A machining process of stainless steel gear for a small-tooth-difference planetary gear mechanism

Abstract

The present application relates to alloy smelting, heat treatment and processing technical field, disclose a kind of machining process of stainless steel gear for small-tooth-difference planetary gear mechanism, comprising the following steps: S1, refining stainless steel ingot, desulfurization and dephosphorization treatment are carried out, then pouring into stainless steel bar;S2, rough turning stainless steel bar and dividing into gear blank section;S3, heat treatment gear blank section, gear blank section is first solution treated, after heat preservation ends, using water quenching, oil quenching or gas cooling mode gear blank section is rapidly cooled to 32 ℃ below, then gear blank section is aged precipitation hardening, after gear blank section air cooling to room temperature;S4, finish turning gear blank section;S5, gear cutting, gear blank section is processed into gear using gear cutting or hobbing processing method;S6, low-temperature annealing, then gear air cooling to room temperature;S7, fine grinding, the surface except tooth part is ground to design size;S8, gear grinding, tooth profile of gear is ground to finished product size.

Description

Technical Field

[0001] This invention relates to the fields of alloy smelting, heat treatment and processing technology, and more specifically to a processing technology for stainless steel gears used in planetary gear transmission mechanisms with small tooth difference. Background Technology

[0002] A planetary gear transmission mechanism with a small tooth difference is a special type of planetary gear transmission mechanism, consisting of meshing internal and external gears, and an output mechanism, wherein the number of teeth on the internal and external gears differs very little. This mechanism offers advantages such as small size, light weight, compact structure, wide transmission ratio range, and high transmission efficiency, and is currently widely used in aerospace, shipbuilding, and engineering machinery industries.

[0003] The core components of a planetary gear transmission mechanism with small tooth difference are the meshing internal and external gears. Under normal operating conditions, internal and external gears made from conventional gear materials can meet the requirements after heat treatment such as carburizing, quenching, or nitriding. However, under certain special operating conditions, such as high-temperature and high-radiation conditions, in order to ensure accuracy and reduce thermal deformation and corrosion loss, internal and external gears need to have high-temperature and corrosion resistance. Among the materials commonly used in the mechanical field, stainless steel has excellent high-temperature and corrosion resistance. However, stainless steel cannot be heat-treated like conventional gear materials, such as carburizing, quenching, or nitriding. Internal and external gears machined directly from commercially available stainless steel are prone to hot brittleness and cold brittleness, and their mechanical properties, high-temperature resistance, and corrosion resistance cannot meet the requirements. In addition, stainless steel itself has high hardness and strength, making it difficult to machine. If tools and machining parameters used for conventional gear materials are used, chips are prone to sticking to the tool, which can easily lead to tool breakage, insufficient machining accuracy, and insufficient surface finish. There is no suitable or mature process in the existing technology for processing stainless steel into gears suitable for use under high temperature and strong radiation conditions. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a machining process for stainless steel gears used in planetary gear transmission mechanisms with small tooth difference. This invention achieves the above objective through the following technical solution.

[0005] A machining process for stainless steel gears used in a planetary gear transmission mechanism with a small tooth difference includes the following steps: S1, refined stainless steel ingots, are stainless steel ingots that are remelted and desulfurized and dephosphorized, and then cast into stainless steel bars. One batch of stainless steel bars is cast for each furnace of molten steel. S2, rough turning of stainless steel bars: using a tungsten-cobalt cemented carbide turning tool to turn stainless steel bars and divide the stainless steel bars into several gear blank segments. Each batch of stainless steel bars is divided into one batch of gear blank segments. During turning, the rake angle α ranges from 16 to 18°, the clearance angle β ranges from 6 to 9°, the principal cutting edge angle ranges from 40 to 80°, the secondary cutting edge angle ranges from 11 to 14°, the inclination angle λs ranges from -4 to 6°, the cutting speed ranges from 40 to 80 m / min, the feed rate ranges from 0.2 to 0.5 mm / r, the depth of cut ranges from 3 to 5 mm, and the allowance relative to the finished product ranges from 6.5 to 8.5 mm per side. Cutting fluid is continuously poured onto the contact position between the turning tool and the workpiece. The cutting fluid is an emulsion with an oil-to-water dilution ratio ranging from 1:20 to 1:18. S3, heat-treated gear blank segment: First, the gear blank segment is solution treated. The holding temperature of the solution treatment is 1025-1055℃, and the holding time is 30-45 minutes. After the holding time is completed, the gear blank segment is rapidly cooled to below 32℃ by water quenching, oil quenching or air cooling. Then, the gear blank segment is subjected to precipitation hardening aging treatment. The holding temperature of the precipitation hardening aging treatment is in the range of 480-620℃, and the holding time is in the range of more than 2 hours. Finally, the gear blank segment is air-cooled to room temperature. S4, finish turning the gear blank section. Use a tungsten-cobalt cemented carbide turning tool to turn the gear blank section. During turning, the rake angle α ranges from 20 to 25°, the clearance angle β ranges from 11 to 12°, the principal cutting edge angle ranges from 4 to 6°, the secondary cutting edge angle ranges from 4 to 6°, the inclination angle λs ranges from 0 to 4°, the cutting speed ranges from 40 to 80 m / min, the feed rate ranges from 0.1 to 0.4 mm / r, and the depth of cut ranges from 0.1 to 0.3 mm. Apply cutting fluid continuously to the contact position between the turning tool and the workpiece. The cutting fluid is an emulsion with an oil-to-water dilution ratio of 1:10 to 1:8. S5, Gear making, using gear shaping or gear hobbing to process the gear blank into gears, the gear tooth tip height coefficient ranges from 0.6 to 0.8, and both the gear shaping cutter and the gear hobbing cutter are tungsten cobalt cemented carbide tools; S6, low-temperature annealing: the gear is placed in an annealing furnace and held at a temperature of 220-280℃ for 1.5-2 hours, and then the gear is air-cooled to room temperature. S7, fine grinding, fine grinding of the surface other than the teeth to the design dimensions; S8, Gear Grinding, involves grinding the tooth profile of the gear to the finished size.

[0006] This method first remelts stainless steel ingots for desulfurization and dephosphorization treatment, then casts them into stainless steel bars. This avoids hot brittleness and cold brittleness, improving mechanical properties, high-temperature resistance, and corrosion resistance. Tungsten-cobalt carbide tools are used for cutting, effectively preventing chipping and minimizing chip and tool adhesion, thus ensuring better machining accuracy and surface finish. After rough turning, the gear blank undergoes solution treatment, precipitation hardening, and aging to enhance its hardness and strength. The machining parameters differ from those used for machining conventional gear materials and have been proven through extensive practical testing to produce high-precision gears. The combined steps of this method form a suitable and mature process for machining gears from stainless steel suitable for use under high-temperature and high-radiation conditions.

[0007] As an optimized machining process, in step S5 above, gear shaping is used for internal gears, and the nominal parameters of the gear shaping cutter are selected according to GB / T 6081-2001 standard. During gear shaping, the rake angle of the gear shaping cutter ranges from 5 to 10°, and the clearance angle ranges from 0 to 8°. For external gears, hobbing is used, and the nominal parameters of the hobbing cutter are selected according to GB / T6083-2016 standard. During hobbing, the rake angle of the hobbing cutter ranges from -1° to -2°, the clearance angle αp of the top edge ranges from 10° to 12°, and the clearance angle of the side edge is ≥3°. The hobbing cutter installation angle Φ = β ± λ, where β is the gear helix angle and λ is the hobbing cutter helix angle. When the helix direction of the hobbing cutter is the same as that of the gear being cut, "+" is used; when the helix direction of the hobbing cutter is opposite to that of the gear being cut, "-" is used. Both internal and external gears can be formed using gear shaping and gear hobbing methods. However, to ensure machining accuracy, this solution uses gear shaping for internal gears and gear hobbing for external gears. Furthermore, the various process parameters during cutting differ from those used for machining conventional gear materials. Extensive practical testing has proven that this method can produce high-precision gears.

[0008] As an optimized processing technique, step S1 above is followed by step S1a, chemical composition analysis. During casting, samples are taken for chemical composition analysis during the smelting process. After casting, samples from each batch of stainless steel bars are taken for finished product chemical composition analysis. The chemical composition analysis is performed according to ASTM A751-2021 standards. Stainless steel bars from batches whose smelting and finished product analyses both meet the set chemical composition requirements proceed to the next step. This further ensures that the processed gears meet the usage requirements.

[0009] As an optimized processing technique, step S3 above is followed by step S3a, corrosion test analysis. At least one gear blank segment from each batch is randomly selected and subjected to a macro-corrosion test according to ASTM E340. Gear blank segments from batches whose macro-corrosion test data meet the set requirements proceed to the next step. This further ensures that the processed gears meet the usage requirements.

[0010] As an optimized processing technique, step S3 above is followed by step S3b, which involves liquid penetrant testing and ultrasonic testing. Each gear blank segment undergoes 100% surface liquid penetrant testing according to the testing method specified in CAP-NDE-V7-032; each gear blank segment undergoes 100% volume ultrasonic testing according to the testing method specified in CAP-NDE-V7-032. Gear blank segments that pass both liquid penetrant and ultrasonic testing proceed to the next step. Only gear blank segments that have passed inspection and testing can proceed to subsequent precision turning and gear manufacturing steps. This approach saves processing costs and improves the yield rate.

[0011] As an optimized processing technique, step S3 above is followed by step S3c, sampling test; Brinell hardness measurement is performed on each gear blank segment, and then 2% of the gear blank segments with the highest hardness are selected from each batch of gear blank segments. A room temperature tensile test specimen, a high temperature tensile test specimen, and three impact test specimens are cut from the large diameter end of the selected gear blank segments using machining methods; 2% of the gear blank segments with the lowest hardness are selected from each batch of gear blank segments, and a room temperature tensile test specimen, a high temperature tensile test specimen, and three impact test specimens are cut from the large diameter end of the selected gear blank segments using machining methods. When cutting the specimen, the longitudinal axis of the specimen should be parallel to the main machining direction of the gear blank segment. When the diameter of the gear blank segment φ ≤ 25 mm, the longitudinal axis of the specimen should be on the centerline of the gear blank segment; when 25 mm < the diameter of the gear blank segment φ ≤ 50 mm, the longitudinal axis of the specimen should be located 12.5 mm away from the heat-treated surface of the gear blank segment; when the diameter of the gear blank segment φ > 50 mm, the longitudinal axis of the specimen should be located at half the radius of the gear blank segment. The three impact specimens should be cut side by side. The room temperature tensile specimens and the high temperature tensile specimens should be standard circular cross-section specimens with a gauge length of 50 mm and a diameter of 12.5 mm as specified in ASTM A370. The specimens should be cut according to ASTM... ASTM A370 specifies room temperature tensile testing and high temperature tensile testing. Impact specimens are prepared according to the Charpy V-notch standard impact specimens specified in ASTM A370. The V-notch axis of the specimen should be aligned and perpendicular to the most recently heat-treated surface of the gear blank. The impact specimens are subjected to Charpy V-notch impact testing according to ASTM A370. The selected gear blanks are subjected to hardness testing according to ASTM A370. The hardness test is performed near the room temperature tensile specimen or the high temperature tensile specimen, or at half the radius of the end of the gear blank. Gear blanks belonging to the batch whose Brinell hardness measurement, room temperature tensile test, high temperature tensile test, impact test, and hardness test data all meet the set requirements proceed to the next step. Only gear blanks belonging to the batch whose measurement and test data all meet the set requirements can proceed to subsequent precision turning and gear making steps. This saves process costs and improves the yield.

[0012] Compared with existing technologies, this invention has the following main advantages: First, the stainless steel ingot is remelted and desulfurized and dephosphorized before being cast into stainless steel bars, avoiding hot brittleness and cold brittleness, and improving mechanical properties, high-temperature resistance, and corrosion resistance. Tungsten-cobalt cemented carbide tools are used during cutting, effectively preventing chipping and minimizing chip and tool adhesion, thus ensuring better machining accuracy and surface finish. After rough turning, the gear blank is treated with solution treatment, precipitation hardening, and aging to enhance its hardness and strength. The cutting process parameters differ from those used for machining conventional gear materials and have been proven through extensive practical testing to produce high-precision gears. The various steps in this invention are combined to form a suitable and mature process for machining gears from stainless steel suitable for use under high-temperature and high-radiation conditions. After each step in the process, component analysis, quality inspection and testing, and sampling experiments are performed to improve the yield and ensure that the machined gears are suitable for use under high-temperature and high-radiation conditions. Attached Figure Description

[0013] Figure 1 This is a schematic cross-sectional view of the internal and external gears in the meshing state in the embodiment. Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings. The drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. To illustrate this embodiment more concisely, some components that are well-known to those skilled in the art but are not related to the main content of the present invention may be omitted in the drawings or description. In addition, for ease of description, some components in the drawings may be omitted, enlarged, or reduced, but this does not represent the actual size or complete structure of the product.

[0015] Examples, such as Figure 1 The image shows internal gear 1 and external gear 2 in a low-tooth-difference planetary gear transmission mechanism used in a nuclear power plant. The operating temperature is 150–200℃. Internal gear 1 has 64 teeth, and external gear 2 has 63 teeth; both have a module of 2.25. This embodiment uses these two gears as examples to introduce a machining process for stainless steel gears used in a low-tooth-difference planetary gear transmission mechanism, including the following steps: S1, Refined Stainless Steel Ingot. This embodiment uses stainless steel ingots with grade 05Cr17Ni4Cu4Nb under the GB / T 20878-2007 standard. The "electric arc furnace + electroslag remelting" smelting method is employed. The stainless steel ingots are remelted for precipitation desulfurization and precipitation dephosphorization treatment, and then cast into stainless steel bars. One batch of stainless steel bars is cast per furnace of molten steel. In other embodiments, the "vacuum arc remelting" smelting method can also be used. During casting, a cut-off amount is left at the beginning and end of the stainless steel bar to remove shrinkage cavities and major segregation.

[0016] S1a, Chemical Composition Analysis. Chemical composition analysis is performed on samples taken during the pouring of each heat of molten steel. After casting, chemical composition analysis is performed on samples taken from each batch of stainless steel bars. The chemical composition analysis is conducted according to ASTM A751-2021 standard. The chemical composition requirements for the smelting analysis, by mass percentage, are: C≤0.07%, Mn≤1%, P≤0.02%, S≤0.015%, Si≤1%, 15%≤Cr≤17.5%, 3%≤Ni≤5%, 3%≤Cu≤5%, 0.15%≤Nb+Ta≤0.45%, Co≤0.05%. The chemical composition requirements for the finished product analysis, by mass percentage, are as follows: C≤0.08%, Mn≤1.03%, P≤0.02%, S≤0.015%, Si≤1.05%, 14.85%≤Cr≤17.7%, 2.93%≤Ni≤5.07%, 2.9%≤Cu≤5.15%, 0.1%≤Nb+Ta≤0.5%, Co≤0.05%. Stainless steel bars from batches whose smelting and finished product analyses both meet the set chemical composition requirements proceed to the next step to further ensure that the processed gears meet the usage requirements.

[0017] S2, Rough turning of stainless steel bar. The stainless steel bar is turned using a tungsten-cobalt carbide turning tool, specifically a YG6X carbide turning tool. The stainless steel bar is divided into several gear blank segments, with one batch of gear blank segments produced from each batch of stainless steel bars. During turning, the rake angle α is 18°, the clearance angle β is 9°, the principal cutting edge angle is 50°, the secondary cutting edge angle is 13°, the inclination angle λs is 0°, the cutting speed is 55 m / min, the feed rate is 0.3 mm / r, the depth of cut is 3 mm, and the allowance relative to the finished product is 7.5 mm per side. Cutting fluid is continuously poured onto the contact area between the cutting tool and the workpiece. The cutting fluid is an emulsion diluted with oil and water at a ratio of 1:20. After turning, the cutting tool immediately leaves the cutting surface.

[0018] S3, Heat-treated gear blank segment. First, the gear blank segment is solution-treated at a temperature of 1025–1055°C for 30–45 minutes. After the solution treatment, the gear blank segment is rapidly cooled to below 32°C using oil quenching. In other embodiments, water quenching or air cooling can also be used to rapidly cool the gear blank segment. Then, the gear blank segment undergoes precipitation hardening aging treatment at a temperature of 595°C for at least 4 hours, followed by air cooling to room temperature. The oxide scale generated during heat treatment is removed by pickling or other suitable methods.

[0019] S3a, Etching Test Analysis. At least one gear blank segment from each batch is randomly selected and subjected to a macro-etching test according to ASTM E340. The acid-etched test specimens taken from the full cross-sections at both ends of the gear blank segment must be free of visible defects such as shrinkage cavities, bubbles, cracks, inclusions, white spots, and flaking. Gear blank segments from the same batch whose macro-etching test data meet the specified requirements proceed to the next step.

[0020] S3b, Liquid penetrant testing and ultrasonic testing. Each gear blank segment undergoes 100% surface liquid penetrant testing according to the testing method specified in CAP-NDE-V7-032. Each gear blank segment also undergoes 100% volume ultrasonic testing according to the testing method specified in CAP-NDE-V7-032. Gear blank segments that pass both liquid penetrant and ultrasonic testing proceed to the next step. Only gear blank segments that have passed inspection and testing can proceed to subsequent precision turning and gear manufacturing steps. This saves on process costs and improves the yield rate.

[0021] S3c, Sampling Test. Brinell hardness was measured on each gear blank segment. Then, from each batch of gear blank segments, 2% and at least one segment with the highest hardness were selected. Using machining methods, one room temperature tensile specimen, one high temperature tensile specimen, and three impact specimens were cut from the large-diameter end of the selected gear blank segment. From each batch of gear blank segments, 2% and at least one segment with the lowest hardness were selected. Using machining methods, one room temperature tensile specimen, one high temperature tensile specimen, and three impact specimens were cut from the large-diameter end of the selected gear blank segment. When taking samples, the longitudinal axis of the specimen should be parallel to the main machining direction of the gear blank segment, i.e., the grain flow direction, which is longitudinal sampling. When the diameter of the gear blank segment φ≤25mm, the longitudinal axis of the specimen should be at the center line of the gear blank segment; when 25mm<gear blank segment diameter φ≤50mm, the longitudinal axis of the specimen should be located 12.5mm away from the heat-treated surface of the gear blank segment; when the diameter of the gear blank segment φ>50mm, the longitudinal axis of the specimen should be located at half the radius of the gear blank segment. The three impact specimens should be taken side by side.

[0022] Both room temperature tensile specimens and high temperature tensile specimens were standard circular cross-section specimens with a gauge length of 50 mm and a diameter of 12.5 mm, as specified in ASTM A370. The specimens were subjected to room temperature and high temperature tensile tests according to ASTM A370. Impact specimens were prepared according to the Charpy V-notch standard impact specimen specifications of ASTM A370. The V-notch axis of the specimens should be aligned and perpendicular to the most recently heat-treated surface of the gear blank segment. The impact specimens were subjected to Charpy V-notch impact tests according to ASTM A370. Hardness tests were performed on the selected gear blank segments according to ASTM A370. Hardness tests were conducted near the room temperature or high temperature tensile specimens, or at half the radius of the end of the gear blank segment.

[0023] Gear blanks belonging to a batch whose Brinell hardness measurement, room temperature tensile test, high temperature tensile test, impact test, and hardness test data all meet the set requirements can proceed to the next step. Only gear blanks belonging to a batch whose measurement and test data all meet the set requirements can proceed to subsequent steps such as precision turning and gear making. This can save on process costs and improve the yield rate.

[0024] S4, Finish turning of the gear blank. The gear blank is turned using a tungsten-cobalt carbide turning tool, specifically a YG6X carbide turning tool. During turning, the rake angle α is 22°, the clearance angle β is 11°, the principal cutting edge angle is 5°, the secondary cutting edge angle is 5°, the inclination angle λs is 0°, the cutting speed is 75 m / min, the feed rate is 0.1 mm / r, and the depth of cut is 0.2 mm. Cutting fluid is continuously poured onto the contact area between the cutting tool and the workpiece; the cutting fluid is an emulsion with an oil-to-water dilution ratio of 1:10.

[0025] S5, Gear Manufacturing. The gear blank is machined into a gear using gear shaping or hobbing methods. The gear addendum coefficient is 0.75. Both the gear shaping cutter and the hobbing cutter are tungsten-cobalt carbide tools. For internal gear 1, gear shaping is used with a shaping accuracy of grade 5. The nominal parameters of the gear shaping cutter are selected according to GB / T 6081-2001 standard, using a tapered shank spur gear shaping cutter. The gear shaping cutter uses a YG6X carbide gear shaping cutter. During gear shaping, the rake angle of the gear shaping cutter is 6° and the clearance angle is 8°. The main process parameters for gear shaping are: stroke rate 60 strokes / min, stroke length 58 mm, circumferential feed rate 0.15 mm / stroke, and radial depth of cut 0.1–0.15 mm per stroke. For external gear 2, a hobbing method is used with a hobbing accuracy of grade 5. The nominal parameters of the hobbing cutter are selected according to GB / T6083—2016 standard, using a Type I standard gear hobbing cutter. A YG6X carbide hobbing cutter is used. During hobbing, the hobbing cutter's rake angle is -2°, the top cutting edge clearance angle αp is 10°, and the side cutting edge clearance angle is 5°. The hobbing cutter mounting angle Φ = β ± λ, where β is the gear helix angle and λ is the hobbing cutter helix angle. A "+" is used when the hobbing cutter's helix direction is the same as the helix direction of the gear being cut, and a "-" is used when the helix direction is opposite to the helix direction of the gear being cut. Among the main process parameters for hobbing, the tooth width feed is 0.15 mm per gear revolution, the radial depth is 0.1–0.15 mm per feed, and the hobbing speed is 15 m / min.

[0026] S6, Low-temperature annealing. The working temperature of the internal gear 1 and external gear 2 processed in this embodiment is 150-200℃, so the gears are placed in the annealing furnace for heat preservation at a temperature of 220-280℃ for 1.5-2 hours, and then the gears are air-cooled to room temperature.

[0027] S7, fine grinding. Align with the tooth pitch circle and fine grind the surfaces outside the teeth to the design dimensions.

[0028] S8, Gear Grinding. Gear grinding is performed using a form grinding method. The grinding wheel is dressed to the finished tooth profile, paying attention to shaping and edge trimming. The runout of the ground outer diameter is aligned to <0.01. The gear tooth profile is ground to the finished size, but the tooth root is not ground. After grinding, the surface usually needs to be inspected for flaws and polished to a roughness Ra <0.2.

[0029] In addition, the surface of the stainless steel bar or gear blank should be inspected very carefully at each stage of the machining process. The surface of the finished bar must not have scaling, cracks, folds, blemishes, porosity, or other defects that would impair its use.

[0030] In this embodiment, stainless steel ingots are first remelted and desulfurized and dephosphorized before being cast into stainless steel bars. This process avoids hot brittleness and cold brittleness, improving mechanical properties, high-temperature resistance, and corrosion resistance. Tungsten-cobalt carbide tools are used for cutting, effectively preventing chipping and minimizing chip and tool adhesion, thus ensuring better machining accuracy and surface finish. After rough turning, the gear blank is treated with solution treatment, precipitation hardening, and aging to enhance its hardness and strength. The machining parameters differ from those used for conventional gear materials and have been proven through extensive practical testing to produce high-precision gears. The steps in this embodiment are combined to form a suitable and mature process for machining gears from stainless steel suitable for use under high-temperature and high-radiation conditions. After each step in the process, component analysis, quality inspection and testing, and sampling experiments are performed to improve yield and ensure the machined gears are suitable for use under high-temperature and high-radiation conditions.

[0031] The above is only one specific embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using the design concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. A machining process for stainless steel gears used in a planetary gear transmission mechanism with a small tooth difference, characterized in that, Includes the following steps: S1, refined stainless steel ingots, are stainless steel ingots that are remelted and desulfurized and dephosphorized, and then cast into stainless steel bars. One batch of stainless steel bars is cast for each furnace of molten steel. S2, rough turning of stainless steel bars: using a tungsten-cobalt cemented carbide turning tool to turn stainless steel bars and divide the stainless steel bars into several gear blank segments. Each batch of stainless steel bars is divided into one batch of gear blank segments. During turning, the rake angle α ranges from 16 to 18°, the clearance angle β ranges from 6 to 9°, the principal cutting edge angle ranges from 40 to 80°, the secondary cutting edge angle ranges from 11 to 14°, the inclination angle λs ranges from -4 to 6°, the cutting speed ranges from 40 to 80 m / min, the feed rate ranges from 0.2 to 0.5 mm / r, the depth of cut ranges from 3 to 5 mm, and the allowance relative to the finished product ranges from 6.5 to 8.5 mm per side. Cutting fluid is continuously poured onto the contact position between the turning tool and the workpiece. The cutting fluid is an emulsion with an oil-to-water dilution ratio ranging from 1:20 to 1:

18. S3, heat-treated gear blank segment: First, the gear blank segment is solution treated. The holding temperature of the solution treatment is 1025-1055℃, and the holding time is 30-45 minutes. After the holding time is completed, the gear blank segment is rapidly cooled to below 32℃ by water quenching, oil quenching or air cooling. Then, the gear blank segment is subjected to precipitation hardening aging treatment. The holding temperature of the precipitation hardening aging treatment is in the range of 480-620℃, and the holding time is in the range of more than 2 hours. Finally, the gear blank segment is air-cooled to room temperature. S4, finish turning the gear blank section. Use a tungsten-cobalt cemented carbide turning tool to turn the gear blank section. During turning, the rake angle α ranges from 20 to 25°, the clearance angle β ranges from 11 to 12°, the principal cutting edge angle ranges from 4 to 6°, the secondary cutting edge angle ranges from 4 to 6°, the inclination angle λs ranges from 0 to 4°, the cutting speed ranges from 40 to 80 m / min, the feed rate ranges from 0.1 to 0.4 mm / r, and the depth of cut ranges from 0.1 to 0.3 mm. Apply cutting fluid continuously to the contact position between the turning tool and the workpiece. The cutting fluid is an emulsion with an oil-to-water dilution ratio of 1:10 to 1:

8. S5, Gear making, using gear shaping or gear hobbing to process the gear blank into gears, the gear tooth tip height coefficient ranges from 0.6 to 0.8, and both the gear shaping cutter and the gear hobbing cutter are tungsten cobalt cemented carbide tools; S6, low-temperature annealing: the gear is placed in an annealing furnace and held at a temperature of 220-280℃ for 1.5-2 hours, and then the gear is air-cooled to room temperature. S7, fine grinding, fine grinding of the surface other than the teeth to the design dimensions; S8, Gear Grinding, involves grinding the tooth profile of the gear to the finished size.

2. The machining process of the stainless steel gear for the planetary gear transmission mechanism with small tooth difference according to claim 1, characterized in that, In step S5, for internal gears, a gear shaping method is used. The nominal parameters of the gear shaping cutter are selected according to GB / T 6081-2001 standard. During gear shaping, the rake angle of the gear shaping cutter ranges from 5 to 10°, and the clearance angle ranges from 0 to 8°. For external gears, a gear hobbing method is used. The nominal parameters of the gear hobbing cutter are selected according to GB / T 6083-2016 standard. During gear hobbing, the rake angle of the gear hobbing cutter ranges from -1° to -2°, the clearance angle αp of the top cutting edge ranges from 10° to 12°, and the clearance angle of the side cutting edge is ≥3°. The hobbing cutter installation angle Φ = β ± λ, where β is the gear helix angle and λ is the helix angle of the gear hobbing cutter. When the helix direction of the gear hobbing cutter is the same as the helix direction of the gear being cut, "+" is used; when the helix direction of the gear hobbing cutter is opposite to the helix direction of the gear being cut, "-" is used.

3. The machining process of the stainless steel gear for the planetary gear transmission mechanism with small tooth difference according to claim 1, characterized in that, The step S1 is followed by step S1a, chemical composition analysis. During casting, samples are taken for chemical composition analysis during smelting. After casting, samples are taken from each batch of stainless steel bars for chemical composition analysis of the finished product. The chemical composition analysis is performed according to the ASTM A751-2021 standard. Stainless steel bars of batches whose smelting analysis and finished product analysis both meet the set chemical composition requirements proceed to the next step.

4. The machining process of the stainless steel gear for the planetary gear transmission mechanism with small tooth difference according to claim 1, characterized in that, Step S3 is followed by step S3a, corrosion test analysis, in which at least one gear blank is randomly selected from each batch of gear blanks and subjected to a macro-corrosion test according to ASTM E340. Gear blanks from the batch to which the macro-corrosion test data meets the set requirements proceed to the next step.

5. The machining process of the stainless steel gear for the planetary gear transmission mechanism with small tooth difference according to claim 1, characterized in that, The step S3 is followed by step S3b, which involves liquid penetration testing and ultrasonic testing. Each gear blank segment undergoes 100% surface liquid penetration testing according to the testing method specified in CAP-NDE-V7-032; each gear blank segment undergoes 100% volume ultrasonic testing according to the testing method specified in CAP-NDE-V7-032; gear blank segments that pass both liquid penetration testing and ultrasonic testing proceed to the next step.

6. The machining process of the stainless steel gear for the planetary gear transmission mechanism with small tooth difference according to claim 1, characterized in that, Step S3 is followed by step S3c, sampling test; Brinell hardness measurement is performed on each gear blank segment, and then 2% of the gear blank segments with the highest hardness are selected from each batch of gear blank segments. A room temperature tensile test specimen, a high temperature tensile test specimen, and three impact test specimens are cut from the large-diameter end of the selected gear blank segments using machining methods. Similarly, 2% of the gear blank segments with the lowest hardness are selected from each batch of gear blank segments, and a room temperature tensile test specimen, a high temperature tensile test specimen, and three impact test specimens are cut from the large-diameter end of the selected gear blank segments using machining methods. Three high-temperature tensile test specimens and three impact test specimens were prepared. When cutting the specimens, the longitudinal axis of the specimens was parallel to the main machining direction of the gear blank segment. When the diameter of the gear blank segment φ ≤ 25 mm, the longitudinal axis of the specimen was on the centerline of the gear blank segment; when 25 mm < the diameter of the gear blank segment φ ≤ 50 mm, the longitudinal axis of the specimen was located 12.5 mm from the heat-treated surface of the gear blank segment; when the diameter of the gear blank segment φ > 50 mm, the longitudinal axis of the specimen was located at half the radius of the gear blank segment. The three impact test specimens should be cut side-by-side. Both the room temperature tensile test specimens and the high-temperature tensile test specimens were prepared according to ASTM standards. The A370 standard specifies a standard circular cross-section specimen with a gauge length of 50 mm and a diameter of 12.5 mm. The specimens are subjected to room temperature tensile tests and high-temperature tensile tests according to ASTM A370. Impact specimens are prepared according to the Charpy V-notch standard impact test specifications of ASTM A370. The V-notch axis of the specimen should be aligned and perpendicular to the most recently heat-treated surface of the gear blank segment. The impact specimens are subjected to Charpy V-notch impact tests according to ASTM A370. The selected gear blank segments are subjected to hardness tests according to ASTM A370. Hardness tests are performed near the room temperature tensile specimen or the high-temperature tensile specimen, or at half the radius of the end of the gear blank segment. Gear blank segments belonging to the batch to which the Brinell hardness measurement, room temperature tensile test, high-temperature tensile test, impact test, and hardness test data all meet the set requirements proceed to the next step.

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