Manufacturing method of rotary member

Abstract

To impart a vibration damping characteristic to a rotary member, while securing excellent strength of the rotary member.SOLUTION: A manufacturing method of a rotary member according to the present disclosure is a method for manufacturing a rotary member having a vibration damping property from raw material steel, the method including forming a workpiece having a recess from the raw material steel. The workpiece is subjected to a carburizing treatment so that the concentration of C in the outer peripheral surface of the rotary member and the vicinity thereof is more than 1.1 mass% and 1.5 mass% or less, which is higher than the concentration of C in the raw material steel. The workpiece is cooled at a cooling rate lower than a critical cooling rate at which an austenite structure of the workpiece is transformed into martensite. After the workpiece is heated in a heating furnace controlled so that the internal temperature reaches a predetermined target temperature, the workpiece is cooled at a cooling rate equal to or higher than a critical cooling rate, and a thermosetting resin is filled in the recess of the workpiece.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a rotating member having vibration damping properties. [Background technology]

[0002] Conventionally, a gear used in a wiper transmission device is known that includes a metal molded member and a plastic filler (see, for example, Patent Document 1). The molded member of this gear includes a toothed rim having an outer tooth row and at least one support element connected to the toothed rim on its inner surface. The plastic filler is formed by pouring a plastic material into the interior region of the molded member and is in at least partial surface contact with the inner surface of the toothed rim. As a result, the plastic filler reduces the gear's tendency to vibrate and reduces noise generated when the gear rotates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2010-519474 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional manufacturing of gears, the plastic material is filled into a molded member while it is heated, for example, to about 40-80°C, and then heated to a higher temperature (for example, about 200°C) after filling to harden it. Therefore, if the molded member is carburized to increase its surface hardness before forming the plastic filling body, the heat required to fill the plastic material will reduce the surface hardness of the molded member, making it impossible to ensure the strength (durability) of the gear as a product.

[0005] Therefore, a main object of the present disclosure is to provide a rotating member with vibration damping properties while ensuring good strength of the rotating member. [Means for solving the problem]

[0006] The manufacturing method of a rotating member disclosed herein is a manufacturing method of a rotating member that manufactures a rotating member having vibration damping properties from a material steel, and includes forming a workpiece having a recess from the material steel, carburizing the workpiece so that the C concentration on the outer peripheral surface of the rotating member and its vicinity is greater than 1.1 mass% and less than 1.5 mass%, which is higher than the C concentration of the material steel, cooling the workpiece at a cooling rate less than the critical cooling rate for transforming the austenitic structure of the workpiece into martensitic, heating the workpiece in a heating furnace controlled so that the internal temperature reaches a predetermined target temperature, and then cooling the workpiece at a cooling rate equal to or greater than the critical cooling rate, and filling the recess in the workpiece with a thermosetting resin.

[0007] The carburizing, cooling, heating in a heating furnace, and subsequent cooling (quenching) steps in the manufacturing method of the present disclosure precipitate (disperse) fine carbides within the workpiece, thereby increasing the workpiece's resistance to temper softening. Therefore, by filling the recesses in the workpiece with a thermosetting resin after the carburizing, cooling, and quenching steps are completed, a decrease in the workpiece's surface hardness due to the temperature rise associated with filling the thermosetting resin can be effectively suppressed. As a result, the manufacturing method of the present disclosure makes it possible to impart vibration damping properties to the rotating member by filling the thermosetting resin while maintaining the strength of the rotating member. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram showing an example of a rotating member manufactured by the manufacturing method of the present disclosure. [Figure 2] 1 is a flowchart illustrating a manufacturing method according to the present disclosure. [Figure 3] FIG. 2 is an explanatory diagram showing an example of a cross-sectional structure of a workpiece that has been subjected to carburizing treatment, cooling treatment, and quenching treatment in the manufacturing method of the present disclosure. [Figure 4]1 is a table showing the measurement results of the surface hardness of workpieces that have been subjected to carburizing treatment, cooling treatment, and quenching treatment in the manufacturing method of the present disclosure. [Figure 5] 10A and 10B are explanatory views showing another example of a rotating member manufactured by the manufacturing method of the present disclosure. [Figure 6] 10A and 10B are explanatory views showing another example of a rotating member manufactured by the manufacturing method of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Next, embodiments of the present disclosure will be described with reference to the drawings.

[0010] FIG. 1 is an explanatory diagram showing an external gear 1 as a rotating member manufactured by the manufacturing method of the present disclosure. The external gear 1 shown in the figure includes a plurality of external teeth 2, which are helical or spur teeth, and a shaft hole 3 through which a shaft (not shown) is inserted. More specifically, the external gear 1 includes a cylindrical rim portion 4 having the plurality of external teeth 2, a cylindrical hub portion 5 extending concentrically with the rim portion 4 and defining the shaft hole 3, and an annular web portion 6 connecting the rim portion 4 and the hub portion 5. The rim portion 4, the hub portion 5, and the web portion 6 define an annular recess 7 extending concentrically with the rim portion 4 and the hub portion 5 and opening at one end of the external gear 1. A vibration damping portion 8 is formed within the recess 7 by filling the inner surface with a thermosetting resin so that it closely contacts the recess 7. As a result, the vibration damping portion 8 damps (absorbs) vibrations during rotation of the external gear 1, thereby suppressing noise generation.

[0011] 2, the external gear 1 is formed by subjecting a bar (workpiece) made of high-Si steel to rough machining (step S100), gear cutting (step S110), carburizing (step S120), cooling (step S130), quenching (step S140), tempering (step S150), filling with thermosetting resin (step S160), and after-baking (step S170). After tempering but before or after filling with thermosetting resin, the external gear 1 may be subjected to a surface hardening treatment such as shot peening, and may further be subjected to a surface treatment such as mirror finishing, if necessary.

[0012] The material steel of the external gear 1 contains 0.15% by mass or more and 0.25% by mass or less of C (carbon), 0.80% by mass or more and 3.00% by mass or less of Si (silicon), 0.70% by mass or more and 1.10% by mass or less of Mn (manganese), 0.03% by mass or less of P (phosphorus), 0.100% by mass or less of S (sulfur), 0.01% by mass or more and 0.50% by mass or less of Cu (copper), 0.01% by mass or more and 0.50% by mass or less of Ni (nickel), 0.20% by mass or more and 0.50% by mass or less of Cr (chromium), 0.50% by mass or less of Mo (molybdenum), 0.30% by mass or less of Al (aluminum), 0.05% by mass or less of N (nitrogen), Fe, and unavoidable impurities.

[0013] The Si concentration in the base steel is preferably 0.80% by mass or more, more preferably 1.00% by mass or more and 1.30% by mass or less. The S concentration in the base steel is preferably 0.03% by mass or less. The Cu concentration in the base steel is preferably 0.05% by mass or more and 0.3% by mass or less. The Ni concentration in the base steel is preferably 0.04% by mass or more and 0.3% by mass or less. The Cr concentration in the base steel is preferably 0.2% by mass or more and 0.4% by mass or less. The Mo concentration in the base steel is preferably 0.05% by mass or more and 0.4% by mass or less. The Al concentration in the base steel is preferably 0.01% by mass or more and 0.04% by mass or less. The N concentration in the base steel is preferably 0.01% by mass or more and 0.03% by mass or less.

[0014] The base steel may also contain one or two of Nb (niobium), Ti (titanium), and B (boron) as optional alloying components. The Nb concentration in the base steel is preferably 0.02 mass% or more and 0.20 mass% or less. The Ti concentration in the base steel is preferably 0.02 mass% or more and 0.20 mass% or less. The B concentration in the base steel is preferably 0.0005 mass% or more and 0.0100 mass% or less.

[0015] The base steel used satisfies the following conditions: [Si] + [Ni] + [Cu] - [Cr] > 0.5 and [Si] ≥ 1.0, where [Si] is the mass percent of Si, [Ni] is the mass percent of Ni, [Cu] is the mass percent of Cu, and [Cr] is the mass percent of Cr. This allows a pearlite structure to be generated by the cooling process in step S130, even if a high concentration of carbon is added to the workpiece by the carburizing process in step S120. Furthermore, by using a high-Si steel with high tempering softening resistance that satisfies [Si] ≥ 0.8 as the base steel, softening of the workpiece due to the filling of the thermosetting resin in step S160 can be effectively suppressed.

[0016] Next, the manufacturing procedure for the external gear 1 will be specifically described.

[0017] To manufacture the external gear 1, a bar made of base steel with the above-described composition is prepared. The bar is then subjected to normalizing in advance, in which the bar is heated to a temperature higher than the A3 transformation point (austenite-ferrite transformation point) corresponding to the C concentration (0.05% by mass or more and 0.30% by mass or less) of the base steel. The bar is then cut to a predetermined length to obtain a workpiece, which is then subjected to rough machining (step S100) and gear cutting (step S110). In step S100, a recess that opens at one end of the workpiece is formed by forging or cutting.

[0018] After the gear cutting process is completed, the workpiece is subjected to a carburizing process (step S120). The carburizing process in step S120 is a so-called vacuum carburizing process in which the workpiece is heated in a vacuum furnace (not shown) into which a hydrocarbon gas (e.g., acetylene gas) is introduced, thereby penetrating and diffusing carbon (C) into the workpiece. During the carburizing process, the pressure inside the vacuum furnace is set to, for example, 2 kPa or less, and the internal temperature of the vacuum furnace is set to, for example, a range of 900-1050°C. The workpiece is heated in the vacuum furnace for a predetermined time (e.g., 60-300 minutes) so that the C concentration in the region corresponding to the surface of the external gear 1 is greater than 1.1% by mass and less than 1.5% by mass. The surface of the external gear 1 refers to the region extending from the outer peripheral surface, including the tooth flanks, tooth tips, and tooth roots (outer peripheral surfaces), to a depth of approximately 20-40 μm. Upon completion of the carburizing process (heating), the workpiece is essentially entirely austenitic.

[0019] After the carburizing treatment (heating) is completed, the workpiece is subjected to a cooling treatment in a reduced-pressure furnace (step S130). The cooling treatment in step S130 involves gradually cooling the workpiece at a cooling rate (e.g., 0.2-5.0°C / s) below the critical cooling rate at which the austenite structure of the workpiece is transformed into martensite. By slowly cooling the workpiece in this manner, the outer and inner peripheral surfaces of the workpiece become primarily pearlite structures, with the ferrite structure increasing toward the interior. This prevents the formation of martensite structures, which are larger in volume than pearlite structures, in the workpiece, thereby suppressing distortion of the workpiece due to heat treatment.

[0020] After the cooling process is completed, the workpiece is subjected to a quenching process (step S140). In the quenching process of step S140, the workpiece that has been subjected to the carburizing process (step S120) and the cooling process (step S130) is heated in a heating furnace that is controlled so that the internal temperature of the workpiece reaches a predetermined target temperature Ttag, and then cooled at a cooling rate equal to or greater than the critical cooling rate. In this embodiment, the target temperature Ttag is set to a constant value (e.g., 800°C) within the range of 770-840°C and equal to or greater than the Acm transformation point. The Acm transformation point is the austenitization temperature corresponding to the C concentration in the surface layer of the external gear 1. Then, in step S140, the workpiece is heated for a predetermined time (e.g., 30-120 minutes) in a heating furnace (not shown) in which the internal temperature is maintained within a range of the target temperature Ttag ±5°C and the carbon potential (CP) is set to, for example, CP = 0.8. This makes it possible to convert the workpiece into an austenitic structure throughout, while suppressing variations in the degree to which carbides precipitated at the grain boundaries of the workpiece dissolve into the grains. Furthermore, by using high-Si steel, which has high temper softening resistance, as the base steel, and by performing the carburizing treatment in step S120, the cooling treatment in step S130, and the quenching treatment in step S140, as shown in Figure 3, fine carbides are precipitated (dispersed) in the workpiece, and the temper softening resistance of the workpiece can be further increased.

[0021] In this embodiment, a so-called continuous furnace is used as the heating furnace. After the workpiece is heated for a predetermined time, it is cooled (rapidly quenched) in the heating furnace using a refrigerant, such as water or cooling oil, at a temperature of 20-200°C at a cooling rate equal to or greater than the critical cooling rate. As a result, a portion of the austenite structure in the region along the outer circumferential surface and the region along the inner circumferential surface (shaft hole 3) of the workpiece is transformed into a martensite structure (quenched martensite structure). As a result, the hardness of the region along the outer circumferential surface and the region along the inner circumferential surface of the workpiece becomes higher than that of the base steel. Furthermore, by setting the refrigerant temperature to 20-200°C, it is possible to reliably prevent an increase in the volume fraction of the retained austenite structure that has not transformed into martensite, even if the C concentration in the region corresponding to the surface layer of the external gear 1 of the workpiece is greater than 1.1% by mass and less than 1.5% by mass. After the quenching process is completed, the workpiece is subjected to a tempering process (step S150). Tempering involves heating the workpiece to a temperature lower than approximately 600°C (for example, at 300°C for 3 hours). By performing quenching and tempering, the toughness of the surface layer of the workpiece is sufficiently ensured.

[0022] After step S150, the recess formed in the workpiece is filled with a thermosetting resin. Examples of suitable thermosetting resins include epoxy resin, phenolic resin, vinyl ester resin, unsaturated polyester resin, and silicone resin. In step S150, the thermosetting resin is heated to, for example, about 40-80°C and filled into the recess in the workpiece. After filling, the resin is further heated to a higher temperature (for example, about 200°C) to harden it. This allows the thermosetting resin to be filled into the recess so that it is in close contact with the inner surface of the recess. After filling with the thermosetting resin is complete, the workpiece is subjected to an after-baking process (step S170) to promote hardening of the thermosetting resin and improve dimensional stability. This results in an external gear 1 with high strength and excellent vibration damping characteristics.

[0023] As described above, when manufacturing the external gear 1 as a rotating member, after the carburizing process (step S120) and the cooling process (step S130), a workpiece made of base steel is heated in a heating furnace controlled so that its internal temperature reaches a predetermined target temperature Ttag, followed by a quenching process (step S140) in which the workpiece is cooled at a cooling rate equal to or greater than the critical cooling rate. These carburizing, cooling, and quenching processes (steps S120-S140) precipitate (disperse) fine carbides in the workpiece, thereby increasing the workpiece's temper softening resistance. Therefore, by filling the recesses in the workpiece with a thermosetting resin after the quenching process is completed (step S160), a decrease in the workpiece's surface hardness due to the temperature increase associated with filling the thermosetting resin can be effectively suppressed. As a result, the manufacturing method disclosed herein makes it possible to impart vibration damping properties to the external gear 1 by filling the thermosetting resin while maintaining the strength of the external gear 1.

[0024] Furthermore, by using high-Si steel, with an Si concentration of 0.80% by mass or more, more preferably 1.0% by mass or more, as the base steel for the external gear 1, softening of the workpiece due to the filling of the thermosetting resin in step S160 can be effectively suppressed. FIG. 4 shows the Vickers hardness [HV] of the interior of a workpiece measured before and after heating versus the distance [mm] from the surface of the workpiece when the workpiece is made of high-Si steel with an Si concentration of 1.8% by mass and subjected to carburizing, cooling, quenching, and tempering (steps S120-S150) and then heated to a predetermined temperature (here, 200°C) corresponding to the temperature applied when the thermosetting resin is filled. The measurement results in FIG. 4 demonstrate that by subjecting a workpiece made of high-Si steel with an Si concentration of 0.80% by mass or more to the above-described carburizing, cooling, and quenching processes, the surface hardness of the workpiece can be maintained approximately the same before and after the thermosetting resin is filled, even if the temperature of the workpiece increases as a result of the thermosetting resin being filled.

[0025] Furthermore, the carburizing, cooling, and quenching treatments (steps S120-S140) reduce the variation in the degree to which carbides precipitated at the grain boundaries of the workpiece dissolve into the grains, preventing the production of a mixture of external gears 1 prone to intragranular fracture and external gears 1 prone to intergranular fracture. This reduces the variation in strength of the external gears 1. Although heating the workpieces in a heating furnace requires time for quenching (heating), heating multiple workpieces at once in the heating furnace reduces the manufacturing cost of the external gears 1 compared to quenching using high-frequency induction heating. This reduces the variation in strength of the external gears 1 while minimizing increases in cost. Furthermore, maintaining the internal temperature of the heating furnace within a range of the target temperature Ttag ±5°C effectively reduces the variation in strength of the external gears 1.

[0026] Furthermore, when the target temperature Ttag in the heating furnace is set within the range of 770-840°C (when the target temperature Ttag is low), the amount of carbide at the grain boundaries increases and the amount of retained austenite in the surface layer decreases compared to when the target temperature Ttag in the heating furnace is set high (for example, when the target temperature Ttag is 870°C). Therefore, by setting the target temperature Ttag in the heating furnace within the range of 770-840°C, it is possible to increase the hardness of the surface layer and further improve the wear resistance of the external gear 1 (rotating member). However, the target temperature Ttag in the heating furnace may also be set at a temperature above 840°C (preferably 870°C or lower). In this way, the workpiece quenched at a higher temperature is rapidly cooled, which introduces more carbon into the grains, strengthening the grains and increasing the amount of retained austenite in the surface layer, thereby further improving the toughness of the external gear 1 (rotating member).

[0027] In the above embodiment, the quenching process, i.e., the heating and rapid cooling of the workpiece, is performed continuously in a heating furnace (continuous furnace), but this is not limiting. That is, the quenching process in step S140 may involve heating the workpiece in a heating furnace and then rapidly cooling the workpiece in cooling equipment separate from the heating furnace.

[0028] The manufacturing method of the present disclosure is not limited to the external gear 1, but may also be used for a stepped gear 1B shown in FIG. 5 . The stepped gear 1B includes a cylindrical rim portion 4B having a plurality of external teeth 2B, which are helical or spur teeth; a cylindrical hub portion 5B extending concentrically with the rim portion 4B and defining a shaft hole 3B; an annular web portion 6B connecting the rim portion 4B and the hub portion 5B; and a cylindrical extension shaft portion 50 extending coaxially from the hub portion 5B and having a plurality of external teeth (helical or spur teeth) 20 with, for example, a smaller pitch circle than the external teeth 2B. In this stepped gear 1B, the rim portion 4B, the hub portion 5B, and the web portion 6B define an annular recess 7B extending concentrically with the rim portion 4B and the hub portion 5B and opening at one end of the stepped gear 1B. A thermosetting resin is filled into the recess 7B so as to closely contact the inner surface, thereby forming a vibration-damping portion 8B. As a result, even in the stepped gear 1B, the vibration attenuating portion 8B can attenuate (absorb) vibrations during rotation, thereby suppressing the generation of noise.

[0029] Furthermore, the manufacturing method of the present disclosure may be used to manufacture a double-stage gear 1C shown in FIG. 6. The double-stage gear 1C is, for example, formed by integrally molding or joining two gears of roughly the same diameter. The double-stage gear 1C includes a cylindrical rim portion 4C having a plurality of external spur teeth 2C, a cylindrical rim portion 40C having a plurality of external spur teeth 20C, a cylindrical hub portion 5C extending concentrically with the rim portions 4C and 40C and defining a shaft hole 3C, an annular web portion 6C connecting the rim portion 4C and the hub portion 5C, and an annular web portion 60C connecting the rim portion 40C and the hub portion 5C. In this double-stage gear 1C, the rim portion 4C, the hub portion 5C, and the web portion 6C define an annular recess 7C extending concentrically with the rim portion 4C and the hub portion 5C and opening at one end (the left end in the figure) of the double-stage gear 1C. The rim portion 40C, hub portion 5C, and web portion 60C also define an annular recess 70C that extends concentrically with the rim portion 40C and hub portion 5C and opens at the other end (the right end in the figure) of the double gear 1C. A vibration-damping portion 8C is formed within the recess 7C by filling it with a thermosetting resin so that it makes close contact with the inner surface, and a vibration-damping portion 80C is formed within the recess 70C by filling it with a thermosetting resin so that it makes close contact with the inner surface. As a result, the vibration-damping portions 8C and 80C damp (absorb) vibrations during rotation of the double gear 1C, making it possible to effectively suppress noise generation.

[0030] Furthermore, the manufacturing method of the present disclosure may be used to manufacture an axial member such as a shaft, a component of a planetary gear, or a bearing part.

[0031] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present disclosure. Furthermore, the above-described embodiment is merely a specific embodiment of the invention described in the Summary of the Invention, and does not limit the elements of the invention described in the Summary of the Invention. [Industrial Applicability]

[0032] The invention of the present disclosure can be used in the rotating member manufacturing industry and the like. [Explanation of symbols]

[0033] 1 External gear, 2,2B,20,2C,20C External tooth, 3,3B,3C Shaft hole, 4, 4B,4C,40C Rim part, 5,5B,5C Hub part, 50 Extension shaft part, 6,6B,6C,60C Web part, 7,7B,7C,70C Recess part, 8, 8B,8C,80C Vibration damping part (thermosetting resin).

Claims

1. A method for manufacturing a rotating member that produces a rotating member having vibration damping properties from a base steel, comprising: forming a workpiece having a recess from the material steel; Carburizing the workpiece so that the C concentration on the outer peripheral surface of the rotating member and in the vicinity thereof is greater than 1.1 mass % and less than 1.5 mass %, which is higher than the C concentration of the base steel; Cooling the workpiece at a cooling rate less than a critical cooling rate at which the austenite structure of the workpiece is transformed into martensite; The workpiece is heated in a heating furnace that is controlled so that the internal temperature reaches a predetermined target temperature, and then the workpiece is cooled at a cooling rate equal to or greater than the critical cooling rate; A method for manufacturing a rotating member, comprising filling the recess of the workpiece with a thermosetting resin.

2. 2. The method for manufacturing a rotating member according to claim 1, the rotating member is a gear including a rim portion having a plurality of teeth, a hub portion, and a web portion connecting the rim portion and the hub portion, A method for manufacturing a rotating member, wherein the recess is defined by the rim portion, the hub portion, and the web portion of the workpiece.

3. 3. The method for manufacturing a rotating member according to claim 1 or 2, A method for manufacturing a rotating member, wherein the base steel contains at least 0.8 mass % Si (silicon).

4. 4. The method for manufacturing a rotating member according to claim 3, The base steel contains 0.15% by mass or more and 0.25% by mass or less of C (carbon), 0.80% by mass or more and 3.00% by mass or less of Si (silicon), 0.70% by mass or more and 1.10% by mass or less of Mn (manganese), 0.03% by mass or less of P (phosphorus), 0.100% by mass or less of S (sulfur), 0.01% by mass or more and 0.50% by mass or less of Cu (copper), 0.01% by mass or more and 0.50% by mass or less of Ni (nickel), 0.20% by mass or more and 0.50% by mass or less of Cr (chromium), 0.50% by mass or less of Mo (molybdenum), 0.30% by mass or less of Al (aluminum), 0.05% by mass or less of N (nitrogen), Fe, and inevitable impurities, and when the content by mass of Si is [Si], the content by mass of Ni is [Ni], the content by mass of Cu is [Cu], and the content by mass of Cr is [Cr], [Si]+[Ni]+[Cu]-[Cr]>0.5 A manufacturing method of a rotating member that satisfies the above.

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