Note: Descriptions are shown in the official language in which they were submitted.
212427~
METHOD AND MACHINE TOOL FOR FINISHING TOOTHINGS ~ -~
Background of the Invention
The present invention relates to a method and
a machine tool for fine-machining of toothings on : .
a machine tool whereby the toothed wheel or gear
wheel to be machined is rotated about its axis of
rotation and is engaged by the abraslve worklng
tool that is rotated about its axis of rotation
such that it comes into contact with the tooth
flanks of the toothed wheel to be machined and
whereby the rotational movement of the axis of
rot~tion of the toothed wheel and the rotational
movement of the axls of rotatlon of the abraslve
working tool are electronically coupled. The
material removal is carried out in general such
that the axis of rotation of the workpiece on the
one hand and of the abrasive working tool on the
other hand extend relative to one another at a so-
called axis cross angle. In some cases it also
possible to provide a parallel arrangement of the
axes of the tool and the workplece for the deslred
material removal which then takeY place by the ~o-
called high gliding durlng rolllng of the tooth
flanges of the workpiece and the tool on one
another.
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For the machining of toothed wheels after
hardenlng different manufacturing processes are
being u~ed at present. Generally, hobbed and
hardened t~othed wheels are provlded with the
final exact prof~le contour in a grinding
operation. Sometimes, after completion of the
yrinding operation, a tooth honing process ls
performed in order to minlmize inaccuracies of the
teeth remaining after grinding. The advantage of
a honing process is that this process requlres
only little time and is especially suitable for
mass production.
In a tooth honing step the toothed wheel to
be machined rotates about its axis of rotation.
It meshes with the honing tool which, in the case
of an outer toothing to be machined, is in the
form of an inner toothed ring. The honing tool
also rotates about its axis of rotation. The
inner toothing of the honing tool can be derived
geometrically from the desired toothing geometry
of the workpiece. In order to achieve material
removal from a toothed wheel that is hard to
machine, the honing tool is provided with abraslve
particles. The machining is carried out such
that, for example, the workpiece is drlvsn and the
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tool follows with a certain amount of drag. By
changing the direction of rotation (pu~h and
pull), the two tooth flanks are machined.
The goal of the honing process i8 to minimize
the tooth inaccuracies remaining after the
grinding process. These tooth inaccuracies
include deviations of the rotational trueness and
of the profile (involute including the desired
corrections) as w~ll as the line of the flanks.
Of special importance for a noise-reduced
operation of the toothed wheel are single pitch
errors and accumulated pitch errors.
High requirements with regard to the quality
of the toothed wheels to be machined have led to
the need for more efficient working tools for
hardened toothed wheels. Regarding tooth honlng
methods, solutions have been suggested in which
the two rotational shafts of the workpiece and the
working tool are no longer independently driven
and are only connected by the drag of the part
that is not being driven and in which the two
rotational shafts are coupled with a defined
coupling means. The latter is preferably done
with the assistance of NC technology in an
electronic manner ("electronic shaft").
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The goal of this measure was to average the
tooth inaccuracies with the honing process, i.e.,
to minimize such tooth inaccuracies during rolling
of the honlng tool on the workpiece, but also to
eliminate such lnaccuracies by forcibly coupling
the rotational shafts axi~.
Extensive tests have shown that with known
honing tools and methods it is indeed possible to
reduce the tooth inaccuracies substantially,
especially devlations of the rotational trueness,
of the contour of the flanks, and of the single
pitch errors of the toothing.
However, it has been shown that especially
the accumulated pltch error of the toothlng, even
when electronlc shafts are being used for the
honing process, the inaccuracies are still very
great and, in general, are outside of the
allowable tolerance range.
Obvlously, the conventional controls
lelectronic shafts), are not able, due to the high
rotational velocity of the workpiece and the
honing tool, to timely detect rotational errors,
i.e., deviations from the ideal rotation which are
usually within the micrometer range, and to induce
the requlred counter movement so that a
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corresponding correction of the abrasion process
can occur.
It is therefore an obJect of the present
invention to provide a method for finishing
toothings that is able to reduce substantlally the
critiaal accumulated pitch error and to provide
for a toothlng of a high quality. The inventive
goal, however, should be reached under the
followlng condltion: the hard machining should be
performed in the shortest possible amount of time
and therefore a honing process ls considered for
the present invention.
Brief Description of the Drawings
This ob~ect, and other obJects and advantages
of the pre~ent invention, will appear more clearly
from the following speciflcatlon in conJunction
with the accompanying drawings, in which:
Fig. 1 shows a workpiece and a
working tool in engagement
during the machining
process; and
Fig. 2 shows the course of the
accumulated pitch error F
over the rotational angle of
the toothed wheel.
212q~7~
Summary of the Invention
Accord~ng to a first method of finishing
teeth including tooth flanks of a toothed wheel
with a machine tool according to the present
invention is primarily characterized by the
following steps:
a) Engaging the toothed wheel with an
abraslve working tool of the machlne -
tool~
b) Rotating for at least one revolution the
toothed wheel about an axi8 of rotation :~.
of the toothed wheel; ~ .
c) Entrainlng the abrasive working tool
with the toothed wheel load-free but in
contact with the toothed flanks of the .
toothed wheel, :~
d) During the at least one revolution,
measuring rotational devlatlons from an :~
ideal rotational meshing between the :
toothed wheel and the abrasive working
tool resulting from tooth inaccuracie~
e) Saving the rotational deviations,
f) Finishlng the toothed wheel with the
abrasive working tool, wherein the step
of finishing includes the following
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steps:
fl) Electronically coupling the rotat$onal
movement about the axis of rotation 2 of
the toothed wheel and the rotational
movement about the axls of rotation of
the abrasive working tool; and
f2) Adding the rotational deviations with
reversed sign at each angular position
for providing the nominal position value
of an angular position for the
rotational movement about the axis of
rotation to be controlled.
In a 8econd, alternative method of the
present invention, the working tool is actively
driven while the toothed wheel to be machined ls
entrained by the workiny tool.
Preferably, the first and second methods
further comprise the step of repeating steps a) to
e) after completion of step b) for measuring
present rotational deviations.
Advantageously, the first and second methods
further comprise the step of continuing finishing
of the toothed wheel pursuant to step fl) when the
present rotational deviations are below a
predetermined maxlmum.
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In another embodiment of the present
lnventlon, the flrst and second methods further
comprise the step of continuing finishing of the
toothed wheel according to step f) wherein in step
f2) the present rotational deviations are added
when the present rotational deviations surpass a
predetermined maximum.
Advantageously, the step of repeating steps
a) to e) and the step of continuing finishing of
the toothed wheel are repeated until the present
rotational deviatlons are below the predetermined
maxlmum.
Advantageously, in the step b2) the
rotational deviations are added only when the
rotatlonal deviations surpass a predetermined
value.
In another embodlment of the present
invention, the first and second method further
comprise the steps of measuring tooth inaccuracies
of the abrasive working tool on a measuring device
and in step f2) correctlng the nominal posltion
value wlth the measured tooth lnaccuracies.
Preferably, the first and second methods
further comprise the step of adJusting in step fl)
the rotational movement about the axls of rotatlon
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of the toothed wheel and the rotatlonal movement
about the axis of rotation of the abrasive working
tool relative to one another according to the
measured tooth inaccuracies.
The present invention further relates to a
machine tool for performlng the two methods of the
present invention.
The measured rotational deviations of the
workpiece from the ideal rotatlon (this could be
called also a teach-in for the present
inaccuracies of the toothing) are used in the
finishing steps such that the measured rotational
deviations have their sign reversed and are used
to compensate the rotational movement so that
exactly at the location~ at which the most
material must be removed, the required hlgh
materlal abrasion takes place. The technlcal
control means of choice i9 a so-called electronic
curve disk which is known as an electronic shaft
coupliny system from printing, paper
manufacturing, and textile machlnes~
With the inventive feature it is thu,~ ensured
that even for the available control system~ a
conslderable reduction of toothlng inaccuracies,
in particular of accumulated pitch errors, can be
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performed because the control knows in time when
a deviation related to a tooth inaccuracy is
coming up so that the control can counter this
effect. The result after the honing process is a
fla~less toothed wheel that with its error margins
lies within the allowable tolerances.
When the most critical inaccuracies, viewed
over the circumference of the toothed wheel, have
been removed, it may be expedlent to continue the
honing process with uncorrected angular positions,
i.e., with an exact unmodified coupling.
Otherwise, there would be the risk that the
correction now produces cups at those locations
that have previously been preferably sub~ected to
material removal. According to a further feature
of the invention it is thus suggested that after
~ompletion of the finishing step a further
measuring of the workplece takes place.
When it ls determined that the greatest
inaccuracies have been removed, the honing proceYs
is continued with uncorrected angular positions.
Otherwise, it is possible to further use
correction values whereby preferably in this ~tep
the newly measured present (current) values are
being used.
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The sequence of finishing, measuring,
finishing advantageously can be continued with
corrected angular positions until the measured
rotational deviations are below a predetermlned
value. Then it is possible to continue machining
with uncorrected angular position (ideal
rotational coupliny). It is not necessarily
required that the measured rotational deviatlons
according to the steps a) to e~ of the inventive
method must be considered over the complete
circumference of the toothing when, for example,
only at one or a few locations a high material
removal is requlred as ls typical for accumulated
pitch errors of toothings. In a further
embodiment of the present invention it is
suggested that the correction of the angular
position for the rotational movement about the
axis of rotation to be controlled is limited to
those angular ranges in which the measured
rotational devlations surpass a predetermined
value of deviation from the ideal rotation.
It is al80 pos8ible that during measurlng of
the lnaccuracles accordlng to the method teps a)
to e) instead of a toothed wheel the abrasive tool
ls rotated and the toothed wheel is entrained ln
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21~270
a load-free manner but such that the tooth flanks
are in contact with the abrasive tool. -~
For increasing the precision of the method it
may be advantageous to ellminate the lnaccuracies
of the tool whlch are usually always present, even
when only in small amounts. This is inventively
achieved such that the inaccuracies of the tool
are measured on a separate measuring device. When
determining the corrected angular positions by
coupling, but also when performing corrections,
the measured inaccuracies of the tool are used to
compensate so that the effect of the tool on the ~-
accuracy of ~he toothlng i9 elimlnated.
Description of Preferred Embodiments
The present invention will now be descrlbed
in detail with the aid of several specific
embodiments utilizing Figures 1 and 2.
Fig. 1 shows the toothed wheel 1 to be
machined. It has an axiY of rotation 2 about
which it is rotated during the honlng process
(direction of rotation A). The toothed wheel 1
me~hes with the abrasive working tool 3 which
rotates about its axi8 of rotatlon 4 (directlon of
rotation B). Represented i~ the simplest ~cenario
for machining a spur gear wlth teeth that extend
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parallel to the axis of rotation 2 (straight
toothlng). The inventive embodlments are also
applicable for slanted toothings and for inner
toothings. In the latter case, the tool has the
shape of a spur gear with outer toothing
(reference numeral 1 of Fig. 1 would then indicate
the tool and reference numeral 3 would then
indicate the workpiece). The axes of rotation 2
and 4 represented in Fig. 1 are shown to extend
parallel to one another for reasons of
simplification. Conventionally, the axes of
rotation extend at an acute angls relative to one
another, the so-called axis crossing angler ln
order to generate the desired material removal.
The abrasive worklng tool (honing wheel) 3
has a counter contour corresonding to the contour
of the workplece 1. Upon rolling of the working
tool 3 and the wor~piece l, the working tool 3
generates at the workpiece 1 exactly the desired
proflle. Materlal removal (abrasion) is performed
because the contact surfaces between the workpiece
and the working tool are provided (on the side of
the working tool) with an abrasive material. It
i~ pos~ible to use a working tool that is
comprlsed entirely of an abraslve material that
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can be dressed or trimmed and which, for example,
is machlned with a diamond-studded trimming wheel
to the desired profile. The tool may also be
comprlsed of a metallic base body that has already
been shaped to an equidistantly smaller shape and
is comprised of a single layer of super-hard
material (for example, CBN) with which the exactly
required tool shape results. The rotatlonal
movement about the axes 2 and 4 tdirection of
rotation A and B) is electronically coupled
(electronic shaft). This means that for each
angular positlon of the shaft of the workpiece a
corresponding angular position of the shaft of the
working tool is present which are electronically
exactly ad~usted and positioned.
According to the present invention, before
the actual machining of the toothed wheel 1 to be
machined, a complete revolution i8 carried out
which is automatically performed by the machine
tool control. The working tool 3 according to
Fig. 1 is in engagement with the workpiece 1. The
working tool 3 rotates without load together with
tha workpiece 1 whereby however a certain braking
moment is ensured so that contact between the
toothed ~lanks of the workpiece 5 and of the
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working tool 6 is ensured. It may be simpler ln
certain cases to rotate the working tool 3 and to
have the workpiece 1 follow. Of course, this
embodiment is also part of the present lnvention.
During the rotation of the toothed wheel 1
the movement ls measured at the working tool 3
that follows the rotational movement, and
especlally the rotatlonal deviations resulting
from toothing inaccuracies of the workpiece 1 with
respect to the ideal rotation are measured and
saved. This is schematically shown in Fig. 2.
Over a complete revolution (2 r ~), the measured
accumulated pitch error Fp is determined. For
each angular position a corrected value (Delta Fp~
of the rotational coupling can be used so that
especially at those locations where the most
material removal i8 required an increased material
removal is performed.
Subsequently, the honing procass ls
performed. The rotational movements of workpiece
1 and working tool 3 are now electronically
coupled (electronic shaft). However, the mea~ured
deviations of rotation (Delta Fp) are used by the
electronic control upon coupllng of the movement
about the two axes of rotation for compensation.
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The machlne tool control for each concrete angular
posltlon determlnes a nominal position value that
has been corrected by the previously measured and
saved rotational deviation value.
The present invention is, of course, in no
way restricted to the specific disclosure of the
specification and drawings, but also encompasses
any modifications wlthin the scope of the appended
claims.
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