Rolling Chamfers On Gear Teeth

Abstract

Gear rolling dies are provided with inclined chamfer-forming ramp surfaces at the bottoms of the tooth spaces adapted to form chamfers at the tops of the gear teeth along the corners defined by the intersection of the crests of the teeth and the flank surfaces.

Description

BRIEF SUMMARY OF THE INVENTION

A requirement of many gears is that the tops of the teeth along the corners defined by the intersection of the crests and the flank surface thereof shall be chamfered. According to the present invention, this is accomplished by providing inclined chamfer-forming ramp surfaces adapted to be engaged by the crests of the teeth of a work gear as it is rolled in pressure contact between a pair of dies. Although finish rolling of gears is found to displace substantially more metal at one side of the teeth than the other side, this will not prevent formation of symmetrical and equal chamfers at opposite sides of the teeth and, moreover, will preserve equality between chamfer previously provided in a roughing operation, such for example as hobbing or shaper cutting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view illustrating the form of an involute tooth of a gear having chamfer.

FIG. 2 is a diagrammatic view similar to FIG. 1 illustrating the form of a tooth after a shaving operation.

FIG. 3 is a diagrammatic view illustrating the change in tooth form resulting from finish rolling.

FIG. 4 is a view illustrating the formation of chamfers in accordance with the present invention.

FIG. 5 is a view illustrating two adjacent teeth of a gear rolling die.

DETAILED DESCRIPTION

At the present time two principal gear finishing operations are provided to follow a gear roughing operation. The finishing operations referred to are shaving and rolling.

In gear shaving, gearlike shaving cutters are provided with teeth having serrations extending vertically up and down the tooth surfaces defining cutting edges adapted to remove metal from the sides of gear teeth rolled in tight mesh at crossed axes with the shaving cutter.

In gear rolling operations presently used in finishing, gear rolling dies in the form of gears are rolled in mesh with the work gear. The gear rolling dies are usually provided in opposed pairs which are moved radially towards each other to produce a measurable reduction in size of the gear and to finish the gear teeth by actually displacing metal.

It has been conventional in gear roughing operations, such for example as hobbing or shaper cutting, to provide a top chamfer in the roughing operation. Referring to the drawings, in FIG. 1 there is illustrated a tooth 10 having generated, usually involute side or flank surfaces 12 and a top or crest surface 14 which without chamfers would intersect at a corner designated 16. However, when the teeth are chamfered in accordance with this practice, the material at and adjacent the corner 16 is removed to provide chamfered surfaces 18. The tooth 10 of FIG. 1 may be considered to be a chamfered tooth formed by one of the gear roughing operations described.

In order to produce gears characterized by the smoothness and accuracy of the tooth surfaces, quality gears today are almost universally given a finishing operation. This may be a shaving operation as indicated previously, or a gear rolling operation. It is a characteristic of the gear shaving operation that roughly equal amounts of material are removed from opposite sides of the teeth. One reason for this is that the usual shaving operation comprises rotating the gear in tight mesh with a shaving cutter in both directions so that neither side of the teeth may be considered as exclusively a driving side or a driven side. Under these circumstances, a tooth modification as suggested in FIG. 2 is produced. Here the tooth is designated 20. In solid outline it is provided with the side surfaces 12, the crest surface 14 and the chamfer surfaces 18. However, in the shaving operation material is removed from the flanks of the teeth along the dot and dash lines indicated at 22 and it will be observed that these lines intersect the chamfer surfaces 18 at points designated 24. Accordingly, while the shaving operation reduces the width of the chamfer surfaces 18, the radial location of the start of chamfer, determined by the location of points 24, is substantially the same at both sides of the teeth.

Gear rolling presents a quite different problem. In the first place, one of the advantages of gear rolling as practiced today is the extremely short time required for the rolling operation. One of the reasons why the gear rolling operation may be completed in as little as three seconds is attributable to the fact that the direction of rotation of the gears and gear rolling dies is not changed. Accordingly, the time required for stopping, reversing and accelerating in the opposite direction is avoided. This however, has a disadvantage in the fact that one side of the gear teeth, simply because of the single direction of rotation, has its profile rolled substantially more than the opposite side. In practice it is found that the coast side of the gear teeth has more metal displaced than the opposite side when the rolling dies are moved radially of the gear under sufficient pressure to displace measurable amounts of material. In practice it is found that the amount of metal displaced or caused to flow at the coast side of the gear teeth may be double or even several times the amount of metal displaced at the opposite side.

Since this occurs, a gear tooth as diagrammatically indicated at 30 in FIG. 3 is produced. Here the original tooth form is illustrated in full lines as having flank surfaces 12, top surface 14 and the chamfer surfaces 18. In this case the profile of the gear teeth after the rolling operation is indicated by the dotted lines at 32. It will be observed in FIG. 3 that the separation between the dotted line 32 at the right side of the tooth and the original tooth profile line 12 is only a fraction of the distance between these lines at the left side of the tooth. Accordingly, if the gear tooth as completed by the roughing operation had the substantially equally located chamfer surfaces 18, the gear rolling operation would produce unsymmetrical chamfer surfaces after the gear rolling operation. Thus the chamfer surface designated 34 after rolling has its radially inner origin point 35 at one side of the teeth, whereas the chamfer surface 36 at the opposite side of the teeth has its radially inner origin shifted to the point 37.

According to the present invention, the substantial equality of the chamfer surfaces produced by the gear roughing operation is preserved. This is accomplished by forming the gear rolling dies, a portion of one of which is designated at 50 so that at the bottom space between adjacent teeth 51 there are provided inclined chamfer-forming ramp surfaces 52. These surfaces as shown are equally and oppositely inclined with respect to a radial line bisecting the tooth space, such as the line 53, and they are of equal extent.

In gear rolling operations, the dies of an opposed pair are moved radially inwardly of the gear towards each other to a predetermined depth and the amount, the slope and the location of the inclined chamfer-forming ramp surfaces 52 are selected such that these surfaces are encountered by corner portions of the gear teeth at the corners defined by the intersections between the crests of the teeth and the side or flank surfaces thereof. As the metal is displaced by the gear rolling operation from the flanks of the teeth it is also displaced at the corners to leave chamfers thereon.

Referring now to FIG. 4, there is illustrated a gear tooth 40, the outline of which after the roughing operation includes the side or flank surfaces 12, the crest surface 14 and, when chamfers are provided in the roughing operation, the chamfer surfaces 18. If the tooth 12 is rolled by dies having the configuration of teeth as illustrated in FIG. 5, the flanks or side surfaces are reduced to the dot and dash lines indicated at 42 and 43 and the corner portions of the teeth are chamfered by the ramp surfaces 52 to provide the chamfer surfaces indicated by dot and dash lines at 44 and 46. It will be observed from an inspection of FIG. 4 that while substantially more metal was displaced from the left-hand side of the teeth to produce the rolled surface 43, nevertheless the radial height of the chamfered surfaces 44 and 46, determined by intersection points 47 and 48 respectively, are substantially equal.

It will be understood that the operation need not be limited to one in which the roughing operation removed the corners of the teeth to provide rough chamfer surfaces 18. The rolling operation will produce these chamfer surfaces even through the rough-cut teeth are not chamfered.

It is of course understood that at one side of the teeth of the gear, during a rolling operation in which rotation takes place in one direction, the sliding contact adjacent the crest of the gear at one side is inwardly or downwardly from the top of the teeth, whereas at the opposite side the direction of slide contact is radially outward or upward from a direction from the pitch line toward the crest of the teeth. Accordingly, the gear rolling operation including the provision of chamfers ad disclosed herein may produce some displacement of material upon the original crest of the teeth and this displacement of material will be greater at one side of the tooth than the other side thereof. This, however, is not disadvantageous as in many operations a final operation removes some material from the crests of the teeth. On the other hand, this is not always necessary and the presence of unequal minor amounts of metal upon the original crests of the teeth is acceptable.

Since the present invention provides substantially equal chamfers on rough-cut teeth finished by a rolling operation, it will be apparent that this permits a desirable overall gear production in which a quantity of gears are rough-cut by conventional roughing operations to configurations illustrated in FIG. 1 in which the teeth are provided with chamfer surfaces 18. Thereafter, some of the gears may be selected at random to be finished by a gear shaving operation to the configurations illustrated in FIG. 2 and the remaining gears may be finished by a gear rolling operation to the configurations illustrated in FIG. 4. In both cases, substantially symmetrically located chamfer surfaces are provided.

It will be recognized that without the provision of the chamfer-forming ramp surfaces 52, the result of gear roll finishes would be as illustrated in FIG. 3 and would result in unsymmetrically located chamfers and perhaps complete elimination of chamfers or some teeth. Thus, the present invention permits simplification of the gear finishing procedure in that substantially symmetrical chamfers may be provided in the roughing operation and substantially symmetrical chamfer surfaces will remain with gear shaving and gear rolling.

Claims

We claim:

1. The method of making finished gears having predetermined chamfers at the intersection between the crests and the generated tooth form sides of its teeth which comprises meshing rough gears in tight mesh with a gearlike finish rolling die having teeth generally conjugate to the desired tooth form on the gears and having oppositely inclined chamfer-forming ramp surfaces at opposite sides of the teeth at the bottoms of the tooth spaces, rotating the gears in a single direction in mesh with the die and relatively moving the gears and die to reduce center distance, thereby finishing the side surfaces of the gear teeth by metal displacement and forming generally symmetrical chamfers originating at substantially the same tooth height by engagement with the ramp surfaces irrespective of the relative amount of material displaced on opposite sides of the gear teeth.

2. The method of claim 1 in which the rough gears prior to finish rolling have chamfers at the tops of the teeth at the corners defined by the intersection between the crests and side surfaces thereof.

3. The method of claim 2 in which the chamfers provided on the teeth of the rough gear are substantially symmetrically located and the ramp surfaces of the dies are positioned thereon to produce substantially symmetrically located chamfer surfaces after rolling.

4. The method of claim 1, which comprises rolling the rough gears between a pair of gearlike die rolls both of which have the inclined chamfer-forming ramp surfaces.

5. The method of making finished gears having predetermined chamfers at the intersection between the crest and generated tooth form and side surfaces which comprises forming a rough gear having substantially the predetermined chamfers, separating the rough-cut gears into two groups, shaving the sides of the teeth of one group to substantially uniform depth thereby reducing the amount of chamfer at opposite sides of each tooth substantially equally, roll finishing the sides of the teeth of the other group by rolling the gears in this group in pressure contact with a gearlike die generally conjugate the gears in a single direction of rotation, thereby displacing substantially more material from one side of the gear teeth than from the other, said roll die having oppositely inclined ramp surfaces at the opposite sides of the bottom of the tooth spaces located to generate by rolling the required tooth chamfers independent of the amount of material displaced from the sides of the teeth.

6. A gear finishing die in the form of a gear having teeth generally conjugate to the desired profile to be formed on the sides of gear teeth by a rolling operation in which oppositely inclined chamfer-forming ramp surfaces are provided at the bottom of the spaces between the teeth of the die.

7. A die as defined in claim 6 in which said ramp surfaces in any tooth space are equally inclined with respect to a line radial of the die and bisecting the said tooth space.