Method and apparatus for manufacturing straight or inclined toothed machine elements, especially spur gears by cold working

A method of, and apparatus for, manufacturing straight or inclined toothed machine elements, especially spur gears, by cold working, which comprises holding under axial prestress a single gear-workpiece blank during a rolling or generating operation between two press punches at such a pressure that under the action of the rolling operation pressure stresses prevail between the press punches and the workpiece, these pressure stresses corresponding at least to the elastic limit of the workpiece material. Further, due to the simultaneous action of the prestressing force and the rolling operation there is formed at least at one of both end surfaces of the workpiece an end surface which is dispositioned exactly perpendicular to the axis of the workpiece.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved method of, and 
apparatus for, manufacturing straight or inclined toothed machine 
elements, especially spur gears, by cold working or rolling. 
Heretofore attempts to fabricate spur gears by cold rolling were 
principally carried out in two different ways: 
According to a first technique the teeth were rolled at a rod-like blank, 
whereafter the individual gears were severed. What is disadvantageous with 
this method is the expensive pretreatment operations carried out upon the 
rod by grinding, something which is necessary in order to ensure for the 
proper guiding of the relatively long parts during rolling. Furthermore, 
the expensive further processing work carried out at the rolled rod by 
sawing and drilling as well as the loss of the rod ends, which possess too 
inaccurate teeth profile, had to be tolerated, with up to 70% of the blank 
having to be cut. Since the cutting work is inaccurate, the cut-off gear 
discs do not possess any exact axial contact surface for the further 
processing work, so that for the exact centering needed for the subsequent 
operations, for instance grinding of the bore, there was only available 
the possibility of reception in the pitch circle, for instance clamping by 
means of inserted roller bodies. In the case of relatively small gears 
this was particularly associated with extreme difficulties and rejection 
of the workpieces. 
The second prior art technique contemplates rolling individual gears. Thus, 
due to axial flow of the material at the region of the teeth there is 
brought about a pronounced axial swelling of the material at the end 
surfaces of the gear. This in turn means that the teeth must be fabricated 
at the blank with large axial tolerances owing to the inaccuracies 
prevailing thereat, and which must be again cut-off following the rolling 
operation. With this procedure there is likewise unavailable any precise 
axial starting surface for the further processing operation following the 
rolling operation, and the procedure is uneconomical due to the cutting 
work. 
For the reasons mentioned the rolling of individual gears has not been 
widely accepted in relation to the rod rolling technique. The rod rolling 
technique, in turn, has certain limitations concerning the economies of 
this process. 
SUMMARY OF THE INVENTION 
Hence, with the foregoing in mind it is a primary object of the present 
invention to provide a method of, and apparatus for, manufacturing 
straight or linear toothed machine elements, especially spur gears, by 
cold rolling, in a manner not associated with the aforementioned drawbacks 
and limitations of the prior art proposals. 
Still a further significant object of the present invention aims at 
fabricating individual gears by cold rolling, while eliminating the 
drawbacks of the prior art techniques, especially as concerns inaccuracy, 
the relatively large cutting waste and the therewith associated increased 
work. 
Another object of the present invention aims at the provision of an 
improved method of, and apparatus for, fabricating individual gears by 
cold rolling in a manner such that at least one end surface of the 
fabricated individual gear has formed thereat during the course of the 
cold rolling work a surface constituting a reference surface which is 
disposed exactly perpendicular to the axis of the workpiece and which 
reference surface is utilized for the subsequent processing or machining 
work, for instance the grinding of the bore. 
Now in order to implement these and still further objects of the invention, 
which will become more readily apparent as the description proceeds, the 
inventive method for manufacturing straight or inclined toothed machine 
elements, especially spur gears, by cold rolling, comprises the steps of 
holding under axial prestress an individual gear-workpiece blank during 
the rolling operation between two press punches at such a pressure that 
under the action of the rolling operation there are produced pressure 
stresses between the work punches and the workpiece, these pressure 
stresses corresponding at least to the elastic limit of the workpiece 
material. Further, due to the simultaneous effect of the prestressing 
force and the rolling operation there is formed at least at one of both 
end surfaces of the workpiece an end surface dispositioned exactly 
perpendicular to the workpiece axis. 
Since the workpiece is prestressed with the mentioned high pressure between 
the press punches at the region of the teeth, there can be at least 
suppressed for the most part an axial deviation of the material at the 
region or zone of the teeth. Furthermore, there is produced at the 
workpiece end surfaces which come into contact with the end surfaces of 
the punches, i.e., the workpiece end surfaces and related punch mutually 
contact one another through an angle extending through 360.degree., a 
surface which is disposed exactly perpendicular to the workpiece axis. 
To the extent that a change of the contact force of the punch is not 
possible or desired, then for the determination of the contact pressure, 
for a given contact force of the punch, the contact surface can be 
appropriately selected. 
For cold rolling there is utilized either radial rolling without axial feed 
or rolling with axially progressive mechanical working or shaping, for 
instance according to German Pat. No. 1,016,228, the disclosure of which 
is incorporated herein by reference. In the first mentioned case, 
according to the method of the invention, the workpiece can be chucked or 
clamped between two round punches, the outer diameter of which is 
approximately equal to the workpiece diameter. In the second mentioned 
case, the generating or rolling tool requires space for its insertion at 
the workpiece, and thus the punch, when used with the method aspects of 
the invention, must possess a contour corresponding to that of the teeth 
to be generated. This contour at most must be the same size and similarly 
shaped or somewhat smaller than the contour of the teeth to be produced at 
the workpiece. This difference in the construction of the outer contour of 
the press punch, which is employed in one case in the form of a round 
"disc" and in the other case, as a toothed element -- depending upon the 
use of the one or other rolling technique -- does not however necessitate 
any principal differences as concerns the inventive concepts. Hence, it 
will suffice in the description hereinafter to consider the method merely 
in terms of a rolling operation with axial feed and employing toothed 
press punches. 
This rolling method can be basically carried out in the manner described in 
German Pat. No. 1,016,222, the disclosure of which is incorporated herein 
by reference, wherein for producing the profile by cold working of the 
workpiece, the workpiece is displaced along its lengthwise axis and 
rotated about such axis and worked externally by means of at least one 
ring-like profiled generating roll or roller. This so-called generating or 
teeth-forming roll is rotatably mounted in a revolving generating or 
rolling head and driven by such rolling head. With each generating roll or 
roller there is accomplished, during a predetermined rapid sequence 
accommodated to the profile pitch or division and the workpiece feed, 
sudden, i.e., briefly effective individual generating or rolling 
operations in the same directional sense and extending predominantly in 
the profile lengthwise direction. Consequently, with the same generating 
roll there can be successively carried out guided or controlled individual 
rolling operations at a helically-shaped zone of the workpiece surface 
adjacent one another in the peripherial direction, the helical-shaped zone 
being governed by the feed of the workpiece. By the same token, there is 
carried out in succession in the profile lengthwise direction individual 
rolling operations which overlap as concerns their application at the 
workpiece. These operations are accomplished such that during the 
individual rolling operations material is displaced along a relatively 
small lengthwise section of the workpiece predominantly in the radial 
direction. 
In order to carry out the aforementioned method aspects in the just 
explained manner, there is also proposed, according to the invention, an 
apparatus for the performance thereof. Such apparatus comprises means for 
displacing the workpiece along its lengthwise axis and for rotating the 
workpiece about its lengthwise axis. Further, there is provided at least 
one generating or rolling head which is driven to revolve in a roll or 
rolling head support and there is provided therein at least one 
planetary-type mounted generating roll which can be driven by the rolling 
head support for machining the workpiece. Also, means serve to coordinate 
the movement of the workpiece and the generating roll. According to 
important aspects of the invention the apparatus further includes two 
press punches which can be tensioned or biased towards one another at the 
means for moving the workpiece. These two press punches in their contour 
possess teeth corresponding to the teeth which are to be fabricated and 
which at most correspond to the outer contour size of the mentioned teeth. 
The punches can be tensioned or biased towards one another by a tie or 
traction rod interconnecting such along the workpiece axis or by the 
provision of means arranged externally of the workpiece. The latter 
technique is presently preferred and will be described more fully 
hereinafter, since such appreciably facilitates automation of the work and 
the employed forces are not limited by the dimensions of the workpiece. 
Since it can happen that the shape of the workpiece in axial direction 
nearer to or further from the press punches does not correspond to what is 
desired, owing to the differences in the flowability of the material, when 
the engagement depth of the rolls at the workpiece is maintained constant 
or in order to form particular shapes, for instance crowning, the 
apparatus of the invention advantageously is equipped with a control 
device for adjusting the spacing of the impact heads -- preferably two 
such impact heads being provided -- from the workpiece axis. 
Since with the mentioned preferred method technique the location of 
engagement or attack of the roller or roll at the workpiece proceeds along 
a helical or screw line, the attack of the roll at the workpiece in the 
peripheral direction is not completely uniform, so that there can occur 
rotation of the workpiece about its lengthwise axis. If the workpiece, 
during its feed, is engaged at its last machined end and displaced in the 
direction of the rolling tool, then this can result in a deviation of the 
teeth in the peripheral direction. On the other hand, if the workpiece is 
engaged at its already rolled end and drawn through the rolling or 
generating zone, then the rotation only always affects the not yet worked 
portion of the workpiece. Now in order to render possible, for carrying 
out the method of the invention, such "drawing" of the workpiece, the 
workpiece is preferably only driven by one press punch which neighbors the 
first machined workpiece end, whereas the second press punch freely moves 
along. In order to align the teeth of both press punches there can be 
employed an axially parallel bolt which interconnects such press punches. 
Such bolt is mounted to be sufficiently movable, preferably elastically 
movable, in one punch, in order to permit a small opposite rotation of the 
punches during rolling. With the inventive method it is thus possible, as 
a general rule, for the mobility of the mentioned alignment bolt to be 
adequate in a range of fractions of a millimeter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Initially, in order to facilitate the understanding of the invention there 
will be partially listed hereinafter the various components constituting 
the apparatus: 
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1 Generating or rolling head 
2 Generating or rolling head 
3 Press punch (moving along) 
3' Press punch contour 
4 Workpiece 
4' Finished workpiece contour 
4'' Raw workpiece contour 
5 Press punch (driven) 
5' Press punch contour (shape identical to the press punch 
contour 3') 
6 Generating roll support for the rolling or generating 
head 1 
6' Generating roll support for the rolling or generating 
head 2 
7 Generating roll for generating roll support 6 
7' Generating roll of generating roll support 6' 
8 Press mandrel for press punch 3 
9 Press mandrel for press punch 5 
10 Thrust bearing or block for press mandrel 9 at workpiece 
headstock 12 
11 Workpiece spindle for driving press mandrel 9 
12 Workpiece headstock for workpiece spindle 11 
13 Spindle drive (dividing gearing) for workpiece spindle 11 
14 Bevel gearing for driving spindle drive 13 with 
synchronous movement derived from generating roll 
support 6' by means of connection shaft 14' 
14' Connection shaft of spindle drive 13 and bevel gearing 14 
15 Feed spindle for displacing workpiece headstock 12 upon 
guides 18 and 18' 
16 Feed nut of feed spindle 15 (with outer toothed rim 
for drive by means of the feed drive 17) 
17 Feed drive 
18 Guide for workpiece headstock 12 at the machine frame 
or stand 35 
18' Guide analogous to the guide 18 
19 Tension or tie rod for the rigid interconnection of 
workpiece headstock 12 and counter-holder or counter- 
support 20 
19' Tension or tie rod analogous to tie rod 19 
20 Counter-holder (counter-support for press punch 3) 
21 Press piston arranged in counter-holder 20 for pressing 
press punch 3 towards press punch 5 by means of work- 
piece 4 
21' Cylinder of press piston 21 
22 Guide of counter-holder 20 at machine frame or stand 35 
22' Guide analogous to guide 22 
23 Templet for copying device 24 
24 Copying device 
25 Thrust rod of copying device 24 
26 Gear rack arranged at thrust rod 25 
26' Pinion driven by gear rack 26 
27 Pinion shaft of pinion 26' of bevel gearing 28 
28 Bevel gearing between pinion shaft 27 and connection 
shaft 29 
29 Connection shaft 
30 Adjustment or setting pinion mounted upon connection 
shaft 29 and in engagement with adjustment nut 31 
30' Adjustment or setting pinion mounted upon connection - shaft 29 and 
in engagement with adjustment nut 31' 
31 Adjustment nut for generating or rolling head 1 
31' Adjustment nut for generating or rolling head 2 
32 External threading at rolling or roller head 1 for 
adjustment nut 31 
32' External threading at rolling or roller head 2 for 
adjustment nut 31' 
33 Return piston arranged in machine frame 35 for rolling 
head 1 for pressing adjustment nut 31 at roller or 
rolling head support 34 
33 Return piston arranged in machine frame 35 for rolling 
head 2 for pressing adjustment nut 31' at roller or 
rolling head support 34' 
34 Roller or rolling head support at machine frame 35 for 
roller or rolling head 1 
34' Roller or rolling head support at machine frame 35 for 
roller or rolling head 2 
35 Machine stand or machine frame 
40 Sleeve (fixed in press punch 3) 
41 Sleeve for guiding entrainment bolt 43 
42 Rubber sleeve between sleeves 40 and 41 
43 Entrainment bolt for aligning the press punches 3 and 5 
50 Projection of press punch 5 for engagement in bore 90 
51 Spring ring mounted at projection 50 for compensating 
diameter differences between projection 50 and bore 90 
52 Bore in projection 50 for entrainment bolt 43 
53 Ejector bolt arranged in press punch 5 
54 Ring rib of press punch 5 
54' Ring rib of press punch 3 
60 Centering ring 
61 Bevel or chamfer at contour 4'' of workpiece 4 
70 Brow of workpiece 4 engaging in press punch contour 3' 
and press punch contour 5' 
80 Surfaces of workpiece 4 vertical or perpendicular to the 
workpiece axis 81 
81 Workpiece axis of workpiece 4 
90 Bore in workpiece 4 
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The apparatus of the invention illustrated by way of example in FIG. 1 will 
be seen to comprise a machine stand or machine frame 35 at which there are 
mounted all of the components or parts which are movable relative to one 
another. The roller or rolling head supports 34 and 34' for the generating 
or rolling heads 1 and 2 are rigidly secured at the machine frame 35 in 
such a manner that the rolling heads 1 and 2 are displaceable vertically 
with respect to the lengthwise axis 81 of the workpiece 4. In order to 
bring about such displacement there is provided at each roller or rolling 
head 1 and 2 external threading 32 and 32', respectively, at which there 
is synchronously adjustable a respective nut 31 and 31' provided with 
teeth at its external circumference or periphery, by means of a respective 
adjustment pinion 30 and 30' via the connection shaft 29. So that the nuts 
or nut members 31 and 31' snugly bear against the associated roller head 
supports 34 and 34', respectively, each rolling head 1 and 2 is connected 
with a piston 33 and 33', respectively, movable in the machine frame 35, 
and working in the direction of the associated arrow. The shaft 29 either 
can be rotated manually for a certain fixed adjustment or setting, or, 
however, it can be adjusted continuously during the rolling operation 
during the course of the rolling work by means of the copying or copier 
device 24, which scans the copying templet 23. For this purpose the copier 
or copying device 24 is connected with a thrust or push rod 25 which 
carries at its one end a gear rack 26. This gear rack 26 drives a pinion 
26' which, in turn, rotates the pinion shaft 27 and thus the bevel gearing 
28. This bevel gearing 28, in turn, drives the shaft 29 of the gears 30 
and 30'. It is possible by virtue of this continuous adjustability of the 
rolling heads 1 and 2 to produce both a desired change in shape at the 
rolled gear as well as also for the formation of undesired changes in 
shape. By virtue of the fact that the workpiece 4 is prestressed or biased 
between the hard press punches 3 and 5, their parts neighboring the press 
punches 3 and 5 cannot deform in the same manner as the intermediate 
region remote from the press punches 3 and 5. Also differences can arise 
between the part of the workpiece 4 machined at the start of the rolling 
operation and the part of the workpiece 4 which is worked towards the end 
of the rolling operation. 
At the rolling head 1 there is mounted the generating roll support 6 where 
there is arranged the generating roll 7 and at the rolling head 2 there is 
mounted the generating roll support 6' with its generating roll 7'. The 
roll supports 6 and 6' can be driven by a motor so as to revolve 
synchronously in the direction of the associated arrows, and the 
generating rolls 7 and 7' machine or process the surface of the workpiece 
4 in the manner previously described, and as such has also been disclosed 
in detail in German Pat. No. 1,016,222. Hence, during each revolution of 
the generating roll supports the workpiece 4 is advanced, in the showing 
of FIG. 1, from the right towards the left along the workpiece axis 81 and 
at the same time further rotated or indexed through one tooth in the 
direction of the arrow 100 shown in FIGS. 3 and 5. The individual points 
of attack of the generating rolls or tools 7 and 7' are thus each 
accomplished along a helical- or screw-like path of travel extending about 
the workpiece and which is determined by the feed movement along the 
workpiece axis 81 and by the rotational movement 100. 
In order to produce the prestress between the press punches 3 and 5, 
indicated by the arrows P in FIG. 2, the following procedures are carried 
out: 
The press punch 5 is supported by means of a press mandrel 9 rigidly 
connected for rotation therewith and a thrust or pressure bearing 10 at 
the workpiece headstock 12. The workpiece headstock 12 is supported, in 
turn, by the feed spindle 15 through the agency of the feed nut 16 and the 
feed drive 17 at the machine frame 35. In order that there is exactly 
accomplished the lengthwise feed movement along the workpiece axis 81 
which is transmitted from the workpiece-feed drive 17 by means of the feed 
spindle 15 to the headstock 12 and from such via the press mandrel 9 and 
the press punch 5 to the workpiece 4, the workpiece headstock 12 is 
additionally mounted by means of the guides 18 and 18' at the machine 
frame 35. 
The workpiece headstock 12 is rigidly connected with the counter-holder or 
counter-support 20 by means of both of the tie or tension rods 19 and 19', 
the counter-support 20 being mounted to be displaceable in the machine 
frame 35 upon the guides 22 and 22' along the workpiece axis 81. The press 
mandrel 8 which is connected with the other press punch 3 is constructed 
as the piston rod of an hydraulic piston 21 which is mounted to be 
displaceable in the counter-support 20 along the workpiece axis 81 and 
freely rotatable about such workpiece axis 81. If a suitable pressurized 
fluid medium, such as pressurized oil, is introduced into the cylinder 
21', then the piston 21 together with the press mandrel 8 and the press 
punch 3 are moved in the direction of the arrow P in FIG. 1 from the left 
towards the right and pressed against the workpiece 4 which is supported 
in the described manner by means of the press punch 5 at the machine frame 
35. The movement which emanates from the workpiece-feed spindle 15, and 
which has already been described, has been indicated in FIG. 1 by the 
arrows 101 at the workpiece headstock 12 and the counter-support 20 in 
order to show that both of these components or parts are interconnected by 
the tension or tie rods 19 and 19' for the simultaneous unidirectional 
movement, which therefore is also transmitted to the workpiece 4 which is 
clamped between the press punches 3 and 5. This workpiece 4, during the 
course of the machining or processing work, thus is moved from the right 
towards the left and at the end of the machining operation is located in 
the position shown in FIG. 1. Due to these operations there is obtained a 
clean straight course of the teeth, because the previously described 
rotation of each workpiece part, which is in the process of being 
machined, is located opposite the already machined workpiece part in this 
manner when the punch 3 is not driven, and which can partially rotate in 
relation to the contact punch 5 in a manner still to be described. 
It is for this reason that it is possible to also accomplish the rotational 
drive of the workpiece 4 by means of the contact punch 5 inasmuch as the 
contact punch 5 is rigidly connected for rotation with the press mandrel 9 
and such with the spindle 11 and by means of a dividing gearing 13 -- here 
shown in simplified illustration -- there can be accomplished the partial 
drive, which gearing 13 can be synchronously driven by means of the bevel 
gearing 14 from the roll support 6' by means of the shaft 14'. Of course, 
there can be provided at such drive, exactly as in the feed drive 17, 
infinite or finite settable gearing means in order to properly accommodate 
to one another the feed movement 101 and the rotational movement 100 of 
the workpiece 4. This gearing means or gearing can be constructed in 
conventional manner. 
Continuing, and with attention directed to FIG. 4, there will now be 
described more fully the clamping or chucking of the workpiece 4. Located 
upon the press mandrel 9 is the press punch 5 possessing the projection 50 
which can be introduced with play into the bore 90 of the raw workpiece or 
blank 4, and centering can be accomplished by means of the spring ring 51. 
Prior to placement upon the projection 50 of the press punch 5 the 
workpiece 4 is faced or turned along its raw or rough contour 4", and its 
end confronting the other press punch 3 is bevelled in a ring-shaped 
manner such has been indicated generally in FIG. 4 by reference character 
61. The exact centering of the workpiece 4 in relation to the press punch 
5 now is accomplished in that a centering ring 60 is pushed onto the 
workpiece from the left towards the right, comes into contact with the 
ring-shaped bevel 61 and the workpiece is thus centered. Now the second 
press punch 3, which is mounted upon its press mandrel 8, is fixedly 
pressed against the workpiece 4 by means of the piston 21 which has been 
previously considered in detail in conjunction with the description of 
FIG. 1, so that the workpiece is prestressed between the press punches 3 
and 5. In order that the workpiece 4, in this prestressed position, is 
seated firmly and non-shiftably, both of the press punches 5 and 3 possess 
substantially ring-shaped protruding ribs 54 and 54', respectively, which 
penetrate into the workpiece 4. Viewed radially and located externally of 
such ribs 54 and 54' there are formed the reference surfaces 80 during the 
course of the rolling operation, which reference surfaces are needed for 
the subsequent further machining of the finished rolled workpiece. The 
surfaces 80 are dispositioned vertically, i.e. perpendicular to the 
workpiece axis 81. 
Since both of the press punches 3 and 5 possess the contours 3' and 5', 
respectively, shown in FIG. 5, which are toothed similar to the later 
formed teeth of the finished workpiece, indicated by reference character 
4' in FIG. 5, it is necessary that both press punches 3 and 5 are aligned 
with one another. To accomplish such alignment the entrainment bolt 43 is 
resiliently mounted in the press punch 3 by means of yet to be described 
sleeves 40, 41 and 42, in such a manner that during contact of the press 
punch 3 at the workpiece 4 this bolt 43 penetrates into the bore 52 of the 
projection 50 of the press punch 5 when the teeth of the press punches 3 
and 5 coincide with one another. Only at this point in time does the press 
punch 3 bear completely at the workpiece 4, as such has already been 
described. As also disclosed heretofore, now since however there occurs a 
certain rotation of the material and thus the workpiece 4 due to the 
intermittent engagement or attack of the generating rolls 7 and 7' which 
is accomplished along a helical line, and which material rotation is 
maintained in the depicted order of magnitude in the range of fractions of 
a millimeter, the bolt 43 is slightly elastically mounted by means of the 
rubber sleeve 42 which is positioned between the other sleeves 40 and 41, 
so that it can permit a slight rotation of the press punch 3 in relation 
to the press punch 5. Consequently, there is provided in the already 
described manner the compensation for a good aligned extent of the teeth. 
As will be seen by referring to FIG. 5, it is necessary in most instances 
to maintain the contours 3' and 5' of the press punches 3 and 5, 
respectively, somewhat smaller than the contour 4' of the teeth of the 
workpiece 4 which are to be produced, in order that the generating rolls 7 
and 7' can sufficiently deeply penetrate into the material of the 
workpiece 4, in order to give such the possibility of resiliently moving 
somewhat into its definitive shape, which has been shown in FIG. 5. These 
slightly smaller contours 3' and 5' of the press punches 3 and 5, 
respectively, now however render possible that a small quantity of 
material can penetrate into the teeth of the press punches 3 and 5 during 
rolling of the portions of the workpiece 4 which are near to the end 
surfaces and to form so-called brows or burrs which are designated by 
reference character 70 and appear at the lower right-hand corner of the 
workpiece 4 in FIG. 4. These brows 70 can be easily removed however after 
the ejection of the workpiece 4 by the ejector bolt or ejector means 53, 
following completion of the rolling operation and shifting away of the 
press punch 3. Furthermore, there are also provided ejectors in the press 
punch 3, but the same have not been particularly shown in order to 
simplify the illustration. 
The reference surfaces 80, which have been considered a number of times 
heretofore, have been found to be especially useful even for the removal 
of the brows or burrs 70, while they are indispensible for grinding out 
the bore 90 of the gear. They provide the possibility of exactly aligning 
the gear upon further processing machines. 
As a general rule the reference surfaces 80 are highly polished and 
compact, because they extend to the region of the workpiece flanks, which 
is at the end of the teeth and at their direct region, in other words at 
that location where the material is caused to flow due to the rolling 
operation, so that such is capable of forming at the correspondingly 
machined hardened surface of the press punch the true or exact reference 
surfaces 80. 
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.