Apparatus for bending strip material into toothed shape

For bending strip material into toothed shape, the strip is introduced once into a pair of toothed jaws and a bending member is moved from one end position to another to bend the strip about one end tooth, one end flank of which is exposed. The strip is removed and then similarly bent about another end tooth, in a preferably mirror-image arranged part of the apparatus, in an opposite bending direction, thereby to form a tooth in the strip. The bending steps are repeated as often as necessary. The invention is particularly applicable to the forming of a toothed band from a plane sheet metal strip.

This invention relates to the bending of strip material into toothed shape, 
and is particularly although not exclusively concerned with producing a 
toothed band from a plane sheet steel strip. 
Toothed bands in the form of a ring are used particularly in planetary 
gearings, as shown, for example, in German Pat. No. 2 545 681. To produce 
such toothed bands as these, there is used an apparatus having a fixed 
part extending in a longitudinal direction with a row of teeth located at 
the front end corresponding to the form of the teeth of the toothed band, 
and having a movable part aligned relative to the longitudinal axis of 
this part with a row of teeth arranged at its front end which are capable 
of being inserted into the teeth of the fixed part. The width of the 
movable part and of the fixed part of the apparatus are the same, thereby 
ensuring mutual engagement of the two front rows of teeth. The plane sheet 
steel strip is introduced between the rows of teeth of both parts, and the 
movable part is subsequently moved in the direction of the fixed part 
until the teeth of the two rows of teeth mesh, thereby forming the toothed 
band. 
In this pressing process, the toothed band is expanded and compressed to an 
excessive degree relative to the neutral axis in the centre, and more 
particularly in the areas of the points of the teeth, with the result that 
the material is overstressed there, so that with prolonged stressing the 
toothed belt may fracture at these critical points, even within a 
comparatively short time. 
The present invention aims to provide, particularly but not exclusively, an 
improved apparatus, with which excessive expansion and compression in the 
critical area of a toothed band can be avoided as it is formed from a 
strip material, such that the fatigue strength of the band can be 
increased to a quite considerable degree. 
According to one aspect of the present invention, there is provided 
apparatus for bending strip material into toothed shape, the apparatus 
comprising: 
bending jaw members having sets of teeth which are adapted to engage with 
one another with a flank of each of two end teeth exposed; 
means for moving said jaw members towards and away from one another to 
bring said sets of teeth into and out of engagement with one another; and 
at least one bending member movable between two end positions to bend strip 
material clamped between said jaw members about said two end teeth 
respectively in turn, in opposite bending directions. 
According to another aspect of the present invention, there is provided a 
method of bending strip material into toothed shape, comprising the steps 
of: 
clamping the strip between toothed bending jaw members such that it is 
clamped, substantially undeformed, by one flank of one end tooth of which 
the other flank is exposed; 
moving a bending member from one end position to another thereby to bend 
the strip in one direction about said one end tooth such that the strip 
abuts both flanks of the tooth; 
removing the strip from the jaw members; 
inserting the strip between toothed bending jaws such that it is clamped, 
substantially further undeformed, by one flank of another end tooth of 
which the other flank is exposed; and 
moving a bending member from one end position to another thereby to bend 
the strip in an opposite direction about said other end tooth such that 
the strip abuts both flanks of the tooth, thereby to form a tooth in said 
strip. 
In one embodiment of the invention, the bending member travels on an 
arcuate path, and is preferably arranged on a rotating disc which is 
connected to an actuating handle. Advantageously, the bending member may 
be formed as a pin which, in one of its end positions, engages in a recess 
in a fixed part of the bending apparatus. The actuating handle co-operates 
with an abutment to define the other end position of the bending member. 
A toothed band may be produced in a preferred arrangement of the invention 
in such a way that only one single tooth is formed at a time, quite in 
contrast to conventional apparatus wherein several teeth are pressed in 
one single operation. Surprisingly enough, it has been discovered that the 
expansion and compression in the critical area of the toothed band when 
the teeth are bent individually is considerably less than in the known 
pressing process during which several teeth in the toothed band are formed 
at the same time. Tests have clearly confirmed that the fatigue strength 
of a preferred toothed band produced in accordance with the invention was 
approximately three times as great as that of a toothed band pressed by 
conventional apparatus.

FIG. 1 is a partial top plan view of the apparatus for producing a toothed 
band from a plane sheet steel strip 1. This apparatus has a fixed part 2 
extending in a longitudinal direction, its longitudinal axis being 
indicated by the reference numeral 3. This part 2 has at a front end 
thereof a row of teeth, the teeth 4,5 of which correspond to the form of 
the teeth of the toothed band to be prepared. In the embodiment shown in 
the drawing the points of the teeth 4,5 lie on an arc. The reference 
numeral 5 denotes one end tooth of the fixed part 2. 
A movable part 6 is aligned relative to the longitudinal axis 3, with a row 
of teeth arranged at a front end thereof, the teeth 7 and 8 of which are 
adapted to engage in the spaces between the teeth 4,5 of the row of teeth 
of the fixed part 2. The reference numeral 8 denotes the end teeth of the 
row of teeth of the movable part 6. The points of the teeth 7,8 also lie 
on an arc in the same way as those of the teeth 4,5. Thus, the toothed 
ends of the parts 2 and 6 constitute toothed bending jaw members. 
A further fixed part 2' and a movable part 6' are respectively arranged in 
mirror image fashion about an axis of symmetry S--S (FIG. 3) which is 
perpendicular to the longitudinal axis 3, the teeth of those two parts 2', 
6' being denoted with corresponding reference numerals 4'-8'. 
The two movable parts 6, 6' are arranged for movement towards and away from 
the respective fixed parts 2, 2', and are guided in longitudinal guideways 
9, 10 (FIG. 1) which, for reasons of clarity, are not included in FIG. 3. 
The two movable parts 6, 6' are connected to strips 11 which are connected 
to a drive (not shown in greater detail) which provides a to- and-fro 
movement. A dual-action pressure medium-controlled cylinder may be used 
for the drive, which bears, directly or indirectly, for example by way of 
a toggle lever mechanism, on the movable parts 6, 6'. The guideways 9, 10 
are mounted on a plate 12 to which the corresponding fixed part 2 and 2' 
respectively is also connected. 
The width b of each fixed part 2, 2' is less than the width B of the 
corresponding movable part 6, 6' by such an amount that the outer flank 8a 
and 8a' of each end tooth 8 and 8' of the movable parts 6 and 6' is 
exposed, as is shown, for example, in FIG. 3 of the drawing. A respective 
member 13, 13', which is arranged for movement on an arcuate path between 
two end positions, is arranged in the region of each end tooth 8 and 8', 
and in the embodiment shown, is formed as a pin which is mounted on a 
rotating disc 14, 14'. The rotating disc 14, 14' pivots in the plate 12 
and is controlled by way of a respective actuating handle 15, 15'. Only 
the axes of the two actuating handles are denoted in FIG. 3 of the drawing 
by 15 and 15' respectively. 
In one end position, each bending member 13 and 13' engages in a respective 
recess 16 and 16' in the respective fixed part 2 and 2'. 
A respective abutment 17 and 17' co-operates with each actuating handle 15 
and 15', to define the other end position of the respective bending 
member. 
The apparatus operates as follows. 
Firstly, one end of the sheet steel strip 1 is clamped in the gap between 
the tooth flank 8b which is an inward continuation of the freely 
projecting tooth flank 8a, and the outer tooth flank 5a of the end tooth 
5, as is shown in the left-hand portion of FIG. 3 of the drawing. One 
outer end of the sheet steel strip 1 is located in the base between the 
teeth 7 and 8 of the movable part 6 of the apparatus. The bending member 
13 occupies the position shown by a continuous line, to which the sheet 
steel strip 1 forms a tangent. The actuating handle 15 is subsequently 
swivelled in a clockwise direction until it rests against the abutment 17. 
The swivelling motion of the actuating handle 15 causes the bending member 
13 likewise to effect a swivelling movement, until it arrives in the 
position denoted by a broken line. The plane sheet steel strip is thus 
bent around the point of the tooth 8 during this motion by the bending 
member 13, which in its final end position, presses the plane sheet strip 
against the freely projecting tooth flank 8a. This final position of the 
plane sheet steel strip 1 is denoted in FIG. 3 of the drawing by a broken 
line. The movable part 6 is then disengaged from the fixed part 2 by being 
displaced to the left in FIG. 3 of the drawing, and the sheet strip 1 is 
released, now having the form shown in FIG. 4 of the drawing. The bent 
part is denoted by the reference numeral 1a. 
The sheet strip 1 thereby formed, without being turned about its 
longitudinal axis, is now inserted between the two parts 2' and 6', such 
as is shown in detail in the right-hand portion of FIG. 3. The bent part 
1a lies between the tooth flank 7a' and the tooth flank 5b', whilst the 
continuous plane portion of the sheet steel strip 1 is clamped in the gap 
between the tooth flank 8b', which is an inward continuation of the freely 
projecting tooth flank 8a', and the outer tooth flank 5a' of the end tooth 
5'. The actuating lever 15', and with it the bending member 13', is then 
swivelled in a counter-clockwise direction into the position represented 
in the right-hand portion of FIG. 3 by a broken line, until it comes to 
rest against the abutment 17'. During this swivelling motion the bending 
member 13' in turn bends the continuous plane sheet steep strip into the 
position shown in broken line. The strip 1 then is as shown in FIG. 5 of 
the drawing, in which an additional bent part 1b follows on from the bent 
part 1a. 
The sheet steel strip 1 with its form according to FIG. 5 is then clamped 
again between the two parts 2 and 6, the bent parts 1a and 1b being 
inserted into the gap between the teeth 5 and 7 and 4 and 7 respectively. 
The individual bending processes are then repeated accordingly until a 
toothed band, which is formed into a toothed ring by welding together the 
two ends, has been produced from the plane sheet steel strip. 
It is an important feature that by bending the individual teeth of the 
toothed band in stages which are staggered in respect of time, the 
critical points are relatively only very slightly stressed, with the 
result that the fatigue strength of the steel band, and hence of the 
toothed ring produced therefrom, can be increased to a quite considerable 
degree. 
The illustrated apparatus may be varied in several ways. For example, the 
two fixed parts 2 and 2' may be formed integrally as a single part. 
Alternatively, the parts referenced 2 and 2' may be made movable, with the 
parts referenced 6 and 6' fixed. The parts 2, 2' may be made wider than 
the parts 6, 6', thereby having more teeth, with appropriate modification 
of the bending members 13, 13'. Although the illustrated apparatus is 
substantially symmetrical about the axis S--S as regards the members 2, 2' 
and 6, 6' and 13, 13', this is not absolutely essential. The teeth between 
which the strip 1 is clamped are advantageously shown in the illustrated 
apparatus as lying on an arcuate path, to facilitate the production of a 
toothed band. Nevertheless, they could be disposed on straight lines if 
desired. Any suitable means for moving the bending members on any suitable 
path may be employed, instead of the arrangement illustrated. 
In an alternative form of the illustrated apparatus, that part of the 
apparatus to the right of the axis of symmetry S--S may be dispensed with. 
In its place, a second bending member 13' is provided in preferably 
mirror-image fashion to the first bending member 13, about the 
longitudinal axis 3, such that it is positioned at the top of the fixed 
part 2, as seen in FIG. 3. Suitable modification of the mounting 
arrangement for the two bending members 13, 13' is then required. 
Conveniently, the two bending members 13, 13' could be mounted on a common 
rotatable disc 14 having one or more actuating handles 15. 
In another variation, the two bending members 13, 13' may be replaced by a 
single bending member adapted to be moved between two stations, for 
carrying out the alternate bending operations.