U.S. patent application number 13/861955 was filed with the patent office on 2014-05-15 for method and device for finishing a workpiece surface.
This patent application is currently assigned to Supfina Grieshaber GmbH & Co. KG. The applicant listed for this patent is Supfina Grieshaber GmbH & Co. KG. Invention is credited to Oliver Hildebrandt.
Application Number | 20140134925 13/861955 |
Document ID | / |
Family ID | 45999667 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140134925 |
Kind Code |
A1 |
Hildebrandt; Oliver |
May 15, 2014 |
METHOD AND DEVICE FOR FINISHING A WORKPIECE SURFACE
Abstract
A method for finish-machining a workpiece surface includes
moving the workpiece surface relative to an active area of the
finishing tool in a rotation direction about a workpiece axis, and
superimposing on the relative movement of the workpiece surface and
the active area an additional oscillatory movement with an
oscillation frequency lower than 20 kHz in a direction
perpendicular to the workpiece surface.
Inventors: |
Hildebrandt; Oliver;
(Hornberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Supfina Grieshaber GmbH & Co. KG |
Wolfach |
|
DE |
|
|
Assignee: |
Supfina Grieshaber GmbH & Co.
KG
Wolfach
DE
|
Family ID: |
45999667 |
Appl. No.: |
13/861955 |
Filed: |
April 12, 2013 |
Current U.S.
Class: |
451/28 ;
451/64 |
Current CPC
Class: |
B24B 21/02 20130101;
B24B 1/04 20130101; B24B 5/42 20130101; B24B 35/00 20130101 |
Class at
Publication: |
451/28 ;
451/64 |
International
Class: |
B24B 1/04 20060101
B24B001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2012 |
EP |
12164131.0 |
Claims
1. A method for finish-machining a workpiece surface with a
finishing tool, comprising: moving the workpiece surface relative
to an active area of the finishing tool in a rotation direction
about a workpiece axis, and superimposing on the relative movement
of the workpiece surface and the active area an additional
oscillatory movement with an oscillation frequency lower than 20
kHz in a direction perpendicular to the workpiece surface.
2. The method of claim 1, wherein the oscillation frequency of the
additional movement is lower than 16 kHz.
3. The method of claim 1, wherein the oscillation frequency of the
additional movement is lower than 1 kHz.
4. The method of claim 1, wherein the oscillation frequency of the
additional movement is greater than 50 Hz.
5. The method of claim 1, wherein the oscillation frequency of the
additional movement is greater than 100 Hz.
6. The method of claim 1, wherein an amplitude of the additional
movement is at least about 5 micrometer and at most about 200
micrometer.
7. The method of claim 1, wherein the workpiece surface and the
active area are not moved relative to each other in a direction
parallel to the workpiece axis.
8. The method of claim 1, wherein the workpiece surface and the
active area are moved back and forth in a direction parallel to the
workpiece axis.
9. The method of claim 8, wherein the oscillation frequency of the
back-and-forth movement in the direction parallel to the workpiece
axis is at least about 1 Hz.
10. The method of claim 8, wherein the oscillation frequency of the
back-and-forth movement in the direction parallel to the workpiece
axis is at most about 50 Hz.
11. The method of claim 8, wherein the oscillation frequency of the
additional oscillatory movement is greater by a factor of 1 to 1000
than an oscillation frequency of the back-and-forth movement in the
direction parallel to the workpiece axis.
12. The method of claim 8, wherein the oscillation frequency of the
additional oscillatory movement is greater by a factor of 6 to 40
than an oscillation frequency of the back-and-forth movement in the
direction parallel to the workpiece axis.
13. The method of claim 8, wherein an amplitude of the
back-and-forth movement in the direction parallel to the workpiece
axis is between about 0.1 mm and about 3 mm.
14. The method of claim 8, wherein an amplitude of the additional
movement is smaller by a factor of 5 to 600 than an amplitude the
back-and-forth movement in the direction parallel to the workpiece
axis.
15. The method of claim 8, wherein an amplitude of the additional
movement is smaller by a factor of 10 to 20 than an amplitude the
back-and-forth movement in the direction parallel to the workpiece
axis.
16. A device for finish-machining a workpiece surface, comprising:
a finishing tool comprising an active area, a rotary drive for
generating a rotary movement of the workpiece surface relative to
the active area of the finishing tool in a rotation direction about
a workpiece axis, and an additional drive constructed to generate
an additional oscillatory movement with an oscillation frequency
lower than 20 kHz in a direction perpendicular to the workpiece
surface, wherein the additional oscillatory movement is
superimposed on the relative movement of the workpiece surface and
the active area.
17. The device of claim 16, wherein the additional drive comprises
a piezoelectric actuator.
18. The device of claim 17, wherein the piezoelectric actuator is
aligned along an additional movement axis and comprises
piezoelectric elements which are stacked along the additional
movement axis.
19. The device of claim 16, wherein the finishing tool is
constructed as a finishing stone.
20. The device of claim 16, wherein the finishing tool is
constructed as a finishing belt, the dice further comprising a
pressing shell for pressing the finishing belt against the
workpiece surface, wherein the pressing shell has a pressing
surface operating transversely to a running direction of the
finishing belt, wherein at least a portion of the pressing surface
is formed by a pressing section that is movable relative to a
stationary shell section along an additional movement axis.
21. The device of claim 20, wherein the pressing section and the
stationary shell section are integrally formed with each other and
interconnected via a connecting portion, wherein the connecting
portion is constructed such that driving forces of the additional
drive cause the pressing section to move along the additional
movement axis.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the priority of European Patent
Application, Serial No. 12 164 131.0-2302, filed Apr. 13, 2012,
pursuant to 35 U.S.C. 119(a)-(d), the content of which is
incorporated herein by reference in its entirety as if fully set
forth herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method for finishing a
workpiece surface with a finishing tool.
[0003] The following discussion of related art is provided to
assist the reader in understanding the advantages of the invention,
and is not to be construed as an admission that this related art is
prior art to this invention.
[0004] A hybrid technology is known from the project
"Ultrasound-assisted Superfinishing of cylindrical precision
components (SoFi--Sonic Finish)" wherein a conventional finishing
process is combined with an ultrasound machining for precision
machining a workpiece. The conventional finishing process includes
a rotational movement of the workpiece relative to the finishing
tool and a low-frequency, oscillatory relative movement of the
workpiece and finishing tool in a direction parallel to a rotation
axis of the workpiece. The ultrasound machining includes a radial
movement of the finishing tool relative to workpiece, which
oscillates at the ultrasound frequency.
[0005] It has been found that the aforedescribed hybrid technology
is problematic in practice. For example, the loads operating on the
finishing tools are so high that the tools need to be replaced
after a relatively short time. Furthermore, a high noise level is
produced, requiring complicated sound abatement measures. Moreover,
aerosols may be produced by nebulization of coolants or lubricants,
which in the worst case may cause an explosion risk. Finally, a
complicated drive with a sonotrode is required to produce a
movement of the finishing tool at ultrasound frequencies, which can
be designed only for a particular ultrasound frequency and for a
certain mass of the finishing tool.
[0006] It would therefore be desirable and advantageous to obviate
prior art shortcomings and to provide an improved method and device
for finish-machining a workpiece surface.
SUMMARY OF THE INVENTION
[0007] According to one aspect of the present invention, a method
for finish-machining a workpiece surface with a finishing tool
includes moving the workpiece surface relative to an active area of
the finishing tool in a rotation direction about a workpiece axis,
and superimposing on the relative movement of the workpiece surface
and the active area an additional oscillatory movement with an
oscillation frequency lower than 20 kHz in a direction
perpendicular to the workpiece surface.
[0008] With the method according to the invention, the active area
of the finishing tool is moved periodically in and opposite to the
direction of the workpiece surface to be machined. This results in
"hammering" processing of the workpiece surface and contact between
the active area and the workpiece surface with alternatingly a
higher pressing force and with a lower pressing force, commensurate
with the oscillation frequency (wherein the active area can also
"lift" off the workpiece surface.)
[0009] The movement of the active area of the finishing tool occurs
along an additional movement axis, which is oriented perpendicular
relative to the workpiece surface to be machined. The oscillation
frequency of the additional movement is lower than ultrasound. It
is lower than 20 kHz, preferably lower than 16 kHz and in
particular lower than 1 kHz.
[0010] The "hammering" processing of the workpiece surface is
advantageous in that the active constituents of the active area,
such as the cutting grains, penetrate deeper into the material of
the workpiece than would otherwise be the case with conventional
finish-machining. This supports the formation of chips and
increases the removal rate compared to conventional
finish-machining.
[0011] The "hammering" processing of the workpiece surface has the
additional advantage that the active ingredients of the active
area, i.e. the cutting grains, are briefly exposed to an increased
pressure load. This supports the formation of chips and thus
produces a self-sharpening effect, which in turn contributes to an
increase in the material removal rate.
[0012] The additional movement according to the invention is also
accompanied by a periodic interruption of the cut or of the chip
formation and thus causes an interrupted ground structure. In
classical finish-machining, continuous, groove-like depressions are
produced, which carry away coolants or lubricants used during
machining of the workpiece surface.
[0013] Due to the interruption of the ground structure, a larger
proportion of coolants or lubricants remain on the workpiece
surface to be machined. This allows the active area of the
finishing tool to better penetrate into the workpiece surface to be
machined. Periodically lifting the finishing tool, i.e.
periodically separating the active area of the finishing tool from
the workpiece surface, allows the coolant to more easily enter the
contact zone and removed material to be better washed out and
transported away. The kinetic energy introduced into the finishing
tool during the additional movement also promotes cleaning of the
finishing tool from abraded material embedded in or on the active
area. Overall, the cutting behavior of the active ingredients of
the finishing tool is significantly improved.
[0014] Moreover, the periodic pressing contact of the active area
with the workpiece surface causes an increase in the residual
compressive stresses in the near-surface portions of the workpiece,
so that the fatigue strength of the workpiece (for example, of a
rolling bearing part or crankshaft) can be increased.
[0015] The increase in the residual compressive stress in the
near-surface portions of the workpiece caused by the additional
machining of the workpiece causes a reduction in the notch effect
and a reduction in the tensile stress which occur in Hertzian
pressing. This also increases the service life of the workpieces
machined according to the present invention.
[0016] Lastly, the above-mentioned interruption of the ground
structure can advantageously reduce a drainage effect in a finished
machined workpiece significantly. This is particularly advantageous
when the workpiece is a bearing ring. Rolling of a rolling element
on the bearing surface of the bearing ring then will no longer
cause a lubricant to be displaced. Corresponding benefits are
attained for hydrodynamic slide bearings, where a better retention
of the lubricant (in particular oil) is ensured.
[0017] According to an advantageous feature of the present
invention, the oscillation frequency of the additional movement may
be higher than about 50 Hz, for example higher than about 100 Hz.
Advantageously, an oscillation frequency range of between about 100
Hz and about 1 kHz may be employed, for example an oscillation
frequency of 200 Hz. This refers particularly to the frequency of
the movement of the active area of the finishing tool along the
axis of the additional movement. The movements in the
aforementioned frequency range can be readily controlled; at the
same time, the advantages described above with reference to the
"hammering" processing of the workpiece surface can be
achieved.
[0018] An amplitude of the additional movement may, for example, be
only 0.1 to 5 micrometers. However, in order to achieve a
significant increase of a material removal rate, it is proposed
that an amplitude of the additional movement (corresponding to half
the stroke of the active area) is at least about 5 micrometers.
This allows, for a typical grain size of the finishing material
(about 10 micrometers), the entire extent of a grain to penetrate
into the material of the workpiece.
[0019] According to another advantageous feature of the present
invention, an amplitude of the additional movement may be, for
example, 0.2 mm to several millimeters. For optimal controllability
of the finishing process, an amplitude of the additional movement
may advantageously be at most about 200 micrometers (a favorable
amplitude value is 50 micrometers). This can also prevent the macro
geometry of the workpiece to be machined from deteriorating when
using the inherently advantageous effects of the inventive method.
An advantageous value for the amplitude of the additional movement
is 100 micrometers.
[0020] According to another advantageous feature of the present
invention, the workpiece surface and the active area not move
relative to each other in a direction parallel to the axis of the
workpiece. Here, a relative movement in a direction parallel to the
workpiece axis used in a conventional finishing process is thus
expressly eliminated. The relative movement between the workpiece
surface and the active area is then based exclusively on the
rotation of the workpiece surface about the workpiece axis and on
the movement of the active area of the finishing tool in a
direction perpendicular to the workpiece surface. Advantageously, a
comparatively complex drive for the oscillatory movement of the
finishing tool and/or of the workpiece in a direction parallel to
the workpiece axis may then be omitted, while still attaining a
sufficiently high material removal rate for a variety of
applications.
[0021] In an alternative embodiment of the invention, the workpiece
surface and the active area may move back and forth relative to
each other in a direction parallel to the workpiece axis. A
conventional oscillatory drive is provided in this case. Such
oscillatory drive is advantageous for realizing particularly high
material removal rates.
[0022] To achieve a high material removal rate and to introduce
into the workpiece a basic structure and increased residual
compressive stress, a workpiece surface may advantageously also be
initially machined using the inventive method (that is, with a
rotary movement of the workpiece and with an additional movement
perpendicular to the workpiece surface and possibly additionally
with an oscillatory movement parallel to the workpiece axis).
Subsequent to this processing operation, the workpiece can then be
further processed with a conventional finishing process (i.e., with
rotary movement of the workpiece and without an additional movement
perpendicular to the workpiece surface and with an oscillatory
movement parallel to the workpiece axis) so as to produce a
particularly fine workpiece surface.
[0023] When an aforementioned oscillatory drive for generating a
relative movement in a direction parallel to the workpiece axis
direction is provided, the oscillation frequency of the
back-and-forth movement in the direction parallel to the workpiece
axis direction may advantageously be at least about 1 Hz.
[0024] When an aforementioned oscillatory drive for generating a
relative movement in a direction parallel to the workpiece axis
direction is provided, the oscillation frequency of the
back-and-forth movement in the direction parallel to the workpiece
axis direction may advantageously be at least about 50 Hz.
[0025] According to another advantageous feature of the present
invention, advantageous oscillation frequencies for a finishing
tool in the form of a finishing belt (in the direction parallel to
the workpiece axis) may be between 1 and 21.67 Hz, for example 5
Hz.
[0026] Advantageous oscillation frequencies for a finishing tool in
the form of a finishing stone (in the direction parallel to the
workpiece axis) may be between 5 and 50 Hz, preferably 33.33
Hz.
[0027] Advantageously, the oscillation frequency of the additional
movement may be greater by a factor between 1 and 1000, in
particular by a factor between 6 and 40, than the oscillation
frequency of the back-and-forth movement in direction parallel to
the workpiece axis. These frequency ratios produce an optimal
combination of a high material removal rate, an increase in the
residual compressive stress in near-surface layers of the workpiece
and a reduced drainage effect compared to a conventional
cross-hatch structure.
[0028] According to another advantageous feature of the present
invention, an amplitude of a back-and-forth movement in the
direction parallel to the workpiece axis (corresponding to one half
of the total stroke) may be between about 0.1 mm and about 3 mm.
Such amplitude range contributes to an increased material removal
rate while maintaining a high dimensional stability of the
workpiece to be machined. A preferred amplitude for a finishing
tool in the form of a finishing belt is 0.5 mm; for a finishing
tool in the form of finishing stone at least 0.5 mm, preferably 1
mm.
[0029] According to another advantageous feature of the present
invention, the amplitude of the additional movement may be smaller
by a factor of 5 to 600, in particular by a factor of 10 to 20,
than the amplitude of the back-and-forth movement in the direction
parallel to the workpiece axis. These amplitude ratios result in an
optimum combination of a high material removal rate, an increase in
the residual compressive stress of near-surface workpiece layers
and reduced drainage effect compared to a conventional cross-hatch
structure.
[0030] Advantageously, the amplitude of the additional movement may
be smaller by a factor of 1 to 5 than the amplitude of the
back-and-forth movement in the direction parallel to the workpiece
axis. These factors are, for example, particularly well suited when
a laterally delimited workpiece surface that is only slightly wider
than the finishing tool (for example the large end bearing of a
crankshaft) needs to be machined. In extreme cases, even factors
from 0.5 to 1 (ratio of the amplitude of the additional movement to
the amplitude of the back-and-forth movement in the direction
parallel to the workpiece axis) or even smaller factors may be
suitable.
[0031] According to another aspect of the invention, a device for
finish-machining a workpiece surface includes a finishing tool
having an active area, a rotary drive for generating a rotary
movement of the workpiece surface relative to the active area of
the finishing tool in a rotation direction about a workpiece axis,
and an additional drive constructed to generate an additional
oscillatory movement with an oscillation frequency lower than 20
kHz in a direction perpendicular to the workpiece surface, wherein
the additional oscillatory movement is superimposed on the relative
movement of the workpiece surface and the active area.
[0032] The device according to the invention shares the advantages
described above in conjunction with the inventive method.
[0033] According to an advantageous feature of the present
invention, the additional drive includes a piezoelectric actuator.
Such an actuator is particularly suitable for generating an
oscillatory movement of a working surface of a finishing tool.
[0034] It will be understood that other types of actuators may be
used instead of a piezoelectric actuator, for example, hydraulic,
pneumatic or electric drives as well as drives based on
magnetostriction.
[0035] When using a piezoelectric actuator, the piezoelectric
actuator may advantageously be aligned along an additional movement
axis for a simple construction, and more particularly piezoelectric
elements stacked along the additional movement axis may be
employed.
[0036] Advantageously, the piezoelectric actuator and finishing
tool may be directly coupled with one another for movement, so that
the movement of the piezoelectric actuator along the additional
movement axis is identical to a movement of the active area along
the additional movement axis. This means that an expansion of the
piezoelectric elements in a direction parallel to the additional
movement axis is directly converted into a corresponding movement
of the active area of the finishing tool, thereby producing a "1:1
conversion" without employing a gear having a step-up or step-down
gear ratio.
[0037] Alternatively, other gear devices, such as levers, may be
provided, which convert a movement of the piezoelectric actuator
into a (preferably greater) movement of the active area of the
finishing tool.
[0038] For a particularly simple transfer of the movement of the
piezoelectric actuator to the finishing tool, it is proposed that a
drive surface of the piezoelectric actuator and the finishing tool
are rigidly connected with each other.
[0039] Alternatively, the piezo actuator may have a force
transmitting surface for transmitting a pressing force generated by
the piezoelectric actuator to a force-receiving surface of the
finishing tool. This enables a "tappet-like" transmission of forces
direction towards the workpiece. A movement of the finishing tool
in the opposite direction can, for example, be generated by an
elastic return deformation of a holder of the finishing tool or by
additional springs.
[0040] Within the context of the invention, the finishing tool may
be constructed as a finishing stone.
[0041] Within the context of the invention, the finishing tool may
be constructed as a finishing belt. In this case, a pressing shell
is preferable used to press the finishing belt against the
workpiece surface, wherein the pressing shell has a pressing
surface acting transversely to the running direction of the
finishing belt, wherein at least a portion of the pressing surface
is formed by a pressing section, which is movable relatively to a
stationary shell section along an additional movement axis. Such
pressing shell enables defined guidance and positioning of
finishing belt, and simultaneously allows a workpiece surface to be
machined by "hammering" in the region of the pressing section.
[0042] According to another advantageous feature of the present
invention, the pressing section and the stationary shell section
may be integrally formed as one piece and interconnected via a
connecting section, wherein the connecting section is formed so
that driving forces of the additional drive cause the pressing
section to move along the additional movement axis. In this way,
the surfaces of the pressing section and of the stationary shell
section facing the workpiece may be produced in one operation and
thus precisely geometrically matched. Simultaneously, the pressing
section and the stationary shell section can be positioned relative
to each other with high accuracy, since a relative movement between
these sections occurs only through an (elastic) deformation of the
connecting section, starting from an undeformed initial
position.
[0043] According to another advantageous feature of the present
invention, an oscillatory drive may be provided for generating a
relative back-and-forth movement of the workpiece surface and the
active area in a direction parallel to the workpiece axis.
[0044] In an alternative embodiment of the invention, an
oscillatory drive for generating a relative back-and-forth movement
of the workpiece surface and the active area in a direction
parallel to the workpiece axis is explicitly not provided.
BRIEF DESCRIPTION OF THE DRAWING
[0045] Other features and advantages of the present invention will
be more readily apparent upon reading the following description of
currently preferred exemplified embodiments of the invention with
reference to the accompanying drawing, in which:
[0046] The drawings show in:
[0047] FIG. 1 a side view of an embodiment of a device according to
the present invention for finish-machining a workpiece surface;
[0048] FIG. 2 an enlarged detail marked in FIG. 1 with II;
[0049] FIG. 3 a front view of the detail of FIG. 2;
[0050] FIG. 4 a detail corresponding to FIG. 2 of another
embodiment of a device for finish-machining a workpiece
surface;
[0051] FIG. 5 a view of the detail of FIG. 4 corresponding to the
view of FIG. 3;
[0052] FIG. 6 a schematic view of a workpiece surface produced with
a conventional finishing process;
[0053] FIG. 7 a schematic view of a workpiece surface produced with
a finishing process according to the present invention;
[0054] FIG. 8 a perspective view of another embodiment of a device
for finish-machining a workpiece surface;
[0055] FIG. 9 a perspective view of another embodiment of a device
for finish-machining a workpiece surface;
[0056] FIG. 10 side view of a part of the device designated FIGS. 8
and 9 with VI, VII;
[0057] FIG. 11 a detail marked in FIG. 10 with XI in an enlarged
scale;
[0058] FIGS. 12-16 side views of embodiments of pressing shells for
use in devices according to FIGS. 8 to 11;
[0059] FIG. 17 a side view of an embodiment of a device for
finish-machining a workpiece surface;
[0060] FIG. 18 a plan view of another embodiment of a device for
finish-machining a workpiece surface;
[0061] FIG. 19 a side view of the device according to FIG. 18;
and
[0062] FIG. 20 a schematic view of a workpiece surface produced
with the devices according to FIGS. 17 to 19.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0063] Throughout all the figures, same or corresponding elements
may generally be indicated by same reference numerals. These
depicted embodiments are to be understood as illustrative of the
invention and not as limiting in any way. It should also be
understood that the figures are not necessarily to scale and that
the embodiments are sometimes illustrated by graphic symbols,
phantom lines, diagrammatic representations and fragmentary views.
In certain instances, details which are not necessary for an
understanding of the present invention or which render other
details difficult to perceive may have been omitted.
[0064] Turning now to the drawing, and in particular to FIG. 1,
there is shown a device for finish-machining a workpiece surface,
with the device being designated by the reference numeral 10. The
device 10 includes a machine frame 12 for placing the device 10 on
a supporting surface 14. The frame has a workpiece holder 16 for
receiving a workpiece 18 to be finish-machined.
[0065] The workpiece 18 has a central workpiece axis 20. The
workpiece 18 is, for example, a bearing ring.
[0066] The device 10 includes a rotary drive 22 for rotating the
workpiece 18 held on the workpiece receptacle 16 about the
workpiece axis 20. The workpiece axis 20 extends coaxially with the
rotation axis of the rotary drive 22.
[0067] In particular, the workpiece 18 has a workpiece surface 24,
which is finish-machined with a finishing tool 26 as described
below, extending concentrically with the workpiece axis 20.
[0068] The finishing tool 26 is, for example, a finishing stone 28.
The finishing tool 26 is supported on a finishing tool holder 30
and can be driven in an oscillatory fashion relative to the
finishing tool holder 30 along an additional movement axis 32 (see
FIG. 2). As a result, an active area 34 of the finishing tool 26
facing the workpiece 24 is moved towards and away from the
workpiece surface 24.
[0069] For generating the movement of the finishing tool 26, the
device 10 includes an additional drive 36, in particular in the
form of a piezoelectric actuator 38. The additional drive 36
generates an oscillatory movement of the active area 34 along the
additional movement axis 32.
[0070] For example, a transmission member 40 is provided, which is
connected to a clamping device 42, for coupling the movement of the
additional drive 36 and the finishing tool 26.
[0071] The clamping device 42 includes, for example, a sleeve 44,
which is set in motion by the transmission member 40 of the
additional drive 36. The sleeve 44 is slideably received in a
housing 46 of the finishing tool holder 30 for movement along the
additional movement axis 32.
[0072] The clamping device 42 further includes a clamping element
48, which is connected to the sleeve 44 by a screw connection,
allowing the finishing stone 28 to be clamped with the clamping
element 48 and sleeve 44.
[0073] The finishing tool holder 30 can be positioned with a
positioning device 50 relative to the frame 12 along a positioning
axis 52 (see FIG. 1). The positioning axis 52 is parallel to the
workpiece axis 20. The positioning device 50 includes a holder 54
which is movable on the frame 12 along a tool axis 53 on which a
carriage 56 is supported for movement along the positioning axis
52.
[0074] The carriage 56 and the finishing tool holder 30 are
connected to each other in such a way that the finishing tool
holder 30 can be positioned relative to the carriage 56 in a
direction perpendicular to the workpiece axis 20. To this end, a
finishing tool guide 57 is provided, with which the finishing tool
holder 30 can be positioned parallel to the tool axis 59. This
allows compensation of the finishing tool 26 for wear and
simplifies handling of the finishing tool 26 in setup or tool
change operations.
[0075] The carriage 56 and the finishing tool holder 30 can be
connected to each other so that the finishing tool holder 30 is
unable to move relative to the carriage 56 in a direction parallel
to the workpiece axis 20.
[0076] Alternatively, the device 10 includes an oscillatory drive
58 for generating a back-and-forth movement of the tool holder 30
in a direction parallel to the workpiece axis 20.
[0077] The oscillatory drive 58 has, for example, a conventional
eccentric drive 60 which will not be explained in detail and which
is driven for rotation about an eccentric axis 62 and generates an
oscillatory movement of a driven element 66 designated by a
double-headed arrow 64. The driven element 66 is fixedly connected
to the finishing tool holder 30, allowing an oscillatory movement
of the driven element 66 to be transmitted to the finishing tool
holder 30 and thus to the finishing tool 26.
[0078] As an alternative to a (hydrodynamic or hydrostatic) sliding
bearing of the sleeve 44 in the housing 46 shown in FIGS. 2 and 3,
the clamping device 42 may also be supported in the housing 46 by
at least one linear rolling guide.
[0079] The clamping device 42 may also be supported for movement
relative to the housing 46 of the finishing tool holder 30 by at
least one membrane element 68 (see FIGS. 4 and 5). The membrane
element 68 preferably extends in a direction perpendicular to the
additional movement axis 32. The membrane element 68 is preferably
formed as an annular disk, which is connected radially outwardly to
the housing 46 and radially inwardly to the sleeve 44.
[0080] Preferably, two membrane elements 68 are provided, which are
arranged in relation to the additional movement axis 32 on opposite
sides of the sleeve 44.
[0081] When the workpiece 18 is machined in a conventional
finishing process, the active area 34 does not move along the
additional movement axis 32. In the conventional process, a
relative movement between the workpiece surface 24 and active area
34 is composed of a rotation of the workpiece surface 24 about the
workpiece axis 20 and an oscillatory movement 64 of the active area
34 parallel to the workpiece axis 20. This produces a cross-hatch
structure 70 characteristic for a conventional finishing process,
which is schematically shown in FIG. 6. The cross-hatch structure
70 includes a plurality of grooves 72 which are continuous and
substantially parallel to each other at least in partial areas,
wherein these grooves 72 intersect with likewise continuous grooves
74. The continuity of the grooves 72 and 74 causes the grooves 72
and 74 to be interconnected at intersections 76 for fluid flow.
This produces in a conventional finishing process an increased
drainage effect, wherein coolants or lubricants are prematurely
removed and must therefore be continuously replenished in
comparatively large quantities.
[0082] When another movement, namely the additional movement of the
finishing tool 26 along the additional movement axis 32, is
superimposed on the relative movement between the workpiece 18 and
finishing tool 26 described above with reference to FIG. 6, a
surface structure 78 shown in FIG. 7 is formed.
[0083] The surface structure 78 also includes grooves 80 and 82
extending at an angle relative to one another. However, the grooves
80 and 82 are not continuous, but have breaks 84, forming mutually
separated grooved portions 86. The grooved portions 86 serve as a
storage space for coolants and lubricants, which in contrast to the
cross-hatch structure 70 illustrated in to FIG. 6 is not
prematurely removed. This not only improves the cooling and
lubrication of the finishing tool 26, but in particular also
reduces the drainage effect of the workpiece surface 24 when using
the workpiece 18.
[0084] FIGS. 8 to 11 show additional embodiments of devices 10 for
finish-machining a workpiece surface 24. These devices 10 include a
finishing tool 26 in the form of a finishing belt 88 (see FIG.
10).
[0085] The device 10 of FIG. 8 includes a frame 12 that can be
placed on a supporting surface 14. The frame 12 is used for
arranging an oscillatory drive designated overall with the
reference numeral 58 and capable of generating an oscillatory
movement of a workpiece holder 16 and a workpiece 18 designated by
a double-headed arrow 64. This oscillatory movement is parallel to
a workpiece axis 20 of the workpiece 18.
[0086] The workpiece holder 16 is part of the rotary drive 22, with
which the workpiece 18 can be driven to rotate about the workpiece
axis 20. The rotary drive 22 includes a headstock 90 and a
tailstock 92. In the embodiment illustrated in FIG. 8, the
headstock 90 and the tailstock 92 are mounted on a driven member 66
of the oscillatory drive 58.
[0087] The device 10 shown in FIG. 9 does not include an
oscillatory drive 58. The headstock 90 and the tailstock 92 are
mounted directly on the frame 12 of the device 10.
[0088] The devices 10 illustrated in FIGS. 8 and 9 have an
identical construction except for the aforedescribed difference
(oscillatory drive 58 available or not available). The following
description therefore applies to both the device 10 of FIG. 8 and
the device 10 of FIG. 9.
[0089] The workpiece surface 24 of the workpiece 18 to be machined
is, for example, a large end bearing surface of a crankshaft which
has a radial offset from the workpiece axis 20. This workpiece
surface 24 then moves in a circle about the workpiece axis 20. The
finishing tool 26 must then be able to also follow this movement of
the workpiece surface 24.
[0090] Therefore, a bearing device 94 is provided for supporting
the finishing tool 26 on the frame 12, wherein the bearing device
94 has two degrees of freedom and allows a movement of the
finishing tool 26 in a plane perpendicular to workpiece axis
20.
[0091] The bearing device 94 includes a pivot portion 96, which is
held on a frame part 102 of the frame 12 by a pivot bearing 98 for
pivoting about a pivot axis 100. The pivot axis 100 extends
parallel to the workpiece axis 20.
[0092] The pivot portion 96 is used to arrange at least one linear
guide 104 (see FIG. 10), with which a bearing member 106 is
supported for movement relative to the pivot portion 96 along a
guide axis 108 of the linear guide 104.
[0093] The bearing portion 106 extends substantially in a plane
perpendicular to the workpiece axis 20.
[0094] The bearing member 106 has an opening 108 through which the
pivot bearing 98 passes.
[0095] The bearing member 106 has a bearing portion end 110 facing
the workpiece 18 for arranging a pressing device 112.
[0096] The pressing device 112 includes at least two gripper arms
114. The gripper arms 114 can be pivoted about gripper arm axes 116
relative to the bearing part 106 (see FIG. 10). The gripper arm
axes 116 extend parallel to the pivot axis 100 of the pivot member
96.
[0097] The gripper arms 114 have at their end facing the work piece
18 a unit 118 which will be described in more detail below with
reference to FIG. 11.
[0098] For generating a pressing force, a conventional pressing
drive 119, which will not be described further, is provided which
applies to the units 118 of the gripper arms 114 forces 120 acting
in the direction toward the workpiece 18.
[0099] The units 118 have a holder 122 which is fixedly connected
to the gripper arms 114 and is configured for arranging a clamping
device for the finishing belt 88.
[0100] The device 10 includes an additional drive 36 in the form of
a piezoelectric actuator 38. The piezoelectric actuator 38 includes
a plurality of piezoelectric elements ("stack") which are stacked
consecutively along the additional movement axis 32.
[0101] The additional drive 36 is rigidly connected to a drive
housing 126 with the gripper arms 114. The front side 128 of the
piezoelectric actuator 38 is connected to a force transmitting
element 130, which has a force transmitting surface 132 that
transmits the pressing force produced by the piezoelectric actuator
38 to a force receiving surface 134 of a driven element 136. The
force transmitting surface 132 and the force receiving surface 134
may also be fixedly interconnected, thereby allowing tensile forces
to be transmitted from the piezoelectric actuator 38 to the driven
element 136.
[0102] For pressing the finishing belt 88 against the workpiece
surface 24, the units 118 each include a corresponding pressing
shell 138, which each have a curved pressing surface 140.
[0103] The pressing shells 138 include a stationary shell portion
142, which is, for example, fixedly connected to the gripper arm
114 by a screw connection 144. The stationary shell portion 142 is
used for arranging a pressing section 146, which is movable
relative to the stationary shell portion 142, namely along the
additional movement axis 32.
[0104] The pressing section 146 has a curved surface 148, which
forms a portion of the pressing surface 140 (the other portion of
the pressing surface 140 is formed by the stationary shell portion
142). The pressing section 146 is formed as a single piece with the
stationary shell portion 142 and is connected thereto via at least
one connecting portion 150.
[0105] For example, the connecting portion 150 is formed as a thin
web 152 which extends transversely, in particular perpendicular, to
the additional movement axis 32. The pressing section 146 is fixed
connected to the driven element 136, so that an expansion of the
piezoelectric actuator 38 operates on the force receiving surface
134 via the force transmitting surface 132 and is thus converted by
the driven element 136 directly into a movement of the pressing
section 146 and hence of the curved surface 146.
[0106] Several embodiments of pressing shells 138 will now be
described with reference to FIGS. 12 through 16. The curved surface
148 of the pressing shell 138 of FIG. 11 formed by the pressing
section 146 is comparatively short, as seen in the direction of the
finishing belt 88, so that the curved surface 148 is smaller than
half of the total pressing surface 140.
[0107] In the embodiment of a pressing shell 138 illustrated in
FIG. 12, the pressing section 146 is enlarged, so that the curved
surface 148 formed by the pressing section 146 is greater than half
of the total pressing surface 140.
[0108] The pressing shell 138 shown in FIG. 13 has the special
feature that the connecting portion 150 in the form of a thin web
with a surface 154 also forms a part of the pressing surface 140.
The pressing surface 140 is thus composed of a curved surface 148
formed by the connecting portion 146, at least one surface portion
154 formed by one or more of the connecting portions 152, and
optionally by an additional surface portion 156 formed by the
stationary shell portion 142.
[0109] In an extreme situation, the entire pressing surface 140 may
be formed by the pressing section 146, which is illustrated in FIG.
14.
[0110] In the embodiments of pressing shells 138 shown in FIGS. 15
and 16, the pressing surface 140 is likewise formed entirely by the
curved surface 148 of the pressing section 146. Additionally, the
stationary shell portion 142 has arms 158, which are provided at
their free ends with pressing elements 160, for example in the form
of pressure rollers. The pressing elements 160 are used for support
on the workpiece 18 so that the workpiece surface 24 to be machined
can be accurately positioned relative to the pressing surface
140.
[0111] When the forces 120 are introduced into the workpiece 18 by
way of the pressing elements 160, a region of the workpiece surface
24 to be machined by "hammering" remains unaffected by the forces
120. The forces 120 generated with the pressing drive 119 and the
surface machining forces generated by the piezoelectric actuator 38
can thus be adjusted independently of one another.
[0112] The pressing elements 160 may act substantially in a
direction parallel to the direction of forces 120 (see FIG. 10), as
shown in the embodiment illustrated in FIG. 15.
[0113] Alternatively, the pressing elements 160 may act
substantially in a direction transverse to the direction of forces
120 (see FIG. 10), as shown in the embodiment illustrated in FIG.
16.
[0114] FIGS. 17 to 19 illustrate embodiments of devices 10 for
finish-machining a workpiece surface 24, wherein an additional
movement axis 32 is not perpendicular to a workpiece surface 24,
but instead parallel thereto (see FIG. 17), or tangentially thereto
(see FIG. 18).
[0115] In the device 10 of FIG. 17, an additional movement of the
active area 34 of the finishing tool 26 in a direction parallel to
the workpiece axis 20 is superimposed on a rotational movement of a
workpiece 18 about the workpiece axis 20, as indicated in FIG. 17
by a small double-headed arrow 162. The additional movement 162 is
generated, for example, by a piezoelectric actuator 38, which
imparts an additional oscillatory movement 162 on a finishing stone
holder 30 and hence on a finishing stone 28.
[0116] A conventional oscillatory movement generated by a
conventional oscillatory drive (in indicated FIG. 17 by a larger
double-headed arrow 64) can also be superimposed on the additional
movement 162.
[0117] In the device 10 illustrated in FIGS. 18 and 19, an
additional movement 162 of the active area 34, which is tangential
to the workpiece surface 24, is superimposed on the rotary movement
of the workpiece surface 24 relative to the active area 34 of the
finishing tool 26. For this purpose, an additional drive 36 in the
form of a piezoelectric actuator may be provided, which drives a
finishing stone holder 30 with a movement aligned with the
additional movement axis 32. A conventional oscillatory movement
parallel to the workpiece axis 20 may here also be optionally
provided (see double-headed arrow 64 in FIG. 19).
[0118] In a conventional finishing process known in the prior art,
an active component of the active area 34 of a finishing tool 26,
for example a grain, produces a sinusoidal active line 164
extending around the workpiece axis 20 on the workpiece surface 24,
as shown in FIG. 20. The device 10 shown in FIGS. 18 and 19 is
capable of producing a generally sinusoidal active line 166, which
is different from the active line 164 in that it is wavelike on a
smaller scale. The active line 166 is essentially composed wave
segments oriented along the course of active line 164.
[0119] When using a device 10 according to FIG. 17, an active line
168 different from the active line 164 can be produced, which has a
coarse path similar to that of the active line 164, but has wave
segments oriented substantially perpendicular to the course of
active line 164.
[0120] While the invention has been illustrated and described in
connection with currently preferred embodiments shown and described
in detail, it is not intended to be limited to the details shown
since various modifications and structural changes may be made
without departing in any way from the spirit and scope of the
present invention. The embodiments were chosen and described in
order to explain the principles of the invention and practical
application to thereby enable a person skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated.
[0121] What is claimed as new and desired to be protected by
Letters Patent is set forth in the appended claims and includes
equivalents of the elements recited therein:
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