U.S. patent number 3,713,315 [Application Number 05/070,377] was granted by the patent office on 1973-01-30 for cold rolling profiles on cylindrical workpieces.
This patent grant is currently assigned to Maag Gear Wheel & Machine Company Limited. Invention is credited to Oskar Maag, Albert Meyer, Otto Wenger.
United States Patent |
3,713,315 |
Meyer , et al. |
January 30, 1973 |
COLD ROLLING PROFILES ON CYLINDRICAL WORKPIECES
Abstract
In a method for cold rolling profiles on the circumference of a
rotating cylindrical workpiece, using tool worms of appropriate
profile, the worms performing generating motions corresponding to
the profile required in successive part-rolling operations by being
moved relative to the workpiece in a closed-circuit locus path
having one axis which is in the direction of and smaller than the
tooth depth, and which substantially smaller than another axis of
said locus which is in the direction of tooth length or thickness,
with each part-rolling operation being performed over the entire
tooth facewidth while the tools are retained, over the workpiece
width, in their dead center position which is a position on said
locus innermost relative to the axis of the workpiece, the profile
being preformed by progressive radial feed of the operating stroke
of the tools and with a number of enveloping planes, and the
profile being subsequently, finish-formed with a larger number of
enveloping planes and with an unchanged inner dead center position
of the tool worms.
Inventors: |
Meyer; Albert (Thalwil,
CH), Wenger; Otto (Zurich, CH), Maag;
Oskar (Zurich, CH) |
Assignee: |
Maag Gear Wheel & Machine
Company Limited (Zurich, CH)
|
Family
ID: |
5745637 |
Appl.
No.: |
05/070,377 |
Filed: |
September 8, 1970 |
Current U.S.
Class: |
72/100; 72/104;
72/95 |
Current CPC
Class: |
B21H
5/02 (20130101) |
Current International
Class: |
B21H
5/00 (20060101); B21H 5/02 (20060101); B21h
005/02 () |
Field of
Search: |
;72/95,100,101,102,103,104 ;29/159.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Larson; Lowell A.
Claims
What we claim and desire to secure by Letters Patent is:
1. In a method for cold rolling a gear tooth profile on the
circumference of a rotationally-driven cylindrical workpiece by
means of tool worms having a reference profile, said tool worms
being adapted to perform generating motions corresponding to the
gear tooth profile to be generated on the workpiece on a
closed-circuit locus having locus having one axis which is in the
direction of and smaller than the tooth depth and which is
substantially smaller than another axis of said locus which is in
the direction of the tooth length or thickness, the improvement
comprising the steps of effecting said rolling in a plurality of
part-rolling operations, each part-rolling operation being
performed over the entire workpiece width with the tool worms being
retained, at least over the tooth facewidth, in an inner dead
center position in said locus, including preforming said tooth
profile in a number of enveloping planes by progressive feed toward
the workpiece of the operating stroke of the tool worms in the
radial direction of the tool worm and workpiece between successive
complete movements in said closed-circuit locus, finish-forming
said profile in a larger number of enveloping planes, each
enveloping plane being accomplished with the tool worms retained in
a said dead center position.
2. A method according to claim 1, wherein each part-rolling
operation is performed with the profile of the tool worms in the
same position relative to the workpiece so that the gear tooth
profile is formed over its entire length in the same enveloping
planes, each said enveloping plane having the same position
relative to the tooth gaps being formed.
3. A method according to claim 2, wherein said preforming is
performed with between 1.5 and 2.5 part-rolling operations for each
rotation of the tool worms, while finish-forming is performed with
a ratio of part-rolling operations for each rotation of the tool
worms which differs from said preforming ratio by a small amount,
said ratio being exactly divisible into a figure no smaller than a
high multiple of the number of teeth of the workpiece.
4. A method according to claim 3, wherein when using two tool worms
diametrically opposed to each other relative to the workpiece, the
worm threads thereof are caused to act symmetrically relative to
the workpiece for each part-rolling operation, so that the torques
acting on the workpiece and resulting from the rolling pressure of
the tools substantially cancel each other.
5. A method according to claim 1, for the cold rolling of helical
gear teeth on the workpiece, wherein in preforming said helical
gear teeth, the setting angle of the tool worms relative to the
workpiece angle is first set to a value larger than that
corresponding to the helix angle and is then reduced in accordance
with the associated reduction of the actual helix angle.
6. A method according to claim 1, wherein after preforming of the
gear tooth profile the feed of the radial stroke of the tool worms
is reduced by a very small amount in order to reduce the rolling
pressure for finish-forming.
7. A method according to claim 1, wherein during the axial stroke
of the tool worms a correcting motion is superimposed on the radial
feed of the tool worms in order to obtain a longitudinally crowned
tooth form.
8. In a machine for cold rolling a gear tooth profile on the
circumference of a rotationally driven cylindrical workpiece
provided with tool worms which are adjustable at an angle and are
supported in tool supports which are radially movable and axially
reciprocable relative to the workpiece, and having a rotary drive
for the tool worms and for the workpiece to impart to both the tool
worms and the workpiece a relative generating motion which
corresponds to the profile to be generated, the improvement
comprising means for reciprocating the tool supports exclusively in
the direction which is radial relative to the workpiece axis, means
for supporting the workpiece in a work slide which can be
reciprocated in parallel to the workpiece axis over more than the
facewidth of the gear teeth being formed on the workpiece, and
means for providing rotational drive of the workpiece spindle
through an interchangeable lead bush to produce the desired
rotation of the workpiece.
9. A machine according to claim 8, comprising a first,
angularly-adjustable slotted link mounted on the work slide and
adapted, during each stroke of the work slide, to axially displace
a driving worm for imparting rotation to the work spindle in order
to counteract inherent generating action of the workpiece during
each part-rolling motion, and a second angularly-adjustable slotted
link to axially displace the tool worms during each stroke of the
work slide in order to counteract inherent generating action of the
tool worms during each part-rolling motion.
10. A machine according to claim 8 comprising a crank together with
a crank rocker, a connecting rod and a two-armed lever for
reciprocating the work slide and so disposed that the sinusoidal
oscillation of the crank rocker is converted into an axial
reciprocation of the work slide so that the work slide moves at a
constant velocity.
11. A machine according to claim 10, comprising a pin about which
said double-armed lever pivots, said pin being slidable to vary the
length of the lever arms of the lever and therefore the length of
the stroke and velocity of the work slide.
12. A machine according to claim 8, comprising an interchangeable
correcting template mounted on the work slide and adapted to
impart, during each stroke of the work slide, an independent axial
displacement to the driving worm for the rotational drive of the
work spindle, said displacement being independent of the slotted
link, in order to influence the tooth direction resulting from the
rolling operation.
13. A machine according to claim 8, comprising a change gear set in
the rotational drive of the tool worms and of the workpiece for
adjusting the number of strokes of the work slide for each tool
worm rotation.
14. A machine according to claim 8, wherein the rotational drive of
the tool worms and of the workpiece is provided with a differential
drive having a planet wheel cage which can, by means of a
changeover clutch, be optionally retained or be coupled with a
supplementary drive having a change gear set.
Description
The invention relates to a method for the cold rolling of a gear
tooth profile on the circumference of a cylindrical work piece, and
to a machine for performing the said method.
A known machine for the cold rolling of gearwheel teeth employs
worm-shaped profiling tools having the reference profile, and being
adapted to perform generating motions relative to the rotationally
driven workpiece and in accordance with the profile to be
generated, and performing successive part-rolling operations on the
workpiece by being moved relative to the workpiece on a
closed-circuit locus having one axis which is in the direction of
and smaller than the tooth depth and which is substantially smaller
than another axis of said locus which is in the direction of the
tooth length or thickness. The tools move in an elliptiform path
(the said closed-circuit locus) which has a minor axis and a major
axis, the extremities of the minor axis being dead center
positions, the inner dead center position being that which is
nearer the axis of the workpiece. The inner dead center position is
defined by the tooth root of the gear which is to be generated.
During each part rolling operation the tool is first moved relative
to the workpiece in the position which is radially the lowest with
respect to the workpiece, and at the end of its stroke, which is
axial relative to the workpiece the tool is lifted from the rolled
gap, to continue in the closed-circuit locus, the said tool being
gradually fed axially forward, between successive locus circuits,
during the continuous part-rolling operations of tools. In each
part-rolling the profiling tools will first finishform the profile
already prerolled and at the end of their motion, while the tools
are radially retracted, an axially adjoining part of the profile
will be preformed. In order to obtain the desired quality of
gearing, finish-forming of the tooth with the reference profile
must be performed with a plurality of; enveloping planes, that is,
the imaginary planes swept by the flanks of the tool worm teeth,
producing (in the preforming stage) visible flats on the gear
teeth; however, a smaller number of enveloping planes would be
sufficient for the preforming of the tooth. However, since
preforming of one portion of the profile and finish-forming of
another portion of the profile have to be performed in one and the
same operation, it follows that the speed at which the profile is
produced is defined by the part rolling operations required for
finish forming.
It is the object of the invention to provide an improved method and
apparatus by means of which the manufacturing speed in cold rolling
of gearwheel profiles on the circumference of a cylindrical
workpiece can be substantially increased.
According to the invention, the rolling is effected in a plurality
of part-rolling operations, each part-rolling operation, is
performed over the entire tooth facewidth with the tool worms being
retained, at least over the tooth facewidth, in an inner dead
center position, as hereinbefore defined, in said locus, said
plurality of operations including preforming the tooth profile in a
number of enveloping planes by progressive feed toward the
workpiece of the operating stroke of the tool worms in the radial
direction of the tool worm and workpiece between successive
complete movements in said closed-circuit locus, and finish-forming
said profile in a larger number of enveloping planes, each
enveloping plane being accomplished with the tool worms retained in
a said inner dead center position.
Since preforming and finish-forming take place successively it is
possible for the feed motion for preforming to be executed without
reference to the finish-forming of the profile. In selecting the
material volume to be deformed in each rolling stroke during the
preforming operation it is merely necessary for the appropriate
choice to be made in accordance with the material to be deformed. A
small number of enveloping planes are sufficient for rough
preforming while the required accuracy of gearing is obtained in
finish-forming with a larger number of enveloping planes.
It is particularly advantageous if each part-rolling operation is
always performed with the same position of the profile of the tool
worms relative to the workpiece so that the tooth profile is formed
over its entire length with the same enveloping planes, each
enveloping plane having the same position relative to the tooth gap
being formed.
In an appropriate embodiment, preforming is performed with between
1.5 and 2.5, but preferably with 2, part-rolling operations for
each rotation of the tool worms while the ratio of part-rolling
operations for each tool worm rotation selected for finish-forming
is smaller or larger by a small amount, said ratio being exactly a
figure no smaller than a high multiple of the number of teeth on
the workpiece. If the profile is produced by means of two
part-rolling operations
for each rotation of the tool worms, the tooth profile will be
preformed with three enveloping planes which are generally
sufficient to closely approach the involute tooth profile.
Finish-forming is then performed with a larger number of enveloping
planes.
A machine for carrying out the said method, provided with tool
worms which are adjustable at an angle and are supported in tool
supports which are radially movable and axially reciprocable
relative to the workpiece, and having a rotary drive for the tool
worm and for the workpiece to impart to both the tool worms and the
workpiece a relative generating motion which corresponds to the
profile to be generated, is characterized in that the tool supports
can be reciprocated exclusively in the direction which is radial
relative to the workpiece axis and that the workpiece is supported
in a work slide which can be reciprocated in parallel to the
workpiece axis over more than the facewidth of the gear tooth being
formed on the workpiece and that the rotational drive of the
workpiece spindle is provided through an interchangeable lead bush
to produce the desired rotation of the workpiece.
To ensure that the tool worm and the workpiece retain their
relative position to each other when each part-rolling operation is
performed, a first angularly adjustable slotted link is preferably
mounted on the work slide and is adapted, during each stroke of the
work slide, to axially displace a driving worm for imparting
rotation to the workpiece in order to counteract the inherent
generating action of the workpiece during each part-rolling motion,
a second angularly-adjustable slotted link being provided to
axially displace the tool worms during each stroke of the work
slide in order to counteract the inherent generating action of the
tool worms during each part-rolling motion.
During the part-rolling motion, the axial stroke of the workpiece
should be performed at a constant velocity which should correspond
to the rolling velocity of the tool worms so that wear thereof is
minimized. In the machine according to the invention this problem
is solved in that a crank with a crank rocker, a connecting rod and
a two-armed lever are provided for reciprocating the work slide and
are so disposed that the sinusoidal oscillation of the rocker crank
is converted into an axial reciprocation of the work slide so that
the work slide moves at constant velocity.
The method according to the invention, and a machine for performing
the method, are disclosed in the following description of an
embodiment of a machine for the cold rolling of gear profiles, and
shown in the accompanying drawings, wherein:
FIG. 1 is a vertical section along the workpiece axis and on the
line 1--1 of FIG. 2;
FIG. 2 is a vertical section on the line 11--11 of FIG. 1, only one
tool support with its drive being shown;
FIG. 3 is a part end elevation, looking in the direction of arrow
111 of FIG. 2;
FIG. 4 is a horizontal section along the line of IV--IV of FIG. 5,
through a workpiece and tool worms during the finish-forming of the
profile in a cold rolling of a straight-tooth spur gear;
FIG. 5 is a vertical section along the line Y--Y of FIG. 4 during
the finish forming of a workpiece having an even number of
teeth;
FIG. 6 is a vertical section similar to FIG. 5 during the
finish-forming of a workpiece having an odd number of teeth;
FIG. 7 shows the path of a tool worm in relation to a workpiece
assumed to be stationary when the tool worm forms the tooth
root;
FIGS. 8 and 9 show the conditions of the tool worm relative to the
workpiece, the ratio of the number of strokes of the workpiece for
each tool worm rotation being K = 2;
FIG. 10 shows an enlarged cross-section through a tooth of the
workpiece;
FIG. 11 is a plan view of the workpiece and tool worms during the
cold rolling of a helical gear;
FIG. 12 is a view corresponding to FIG. 7 but showing the cold
rolling of teeth with longitudinal crowning; and
FIG. 13 is a view corresponding to FIG. 12, showing the
simultaneous cold rolling of two gearwheels with longitudinally
crowned teeth.
In the machine illustrated in FIG. 1 to 3 for cold rolling helical
gear on the circumference of a cylindrical workpiece, the said
cylindrical workpiece 1 is retained, as shown in FIG. 1, at one of
its ends by means of a clamping device 2 of a work spindle 3
journaled in a spindle-bearing pedestal 4 at the end, the left-hand
end in FIG. 1, of a yoke-shaped work slide 5. At its other end the
workpiece 1 is supported in the work slide 5 by means of a work
holder 6 having a mandrel 7. The work slide 5 is slidably guided by
V-shaped guide surfaces 8 thereon sliding in corresponding guide
surfaces 9 in a machine frame 10, said guide surfaces 8 being
disposed on both sides of the workpiece and extending in parallel
to the axis X thereof.
A lead bush 11, having helical guide grooves 12 of a lead
approximately equal to the lead of the gear tooth helix, is
flange-mounted on the end of the work spindle 3 remote from the
workpiece. Sliding blocks 13, disposed in the interior of a driver
collar 14, co-operate with the guide grooves 12, the drive collar
14 being mounted on the end face of the hollow boss 15 of a
wormwheel 16 which is immovable axially but is rotatably journalled
in the machine frame 10. By virtue of this arrangement, a
reciprocating motion of the work slide 5 imparts to the workpiece a
rotating motion corresponding to the desired helix angle of the
profile which is to be generated. The lead bush 11 together with
the associated driver collar 14 is interchangeable.
The work slide 5 is caused to move axially of the workpiece 1 by a
crank rocker 20 through a double-armed lever 18, hinged on said
work slide by means of a bolt 17, and a connecting rod 19. The
crank rocker 20 is caused to reciprocate, on an axle bolt 21
supported in the frame 10, by a crank 22 (FIG. 2) the crank pin 23
of which carries a sliding block 24 which is guided in a
longitudinal guide 25 in the crank rocker 20. The crank 22 is
disposed at one end of a shaft 26 which is driven from a main shaft
29 of the machine through a gearwheel pair 27, 28, the said main
shaft in turn receiving its drive from a motor 31 through a belt
30. The sinusoidal oscillation of the crank rocker 20 obtained from
the crank 22 is converted into an axial reciprocating motion of the
work slide 5 by an appropriate choice of the dimensions of the
double-armed lever 18, the connecting rod 19 and the crank rocker
20 whereby the motion of the work slide 5 to the right (FIG. 1) is
extended so as to be performed practically at constant velocity.
Accordingly, the workpiece 1 is moved axially practically at
constant velocity during its motion to the right during which, as
will be described later, partial rolling operations are performed
thereon.
The double-armed lever 18 contains a guide slot 32 in which a
slotted link 34 is guided, said slotted link accommodating a pivot
pin 33. The pivot pin 33 is mounted on a bracket 35 which slides in
a guide 36 on the frame 10 in a direction which is radial relative
to the workpiece axis X, said bracket being adjustable by means of
a spindle 37 and a worm drive 38 so that displacement of the
pivoting pin 33 of the double-armed lever 18 enables the length and
therefore the velocity of the axial motion of the work slide to be
adjusted.
The profiling tools 40 take the form of worms (hereinafter referred
to as tool worms) of which the normal section through the threads
has the basic rack profile of the gear being rolled. In the
illustrated machine, and as shown in FIG. 4, two tool worms are
provided and are disposed diametrically opposite each other, FIG. 2
showing only one of the tool worms 40 together with its drive.
The trunnions 41 of a tool worm 40 are rotatably supported in a
tool head 42. The tool head is supported by means of a circular
guide 43 on a tool carrier 44 so as to be angularly adjustable
about an axis Y which intersects the workpiece axis and the axis of
the tool worm 40 at right angles. For the sake of simplicity, the
tool head 42 in FIG. 2 is shown so adjusted that the axis of the
tool worm 40 is disposed in the plane of the drawing. When straight
teeth are cold rolled, the axis of the tool worm 40 will of course
be inclined relative to the said plane at an angle similar to the
pitch angle of the screw thread of the tool worm.
The tool carrier 44 is guided in a guide 45 of the machine frame 10
along the said axis Y. An annular piston 48, constantly biased, by
means of one of the branches of an oil distribution network 49 from
a pressure source 50, in the direction of lift-off of the tool worm
40 from the workpiece 1, is provided on a rearward extension 46, of
smaller diameter, of the tool carrier 44, the extension 46 being
guided in a bore 47 in the machine frame.
The rearward extension 46 of the tool carrier 44 extends through an
opening 51 in a wedge 52 whose rear inclined wedge surface 53 is
supported on a correspondingly inclined guide surface 54 in the
machine frame, and whose front surface 55 is disposed at right
angles to the axis Y and bears on the end face of a nut 56 for the
feed of the tool worm 40, the said nut co-operating with
screwthreading 57 on the external surface of a shoulder 58 on the
rearward extension 46 of the tool carrier 44. The external
circumference of the feed nut 56 is provided with worm wheel
gearing 59 and can be rotated by means of a worm 60 from a control
drive 61 for controlling the feed motion of the tool worm.
The oil pressure acting on the annular piston 48 ensures that the
tool support 44 is constantly thrust by the feed nut 56 against the
wedge 52.
A piston 62, slidable in a cylinder bore 63, which is biased by the
oil pressure of the coil pressure supply network 49, thrusts on the
broad end of the wedge 52. The piston 62 retains the narrow end of
the wedge 52 constantly in physical contact with a tappet 64 which
in turn bears on a tappet roller 65, supported on one arm 66 of a
rocker lever, the other arm 67 of which co-operates through a cam
follower roller 68 with a disc cam 69 which is mounted on a shaft
70 driven through a bevel gear pair 71, 72 from the shaft 26.
Rotation of the disc cam 69 is accompanied by reciprocation of the
wedge 52 and therefore by reciprocation of the tool carrier 44 with
the tool head 42 and the tool worm 40. A connecting rod 73, hinged
on the end of the arm 67 of the rocker lever 66, 67, and connected
with a corresponding rocker lever of the reciprocating drive of the
second tool worm, not shown ensures that the latter performs the
same reciprocating motions.
Reciprocation of the workpiece 1 in the direction of the axis X and
of the tool slide 40 in the direction of the axis Y both derive
from the same shaft 26 and therefore are in synchronism with each
other, and a relative generating motion, corresponding to the
profile to be generated, is imparted to both the tool worm and the
workpiece.
To perform the generating motion, the workpiece 1 is rotated by the
main shaft 29. As can be seen in FIG. 1, the main shaft 29 drives,
through a bevel drive 74, a reduction shaft 75, a gear wheel pair
76, a differential transmission 77, a change gear set 78,
gearwheels 79, 80, 81, a partial change gear set 83, a bevel drive
84 and a gearwheel pair 85, 86, a worm 87 which meshes with the
wormwheel 16 which in turn drives the work spindle 3 and therefore
the tool through the driver collar 14 and the lead bush 11.
One pinion on the input shaft 88 of the differential transmission
77 drives a gearwheel 90 through a toothed belt 89, the gearwheel
90 being freely rotatable on a shaft 91. The control member of a
dog clutch 92 is slidably mounted on the shaft 91 and can be
optionally engaged with the dogs of a wormwheel 94, rotatable in
the machine frame 10 by an adjusting worm 93, in order to couple
the shaft 91 to the wormwheel 94, or may be engaged with dogs on
the gearwheel 90 in order to couple the shaft 91 to the gearwheel
90. In the latter case, a supplementary rotating motion is imparted
to the planet gear cage 97 of the differential transmission 77, and
therefore to the output shaft 98 of the said differential
transmission, through the toothed belt drive 89, 90, the shaft 91,
a change gear set 95 and a pinion 96, while in the former case the
planet gear cage 97 is retained motionless by means of the dog
clutch 92. The partial change gear set 83 is defined by the desired
number of teeth of the gearing to be produced on the circumference
of the workpiece 1. The purpose of the two change gear sets 78 and
95 will be described subsequently.
To rotate the tool worms 40, a shaft 99, disposed in the drive line
for the workpiece 1 and having mounted thereon the last wheel of
the change gear transmission 78 and the gearwheel 79, is extended
and drives, through a bevel drive 100, a shaft 101 (FIG. 2) from
which rotation of both tools is derived.
At each end the shaft 101 is provided with one pinion 102 of an
axially slidable toothed belt drive 103 which in turn drives a
shaft 104, journaled on the geometrical axis Y in the tool support
44. The aforementioned shaft 104 in turn drives, through a bevel
drive 105, a gearwheel 106 which meshes, by way of an intermediate
wheel 107, with a gearwheel 108 provided on the lower trunnion 41
of a tool worm 40.
The reciprocating drive for the work slide 5 and the reciprocating
drive for the tool support 44 are matched to each other so that the
tool worms 40 assume their inner dead center position relative to
the workpiece axis X (FIGS. 1 and 2) when the work slide 5 is moved
to the right in FIG. 1. This motion is therefore accompanied by the
part rolling motions of the tool worms 40 on the workpiece. It is
desirable that the profile of the worm thread of each tool worm 40
retains its position unchanged during each part rolling operation
relative to the tooth gap to be rolled into the workpiece 1. To
this end the tendency, because of the rotation each tool worm 40,
of the points of contact between the worm tooth flanks and the
workpiece tooth flanks to wander off-center towards the left or
right (FIGS. 5,6,8 and 9) and, as a result, up or down between
tooth tip and tooth root (which produces the action known as
inherent generating action) is counteracted by axial displacement
of the tool worm and by movement of the workpiece slide 5 to the
right.
Means for obtaining compensation of the tool worm rotation during
the motion of the work slide 5 to the right will now be
described.
The trunion 41 of the tool worm 40, at the top in FIG. 2, is
journaled in a cylindrical bore 109, closed at one end, into which
a branch of the oil pressure distribution network 49 extends, so
that the end face of the aforementioned trunnion 41 is constantly
biased with oil pressure. Accordingly, the tool worm 40 is retained
by means of a thrust bearing 110 in contact with a tappet 111 whose
rear end bears by way of a needle bearing 112, on a wedge 113 which
is adapted to reciprocated in the tool head 42.
The reciprocating motion of the wedge 113 of each of the two tool
worms 40 is directly derived from the motion of the work slide 5.
To this end, the underside of the work slide is provided with an
angularly-adjustable slotted link 114 with a slotted link guide 115
(FIG. 1). The slotted link 114 may be adjusted angularly by an
adjusting worm 116 and may be retained in the selected position by
means of a locking nut 117. A sliding block 118 slides in the
slotted link guide 115 and is supported on a pin 120 which extends
upwardly from a slide 119. The slide 119 is supported in a guide
121 in the machine frame 10 and extends at right angles to the
workpiece axis X. Each end of the slide 119 has joined to it one
end of a connecting rod 122 for the reciprocating drive of the
wedges 113 of both tool worms 40. At its other end, each connecting
rod 122 is hinged to one end of a double-armed lever 123, the other
end of which lever is connected by a connecting rod 124 to one end
of a double-armed lever 125 supported in the tool head 42, the
connecting rod 124 extending along the axis Y of the tool carrier
144 and through a longitudinal bore in the shaft 104, the other end
of the double-armed lever 125 being adapted to move the wedge 113.
To prevent the reciprocating motion of the tool carrier 44 from
affecting the reciprocating motion of the wedge 113, the
double-armed lever 123 is supported, as shown in FIG. 3, on a
pivoting pin 126 the ends of which are supported in double-armed
levers 127 which are always of the same length as the lever 123,
one of the ends of each lever 127 being pivotally mounted in bosses
128 on the rearward end of the tool carrier extension 46, while the
other end of each double-lever 127 is guided, by a pivot pin having
a head 129 providing a sliding block, in a slotted link guide 130
in the machine frame 10.
The apparatus by means of which the inherent generating action on
the workpiece 1 is counteracted during the motion of the work slide
5 to the right, is disclosed in FIG. 1.
A slotted link 131, angularly adjustable by means of an adjusting
screw 132 around a horizontal axis and at an angle relative to the
workpiece axis X, is supported on a bracket on the spindle-bearing
pedestal 4. A block 134, in which a pin on one end of a
double-armed lever 135 is journaled, slides in a guide 133 in the
slotted link 131. The double-armed lever 135 pivots about an
eccentric bearing pin 136 on a shaft 137 which is supported in a
bracket 138 of the machine frame. The other end of the double-armed
lever 135 is formed into a clevis 139 from which two trunnions
extend inwardly into an annular groove 140 between two collars on
the shaft of the worm 87 which is adapted to rotate the work
spindle 3.
When the slotted link 131 is adjusted as illustrated in FIG. 1, a
motion of the work slide 5 to the right causes the double-armed
lever 135 to be pivoted in the anticlockwise direction and the worm
87, constantly driven in the anticlockwise direction (when viewed
from above) is moved downwardly, so that with an appropriate
setting of the slotted link 131 the wormwheel 16 for driving work
spindle 3 remains stationary while the work slide 5 moved to the
right. During this operation, the work spindle 3 with the workpiece
1 performs only the rotation defined by the guide grooves 12 in the
lead bush 11, said rotation being selected in accordance with the
desired pitch angle of the gearing to be generated.
It is however not necessary for a separate lead bush 11 to be
provided for any helix angle that may be encountered. A few lead
bushes with graded pitch angles of the guide groove 12 are
sufficient; for a desired and defined helix angle the lead bush 11
with the associated driver collar 14 is fitted into the machine,
the guide groove 12 having the pitch angle nearest to the desired
helix angle. The desired helix angle may then be obtained by
corresponding additional adjustment on the slotted link 131 which
is set up so that the worm wheel 16 does not remain stationary when
the work slide 5 moves to the right but experiences the required
small supplementary rotation or reverse rotation which is necessary
to obtain for the gear tooth system of the workpiece 1 the helix
angle which is slightly larger or smaller relative to the pitch of
the guide grooves 12 of the lead bush 11.
It is of course also necessary for the crossing angle of the axis
of the tool worm 40 relative to the workpiece axis X to be adjusted
in accordance with the helix angle of the gear tooth system of be
generated. This setting is obtained in that the tool head 42 is
adjusted by its circular guide 43 to the corresponding angle
relative to the workpiece axis X by means of a control drive 141
through a worm 142 which meshes with worm gearing 143 formed on the
circumference of the tool head.
It may be assumed that a straight-tooth spur gear is to be produced
with the machine described hereinabove. To this end, a cylindrical
member, the external diameter corresponding approximately to the
pitch circle diameter of the gearwheel to be generated, is
connected to the work spindle 3 by means of the clamping device 2
into which the said workpiece is thrust by the work holder 6. Since
straight-tooth gearing is to be obtained, the tool head 42 is
adjusted, by the control drive 141, relative to the tool support 44
so that the axis of the tool worm 40 intersects with the workpiece
Axis X at the pitch angle of the tool worm. When the tool carrier
44 assumes its inner dead center position the feed of the tool
worms 40 relative to the workpiece is obtained by virtue of the
fact that the feed nut 56 is rotated by the control drive 61, by
way of the worm drive 60, 59, until the external diameter of the
tool worm 40 is just clear of the workpiece 1.
Also, when the tool support 44 is in the inner dead center
position, the tool worms 40 have their screw threads adjusted
symmetrically relative to the workpiece axis X, namely by rotation
of the worm 93 when the dog clutch 92 is coupled to the wormwheel
94. Since the input shaft 88 of the differential transmission 77 is
stationary when the motor is switched off, rotation of the
adjusting screw 93 of the planet wheel cage 97, and therefore the
output shaft 98 of the differential transmission, causes the tool
worms 40 to be rotated through the earlier-described supplementary
rotation until the desired symmetrical position relative to the
workpiece is obtained.
The position of symmetry of the tool worms 40 relative to the
workpiece axis X for a workpiece wheel 1 with an even number of
teeth is shown in FIG. 5 in which, in the interests of
simplification, the axes of the tool worms are shown tipped into
the plane of the drawing. In actual fact, however, in the case of a
workpiece wheel 1 with straight teeth, the axes would pass through
the plane of the drawing at an angle equal to the pitch angle of
the worm thread. In this position of symmetry, the center lines of
the two diametrically opposed sections through the worm threads of
the two tool worms coincide in a section extending along the plane
which is normal to the workpiece axis X and with the shortest
connecting line between the said axes which intersect the workpiece
axis and the axes of the tool worms at right angles.
FIG. 6 shows the position of symmetry of the tool worms with an odd
number of teeth of the workpiece wheel 1. In this case, one tool
worm is rotated through 180.degree. relative to its position in
FIG. 5 so that in the normal section to the workpiece axis X
described herein, the worm thread of one tool worm is disposed
diametrically opposite to the gap between two adjacent turns of the
worm thread of the other tool worm.
When the tool worms act on the workpiece in the position of
symmetry, the pressures exerted by each tool worm on the workpiece
are already automatically compensated on each tool worm with
respect to the tangential components and the radial pressures are
eliminated by virtue of the fact that the tool worms are disposed
diametrically opposite each other.
The motor 31 is started after the pivot pin 33 of the double-armed
lever 18 is adjusted by the worm drive 38 and the spindle 37 so
that the axial motion of the work slide 5 is greater than the tooth
width of the workpiece 1 and after the work slide velocity during
the right-hand motion is set, in accordance with calculations, to
correspond to the rolling speed of the tool worms. Accordingly, and
by means of the crank 22, the work slide 5 is axially reciprocated
in the direction of the workpiece axis X and, by means of the disc
cam 69, the tool supports 44 are reciprocated by the wedges 52 in
synchronism and in the direction of the axis Y. The disc cam 69 is
so constructed that the tool worms 40 obtain and retain their inner
dead center position when the work slide in FIG. 1 moves to the
right. The path traversed by the tool worms 40 relative to the
workpiece 1 (a closed-circuit locus), designated with the numeral
144 in FIG. 7, results from the synchronized reciprocating motion
between the workpiece and the tool worms.
During the reciprocating motion of the workpiece and the tool worm,
both are rotated by the above-described rotary drive so that an
inherent generating action, corresponding to the profile to be
generated, is obtained between the tool worms and the workpiece,
but this inherent generating action is counteracted by the
above-described counter-generating apparatus, operating in
synchronism with the work slide motion, namely the apparatus for
the axial displacement of the tool worms 40 and the apparatus for
the axial displacement of the driving worm 87, such compensation
taking place during the time in which the tool worms 40 are
disposed in their inner dead-center position and when the work
slide acts to the right upon the workpiece 1.
For preforming, the tool worms 40 are gradually, or in steps,
advanced by means of their associated control drive 61 towards the
workpiece axis X until the tooth profile is rolled from the
workpiece over its full height. The speed at which the tool worm
feed is applied depends solely on the properties of the material of
the workpiece. It is not necessary for the feed to be applied
uniformly or in equal steps; it may be so selected that
approximately the same workpiece volume is displaced with each
part-rolling operation.
When the workpiece gearing is being preformed, the dog clutch 92 is
engaged with the dogs of the worm wheel 94 which is retained in
position by the adjusting worm 93. The dog clutch retains the shaft
91 and therefore the planet wheel cage 97 of the differential
transmission through the change gear set 95 and the pinion 96. The
gearing is preformed with a few enveloping planes. For example it
may be assumed that the change gear set 78 is so selected that for
each rotation of the tool worm 40, and therefore one tooth pitch on
the gearing to be generated, the work slide 5 performs two strokes
and the ratio of workpiece strokes per tool rotation is K = 2. The
two positions assumed by each tool worm in the two stokes and
relative to the workpiece are illustrated in FIGS. 8 and 9 which
represent the engagement of the tool worm and workpiece at the end
of the preforming operation. In FIG. 8 in the middle of one tool
tooth is opposite to the middle of a tooth gap of the workpiece.
One tool tooth forms the tooth root of the tooth gap while the two
adjacent tool teeth form the tip of the tooth profile of the two
workpiece teeth adjacent to the gap. In FIG. 9 a tooth gap on the
tool is disposed opposite to a tooth on the workpiece. In this
configuration the middle zones of the two flanks of the workpiece
tooth are formed. FIG. 10 shows a cross-section through a tooth of
the workpiece wheel 1 in greatly enlarged form. The line 145
indicates the profile of the tooth which is not yet preformed over
its entire height while the line 146 represents the profile of the
finish-formed tooth 147. The profile of the tooth, preformed to its
full height, was not shown because on the drawing this could not be
clearly distinguished from the tooth profile 146. FIGS. 8 to 10
therefore disclose that, given a ratio of workpiece stroke to
workpiece rotation of K = 2, the teeth are preformed with three
enveloping planes to a tooth profile which is a good approximation
to the tooth profile of the finished tooth form.
If preforming is to be preformed with more than three enveloping
planes, the change gear set 78 is so selected that the number of
workpiece strokes for each tool rotation differs from K = 2 but
remains between K = 1.5 and K = 2.5. The value of K is so selected
that the same meshing position between toolworm and workpiece is
periodically repeated after a few teeth, depending on the desired
number of enveloping planes, the number of said teeth having to be
so selected that a multiple thereof deviates by one tooth from the
number of teeth of the workpiece wheel.
When gear-generating is performed over the entire height, the tool
worms 40 are retracted by a small amount by operating the control
drive 61 in order to reduce the pressure acting upon the workpiece.
Furthermore, for finish-forming, the dog clutch 92 in FIG. 1 is
moved to the right to engage with the dogs on the gearwheel 90 so
that the planet wheel cage 97 will then be rotated by the input
shaft 88 of the differential transmission 77 via the gear drive 89,
90, the shaft 91, the change-gear set 95 and the pinion 96 so that
the output shaft 98 of the differential transmission is provided
with a supplementary rotation. The change-gear set 95 is previously
so selected that the supplementary rotation of the output shaft of
the differential transmission causes the ration K of the number of
strokes of the workpiece slides 5 relative to the tool worm
rotation to become smaller, by a small amount, than for the
preforming operation, so that it becomes aperiodic, for example K =
13/7, and to enable the tooth profile to be finish-formed with a
greater number of enveloping planes than in the preforming
operation.
A displacement of the pivoting pin 33 of the double-armed lever 18
to adapt the reciprocating speed of the tool slide 5 in its
right-hand motion to the changed rolling speed of the tool worms is
not generally necessary. The operating speed in preforming is so
adjusted that the tip zone of the worm profile performs a pure
rolling motion relative to the workpiece because the principal
rolling work in preforming is performed by the tip zone of the worm
thread of the tool worms. If engagement of the additional rotation
of the output shaft 98 of the differential transmission 77
increases the rotational speed of the tool worms 40 while the tool
slide 5 retains the same receiprocating speed, the zone of the worm
thread profile in which a pure rolling motion is performed will be
displaced further inwardly relative to the tool worms and into the
pitch circle zone. However, this is desirable because in
finish-forming the rolling work is distributed approximately
unformly over the entire height of the profile.
To produce a helical gear, a lead bush 11 with the appropriate
driver coller 14 is selected, the guide grooves 12 having a pitch
angle which is nearest to the desired helix angle .beta., said lead
bush being mounted in the machine. The difference between the helix
angle .beta. and the pitch angle of the guide grooves 12 is then
adjusted, as described above, by the adjusting worm 132 on the
slotted link 131. The tool heads 42 with the two tool worms 40 are
also adjusted by their control drive 41, as shown in FIG. 11, so
that the axis of the tool worms intersects the workpiece axis X at
an angle .gamma. which is obtained from the desired helix angle
.beta. of the gearing to be generated and the pitch angle of the
tool worms.
Preforming and finish forming is then performed fundamentally in
the same manner as in the production of straight-toothed gear
wheels. However, since the helix angle of the gear tooth system is
measured on the pitch circle and is greater on the tooth tip than
on the pitch circle, the tool worms are appropriately adjusted to a
somewhat larger angle at the beginning of the preforming operation,
said angle being progressively reduced with progressive feed of
tool worms 40 by operating the coupled control drives 141 of the
two tool heads 42 in steps of .DELTA..gamma. until it corresponds
to the helix angle .beta. of the geartooth system when the tool
worms have fully penetrated.
It is found, particularly in the preforming of helical gearing and
in particular helical gearing having a large helix angle, that the
tool worms 40 are displaced from the tooth direction at the
beginning and end of each part-rolling operation. This is due to
the fact that they enter into the workpiece and emerge therefrom at
an angle and that, accordingly, at this moment of time and tool
worm can thrust on the workpiece only in a tangential direction. To
compensate for this effect, a correcting template 145 may be
mounted on the bracket of the spindle-bearing pedestal 4 of the
work slide 5, said bracket supporting the slotted line 131. A
follower roller 146 on one end of a lever 147 (the right hand end
in FIG. 1) co-operates with the template 145, the middle of said
lever being pivotably joined to the end of a lever 148 which in
turn is mounted on the shaft 137 which carries the eccentric pin
136 which functions as the bearing journal for the double-armed
lever 135. The piston rod of a piston 149 is hinged on the left
hand end of the lever 147 and the piston rod of a piston 150 is
hinged on the right hand end of the said lever. In FIG. 1 it is
assumed that a changeover valve 151 is so adjusted that the
underside of the piston 149 and the top of the piston 150 are
connected to the oil pressure distribution network 49, and the
oppositely-disposed sides of the pistons are connected to a return
line 152 which extends to an oil sump.
The piston 149 bears at its upper end against an abutment so that
the left hand end of the lever 147 is able to pivot around a fixed
point. The follower roller 146 disposed on the right nand end of
the lever 147 is constantly maintained in contact with the template
145 by virtue of the oil pressure acting on the top of the piston
150. Accordingly, the template 145 ensures that during the
reciprocating motion of the work slide the eccentric pin 137 is
moved up and down by means of the levers 147 and 148, and the
driving worm 87, which rotates the work spindle 3, has an axial
displacement imparted to it, said axial displacement being
superimposed on the axial displacement provided by the slotted link
131 through the lever 135. The shape of the template 145 is so
selected that the rotary motion superimposed and imparted on the
workpiece during the run in and run out of the tool worms, rotates
the workpiece opposite to the tool worms. The shape of the template
is defined by virtue of trial gear-generating operations.
If the action of the template 145 is to be discontinued, which may
be desirable in cold rolling of straight gearing or in
finish-forming or at the end of finish-forming of helical gearing,
the changeover valve 151 is moved into a second position in which
oil pressure is applied to the top of the piston 149 and the
underside of the piston 150 and the oppositely-disposed sides of
the pistons are connected to the return line 152. Accordingly, the
left-hand piston 149 is moved into its lower limiting position and
the right-hand piston 150 into its upper limiting position in the
associated cylinders. Since the middle of the lever 147 is
pivotably joined to the end of the lever 148, the aforementioned
action does not vary the position of the lever 148 relative to its
center position so that the eccentric pivoting pin 136 for the
double-armed lever 135 retains its position when the action of the
template 145 is discontinued.
If longitudinally-crowned gearing is to be produced, the disc cam
69, controlling the reciprocating motion of the wedge 52 for
operating the tool slide 44 in the Y direction, is replaced by
another disc cam which, as indicated by broken lines in FIG. 2, is
slightly raised in the zone corresponding to the inner dead center
position of the tool slides. Accordingly, the said tool slides are
retracted during each part-rolling operation in the cetnral zone by
an amount .DELTA.Y as indicated in FIG. 12 in which the path 153 of
the tool worms relative to the workpiece is shown with a disc cam
69 corrected in the manner described hereinbefore.
The machine described hereinabove is also suitable for
simultaneously cold rolling more than one gearwheel. A disc cam 69,
in which two raised position are provided in the zone corresponding
to the inner dead center position of the tool worms is used if the
aforementioned gearwheels are to be provided with longitudinal
crowning, so that the path 154, illustrated in FIG. 13, is obtained
for the motion of the tool worms relative to the workpieces.
* * * * *