U.S. patent application number 15/299005 was filed with the patent office on 2017-02-09 for method for machining a workpiece having an irregular edge.
The applicant listed for this patent is MTU Aero Engines AG. Invention is credited to Christian Bichlmaier, Martin Pernleitner, Carsten Zscherp.
Application Number | 20170036284 15/299005 |
Document ID | / |
Family ID | 45841336 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170036284 |
Kind Code |
A1 |
Pernleitner; Martin ; et
al. |
February 9, 2017 |
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.
Inventors: |
Pernleitner; Martin;
(Dachau, DE) ; Bichlmaier; Christian;
(Greifenberg, DE) ; Zscherp; Carsten;
(Groebenzell, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MTU Aero Engines AG |
Muenchen |
|
DE |
|
|
Family ID: |
45841336 |
Appl. No.: |
15/299005 |
Filed: |
October 20, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13804217 |
Mar 14, 2013 |
9500082 |
|
|
15299005 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01D 5/225 20130101;
F01D 5/143 20130101; F05D 2230/10 20130101; F05D 2220/323 20130101;
F05B 2230/101 20130101; Y02T 50/673 20130101; F01D 5/02 20130101;
Y02T 50/60 20130101; B23H 9/10 20130101; F01D 25/28 20130101; C25F
3/00 20130101; F05D 2230/11 20130101; B23H 3/00 20130101 |
International
Class: |
B23H 9/10 20060101
B23H009/10; F01D 5/14 20060101 F01D005/14; C25F 3/00 20060101
C25F003/00; F01D 5/22 20060101 F01D005/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2012 |
EP |
12159601.9 |
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
[0001] This is a Divisional of U.S. patent application Ser. No.
13/804,217, filed Mar. 14, 2013 and claims the benefit of European
Patent Application EP 12159601.9, filed Mar. 15, 2012, both
applications are hereby incorporated by reference herein.
[0002] The present invention relates to a method for machining a
workpiece, in which an electrode is situated at a distance from the
workpiece to be machined and is 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, and the electrode is moved at least
partially with the electrode surface parallel to the surface to be
machined, so that, during the approach to the workpiece, areas of
the workpiece having an irregular edge occur as a result of being
machined at a different intensity. Furthermore, the present
invention relates to blade ring segments for a blade ring of a
turbomachine and a corresponding blade ring, the blade ring
segments being manufactured with the aid of the method defined
above.
BACKGROUND
[0003] For turbomachines such as gas turbines or aircraft engines,
blade rings may be used in which a plurality of blade ring segments
is assembled, each having at least one blade and an inner shroud
and/or an outer shroud to form a blade ring. The blade profiles of
the individual blade ring segments define an annular space between
them through which the working gas flows, the annular space being
delimited by the shrouds, and the shrouds have corresponding
annular space delimiting surfaces.
[0004] Such blade ring segments are manufactured by casting or
forging according to the prior art, forging being necessary to
increase the strength when using newer and lighter materials in
particular, e.g., TiAl materials. Blade ring segments manufactured
accordingly must be remachined mechanically to achieve the desired
surface shape by using electrochemical machining methods, for
example, in which electrochemical material removal from the
workpiece surface to be machined is achieved with the aid of
working electrodes and suitable electrolytes. During
electrochemical machining, the working electrode is brought in a
linear movement close to the surface of the workpiece to be
machined, so that a corresponding material removal takes place due
to the potential set between the working electrode and the
workpiece surface to be machined. Due to the linear movement of the
electrode in the direction of the workpiece surface to be machined
during the machining, the material removal varies, depending on the
distance from the surface to be machined and the duration of the
machining. Accordingly, due to a predefined path of movement of the
electrode and the geometry of the blade ring segment, a height
profile may develop along the end edge of shrouds of the blade ring
segment, in particular in the case of end areas of outer shrouds,
which are designed in a Z shape and are used for a form-locking
connection of adjacent blade ring segments when the end edge of the
shroud is situated at various distances from the electrode for
different lengths of time. Due to the electrochemical machining of
the shroud while the electrode is being moved over the Z-shaped end
of the shroud, there is thus removal of different amounts of
material along the Z-shaped edge, so that in the case of adjacent
blade ring segments, steps appear between the annular space
delimiting surface, which results in a negative influence on the
flow conditions in the annular space.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide a method
for machining a workpiece, while avoiding the corresponding
problems, such as those defined in the related art, and this method
is to be used in particular for machining blade ring segments for
blade rings of turbomachines. In addition, blade ring segments
and/or blade rings are to be provided in which the problem of steps
between adjacent annular space delimiting surfaces on shrouds is
avoided.
[0006] The present invention provides that during machining of a
workpiece, for example, a blade ring segment using at least one
electrode which is situated at a distance from the workpiece to be
machined and is moved linearly in the direction of the workpiece to
be machined, a difference in material removal and a corresponding
development of an edge which is irregular with respect to the
height profile may be counteracted in that, in the area of the
machining of the edge at a different intensity, the surface to be
machined is formed with a correspondingly counter-directional
height profile according to the course of the edge. In other words,
if the electrode moves with at least a fraction of its movement,
i.e., with a subvector of the movement vector parallel to the
surface of the workpiece to be machined, and if a section of the
end of the surface of the workpiece to be machined is aligned
obliquely to a guide edge of the machining electrode leading in the
direction of movement of the electrode, then the case will occur
that the electrode reaches certain areas of the workpiece surface
to be machined sooner and machines them for a longer time or at a
smaller distance than other areas, resulting in the material being
removed at a different intensity there. This may be compensated by
providing a height profile for the surface to be machined, so that
the edge is corrected with respect to the height profile.
[0007] Accordingly, an elevated profile and therefore less material
removal may be provided in areas which interact with the electrode
for a longer period of time or starting at an earlier point in
time, whereas in areas which interact with the electrode later or
for a shorter period of time, there is greater material removal or
a corresponding valley or a reduced height profile.
[0008] This method may be used with all methods in which electrodes
are moved with respect to a workpiece surface to be machined
accordingly, such as, for example, the electrochemical machining
(ECM), erosion, electrodischarge machining (EDM) or electrochemical
discharge machining (ECDM).
[0009] The method according to the present invention may be used in
particular for machining blade ring segments of a blade ring having
an outer shroud and/or an inner shroud, to adapt the edges of the
shrouds of adjacent blade ring segments to one another.
[0010] This method may thus be used for mutual adaptation of the
Z-shaped edges of adjacent shrouds of blade ring segments; a wavy
topography may be provided according to the Z profile of one end of
a shroud or a wavy height profile may be provided on the annular
space delimiting surface of the shroud.
[0011] In the case of a direction of movement of the electrode
across the end of the shroud having the Z-shaped profile, the wavy
height profile of the annular space delimiting surface may be
designed in such a way that peaks are provided at the protrusions
of the Z profile and valleys are provided at the recessed areas of
the Z profile. These peaks and valleys of the wavy height profile
may be continued according to the direction of machining with which
the electrode is moved with respect to the annular space delimiting
surface, namely, for example, in the circumferential direction of
the blade ring, for which the blade ring segment is provided when
the direction of movement of the electrode is in this
direction.
[0012] The wavy height profile may be provided in particular on the
pressure-side annular space delimiting surface since the effects of
the wave shape on the flow conditions have less impact there.
[0013] A corresponding blade ring having blade ring segments which
have wavy annular space delimiting surfaces may be designed in such
a way that straight planar annular space delimiting surfaces are
adjacent to wavy annular space delimiting surfaces in alternation,
the wavy annular space delimiting surfaces having an adaptation of
the edge to the adjacent blade ring segment. Consequently, blade
ring segments having a wavy annular space delimiting surface and a
smooth planar annular space delimiting surface may be situated in
alternation. In the same way, it is conceivable to provide blade
ring segments having two wavy annular space delimiting surfaces in
alternation, while the adjacent blade ring segment does not have
any wavy annular space delimiting surface but instead has only
smooth planar annular space delimiting surfaces. A smooth planar
annular space delimiting surface is understood to be a surface
which does not have any wavy adaptation of the surface topography
according to the present invention.
[0014] The different configurations of the blade ring segments may
be combined with one another accordingly, so that, for example,
blade ring segments, each having a wavy annular space delimiting
surface, are initially situated side by side and then there is a
transition to an alternating configuration of blade segments having
either two wavy annular space delimiting surfaces or having no wavy
annular space delimiting surface.
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.degree. 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.
* * * * *