US3623275A

US3623275A - Composite abrasive finishing tool

Info

Publication number: US3623275A
Application number: US875383A
Authority: US
Inventors: Charles G Koella
Original assignee: Michigan Tool Co
Current assignee: Michigan Tool Co
Priority date: 1969-11-10
Filing date: 1969-11-10
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30
Also published as: GB1257149A; FR2071670A5; DE2054502A1

Abstract

A GEAR-SHAPED ABRASIVE FINISHING TOOL AND THE METHOH OF FORMING SUCH A TOOL IN WHICH ATY LEAST A PORTION OF THE TOOTH ELEMENTS THEREOF ARE PROVIDED WITH WORKING FACES HAVING CONTROLLED VARIATIONS IN THEIR ABRASSIVE PROPERTIES SO AS TO PROVIDE A SELECTED ABRASIVE FISHING ACTION ON GEARS BEING FINISHED THEREBY.

Description

Nov. 30, 1971 c. G. KOELLA 3,623,275

COMPOSITE ABRASIVE FINISHING TOOL Filed Nov. 10, 1969 s ink United States Patent O 3,623,275 COMPOSITE ABRASIVE FINISHING TOOL Charles G. Koella, Rochester, Mich., assignor to Michigan Tool Company Filed Nov. 10, 1969, Ser. No. 875,383 Int. Cl. B24d 5/14 US. Cl. 51-206 R 8 Claims ABSTRACT OF THE DISCLOSURE A gear-shaped abrasive finishing tool and the method of forming such a tool in which at least a portion of the .tooth elements thereof are provided with Working faces having controlled variations in their abrasive properties so as to provide a selected abrasive finishing action on gears being finished thereby.

BACKGROUND OF THE INVENTION Abrasive gear-shaped finishing tools of the general type to which the present invention is applicable are in wide spread commercial use for accurately finishing the surfaces of tooth elements on workpieces such as gears, for example. conventionally, the abrasive finishing tool is mounted in a finishing machine such that the finishing tool is disposed in tight meshing relationship with the gear to be finished. The disposition of the abrasive finishing tool relative to the workpiece usually is at crossed axes and during the finishing operation, the tool and workpiece are reciprocated longitudinally relative to each other during their rotation so that the full face width of each tooth of the workpiece is traversed by the abrasive teeth of the gear-shaped finishing tool. Usually the direction of rotation of the finishing tool and workpiece are reversed each time the direction of traversing movement is reversed so that both faces of each gear tooth are provided with an accurate surface finish and profile.

In accordance with the foregoing technique, corrections in dimensional inaccuracies of hardened gear teeth, such as minor inaccuracies, involute profile, lead and runout caused during heat treating operations, can be readily accomplished. The correction of such dimensional inaccuracies provides for improved contact patterns between the working faces of mating gear teeth providing substantial reductions in the operating noise level, as well as increased durability and operating life of the gear train. This practice has now substantially eliminated the necessity of matching and lapping gears in pairs, which constitutes a costly and time-consuming practice.

While the foregoing technique has been found eminently satisfactory for abrasively finishing or honing the surfaces of most hardened gears, the use of such abrasive gear-shaped finishing tools has not been satisfactorily applied to finishing high-precision gears in which dimensional tolerances must be maintained within millionths of an inch. In the finishing of such precision-type gears, it is frequently found that selective variations must be provided in the degree of finishing applied to different portions of the working face of the gear teeth so as to provide finished gears which are Within the precise dimensional tolerances. In accordance with the present invention, it is now possible to selectively hone or abrasively finish gear teeth surfaces without destroying areas which are within the precise dimensional tolerances during the finishing of other tooth areas that require stock removal and/ or surface polishing. Accordingly, extremely accurate honing of precision gears can now be achieved employing automatic finishing machinery, thereby obviating the costly, time-consuming manual finishing methods heretofore employed in correcting such precision gears.

SUMMARY OF THE INVENTION The foregoing and other advantages of the present invention are achieved by an abrasive gear-shaped finishing tool consisting of a cylindrical body having a plurality of tooth elements disposed therearound which are adapted to be positioned in meshing relationship with a workpiece to be finished. Each of the tooth elements of the finishing tool includes a working face which is adapted to be disposed in bearing contact with the corresponding face of gear teeth on the workpiece. At least some of the tooth elements of the abrasive gear-shaped finishing tool are provided with working faces that are of a composite construction consisting of a plurality of sections which are of controlled different abrasive finishing characteristics so as to provide a corresponding controlled variation in the degree and type of finishing action imparted to the surfaces of the tooth elements of workpieces being finished.

In its method aspects, the present invention provides for a simple and economical process for forming abrasive finishing tools wherein at least the working faces of the tooth elements thereof can be provided with controlled variations in their abrasive properties consistent with the abrasive finishing action to be applied to precision gears. In accordance with this method, all or selected ones of the tooth elements can be provided with variations in their abrasive properties along the length of their working faces as well as selected variations in the magnitude of surface area of such variant abrasive characteristics.

Still additional advantages and benefits of the present invention will become apparent upon a reading of the description of the preferred embodiments taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary perspective view of a gearshaped finishing tool disposed in crossed axis meshing relationship with a workpiece to be finished;

FIG. 2 is a fragmentary side elevational view, partly in section, of an abrasive gear-shaped finishing tool having a composite tooth construction;

FIG. 3 is a transverse vertical sectional view taken through a typical mold for casting the blank for preparing the composite gear-shaped finishing tool; and

FIG. 4 is a fragmentary plan view of a portion of a mold of the type shown in FIG. 3 having a gear-shaped blank positioned therein preparatory to a final casting operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the drawings, an abrasive gear-shaped finishing tool 6 is shown in FIGS. 1 and 2 and comprises a cylindrical body having a plurality of tooth elements 8 disposed therearound. The tooth elements 8 are conjugate to and are adapted to be disposed in tight meshing relationship with a toothed workpiece such as the gear 10 shown in FIG. 1. The finishing tool 6! is conventionally comprised of an inner hub section 12 which may be of a synthetic, metallic or composite construction, around the periphery of which the abrasive tooth elements are disposed. The finishing tool is adapted to be mounted on a spindle of a conventional finishing machine and is rotated in crossed axes relationship with the gear 10, while concurrently undergoing longitudinal reciprocation so as to provide the requisite abrasive finishing action on the working faces of the gear teeth.

The outer portion of the finishing tool 6, including the tooth elements 8 thereon, is composed of an abrasive matrix comprising a mixture of a suitable binding agent in combination with a controlled proportion of abrasive granules of a selected size and composition in further combination with various filler materials to impart the desired abrasive finishing characteristics to the finishing tool. Conventionally, the binding agent comprises a suitable synthetic resin, of which copolymers of polyainide resins and epoxy resins in accordance with the disclosure of US. Pat. 3,212,869 and polyurethane resins of the type disclosed in US. Pat. 3,183,633, are conventionally preferred. The foregoing resins possess the requisite strength and flexibility to provide satisfactory finishing operations of a large number of gear-shaped workpieces and possess the requisite impact resistance, strength, wearresistance and resiliency to provide for a prolonged tool life. It will be understood that alternative satisfactory bonding agents including epoxy resins, phenolic resins, urea formaldehyde resins, synthetic rubbers, etc., can also be satisfactorily employed in accordance with the practice of the present invention when they are compounded to provide the desired physical properties consistent with the intended end use of the abrasive finishing tool.

Regardless of the specific chemical composition of the binding agent employed, the abrasive matrix can contain abrasive particles in controlled amounts up to about 80% of the total abrasive matrix. The abrasive constituent itself can comprise any one of a variety of finely-particulated abrasive materials of the types well known in the art, including abrasive particles such as silicon carbide, aluminum oxide, diamonds, glass, silicon dioxide, etc. The size of the abrasive particles can broadly range from about 54 grit to about 500 grit and may comprise particles which are all of substantially the same size or, alternatively, a mixture of particles of different sizes so as to provide the desired abrasive finishing action. Abrasive particles having particle sizes of a magnitude of about 500 grit serve primarily as a filler to the resin binding constituent and impart an extremely fine surface finish to the work faces of tooth elements on a workpiece 'being finished thereby. On the other hand, abrasive particles of a larger grit size usually in the range of 54 to 22 grit effect relatively rapid metal removal from the tooth elements of the workpiece being finished.

The abrasive matrix can also include varying amounts of suitable filler materials which serve primarily as extenders of the resin abrasive mixture. Such fillers also contribute to the final physical properties of the abrasive tool, as well as imparting a desired surface finishing characteristic to the abrasive tooth elements. Conventionally, non-wicking or non-absorbent type filler materials are preferably employed which facilitate obtaining a homogeneous blend of the abrasive matrix and further add weight and strength thereto. Filler materials of the foregoing type which have been found satisfactory for this purpose include airborne silica, which is thixotropic and aids in maintaining a substantially uniform suspension of the abrasive particles in the binding agent during the setting or curing of the matrix after casting. Alternative filler materials which can be satisfactorily employed include fiber glass, calcium phosphate, calcium sulfate, zinc oxide, carbon black, graphite, etc.

In accordance with the foregoing, the abrasive matrix comprises the binding agent, a controlled proportion of abrasive particles, and filler materials. Conventionally, the binding agent can be used in amounts ranging from about 20% to about 80% by weight and preferably from about 40% to about 60% by weight of the total abrasive matrix. The abrasive particles, on the other hand, are used in amounts up to about 80% by weight and, more usually, when abrasive action is desired, in amounts of from about 30% to about 50%. Filler materials ordinarily are employed in amounts up to about 50% by weight, and more usually, in amounts of from about to about by weight. The specific amount of abrasive material used will depend on whether it is desired that selective portions of the working face of the tooth elements of an abrasive finishing tool are to provide an abrasive finishing operation or merely are intended to provide a slight polishing operation without appreciably removing any metal from the gear-shaped workpiece being finished.

A typical gear-shaped finishing tool in which the tooth elements are of a composite construction is shown in FIG. 2. In the specific embodiment illustrated, the outer or addendum portion 14 of the tooth element is composed of an abrasive mixture which is integrally bonded and interlocked to the dedendum portion 16, which is of a different abrasive matrix composition, providing thereby a working face 18 of each tooth element, which is of a composite construction and provides for controlled variations in its abrasive finishing characteristics. In the arrangement illustrated in FIG. 2, the addendum portion 14 extends radially outwardly of the pitch circle 20, indicated in dashed lines, dividing the working face 18 of the abrasive tooth elements into substantially two equal sections. It is usually preferred, particularly when the addendum and dedendum portions of the tooth elements are of substantially different abrasive cutting action, that the point of juncture between the addendum portion and dedendum portion be staggered or offset between adjacent tooth elements so as to provide a blending of the abrasive finishing action on the tooth elements of a gear being finishing. This can satisfactorily be achieved in accordance with the practice of the method aspects of the present invention by forming an original abrasive finishing tool and thereafter machining or otherwise removing the tip portions of the abrasive tooth elements in a circular pattern disposed slightly eccentric or offcenter to the axis of the finishing tool. In such manner, the radial depth of the addendum portion 14 of the tooth element will vary around the entire finishing tool in accordance with the dotted line indicated at 22 in FIG. 2, which is disposed eccentric to the pitch circle 20 in an exaggerated relationship for the purposes of illustration.

It will also be appreciated that selected variations in the abrasive finishing characteristics of such gear-shaped finishing tools can be achieved in which only certain ones of the tooth elements are provided with a composite construction while remaining tooth elements consist of the same uniform abrasive matrix.

It will also be understood that the bonding agent used for different sections of the composite tooth elements 8 of the finishing tool may be identical to or may be of different chemical composition to provide the desired re sultant physical and abrasive characteristics of the composite finishing tool. In accordance with the preferred binding agents as disclosed in the two aforementioned US. patents, which are owned by the same assignee as the present invention, the abrasive matrix consists of a polyamide cured epoxy resin or, alternatively, a polyurethane resin binder. The addendum portion preferably is comprised of the epoxy polyamide resin binder which provides for a tenacious bond to the dedendum or hub portion of the finishing tool, which may be of a similar resin binder or may also consist of a polyurethane-type binding agent. In any event, the addendum portion is preferably mechanically interlocked to the dedendum portion of the composite tooth element, further enhancing the strength of such a composite tooth structure and minimizing any tendency of separation of the two portions at their parting lines. Typical of a variety of mechanical interlocking devices that can be satisfactorily employed for this purpose are apertures indicated at 24 in FIGS. 2 and 4, which are provided and extend radially inwardly of the dedendum portions of the tooth elements which are adapted to become filled with and rigidly interlocked with the abrasive matrix of the addendum portion of the tooth element.

The specific abrasive characteristics of the addendum and dedendum portions 14, 16 of the tooth elements are selected so as to apply the appropriate corrective action to the faces of the gear-shaped workpieces in accordance with the dimensional inaccuracies present. In those instances where the gear workpiece is to receive finishing action along the dedendum portion of the tooth elements, the addendum portions of the brasive finishing tool are provided with the desired type and quantity of abrasive particles, while the dedendum portion may be completely devoid of any abrasive materials or may contain a lesser proportion of smaller grit size particles to impart only a minimal abrasive finishing action to the addendum portions of the tooth elements on the workpiece. When the addendum of the tooth elements on a workpiece are to be subjected to abrasive corrective action, then converse formulation of the composite tooth elements of the finishing tool is provided to apply the desired localized and controlled corrective action without disturbing those surfaces of the workpiece which are within permissible dimensional tolerances. It will be apparent from the foregoing that large variations in the selected abrasive finishing characteristics of composite finishing tools made in accordance with the practice of the present invention is feasible to adapt such finishing tools for automatic finishing of precision gears, thereby eliminating the heretofore time-consuming manual correction of such dimensional inaccuracies.

In accordance with the method aspects of the present invention, the composite gear-shaped finishing tool is prepared by employing a mold assembly as illustrated in FIGS. 3 and 4 of the drawing. The mold, as illustrated, consists of a circular base plate 26 on which an internal master gear 28 is detachably secured and is disposed with the tooth elements thereof concentric to a central stud 30. In the specific embodiment shown, the hub 12 of the finishing tool is itself of a composite construction and comprises an inner metallic hub section 32 and a plastic rim section 34 securely bonded thereto and extending radially outwardly therefrom to a point adjacent to the tooth elements on the master internal gear 28. The composite hub is clamped in position on the base plate 26 by a clamping member 35, removably secured to the central stud 30. The space extending between the periphery of the plastic rim 34 and the internal gear mold 28 is adapted to be filled with a suitable liquid mixture consisting of the resin bonding agent and appropriate proportions of suitable filler materials and/or abrasive particles consistent with the intended abrasive finishing action that is desired with respect to the dedendum portion of the tooth elements thereof. After a casting of the abrasive matrix and a curing thereof, the excess portion 36 overflowing the annular casting cavity is machined away and thereafter sections of all or selected ones of the resultant tooth elements are removed for a selected depth, enabling supplemental replacement of the removed portions with an abrasive matrix of an alternative abrasive finishing characteristic.

As previously indicated, it is preferred in accordance with the practice of the present invention to remove the tip of the tooth elements of the preliminarily formed abrasive finishing tool blank in a manner so that the points of the machined tooth elements lay in a circle which is disposed eccentric to the pitch circle of the abrasive tooth elements. In this way, a controlled variation in the area of the two sections of the working faces of the tooth elements is achieved, providing a smooth transition in the surface finish and contour of the tooth elements of a workpiece finished thereby.

The resultant gear blank indicated at 38 in FIG. 4 is thereafter reinserted in a mold assembly of the same or similar type as that shown in FIG. 3, which similarly is provided with an encircling master internal gear 28. After placement of the finishing tool blank in the mold assembly and a clamping thereof in appropriate registration relative to the master internal gear 28, the terminal cavities indicated at 40 are filled with a liquid abrasive mixture which, upon subsequent curing, becomes tenaciously bonded to the end portions of the tooth elements of the 'blank. As previously indicated, it is usually preferred to provide a mechanical interlock between the dedendum and addendum portions of the composite tooth elements and this can be conveniently achieved in accordance with the practice of the present invention by drilling or otherwise machining suitable cavities, such as the apertures 24, inwardly of the ends of the dedendum portions of the gear blank such that the second liquid abrasive mixture during casting thereof flows inwardly of such apertures and upon curing becomes mechanically interlocked therewith. Upon curing and/or hardening of the addendum sections of the composite finishing tool, it is removed from the mold assembly and finished, if necessary, along the side faces thereof to provide the desired tooth width consistent with the intended end use of the finishing tool.

In order to further illustrate the practice of the present invention, typical examples are provided of suitable mixtures of binding agents containing abrasive particles which can be satisfactorily employed for forming composite tooth elements of the types previously disclosed. It will be understood that these examples are provided for illustrative purposes and are not intended to be limiting of the invention as set forth in the subjoined claims.

EXAMPLE I A composite abrasive finishing tool is fabricated employing a composite hub structure as shown in FIG. 3, which is placed in a mold assembly and a liquid resin abrasive mixture is poured in the annular cavity, effecting a filling thereof. The resin abrasive mixture has a composition as follows:

Ingredient: Percent by weight Polyamide resin 40 Epoxy resin 20 Zinc oxide filler 40 Total a 100 The polyamide resin used is commercially available from General Mills, Inc., under the designation of Versamidel40, and is derived from the condensation of dibasic polymerized fatty acids and polyamine having a resultant amine value of 377, a specific gravity of 0.97 and a Brookfield viscosity of 5 poises at C. The epoxy resin is commercially available from General Mills, Inc., under the designation Genepoxy-190, and is derived from the polymerization of bis-phenol-A and epichlorohydrin, providing a resin having an epoxide equivalent value of 187-191, a Brookfield viscosity of from about 11,000- 16,000 centipoises at 25 C., and a specific gravity of 1.18.

The mixture of the epoxy resin, polyamide resin and filler is made by gentle mixing to minimize entrapment of air and the resultant blend is thereafter allowed to stand for a period of twenty minutes to enable escape of the major portion of entrapped air bubbles. A suitable release agent, such as a silicon fluid designated as No. 20 available from Dow-Corning Corporation, is applied in the form of a solvent solution to the surfaces of the mold, whereafter the volatile solvent consisting of a mixture of toluene and alcohol is allowed to evaporate. The resultant resin mixture containing the filler is poured in the annular region between the peripheral portion of the hub and the internal master gear and allowed to solidify at atmospheric pressure and at room temperature for a period of about 12 hours. Thereafter the excess portion of the cured mixture is trimmed from the upper surface of the blank after extraction thereof from the mold and the tip portions of the tooth elements are removed in a lathe employing a silicon carbide cutting tool wherein the tooth elements are eccentrically trimmed to .a point 20% outwardly of the pitch circle to a point 20% inwardly of the pitch circle diametrically opposite thereto. The resultant machined gear blank is thereafter replaced in the mold assembly with a new coating of release agent and a second resin abrasive mixture is prepared having a composition as follows:

Ingredient: Percent by weight Polyamide resin 21.6 Epoxy resin 11.6 Abrasive-8 grit silicon carbide 33.4 Abrasive-54 grit alumina 33.4

Total 100 The polyamide resin and epoxy resin are identical to those empolyed in preparing the blank of the abrasive finishing tool. The resultant resin abrasive mixture similarly is mixed and is poured in the terminal tooth cavities 40 illustrated in FIG. 4 and is allowed to cure for a period of 12 hours at atmospheric pressure and at room temperature. The resultant composite tool is thereafter removed and the side surfaces thereof are trimmed, providing a finishing tool of the desired width and possessing a dual abrasive finishing characteristic along its working tooth surfaces.

EXAMPLE II A similar abrasive finishing tool having composite tooth elements is prepared wherein a composite hub of the type employed in Example I is used in forming a blank with the peripheral portion consisting of a resin abrasive mixture of the following composition:

Ingredient: Percent by weight Polyamide resin 19.9 Epoxy resin 13.3 Abrasive-8O grit silicon carbide 33.4 Abrasive-54 grit alumina 33.4

Total 100 After casting and curing the gear blank, the tooth elements thereof are machined as previously described in Example I and a 0-50 resin filler composition consisting of 25% epoxy resin, 25% polyamide resin and 50% filler, consisting of carbon black and zinc oxide, is prepared which is cast in the peripheral cavities forming a composite finishing tool. In this specific instance, the addendum portions of the tooth element of the finishing tool possess only minimal finishing action, whereas the dedendum portions effect an abrasive finishing action on the addendum portions of a workpiece to be finished.

EXAMPLE III A similar composite finishing tool is prepared in which a polyurethane resin is employed for forming the peripheral portion of the finishing tool blank wherein the polyurethane resin comprises 30% by weight of the mixture with the balance consisting of a 50-50 mixture of a No. 80 silicon carbide grit and-a No. 54 aluminum oxide grit. The peripheral tooth tip portions of the finishing tool are composed of a resin abrasive mixture consisting of 21.9% polyamide resin, 11.6% epoxy resin, a 36-grit alumina abrasive present in an amount of 59.8% and the balance a ZOO-grit alumina.

The foregoing composite finishing tool provides a higher abrasive action along the dedendum portions of the working faces of its tooth elements and a lesser abrasive action along the addendum sections of the working faces thereof.

While it will be apparent that the description of the preferred embodiments are well calculated to provide the benefits and advantages as herein described, it will be understood that the invention is susceptible to variation, modification and change without departing from the spirit thereof.

What is claimed is:

1. An abrasive gear-shaped finishing tool comprising a cylindrical body having a plurality of tooth elements therearound adapted to be disposed in meshing relationship with a workpiece to be finished, each of said tooth elements including a Working face comprised of a bonded matrix, at least a portion of said tooth elements being of a composite construction wherein said working face thereof is divided into a plurality of sections each having a different abrasive finishing characteristic in order to impart selected variations in the abrasive finishing action on a workpiece being finished.

2. The abrasive gear-shaped finishing tool as defined in claim 1, wherein said working face of the composite said tooth elements is divided into two radially displaced sections.

-3. The abrasive gear-shaped finishing tool as defined in claim 1, wherein all of said tooth elements of said finishing tool are of a composite construction.

4-. The abrasive gear-shaped finishing tool as defined in claim 1, wherein at least the peripheral portion of said body and said tooth elements are comprised of said bonded matrix.

5. The abrasive gear-shaped finishing tool as defined in claim 1, wherein the composite said tooth elements comprise a dedendum portion composed of a bonded abrasive matrix of a first composition and an addendum portion of a bonded abrasive matrix of a second composition provided with a controlled different abrasive mixture, said addendum and dedendum portions tenaciously bonded to each other forming an integral composite tooth element.

6. The abrasive gear-shaped finishing tool as defined in claim 1, wherein at least one of said sections of said working face is composed of a bonded matrix substantially devoid of an abrasive particles therein, thereby rendering that section substantially ineffectual in removing material from a workpiece during a finishing operation.

7. The abrasive gear-shaped finishing tool as defined in claim 1, wherein said tooth elements terminate in a tip portion and said working face of the composite said tooth elements is divided into two radially displaced sections joined at a boundary disposed substantially parallel to said tip portion of said tooth elements.

8. The abrasive gear-shaped finishing tool as defined in claim 5, wherein said addendum portion and said dedendum portion include mutually coacting means for effecting a mechanical interlock therebetween.

References Cited UNITED STATES PATENTS 1,422,200 7/ 1922 Harris 51-20-7 2,815,746 12/ 1957 Schwarzkopf et a1. 51206 X 2,913,858 11/1959 Praeg et al. 51--206 R 2,980,966 4/1961 Praeg 51--2 06 R X 3,183,633 5/1965 Decker 51206 R 3,550,330 12/1970 Nakamura 51-287 FOREIGN PATENTS 800,680 8/1958 Great Britain 5l--206 R 864,688 4/ 1961 Great Britain 51206 R LESTER M. SWINGLE, Primary Examiner