US 3909990 A
Operating gears or gear-like dies in the form of hypoid gears and pinions are finished by running them in mesh, preferably without substantial relative movement other than rotation, with a honing or polishing tool in the form of a mating hypoid pinion or gear, respectively.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 1111 3,909,990
Tersch Oct. 7, 1975  FINISHING HYPOID GEARS 3,088,251 5/1963 Davis 51/206 P x 1 Inventor: Richard Tersch, Poime 33553133? 211322 ififiifimis rzjiij JIJJJJJJJ.'..?.3 Woods, Mlch- 3,293,805 12/1966 Davis 51/287 9 3,623,275 11/1971 Koella... 5l/206  Asslgnee' Santa Momca 3,708,925 1/1973 Ainoura. 51/287 3,740,904 6/1973 Ainoura 5l/287 22] Filed: 06:. 24, 1973 Primary Examiner--Donald G. Kelly  Appl' 409l66 Attorney, Agent, or Firm-Whittemore, Hulbert &
Belknap  us. Cl 51/287; 51/204  Int. Cl? B24B 1/00; B24B 19/00 57 ABSTRACT  Field of Search 51/287 206 52 O eratin ears or ear-like dies in the form of h oid 51/52 HB, 105 R, 105 HB, 317, 31s, 26 P g gears and pinions are fimshed by runnmg them In  References Cited mesh, preferably without substantial relative movement other than rotation, with a honing or polishing UNITED STATES PATENTS tool in the form of a mating hypoid pinion or gear, re-
2,913,858 11/1959 Praeg 51/287 ux spectively, 2,942,389 6/1960 Praeg 51/287 2,980,966 4/1961 Praeg 51 /287 x 13 Claims 1 Drawmg F 2"" U.S. Patent Oct. 7,1975 3,909,990
FINISHING HYPOID GEARS BRIEF SUMMARY OF THE INVENTION Efforts to hone bevel gears, and particularly hypoid gears, to final form by running them in mesh with abrasive tools in the form of hypoid pinions and gears respectively, for the primary purpose of removing nicks and burrs have generally not been completely satisfactory. This is to be contrasted with the situation where nicks and burrs are successfully removed from cylindrical gears by rolling them in mesh with conjugate cylindrical gearlike honing tools at crossed axes while providing a relative reciprocation therebetween in a plane parallel to the axes of both. In this case a nick or burr contacts different portions of the hone teeth so that it is removed without causing appreciable damage to the honing tool. Since bevel gearing, particularly hypoid gearing, cannot be provided with a relative traverse, as in the case of cylindrical gearing, and a nick or burr on a tooth of the hypoid gear of pinion contacts the same zone on the tool at every rotation, thus quickly breaking down the honing tool.
However, in the case of bevel gearing, and particularly hypoid gearing which requires a smoother surface finish than can be produced practically by grinding, it is possible to produce such a finish by employing special polishing tools formed of materials capable of producing a very fine abrading or polishing action.
A particularly useful application of the present invention is in the'manufacture of rolling dies in the form of hypoid gears or pinions. such dies are formed of die steel or high speed steel, finished to required form, hardened to 60-65 Rockwell C, and thereafter ground or otherwise treated for final correction of tooth form in hardened condition. Finally, the die is polished to provide a very fine surface finish without however appreciably affecting tooth form.
The polishing tool may be formed of a relatively soft yieldable material such for example as a solid polyurethane provided at the surfaces of the gear teeth with a multiplicity of pores of controlled size. Such a material is disclosed in commonly assigned Franco application Ser. No. 317,109 filed Dec. 21, 1972. Where the tool is in the form of the yieldable material provided with surface pores, the abrasive is furnished in a compound which is supplied to be carried at the surface of the teeth of the tool with abrasive particles becoming embedded in the pores thereof.
With these tools the operation involves rotating the tool and mating bevel gear in mesh with the same relationship between the axes thereof as exists between mating gears and pinions while the parts are maintained in tight mesh under relatively light pressure. Alternatively, the tool may be formed with some backlash, and one ofthe parts positively driven in rotation and driving the other part against a predetermined brake action.
BRIEF DESCRIPTIONN OF THE DRAWING The FIGURE illustrates the relationship between a hypoid gear pinion.
DETAILED DESCRIPTION Referring now to the drawing, there is illustrated a hypoid gear having teeth 12 in mesh with the teeth 14 of a hypoid pinion 16.
In accordance with the present invention the gear 10 may be polished by rotating it in mesh with a polishing tool having the form of the hypoid pinion l6. Alternatively, the teeth of a hypoid pinion 16 may be finished by rolling it in mesh with a finishing tool in the form of the hypoid gear 10. In the usual operation the hypoid gear and pinion members, one of which is in the form of a polishing tool, are rotated with the teeth thereof in pressure contact. The pressure contact may be brought about by meshing the gear and pinion members in tight mesh so that each tooth thereof is contacted simultaneously at opposite sides by teeth of the mating mem ber. In this case a relatively light pressure is maintained between the members.
Alternatively, the arrangement may be such that the teeth of the hypoid gear and pinion members are in loose mesh, with one of the members being positively rotated and the other member being driven against a suitable brake action by rotation of the first member. The speed of rotation is between 250 and 1000 feet per minute pitch line velocity.
The tool is formed of relatively soft material such as the polyurethane disclosed in the' above identified copending Franco application, and the abrasive particles are supplied in the form of a finishing compound. In this case the abrasive particles in the compound are in part picked up by the pores at the surface of the teeth of the tool and are drawn across the surface of the teeth of the work gear.
For completeness herein, it may be noted that the polyurethane resin specifically disclosed in the Franco application is compounded to have a hardness of between Durometer A scale and 55 Durometer D scale, and a value of about Durometer A has been found to be very satisfactory.
During the polishing operation a liquid polishing compound containing very fine abrasive particles such for example as a 500 grit lapping compound is supplied to the periphery of one of the members, preferably the polishing tool, and is carried on the teeth of the members around the zone of mesh where the polishing ac tion is obtained as a result of the sliding contact between the teeth of the gear and polishing tool.
The polishing tool is driven in rotation at a substantial speed as for example 240 RPM, giving rise to a peripheral speed of approximately 520 feet per minute. It will of course be understood that this does not represent the velocity of the sliding action between engaged surface areas of the teeth of the tool and gear since this sliding action occurs at a much lower velocity.
While the polishing operation has been carried out successfully as noted above, employing a polishing compound having polishing grains or particles of a size not exceeding 500 mesh, the polishing compound may contain polishing solids all of which are of substantially smaller size. Such a compound for example may contain jewelers rouge or yellow aluminum oxide particles. In general, the time required for the operation may be reduced by employing as large particle size in the polishing compound as are found to be capable of producing the required surface finish.
While excellent results have been obtained in carrying out the herein described method, while maintaining the work gear and tool in fixed positional relationship, and preventing any relative movement therebetween except for the rotation thereof, and the necessary approach to provide the required polishing pressure, it is within the scope of the present invention, if desired, to superimpose on the relative rotation additional slight relative movements such as limited oscillation in directions which may correspond with the direction of the gear axis, the pinion axis, or a direction which is perpendicular to both axes, or any combination of such movements. Any suitable apparatus for superimposing such additional limited relative motion between the gear and tool on the simple rotation thereof may be employed.
Practice of the method disclosed herein and use of the hypoid gear polishing tools disclosed herein. permits final finishing operations of high accuracy in bevel, and particularly hypoid gearing, after a preliminary finishing operation, to a required high quality surface finish in a finishing operation which takes only a few seconds per piece.
It is to be understood that the present operation is limited to a surface finishing operation and is not intended to remove nicks or burrs or to correct errors in tooth form, tooth spacing or the like.
While it has previously been stated that the present invention is particularly useful in the final finishing of dies in the form of hypoid gears or pinions formed of high speed steel and hardened to a Rockwell hardness of 60-65 Rockwell C, with a value of about 62 Rockwell C being typical, the invention has application also to the production of operating hypoid gearing.
In the manufacture of hypoid gearing for use as master rolling dies, the gears or pinions are initially cut to approximate form, are thereafter heat treated, and the teeth of the gear members after heat treatment are corrected to final form by a finishing operation such as lapping. If the hypoid gear members do not have nicks and burrs in the surfaces of the teeth, or if such nicks and burrs have been removed by a secondary operation such as grinding, the teeth may be semi-finished or further semi-finished by honing. The honing operation is carried out by running the hypoid gear or pinion in mesh with a conjugate gear or pinion formed of gear honing material as described in Praeg US. Pat. No. 2,942,389. This operation is normally not intended to remove substantial amounts of material, and where a hypoid hone is employed, the abrasive particles are relatively fine so that the operation is more properly described as a polishing operation than one in which appreciable stock removal takes place.
As a final operation a further polishing operation may be provided in which the hypoid gears are run in mesh with conjugate hypoid tools formed of relatively soft finishing material as described in the foregoing.
The foregoing sequence of operations is of course available for use in making operating gears, but usually the cost restricts usage to dies. However, it may by used in making highly accurate, fine finished master gears for various uses, such as in the manufacture of hypoid honing tools, where cost is not controlling.
It will of course be appreciated that where the initial cutting operation is carried out under sufficiently controlled conditions, and where the heat treatment likewise is controlled so as to eliminate substantial distortion, the step of grinding and/or fine honing may be omitted and the hypoid gear part finally finished after heat treatment by polishing with the relatively soft polishing tool disclosed herein.
In an alternative method of producing operating hypoid gear and pinion members, the member is initially cut to approximately final form and before heat treatment is subjected to a rolling operation which imparts to the teeth of the member a form such that after heat treatment the tooth form will be substantially as desired. After the heat treatment operation has hardened the material of the gear, it is subjected to a polishing operation, which may consist of the final polishing operation obtained by running it in mesh with the relatively soft hypoid polishing tool.
Similarly, the production of master rolling dies in the form of hypoid gears and pinions formed of hardened die steel high speed steel is in accordance with the present invention, characterized in that the final finishing operation is essentially a polishing operation which does not significantly change tooth form but which has the effect of producing a much'finer micro-inch surface finish. This may be accomplished with the relatively harder hypoid honing tool containing relatively fine abrasive material, but preferably it is carried out by running the die in mesh under light' pressure conditions with the relatively soft finishing tool disclosed herein. A 2-4 micro-inch finish is readily obtained.
In practice it has been found desirable to finish hypoid form dies so as to have a surface finish of 46 micro-inches. As previously noted, before polishing a hypoid gear-shaped member with the relatively soft tool disclosed herein, it is essential to eliminate nicks and burrs, and this is done by grinding, after which the dies are honed, preferably in two steps, to semi-finish and further semi-finish before final polishing.
While the speed of rotation may be varied it is preferred to provide a pitch line velocity of the bevel gear and pinion of 1001,000 feet per minute.
Where the term bevel gear is employed, it is to be understood to include hypoid, and the term gear is to be understood to include both gears and pinions.
What I claim as my invention is:
1. The method of making highly accurate hypoid form master dies having a surface finish on tooth profiles of about 4-6 micro-inches which comprises heat treating a cut hypoid gear of high speed steel to a hardness of about 60-65 Rockwell C, thereafter grinding the gear to improve form and eliminate any nicks and burrs, and to cause the surface finish of its tooth profiles to approach the desired range, and finally polishing the ground gear by rolling it in mesh with an abrasive hypoid polishing tool whose teeth have a surface hardness of between Durometer A and 55 Durometer D with its teeth in light pressure contact with the teeth of the tool at a peripheral speed of about lOOl,OOO feet per minute for a few seconds to produce a micro-inch finish of about 46 on the tooth profiles.
2. The method as defined in claim 1 which comprises honing the gear after grinding and before polishing in which the honing is performed in two steps in which the successive steps both improve surface finish.
3. The method as defined in claim 1 which comprises meshing the gear and polishing tool in tight mesh to cause light pressure contact between both sides of the teeth of the gear and tool.
4. The method as defined in claim 1 which comprises meshing the gear and polishing tool in loose mesh, driving either the gear or tool in rotation and opposing rotation of the other to cause light pressure contact between the teeth of the gear and tool at one side thereof only.
5. The method as defined in claim 1 which comprises providing rotation of the tool and gear at a peripheral speed of about 500 feet per minute.
6. The method as defined in claim 1 in which the polishing tool has a hardness at the surfaces of its teeth of 5 about 95 Durometer D.
7. The method as defined in claim 1 in which the polishing tool has teeth which are essentially a solid elastomer except for the surfaces thereof which engage the teeth of the work gear, which tooth surfaces have a multiplicity of pores opening into the said tooth surfaces.
8. The method as defined in claim 7 which comprises providing fine abrasive particles on the tool teeth which at least in part enter into pores in the surfaces of the tool teeth and are drawn across the surfaces of the gear teeth.
9. The method as defined in claim 8 in which the abrasive has particles which do not exceed about 500 mesh in size.
10. The method of final finishing a hardened steel gear rolling die member in the form of a hypoid gear without measurably changing tooth form which comprises rolling it in mesh with a gear polishing tool memher in the form of a hypoid gear conjugate to the steel gear with mating tooth surfaces of said steel gear and tool teeth in light pressure contact, the tool having tooth surface portions having a hardness of between Durometer A and 55 Durometer D, driving one of the members directly at a peripheral speed of lOO-i,000 feet per minute and introducing an abrasive compound having abrasive particles onto the meshing teeth of said members.
11. The method as defined in claim 10 in which the polishing tool has a hardness at the surface of its teeth of about Durometer D.
12. The method as defined in claim 10 in which the polishing tool has teeth which are essentially a solid elastomer except for the surfaces thereof which engage the teeth of the work gear, which tooth surfaces have a multiplicity of pores opening into the said tooth surfaces.
13. The method as defined in claim 12 in which the particles at least in part enter the pores in the surfaces of the tool teeth and are drawn across the surfaces of the gear teeth.