METHOD FOR MACHINING A WORKPIECE HAVING AN IRREGULAR EDGE

Abstract

A method for machining a workpiece is provided. An electrode is moved linearly in the direction of the workpiece to cause material to be removed from the workpiece, at least one end of a surface of the workpiece running obliquely to a guide edge of the electrode machining this surface. The electrode is moved at least partially with the electrode surface parallel to the surface, so that during the approach to the workpiece, areas of the workpiece having an irregular edge machined at a different intensity are formed, the difference in intensity of machining on the edge of the surface to be machined being compensated in that the surface to be machined is provided with a height profile adapted to the shape of the end of the surface to be machined. A blade ring segment and blade ring is also disclosed.

Claims

1. A method for machining a workpiece, an electrode being situated at a distance from a workpiece to be machined and moved linearly in the direction of the workpiece to be machined to cause material to be removed from the workpiece during the approach to the workpiece, at least one end or one section of one end of a surface of the workpiece to be machined running obliquely to a guide edge of the electrode machining this surface, the method comprising: moving the electrode at least partially with the electrode surface parallel to the surface to be machined, so that during an approach of the electrode to the workpiece, areas of the workpiece having an irregular edge machined at a different intensity are formed, the difference in intensity of machining on the edge of the surface to be machined being compensated in that the surface to be machined is provided with a height profile adapted to the shape of the end of the surface to be machined.

2. The method as recited in claim 1 wherein the height profile, in areas in which the end of the surface to be machined protrudes in the opposite direction from the direction of movement component parallel to the surface, and is passed by the guide edge of the electrode first, a lesser material removal and thus an elevated profile is provided than in areas in which the end of the surface to be machined is recessed in the direction of the direction of movement component parallel to the surface and is passed by the guide edge of the electrode at a later point in time and therefore a lowered profile is provided.

3. The method as recited in claim 1 wherein the machining includes electrochemical machining (ECM), erosion, electrodischarge machining (EDM) or electrochemical discharge machining (ECDM).

4. The method as recited in claim 1 wherein workpiece includes blade ring segments of a blade ring having an outer and/or inner shroud, and the machining of the blade ring segments is used to adjust the boundary edges of adjacent blade ring segments to one another.

5. The method as recited in claim 4 wherein the electrode is moved with at least one movement component across a Z-shaped edge of one of the outer and inner shrouds in the circumferential direction of the blade ring, so that the one shroud receives a height profile having peaks and/or valleys running in the circumferential direction, the peaks being provided in the area of the sections of the end of the one shroud protruding in the circumferential direction, and the valleys being provided in areas of the sections of the end of the one shroud recessed in the circumferential direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings show the following in purely schematic representations:

[0016] FIG. 1 shows part of a blade ring of a turbomachine having adjacent blade ring segments according to the related art in a perspective representation;

[0017] FIG. 2 shows a top view onto a blade ring segment;

[0018] FIG. 3 shows a partial sectional representation of the blade ring segment from FIG. 2 according to sectional line B-B;

[0019] FIG. 4 shows a representation of ECM machining of a shroud having a Z-shaped end edge; the partial view a) shows a top view, the partial view b) shows a side view and the partial view c) shows a frontal view; and

[0020] FIG. 5 shows a perspective representation similar to the representation in FIG. 1 having a wavy annular space delimiting surface according to the present invention.

DETAILED DESCRIPTION

[0021] Additional advantages, characteristics and features of the present invention will become explicit in the following detailed description of one exemplary embodiment. However, the present invention is not limited to this exemplary embodiment.

[0022] FIG. 1 shows a part of a blade ring having two adjacent blade ring segments 1 and 2, such as those used in turbomachines, for example, gas turbines or aircraft engines. In the shown exemplary embodiment, adjacent blade ring segments 1 and 2 have two shrouds having annular space delimiting surfaces 5 and 6, which are designed to be complementary to one another at their end edges in a Z shape, so that blade ring segments 1 and 2 are joined together in a form-locked manner. This Z-shaped profile is usually provided on the outer shrouds, FIG. 1 being rotated by 180 for a better representation, so the outer shroud is shown at the bottom.

[0023] Blade ring segments 1 and 2 each have a blade profile 3 and 4, which are situated obliquely or transversely and/or with a curve with respect to the circumferential direction of the blade ring.

[0024] FIGS. 2 and 3 show a top view (FIG. 2) of a blade ring segment 1 as well as a sectional representation (FIG. 3) along sectional line B-B from FIG. 2.

[0025] In manufacturing the corresponding blade ring segments, they must undergo final machining to impart the shape in particular when the blade ring segments have been manufactured by forging technology to impart the required strength to the blade ring segments through forging. This is the case, for example, with blade ring segments that are to be manufactured from lightweight TiAl materials. Electrochemical machining methods may be considered as a possible method of machining the blade ring segments and in particular the blade profile surfaces and shroud surfaces 5 and 6, which delimit the so-called profile space between blade profiles 3, 4. During so-called electrochemical machining, ECM, one or multiple shape electrodes are situated near the workpiece surfaces to be machined and are moved in the direction of the workpiece surface up to a defined distance from it, so that material is removed at the workpiece surface to be machined due to an applied potential between the electrode and the workpiece surface in the presence of a suitable electrolyte. With respect to the material removal, the duration of machining and the distance of the electrode from the workpiece surface to be machined are essential.

[0026] FIG. 3 shows, for example, the direction of movement, indicated by arrows 8, or the direction of attack of the electrodes for the machining of the profile surfaces of blade profile 3 and annular space delimiting surface 5 of blade ring segment 1. The movement of the electrode during ECM machining is linear. With a certain configuration of the workpiece surface to be machined with respect to the working electrode during the approach, this may result in removal of different amounts of material in different areas of the workpiece surface. For example, at the ends of the shrouds having a Z profile, this will result in the edges of the annular space delimiting surfaces 5, 6 having a different height profile. In the case of adjacent blade ring segments 1 and 2, steps 7 may thus present in the contact areas of adjacent blade ring segments 1, 2, which are undesirable since they may have an unfavorable influence on the flow conditions in the annular space.

[0027] FIGS. 4a through 4c schematically show once again how stages 7 may be formed in adjacent ring segments 1, 2. FIG. 4a shows the top view onto a shroud 10 having a Z-shaped end edge 13, where a working electrode 11 is being displaced over shroud 10 for machining shroud 10 according to the direction of movement characterized by movement arrow 12. This need not be a strictly parallel movement of electrode 11 along shroud 10 or the surface to be machined but in principle a movement component, i.e., a movement subvector, in accordance with direction of movement 12 is sufficient. FIG. 4a shows clearly that electrode 11 with its guide edge 14 in the case of Z-shaped end edge 13 initially reaches protruding tips 15 of the Z profile, so that machining, i.e., material removal, begins there. With additional movement in the direction of movement 12, the machining proceeds so that end edge 13 is reached in the area of indentations or recesses 16 and the machining, i.e., material removal, begins there. However, the movement of electrode 11 in the direction of movement 12 produces a wedge-shaped removal as illustrated in subfigure b) of FIG. 4. Since edge 13 does not run perpendicularly to direction of movement 12, this results in an image showing that a great deal of material removal has taken place in the area of tips 15 in the frontal view, i.e., in a view according to direction of movement 12, whereas a lesser material removal has occurred in the area of recessed areas 16, resulting in a height profile of edge 13. Since machining takes place in the same way in an adjacent blade ring segment, this yields the steps shown in FIG. 1 in the contact areas, but this is undesirable.

[0028] The present invention now proposes to correct the height profile at the edge or adjust it to an adjacent blade ring segment, so that a wavy height profile is established on at least one annular space delimiting surface of a blade ring segment. This is illustrated in FIG. 5. In the specific embodiment shown here, the pressure-side annular space delimiting surface 6 of blade ring segment 2 is designed with a wavy shape, whereas the adjacent annular space delimiting surface 5 is designed to be smooth on the intake side of blade ring segment 1. The wavy shape of annular space delimiting surface 6 is adapted to the edge, so that a peak in the height profile is formed in the area of the protruding edge, i.e., in the area of protrusions 15, whereas valleys in the topography of the wavy height profile of annular space delimiting surface 6 are formed in the area of recesses 16. The wavy height profile of annular space delimiting surface 6 continues in accordance with the linear movement of the electrode and has an extent in the circumferential direction of the blade ring in the present specific embodiment, for example.

[0029] The amplitude of the wavy height profile depends on the radius of the blade ring, the number of blade ring segments, the shape angle and the shape inclination of the shroud and the Z shape of the end area of the shroud. For example, the smaller the radius of the blade ring or the smaller the number of blade ring segments, the more pronounced should be the design of the wavy height profile. The order of magnitude of the amplitude of a corresponding wavy height profile is in the range of 0.2 mm to 1 mm, preferably 0.4 mm to 0.8 mm or 0.5 mm to 0.6 mm with a blade ring diameter in the range of 400 mm to 450 mm and the number of blade ring segments being in the range of 75 to 80.

[0030] Although the present invention has been described in detail on the basis of the exemplary embodiment, it is self-evident to those skilled in the art that the present invention is not limited to this exemplary embodiment. Instead, modifications are possible in that individual features may be omitted or different combinations of features may be used without departing from the extent of protection of the accompanying claims. The present disclosure includes in particular all combinations of all individual features presented here.