JP2023007221A - High-precision gear processing method - Google Patents

Abstract

To provide a processing method that can form a lubrication surface of a plateau structure on a tooth surface of a gear while maintaining high-precision processing state.SOLUTION: Blast treatment for a gear, which has been finished with high precision in such a manner that after performance of gear cutting and heat treatment, further finishing has been performed with precision of N5 class or more in JIS B 1702-1:1998 and an arithmetic average roughness Ra of 0.2 μm or less, is performed in such a manner that an elastic polishing material with irregularly shaped hard abrasive grains carried thereon is injected to a tooth surface of the gear substantially vertically to form fine irregularities on the tooth surface. Thereafter, polishing is performed by polishing the tooth surface and removing a protrusion of the irregularity, thereby flattening. Thus, a surface of a plateau structure having a gouge, which is a recess of which an open width is narrower and a depth is deeper compared to the protrusion of the irregularity formed before the blast treatment, and a protrusion which is formed between gouges and of which an upper end is flattened, is formed on the tooth surface, a surface roughness of the tooth surface and decrease in processing precision are suppressed within a prescribed range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for machining high-precision gears, and more specifically, a plateau structure that is finished with high machining accuracy and consists of concave portions that serve as oil reservoirs on the tooth surface and convex portions with flattened tops. It relates to a method of machining a high-precision gear that makes it possible to obtain a gear with a surface of

In recent years, in many cutting-edge industrial fields such as electric vehicles and robotics, gears have come to be required to have a high degree of quietness.

In response to such demands for higher precision, gear machining methods are being reviewed.

As an example, in conventional gear processing, as shown in Fig. 5(A), after turning the material, the gear is gear-cut with a bob machine or the like. After the heat treatment, heat treatment is performed, and after that, only hard turning is performed as finish machining, and it is general that no further machining is performed on the tooth flank after heat treatment.

On the other hand, in recent years, in gear processing to meet the demand for higher precision, as shown in Fig. 5 (B), after heat treatment, hard turning is performed, followed by tooth surface grinding ("Gear grinding" in the figure). and gear honing ("honing" in the figure), etc., are performed on the tooth surface, and the process of processing the roughness and dimensional accuracy of the tooth surface with higher precision is now being implemented (Non-Patent Document 1 reference).

On the other hand, the transmission efficiency of gears depends on the lubricity of the gear tooth flanks, and it has long been known that it is effective to process the tooth flanks into a plateau structure surface in order to improve such lubricity. ing.

Here, the surface of the plateau structure is, for example, as shown in FIG. It is a surface having a shape, and the surface of such a plateau structure is industrially important as the structure of the sliding surface.

As a method of forming such a plateau structure surface on the tooth flank of a gear, Patent Document 1 listed below discloses a method of forming by blasting.

Specifically, Patent Document 1 proposes the following three methods shown in FIGS.

The first method is to perform "shot peening" to form dimples by projecting shots made of steel balls etc. as a projection material to the gear that has undergone "tooth cutting", and then perform "carburizing" as a heat treatment. After that, remove the sharp points generated between the dimples during shot peening by "abrasive flow processing" in which the gear is placed in the flow of the mixture of abrasive grains and viscous fluid and polished. Thus, a plateau surface is formed [FIG. 7(A)].

The second method is to perform "mirror surface shot peening", which shoots a blast material with abrasive grains attached around the elastic and sticky core to the gear that has undergone "tooth cutting". After forming the dimples, "carburizing treatment" is performed, and then "mirror shot peening" is performed again, and the sharp edges generated between the dimples are removed by polishing to form a plateau surface [ FIG. 7(B)].

The third method is to apply the above-mentioned "shot peening" to the gear that has been subjected to "tooth cutting" to form dimples, then perform the "carburizing treatment", and then perform the above-mentioned "mirror surface shot." A plateau surface is formed by polishing and removing sharp edges generated between dimples during the shot peening process [Fig. 7(C)].

Japanese Patent Application Laid-Open No. 2004-345022

Masakazu Nabekura, Michiaki Hashiya, Yukihisa Nishimura, Masakatsu Fujita, Sekikoto Yanagi, Masanobu Mizaki, "Gear processing machines and precision cutting tools that support the production of transmission gears for automobiles," Mitsubishi Heavy Industries Technical Report VOL, 43 NO. 3:2006 (https://www.mhi.co.jp/technology/review/pdf/433/433041.pdf)

As mentioned above, it is necessary to machine gears with high precision due to the need for quietness. If a plateau structure surface can be formed on the tooth flank of the gear while maintaining

However, processing the tooth flank of the gear to form the surface of the plateau structure described above involves forming recesses that serve as oil reservoirs and processing the surface into an uneven shape. The surface roughness increases, and the machining accuracy decreases due to changes in dimensions and shape.

In particular, in the method described in Patent Document 1 mentioned above, steel balls, etc. A dimple with a wide opening width is formed by widening the trough portion by colliding a shot composed of The surface has a plateau structure as shown in C) ([0019] of Patent Document 1).

As a result, when forming the surface of the plateau structure by the method described in Patent Document 1, as a result of forming dimples with relatively wide opening widths as shown in FIG. The surface roughness becomes large and the dimensional accuracy becomes low, so that it is not possible to meet the recent demand for high accuracy.

Further, in the method described in Patent Document 1, as shown in FIGS. 6A and 6B, the collision of shots made of steel balls or the like crushes some of the convex portions to form valleys in the unevenness. Since dimples are formed by greatly enlarging a portion (recess), the formation of dimples greatly changes the shape of the tooth flank of the gear.

From these points, it is considered that the method described in Patent Document 1 requires the formation of dimples before the heat treatment (surface hardening process) (Claim 5 of Patent Document 1, etc.).

That is, in order to form dimples accompanied by large plastic deformation as in Patent Document 1, it is necessary to perform the heat treatment in a state in which the base material hardness of the gear is low (thus, in a state in which plastic deformation is likely to occur). At the same time, in order to obtain gear machining accuracy, changes in the shape and dimensions of the tooth flanks that have been greatly deformed by the formation of dimples are adjusted by hard turning [see Fig. 5 (A) and (B)], etc., which is performed after heat treatment. There is a need to.

As described above, the method described in Patent Document 1 requires the formation of dimples before heat treatment. For example, a gear that has been completed as a gear and once incorporated into an automobile or the like as a part or the like is targeted for processing, and it is not possible to subsequently form a surface of a plateau structure on the tooth flank of this gear.

In this way, the processing method described in Patent Document 1 forms dimples with relatively wide opening widths, so even if a plateau-structured surface can be formed on the tooth flank of the gear, , the tooth flank of the obtained gear has a large surface roughness and a low processing accuracy.

In addition, in the processing method described in Patent Document 1, it is essential to form dimples before heat treatment, and since the formation of dimples greatly deforms the tooth flank, heat treatment and high-precision finishing are performed. It is also impossible to form a lubricating surface with a plateau structure afterward for a gear that has been assembled, for example, a gear that has been assembled as a part in an automobile or the like.

Here, in the case of forming recesses that will become oil reservoirs by blasting, it is common practice to form "dimples", which are semicircular recesses with relatively narrow opening widths, as in Patent Document 1 cited above. It's here.

However, the inventors of the present invention reviewed this point again, and even if a recess with a narrow opening width compared to such a "dimple" is formed, as long as the depth of the recess is secured, , it should be possible to exhibit the function as an oil reservoir, and it was surmised that it is not necessarily necessary to form dimples with wide openings as in Patent Document 1. Furthermore, it was inferred that it is not necessary to provide the concave portions with a sufficient depth more densely than necessary.

If it is possible to impart lubricity to the tooth flank by forming such narrow and deep recesses at a low density, the surface of the plateau structure can be formed with a smaller amount of deformation on the tooth flank of the gear. Formation of a surface with a plateau structure while suppressing an increase in surface roughness and a decrease in dimensional accuracy compared to the case of forming dimples with a wide opening width as in the above-mentioned Patent Document 1 should be able to do

On the other hand, in order to form recesses with narrow opening widths on gears that have been hardened by heat treatment, simply injecting and colliding abrasive grains with a fine particle size corresponding to the opening width is not enough. Since the mass of each grain is small and the collision energy is small, even if a narrow recess can be formed in the collision part, a deep recess cannot be formed, and the function as an oil pool is obtained. Therefore, it is necessary to devise ways to solve such problems.

One method for solving this problem is to inject abrasive grains at a high speed to increase the impact energy, but not all blasting devices have such a capability.

In addition, even if fine abrasive grains corresponding to the opening width can be jetted at high speed, if the abrasive grains hit the tooth flank evenly, deep recesses are formed at high density so that they are adjacent to each other over the entire surface. At the same time, a high point corresponding to the depth is formed between the recesses [see FIG. 2(B')].

As a result, in subsequent processes, the tooth flank with a plateau structure, which is created by grinding and removing the high-density cusps, is subject to large changes in size and shape due to the increased volume of grinding and removal. becomes [see FIG. 2(C')].

However, it is not necessary to provide the deep recesses that become oil reservoirs adjacent to each other at a high density. can be kept small. In other words, it is necessary to devise ways to form deep concave portions at a low density.

The present invention was made based on the idea of the inventors. The present invention maintains the high-precision machined state of the gear finished with high precision, and has a relatively narrow opening width and depth on the tooth flank. It is an object of the present invention to provide a machining method for a high-precision gear capable of forming a lubricating surface having a plateau structure in which deep concave portions are formed at a low density.

Means for solving the problems are described below together with the symbols used in the mode for carrying out the invention. This code is for clarifying the correspondence between the description of the claims and the description of the mode for carrying out the invention, and needless to say, it is used restrictively to interpret the technical scope of the present invention. not a thing

In order to achieve the above object, the method of machining a high-precision gear according to the present invention comprises:
After gear cutting with a bobbing machine and heat treatment such as carburizing, finish processing such as tooth surface polishing and gear honing is performed to achieve an accuracy grade of N5 or higher specified in JIS B 1702-1:1998. Gears that have been finished with precision and have a surface arithmetic mean roughness Ra of 0.2 μm or less are targeted for processing,
An irregular shape with corners, for example, hard abrasive grains such as ceramics and diamonds are attached to the surface of the elastic body, or an elastic abrasive material that is kneaded into the elastic body is applied almost perpendicularly to the tooth surface of the gear. A blasting treatment (first blasting treatment) for forming fine irregularities on the tooth surface by jetting;
polishing the tooth surface after the blasting treatment (first blasting treatment) to remove the tops of the convexes of the unevenness and flatten it;
A gouge, which is a concave portion having a narrower opening width and a deeper depth than the uneven concave portion formed before the blasting treatment on the tooth surface, and a flattened upper end formed between the gouge. forming a plateau-structured surface with ridges;
Arithmetic mean roughness Ra, single pitch error fpt, cumulative pitch error Fp, total tooth profile error It is characterized in that increases in both Fα and total tooth trace error Fβ are suppressed to 30% or less (claim 1).

here,
Arithmetic mean roughness Ra is extracted from the roughness curve by the reference length (l) in the direction of the average line, summed the absolute value of the deviation from the average line of this extracted part to the measurement curve, and averaged and specified in JIS B 0601:2001.

Further, the single pitch error fpt, cumulative pitch error Fp, total tooth profile error Fα, and total tooth trace error Fβ in JIS B 1702-1:1998 are as follows.
Single pitch error fpt: The difference between the actual pitch and the theoretical pitch on the pitch circle of adjacent tooth flanks on the same side.
Cumulative pitch error Fp: The maximum cumulative pitch error in the entire tooth flank area of the gear, expressed by the total amplitude of the cumulative pitch error curve.
Total tooth profile error Fα: Distance between design tooth profile diagrams sandwiching the actual tooth profile within the determined tooth profile inspection range.
Total tooth trace error Fβ: The distance between two design tooth traces sandwiching the actual tooth trace within the determined tooth trace inspection range.

In the blasting treatment (first blasting treatment) described above, the median diameter of the elastic body is 0.1 to 2.0 mm, and the median diameter of the abrasive grains is 10 to 500 μm. It can be performed at a pressure of 0.2 to 0.5 MPa (claim 2).

Further, the polishing treatment may be performed by a second blasting treatment in which abrasive grains are adhered to the surface of an elastic body or an elastic abrasive material kneaded into an elastic body is jetted at an acute angle to the tooth surface. (Claim 3).

In this case, the second blasting treatment is carried out using an elastic abrasive having a median diameter of 0.1 to 2.0 mm for the elastic body and a median diameter of 20 μm or less for the abrasive grains, at a jet pressure of 0.1 mm. It can be performed at 1 to 0.3 MPa (claim 4).

The second blasting can be performed at an inclination angle θ of preferably 20 to 60°, more preferably 25 to 35° with respect to the tooth surface (claim 5).

Due to the configuration of the present invention described above, the gear machined by the high-precision gear machining method of the present invention has a plateau structure surface formed on the tooth flank, but the surface roughness is small and It was possible to have a contradictory structure at the same time that it was machined in a highly accurate machining state.

As a result, the gears machined by the method of the present invention are machined with high machining accuracy, so that the operating noise is small and quietness is realized. The transmission efficiency could be improved by improving the lubricity of the surface.

That is, in the method of the present invention, the concave portion formed as the oil reservoir is formed as the above-mentioned "gouge" which is a concave portion having a relatively narrow opening width and a large depth, thereby ensuring the function as an oil reservoir. By reducing the amount of deformation that occurs on the tooth flank due to the low-density formation of gouges, the gear can be maintained in a highly-precise machined state.

On the other hand, since the gear tooth flank hardened by heat treatment is in a state where it is difficult for deformation to occur, even if only fine abrasive grains with a small mass per grain are sprayed alone, deep recesses can be formed on the tooth flank. Can not do it.

However, in the method of the present invention, by adopting a configuration in which an elastic abrasive material made by adhering abrasive grains to the surface of an elastic body or kneading it is ejected, when abrasive grains collide with the tooth surface, the abrasive grains , By adding not only the mass of the abrasive grains but also the collision energy corresponding to the mass of the elastic body, it is possible to form a narrow and deep recess on the tooth surface where the abrasive grains collide. It has become.

Furthermore, the length of the abrasive grains protruding from the surface of the elastic abrasive material varies in size. As a result, when long protruding grains collide with the tooth surface, gouges are formed, but shallow recesses are formed where short protruding grains collide.

Therefore, the gouge formed by the collision of the elastic abrasive material has a low density, the number of pointed ends corresponding to the gouge is reduced, and the volume to be polished and removed in the formation of the plateau structure is also small [Fig. 2 (B), See (C)].

As a result, it is possible to form the surface of the plateau structure after the gear is machined with high precision through heat treatment, and even after the surface of the plateau structure is formed, the original machined with high precision can be obtained. It is possible to suppress the increase in the surface roughness of the surface and the processing error in the range of 30% or less.

Explanatory drawing of the manufacturing process of a gear including the manufacturing method of the high-precision gear of this invention. It is a schematic diagram showing the uneven state of the tooth surface of the gear that changes according to the manufacturing process, (A) is untreated, (B) is the blasting treatment of the present invention using an elastic abrasive for (A) (first blasting) (Example), (C) is (B) after polishing (second blasting) (Example), (B') is (A) with a normal abrasive at high speed (C') is a result of polishing (B') (comparative example). It is explanatory drawing of each processing method by the method of this invention, (A) is explanatory drawing of a blasting process (1st blasting process), (B) is polishing process (2nd blasting process). Roughness curves in the tooth profile direction of the tooth surface of the gear, (A) being untreated and (B) being treated by the method (example) of the present invention. It is explanatory drawing of the manufacturing process of the conventional gear, (A) is a manufacturing process of a general gear, (B) is a manufacturing process of a high-precision gear. It is an explanatory view of the formation state of the plateau structure surface in the conventional (Patent Document 1), (A) is the state after gear cutting, (B) is the state after gear cutting and dimple formation is performed, and (C) is polished. A state in which the tip between the dimples has been removed by 3A to 3C are process diagrams of a method for forming three plateau structure surfaces disclosed in Patent Document 1. FIG.

Next, embodiments of the present invention will be described below with reference to the accompanying drawings.

〔Processing object〕
As shown in Fig. 1, the high-precision gear machining method of the present invention includes "heat treatment" such as carburizing and induction hardening, followed by "hard turning" and tooth surface polishing ("grinding" in the figure). ) and/or gear honing ("Honing" in the figure), etc., are subjected to high-precision finishing, and the accuracy is equal to or higher than the N5 grade accuracy specified in JIS B 1702-1: 1998, and the tooth surface Gears finished with high accuracy and having an arithmetic mean surface roughness Ra of 0.2 μm or less are targeted for processing.

As long as such gears are to be treated, the treatment method of the present invention may be applied to gears in the final stage of the manufacturing process, or may be applied to gears once installed as parts of automobiles and the like and used. The processing method of the present invention may be implemented afterward for the gears that have been removed.

High-precision gears to be processed in the present invention include carburized hardened steel, carbon steel for machine structural use, chromium molybdenum steel, and various materials known as materials for gears.

A high-precision gear having a precision grade equal to or higher than the above-mentioned accuracy class and having a surface roughness equal to or lower than the above-mentioned surface roughness can be manufactured by, for example, the process shown as "machining of high-precision gear" in FIG.

The "material" in the process shown in Fig. 1 is the above-mentioned steel material cut to a size suitable for manufacturing individual gears. , After that, "gear cutting" is performed using a bobbing machine or the like.

If roughness remains on the tooth surface after gear cutting, perform processing such as shaving as necessary to improve the roughness of the tooth surface. "I do.

After heat treatment, processing such as "hard turning", tooth surface polishing ("grinding" in the figure) and / or gear honing ("honing" in the figure) are performed to achieve the above-mentioned accuracy grade or higher, and It is possible to obtain a gear whose surface is finished with high accuracy such that the arithmetic mean roughness Ra is 0.2 μm or less.

FIG. 2(A) shows the surface cross-sectional shape of the tooth flank of the gear finished with high precision in this way.

As shown in FIG. 2(A), the tooth flanks of a gear that has been finished with high precision have concave and convex portions with relatively wide openings and concave and convex shapes.

In addition, the machining process of the high-precision gear to be processed in the present invention is not limited to the example shown in FIG. It may be omitted, and conversely, when performing shaving before heat treatment, tooth surface polishing (grinding) after heat treatment may be omitted. Some of the processes may be omitted or replaced with other processes as long as they can be finished with a high precision equal to or less than the surface roughness.

In the present invention, for gears that have been finished with high precision in this way, as will be described later, a "blasting process (first blasting process)" in which an elastic abrasive is jetted to form unevenness on the tooth surface; The processing method of the present invention is performed, which consists of a "polishing process" for polishing and removing the peaks of the projections of the unevenness formed by the blasting process to flatten the surface.

[Blasting (first blasting)]
As described above, after the heat treatment, blasting (first blasting) is performed on the gear tooth flanks that have undergone high-precision finish machining to form recesses that will serve as oil reservoirs on the gear tooth flanks. .

In this blasting process (first blasting process), as shown in Fig. 3(A), hard abrasive grains are attached to the surface of the core elastic material, or an elastic abrasive material kneaded is applied to the gear to be processed. The injection direction is almost perpendicular to the tooth surface.

Elastic materials used for elastic abrasives include low modulus elastic materials such as rubber and thermoplastic elastomers, resin foams, and other viscoelastic materials (e.g. crushed plant rhizomes, konjac and gelatin). ) etc. can be used.

Further, when the hard abrasive grains are attached to the surface of the elastic body, it is preferable that the variation in grain size is large. By doing so, the protrusion length of the hard abrasive grains from the surface of the elastic body varies, and the opening width is narrow and deep on the tooth surface of the collision part with the hard abrasive grains with a long protrusion length. Recesses (gouges) can be formed at a low density. On the other hand, when hard abrasive grains are kneaded into an elastic body, there is no need for large variations in grain size. The reason is that the kneaded abrasive grains are embedded in the elastic body, but the depth is random, so even if the variation in grain size is small, the amount of protrusion (the length of protrusion from the surface of the elastic body) varies greatly. Therefore, it is possible to form a gouge with a low density as well. The appropriate degree of dispersion of the hard abrasive grains varies depending on the combination of the diameter of the elastic body and the grain size of the hard abrasive grains, whether they are attached to the surface of the elastic body or kneaded into the elastic body.

As the material of such abrasive grains, a hard material such as ceramics such as alumina or SiC or diamond is selected so that the above-mentioned recesses can be formed on the hardened tooth flank after heat treatment.

Here, it is possible to form recesses on the tooth flank by general sandblasting, in which hard abrasive grains of the size mentioned above are directly blasted onto the gear tooth flank. Since the collision energy at the time corresponds to the mass of one abrasive grain, the depth of the recess formed is shallow with respect to the width of the opening and does not sufficiently function as an oil reservoir.

On the other hand, if a sandblasting machine with a high jetting capacity is used, it becomes possible to jet abrasive grains at high speed, and by increasing the impact energy, it is possible to form deep recesses (gouges) [see Fig. 2 (B')]. However, if the high-speed jetted abrasive grains are evenly applied to the tooth surface, the gouge will be formed with a higher density than necessary, which will increase the size and shape changes that occur on the tooth surface after the plateau structure is formed [Fig. 2 (C')].

On the other hand, when forming recesses (gouges) by spraying the elastic abrasive described above, the recesses having relatively narrow opening widths corresponding to the grain size of the abrasive grains are formed on the tooth flank where the abrasive grains collide. On the other hand, the mass of the entire elastic abrasive including the elastic carrier is added to the tooth flank where it collides with the abrasive grains. A recess can be formed.

In addition, as described above, the elastic abrasive used in the blasting treatment (first blasting treatment) in the present invention has variations in the length of the abrasive grains protruding from the surface of the elastic body as described above. When abrasive grains protruding longer than the surface of the body collide, a gouge with a narrower opening width and deeper than the original recess is formed, but a shallow recess is formed where the abrasive grains protruding shorter than the surface of the elastic body collide. See FIG. 2(B)], and as a result, the formation density of gouges after the polishing process can be kept low [see FIG. 2(C)].

Thus, in the blasting treatment (first blasting treatment) adopted in the present invention, when the abrasive grains collide with the tooth surface, the elastic body puts the mass of the elastic carrier on the abrasive grains and pushes the abrasive grains into the tooth surface. From this point of view, as the elastic body mentioned above, one with a median diameter of 0.1 to 2.0 mm is used, and an elastic abrasive composed of such abrasive grains and an elastic body is used. , injection pressure 0.2~0.5MPa.

As for these conditions, it is preferable to select the optimum conditions from those within the above-described numerical ranges in consideration of the machining efficiency based on the tooth size, material, etc. of the gear to be processed.

In this way, by injecting the elastic abrasive in the blasting process (first blasting process), the tooth surface of the gear, which was in the state shown in Fig. 2(A) in the untreated state, was changed to the state shown in Fig. 2(B). As shown in , compared to the uneven recesses formed on the tooth flank before the blasting (first blasting), recesses (gouges) with narrower opening widths and deeper depths are formed. be.

[Polishing treatment (second blasting treatment)]
On the tooth flank of the gear on which the unevenness is formed by the above-described blasting process (first blasting process), as described with reference to FIG. A gouge is formed, but a convex portion having a sharp shape is formed between adjacent concave portions (gouges).

Therefore, in the processing method of the present invention, after the blasting treatment (first blasting treatment), the polishing treatment (second blasting treatment) is performed to polish and remove the apex of the projections to form a flat shape. , a flat plateau surface is formed at the upper end of the convex portion.

Such a polishing method is not particularly limited, and various known methods can be used. A second blasting process is performed by injecting at an acute angle (θ) to the

The elastic abrasive used in the second blasting process is also made by attaching abrasive grains to the surface of the elastic body or kneading abrasive grains into the elastic body. It is possible to use the same elastic abrasive as used in .

In the first blasting process, the elastic body functions as a weight for pressing the abrasive grains into the tooth surface. There is no function, and there is no particular limitation on the dimensions of the elastic body, and it is possible to select from a range of various dimensions.

In the present embodiment, the median diameter of the elastic abrasive used in the second blasting is set to An elastic body with a thickness of 0.1 to 2.0 mm was used.

The material and shape of the abrasive grains used for the elastic abrasive are not particularly limited, and various known abrasives can be used as long as they can grind the tooth surface of the gear and flatten the tip of the convex part. .

In addition, the particle size of the abrasive grains is not particularly limited as long as it can be flattened by removing the tip of the protrusion while leaving the recesses of the unevenness formed in the first blasting process. Abrasive grains having a grain size smaller than that of the elastic abrasive used in the blasting process of No. 1 are used, and in this embodiment, as an example, grains having a median diameter of 20 μm or less are used.

In FIG. 3, the elastic abrasive for polishing (second blasting) shown in FIG. 3(B) is replaced with the elastic abrasive for blasting (first blasting) shown in FIG. Similar to , the figure shows an elastic abrasive material with variations in the length of the abrasive grains protruding from the surface of the elastic body, but the abrasive grains used for the elastic abrasive material for the polishing process (second blasting process) are not necessarily the same as the abrasive grains. It is not necessary to use those with different protrusion lengths, and it is also possible to use those with uniform protrusion lengths.

The elastic abrasive described above is jetted at an acute angle to the tooth flank of the gear.

The injection angle θ with respect to the tooth surface (see FIG. 3B) is preferably 20° to 60°, more preferably 25° to 35°.

In this way, by spraying the elastic abrasive against the tooth surface at an acute angle as indicated by the arrow in Fig. 3(B), the injected elastic abrasive collides with the tooth surface, and then the surface of the tooth surface. By sliding horizontally along the , the tips of the uneven protrusions formed during the first blasting process are polished and removed to be flattened.

As shown in FIG. 2(C), after the second blasting process is performed in this way, the tooth flank has a relatively narrow opening width and a deep concave portion (gouge) formed as an oil reservoir. It is possible to form a lubricating surface with a plateau structure in which convex portions having flattened top surfaces (plateau surfaces) are formed between adjacent concave portions (gouges).

In this way, by applying the machining method of the present invention to the gear finished with high precision, the lubrication of the plateau structure can be achieved without significantly reducing the arithmetic mean roughness Ra of the original tooth flank and the machining accuracy. It is possible to form a plane.

As a result, we were able to obtain a gear that simultaneously achieves quietness due to high-precision finishing and improved lubricity due to the formation of a lubricating surface with a plateau structure.

The test results of machining high-precision gears by the machining method of the present invention are shown below.

[Purpose of the test]
The surface structure of the lubricating surface of the plateau structure formed on the tooth surface of the high-precision gear machined by the method of the present invention is confirmed, and it is confirmed that the deterioration of surface roughness and machining accuracy can be suppressed.

〔Test method〕
A lubricating surface with a plateau structure was formed by the processing method of the present invention on a gear finished to the N5 grade processing accuracy specified in JIS B 1702-1:1998.

As a comparative example, a lubricating surface with a plateau structure was formed by performing a polishing process after forming dimples by shot peening on the same treated object.

The processing conditions for Examples and Comparative Examples are shown in Table 1 below.

In both the first blasting treatment and the second blasting treatment, an elastic abrasive having a structure in which abrasive grains were kneaded into an elastic body was used.

As the blasting device, a commercially available air-type blasting device (manufactured by Fuji Seisakusho) was used.

〔Test results〕
Table 2 below shows the surface conditions of the untreated gears and the gears of Examples and Comparative Examples after treatment under the above conditions.

FIG. 4(A) shows the roughness curve in the tooth profile direction of the tooth surface of the untreated gear, and FIG. 4(B) shows the roughness curve in the tooth profile direction of the gear of the example.

[Discussion]
(1) Comparison of surface roughness Comparing the surface roughness parameters before and after processing, the arithmetic mean roughness Ra of the example shows a slight increase (approximately 26% increase) compared to the untreated value. There was no significant change, and it was confirmed that according to the method of the present invention, an increase in surface roughness could be suppressed even by forming a lubricating surface with a plateau structure.

On the other hand, on the tooth flank of the gear treated by the method of the comparative example, the arithmetic mean roughness Ra was greatly increased (640% increase) compared to the untreated state, and the lubricating surface of the plateau structure It has been confirmed that the surface roughness increases in exchange for the formation, and the processing method of the present invention that uses an elastic abrasive in the first blasting process improves the lubricating surface of the plateau structure while maintaining processing accuracy. It was confirmed that it is effective in forming.

(2) Comparison of Concavo-convex Shape In the tooth flanks of the gears treated by the method of the example, the value of skewness Rsk greatly increased (approximately 15 times) on the negative side compared to the untreated gears. The protruding valley depth Rvk is increased about 2.5 times with respect to the treated surface.

From these numerical values, it can be seen that in the gears treated by the method of the example, recesses with narrower opening widths and deeper recesses were formed than the uneven recesses that occurred on the tooth flanks of untreated gears. This is also confirmed by comparing the roughness curve of the untreated tooth flank shown in FIG. 4(A) and the roughness curve of the tooth flank after treatment under the conditions shown in FIG. can be confirmed.

Furthermore, in the gears of the examples, the load length ratio Mr1 is about 60% of that of the untreated gear, and the ratio of the protruded peaks is reduced (the upper end of the protruded part is flat). ), which means that a lubricating surface with a plateau structure is formed.

On the other hand, it can be inferred from the value of the load length ratio Mr1 that the gear processed by the method of the comparative example also has a lubricating surface with a plateau structure in which the top of the convex portion is flattened. However, from the value of skewness Rsk, the recess formed by the method of the comparative example has a larger opening width than that of the present invention. It is thought that the numerical value that is the standard of the accuracy grade described later is greatly increased (the processing accuracy is lowered).

In addition, the concave portion formed by the method of the comparative example is shallower than the concave portion (gouge) formed by the method of the example from the value of the protruding valley depth Rvk, and functions as an oil reservoir. , the lubricity of the tooth surface is also inferior to that of the present invention.

(3) Comparison of processing accuracy
Among the individual errors of the gear carrier specified in JIS B 1702-1:1998, single pitch error fpt, cumulative pitch error Fp, total tooth profile error Fα, and total tooth trace error Fβ. In the case of gears, although a slight increase can be seen in all numerical values compared to the untreated gear, the rate of increase can be suppressed to 30% or less compared to the untreated state.

Therefore, for example, by finishing the gear with an error (high accuracy) that is about 30% smaller than the upper limit of the individual error specified for N5 class, the lubricating surface of the plateau structure can be obtained by the method of the present invention. Even after forming, it is possible to maintain the processing accuracy of the gear to be processed within the N5 class range.

In fact, under the test conditions of this embodiment, the gear errors (single pitch error fpt, cumulative pitch error Fp, total tooth profile error Fα, total tooth trace error Fβ) after processing by the method of the present invention are all N5 class. was within the upper limits specified as

From these results, it is clear that the method of the present invention can meet the contradictory requirements of forming a lubricating surface with a plateau structure on the tooth flank while maintaining the machining accuracy of a highly-finished gear. It could be confirmed.

On the other hand, in the gear machined by the method described in the comparative example, any of the single pitch error fpt, the cumulative pitch error Fp, the total tooth profile error Fα, and the total tooth trace error Fβ compared to the unprocessed state. Both numerical values show a significant increase, and in the test results under the conditions described above, in the gear of the comparative example, except for the total tooth profile error Fα, other errors exceed the upper limit values stipulated in class N5. Therefore, in the method of the comparative example, it was not possible to achieve both the maintenance of the machining precision of the gear finished with high precision and the formation of the lubricating surface of the plateau structure.

Claims (5)

After gear cutting and heat treatment, finish processing is performed to achieve an accuracy of at least N5 grade accuracy specified in JIS B 1702-1: 1998, and the arithmetic mean roughness Ra of the surface is 0.2 μm. Gears that have been finished with high precision as follows are targeted for processing,
Hard abrasive grains having an irregular shape with corners are attached to the surface of an elastic body, or an elastic abrasive material kneaded into an elastic body is sprayed almost perpendicularly to the tooth surface of the gear, and the tooth surface is Blasting to form fine unevenness on the
polishing the tooth surface after the blasting treatment to remove the tops of the uneven protrusions for flattening;
A gouge, which is a concave portion having a narrower opening width and a deeper depth than the uneven concave portion formed before the blasting treatment on the tooth surface, and a flattened upper end formed between the gouge. forming a plateau-structured surface with ridges;
Increase in arithmetic mean roughness Ra, single pitch error, cumulative pitch error, total tooth profile error, and total tooth trace error of the tooth flank of the gear after the polishing treatment with respect to the tooth flank of the gear before the blasting treatment A method for machining a high-precision gear characterized by suppressing each of the above to 30% or less. The elastic body of the elastic abrasive used in the blasting process has a median diameter of 0.1 to 2.0 mm, and the abrasive grains have a median diameter of 10 to 500 μm. 2. A machining method for a high-precision gear according to claim 1, wherein the injection is performed at an injection pressure of 0.2 to 0.5 MPa. The polishing treatment is performed by a second blasting treatment in which abrasive grains are adhered to the surface of an elastic body or an elastic abrasive material kneaded into an elastic body is jetted at an acute angle to the tooth surface. Item 3. A method for machining a high-precision gear according to item 1 or 2. The elastic body of the elastic abrasive used in the second blasting has a median diameter of 0.1 to 2.0 mm, and the abrasive grains have a median diameter of 20 μm or less. 4. The method of machining a high-precision gear according to claim 3, wherein the elastic abrasive is injected at an injection pressure of 0.1 to 0.3 MPa. 5. A machining method for a high-precision gear according to claim 3, wherein said second blasting is performed at an inclination angle of 20 to 60 degrees with respect to the tooth flank.

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