a function of the perpendicularity of the workpiece40to the Z-axis. The automatic adjustment may include orienting the wire26to be parallel with a surface of the workpiece40. In some embodiments, the CMM probe32may be used to determine an orientation of the surface of the workpiece40. Based on the determined orientation of the surface, the wire electrode26may be oriented to be parallel with the surface of the workpiece40. For example, the methods described herein can be used to perform rework on firtree-shaped slots42that have a substantially uniform or non-uniform through-thickness profile.

FIG. 7depicts the live rim region54of the firtree-shaped slot42ofFIG. 3A. To repair the imperfection46, the wire electrode26may be programmed to move along one or more rework cutting paths51via suitable CNC program (e.g., G-codes) generated via suitable CAD/CAM system based on a CAD model of the slot42. In some embodiments, the rework cutting paths51may be configured to also remove linear marks that may have been formed by an electrical touching procedure used to locate firtree-shaped slot42. The rework cutting paths51may be configured to machine an entirety of firtree-shaped slot42or only one or more portion(s) of firtree-shaped slot42depending on the number and location(s) of imperfection(s)46. In some embodiments, different rework cutting paths51may be used to perform different rework wire EDM passes on workpiece40using the same or different process parameters. In some embodiments, one rework cutting path51may be used to perform multiple rework wire EDM passes on workpiece40. In some embodiments, the one or more rework cutting paths51used for repairing the firtree-shaped slot42are the same as or different from the one or more original cutting paths50used for forming the firtree-shaped slot42in the first place. Lead-in and/or lead-out portions that may be tangential to the surface of the workpiece40may be incorporated into the rework cutting path(s)51in cases where the rework cutting path(s)51may be shorter than the original cutting path50.

In some embodiments, determining the one or more rework cutting paths51includes the application of tool offsets to the one or more original cutting paths50(or part thereof) used for forming the firtree-shaped slot42to progressively move the wire26into the workpiece40with successive passes. The portion of the one or more original cutting paths50and the amount of offsets to be applied may be determined based on the nature of the imperfection46on the firtree-shaped slot42. For instance, in a case where the imperfection46is a recess formed on a surface of the firtree-shaped slot42, it may be required that a certain offset be applied to a portion of the one or more original cutting paths50containing the recess in order to partially or fully smooth out the surface62at the location of the imperfection46.

In some embodiments, the offsets applied to the one or more original cutting paths50or rework cutting paths51for the purpose of reworking may be limited by an upper and a lower limit based on the tolerance band B illustrated inFIG. 3Aand optionally also based on the starting location of firtree-shaped slot42within tolerance band B. An upper offset limit and a lower offset limit may serve as a maximum and minimum, respectively, to which the one or more original cutting paths50can be modified to produce the one or more rework cutting paths51while still respecting the tolerance band B.

In some embodiments, the offsets applied to the one or more original cutting paths50or rework cutting paths51may be set to create a spark condition that provides a desired amount of material removal. In some embodiments, this may require that the wire electrode26be within a few microns from the region of the firtree-shaped slot42being reworked. The material being cut as well as a thickness of the firtree-shaped slot42may also be considered when setting the offsets to be applied to the one or more original cutting paths50or rework cutting paths51.

In some embodiments, multiple (e.g., three) cutting passes of wire EDM may be performed to repair the firtree-shaped slot42. The multiple passes may be conducted using different sets of parameters (e.g., spark energy intensity, machine path offset between different cutting passes, polishing) to reach a desired surface finish condition, metallurgy characteristics and geometry precision. Increasing the number of passes may improve surface condition, metallurgy characteristics and geometric precision of the repaired firtree-shaped slot42. However, increasing the number of passes could also result in longer reworking time and higher operating costs. Therefore, each of the multiple passes may be tailored to optimize the repair of the firtree-shaped slot42. Spark energy intensity may refer to the current intensity, the voltage intensity and the duration of its on-time. Higher energy spark intensities may allow for higher material removal rates, but may increase the likelihood of linear defects (i.e. cavities, bumps) being formed and may provide a rougher surface finish of the firtree-shaped slot42. Therefore, it may be desirable to have higher spark energy intensities for the initial cutting pass(es) and lower spark energy intensities for subsequent passes. The subsequent cutting passes having lower spark energy intensities may assist in repairing rough surfaces created by the initial cutting passes and correcting metallurgical characteristics of surfaces of the slot42to provide a desired surface integrity. The material being cut as well as a thickness of the slot42may be considered when setting the spark energy intensities of the passes.

In some embodiments, an amount of material expected to be removed in a cutting pass may be considered when setting a tool offset to be applied to an original cutting path50or rework cutting path51for a subsequent cutting pass.

In some embodiments, three cutting passes may be performed to repair the firtree-shaped slot42. A first cutting pass, a “roughing” pass, may be set to a first spark energy intensity to provide a high material removal rate. The roughing pass may form rough surfaces and/or linear defects (i.e. cavities, bumps) on surfaces of the firtree-shaped slot42. A second cutting pass (“finishing” pass) and a third cutting pass (“polishing” pass) each may be set to a spark energy intensity that is lower than the first spark energy intensity. These passes may be used to smoothen rough surfaces created by the roughing pass and correct metallurgical characteristics of surfaces of the firtree-shaped slot42to provide a desired surface integrity. Performing cutting passes at higher spark energy intensities, may increase the formation of rough surfaces and/or linear defects on the firtree-shaped slot42. To minimize the formation of rough surfaces and/or linear defects on the firtree-shaped slot42, a speed of the wire electrode26may be increased for cutting passes performed at higher spark energy intensities. In some embodiments, a speed of the wire electrode26may be greater for the first cutting pass in comparison to the second and third cutting passes.

FIG. 8is a flowchart illustrating an exemplary method100for repairing a firtree-shaped feature of a part using wire EDM. Method100can be performed using machine20described herein or another machine. It is understood that aspects of method100can be combined with aspects of other methods described herein. In various embodiments, method100includes:receiving the part (e.g., workpiece40) having a firtree-shaped feature (e.g., firtree-shaped slot42) requiring rework (see block102);installing the part in machine20configured for wire EDM (see block104);locating the firtree-shaped feature relative to a datum of machine20(see block106; andperforming wire EDM on the firtree-shaped feature (see block108).

In some embodiments, method100may also include detecting one or more imperfections46that may be repaired by wire EDM rework. The imperfection(s)46may be detected by visual inspection. Alternatively, the imperfection(s)46may be detected using metrology equipment.

Locating the firtree-shaped feature42relative to a datum of machine20may include one or more steps described above and/or other part-locating approach(es) that may provide acceptable accuracy.

Performing wire EDM on the firtree-shaped feature42may include performing one or more (e.g., three) wire EDM passes on one or more portions of the firtree-shaped feature42.

FIG. 9is a flowchart illustrating an exemplary method200for manufacturing a disc of a bladed rotor having a firtree-shaped profile (e.g., firtree-shaped slot42). Method200can be performed using machine20described herein or using another machine. It is understood that aspects of method200can be combined with aspects of other methods described herein. In various embodiments, method200includes:using the wire EDM machine20, machining firtree-shaped slot42in a disc-shaped workpiece40using wire EDM, the firtree-shaped slot42extending radially inwardly from a periphery of the workpiece40(see block202);removing the workpiece40from the machine20(see block204);after a portion of the firtree-shaped slot42requiring rework has been identified, installing the workpiece40in the same or another wire EDM machine (see block208);locating the firtree-shaped slot42relative to a datum of the same or the other wire EDM machine (see block210); andperforming wire EDM on the portion of the firtree-shaped slot requiring rework (see block212).

Method200may include the original machining of firtree-shaped slot42by using wire EDM or other material removal process(es). The identification of the portion(s) requiring rework (see optional block206) may include the detection of one or more imperfections46by way of visual inspection for example. It is understood that the original wire EDM of the firtree-shaped slot42and the reworking of the firtree-shaped slot42may be conducted on the same or on different wire EDM machines.

The above description is meant to be exemplary only, and one skilled in the relevant arts will recognize that changes can be made to the embodiments described without departing from the scope of the invention disclosed. The present disclosure may be embodied in other specific forms without departing from the subject matter of the claims. The present disclosure is intended to cover and embrace all suitable changes in technology. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. Also, the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.