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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a new and improved construction of gear
grinding machine and method of grinding gear teeth flanks at such machine.
Generally speaking, the gear grinding machine of the invention is of the
type comprising a workpiece support and a tool base which are movable
relative to one another for partial movements of the workpiece, for
setting the gear teeth data, for movements for forming a tooth profile,
and for the to-and-fro lengthwise or longitudinal stroke along the tooth
flanks to be ground. Additionally, there is provided a grinding wheel
support which is pivotably mounted at the tool base for pivotal movement
about a pivot axis. A grinding wheel is mounted to be rotatably drivable
at the grinding wheel support, the rotational axis of the grinding wheel
extending transversely to the pivot axis of the grinding wheel support.
In German Patent Publication No. 2,641,554 applicant has disclosed a gear
grinding machine of this species. In that prior art construction two
dished or plate-shaped grinding wheels or disks are each mounted at a
respective pivotal grinding support or grinding wheel support, for
accomplishing simultaneous grinding of a right tooth flank and a left
tooth flank. The pivot axis of each grinding wheel support intersects the
rotational axis of the related grinding wheel at right angles and extends
at least approximately through the grinding point where the grinding wheel
contacts the tooth flank and also would still contact the same if the more
or less enlarged contact surface between the grinding wheel and the tooth
flank, in end section, were reduced to a point with infinite small advance
or feed. In order to produce involute-shaped tooth profiles, the
heretofore proposed machine is equipped with a generating drive, by means
of which there can be accomplished in conventional fashion, a generating
motion between the gear to be ground and both of the grinding wheels. The
degree of pivoting of both grinding wheel supports solely has the purpose
of insuring that both grinding wheels can be adjusted at an inclination in
relation to one another and in relation to the generating plane. The once
selected setting or adjustment is continuously maintained during grinding
of a given tooth profile. According to this prior art proposal the
connection line of the grinding points or contact zones of both grinding
wheels is continuously maintained during the grinding operation, at such a
spacing from the base circle of the gear teeth to be ground that, in each
terminal position of the generating movement, one of the grinding wheels
machines a tooth tip, and, at the same time, the other grinding wheel
machines a tooth root. This setting of the grinding wheels results in the
grinding-pressure angle or angle of attack of each grinding wheel
continuously changing during the generating movement, and specifically,
with a spacing radially within the tangential plane at the base circle,
between a maximum at the tooth tip to a minimum at the tooth base and
vice-versa, and with a spacing radially externally of the tangential plane
at the base circle, between a minimum at the tooth tip to a maximum at the
tooth root and vice-versa.
Under the terms "grinding-pressure angle or angle of attack" there is to be
understood, just as was the case for the aforementioned prior art patent
publication referred to above, and equally of the disclosure of the
instant invention, the angle between the tangent at the tooth profile of
the workpiece and the planar surface of the grinding wheel.
The continuous change of the grinding-angle of attack affords the advantage
that appreciably more grinding grains or granules can participate in the
machining or metal removal work than was possible with the older
techniques where the grinding wheels or each grinding wheel acted by means
of an edge, which had to be maintained sharp at all times, with a fixed
grinding-angle of attack at the workpiece. This in effect means that
already, according to the heretofore known proposal, the number of
grinding grains participating in the grinding work is increased, so that
also then when the grinding wheels are relatively seldomly dressed, there
is always available a sufficient number of sharp-edged grinding grains, so
that there can be removed from the workpiece a multiplicity of small
individual chips or cuttings. By virtue of the continuous change of the
grinding-angle of attack there is made better use of the pore volume of
the grinding wheel for removal of the chips or cuttings. Due to the
changing grinding-angle of attack there also is continuously altered the
flow angle of the chips or the like. Consequently, there is a lesser
danger that the chips will tend to wedge into the pores, which, in turn,
has the benefit that there is reduced the danger of grinding wheel burn.
Because of the balance effect, associated with the continuously changing
grinding-angle of attack, the grinding grains tend to break away before
they become excessively dull. This phenomenon leads to the result that,
according to the prior art proposal, there can be obtained a higher
grinding efficiency and there is reduced the consumption or using up of
the grinding wheel which is caused by the dressing work.
According to the heretofore known prior art proposal the change of the
grinding-angle of attack, arising during the generating movement between
the grinding wheels and workpiece, exclusively is a consequence of the
aforementioned spacing between the connection line of the grinding points
of both grinding wheels and the base circle of the gear. This spacing
cannot be selected to be randomly large, since otherwise the ground tooth
profile would deviate, to an undesired degree, from a purely involute
profile. Consequently, the advantages of an increased grinding efficiency,
which are attributable to changing the grinding-angle of attack during
each generating stroke, in other words, an increased volume of material
removal per unit of time and a reduced consumption of the grinding wheels
per unit of machined workpiece volume, can only be obtained to a limited
degree and dependent upon the data of the gear teeth which are to be
ground.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind it is a primary object of the present
invention to provide a new and improved construction of gear grinding
machine and method of grinding gear teeth flanks at such machine, which is
not afflicted with the aforementioned drawbacks and limitations of the
prior art proposals.
Still a further significant object of the present invention aims at
providing a new and improved construction of a gear grinding machine of
the previously described character which is designed such that it enables
a still greater increase of the grinding efficiency or capacity,
independent of the data of the gear teeth which are to be ground.
Yet a further significant object of the present invention is directed to
the provision of a novel gear grinding machine and method of grinding gear
teeth flanks at such machine in a manner not afflicted with the
aforementioned shortcomings of the prior art proposal, and wherein such
machine and method is economical in its operation, extremely reliable,
affords high precision grinding work, and further, the grinding machine
itself is relatively simple in construction, economical to manufacture,
not readily subject to breakdown or malfunction and requires a minimum of
maintenance and servicing.
Now in order to implement these and still further objects of the invention,
which will become more readily apparent as the description proceeds, the
gear grinding machine of the present development is manifested by the
features that the grinding wheel support is connected with the tool base
by means of a pivot drive which, during grinding of a tooth flank, renders
possible random or arbitrary changes of the grinding-angle of attack
between the grinding wheel and the tooth flank within predetermined
limits.
This solution is basically independent of whether (i) the grinding machine
is equipped with one or two grinding wheels, (ii) the relative movements
between the workpiece and the grinding wheel or grinding wheels is
controlled by a generating drive or, for instance, by a templet, or, by
the program of a computer according to coordinates. The advantages of a
random pivoting of the grinding wheels are also independent of whether the
connection line of the grinding points of two simultaneously effectual
grinding wheels which work a right tooth flank and a left tooth flank, is
maintained at a spacing from the base circle of the gear teeth.
If a gear grinding machine containing the features of the invention is
provided, like the heretofore known machines of the previously mentioned
type, with a generating drive for producing an involute-shaped relative
movement between the workpiece support and grinding wheel, then the pivot
axis of the grinding wheel support, just as was the case with the
heretofore known prior art proposal, advantageously extends at least
approximately through the grinding point of the related grinding wheel. In
this case there can then be dispensed with, in any event, correction
movements of the grinding wheels if there are not required deviations from
the involute profile, such as for instance, tooth tip and/or tooth root
reduction. It is even possible to accomplish according to plan, tooth tip
and tooth root reductions by a certain deviation of the grinding point
from the pivot axis of the related grinding wheel support.
By virtue of the inventive construction of a machine of the previously
mentioned type there is furthermore attained the possibility of realizing
the advantage of a considerably increased grinding efficiency even without
the use of the conventional generating drive or gearing. This is
accomplished, according to a further construction of the invention, in
that the pivot axis of the grinding wheel support extends in spaced
relationship from the grinding point of the related grinding wheel and the
grinding wheel is mounted upon a pillow or bearing block which is
adjustable, in relation to the grinding wheel support, in two directions
enclosing a right angle with one another.
If there are to be ground tooth flanks upon a gear grinding machine of the
previously mentioned species, possessing a drive or gearing arrangement
for the to-and-fro generating movements between the tooth flank and
grinding wheel, then, in accordance with the heretofore known proposal,
the grinding-angle of attack can increase or decrease along the path from
the tooth root to the intermediate region of the tooth flank. According to
the invention this grinding technique is further expanded upon in that,
the grinding-angle of attack is increased along the path from the tooth
tip to the intermediate region of the tooth flank, at that location
reaches it maximum, and then is again reduced. Stated another way: the
grinding-angle of attack, as contemplated by the invention, increases
along the path of the grinding point over the tooth flank from the tooth
tip to the intermediate region of the tooth flank and from that location
again reduces towards the tooth root or base. During generating grinding
the workpiece velocity is greatest at the intermediate region of the tooth
flank, whereas it temporarily reaches the value null at the reversal
points of the generating motion at the tooth tip and at the tooth root.
Increasing the grinding-angle of attack to a maximum at the intermediate
region of the tooth flank, as contemplated by the invention, means that
the grinding wheel, at the location where the workpiece velocity is
greatest, also insures for the most effective emptying of the pores of the
grinding wheels, and thus, there can be increased the volume of the
machining or cutting work.
If, on the other hand, a gear grinding machine, as contemplated by the
invention, is constructed such that the pivot axis of the grinding wheel
support extends in spaced relationship from the grinding point of the
related grinding wheel and the grinding wheel is mounted upon a pillow
block displaceable, in relation to the grinding wheel support, in two
directions enclosing a right angle with one another and with the pivot
axis, then it is possible to deviate from the conventional
partial-generating method in that, the to-and-fro generating motions
between the tooth flank and grinding wheel are simulated inasmuch as the
grinding wheel is pivotable to-and-fro about the pivot axis. This pivot
axis extends approximately through the intersection point of two tangents
at the base circle of the gear teeth which are to be ground, wherein the
one tangent extends through the tooth tip point and the other tangent
through the tooth base point of the tooth profile. For obtaining the
desired tooth profile it is possible to vary, during the pivoting, the
spacing of the pivot axis from the work or operating point of the grinding
wheel.
The requisite coordination between the pivoting of the grinding wheel and
the changes of the spacing of the pivot axis from the work point is
advantageously controlled by a computer in which there is stored the
desired tooth flank profile and the desired changes of the grinding-angle
of attack and the permissible changes of the spacing of the pivot axis
from the work point of the grinding wheel, in consideration of the
available work space. It is of course evident that in such computer there
can be infed, at relatively brief time intervals, also data which can be
determined by scanning the work surface of the grinding wheel and provides
information concerning its wear and which, finally, also serves for taking
into account the wear of the grinding wheels by compensating measures.
In order to perform the inventive method which has been described
heretofore, the position of the pivot axis of the grinding wheel is
beneficially chosen such that the amount, by which there must be varied
the spacing of the pivot axis from the work point, does not exceed 10
millimeters. Preferably, the variation of the spacing of the pivot axis
from the work point, during grinding of a tooth flank, amounts to about
0.5 millimeter.
With the different exemplary embodiments of the inventive method it is
furthermore advantageous if the difference between the largest and the
smallest grinding-angle of attack, during grinding of a tooth flank, is
limited to about 0.5.degree. to 25.degree.; preferably this difference
amounts to about 1.degree. to 4.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than those set
forth above, will become apparent when consideration is given to the
following detailed description thereof. Such description makes reference
to the annexed drawings wherein:
FIG. 1 is a perspective view of a gear grinding machine for grinding
straight toothed-spur gears;
FIG. 2 schematically illustrates the interaction or engagement relationship
between a tooth flank and the grinding wheel of the gear grinding machine
of FIG. 1, the gear being shown in end or front section;
FIG. 3 is a fragmentary perspective view illustrating details of a gear
grinding machine having a simplified construction from that shown in the
embodiment of FIG. 1;
FIG. 4 is a diagram illustrating the changes of the grinding-angle of
attack during a generating stroke of the machine illustrated in FIG. 3;
and
FIG. 5 is a perspective view of a gear grinding machine for grinding
helical spur gears.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, the exemplary embodiment of gear grinding
machine, illustrated in FIG. 1, will be seen to comprise a machine bed 2
upon which there is attached a workpiece mounting or support arrangement
4. In the workpiece mounting or support arrangement 4 there is rotatably
mounted a workpiece support or carrier 6 for rotational movement about an
essentially horizontally dispositioned workpiece axis A. The workpiece
support 6 is constructed for clamping or chucking thereat a workpiece here
constituted by a gear 8, the gear flanks of which should be ground.
Belonging to the workpiece mounting or support arrangement 4 is a not
particularly illustrated, but conventional, indexing apparatus, rendering
possible the stepwise rotational indexing of the gear 8 in accordance with
the tooth pitch.
Arranged at the machine bed 2 are essentially horizontal guides or
guideways 10 extending substantially at right angles to the workpiece axis
A. A bed carriage or slide 12 is displaceable along the guides 10. This
bed carriage or slide 12, in turn, is provided with guides or guideways 14
extending essentially parallel to the workpiece axis A. Mounted parallel
to the guides 14 is a threaded spindle 16 in the bed carriage or slide 12.
The threaded spindle 16 can be driven by a suitable drive motor 18 which
is attached at the bed carriage or slide 12 and meshes with an upright or
stand 20 displaceable, along the guides 14, upon the bed carriage 12. This
upright 20 is equipped with vertical guides or guide means 22, along which
there is adjustable a tool base or base member 24.
The tool base member 24 has the configuration of an essentially flat or
planar plate extending orthogonally with respect to the workpiece axis A.
Machined at the tool base member 24 are mutually concentric arcuate guides
26, the axis of which, designated hereinafter as the pivot axis B, extends
essentially parallel to the workpiece axis A. A likewise substantially
plate-shaped grinding support or grinding wheel support 28 is guided at
the arcuate guides 26 in such a manner that it can pivot or rock about the
pivot axis B. The grinding support 28 is operatively connected with the
tool base member 24 by means of a pivot drive 30. This pivot drive 30 is
provided with a drive motor 32 arranged at the tool base member 24, a
crank pin 34 driven by the motor 32 and having adjustable eccentricity,
and a connecting rod 36 mounted at one end at the crank pin 34 and at the
other end at the grinding support or grinding wheel support 28 and having
an adjustable length.
The grinding support 28 is provided with guides or guide means 38 at the
side facing away from the tool base member 24. These guides 38 extend at
right angles with respect to the pivot axis B. Along the guides 38 there
is displaceable a radial carriage or slide 42, by means of a motor 40
arranged at the grinding support 28. This radial carriage 42, in turn,
possesses guides or guide means 44, likewise extending at right angles or
orthogonally with respect to the pivot axis B and, at the same time, at
right angles with respect to the guides or guide means 38. By means of a
motor 46 arranged at the radial carriage 42 a pillow or bearing block 48
or equivalent structure can be adjusted along the guides 44. Mounted upon
the pillow or bearing block 48 or equivalent structure is a grinding
spindle 50, extending parallel to the guides 44, carrying a dished
grinding wheel or disk 52 and being rotatably drivable by means of a drive
motor 54 arranged at the pillow or bearing block 48. The geometric axis of
the grinding spindle 50--also sometimes referred to herein as the grinding
wheel spindle--and the grinding wheel 52 will be designated hereinafter as
the rotational axis C.
The radial carriage 42 possesses a further guide or guide means 56,
extending essentially parallel to the guides 44, and along which there is
adjustable, by means of a motor 58 or the like, a dressing carriage or
slide 60. Upon the dressing carriage 60 there is guided a guide bolt 62,
or equivalent structure, extending essentially at right angles to the axis
of rotation C and adjustable in its lengthwise direction by means of a
motor 64. The guide bolt 62 carries a bearing or mounting bracket 66 in
which there is mounted a diamond roll 68 for dressing the grinding wheel
52. This diamond roll 68 or other suitable dressing tool is rotatably
drivable, by means of a suitable drive motor 70 arranged at the bearing or
mounting bracket 66, in the same or opposite direction in relation to the
rotational sense of the grinding wheel 52.
Continuing, displaceably guided upon the dressing carriage or slide 60 is a
feeler carriage or slide 72 for movement essentially parallel to the pivot
axis B. A drive motor 74 is arranged at the dressing carriage 60 in order
to displace the feeler carriage or slide 72. Mounted at the feeler
carriage 72 is a feeler shaft 76 which extends essentially at right angles
with respect to the pivot axis B and the rotational axis C. This feeler
shaft 76 carries at one end a feeler or sensor 78, and at its other end a
lever 80. The feeler 78 is provided for the purpose of feeling or scanning
the grinding wheel 52. Operatively associated with the lever 80 is a
switch 82 or equivalent structure arranged at the feeler carriage 72, this
switch 82 then being actuated by the lever 80 whenever the grinding wheel
52 has been worn by a predetermined amount.
With the exemplary embodiment of gear grinding machine, as shown in FIG. 1,
the gear 8 is stationary during such time as one of its tooth flanks is
ground. The pillow or bearing block 48 is adjusted in such a way that the
grinding point P.sub.1, where the grinding disk 52, driven by the drive
motor 54, contacts a tooth flank has a spacing r.sub.M from the pivot axis
B. During grinding the grinding support 28 together with the pillow block
48 and the grinding wheel 52 carry out to-and-fro pivotal movements or
oscillations about the pivot axis B, such being caused by the pivot drive
or drive means 30. These pivotal movements have superimposed thereon
movements of the pillow block 48 along the guides 44 in such a manner that
the grinding point P.sub.1 moves to-and-fro between a point P.sub.a at the
tooth tip and point P.sub.f at the tooth root or base, if the upright 20
were stationary. However, in fact the upright 20, during grinding, is
displaced continuously along the guides 14, so that the grinding point
P.sub.1 migrates in a zig-zag configuration over the tooth flank.
The movements of the pillow block 48 along the guides 44 are necessary,
because the tooth profile which is to be ground can deviate to various
degrees from an arc, and therefore, cannot be ground merely by the pivotal
movements of the grinding wheel 52 about the pivot axis B. The magnitude
of the requisite movements of the pillow or bearing block 48 along the
guides 44, which in end effect constitute axial movements of the grinding
wheel 52, depends upon the location of the pivot axis B in relation to the
tooth flank to be ground. According to the showing of FIG. 2, the pivot
axis B preferably extends at the region of a point P.sub.2 where two
predetermined tangents intersect one another at the base circle (radius
r.sub.b) of the gear teeth to be ground, namely the tangent t.sub.a
through the tooth tip point P.sub.a and the tangent t.sub.f through the
tooth root point P.sub.f. The pivotal movements of the grinding wheel 52
about the pivot axis B, generated by the pivot drive 30, are continuously
combined, during the grinding, with axial displacements of the grinding
wheel 52, in other words with displacements of the pillow or bearing block
48, generated by the drive motor 46, along the guides 44 and the
displacements of the radial carriage 42 along the guides 38, produced by
the motor 40, in such a manner that, on the one hand, there is produced
the desired tooth flank profile and, on the other hand, there continuously
changes the grinding-angle of attack .gamma..sub.E.
The gear grinding machine of FIG. 1, described previously as to its
construction and mode of operation, does not require a generating drive or
gearing of conventional construction for producing the generating
movements between the gear 8 and the grinding wheel 52. This is so because
all of the requisite movements, with the gear 8 stationary, can be
produced as movements of the grinding wheel 52 by the pivot drive 30 and
by the drive motors 40 and 46.
In contrast thereto, the embodiment of FIG. 3 requires the utilization of a
generating drive or gearing of conventional construction, for producing
the generating movements between the gear 8 and the grinding wheel 52,
wherein rotational and translatory components of such generating movements
can be divided between the gear 8 and the grinding wheel 52. It is
possible, for instance, that the gear 8 performs the rotational components
of the generating or rolling movement in the form of to-and-fro rotations
about the workpiece axis A, whereas the grinding wheel 52 has imparted
thereto the translatory movement components in that, the bed carriage 12
is moved to-and-fro along the guides 10. The machine construction shown in
FIG. 3, like that of the embodiment of FIG. 1, has a tool base member 24
provided with arcuate guides 26. Pivotally mounted at the arcuate guides
26 is a simplified grinding support or grinding wheel support 28' for
pivotal movement about the pivot axis B. In order to pivot or rock the
grinding support 28 there is also here provided a pivot drive 30, which
can be constructed as in FIG. 1, but however also for instance can be
designed as a piston-and-cylinder unit which is hingedly connected, on the
one hand, with the tool base member 24, and, on the other hand, with the
grinding support 28'.
The grinding machine of FIG. 3 differs from that shown and discussed above
with respect to FIG. 1 particularly in that the grinding spindle 50 is not
directly connected, rather by means of a belt drive 84 with a drive motor
54' for driving the grinding wheel 52. This drive motor 54' is attached at
the tool base 24, and thus, does not participate in the pivotal movements
of the grinding support 28'. The belt drive 84 is readily capable of
compensating the relatively small angular changes between the rotational
axis C of the grinding wheel 52 and the axis of the motor 54. The grinding
wheel 52 is adjusted such that its grinding point P.sub.1 always is
located at the pivot axis B. The pivotal movements of the grinding wheel
52 about the pivot axis B therefore do not have any effect upon the tooth
shape or profile, which is determined by the generating movements between
the gear 8 and the grinding wheel 52. The sole purpose of pivoting of the
grinding wheel 52 about the pivot axis B is to alter the grinding-angle of
attack .gamma..sub.E, by means of which always other annular or
ring-shaped zones of the grinding wheel 52 come into engagement with the
tooth flank, thereby increasing the grinding efficiency or capacity. An
example of an advantageous course of the grinding-angle of attack
.gamma..sub.E throughout the generating stroke H has been shown in FIG. 4.
Now the gear grinding machine illustrated in FIG. 5 corresponds to the
embodiment of FIG. 1, with the difference that it is also suitable for
grinding a helical gear 8'. To this end there is required a helical
relative movement between the helical tooth-gear 8' and the grinding wheel
52, which must be synchronized with the movements of the upright or stand
20 along the guides 14 of the bed carriage 12. For this purpose there is
attached, in known manner at the workpiece support 6, a rolling block 86
connected by means of the rolling tapes 88 with a rolling tape carriage
90. The rolling tapes 88 are guided over deflection rolls 92 mounted at
the rolling tape carriage 90. This rolling tape carriage 90 is
displaceably guided in one of the guides 10 of the machine bed 2 for
movement essentially at right angles to the workpiece axis A and is
connected, by means of a cam block or follower 94 mounted thereat, with a
cam guide 96 or equivalent camming means, which extends in an essentially
horizontal plane and, in accordance with the desired tooth helix angle,
can be inclinably adjustably attached at the upright or stand 20.
In accordance with the desired gear tooth-helix angle it is also necessary
to inclinably or obliquely position the grinding wheel 52. For this
purpose the grinding spindle 50 is mounted, on the one hand, in a sleeve
or bushing 110, and, on the other hand, in a ring 100 or equivalent
structure. This sleeve 110 is mounted at a rigid leg 102 of the pillow or
bearing block, here designated by reference character 48', for pivotal
movement about an axis extending essentially at right angles with respect
to the pivot axis B and the axis of rotation C. The ring or ring member
100 is pivotably mounted at a bracket or strap 104 or the like about an
axis which is parallel to the aforementioned pivot axis of the sleeve 110.
This bracket 104 is adjustably attached at an articulated or hinged leg
106 of the pillow or bearing block 48' by means of a clamping device 108.
A support 98 is mounted upon the sleeve 110 and can be moved away from or
towards the grinding wheel 52, by means of a gear rack drive 112 having a
drive motor 114. Hence, it is possible to compensate the axial grinding
wheel-wear by axially adjusting the grinding wheel 52 by means of the
motor 46', and in synchronism with such adjustment there is always
adjusted by the same amount the support 98.
With the machine construction of FIG. 5, the support 98 assumes part of the
function of the radial carriage 42 provided for the embodiment of gear
grinding machine shown in FIG. 1. Thus, at the support 98 there is
provided a guide 56', along which there is adjustable, by means of a
suitable drive motor 58', a dressing carriage or slide 60'. Also in this
case there is mounted upon the dressing carriage 60' a diamond roll 68'
and rotatably drivable by means of a suitable drive motor 70'. A feeler
carriage 72' is adjustable, by means of a motor 74', along the guide 56',
at the other side of the grinding wheel 52. Mounted in a manner similar to
the feeler 78 of the arrangement of FIG. 3, here there is mounted a feeler
78' at the feeler carriage 72'.
While there are shown and described present preferred embodiments of the
invention, it is to be distinctly understood that the invention is not
limited thereto, but may be otherwise variously embodied and practiced
within the scope of the following claims. Accordingly,
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