A method for preparing a vacuum low-temperature active brazing inner steel outer aluminum composite pin gear shell

Abstract

The present application relates to the field of precision transmission equipment manufacturing technology, and particularly relates to a preparation method of a vacuum low-temperature active brazing inner steel outer aluminum composite needle tooth shell, which comprises the following steps: 1, constructing a three-layer composite structure of a rigid inner sleeve, a filler transition layer and an aluminum outer sleeve; 2, after precise machining and pretreatment of the composite structure, performing high-vacuum three-stage stepwise temperature control low-temperature active brazing in a high-vacuum brazing furnace, grading stress relief annealing and deep cold dimensional stabilization treatment; 3, taking the end face and the center hole of the composite component as a unified precision reference, after overall closed-loop precision machining, using a high-precision coordinate grinding machine to precisely machine the needle tooth mounting hole; 4, strengthening the partitioned surface and performing safety detection. The present application realizes overall innovation from five dimensions of material system, interface structure, brazing process, heat treatment system and precision control route, and completely solves the technical problems of composite loosening, brittle phase cracking, precision loss of control, deformation out of tolerance, interface cavity and brazing defects and the like which have existed in the industry for a long time.

Description

Technical Field

[0001] This invention relates to the field of precision transmission equipment manufacturing technology, specifically to a method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle tooth shell. Background Technology

[0002] As a core functional component of industrial robots, high-end CNC machine tools, aerospace transmission systems, and precision automated production lines, the power density, dynamic response performance, transmission accuracy, noise level, service life, and reliability of RV reducers are highly dependent on the structural design, material system, interface bonding performance, and manufacturing precision of the pin gear housing.

[0003] As a key static load-bearing component inside the RV reducer, the needle tooth housing constrains the movement trajectory of the needle teeth, bears alternating meshing loads, and ensures the meshing accuracy and transmission smoothness of the cycloidal wheel. It is subjected to high torque, high speed, alternating stress, and continuous operation conditions for a long time. Therefore, it is required to have the following characteristics: high structural rigidity, high surface hardness, excellent wear resistance, low rotational inertia, high heat dissipation efficiency, high dimensional stability, and high interface bonding reliability.

[0004] Currently, the main technical solutions used for needle tooth housings in the industry are as follows, all of which have significant and difficult-to-overcome technical defects: 1. The all-steel needle tooth shell is made of bearing steel or alloy structural steel such as GCr15, 16MnCr5, and 20CrMnTi through forging, cutting, and heat treatment. It has excellent rigidity, wear resistance, and dimensional stability, but it has high density, high overall weight, and large moment of inertia. During high-speed operation, the heat dissipation efficiency is poor and the internal temperature rise is significant, which seriously restricts the improvement of the robot's dynamic response speed, acceleration performance, and power density.

[0005] 2. The all-aluminum alloy needle tooth housing is lightweight and has excellent heat dissipation performance. However, the aluminum alloy has low surface hardness, poor wear resistance, and low elastic modulus. Under long-term alternating loads, the needle tooth mounting holes are prone to wear, hole enlargement, reduction of dimensional and positional accuracy, and local plastic deformation. It cannot meet the requirements of heavy load, long life, and high precision working conditions, and can only be applied to light load, low precision, and short life transmission scenarios.

[0006] 3. Traditional interference fit, adhesive bonding, and ordinary welding composite pin tooth shell interfaces rely solely on friction, adhesive force, or local welding to achieve bonding, resulting in low bonding strength. Long-term operation is prone to problems such as circumferential relative rotation, axial movement, loosening, abnormal noise, and premature failure. The assembly stress is high, and the overall deformation after composite is difficult to control. The position, coaxiality, end face parallelism, and perpendicularity of the pin tooth holes cannot meet the precision tolerance requirements of GB / T 1804 and GB / T 1184.

[0007] 4. Direct fusion welding or metallurgical bonding of steel and aluminum at high temperatures easily generates continuous brittle intermetallic compounds such as FeAl3 and Fe2Al5, resulting in extremely poor interfacial toughness, easy cracking, delamination, and fatigue failure, which cannot meet the long-term reliability requirements of precision transmission components.

[0008] Conventional aluminum-steel brazing processes often result in excessively high brazing temperatures, leading to overheating of the aluminum matrix, coarse grains, and softening of the steel matrix during annealing. Furthermore, the brazing filler metal exhibits poor wettability, high interface porosity, and insufficient bonding strength. The lack of a mechanical interlocking structure prevents the process from withstanding large-torque alternating loads. Finally, the absence of a comprehensive precision control system for the entire heat treatment, brazing, and finishing process makes it difficult to achieve high-precision, low-deformation, and highly consistent mass production.

[0009] Therefore, existing technologies cannot simultaneously meet the seven core requirements of high wear resistance, lightweight, high bonding strength, no brittle phase, low deformation, high precision, stable and controllable process, and industrial mass production. Developing an innovative, highly reliable, high-precision, and lightweight inner steel and outer aluminum composite needle tooth shell preparation method has become the core technological breakthrough for the high-end and lightweight upgrade of RV reducers. Summary of the Invention

[0010] To address the problems existing in the prior art, the purpose of this invention is to provide an original core technology approach that achieves the following: high rigidity, high wear resistance, and high precision meshing and load-bearing of the steel inner sleeve; lightweight, high heat dissipation, and low inertia structural support of the aluminum outer sleeve; no brittle phases at the interface, high bonding strength, and never loosening; minimal overall deformation, extremely high precision, and stable and reliable performance. This is achieved through a vacuum low-temperature active brazing method for preparing a steel-aluminum composite needle-tooth shell. This method utilizes functional layered structural design, a dovetail self-locking mechanical interlocking structure, an AlSiNiRE low-temperature active brazing system, vacuum three-stage stepped temperature-controlled brazing, graded stress-relief annealing, cryogenic dimensional stabilization, and unified benchmark closed-loop precision machining.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, comprising the following steps: Step 1: Construct a three-layer composite structure consisting of a steel inner sleeve, a brazing transition layer, and an aluminum outer sleeve. The steel inner sleeve is a thin-walled, high-strength sleeve structure with evenly distributed pin-tooth mounting holes along the circumference of the inner wall. The outer wall is machined with multiple inverted trapezoidal dovetail self-locking grooves. The brazing transition layer uses Al10Si2Ni0.5RE active low-temperature brazing filler. The aluminum outer sleeve adopts a composite structure of a solid reinforcing ring and a spiral heat dissipation fin. The assembly stop surface and both end faces retain solid rigid rings, and a spiral heat dissipation groove is opened on the outer circle. Step 2: After precision machining and pretreatment of the composite structure, it is subjected to high-vacuum three-stage stepped temperature-controlled low-temperature active brazing in a high-vacuum brazing furnace, followed by graded stress-relief annealing and deep cryogenic dimensional stabilization treatment. Step 3: Using one end face of the composite component and the center hole as a unified precision datum, after overall closed-loop precision machining, the pin tooth mounting hole is precision machined using a high-precision coordinate grinding machine; Step 4: Strengthen the surface of the partition and conduct a safety test.

[0012] In the above-mentioned method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, in step 1, the width of the inverted trapezoidal dovetail self-locking groove is 2.0±0.05 mm, the depth is 1.0±0.05 mm, the side wall inclination angle is 15°, and the top and bottom of the groove are transitioned with a radius of R0.5 mm.

[0013] In the above-described method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, step 2, the precision machining of the composite structure includes: The steel inner sleeve is made of 16MnCr5 low carbon alloy carburized steel. The pin tooth mounting hole, end face, outer circle mating surface, pin tooth bottom hole, and dovetail self-locking groove of the steel inner sleeve are machined by CNC turning. The aluminum outer sleeve is made of 6061T6 aluminum alloy. The inner hole, outer circle, stepped surface, spiral heat dissipation groove and solid reinforcing ring of the aluminum outer sleeve are machined by CNC turning. The inner hole is machined with meshing teeth corresponding to the dovetail self-locking groove of the steel inner sleeve. The brazing transition layer uses Al10Si2Ni0.5RE active low-temperature brazing foil, which is uniformly wrapped around the outer circular mating surface of the steel inner sleeve. The dovetail self-locking groove is filled with brazing paste for reinforcement.

[0014] In the above-described method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, step 2 includes the following pretreatment: The steel inner sleeve is heat-treated by vacuum pulse carburizing and quenching followed by low-temperature tempering. The inner hole mating surface of the aluminum outer sleeve is treated with laser micro-roughening to form a uniform micro-uneven structure, removing the oxide film. High-vacuum plasma cleaning is then used to remove surface oil, impurities, and oxide layers. A high-precision coaxial positioning fixture is used at the brazing filler metal transition layer to control the coaxiality and end face runout of the fixture, precisely aligning and assembling the steel inner sleeve and aluminum outer sleeve, with an axial preload of 3~5kN applied.

[0015] The above-mentioned method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell involves vacuum pulse carburizing and quenching followed by low-temperature tempering heat treatment of the steel inner sleeve. The preheating temperature is 450℃, and the holding time is 60 min. The carburizing temperature is 920~930℃, the carbon potential is 1.0%~1.2%, the carburizing time is 4.0~5.0 h, and the effective hardened layer depth is 0.8~1.2 mm. High-temperature diffusion temperature: 920℃; diffusion time: 1.5~2.0h. Quenching temperature 840~850℃, high-pressure nitrogen quenching pressure 8~10 bar, cooling rate ≥25℃ / s; Tempering temperature 180~200℃, holding time 2.5~3.0h; After heat treatment, the surface hardness of the steel inner sleeve is HRC58~62, the core hardness is HRC30~38, and there is no oxidation, no decarburization, and no metallographic cracks. Precision grinding of the outer cylindrical mating surface, with dimensional tolerance of 0~+0.02mm, roundness ≤0.005mm, cylindricity ≤0.008mm, and surface roughness Ra≤0.8μm; Precision grinding of both ends, with parallelism ≤0.01mm, flatness ≤0.008mm, and perpendicularity to the outer circle ≤0.01mm.

[0016] In the above-described method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle-tooth shell, in step 2, the vacuum degree inside the high-vacuum brazing furnace is ≤5×10⁻⁶. -3 Pa, filled with high-purity argon gas for protection, the high-vacuum three-stage stepped temperature-controlled low-temperature active brazing includes: Step 2-1: Preheating stage: Heat to 280~320℃ and hold for 15 minutes to remove adsorbed gases, moisture and assembly stress; Step 2-2: Active diffusion stage: Heat to 520~540℃ and hold for 10 min. Rare earth elements activate the interface, break the oxide film, and promote interface diffusion. Steps 2-3: Low-temperature brazing stage: Heat to 580~600℃ and hold for 15~20 minutes. The brazing filler metal is fully wetted, spread, filled and diffused, completely inhibiting the formation of continuous brittle phases of FeAl3 and Fe2Al5. Steps 2-4: Gradient cooling stage: furnace cooling to 200°C at a rate of ≤3°C / min, followed by cooling to room temperature with high-purity nitrogen to avoid thermal stress and deformation.

[0017] In the above-mentioned method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, step 2, the graded stress-relief annealing and cryogenic dimensional stabilization treatment includes: Step a: Interface stress relief annealing: Heat to 180℃ and hold for 2 hours to eliminate brazing thermal stress; Step b: Stabilization and aging of aluminum jacket: Heat to 160℃ and hold for 4 hours to ensure the dimensional stability of the aluminum jacket; Step c: Cryogenic treatment: Hold at 60℃ for 1 hour to further stabilize dimensions, eliminate residual austenite, reduce internal stress, and improve accuracy retention.

[0018] In the above-mentioned method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, step 3 includes the closed-loop finishing process, which includes precision machining of the outer circle, stepped surface, and heat dissipation groove of the aluminum outer shell, precision grinding of both end faces with parallelism ≤0.008mm, flatness ≤0.006mm, end face perpendicularity ≤0.015mm, chamfering of all sharp edges with C0.3, removing burrs and flash, and eliminating stress concentration.

[0019] In the above-mentioned method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell, in step 3, when finishing the needle mounting hole, the machining process adopts micro-lubrication and cooling, the hole diameter tolerance is H6 grade, roundness ≤0.002mm, cylindricity ≤0.005mm, positional accuracy ≤4μm, and surface roughness Ra≤0.05μm.

[0020] The above-mentioned method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell includes step 4 as follows: The inner wall of the needle-tooth hole is treated with hard chrome plating, with a plating thickness of 10μm and a hardness of HV900~1000. The outer surface of the aluminum jacket is treated with hard anodizing, with an oxide film thickness of 15μm and a hardness of HV300~400; Special tooling is used to shield the assembly stop, end face, and mating surface, without surface treatment; The safety inspection includes: dimensional accuracy, geometric tolerance, surface hardness, interfacial shear strength, interfacial void ratio, coaxiality, pinhole position accuracy, surface roughness, and internal defect detection. Components are put into storage after all of them pass the inspection.

[0021] The beneficial effects of the present invention, a method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle tooth shell, are as follows: The present invention achieves comprehensive innovation from five dimensions: material system, interface structure, brazing process, heat treatment regime, and precision control route. It completely solves the technical problems that have long existed in the industry, such as composite loosening, brittle phase cracking, precision loss, deformation deviation, interface voids, and brazing defects, and meets the needs of heavy-duty, long-life, low-temperature rise, high precision, and mass industrial manufacturing of precision reducers such as RV42N. Attached Figure Description

[0022] Figure 1 This is an overall cross-sectional view of the composite needle-tooth shell of the present invention; Figure 2 This is a schematic diagram of the dovetail self-locking groove structure of the steel inner sleeve of the present invention; Figure 3 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described below in conjunction with specific embodiments and accompanying drawings.

[0024] Example 1 A method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell includes the following steps: Step 1: Construct a three-layer composite structure consisting of a steel inner sleeve 1, a brazing transition layer 4, and an aluminum outer sleeve 2. The steel inner sleeve is a thin-walled, high-strength sleeve structure with pin-tooth mounting holes 5 evenly distributed along the circumference of the inner wall. The outer wall is machined with multiple inverted trapezoidal dovetail self-locking grooves 6. The brazing transition layer uses Al10Si2Ni0.5RE active low-temperature brazing filler. The aluminum outer sleeve adopts a composite structure of a solid reinforcing ring 3 and a spiral heat dissipation fin. The assembly stop surface and both end faces retain solid rigid rings, and a spiral heat dissipation groove is opened on the outer circle.

[0025] Step 2: After precision machining and pretreatment of the composite structure, it is subjected to high-vacuum three-stage stepped temperature-controlled low-temperature active brazing in a high-vacuum brazing furnace, followed by graded stress-relief annealing and deep cryogenic dimensional stabilization treatment.

[0026] Step 3: Using one end face of the composite component and the center hole as a unified precision datum, after overall closed-loop precision machining, the pin tooth mounting hole is precision machined using a high-precision coordinate grinding machine.

[0027] Step 4: Strengthen the surface of the partition and conduct a safety test.

[0028] Example 2 like Figures 1-3 As shown, a method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle tooth shell includes the following steps.

[0029] S1: Composite structure topology optimization and interface dovetail self-locking structure design.

[0030] A three-layer composite structure is constructed, consisting of a steel inner sleeve 1, a brazing filler transition layer 4, and an aluminum outer sleeve 2. The steel inner sleeve is a thin-walled, high-strength sleeve structure with evenly distributed pin-tooth mounting holes 5 along the circumference of the inner wall. The outer wall is machined with multiple inverted trapezoidal dovetail self-locking grooves 6, with a groove width of 2.0±0.05mm, a groove depth of 1.0±0.05mm, and a side wall inclination angle of 15°. The top and bottom of the grooves are transitioned with a radius of 0.5mm to achieve dual mechanical locking of circumferential anti-torsional self-locking and axial anti-migration. The brazing filler transition layer uses Al10Si2Ni0.5RE active low-temperature brazing filler with a thickness of 0.08~0.12mm. Ni and rare earth RE elements are added to the brazing filler to inhibit the formation of brittle intermetallic compounds, improve interface wettability, reduce brazing temperature, and improve interface bonding strength. The aluminum outer sleeve adopts a composite structure of solid reinforcing rings and spiral heat dissipation fins. A 6mm solid rigid ring is retained on the assembly stop surface and both end faces, and spiral heat dissipation grooves are opened on the outer circle to maximize lightweight, maintain structural rigidity, and significantly improve heat dissipation efficiency.

[0031] S2: Precision machining and vacuum carburizing and quenching strengthening of the steel inner sleeve.

[0032] The inner steel sleeve is made of 16MnCr5 low-carbon alloy carburizing steel; the pin tooth mounting holes, end faces, outer cylindrical mating surfaces, pin tooth bottom holes, and dovetail self-locking grooves are CNC turned; vacuum pulse carburizing and quenching + low-temperature tempering heat treatment is adopted: preheating temperature 450℃, holding time 60 min; carburizing temperature 920~930℃, carbon potential 1.0%~1.2%, carburizing time 4.0~5.0 h, effective hardened layer depth 0.8~1.2 mm; high-temperature diffusion temperature 920℃, diffusion time 1.5~2.0 h; quenching temperature 840~850℃, high-pressure nitrogen quenching pressure 8~10 bar, cooling rate ≥25℃ / s; tempering temperature 180~200℃, holding time 2.5~3.0 h. h; After heat treatment, the surface hardness of the steel inner sleeve is HRC58~62, the core hardness is HRC30~38, and there is no oxidation, no decarburization, and no metallographic cracks; the outer cylindrical mating surface is precision ground with a dimensional tolerance of 0~+0.02 mm, roundness ≤0.005 mm, cylindricity ≤0.008 mm, and surface roughness Ra≤0.8 μm; the two end faces are precision ground with parallelism ≤0.01 mm, flatness ≤0.008 mm, and perpendicularity to the outer circle ≤0.01 mm.

[0033] S3: Precision machining of aluminum jacket and interface activation treatment.

[0034] The aluminum jacket is made of 6061T6 aluminum alloy; the inner hole, outer circle, stepped surface, spiral heat dissipation groove, and solid reinforcing ring 3 are CNC turned; the inner hole is machined with dovetail self-locking grooves corresponding to the steel inner sleeve to form meshing teeth with a clearance ≤0.02 mm; the inner hole mating surface is treated with laser micro-roughening to form a uniform micro-concave-convex structure, remove oxide film, and improve brazing filler metal wettability; high vacuum plasma cleaning for 15 min is used to remove surface oil, impurities, and oxide layer to ensure ultra-high interface cleanliness.

[0035] S4: Pre-positioning of active solder and high-precision coaxial positioning assembly.

[0036] The brazing filler metal uses Al10Si2Ni0.5RE active low-temperature brazing filler metal foil with a thickness of 0.10 mm. The brazing filler metal foil is evenly wrapped around the outer circular mating surface of the steel inner sleeve, and the dovetail self-locking groove is filled with brazing paste for reinforcement. A high-precision coaxial positioning fixture is used, with a fixture coaxiality ≤0.005 mm and end face runout ≤0.008 mm. The steel inner sleeve and aluminum outer sleeve are precisely aligned and assembled, and an axial preload of 3~5 kN is applied to ensure that the interface is tightly fitted, without gaps or misalignment.

[0037] S5: High-vacuum three-stage stepped temperature-controlled low-temperature active brazing.

[0038] Brazing is performed in a high-vacuum brazing furnace with a vacuum level ≤5×10⁻⁶. -3Pa, filled with high-purity argon for protection; 1) Preheating stage: heat up to 280~320℃, hold for 15 min to remove adsorbed gas, moisture and assembly stress; 2) Activated diffusion stage: heat up to 520~540℃, hold for 10 min to activate the interface with rare earth elements, break the oxide film and promote interface diffusion; 3) Low temperature brazing stage: heat up to 580~600℃, hold for 15~20 min to fully wet, spread, fill and diffuse the brazing filler metal, and completely inhibit the formation of continuous brittle phases of FeAl3 and Fe2Al5; 4) Gradient cooling stage: furnace cool to 200℃ at a rate of ≤3℃ / min, fill with high-purity nitrogen and cool to room temperature to avoid thermal stress and deformation.

[0039] S6: Graded stress-relief annealing and cryogenic dimensional stabilization treatment.

[0040] 1) Interface stress relief annealing: Heat to 180℃ and hold for 2 hours to eliminate brazing thermal stress; 2) Aluminum jacket stabilization aging: Heat to 160℃ and hold for 4 hours to ensure the dimensional stability of the aluminum jacket; 3) Cryogenic treatment: Hold at 60℃ for 1 hour to further stabilize dimensions, eliminate residual austenite, reduce internal stress, and improve accuracy retention.

[0041] S7: Unified benchmark overall closed-loop precision machining.

[0042] Using the end face and center hole of the composite component as a unified precision datum; precision machine the outer circle, stepped surface, and heat dissipation groove of the aluminum outer sleeve, with dimensional tolerances in accordance with GB / T 1804m; precision grind both end faces, with parallelism ≤0.008 mm, flatness ≤0.006 mm, and end face perpendicularity ≤0.015 mm; all sharp edges are chamfered to C0.3 to remove burrs and flash, and to eliminate stress concentration.

[0043] S8: Ultra-precision machining of needle tooth mounting hole coordinates on a grinding machine.

[0044] The pin tooth mounting holes are precision machined using a high-precision coordinate grinding machine; the hole diameter tolerance is H6 grade; roundness ≤ 0.002 mm; cylindricity ≤ 0.005 mm; position accuracy ≤ 4 μm; surface roughness Ra ≤ 0.05 μm; micro-lubrication and cooling are used during the machining process to avoid thermal deformation.

[0045] S9: Partitioned surface strengthening treatment and full performance testing.

[0046] The inner wall of the pinhole is hard chrome plated with a thickness of 10 μm and a hardness of HV900~1000; the outer surface of the aluminum jacket is hard anodized with an oxide film thickness of 15 μm and a hardness of HV300~400; the assembly stop, end face, and mating surface are shielded by special tooling and are not surface treated; the finished product inspection includes: dimensional accuracy, geometric tolerance, surface hardness, interfacial shear strength, interfacial void ratio, coaxiality, pinhole position accuracy, surface roughness, and internal defect detection. Only after all of them pass the inspection can the product be put into storage.

[0047] The composite needle shell prepared by the above-mentioned vacuum low-temperature active brazing method for inner steel and outer aluminum composite needle shells has optimal functional layering and synergy. The steel inner sleeve achieves high wear resistance, high rigidity, and high precision meshing load bearing; the aluminum outer sleeve achieves lightweight, high heat dissipation, and low rotational inertia. Compared with all-steel needle shells, it reduces weight by 35%~42% and reduces temperature rise by 20~30℃ at high speed.

[0048] The interface features a double-locking mechanism that will never come loose. The dovetail mechanical self-locking structure combined with active brazing metallurgical composite effect ensures an interface shear strength of ≥105MPa. During long-term operation, there is no relative rotation, no axial movement, no loosening, and no abnormal noise.

[0049] Completely eliminates brittle phases; low-temperature brazing + Ni / RE composite filler metal completely inhibits the formation of continuous FeAl brittle compounds, improving interface toughness by more than 350%, resulting in no cracks, no delamination, and no fatigue failure.

[0050] It has extremely high precision and permanent stability, with composite deformation ≤0.008mm / 100mm, coaxiality ≤0.008mm, pin tooth hole position accuracy ≤4μm, and precision retention improved by more than 50%.

[0051] The process is stable and can be mass-produced without the need for 3D printing equipment. It can be mass-produced using a traditional vacuum brazing furnace, and the cost is only 1 / 5 of that of SLM bimetallic printing, with a yield rate of ≥99%.

[0052] The interface void ratio is extremely low, and the active solder has excellent wettability. The interface void ratio is ≤1.0%, which is far superior to the industry standard.

[0053] Example 3 RV42N is being mass-produced industrially.

[0054] S1: Construct a composite structure of steel inner sleeve, brazing filler layer, and aluminum outer sleeve. The dovetail groove of the steel sleeve is 2.0mm wide and 1.0mm deep. The aluminum sleeve is equipped with a 6mm solid reinforcing ring and spiral heat dissipation fins.

[0055] S2: The inner sleeve of 16MnCr5 steel is vacuum carburized and quenched, with a surface hardness of HRC59~61, and the outer diameter is precision ground to φ148.00~φ148.02 mm.

[0056] S3: Laser micro-roughening of the inner hole of 6061 aluminum sleeve + plasma cleaning.

[0057] S4: Pre-placed Al10Si2Ni0.5RE solder foil, coaxial tooling assembly, axial preload 4kN.

[0058] S5: Vacuum brazing: Vacuum degree 3×10 -3 Pa, 590℃ for 18 min, then gradient cooling.

[0059] S6: Stress relief at 180℃ + aging at 160℃ + cryogenic treatment at 60℃.

[0060] S7: Precision turning and grinding according to unified standards, with an end face parallelism of 0.008mm.

[0061] S8: Grind the needle tooth hole to φ8H6, positional accuracy 4μm, Ra 0.05μm.

[0062] S9: The pinholes are plated with hard chrome for 10μm, and the aluminum sleeve is hard anodized for 15μm. All parts pass inspection.

[0063] The above embodiments are merely illustrative of the structural concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle-tooth shell, characterized in that, Includes the following steps: Step 1: Construct a three-layer composite structure consisting of a steel inner sleeve, a brazing transition layer, and an aluminum outer sleeve. The steel inner sleeve is a thin-walled, high-strength sleeve structure with evenly distributed pin-tooth mounting holes along the circumference of the inner wall. The outer wall is machined with multiple inverted trapezoidal dovetail self-locking grooves. The brazing transition layer uses Al10Si2Ni0.5RE active low-temperature brazing filler. The aluminum outer sleeve adopts a composite structure of a solid reinforcing ring and a spiral heat dissipation fin. The assembly stop surface and both end faces retain solid rigid rings, and a spiral heat dissipation groove is opened on the outer circle. Step 2: After precision machining and pretreatment of the composite structure, it is subjected to high-vacuum three-stage stepped temperature-controlled low-temperature active brazing in a high-vacuum brazing furnace, followed by graded stress-relief annealing and deep cryogenic dimensional stabilization treatment. Step 3: Using one end face of the composite component and the center hole as a unified precision datum, after overall closed-loop precision machining, use a high-precision coordinate grinding machine to precision machine the pin tooth mounting hole; Step 4: Strengthen the partitioned surface and conduct a safety test.

2. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle-tooth shell according to claim 1, characterized in that, In step 1, the inverted trapezoidal dovetail self-locking groove has a groove width of 2.0±0.05 mm, a groove depth of 1.0±0.05 mm, a side wall inclination angle of 15°, and a groove top and bottom with a radius of 0.5 mm.

3. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell according to claim 1, characterized in that, In step 2, the precision machining of the composite structure includes: The steel inner sleeve is made of 16MnCr5 low carbon alloy carburized steel. The pin tooth mounting hole, end face, outer circle mating surface, pin tooth bottom hole, and dovetail self-locking groove of the steel inner sleeve are machined by CNC turning. The aluminum outer sleeve is made of 6061T6 aluminum alloy. The inner hole, outer circle, stepped surface, spiral heat dissipation groove and solid reinforcing ring of the aluminum outer sleeve are machined by CNC turning. The inner hole is machined with meshing teeth corresponding to the dovetail self-locking groove of the steel inner sleeve. The brazing transition layer uses Al10Si2Ni0.5RE active low-temperature brazing foil, which is uniformly wrapped around the outer circular mating surface of the steel inner sleeve. The dovetail self-locking groove is filled with brazing paste for reinforcement.

4. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell according to claim 3, characterized in that, In step 2, the preprocessing includes: The steel inner sleeve is heat-treated by vacuum pulse carburizing and quenching followed by low-temperature tempering. The inner hole mating surface of the aluminum outer sleeve is treated with laser micro-roughening to form a uniform micro-uneven structure, removing the oxide film. High-vacuum plasma cleaning is then used to remove surface oil, impurities, and oxide layers. A high-precision coaxial positioning fixture is used at the brazing filler metal transition layer to control the coaxiality and end face runout of the fixture, precisely aligning and assembling the steel inner sleeve and aluminum outer sleeve, with an axial preload of 3~5kN applied.

5. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell according to claim 4, characterized in that, When the steel inner sleeve is subjected to vacuum pulse carburizing and quenching followed by low-temperature tempering heat treatment, the preheating temperature is 450℃ and the holding time is 60 min; the carburizing temperature is 920~930℃, the carbon potential is 1.0%~1.2%, the carburizing time is 4.0~5.0 h, and the effective hardened layer depth is 0.8~1.2 mm. High-temperature diffusion temperature: 920℃; diffusion time: 1.5~2.0h. Quenching temperature 840~850℃, high-pressure nitrogen gas quenching pressure 8~10 bar, cooling rate ≥25℃ / s; Tempering temperature 180~200℃, holding time 2.5~3.0h; After heat treatment, the surface hardness of the steel inner sleeve is HRC58~62, the core hardness is HRC30~38, and there is no oxidation, no decarburization, and no metallographic cracks. Precision grinding of the outer cylindrical mating surface, with dimensional tolerance of 0~+0.02mm, roundness ≤0.005mm, cylindricity ≤0.008mm, and surface roughness Ra≤0.8μm; Precision grinding of both ends, with parallelism ≤0.01mm, flatness ≤0.008mm, and perpendicularity to the outer circle ≤0.01mm.

6. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell according to claim 1, characterized in that, In step 2, the vacuum degree inside the high-vacuum brazing furnace is ≤5×10⁻⁶. -3 Pa, filled with high-purity argon gas for protection, the high-vacuum three-stage stepped temperature-controlled low-temperature active brazing includes: Step 2-1: Preheating stage: Heat to 280~320℃ and hold for 15 minutes to remove adsorbed gases, moisture and assembly stress; Step 2-2: Active diffusion stage: Heat to 520~540℃ and hold for 10 min. Rare earth elements activate the interface, break the oxide film, and promote interface diffusion. Steps 2-3: Low-temperature brazing stage: Heat to 580~600℃ and hold for 15~20 minutes. The brazing filler metal is fully wetted, spread, filled and diffused, completely inhibiting the formation of continuous brittle phases of FeAl3 and Fe2Al5. Steps 2-4: Gradient cooling stage: furnace cooling to 200°C at a rate of ≤3°C / min, followed by cooling to room temperature with high-purity nitrogen to avoid thermal stress and deformation.

7. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle-tooth shell according to claim 1, characterized in that, In step 2, the graded stress-relief annealing and cryogenic dimensional stabilization treatment includes: Step a: Interface stress relief annealing: Heat to 180℃ and hold for 2 hours to eliminate brazing thermal stress; Step b: Stabilization and aging of aluminum jacket: Heat to 160℃ and hold for 4 hours to ensure the dimensional stability of the aluminum jacket; Step c: Cryogenic treatment: Hold at 60℃ for 1 hour to further stabilize dimensions, eliminate residual austenite, reduce internal stress, and improve accuracy retention.

8. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell according to claim 1, characterized in that, In step 3, the closed-loop finishing includes precision turning of the outer circle of the aluminum jacket, the stepped surface, and the heat dissipation groove; precision grinding of both end faces with parallelism ≤0.008mm, flatness ≤0.006mm, and end face perpendicularity ≤0.015mm; blunting of all sharp edges to C0.3; removal of burrs and flash; and elimination of stress concentration.

9. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle shell according to claim 1, characterized in that, In step 3, when finishing the needle mounting hole, the machining process uses micro-lubrication and cooling, with hole diameter tolerance grade H6, roundness ≤0.002mm, cylindricity ≤0.005mm, positional accuracy ≤4μm, and surface roughness Ra≤0.05μm.

10. The method for preparing a vacuum low-temperature active brazing inner steel and outer aluminum composite needle-tooth shell according to claim 1, characterized in that, Step 4 includes: The inner wall of the needle-tooth hole is treated with hard chrome plating, with a plating thickness of 10μm and a hardness of HV900~1000. The outer surface of the aluminum jacket is treated with hard anodizing, with an oxide film thickness of 15μm and a hardness of HV300~400; Special tooling is used to shield the assembly stop, end face, and mating surface, without surface treatment; The safety inspection includes: dimensional accuracy, geometric tolerance, surface hardness, interfacial shear strength, interfacial void ratio, coaxiality, pinhole position accuracy, surface roughness, and internal defect detection. Components are put into storage after all of them pass the inspection.

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