Metal deforming – By use of tool acting during relative rotation between tool... – During rotation of work
Reexamination Certificate
2000-07-13
2001-08-28
Tolan, Ed (Department: 3725)
Metal deforming
By use of tool acting during relative rotation between tool...
During rotation of work
C072S084000, C072S107000, C072S110000, C072S121000, C029S893320
Reexamination Certificate
active
06279366
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an item with external teeth, such as a gear, and a method of forming the item.
Conventionally, formation of an item with external teeth such as a gear is implemented by a method of forming teeth by cutting a workpiece such as a forged blank into shape or a method of forming teeth by forging a workpiece into shape. In the former method of teeth formation by cutting, however, the working speed is too low and a grinding process is required for improving the surface roughness of the teeth after the cutting process. Accordingly, the former method involves much time taken for teeth formation. On the other hand, the latter method of teeth formation by forging causes problems of enormous expense in plant and equipment, difficulty in fabricating a die and deterioration in work environment due to the use of lubricant, for example, in a Bonderite process, for the purpose of increase in die life and formability.
Meanwhile, as disclosed in the specification and drawings of German Patent Publication No. 19613457, there is a method of generating external teeth in the outer periphery of a workpiece with the use of an external gear tooth generating device including a form roller having an outer periphery formed with four gear-like tooth generating sections of different tooth heights changed in four steps along the rotation axis of the roller to increase the outer diameter of the roller in a stepwise manner. In this method, the tooth generating sections are pressed in increasing order of tooth height against the outer periphery of a rotating workpiece so that the rotation force of the workpiece is transmitted to the form roller. The form roller thereby step wise generates a plurality of teeth of given shape in the outer periphery of the workpiece while rolling therealong. According to this method of external teeth generation, since the teeth are generated by plastic deformation of a workpiece, the drawbacks due to cutting as described above cannot be caused. In addition, since the form roller can be made relatively cheap and easily, the problems due to forging as described above never occur. It is to be noted that the reason why the generation of teeth of given shape (tooth grooves of given depth) is made stepwise in four divided generating steps is that teeth generation in a single step would create extended or recessed tooth portion thereby not providing a complete tooth profile.
Furthermore, in the above method of external teeth generation, since both the workpiece and the form roller are rolled one along another to generate the external teeth, it is difficult that the tooth generating sections of the form roller are pressed evenly against both sides of each tooth which serve as mating surfaces of each of fully generated teeth. As a result, the mating surfaces of each of the teeth easily produce a variation in forming accuracy. This is a serious problem for gears requiring high accuracy. In order to eliminate such a variation, the teeth must be finished by cutting. In this case, however, the flow line of metal texture having been formed along the tooth profile during the tooth generating process is broken, resulting in decreased strength.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to generate external teeth in the outer periphery of a workpiece with high efficiency and accuracy and without decreasing strength.
To attain the above object, the present invention is characterized by generating external teeth in the outer periphery of a workpiece (metallic material) by using cold pressing in addition to form rolling in which the workpiece and a form roller are rolled one along another as disclosed in the above Publication.
More specifically, the present invention is directed to an item with external teeth and a method of forming the item. The invention as claimed in Claims
1
through
5
relates to the item with external teeth, and the invention as claimed in Claims
6
through
10
relates to the method of forming the item. In these Claims, the following solutions are taken.
A solution taken in the invention of Claim
1
is directed to an externally-toothed item having an outer periphery formed with a plurality of external teeth, and is characterized in that the external teeth are generated stepwise in the outer periphery of a metallic material by pressing a plurality of gear-like tooth generating sections of a form roller, the plurality of gear-like tooth generating sections being arranged along the rotation axis of the form roller in the outer periphery of the form roller to increase tooth heights of the tooth generating sections in a stepwise manner along the rotation axis, against the outer periphery of the rotating metallic material in increasing order of tooth height of the tooth generating sections while transmitting the rotation force of the metallic material to the form roller to roll the form roller along the outer periphery of the metallic material, and are finished to size by cold pressing.
With the above construction, even if the mating surfaces of each of the teeth produce a variation in forming accuracy by form rolling, such a variation due to form rolling is leveled in the succeeding cold pressing step so that the teeth can be finished with high accuracy. In addition, since such leveling is made by cold pressing, the flow line of metal texture can be prevented from being broken thereby ensuring strength.
A solution taken in the invention of Claim
2
is characterized in that in the externally-toothed item of claim
1
, the form roller is constructed so that the tooth generating sections have equal distances between the rotation axis of the form roller and respective tooth tip faces of the tooth generating sections and such different distances between the rotation axis and respective bottom lands of the tooth generating sections as decreased in plural steps along the rotation axis to increase tooth heights of the tooth generating sections in a stepwise manner along the rotation axis.
With this construction, an example of the form roller is embodied.
A solution taken in the invention of Claim
3
is characterized in that in the externally-tooth item of claim
2
, the form roller is constructed so that in generating the teeth, the tooth generating sections are consecutively pressed in increasing order of the tooth height against the metallic material without stopping the rotation of the metallic material.
With this construction, the tooth generating sections have equal distances between the rotation axis of the form roller and their respective tooth tip faces, i.e., equal outer diameters, and the next-step tooth generating section does not protrude beyond the preceding-step one. Therefore, such a phenomenon that the metallic material may be held by engagement on a shoulder of the next-step tooth generating section protruding beyond the preceding-step one against relative movement from the preceding-step tooth generating section to the next-step one never occurs. Accordingly, while only a slight backward movement of the form roller is necessary for the purpose of smooth movement of the next-step tooth generating section onto the metallic material in making the next-step tooth generating section ready for working the metallic material, the form roller can be moved along its rotation axis as the metallic material is rotated without stopping its rotation. As a result, the time taken to generate teeth can be reduced as compared with the case of repeating rotation and stop of the metallic material, thereby increasing the efficiency of teeth generation.
A solution taken in the invention of Claim
4
is characterized in that in the externally-toothed item of claim
1
, the form roller is constructed so that the tooth generating sections have equal distances between the rotation axis of the form roller and respective bottom lands of the tooth generating sections and such different distances between the rotation axis and respective tooth tip faces of the tooth generating sections as
Nixon & Peabody LLP
Robinson Eric J.
Samtech Corporation
Tolan Ed
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