METHOD FOR PRODUCING A WORKPIECE, IN PARTICULAR A TURBINE BLADE, USING A MILLING TOOL

Abstract

A method for manufacturing a workpiece (28) using a milling cutter configured as a conically convex milling cutter (10) is provided. The conically convex milling cutter (10) comprises a shank (12) and a conically convex milling cutter portion (14) connected at the end to the shank (12) directly or through a transition (16). The conically convex milling cutter (10) has a first and a second cutting area (24, 26), wherein the first cutting area (24) is provided on the shank (12) or/and at the transition (16), and wherein the second cutting area (26) is provided on the conically convex milling cutter portion (14). The method comprises the following steps: A) roughing a blank portion (30) using the conically convex milling cutter (10), wherein the latter is inclined relative to a current feed direction (40) at a reference point (38) of the conically convex milling cutter (10) within a first machining angle range (α1, β1) such that machining is performed with the first cutting area (24) of the conically convex milling cutter (10), wherein the second cutting area (26) remains passive during machining, and B) finishing at least a part of the rough blank portion (46) using the conically convex milling cutter (10), wherein the latter is inclined relative to the current feed direction (40) at the reference point (38) of the conically convex milling cutter (10) within a second machining angle range (α2, β2) in such a way that machining is performed with the second cutting area (26) of the conically convex milling cutter (10), wherein the second cutting area (26) engages with the blank (30).

Claims

1-17. (canceled)

18. A method for manufacturing a workpiece using a milling tool configured as a conically convex milling cutter, the conically convex milling cutter comprising: a shank and a conically convex milling cutter portion connected to the shank directly or through a transition, wherein the conically convex milling cutter has a first and a second cutting area, wherein the first cutting area is provided on the shank or/and at the transition, and wherein the second cutting area is provided on the conically convex milling cutter portion, the method comprising the steps of: (A) roughing a blank portion using the conically convex milling cutter, wherein the latter is inclined relative to a current feed direction at a reference point of the conically convex milling cutter within a first machining angle range such that machining is performed with the first cutting area of the conically convex milling cutter, wherein the second cutting area remains passive during machining, and (B) finishing at least a part of the rough blank portion using the conically convex milling cutter, wherein the latter is inclined relative to the current feed direction at the reference point of the conically convex milling cutter within a second machining angle range in such a way that machining is performed with the second cutting area of the conically convex milling cutter, wherein the second cutting area engages with the blank.

19. The method of claim 18, wherein the conically convex milling cutter is variably movable during step (A) of roughing and step (B) of finishing within the first machining angle range and the second machining angle range, respectively.

20. The method of claim 18, wherein the first and the second machining angle ranges overlap or are adjacent to each other or are spaced from each other by an amount.

21. The method of claim 18, wherein step (A) of roughing and step (B) of finishing are carried out alternately on different blank portions.

22. The method of claim 18, characterized in that the conically convex milling cutter is tilted at a first camber angle in the direction of the feed direction of the conically convex milling cutter during roughing) within the first machining angle range.

23. The method of claim 18, wherein the conically convex milling cutter is tilted at a second camber angle in the direction of the feed direction of the milling cutter during finishing) within the second machining angle range.

24. The method of claim 18, wherein in step (A), the conically convex milling cutter is inclined laterally with respect to the feed direction at a first inclination angle during roughing within the first machining angle range.

25. The method of claim 18, wherein in step (B), the milling cutter is inclined laterally with respect to the feed direction at a second inclination angle during finishing within the second machining angle range.

26. The method of claim 18, wherein in step (A) during roughing or/and in step (B) during finishing, a relative movement between the conically convex milling cutter and the blank takes place continuously, wherein: the conically convex milling cutter moves around the blank or the rough blank or/and the blank or the rough blank is continuously guided relative to the conically convex milling cutter along defined milling paths.

27. The method of claim 26, wherein the milling paths differ from each other in step (A) during roughing and in step (B) during finishing.

28. The method of claim 26, wherein the milling paths are spaced apart from each other by defined path distances in step A) during roughing and in step B) during finishing.

29. The method of claim 18, wherein a cone angle between a longitudinal axis of the milling cutter and a circumferential surface of a cone underlying the conically convex milling cutter portion is in an angular range of 50° to 85°.

30. The method of claim 18, wherein a ratio of a transition radius to a shank diameter is between 0% and 30%.

31. The method of claim 18, wherein a ratio of a curvature radius of a peripheral surface of the conically convex milling cutter portion to a shank diameter of the milling cutter is 2 to 50.

32. The method of claim 18, wherein the transition between the shank and the conically convex milling cutter portion is at least one of continuous, gradual and sharp.

33. The method of claim 18, wherein the shank is configured at least one of substantially cylindrical, substantially conical, and conical-cylindrical.

34. The method of claim 18, wherein the shank is composed of different conical portions and cylindrical portions.

35. The method of claim 18, wherein the conically convex milling cutter portion tapers toward a tip or an end face.

36. The method of claim 18, wherein a ball-shaped tip is present at an exposed end of the conically convex milling cutter portion.

Description

[0058] In the drawings:

[0059] FIGS. 1A-1C are a side view of a conically convex milling cutter in FIG. 1A and an enlargement of section X of the conically convex milling cutter of FIG. 1A in FIGS. 1B and 1C;

[0060] FIGS. 2A-2C are embodiments of a conically convex milling cutter with (FIG. 2A) and without (FIG. 2B, 2C) a transition as well as with (FIG. 2B) and without (FIGS. 2A and 2C) a ball-shaped tip;

[0061] FIGS. 3A-3D are side views of a conically convex milling cutter with (FIGS. 3A and 3B) and without (FIGS. 3C and 3D) a transition as well as an illustration of a first (FIGS. 3A and 3C) and a second cutting area (FIGS. 3B and 3D);

[0062] FIGS. 4A-4C are examples of workpieces machined using the method according to the invention in the form of a turbine blade (FIG. 4A) with the corresponding blank (FIG. 4B) and an aerospace part (FIG. 4C);

[0063] FIGS. 5A-5C are illustrations of roughing a blank portion using a conically convex milling cutter at a machining point using three perspective views;

[0064] FIGS. 6A-6C are illustrations of roughing a blank portion using a conically convex milling cutter at another machining point using three perspective views;

[0065] FIG. 7 is a perspective view of a blank including a rough blank portion;

[0066] FIGS. 8A-8C are illustrations of finishing a rough blank portion using a conically convex milling cutter at a machining point using three perspective views;

[0067] FIGS. 9A-9C are illustrations of finishing a rough blank portion using a conically convex milling cutter at another machining point using three perspective views;

[0068] FIG. 10 is an illustration of an alternative of finishing a rough blank portion using a conically convex milling cutter at a machining point;

[0069] FIG. 11 is a perspective view of a blank including a rough and finished blank portion;

[0070] FIGS. 12A-12C are various illustrations visualizing milling paths of the conically convex milling cutter during roughing and/or finishing of a blank without (FIGS. 12A and 12C) and with (FIG. 12B) connecting segments between the milling paths, using the example of a turbine blade (FIGS. 12A and 12B) and an aerospace part (FIG. 12C); and

[0071] FIGS. 13A-13C show further milling cutter geometries that may be used for implementing the method according to the invention.

[0072] FIG. 1A shows a conically convex milling cutter 10 adapted to carry out the method according to the invention. In this embodiment, the milling cutter 10 comprises a substantially cylindrical shank 12 and a conically convex milling cutter portion 14 which in the embodiment shown in FIGS. 1A to 1C is connected to the shank 12 through a transition 16. Further, the milling cutter 10 shown in FIG. 1A has a tip 18 in the form of a ball-shaped tip 18′ on a tapered end side of the conically convex milling cutter portion 14.

[0073] The conically convex shape of the milling cutter portion 14 is shown in the enlarged cutout of FIG. 1B in which the dashed line 19 indicates an imaginary rectilinear convex course 19 of a circumferential surface of a cone underlying the milling cutter portion 14 to illustrate an actual curvature radius 22 of the circumferential surface 20 of the conically convex milling cutter portion 14. The curvature radius 22 of the conically convex milling cutter portion may be between 400 mm and 600 mm, preferably between 450 mm and 550 mm, particularly preferably approx. 500 mm.

[0074] A cone angle y of the conically convex milling cutter portion 14 between a circumferential surface of a cone underlying the conically convex milling cutter portion 14, which may be defined with respect to the imaginary straight line 19 of the circumferential surface 20 of the milling cutter portion 14, and a longitudinal axis of the milling cutter 23 through the conically convex milling cutter 10 may be between 50° and 85°, preferably 75°.

[0075] The transition 16 between the milling cutter portion 14 and the shank 12 is optional. Examples of the milling cutter 10 with and without transition 16 are shown in FIG. 2A and FIGS. 2B and 2C, respectively. Furthermore, the ball-shaped tip 18′ mentioned at the beginning is optional. Alternatively, the milling cutter portion 14 may have a flat tip 18″ at its front tapered end side, as shown in FIGS. 2A and 2C, or any other suitable shape of tip 18. It is understood that the presence of the transition 16 and the choice of the tip 18 of the milling cutter portion are independent features, meaning that, for example, the milling cutter with transition 16 shown in FIG. 2A may also have a ball-shaped tip 18′.

[0076] Where there is a transition 16, preferably a ratio of a transition radius 17 to a shank diameter is between 0% and 30%, preferably a transition radius 17 of 0% means that there is no transition radius 17 between the shank 12 and the conically convex milling cutter portion 14.

[0077] In the method according to the invention, two steps are carried out, namely a step of roughing and a step of finishing. For this purpose, the conically convex milling cutter 10 may have two cutting areas 24, 26 adapted to the respective step, which may be used for machining in the corresponding steps of the method. As shown in FIG. 3A and FIG. 3C, respectively, the first cutting area 24 is arranged on the shank 12 and, if there is a transition 16, also on the transition 16. The first cutting area 24 may extend along only a portion of the shank 12, the portion of the shank 12 adjoining the conically convex milling cutter portion 14 or the transition 16 if there is such a transition.

[0078] Whether or not there is a transition 16, the second cutting area 26 is provided on the conically convex milling cutter portion 14, preferably on its peripheral surface 20, as can be seen in FIGS. 3B and 3D.

[0079] If the first cutting area 24 is formed by both the shank 12 and the transition 16, a maximum diameter of the conically convex milling cutter portion 14 may be smaller than a shank diameter. Otherwise, if there is no transition 16 and the first cutting area 24 is disposed solely on the shank 12, the maximum diameter of the conically convex milling cutter portion 14 may be equal to the shank diameter.

[0080] A conically convex milling cutter 10 as described above may be used to machine any blank and consequently to manufacture a workpiece 28 of any size and shape. For example, the blank 30 shown in perspective in FIG. 4A, in which the desired workpiece shape is already visible, may be used to manufacture the workpiece 28 shown in FIG. 4B in the form of a turbine blade 32. It is understood that the blank 30 may have any shape, for example, it may have the shape of a cuboid. Alternatively, FIG. 4C shows a workpiece 28 in the form of an aerospace part 34, which may likewise be manufactured using the method according to the invention.

[0081] In the following, the method step of roughing will be explained in more detail with reference to FIGS. 5A-5C as well as 6A-6C. As can be seen in these figures, the first cutting area 24 of the conically convex milling cutter 10 is engaged with the blank 30 during roughing. FIGS. 5A-5C show a machining point P1 of the method in which a portion of the blank 30 has already been subjected to roughing and therefore has a reduced material thickness compared to the portion not subjected to roughing.

[0082] A visualization of the milling operation completed by the milling cutter 10 may be provided using a milling path 36, which may relate to a reference point 38 on the milling cutter 10, for example, to a tip of the conically convex milling cutter portion 14, as in the embodiment shown in FIGS. 5A to 5C. In FIGS. 5A to 5C, the respective milling path is shown in dashed lines and indicates the path of the milling cutter 10 during roughing of the blank 30 up to the depicted machining point P1.

[0083] Referring to FIGS. 5A to 5B, the first machining angle range of the milling cutter 10 at the machining point P1 comprises an angular inclination of the milling cutter 10 in a current feed direction 40 at the reference point 38 at a first camber angle α1. The first camber angle α1 may be defined between the longitudinal axis of the milling cutter 23, shown as a dashed line, and a surface normal 44, shown as a dashed arrow, at a machining point P1 of the blank 30, and may indicate tilting of the milling cutter 10 in the feed direction 40. The feed direction 40 at the machining point P1 is generally perpendicular to the surface normal 44 at that machining point P1. The first camber angle α1 is preferably to be chosen such that the second cutting area 26 of the milling cutter 10 remains passive during roughing of the blank 30. This can be seen, for example, in FIGS. 5A to 5C, in which the conically convex milling cutter portion 14 does not engage with material of the blank 30. The amount by which the camber angle α1 may be larger than a circumferential surface angle θ may depend on the curvature radius 22 of the conically convex milling cutter portion 14. For example, the smaller the curvature radius 22, i.e. the larger the curvature of the conically convex milling cutter portion 14, the larger the amount can be.

[0084] In another embodiment (not shown), during roughing, the milling cutter 10 may not only be tilted at the first camber angle α1 in the feed direction 40 but may also be inclined laterally with respect thereto at a first inclination angle β1. The lateral inclination may be chosen depending on the blank 30 or workpiece 28 being machined and may improve cutting conditions or may be essential for collision avoidance. In this embodiment, the first machining angle range includes both tilting the milling cutter 10 in the feed direction 40 at a first camber angle α1 and inclining it laterally, for example transversely, thereto at a first inclination angle β1.

[0085] Roughing of the blank 30 at a further machining point P2 is illustrated in FIGS. 6A to 6C; since their perspective views correspond to those in FIGS. 5A to 5C, the previous discussion of FIGS. 5A to 5C applies analogously to FIGS. 6A to 6C. The first camber angle α1 may be different at different machining points P1, P2 of the blank 30 but may also be the same during machining of the entire blank 30 or in a portion thereof. The first camber angle α1 at the further machining point P2 is further defined analogously to the previous discussion of FIG. 5A, namely as a tilting of the milling cutter 10 at the further machining point P2 in the current feed direction 40, wherein the first camber angle α1 may be defined between the longitudinal axis of the milling cutter 23 and the surface normal 44 at the reference point 38.

[0086] When machining a blank 30, such as a turbine blade 32, where a thickness is small compared to the length and width, it may be an advantage to machine the blank 30 in portions to avoid unwanted vibration of the blank 30 during roughing or/and finishing due to the movements of the milling cutter 10. A blank 30 in which only a blank portion 46 of the blank 30 was subjected to roughing is shown in FIG. 7. The grooves 48 visible in this blank portion 46 result from a chosen roughing allowance that may vary from portion to portion or also within a portion.

[0087] Roughing of the blank portion 46 may be followed by finishing of this blank portion 46 or at least a section thereof. A visualization of the finishing at a machining point P3 is shown in FIGS. 8A to 8C, in which a section 50 of the blank portion 46 has already been finished. The milling path 36, which is also referenced to the tip of the conically convex milling cutter portion 14 in this example, shows the finishing performed up to the machining point shown.

[0088] During finishing, the second cutting area 26 of the conically convex milling cutter 10 engages with material of the rough blank portion 46, preferably with a peripheral surface portion of the peripheral surface 20 of the conically convex milling cutter portion 14 contacting material to be finished. This peripheral surface portion of the peripheral surface 20 extends, for example, between the tip 18 of the milling cutter portion 14 and the transition 16 or, if there is no transition 16, the shank 12. A contact point 52 between the peripheral surface portion and the already rough and finished blank portion 46 or the workpiece is highlighted in FIG. 8A by a contact point 52. A precise location of the contact point 52 on the circumferential surface portion in the second cutting area 26 may be fine-tuned through the choice of the lateral second inclination angle β2.

[0089] In the example shown, the roughing allowance was chosen to be somewhat larger so that roughing with the first cutting area 24 also takes place during finishing with the second cutting area 26, as can be seen in FIG. 8A, for example. Nevertheless, in this case only the second cutting area 26 has a shaping effect, the first cutting area 24 does not have such an effect.

[0090] Referring to FIGS. 8A to 8C, the second machining angle range of the conically convex milling cutter 10 at the machining point P3 includes inclining the milling cutter 10 laterally with respect to a current feed direction 40 at the reference point 38 at a second inclination angle β2. The second inclination angle β2 may be defined between the longitudinal axis of the milling cutter 23, shown as a dashed line, and the surface normal 44, shown as a dashed arrow, and may indicate a lateral inclination of the milling cutter 10 with respect to the current feed direction 40 of the milling cutter 10 at the machining point P3. The second inclination angle β2 is preferably to be chosen such that the second cutting area 26 of the milling cutter 10 engages with material of the rough blank portion 46 during finishing.

[0091] Finishing of the rough blank portion 46 at a further machining point P4 is illustrated in FIGS. 9A to 9C; since their perspective views correspond to those in FIGS. 8A to 8C, the previous discussion of FIGS. 8A to 8C applies analogously to FIGS. 9A to 9C. The second inclination angle β2 may be different at different machining points P3, P4 of the rough blank 46, but it may also be the same and remain unchanged during machining of the rough blank portion 46 or a section thereof. The second inclination angle β2 at the further machining point P4 is further defined analogously to the previous discussion of FIG. 8A, namely as a lateral inclination of the milling cutter 10 at the further machining point P4 with respect to the current feed direction 40 of the milling cutter 10, wherein the second inclination angle β2 may be defined between the longitudinal axis of the milling cutter 23 and the surface normal 44 at the reference point 38.

[0092] In another embodiment shown in FIG. 10, during finishing, the milling cutter 10 may not only be inclined at the second inclination angle β2 but may also be tilted at a second camber angle α2 in the current feed direction 40. The second camber angle α2 in the feed direction 40 may be defined between the longitudinal axis of the milling cutter 23 and the surface normal 44 at the reference point 38. In this embodiment, the second machining angle range is consequently determined by two angles, the second camber angle α2 in the feed direction and the second inclination angle β2 laterally, for example transversely, thereto.

[0093] In general, a first camber angle range in which the first camber angle α1 for roughing can be specified may overlap a second camber angle range in which the second camber angle α2 for finishing can be specified. Alternatively or additionally, a first inclination angle range in which the first inclination angle β1 for roughing can be specified may overlap a second inclination angle range in which the second inclination angle β2 for finishing can be specified. Alternatively, the aforementioned camber angle ranges or/and inclination angle ranges may be ranges separate from each other. A blank 30 comprising the rough and finished blank portion 54 and an unmachined blank portion 56 is shown in FIG. 11. The machining of the blank portion 56 may be performed by roughing and finishing as previously explained. Preferably, another blank portion is first subjected to roughing and then finished for this purpose. The roughing and subsequent finishing of a blank portion may be continued until all blank portions of the blank have been subjected to roughing and finishing, i.e. the machined workpiece 28 is completed. Such alternating, portion-by-portion machining of the blank 30 may increase the blank's stability during milling.

[0094] In other words, the roughing and finishing steps are carried out in this sequence and, if necessary, repeated in a further, for example subsequent, blank portion. This procedure is particularly suitable for the manufacture of turbine blades 32, with finishing preferably being carried out only in blank portions that have previously be subjected to roughing.

[0095] It is understood that as an alternative roughing of the entire blank may be performed before finishing. However, this procedure is only recommended if the rough blank still has sufficient stability to counteract vibration during subsequent finishing.

[0096] Furthermore, it is an advantage if finishing is not performed too close to a transition area between a rough and a non-rough blank portion as a comparatively large amount of material may still be present in this transition area. If this material were to be collected during finishing, the service life of the milling cutter could be reduced due to increased wear. Consequently, the finished blank portion may be smaller than the blank portion previously subjected to roughing. It is understood that the last rough blank portion may be completely finished.

[0097] In the following, milling paths 36 usable for roughing and finishing are explained with reference to the illustrations in FIGS. 12A to 12C. The milling path 36 may be closed, as shown in FIG. 12A, and may be, for example, a continuous coil 56. In other words, the milling cutter 10 may be guided continuously, preferably completely, circumferentially around the blank 30 or the rough blank 46 during roughing or/and finishing, preferably continuously contacting the blank 30. A direction of rotation of the milling path 36 may be arbitrary during roughing and/or finishing.

[0098] Alternatively, as shown in FIG. 12B, the milling paths 36 may be separate milling paths 58 that may be connected to each other through connecting segments 60 between the milling paths 58. In other words, the milling cutter 10 may, during roughing or/and finishing, pass around the blank 30 or rough blank 46 along a milling path 58′, then be disengaged from the blank 30 or rough blank 46 and guided along a connecting segment 60′ to subsequently re-engage with the blank 30 or rough blank 46 and be guided around the blank 30 or rough blank 46 along another milling path 58″. Preferably, the milling paths 58 run parallel to and separate from each other. The milling cutter 10 may thus be continuously guided around the workpiece 28 using the connecting elements 60.

[0099] Independent of a course of the milling path(s) 36, 56, 58, a path distance 62 may be defined between them, for example between revolutions of the continuous coil 56 or the separate milling paths 58. It is calculated, for example, from the tool geometry and the desired accuracy. It is understood that a contour, for example the contour 48 after roughing, may be smoother when the path distance 62 is smaller than when it is larger.

[0100] Further, FIG. 12C shows possible milling paths 36 on an aerospace part 34 that are spaced apart by the path distance 62 and extend from one side to the other. In this example, the milling path 36 are not circumferential and, ideally, open on both sides.

[0101] In addition to the milling cutter geometry according to the above description with reference to FIGS. 1 to 3, FIGS. 13A to 13C show further alternative milling cutter geometries. While the same reference signs are used for the same components as above, the following description applies additionally.

[0102] FIG. 13A shows a milling cutter 10 with a substantially conical shank 12′ that merges into the conically convex milling cutter portion 14 via the transition 16.

[0103] FIG. 13B shows a milling cutter 10 with a substantially cylindrical shank portion 12 that merges directly, i.e. without a rounded transition, into a conical shank portion 12′. The conical shank portion 12′ is then followed by the transition 16 that merges into the conically convex milling cutter portion 14.

[0104] FIG. 13C shows a milling cutter 10 with a first substantially cylindrical shank portion 121 that merges directly, i.e. without a rounded transition, into a conical shank portion 12′. The conical shank portion 12′ is in turn immediately followed by a second substantially cylindrical shank portion 122 of a smaller diameter. It merges into the conically convex milling cutter portion 14 via the transition 16.