Internal gear manufacturing process method

Abstract

The invention belongs to the technical field of gear machining, and particularly relates to an internal gear manufacturing process method. According to the method, the internal gear is machined to the target size at a time, the requirement for secondary machining after heat treatment deformation in a traditional technology is reduced, and the technological process is simplified; the machined internal gear is subjected to chemical cleaning, residues on the surface of the internal gear can be effectively removed, and then the quality and uniformity of subsequent nitriding treatment are improved; when nitriding treatment is carried out in a vacuum nitriding furnace, the end face of the internal gear is clamped and limited, the deformation problem of the internal gear in the heat treatment process is prevented, and the requirement for internal tooth profile correction is reduced; and finally, the internal gear subjected to nitriding treatment is subjected to electrolytic polishing, and the smoothness and friction performance of the surface of the internal gear can be further improved. Through the technological method, the machining technological process of the internal gear can be simplified, meanwhile, the problem of deformation of the internal gear in the heat treatment machining process can be effectively prevented, and therefore the machining efficiency of the internal gear is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of gear processing, and specifically relates to a process method for manufacturing internal gears. Background Art

[0002] In the planetary gear structure of the automotive gearbox, the internal teeth of the sun gear need to undergo precision machining and grinding. However, after heat treatment, the internal gear often has serious deformation problems. Due to the influence of deformation, it is necessary to reserve enough secondary processing volume during the initial processing so that the internal tooth shape can be corrected by secondary grinding wheel grinding after heat treatment. The secondary grinding process usually requires the use of a precision five-axis internal gear grinder to ensure the accuracy of the internal tooth shape. When the precision five-axis internal gear grinder is performing the grinding operation, in order to ensure the processing accuracy, the precision-formed internal gear grinding wheel needs to be frequently replaced, which not only increases the complexity and cost of the operation, but also reduces production efficiency. Summary of the invention

[0003] One of the inventive purposes of the present application is to provide a process method for manufacturing internal gears, in which there is no need to reserve secondary processing capacity. Instead, the internal gear is processed to a target size once, the end face of the internal gear is clamped and limited, and the surface of the internal gear is heat treated in a vacuum nitriding furnace. This process method improves the production efficiency of the internal gear.

[0004] According to an embodiment of the present application, a first aspect provides an internal gear manufacturing process method, the internal gear manufacturing process method comprising:

[0005] Machining the internal gear to the target size in one go;

[0006] Chemically cleaning the surface of the internal gear after the primary processing;

[0007] Clamping and limiting the end face of the chemically cleaned internal gear, and subjecting the clamped and limited internal gear to nitriding treatment in a vacuum nitriding furnace;

[0008] The nitrided internal gear is electrolytically polished.

[0009] In one embodiment, machining the internal gear to a target size in one step comprises:

[0010] After the internal gear is hobbed to the target size, the end face flatness of the internal gear is ground to less than or equal to 0.01mm.

[0011] In one embodiment, chemically cleaning the surface of the internal gear after the primary processing comprises:

[0012] Removing organic pollutants from the surface of the internal gear by a first alkali wash;

[0013] Performing a first pickling on the internal gear after the first alkali washing to remove the oxide film on the surface of the internal gear;

[0014] The internal gear after the first pickling is pickled for the second time to remove the oxide layer on the surface of the internal gear.

[0015] In one embodiment, removing organic pollutants from the surface of the internal gear by the first alkali washing comprises:

[0016] The surface of the inner gear is firstly alkaline washed by an aqueous solution of sodium hydroxide or sodium carbonate with a concentration of 2% to 15% and a temperature of 50° C. to 70° C.

[0017] In one embodiment, the first pickling of the internal gear after the first alkali washing to remove the oxide film on the surface of the internal gear comprises:

[0018] The surface of the internal gear is pickled for the first time by using an aqueous solution of sulfuric acid, phosphoric acid or nitric acid with a solution concentration of 10% to 30% and a temperature of 20° C. to 50° C.

[0019] In one embodiment, the step of performing a second pickling on the internal gear after the first pickling to remove the oxide layer on the surface of the internal gear comprises:

[0020] The surface of the internal gear is pickled for the second time by using an aqueous solution including a nitric acid concentrate with a concentration of 10% to 30% and a hydrofluoric acid with a concentration of 0.5% to 5%.

[0021] In one embodiment, clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the internal gear in a vacuum nitriding furnace comprises:

[0022] When the end face of the internal gear after chemical cleaning is clamped and limited, the horizontality of the surface in contact with the end face of the internal gear is less than or equal to 0.01 mm.

[0023] In one embodiment, clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the internal gear in a vacuum nitriding furnace comprises:

[0024] The vacuum degree in the vacuum nitriding furnace is controlled to be lower than 0.001 Pa.

[0025] In one embodiment, the step of clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the internal gear in a vacuum nitriding furnace further comprises:

[0026] isothermal nitriding treatment of the internal gear at a temperature of 500° C. to 520° C.;

[0027] After the internal gear is subjected to isothermal nitriding treatment, the internal gear is subjected to annealing treatment at a temperature of 500° C. to 520° C.;

[0028] After the internal gear is annealed, the temperature of the vacuum nitriding furnace is lowered to 200° C., and the internal gear is taken out of the vacuum nitriding furnace and then cooled.

[0029] In one embodiment, electrolytic polishing the nitrided internal gear comprises:

[0030] When the internal gear is electropolished, the surface roughness of the internal gear is processed to 0.01 μm to 0.1 μm.

[0031] In the manufacturing process of the internal gear of the present application, the need for secondary processing after heat treatment deformation in the traditional process is reduced by processing the internal gear to the target size once, thereby simplifying the process flow; chemical cleaning of the processed internal gear can effectively remove the residues on the surface of the internal gear, such as organic pollutants or oxide film or oxide layer, thereby improving the quality and uniformity of the subsequent nitriding treatment; by clamping and limiting the end face of the internal gear during the nitriding treatment in the vacuum nitriding furnace, the deformation problem of the internal gear during the heat treatment process is prevented, and the need for internal tooth shape correction is reduced; finally, the internal gear after nitriding treatment can be further improved by electrolytic polishing, and the surface finish and friction performance of the internal gear can be further improved. Through this process method, the processing process of the internal gear can be simplified, and the deformation problem of the internal gear during the heat treatment process can be effectively prevented, thereby improving the processing efficiency of the internal gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Flow chart of a method for manufacturing an internal gear in one embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0034] It should be noted that the illustrations provided in this embodiment are only used to schematically illustrate the basic concept of the present invention.

[0035] The structures, proportions, sizes, etc. illustrated in the drawings in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportion or adjustment of size should still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0036] The directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "middle", "longitudinal", "lateral", "horizontal", "inner", "outer", "radial", "circumferential" and the like in this specification are based on the directions or positional relationships shown in the drawings and are only for the convenience of simplifying the description. They do not indicate or imply that the devices or elements referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0037] As described in the background, in the planetary gear structure in the automotive gearbox, the internal teeth of the sun gear need to undergo precise machining and grinding. However, after heat treatment, the internal gear often has serious deformation problems. Due to the influence of deformation, it is necessary to reserve sufficient secondary processing volume during the initial processing so that the internal tooth shape can be corrected by secondary grinding wheel grinding after heat treatment. The secondary grinding process usually requires the use of a precision five-axis internal gear grinder to ensure the accuracy of the internal tooth shape. When the precision five-axis internal gear grinder performs the grinding operation, in order to ensure the processing accuracy, it is necessary to frequently replace the precision-formed internal gear grinding wheel, which not only increases the complexity and cost of the operation, but also causes a decrease in production efficiency. In this method, after the internal gear is directly processed to the target size once by simplifying the process, the end face of the internal gear is clamped and limited and nitrided in a vacuum nitriding furnace, in order to avoid the problem of secondary processing of deformation of the internal gear during heat treatment, thereby improving the processing efficiency of the internal gear.

[0038] like Figure 1 As shown, Figure 1 Flow chart of an internal gear manufacturing process method in one embodiment of the present application, wherein the internal gear manufacturing process method includes:

[0039] S110: Process the internal gear to the target size at one time;

[0040] S120: chemically cleaning the surface of the internal gear after the primary processing;

[0041] S130: clamping and limiting the end face of the internal gear after chemical cleaning, and performing nitriding treatment on the internal gear after clamping and limiting in a vacuum nitriding furnace;

[0042] S140: Electrolytically polish the nitrided internal gear.

[0043] In traditional internal gear processing, it is usually necessary to reserve a machining allowance before heat treatment to cope with deformation caused during the heat treatment process. However, in the process method step S110 of this embodiment, the internal gear is processed to the target size in one go, which simplifies the processing flow and avoids the complexity and cost of secondary processing. That is, in step S110 of this embodiment, the solution of reserving a machining allowance is not adopted, but the internal gear is directly processed to the target size in one go.

[0044] After machining, impurities such as oil, oxides, etc. often remain on the surface of the internal gear. If these impurities are not removed in time, they will have an adverse effect on the subsequent heat treatment process, especially the nitriding effect. In step S120, through the chemical cleaning step, these contaminants can be completely removed to ensure the cleanliness of the surface of the internal gear, which helps nitrogen atoms to evenly penetrate into the surface layer of the material during the nitriding process, improve the uniformity and quality of the nitriding layer, and thus enhance the surface hardness and wear resistance of the internal gear.

[0045] During the heat treatment process, the end face of the internal gear is easily deformed due to uneven thermal stress, which will directly affect the accuracy of the internal gear. In step S130, the end face of the internal gear is clamped and limited by a clamping device in advance, thereby effectively preventing the internal gear from being deformed by heat during heat treatment in a vacuum nitriding furnace, ensuring the shape stability of the internal gear during the entire nitriding process, thereby reducing the probability of internal gear deformation and reducing the need for subsequent internal gear shape correction.

[0046] After nitriding, although the surface hardness and wear resistance of the internal gear are significantly improved, a certain surface roughness or oxide layer may be generated. In step S140, the surface of the internal gear after nitriding is treated by electrolytic polishing, which can further remove the surface irregular structure, thereby significantly improving the surface finish of the internal gear and reducing the surface friction coefficient.

[0047] The internal gear manufacturing process method in this embodiment can significantly reduce the need for secondary processing caused by deformation after heat treatment in traditional internal gear processing, thereby reducing the complexity and cost of production. During the nitriding process, the deformation problem of the internal gear is effectively controlled by clamping and limiting the end face of the internal gear, further improving the processing accuracy; finally, the internal gear is electrolytically polished to improve the surface quality and friction performance of the internal gear.

[0048] In one embodiment, machining the internal gear to the target size in one step includes: after hobbing the internal gear to the target size, grinding the end surface flatness of the internal gear to be less than or equal to 0.01 mm.

[0049] In this embodiment, by hobbing the internal gear to the target size at one time, the complexity of secondary processing required due to deformation of the internal gear after heat treatment in the traditional process is avoided, the overall processing flow is effectively shortened, and unnecessary processing steps are reduced, thereby reducing manufacturing costs. Secondly, the flatness of the end face of the internal gear is ground to 0.01mm, which can improve the assembly accuracy of the internal gear. At the same time, the higher flatness can also ensure the stability of the gear during rotation and reduce vibration and noise problems caused by uneven meshing. In addition, the end face flatness of the internal gear is ground to less than 0.01mm, which also provides a more stable benchmark for subsequent vacuum nitriding treatment. Due to the high flatness of the end face, the internal gear can be clamped and positioned more accurately in the nitriding furnace, ensuring that the internal gear is heated evenly during the nitriding process, further reducing the risk of deformation during heat treatment.

[0050] In one embodiment, chemically cleaning the surface of an internal gear after a processing includes: removing organic pollutants on the surface of the internal gear through a first alkaline wash; performing a first pickling wash on the internal gear after the first alkaline wash to remove the oxide film on the surface of the internal gear; and performing a second pickling wash on the internal gear after the first pickling wash to remove the oxide layer on the surface of the internal gear.

[0051] In this embodiment, firstly, after the internal gear is machined once, a large amount of organic matter such as grease and lubricant often remains on its surface. These organic pollutants will not only affect the surface contact quality in the subsequent process, but may also decompose in a vacuum environment, produce gases that are not conducive to nitriding and affect the nitriding effect. Therefore, these organic pollutants can be effectively removed through the first alkali washing. The alkaline solution in the alkali washing can undergo a saponification reaction with the grease organic matter, dissolve and remove the organic residues on the surface of the internal gear, and avoid the problem of uneven pickling due to the presence of surface pollutants; then, a relatively strong oxide film may still exist on the surface of the internal gear after alkali washing. The oxide film is a protective layer formed when the metal surface is exposed to the air, but before the nitriding treatment, the oxide film will hinder the penetration of nitrogen atoms into the surface layer of the internal gear, thereby affecting the depth and uniformity of nitriding. Through the first pickling, this oxide film can be effectively removed, ensuring that nitrogen atoms can penetrate smoothly during nitriding and avoiding the barrier effect caused by the oxide film. Finally, in this embodiment, a second pickling step is provided, which can further treat the surface of the internal gear, reduce the residual oxide layer on the surface of the internal gear, and provide a more uniform and unobstructed penetration environment for the subsequent nitriding treatment.

[0052] In this embodiment, the organic pollutants and the oxide layer on the surface of the internal gear can be removed by one alkali wash and two acid washes, and excellent surface conditions are provided for the penetration of nitrogen atoms in the subsequent nitriding treatment.

[0053] Further, in one embodiment, removing organic pollutants from the surface of the internal gear by the first alkali washing includes:

[0054] The inner gear surface is first alkaline washed with an aqueous solution of sodium hydroxide or sodium carbonate at a concentration of 2% to 15% and a temperature of 50°C to 70°C.

[0055] In this embodiment, an aqueous solution of sodium hydroxide or sodium carbonate is used for alkaline washing, which can effectively saponify with organic matter, decompose and remove pollutants. Sodium hydroxide and sodium carbonate are both strong bases that can react quickly with oil and grease pollutants to separate them from the metal surface. By adjusting the concentration of the alkaline solution between 2% and 15%, different degrees of pollutants can be flexibly dealt with; when the concentration is higher, the reaction rate is faster, which is suitable for heavily polluted surfaces, while when the concentration is lower, it is suitable for lightly polluted cleaning. Ensuring that the concentration of the aqueous solution is within this range can fully remove pollutants without causing corrosion or other unnecessary damage to the surface of the internal gear. Secondly, the temperature of the alkaline washing is controlled between 50°C and 70°C, which can significantly improve the cleaning efficiency. The increase in temperature helps to accelerate the dissolution and reaction rate of organic matter, while increasing the fluidity of the solution, making the cleaning effect more uniform.

[0056] In another embodiment, performing a first pickling on the internal gear after the first alkali washing to remove the oxide film on the surface of the internal gear comprises:

[0057] The surface of the internal gear is first pickled by an aqueous solution of sulfuric acid, phosphoric acid or nitric acid with a solution concentration of 10% to 30% and a temperature of 20°C to 50°C.

[0058] In this embodiment, after the initial processing and alkali washing, although most of the organic pollutants on the surface of the inner gear are removed, due to long-term exposure to the air, an oxide film will inevitably form on the metal surface. Although the oxide film can play a certain protective role on the metal in the atmospheric environment, for heat treatment processes such as nitriding that require surface activity, the oxide film is an important barrier to the diffusion of nitrogen atoms. Therefore, before entering the nitriding treatment, the oxide film on the surface of the inner gear must be thoroughly removed by pickling to ensure the effectiveness of the subsequent process. By selecting sulfuric acid, phosphoric acid or nitric acid for pickling, these acid solutions can effectively react chemically with the oxide film, dissolve and remove the surface oxide. Secondly, the concentration range of the solution is set to 10% to 30%. When the concentration is low, the pickling reaction speed is slow, which is suitable for thinner or less oxide films; when the oxide film is thicker, a solution with a higher concentration can accelerate the reaction process and ensure the effective removal of the oxide film. Within this range, pickling can not only completely remove the oxide film, but also avoid the acid solution from being too strong and causing unnecessary corrosion to the metal matrix, ensuring the surface integrity of the gear and the subsequent treatment effect. At the same time, the temperature setting range of the concentrated solution is 20℃ to 50℃. By controlling the pickling temperature, the chemical reaction rate can be significantly accelerated and the cleaning efficiency can be improved. The researchers proposed that within this temperature range, the pickling process can be completed in a relatively short time, avoiding the damage to the metal surface that may be caused by long-term acid etching.

[0059] In another embodiment, performing a second pickling on the internal gear after the first pickling to remove the oxide layer on the surface of the internal gear comprises:

[0060] The surface of the inner gear is pickled a second time by an aqueous solution including a nitric acid concentrate with a concentration of 10% to 30% and a hydrofluoric acid with a concentration of 0.5% to 5%.

[0061] In this embodiment, the surface of the inner gear after the first pickling is pickled for the second time by using a concentrated nitric acid solution with a concentration of 10% to 30% and an aqueous solution of hydrofluoric acid with a concentration of 0.5% to 5%. The main purpose of this step is to further remove the oxide layer that may still remain after the first pickling. Among them, nitric acid is a strong oxidizing acid, which can effectively oxidize and dissolve the oxide on the metal surface during the pickling process. By treating with a nitric acid solution with a concentration of 10% to 30%, the more stubborn oxide layer on the surface of the inner gear can be quickly and efficiently removed. After the first pickling, although the oxide film on the surface has been removed, there may still be some more stubborn oxide layers or tiny residues that are difficult to handle on the metal surface. These residual oxides will hinder the uniform diffusion of nitrogen atoms in the subsequent nitriding treatment and affect the quality of the nitriding layer. Therefore, the second pickling using nitric acid to further remove the residual oxide layer is very important for ensuring the activity of the surface. Secondly, hydrofluoric acid can dissolve stubborn oxide layers such as silicates. Although the main material of the internal gear is usually steel or iron-based alloy, complex oxide combinations may be formed on the surface during the manufacturing process, such as oxides containing a small amount of silicon, chromium and other elements. It is difficult to completely remove these layers by ordinary pickling. By using hydrofluoric acid in the second pickling, it can be ensured that these difficult-to-remove oxides are completely treated, providing a metal surface without a residual oxide layer for subsequent processes, thereby greatly improving the effect of nitriding treatment. The concentration of hydrofluoric acid is controlled between 0.5% and 5%, which can fully remove complex oxides while avoiding excessive corrosion to the internal gear matrix and ensuring the integrity of the metal matrix.

[0062] In one embodiment, clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the internal gear in a vacuum nitriding furnace includes:

[0063] When the end face of the internal gear after chemical cleaning is clamped and limited, the horizontality of the surface in contact with the end face of the internal gear is less than or equal to 0.01 mm.

[0064] In this embodiment, the main goal of the nitriding treatment is to improve the surface hardness and wear resistance of the internal gear, and this process relies on the uniform penetration of nitrogen atoms. If before the nitriding treatment, the internal gear is slightly tilted or unevenly fitted when clamped, it may cause the surface of the internal gear to be subjected to uneven thermal stress distribution during the nitriding process. This uneven stress distribution phenomenon can easily cause the internal gear to deform, thereby affecting the accuracy of the tooth shape. Therefore, by controlling the horizontality with the end face of the internal gear during the clamping limit to a range of less than or equal to 0.01 mm, it can be ensured that the internal gear is heated smoothly during the entire nitriding process, thereby ensuring that the nitrogen atom penetration of the gear surface layer is more uniform, and improving the depth uniformity and hardness consistency of the nitriding layer.

[0065] In one embodiment, clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the clamped and limited internal gear in a vacuum nitriding furnace includes: controlling the vacuum degree in the vacuum nitriding furnace to be lower than 0.001Pa.

[0066] In this embodiment, nitrogen atoms diffuse into the surface of the gear under high temperature to form a nitrided layer with high hardness and wear resistance. However, the efficiency and uniformity of nitrogen atom penetration largely depend on the purity and stability of the nitriding environment. Under a higher vacuum degree, the movement path of nitrogen molecules is extended, and nitrogen atoms are more easily and evenly diffused to the surface of the inner gear, ensuring the depth and hardness uniformity of the nitriding layer. When the vacuum degree is controlled at less than 0.001Pa, the gas impurity content in the vacuum furnace is extremely low, thereby minimizing the interference of impurity gases, such as oxygen, water vapor, etc., on the nitriding process.

[0067] In one embodiment, the end face of the internal gear after chemical cleaning is clamped and limited, and the internal gear after clamping and limiting is nitrided in a vacuum nitriding furnace, and the internal gear is also subjected to constant temperature nitriding at a temperature of 500°C to 520°C; after the constant temperature nitriding of the internal gear, the internal gear is annealed at a temperature of 500°C to 520°C; after the annealing of the internal gear, the temperature of the vacuum nitriding furnace is reduced to 200°C, and the internal gear is taken out of the vacuum nitriding furnace and cooled.

[0068] In this embodiment, first, in the constant temperature nitriding treatment step at 500°C to 520°C, appropriate thermal energy can be provided to promote the diffusion and penetration of nitrogen atoms. This diffusion process allows nitrogen atoms to enter the surface layer of the internal gear material to form a nitrided layer, which effectively improves the surface hardness and wear resistance of the internal gear. After the nitriding treatment, annealing treatment is carried out in the range of 500°C to 520°C. The purpose of the annealing treatment is to reduce the internal stress of the internal gear after nitriding through a thermal stabilization process, so that the internal structure of the material is more uniform. After the annealing treatment, the temperature of the vacuum nitriding furnace is gradually lowered to 200°C, and then the internal gear is taken out for natural cooling to avoid the accumulation of thermal stress caused by sudden cooling, thereby further reducing the risk of deformation of the internal gear.

[0069] In one embodiment, electrolytically polishing the nitrided internal gear includes: processing the surface roughness of the internal gear to 0.01 μm to 0.1 μm during electrolytic polishing of the internal gear.

[0070] In this embodiment, the internal gear after nitriding treatment is electropolished, and the specific step is to process the surface roughness of the internal gear to 0.01μm~0.1μm. The purpose is that although the surface hardness and wear resistance of the internal gear after nitriding treatment are significantly improved, a certain surface roughness and oxide layer will inevitably be formed. The untreated rough surface may increase the friction coefficient and local stress concentration during the gear meshing process, thereby aggravating the wear of the gear and reducing its service life. Therefore, the electrolytic polishing technology is used for surface treatment, which can remove microscopic surface protrusions and surface defects through electrochemical reaction, thereby effectively improving the surface quality of the gear.

[0071] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for manufacturing an internal gear, characterized in that: The internal gear manufacturing process method comprises: Machining the internal gear to the target size in one go; Chemically cleaning the surface of the internal gear after the primary processing; Clamping and limiting the end face of the chemically cleaned internal gear, and subjecting the clamped and limited internal gear to nitriding treatment in a vacuum nitriding furnace; The nitrided internal gear is electrolytically polished.

2. The internal gear manufacturing process according to claim 1, characterized in that: The one-time machining of the internal gear to the target size includes: After the internal gear is hobbed to the target size, the end face flatness of the internal gear is ground to less than or equal to 0.01mm.

3. The internal gear manufacturing process according to claim 1, characterized in that: The chemical cleaning of the surface of the internal gear after the primary processing comprises: Removing organic pollutants from the surface of the internal gear by a first alkali wash; Performing a first pickling on the internal gear after the first alkali washing to remove the oxide film on the surface of the internal gear; The internal gear after the first pickling is pickled for the second time to remove the oxide layer on the surface of the internal gear.

4. The internal gear manufacturing process according to claim 3, characterized in that: The step of removing organic pollutants from the surface of the internal gear by the first alkali washing comprises: The surface of the inner gear is firstly alkaline washed by an aqueous solution of sodium hydroxide or sodium carbonate with a concentration of 2% to 15% and a temperature of 50° C. to 70° C.

5. The internal gear manufacturing process according to claim 4, characterized in that: The first pickling of the internal gear after the first alkali washing to remove the oxide film on the surface of the internal gear comprises: The surface of the internal gear is pickled for the first time by using an aqueous solution of sulfuric acid, phosphoric acid or nitric acid with a solution concentration of 10% to 30% and a temperature of 20° C. to 50° C.

6. The internal gear manufacturing process according to claim 5, characterized in that: The step of performing a second pickling on the internal gear after the first pickling to remove the oxide layer on the surface of the internal gear comprises: The surface of the internal gear is pickled for the second time by using an aqueous solution including a nitric acid concentrate with a concentration of 10% to 30% and a hydrofluoric acid with a concentration of 0.5% to 5%.

7. The internal gear manufacturing process according to claim 1, characterized in that: The step of clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the internal gear in a vacuum nitriding furnace comprises: When the end face of the internal gear after chemical cleaning is clamped and limited, the horizontality of the surface in contact with the end face of the internal gear is less than or equal to 0.01 mm.

8. The internal gear manufacturing process according to claim 1, characterized in that: The step of clamping and limiting the end face of the internal gear after chemical cleaning, and nitriding the internal gear in a vacuum nitriding furnace comprises: The vacuum degree in the vacuum nitriding furnace is controlled to be lower than 0.001 Pa.

9. The internal gear manufacturing process according to claim 8, characterized in that: The step of clamping and limiting the end face of the internal gear after chemical cleaning, and subjecting the clamped and limited internal gear to nitriding in a vacuum nitriding furnace also includes: isothermal nitriding treatment of the internal gear at a temperature of 500° C. to 520° C.; After the internal gear is subjected to isothermal nitriding treatment, the internal gear is subjected to annealing treatment at a temperature of 500° C. to 520° C.; After the internal gear is annealed, the temperature of the vacuum nitriding furnace is lowered to 200° C., and the internal gear is taken out of the vacuum nitriding furnace and then cooled.

10. The internal gear manufacturing process according to claim 1, characterized in that: The electrolytic polishing of the nitrided internal gear comprises: When the internal gear is electropolished, the surface roughness of the internal gear is processed to 0.01 μm to 0.1 μm.

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