Processing method of high-precision gears

Abstract

The present invention provides a method for machining high-precision gears, capable of maintaining a high-precision machining state and forming a platform structure on the gear tooth surface. A gear that has been subjected to high-precision finishing after tooth cutting and heat treatment, and has been high-precision finished to an accuracy of N5 or higher in accordance with JIS B 1702-1:1998 and an arithmetic mean roughness Ra of 0.2 μm or less, is subjected to a blasting treatment in which an elastic abrasive material carrying irregularly shaped hard abrasive grains is sprayed approximately perpendicularly to the gear tooth surface to form minute concavities and convexities on the tooth surface. The tooth surface is then polished to remove the tops of the convex and concave portions, thereby flattening the surface. This forms a surface with a platform structure on the tooth surface, the surface having concave portions, i.e., grooves, having a narrower opening width and a deeper depth than the concave and convex portions formed before the blasting treatment, and convex portions, formed between the grooves and having their upper ends flattened, while suppressing the reduction in surface roughness and machining accuracy of the tooth surface within a specified range.

Description

Technical Field

[0001] The present invention relates to a method for machining high-precision gears, and more particularly, to a method for machining high-precision gears that can obtain a gear that is finished with high machining accuracy and has a surface having a platform structure composed of a concave portion serving as an oil reservoir and a convex portion with a flattened top. Background Art

[0002] In recent years, in many cutting-edge industries such as electric vehicles and robotics, gears have been required to be quieter and have higher processing precision than ever before.

[0003] In response to such high-precision requirements, the gear processing method was re-examined.

[0004] As an example, in the past gear processing, Figure 5 As shown in (A), for gears that are processed by hobbing machines after turning the raw material, the tooth surface shape is corrected by shaving processing before heat treatment as needed, and then heat treatment is performed. After that, hard turning processing is generally only performed as finishing, and no further processing is performed on the tooth surface after heat treatment.

[0005] On the other hand, in recent years, gear processing in response to the demand for high precision has become more and more popular. Figure 5 As shown in (B), after the heat treatment, hard turning is performed, and then the tooth surface is subjected to tooth surface grinding ("gear lapping" in the figure) and gear honing ("honing" in the figure) and other processes, and a process is implemented to process the roughness and dimensional accuracy of the tooth surface with higher precision (refer to non-patent document 1).

[0006] On the other hand, the transmission power of gears is affected by the lubricity of the combined tooth surfaces. In order to improve such lubricity, it has long been known that processing the tooth surfaces into a platform structure is effective.

[0007] Here, the surface of the terrace structure is, for example, Figure 6 As shown in (C), it is a surface with a concave-convex shape consisting of a convex portion whose top is flattened to reduce the contact resistance with the opposing tooth surface, and a concave portion that functions as an oil reservoir. Since such a platform structure surface is of great importance in the industry as a sliding surface structure, its evaluation method is specified in JIS B0671:2002.

[0008] As a method of forming such a surface of a terrace structure as a tooth surface of a gear, Patent Document 1 described later discloses a method of forming the surface by blasting.

[0009] Specifically, Patent Document 1 discloses a method for forming such a terrace structure surface. Figure 7 The following three methods are shown in (A) to (C).

[0010] The first method is to subject a gear that has undergone "tooth cutting" to "shot peening" by projecting a shot made of a steel ball or the like as a projectile to form pits, then perform "carburizing" as a heat treatment. Thereafter, "abrasive flow machining" is performed by grinding the gear in a flow of a mixture of abrasive grains and a viscous fluid to remove the sharp edges between the pits during shot peening and form a flat surface ( Figure 7 (A)).

[0011] The second method is to perform "mirror shot peening" on the gear that has been "tooth cut" to form pits by projecting abrasive grains around the core with elasticity and adhesiveness. Then, "carburization" is performed. After that, "mirror shot peening" is performed again to remove the tips between the pits by grinding, thereby forming a land surface ( Figure 7 (B)).

[0012] The third method is to perform the above-mentioned "shot peening" on the gear that has been subjected to "tooth cutting" to form pits, then perform "carburizing treatment", and then perform the above-mentioned "mirror shot peening" to remove the tips between the pits during the shot peening by grinding, thereby forming a flat surface ( Figure 7 (C)).

[0013] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-345022

[0014] Non-Patent Literature 1: Masakazu Nabekura, Michiaki Hashitani, Yukihisa Nishimura, Masakatsu Fujita, Yoshiko Yanase, and Masanobu Misaki, "Gear Processing Machines and Precision Cutting Tools Supporting the Production of Automotive Transmission Gears," Mitsubishi Heavy Industries Technical Bulletin, Vol. 43, No. 3, 2006

[0015] As mentioned above, due to the requirement of quietness, gears are required to be processed with high precision. On the other hand, for the lubrication of the gears, it is effective to set the tooth surface as a platform structure surface. If a high-precision processing state can be maintained and a platform structure surface can be formed on the tooth surface of the gear, a gear that takes both quietness and lubricity into consideration can be obtained.

[0016] However, the processing of the gear tooth surface to form the surface of the platform structure mentioned above is a processing that forms a recessed portion that serves as an oil storage portion and processes the surface into a concave and convex shape. By performing such processing, the surface roughness of the gear tooth surface increases, and the processing accuracy is reduced due to changes in size and shape.

[0017] In particular, in the method described in Patent Document 1, the tooth surface ( Figure 6 (A)) by causing a projectile composed of a steel ball or the like to collide with the projectile to expand the valley portion, thereby forming a pit with a wide opening width ( Figure 6 (B)), then the tip is removed by surface grinding, thereby making the tooth surface Figure 6 The surface of the terrace structure shown in (C) (Patent Document 1,

[0019] ).

[0018] As a result, when a terrace structure surface is formed by the method described in Patent Document 1, Figure 6 As shown in (C), a pit with a relatively wide opening width is formed. As a result, the surface roughness of the tooth surface finally obtained becomes large and the dimensional accuracy is also reduced, which cannot meet the recent demand for high precision.

[0019] In addition, in the method described in Patent Document 1, Figure 6 As shown in (A) and (B), the collision of a projectile composed of a steel ball or the like causes a portion of the convex portion to be flattened, thereby greatly expanding the valley portion (concave portion) of the concave and convex portion to form a pit. Therefore, the formation of the pit causes the shape of the gear tooth surface to change significantly.

[0020] From these viewpoints, it is considered that in the method described in Patent Document 1, it is necessary to form the pits before the heat treatment (surface hardening treatment step) (claim 5 of Patent Document 1, etc.).

[0021] That is, in order to form the dimples accompanied by large plastic deformation as in Patent Document 1, it is necessary to perform the process in a state where the base material of the gear before heat treatment has a low hardness (and therefore is easily plastically deformed), and in order to obtain the machining accuracy of the gear, it is necessary to perform hard turning after heat treatment (see Figure 5 (A), (B)) etc. are used to adjust the changes in the shape and size of the tooth surface that is greatly deformed by the formation of the pit.

[0022] Thus, in the method described in Patent Document 1, the pits must be formed before the heat treatment, and therefore, it needs to be assembled into the gear manufacturing process for implementation. If a gear that has already been heat treated and finished, for example, a gear that has been completed as a gear and temporarily assembled as a component in an automobile, etc., is used as the treatment object, it is impossible to subsequently form a platform structure surface on the tooth surface of the gear.

[0023] Thus, in the processing method described in Patent Document 1, since pits with relatively wide opening widths are formed, even if a terrace structure surface can be formed on the gear tooth surface, the surface roughness of the resulting gear tooth surface is large and the processing accuracy is low.

[0024] Furthermore, in the processing method described in Patent Document 1, pits must be formed before heat treatment, and the tooth surface is significantly deformed due to the formation of the pits. Therefore, for gears that have undergone heat treatment and high-precision finishing, such as gears that are temporarily assembled as components in automobiles, etc., it is impossible to subsequently form a lubricating surface with a platform structure.

[0025] Here, when forming the recessed portion serving as the oil reservoir by blasting, a semicircular arc-shaped recessed portion, ie, a "dimple" having a relatively narrow opening width is generally formed as described in Patent Document 1 mentioned above.

[0026] However, the inventors of the present invention have re-examined this point and have speculated that even when recesses with opening widths narrower than these "pits" are formed, if the depth of the recesses can be ensured, they should still be able to function as oil reservoirs, and that it is not necessary to form recesses with wide opening widths as in Patent Document 1. Furthermore, it is speculated that it is not necessary to provide recesses with a sufficient depth at an excessively high density.

[0027] Furthermore, if lubricity can be imparted to the tooth surface by forming such recesses having a narrow opening width and a deep depth at a low density, a surface having a platform structure can be formed with a smaller deformation relative to the tooth surface of the gear. Compared with the case where recesses having a wide opening width are formed as in the above-mentioned Patent Document 1, the increase in surface roughness and the decrease in dimensional accuracy should be suppressed, and the surface of the platform structure can be formed.

[0028] On the other hand, for gears whose hardness has been increased by heat treatment, in order to form a recess with a narrow opening width, abrasive particles with a small particle size proportional to the opening width are simply sprayed and caused to collide. Since the mass of a single abrasive particle is small and the collision energy is small, even if a recess with a narrow opening width can be formed in the collision part, a deeper recess cannot be formed, and it may not be possible to obtain the function as an oil storage part. It is necessary to find a way to solve this problem.

[0029] As one method to solve the above problem, there is a method of spraying abrasive particles at high speed to increase their collision energy. However, not all shot peening devices have such a capability.

[0030] Furthermore, even if abrasive particles of a small size that is proportional to the opening width can be ejected at high speed, when the abrasive particles hit the tooth surface without omission, deep recesses are formed in a high density in a neighboring manner over one surface, and high tips corresponding to the depth are formed between the recesses (see Figure 2 (B')).

[0031] As a result, in the subsequent process, the tooth surface of the terrace structure that can grind away the high-density tip portion has a large volume to be ground and removed, so the size and shape are greatly changed (see Figure 2 (C')).

[0032] However, the deep recesses that serve as oil reservoirs do not need to be arranged adjacent to each other at a high density. It is sufficient to arrange them at a low density with appropriate spacing. This minimizes changes in the size and shape of the platform structure after it is formed. In other words, a method for forming the deep recesses at a low density is needed. Summary of the Invention

[0033] The present invention was completed under the conception of such an inventor, and its purpose is to provide a high-precision gear processing method that can maintain the high-precision processing state of the gear that is finished to high precision, and can form a platform structure lubrication surface on the tooth surface, and a concave portion with a relatively narrow opening width and a relatively deep depth is formed at a low density on the lubrication surface.

[0034] Hereinafter, the means for solving the problem will be described together with the reference numerals used in the embodiments. These reference numerals are used to clarify the correspondence between the claims and the embodiments, and are not intended to limit the technical scope of the present invention.

[0035] The method for machining a high-precision gear of the present invention for achieving the above-mentioned object is as follows:

[0036] Gears that have been finished after gear cutting and heat treatment to a precision grade of N5 or higher as specified in JIS B1702-1:1998 and a surface arithmetic mean roughness Ra of 0.2 μm or less are the subject of treatment. Blasting (first blasting) and grinding are performed.

[0037] In the blasting process, an elastic abrasive material obtained by attaching angular irregular hard abrasive grains to the surface of an elastic body or mixing them into the elastic body is blasted substantially perpendicularly to the tooth surface of the gear, thereby forming minute irregularities on the tooth surface.

[0038] In the grinding process, the tooth surface after the blasting process (first blasting process) is ground to remove the tops of the convex and concave portions to flatten the surface.

[0039] A terrace structure is formed on the tooth surface, wherein the terrace structure has concave portions having narrower opening widths and deeper depths than the concave and convex portions formed before the blasting treatment, and convex portions formed between the concave portions and having flattened upper ends.

[0040] Compared with the tooth surface of the gear before the blasting treatment, the increases in the arithmetic mean roughness Ra, single pitch deviation, cumulative pitch deviation, total tooth profile error and total tooth direction error of the tooth surface of the gear after the grinding treatment are all suppressed to less than 30%.

[0041] Here,

[0042] The arithmetic mean roughness Ra is a value obtained by extracting a reference length (l) from a roughness curve in the direction of its mean line, summing up and averaging the absolute values ​​of the deviations from the mean line of the extracted portion to the measurement curve, and is specified in JISB 0601:2001.

[0043] In addition, the individual pitch deviation fpt, ​​the cumulative pitch deviation Fp, the total tooth profile error Fα, and the total tooth direction error Fβ in JIS B 1702-1:1998 are respectively as follows.

[0044] Single pitch deviation fpt: the difference between the actual pitch and the theoretical pitch on the pitch circle of adjacent tooth surfaces on the same side.

[0045] Cumulative pitch deviation Fp: The maximum cumulative pitch deviation in the entire tooth surface area of ​​the gear, represented by the full amplitude of the cumulative pitch deviation curve.

[0046] Total tooth profile error Fα: The distance between the designed tooth profile lines and the actual tooth profile within the determined tooth profile inspection range.

[0047] Total tooth trace error Fβ: The distance between the two designed tooth traces sandwiching the actual tooth trace within the determined tooth trace inspection range.

[0048] The blast treatment (first blast treatment) can be performed using an elastic abrasive having a median particle size of 0.1 to 2.0 mm for the elastic body and a median particle size of 10 to 500 μm for the abrasive grains at a blast pressure of 0.2 to 0.5 MPa.

[0049] Furthermore, the polishing process may be performed by a second blasting process in which an elastic abrasive material obtained by adhering abrasive grains to the surface of an elastic body or mixing them into the elastic body is blasted at an acute angle with respect to the tooth surface.

[0050] In this case, the second blast treatment can be performed at a blast pressure of 0.1 to 0.3 MPa using an elastic abrasive having a median particle size of 0.1 to 2.0 mm for the elastic body and a median particle size of 20 μm or less for the abrasive grains.

[0051] The second blasting treatment can be performed at an inclination angle θ of preferably 20 to 60°, more preferably 25 to 35°, relative to the tooth surface.

[0052] According to the structure of the present invention described above, the gear processed by the high-precision gear processing method of the present invention can simultaneously have a surface with a platform structure formed on the tooth surface and process such an opposite structure in a state of small surface roughness and high precision.

[0053] As a result, the gear processed by the method of the present invention is processed with high processing accuracy, has low working noise, achieves quietness, and forms a lubricating surface with a platform structure, thereby improving the lubricity of the tooth surface and improving the transmission power.

[0054] That is, in the method of the present invention, the function of the oil storage portion is ensured by forming the recessed portion formed as an oil storage portion into a recessed portion with a relatively narrow opening width and a deep depth, that is, the above-mentioned "groove", and the deformation generated on the tooth surface is reduced by forming the groove at a low density, thereby maintaining the gear in a high-precision processed state.

[0055] On the other hand, the tooth surfaces of gears hardened by heat treatment are in a state that is less susceptible to deformation. Therefore, it is not possible to form deep recesses on the tooth surfaces by simply blasting tiny abrasive grains with a small mass per grain.

[0056] However, in the method of the present invention, by spraying an elastic grinding material formed by adhering abrasive grains to the surface of an elastomer or mixing into the surface of an elastomer, when the abrasive grains collide with the tooth surface, not only the collision energy of the mass of the abrasive grains but also the collision energy of the mass of the elastomer is generated, thereby forming a recess with a narrow opening width and a deep depth on the tooth surface at the collision portion of the abrasive grains.

[0057] Furthermore, the lengths of the abrasive grains protruding from the surface of the elastic abrasive vary in size. As a result, when the longer protruding abrasive grains collide with the tooth surface, grooves are formed, while where the shorter protruding abrasive grains collide, shallower recesses are formed.

[0058] Therefore, by making the grooves formed by the collision of the elastic abrasive material low-density, the number of tips formed corresponding to the grooves is reduced, and the volume to be ground and removed in the formation of the platform structure is also reduced (see Figure 2 (B), (C)).

[0059] As a result, for gears that have undergone high-precision processing through heat treatment, a platform structure surface can be formed afterwards, and after the platform structure surface is formed, the increase in surface roughness and processing error of the original surface processed with high precision can be suppressed to a range below 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is an explanatory diagram of a gear manufacturing process including a high-precision gear processing method according to the present invention.

[0061] Figure 2 Schematic diagrams showing the uneven state of the tooth surface of a gear that changes according to the manufacturing process, (A) is a schematic diagram of an untreated gear, (B) is a schematic diagram of (A) subjected to the blasting treatment of the present invention (first blasting treatment) using an elastic abrasive (Example), (C) is a schematic diagram of (B) subjected to the grinding treatment (second blasting treatment) (Example), (B') is a schematic diagram of (A) subjected to the blasting treatment using a conventional abrasive at high speed (Comparative Example), and (C') is a schematic diagram of (B') subjected to the grinding treatment (Comparative Example).

[0062] Figure 3 These are explanatory diagrams of the respective treatment methods according to the method of the present invention, wherein (A) is an explanatory diagram of the blasting treatment (first blasting treatment), and (B) is an explanatory diagram of the polishing treatment (second blasting treatment).

[0063] Figure 4 : are roughness curves of the tooth surface of the gear in the tooth profile direction, (A) is the roughness curve of the tooth surface of the untreated gear in the tooth profile direction, and (B) is the roughness curve of the tooth surface of the gear after being treated by the method (embodiment) of the present invention.

[0064] Figure 5 These are explanatory diagrams of conventional gear processing steps. (A) is an explanatory diagram of a normal gear processing step, and (B) is an explanatory diagram of a high-precision gear processing step.

[0065] Figure 6 These are illustrations of the formation state of the platform structure surface in the past (Patent Document 1), (A) is an illustration of the state after tooth cutting, (B) is an illustration of the state after pits are formed after tooth cutting, and (C) is an illustration of the state after the tip portions between the pits are removed by grinding.

[0066] Figure 7 (A) to (C) are process diagrams of a method for forming a three-terrace structure surface disclosed in Patent Document 1. DETAILED DESCRIPTION

[0067] Next, embodiments of the present invention will be described below with reference to the drawings.

[0068] (Processing Object)

[0069] like Figure 1As shown, the high-precision gear processing method of the present invention is for processing the following gear, which is subjected to "heat treatment" such as carburizing and quenching and high-frequency quenching, and then subjected to high-precision finishing treatment such as "hard turning", tooth surface grinding ("gear lapping" in the figure) and / or gear honing ("honing" in the figure), and is finished to a high precision of higher than the N5 grade specified in JIS B 1702-1:1998 and an arithmetic mean roughness Ra of the tooth surface of not more than 0.2μm.

[0070] If such a gear is selected as the treatment object, the treatment method of the present invention can be performed on the gear at the final stage of the manufacturing process, or the treatment method of the present invention can be performed afterwards on the gear temporarily installed and used as a part of an automobile, etc.

[0071] As the high-precision gears to be processed in the present invention, gears made of various known materials in addition to carburized and hardened steel, carbon steel for mechanical structures, and chrome-molybdenum steel can be processed.

[0072] As an example, high-precision gears with a precision level above the above and a surface roughness below the above can be Figure 1 It is manufactured according to the process shown as "Processing of High-Precision Gears" in the previous section.

[0073] Figure 1 The "raw material" in the steps shown refers to cutting the above-mentioned steel material into a size suitable for the manufacture of each gear, "turning" the raw material into the approximate outer shape of the gear to be formed, and then "gear cutting" using a gear hobbing machine or the like.

[0074] If roughness remains on the tooth surface after "tooth cutting", "tooth shaving" or other processing is performed as needed to improve the tooth surface roughness, and then "heat treatment" such as carburizing and quenching, high-frequency quenching, etc. is performed.

[0075] After heat treatment, by performing processing such as "hard turning", tooth surface grinding ("gear grinding" in the figure) and / or gear honing ("honing" in the figure), high-precision gears can be obtained with a finishing accuracy above the above-mentioned accuracy level and an arithmetic mean roughness Ra of the surface of less than 0.2μm.

[0076] Figure 2 (A) shows the surface cross-sectional shape of the tooth surface of the gear finished to high precision in this manner.

[0077] like Figure 2 As shown in (A), the tooth surface of the gear finished to high precision has smooth concavoconvex shapes with concave portions having relatively wide opening widths.

[0078] In addition, the processing steps of the high-precision gears to be processed in the present invention are not limited to Figure 1 For example, when the tooth surface is ground (lapping) after the heat treatment, the tooth shaving before the heat treatment can be omitted. Conversely, when the tooth shaving before the heat treatment is performed, the tooth surface grinding (lapping) after the heat treatment can be omitted. As long as the high precision above the above-mentioned accuracy level and below the above-mentioned surface roughness can be achieved, part of the process can be omitted or replaced by other processes.

[0079] Thus, in the present invention, as described later, the processing method of the present invention is performed on gears that are finished to high precision. The processing method of the present invention includes "blasting treatment (first blasting treatment)" of spraying elastic abrasive material to form concavities and convexities on the tooth surface, and "grinding treatment" of grinding and removing the tips of the convex portions of the concavities and convexities formed by the blasting treatment to flatten them.

[0080] (Spraying Process (First Spraying Process))

[0081] As described above, the gear tooth surfaces that have been subjected to high-precision finish machining after heat treatment are subjected to blasting treatment (first blasting treatment) for forming recessed portions serving as oil reservoirs on the gear tooth surfaces.

[0082] In this spraying process (first spraying process), as Figure 3 As shown in (A), an elastic abrasive material is sprayed onto the tooth surface of the gear to be processed in a direction substantially perpendicular to the tooth surface of the gear to be processed, wherein the elastic abrasive material is adhered to the surface of the elastic body as the core or the elastic body is mixed with the hard abrasive.

[0083] As the elastic abrasive, there can be used elastic bodies having a low elastic modulus such as rubber and thermoplastic resin elastomers, resin foams, and other viscoelastic bodies (such as crushed plant roots, konjac, and gelatin).

[0084] Furthermore, when hard abrasive particles are attached to the surface of an elastomer, the greater the variation in their particle size, the better. This allows for variations in the length of the hard abrasive particles protruding from the elastomer's surface, allowing for the formation of narrow, deep gouging (grooves) at a low density on the tooth flanks where the hard abrasive particles with long protrusions collide. On the other hand, when hard abrasive particles are mixed into an elastomer, a large variation in particle size is not necessary. This is because the mixed abrasive particles are embedded in the elastomer at a random depth. Therefore, even with a small variation in particle size, the large variation in the protrusion length (the length of the protrusion from the elastomer's surface) allows for the formation of low-density gouging. Furthermore, whether attached to the surface of an elastomer or mixed into the elastomer, the appropriate degree of variation in hard abrasive particles varies depending on the combination of the elastomer's diameter and the particle size of the hard abrasive particles.

[0085] As the material of such abrasive grains, ceramics such as alumina and SiC, or hard materials such as diamond are selected so that the above-mentioned recessed portions can be formed on the tooth surface hardened after heat treatment.

[0086] Here, a recess can also be formed on the tooth surface by a conventional sandblasting process in which hard abrasive grains of the above-mentioned size are directly projected onto the tooth surface of the gear. However, in this case, the collision energy when the abrasive grains collide with the tooth surface corresponds to the mass of one abrasive grain. Therefore, the depth of the recess formed is shallow relative to the opening width and cannot fully function as an oil reservoir.

[0087] On the other hand, if a sandblasting device with high blasting capacity is used, high-speed blasting of abrasive particles can be achieved, thereby increasing the collision energy and forming deeper recesses (grooves) (see Figure 2 (B')), but if the high-speed abrasive particles are allowed to collide with the tooth surface without omission, grooves will be formed at an excessively high density, increasing the size and shape changes on the tooth surface after the plateau structure is formed (refer to Figure 2 (C')).

[0088] In contrast, when a recess (groove) is formed by spraying the above-mentioned elastic abrasive material, a recess having a relatively narrow opening width corresponding to the particle size of the abrasive is formed on the tooth surface of the collision portion with the abrasive. On the other hand, on the tooth surface of the collision portion with the abrasive, the mass of the abrasive plus the mass of the entire elastic abrasive including the elastic carrier concentrates the collision energy, thereby forming a relatively deep recess.

[0089] Furthermore, as described above, the elastic abrasive used in the blasting process (first blasting process) of the present invention has variations in the length of the abrasive grains protruding from the surface of the elastic body. As a result, when the abrasive grains protruding longer from the surface of the elastic body collide, a groove having a narrower opening width and a deeper depth than the original recess is formed. However, a shallower recess is formed at the portion where the abrasive grains protruding shorter from the surface of the elastic body collide (see FIG. Figure 2 As a result, the density of grooves formed after the grinding process can be suppressed to a low level (refer to Figure 2 (C)).

[0090] Thus, in the blasting process (first blasting process) adopted in the present invention, the elastomer has the function of a counterweight, which is used to apply the mass of the elastic carrier to the abrasive when the abrasive collides with the tooth surface and press the abrasive into the tooth surface. From this point of view, as the above-mentioned elastomer, an elastomer with a median particle size of 0.1 to 2.0 mm is used, and the elastic grinding material composed of such abrasive and elastomer is blasted at a blasting pressure of 0.2 to 0.5 MPa.

[0091] For these conditions, it is preferable to select optimal conditions from the above-mentioned numerical range based on the tooth size, material, etc. of the gear to be processed and in consideration of processing efficiency.

[0092] In this way, the elastic abrasive is sprayed by the spraying process (first spraying process), thereby Figure 2 On the tooth surface of the gear in the state shown in (A), as Figure 2 As shown in (B), compared with the concavo-convex concave portions formed on the tooth surface before the blasting process (first blasting process), concave portions (grooves) having a narrower opening width and a deeper depth are formed.

[0093] (Polishing Treatment (Second Blasting Treatment))

[0094] On the tooth surface of the gear formed with concavoconvex by the above-mentioned blasting process (first blasting process), as shown in FIG. Figure 2 As described in (B), recesses (grooves) having a relatively narrow opening width and a deep depth are formed, but convex portions having a sharp shape are formed between adjacent recesses (grooves).

[0095] Therefore, in the processing method of the present invention, after the blasting treatment (first blasting treatment), a grinding treatment (second blasting treatment) is performed to grind and remove the tip of the protrusion to form a flat shape, thereby forming a flat terrace surface at the upper end of the protrusion.

[0096] Such a grinding method is not particularly limited and can be implemented by various known methods, but in the present embodiment, as such a grinding method, Figure 3As shown in (B), a second blasting process is performed in which the elastic abrasive is blasted at an acute angle (θ) with respect to the tooth surface.

[0097] The elastic abrasive used in the second blasting process is also a material that makes abrasive grains adhere to the surface of the elastic body or mix abrasive grains into the elastic body. As the material of the elastic body, the same elastic abrasive used in the above-mentioned first blasting process can be used.

[0098] In the first blasting process, the elastomer has a function as a counterweight for pressing the abrasive grains into the tooth surface, but the elastomer of the elastic grinding material used in the second blasting process does not have such a counterweight function. The size of the elastomer is not particularly limited and a variety of sizes can be selected.

[0099] In this embodiment, as in the first blasting process, an elastic abrasive having a median particle size of 0.1 to 2.0 mm is also used for the second blasting process so that the first and second blasting processes can be performed using a common blasting processing device.

[0100] The material and shape of the abrasive grains used in the elastic abrasive are not particularly limited, and various known materials can be used as long as they can grind the tooth surface of the gear and flatten the tip of the convex portion.

[0101] In addition, there is no particular limitation on the particle size of the abrasive as long as the concave portions of the convex and concave portions formed in the first blasting process can be retained and the front end portions of the convex portions can be removed to make them flat. It is preferred to use abrasive particles with a particle size smaller than that of the elastic grinding material used in the first blasting process. In this embodiment, as an example, abrasive particles with a median particle size of less than 20 μm are used.

[0102] In addition, Figure 3 In Figure 3 The elastic abrasive material used for the grinding process (second blasting process) shown in (B) is Figure 3 The elastic abrasive material used in the blasting treatment (first blasting treatment) shown in (A) is the same as the elastic abrasive material used in the blasting treatment (first blasting treatment). The figure shows an elastic abrasive material in which the length of the abrasive grains protruding from the surface of the elastomer is deviated. However, the abrasive grains used in the elastic abrasive material used in the grinding treatment (second blasting treatment) do not necessarily have to be abrasive grains with a deviated protruding length. Raw materials with uniform protruding length can also be used.

[0103] The elastic abrasive material described above is sprayed at an acute angle to the tooth surface of the gear.

[0104] The injection angle θ relative to the tooth surface (refer to Figure 3 The angle (B)) is preferably 20° to 60°, more preferably 25° to 35°.

[0105] In this way, Figure 3 As shown by the arrow in (B), the elastic abrasive is sprayed at an acute angle to the tooth surface. After colliding with the tooth surface, the sprayed elastic abrasive slides horizontally along the surface of the tooth surface, thereby grinding and removing the front end of the convex and concave portion formed during the first spraying treatment to flatten it.

[0106] like Figure 2 As shown in (C), a lubricating surface with a platform structure can be formed on the tooth surface after the second injection treatment, in which a concave portion (groove) with a relatively narrow opening width and a deep depth is formed as an oil storage portion, and a convex portion with a flattened top surface (platform surface) is formed between adjacent concave portions (grooves).

[0107] Thus, by applying the machining method of the present invention to a gear that has been finished to high precision, a lubricating surface with a terrace structure can be formed without significantly reducing the arithmetic mean roughness Ra and machining accuracy of the original tooth surface.

[0108] As a result, a gear can be obtained that achieves both quietness due to high-precision finishing and improved lubricity due to the formation of the lubricating surface of the platform structure.

[0109] (Example)

[0110] The test results of machining high-precision gears using the machining method of the present invention are shown below.

[0111] (Purpose of the test)

[0112] The surface structure of the lubricating surface of the terrace structure formed on the tooth surface of the high-precision gear processed by the method of the present invention was confirmed, and it was confirmed that the reduction in surface roughness and processing accuracy could be suppressed.

[0113] (Test method)

[0114] A gear that had been finished to the N5 level of machining accuracy specified in JIS B 1702-1:1998 was used as a processing object, and a lubricating surface of a platform structure was formed by the machining method of the present invention.

[0115] As a comparative example, the same treatment object was subjected to a grinding process after forming pits by shot peening to form a lubricated surface of a terrace structure.

[0116] The treatment conditions of Examples and Comparative Examples are shown in Table 1 below.

[0117] (Table 1)

[0118] Processing conditions of Examples and Comparative Examples

[0119]

[0120] In addition, in both the first blasting process and the second blasting process, a material having a structure in which abrasive grains are mixed into an elastic body is used as the elastic abrasive.

[0121] In addition, as the blast processing device, a commercially available air blast processing device (manufactured by Fuji Manufacturing Co., Ltd.) was used.

[0122] (Test results)

[0123] The surface conditions of the untreated gears and the gears of Examples and Comparative Examples treated under the above-mentioned conditions are shown in Table 2 below.

[0124] In addition, Figure 4 (A) shows the roughness curve of the tooth surface of the untreated gear in the tooth profile direction. Figure 4 (B) shows a roughness curve in the tooth profile direction of the gear of the embodiment.

[0125] (Table 2)

[0126] Test results

[0127]

[0128] (Inspection)

[0129] (1) Comparison of surface roughness

[0130] A comparison of the surface roughness parameters before and after processing confirmed that for the arithmetic mean roughness Ra, the value of the embodiment showed a slight increase (increase of about 26%) relative to the untreated value, and no major change was found. According to the method of the present invention, even if a lubricating surface with a platform structure is formed, the increase in surface roughness can be suppressed.

[0131] In contrast, it was confirmed that in the tooth surface of the gear treated by the method of the comparative example, the arithmetic mean roughness Ra increased significantly (by 640%) compared with the untreated state, and the increase in surface roughness resulted in the formation of a lubricating surface of a platform structure. It was confirmed that the processing method of the present invention using an elastic abrasive in the first blasting treatment is effective in maintaining processing accuracy and forming a lubricating surface of a platform structure.

[0132] (2) Comparison of concave and convex shapes

[0133] In the tooth surface of the gear treated by the method of the embodiment, the value of the skewness Rsk increases significantly to the negative side (about 15 times) compared with the untreated gear, and the protruding valley depth Rvk increases about 2.5 times compared with the untreated surface.

[0134] As can be seen from these values, the gears treated by the method of the embodiment have recesses with narrower opening widths and deeper depths than the recesses of the concave and convex portions produced on the tooth surfaces of the untreated gears. Figure 4 The roughness curve of the untreated tooth surface shown in (A) is Figure 4 This can also be confirmed by comparing the roughness curves of the tooth surfaces after treatment under the conditions of the embodiment shown in (B).

[0135] Furthermore, in the gear of the embodiment, the load length ratio Mr1 is about 60% of that of the untreated gear, and the ratio of the protruding peak portion is reduced (the upper end of the protrusion is flat), which shows that a lubricating surface with a terrace structure is formed.

[0136] In contrast, in the gear processed by the comparative example method, based on the value of the load length ratio Mr1, it can be inferred that the lubrication surface of the platform structure is flattened at the top of the convex portion formed on the tooth surface, but based on the value of the skewness Rsk, the opening width of the concave portion formed by the comparative example method is larger than that of the concave portion of the present invention. It is believed that the formation of such a concave portion with a large opening width will cause the numerical value that serves as the benchmark for the accuracy grade described later to increase significantly (reduced processing accuracy).

[0137] Furthermore, based on the value of the protruding valley depth Rvk, the recess formed by the comparative example method is shallower than the recess (groove) formed by the example method, and it is speculated that the function as an oil reservoir and the lubricity of the tooth surface are inferior to those of the present invention.

[0138] (3) Comparison of machining accuracy

[0139] Among the individual errors of the gear unit specified in JIS B 1702-1:1998, the individual pitch deviation fpt, ​​the cumulative pitch deviation Fp, the total tooth profile error Fα, and the total tooth direction error Fβ are observed. Compared with the unprocessed gear, the gear processed by the method of the embodiment shows a slight increase in each value, but the increase rate can be suppressed to less than 30% relative to the unprocessed state.

[0140] Therefore, the gear can be finished with a smaller error (high precision) of about 30% relative to the upper limit value of the individual error determined as, for example, level N5. Thus, even after the lubrication surface of the platform structure is formed by the method of the present invention, the processing accuracy of the gear to be processed can be maintained within the range of level N5.

[0141] In fact, under the test conditions of this embodiment, the errors of the gears processed by the method of the present invention (single pitch deviation fpt, ​​cumulative pitch deviation Fp, total tooth profile error Fα, total tooth direction error Fβ) are all within the upper limit value range specified as level N5.

[0142] From these results, it was confirmed that the method of the present invention can meet the conflicting requirements of forming a lubricating surface with a land structure on the tooth surface while maintaining the machining accuracy of a gear finished to high precision.

[0143] In contrast, in the gears processed by the method described in the comparative example, the values ​​of the single pitch deviation fpt, ​​the cumulative pitch deviation Fp, the total tooth profile error Fα, and the total tooth direction error Fβ all showed a significant increase compared to the unprocessed state. In the test results under the above conditions, in the gears of the comparative example, except for the total tooth profile error Fα, the other errors exceeded the upper limit value specified by the N5 level. The comparative example method cannot take into account both the maintenance of the processing accuracy of the gears that are finished to high precision and the formation of the lubricating surface of the platform structure.

Claims

1. A method for processing high-precision gears, characterized in that: Gears that have undergone gear cutting and heat treatments such as carburizing and quenching or high-frequency quenching and are then finished to a precision level of N5 or higher as specified in JIS B 1702-1:1998, with an arithmetic mean surface roughness Ra of 0.2 μm or less, are the subject of treatment. Blasting and grinding are performed. In the blasting process, an elastic abrasive material obtained by attaching angular irregular hard abrasive grains to the surface of an elastic body or mixing them into the elastic body is blasted perpendicularly to the tooth surface of the gear, thereby forming minute irregularities on the tooth surface. The minute irregularities include recessed portions having a narrower opening width and a deeper depth than the recessed portions of the irregularities formed before the blasting process, i.e., grooves. In the grinding process, the tooth surface after the blasting process is ground to remove the tops of the convex portions formed between the grooves to flatten the tooth surface. A platform structure is formed on the tooth surface, the platform structure having the grooves and convex portions formed between the grooves and having flattened upper ends, and Compared with the tooth surface of the gear before the blasting treatment, the increases in the arithmetic mean roughness Ra, single pitch deviation, cumulative pitch deviation, total tooth profile error and total tooth direction error of the tooth surface of the gear after the grinding treatment are all suppressed to less than 30%.

2. The method for processing high-precision gears according to claim 1, characterized in that: The elastic abrasive used in the blasting process has a median particle size of the elastic body of 0.1 to 2.0 mm, a median particle size of the abrasive grains of 10 to 500 μm, and the blasting of the elastic abrasive is performed at a blasting pressure of 0.2 to 0.5 MPa.

3. The method for processing a high-precision gear according to claim 1 or 2, characterized in that: The grinding process is performed by a second blasting process in which an elastic abrasive material obtained by adhering abrasive grains to the surface of an elastic body or mixing them into the elastic body is blasted at an acute angle with respect to the tooth surface.

4. The method for processing high-precision gears according to claim 3, characterized in that: The elastic abrasive used in the second blasting process has a median particle size of the elastic body of 0.1 to 2.0 mm, a median particle size of the abrasive grains of 20 μm or less, and is blasted at a blasting pressure of 0.1 to 0.3 MPa.

5. The method for processing high-precision gears according to claim 3, characterized in that: The second blasting treatment is performed at an inclination angle of 20° to 60° with respect to the tooth surface.

6. The method for machining high-precision gears according to claim 4, characterized in that: The second blasting treatment is performed at an inclination angle of 20° to 60° with respect to the tooth surface.

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