A special cross-roller bearing salt spray resistant high anti-rust composite processing method for robots

Abstract

The application relates to the technical field of precision bearing composite machining, and discloses a salt-fog-resistant high-rust-resisting composite machining method for crossed roller bearings special for robots, which comprises the following steps: S1, pretreatment: adopting GCr15 bearing steel material to perform hot forging forming machining; S2, rough machining and heat treatment: performing rough turning and finish turning machining on a bearing ring blank, and adopting a vacuum quenching and low-temperature tempering composite heat treatment process to perform treatment after finish turning is completed; S3, semi-finish grinding machining: performing semi-finish grinding machining on an outer circle and a raceway of the bearing ring after heat treatment; S4, QPQ treatment: performing QPQ salt bath nitriding and oxidation composite treatment on the semi-finish ground ring; S5, finish grinding machining: performing finish grinding machining on an outer circle, a raceway and an inner circle of the treated ring, and the total machining allowance of finish grinding is controlled to be 3-5 micrometers; and S6, post-treatment step; the method solves the technical problems that the existing crossed roller bearings for robots are prone to rust under special working conditions such as high humidity and marine climate, and the conventional rust-proof means cannot consider the bearing precision, rigidity and long-acting rust-proof.

Description

Technical Field

[0001] This invention belongs to the field of precision bearing composite machining technology, specifically relating to a salt spray resistant and rust-resistant composite machining method for robot-specific crossed roller bearings. Background Technology

[0002] Crossed roller bearings for robot joints are used in the rotary joints of humanoid robots, quadruped robots, and industrial robots. The positioning accuracy of the robot depends on the accuracy of the crossed roller bearings in this part, so high rigidity, high rotational accuracy and long service life are required.

[0003] Under normal operating conditions, existing crossed roller bearings can meet the requirements. However, in high humidity, marine climates, chemical environments, and outdoor conditions, the bearings are prone to corrosion, leading to: 1. Decreased bearing rotation accuracy, and in severe cases, jamming or seizing. 2. Reduced bearing rigidity and inaccurate positioning accuracy; 3. In a salt spray environment, problems such as pitting corrosion, rust spots, and material peeling may occur in the short term; 4. Lifespan is significantly shortened.

[0004] Existing rust prevention methods have the following defects and shortcomings: 1. Using surface electroplating processes (conventional electroplating processes include chromium plating, nickel plating, zinc plating, and zinc-nickel alloy plating) will reduce the precision of the bearing after electroplating, making it impossible to perform secondary processing. Secondary processing will damage the electroplating layer and cause it to lose its rust-proof ability.

[0005] 2. Poor adhesion between the electroplated layer and the bearing surface after electroplating leads to peeling of the electroplated layer during use, indirectly causing bearing failure.

[0006] 3. Using ordinary rust-preventive oil results in a short salt spray test time, usually less than a few hours.

[0007] 4. Other surface treatment processes such as oxidation and spraying will lead to a decrease in surface quality after surface treatment. After direct assembly, the precision of the finished bearing cannot meet the P4 grade requirements. Further processing after surface treatment will damage the rust prevention performance.

[0008] Therefore, there is an urgent need for a composite machining method that balances precision, rigidity, and long-term rust prevention for cross roller bearings used in robot joints. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a composite processing method for salt spray resistant and rust-resistant cross roller bearings for robots, thereby solving the technical problem that existing robot cross roller bearings are prone to corrosion under special working conditions such as high humidity and marine climate, and that conventional rust prevention methods cannot simultaneously ensure bearing precision, rigidity, and long-term rust prevention.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A composite machining method for salt spray resistant and rust-resistant cross roller bearings for robots includes the following steps: S1 Pretreatment: GCr15 bearing steel is used for hot forging to effectively remove defects such as porosity, looseness and segregation in the billet, and to form a dense internal metal structure to form a bearing ring blank. S2 Rough machining and heat treatment: The bearing ring blank obtained in step S1 is rough turned and finish turned to effectively remove defects such as porosity, looseness and segregation in the blank and to make the internal structure of the metal dense. After finish turning, vacuum quenching and low temperature tempering composite heat treatment process is used. S3 Semi-finish grinding: The bearing rings after heat treatment in step S2 are semi-finish ground on the outer diameter and raceway. S4 QPQ treatment: The bearing ring after semi-fine grinding in step S3 is subjected to QPQ salt bath nitriding and oxidation composite treatment to form a double-layer anti-rust composite layer of "compound bright layer + diffusion layer" on the bearing surface. S5 Precision Grinding: The outer circle, raceway, and inner circle of the ring after step S4 are precision ground. The total machining allowance for precision grinding is controlled at 3-5μm. Only the micro-deformation layer on the surface of the ring is removed to avoid grinding through the compound white bright layer. This ensures that the final ring surface retains a white bright layer of ≥5μm to ensure rust prevention. In other words, the micro-deformation of QPQ treatment is offset by precision grinding with a small allowance to ensure the P4 grade accuracy of the bearing, while retaining a sufficiently thick rust-proof composite layer. S6 Post-processing: After fine grinding, the bearing rings are ultrasonically cleaned with a cleaning agent to thoroughly remove grinding debris and residual grinding fluid from the surface of the rings. After cleaning, they are dried with hot air to ensure that the surface of the rings is clean and dry. After drying, the rings are immersed in environmentally friendly rust-preventive oil for sealing treatment, so that the rust-preventive oil fully fills the micro gaps on the surface of the rings and forms an oil film protective layer. After immersion, the excess rust-preventive oil is drained, and the bearing ring processing is completed.

[0011] Preferably, in step S2, the outer diameter and inner raceway of the bearing ring after rough turning and finish turning are reserved with a margin of 0.15-0.20mm.

[0012] Preferably, the composite heat treatment process in step S2 is as follows: first, quenching is performed in a vacuum environment, and the holding time is 60-90 min, depending on the wall thickness of the ring, which is 10-90 mm; then, three low-temperature temperings are performed, with a tempering temperature of 160-180℃ and a holding time of 120 min for each tempering, and the ring is cooled to room temperature in the furnace after tempering.

[0013] Preferably, the quenching temperature is 840-860℃, and the quenching cooling medium is high-speed nitrogen.

[0014] This step ensures the bearing ring hardness meets the standard through vacuum quenching, and three low-temperature tempering processes fully eliminate quenching internal stress, effectively improving the dimensional stability of the bearing ring. Ultimately, the bearing ring hardness is strictly controlled within HRC58-60 to meet the high rigidity requirements of robot bearings.

[0015] Preferably, in step S3, the surface roughness Ra of the ring after semi-finishing is controlled to be ≤0.8μm, and a machining allowance of 0.015-0.025mm is reserved.

[0016] This machining allowance includes the deformation allowance after QPQ treatment and the allowance for subsequent fine grinding. The specific reason for setting it is as follows: A. Surface roughness Ra≤0.8μm: Ensure that the surface of the ring is free of obvious processing scratches and burrs, providing a flat base for subsequent QPQ treatment, and avoiding uneven thickness and reduced adhesion of the anti-rust layer after QPQ treatment due to surface defects; B. Total machining allowance 0.015-0.025mm: This allowance is a reasonable ratio of QPQ treatment deformation allowance + subsequent fine grinding machining allowance, in which QPQ treatment deformation allowance accounts for 60%-70% and fine grinding machining allowance accounts for 30%-40%. This ratio can both offset the micro deformation of the ring during QPQ treatment and reserve sufficient correction allowance for subsequent fine grinding, while avoiding excessive allowance that would cause subsequent fine grinding to wear through the anti-rust composite layer.

[0017] Preferably, the QPQ salt bath nitriding and oxidation composite treatment in step S4 includes the following steps: S41: Ultrasonic degreasing is used at a temperature of 65-85℃ for 20-25 minutes to thoroughly remove cutting fluid, oil, and dust from the surface of the raceway. After degreasing, hot air drying is performed at a temperature of 80-110℃ for 10-15 minutes to ensure that there is no moisture residue on the surface of the raceway and to avoid pinholes and bubbles during the nitriding process. S42 Salt Bath Nitriding: The pretreated rings are placed in a nitriding salt bath furnace. The nitriding temperature is controlled at 560-580℃ and the nitriding time is 110-130min. Through the penetration and diffusion of nitrogen atoms, a dense compound layer is formed on the surface of the rings. S43 Salt Bath Oxidation: After nitriding, the ring is transferred into an oxidation salt bath furnace. The oxidation temperature is controlled at 380-395℃ and the oxidation time is 25-40 minutes. A thin and dense oxide film is formed on the surface of the compound layer, which improves the rust prevention performance.

[0018] In step S42, the compound layer has a thickness of 11-16 μm, and its main components are Fe3N and Fe4N. In step S43, the oxide film has a thickness of 110-130 μm. The double-layer structure is metallurgically bonded to the bearing steel substrate, with strong adhesion and no risk of peeling.

[0019] Preferably, the fine grinding process in step S5 includes the following steps: S51 Grinding allowance allocation: The machining allowance of the outer circle of the ring after step S4 is controlled at 0.02-0.05mm, and the machining allowance of the inner raceway of the ring is controlled at 0.01-0.03mm, to accommodate the difference in deformation in different parts; S52: The grinding process is combined with a high-performance fully synthetic metalworking fluid to avoid grinding heat during the grinding process, which may cause micro-deformation of the ring, and at the same time prevent grinding debris from scratching the surface of the ring. S53 Grinding Wheel Selection: Select the appropriate grinding wheel and grinding machine based on the outer diameter and inner raceway of the raceway; S54 Grinding Parameters: Select parameters for external cylindrical grinding machines and grooved grinding machines respectively. The parameters include grinding wheel linear speed, workpiece rotation speed, fine grinding feed, fine grinding speed, finishing grinding amount and finishing grinding delay. S55: Select the appropriate processing technology to complete the fine grinding.

[0020] Preferably, step S55 includes the following steps: S551 Grinding Wheel Dressing: Diamond single-point dressing pen, correction amount 6μ / time, dressing speed adapted to grinding wheel linear speed, ensuring smooth grinding surface and improving grinding accuracy; S552: The external cylindrical grinding uses an electromagnetic centerless chuck, and the raceway grinding uses a floating support chuck. The clamping runout is ≤1μ, which avoids clamping stress from causing deformation of the ring and local grinding through the QPQ anti-rust layer during grinding. S553: ​​Grinding wheel spindle vibration value ≤1.5μ, to prevent grinding marks caused by grinding wheel vibration during grinding and to ensure the surface quality of the bearing ring.

[0021] Preferably, the sealing treatment time in step S6 is within 30 minutes after drying, and the soaking time is 10-15 minutes.

[0022] Compared with the prior art, the beneficial effects of the present invention are: The processing method of this invention, through precise process design and parameter matching at each step, completely solves the core pain points of existing technologies, achieving three performance guarantees: "high precision, high rigidity, and long-lasting rust prevention"; and all performance indicators have been verified through actual testing. Specifically: 1. Balancing P4-level high precision with long-lasting rust prevention, resolving the core contradiction of "the incompatibility between rust prevention and precision": Through the innovative process of "semi-fine grinding + QPQ treatment + 3-5μ small-allowance fine grinding", a long-lasting anti-rust composite layer is first formed through QPQ treatment, and then the micro-deformation of QPQ treatment is corrected through small-allowance fine grinding. In the end, the surface roughness Ra of the bearing ring is guaranteed to be ≤0.2μm, and all accuracy meets the P4 level rotational accuracy requirements. At the same time, a compound white bright layer of ≥5μm is retained after fine grinding, without damaging the structure of the anti-rust composite layer. This process achieves dual protection of accuracy and rust prevention.

[0023] 2. The anti-rust layer has strong adhesion, is wear-resistant and corrosion-resistant, and its salt spray anti-rust performance is improved by more than 6 times: The bright white layer and diffusion layer formed by QPQ treatment are metallurgically bonded to the GCr15 bearing steel substrate, with a bonding strength ≥50N / mm², which is much stronger than the physical bonding of electroplating layers. There is no risk of coating peeling during high-frequency rotation and vibration of robot joints. In addition, the bright white layer itself has a hardness ≥HV800 and high wear resistance, which complements the high rigidity of GCr15 bearing steel, solving the problems of pitting corrosion, rust spots and material peeling under special working conditions from the root.

[0024] 3. The bearings exhibit excellent dimensional stability and overall performance, resulting in a significantly extended service life under special operating conditions: A adopts a vacuum quenching + three-stage low-temperature tempering process to fully eliminate internal stress. The dimensional deformation of the bearing ring is ≤4μ in the temperature range of -40℃ to 80℃, and the dimensional stability is excellent. Hot forging of material B pretreatment makes the metal structure dense. Combined with QPQ surface strengthening treatment, the overall rigidity of the bearing is increased by more than 15%, and the wear resistance is increased by more than 20%. In the durability test under simulated marine climate conditions, the bearings processed by this technology have a continuous operating life of ≥8000 hours, which is more than 3 times longer than the service life of existing bearings.

[0025] 4. The process is environmentally friendly, highly operable, and suitable for large-scale mass production: The entire processing technology uses environmentally friendly salt bath agents, phosphate-free cleaning agents, and environmentally friendly rust-preventive oils, with no heavy metals, harmful exhaust gases, or wastewater discharge, and complies with national environmental emission standards. B. The parameters of each process step are clear and controllable, requiring no special equipment, and can be directly adapted to minor modifications of existing bearing processing production lines; The C process has good repeatability and a yield of ≥98%, meeting the needs of large-scale, high-precision machining and manufacturing of robot bearings, and possesses good industrial application value and market prospects. Detailed Implementation

[0026] The core process of this invention, "QPQ treatment + small-margin precision grinding", has good process adaptability. It can be used not only for cross roller bearings of robot joints, but also for the processing and manufacturing of other precision shafts of humanoid robots and industrial robots. Only the nitriding / oxidation temperature and time parameters of QPQ treatment need to be adjusted according to the bearing substrate material and actual working conditions, all of which are within the scope of this processing technology concept.

[0027] Bearings processed using this technology are not only suitable for the robotics field, but can also be extended to marine equipment, outdoor engineering machinery, chemical equipment, and other fields that require high-precision, long-lasting rust-proof bearings, making them widely applicable.

[0028] First Embodiment

[0029] A composite machining method for salt spray resistant and rust-resistant cross roller bearings for robots includes the following steps: S1 Pretreatment: GCr15 bearing steel is used for hot forging to effectively remove defects such as porosity, looseness and segregation in the billet, and to form a dense internal metal structure to form a bearing ring blank. S2 Rough Machining and Heat Treatment: The bearing ring blank obtained in step S1 is rough turned and finish turned. Rough turning removes most of the machining allowance, and finish turning ensures the basic dimensional accuracy of the ring's shape and inner hole, leaving a reasonable finishing allowance for subsequent grinding (0.15-0.20mm allowance for outer diameter and inner raceway). After finish turning, a vacuum quenching and low-temperature tempering combined heat treatment process is used. The composite heat treatment process is as follows: First, quenching is performed in a vacuum environment at a temperature of 840-860℃. The holding time is set according to the wall thickness of the ring, i.e., the ring wall thickness is 10-90mm and the holding time is 60-90min. The quenching cooling medium is high-speed nitrogen to ensure uniform cooling of the ring and avoid quenching deformation. Then, three low-temperature tempering processes are performed at a temperature of 160-180℃, with each tempering holding time of 120min. After tempering, the ring is cooled to room temperature in the furnace. S3 Semi-finish grinding: The bearing ring after heat treatment in step S2 is semi-finish ground on the outer circle and raceway. The surface roughness Ra of the ring after semi-finish grinding is controlled to be ≤0.8μm. A machining allowance of 0.015-0.025mm is reserved. The machining allowance includes the deformation allowance after QPQ treatment and the allowance for subsequent fine grinding. S4 QPQ treatment: The rings after semi-fine grinding in step S3 are subjected to QPQ salt bath nitriding and oxidation composite treatment. S41: Ultrasonic degreasing is used at a temperature of 65-85℃ for 20-25 minutes to thoroughly remove cutting fluid, oil, and dust from the surface of the raceway. After degreasing, hot air drying is performed at a temperature of 80-110℃ for 10-15 minutes to ensure that there is no moisture residue on the surface of the raceway and to avoid pinholes and bubbles during the nitriding process. S42 Salt Bath Nitriding: The pretreated rings are placed in a nitriding salt bath furnace. The nitriding temperature is controlled at 560-580℃ and the nitriding time is 110-130min. Through the penetration and diffusion of nitrogen atoms, a dense compound layer is formed on the surface of the rings. S43 Salt Bath Oxidation: After nitriding, the ring is transferred into an oxidation salt bath furnace. The oxidation temperature is controlled at 380-395℃ and the oxidation time is 25-40 minutes. A thin and dense oxide film is formed on the surface of the compound layer to improve the rust prevention performance. In step S42, the thickness of the compound layer is 11-16 μm; in step S43, the thickness of the oxide film is 110-130 μm. S5 Fine grinding: The outer circle, raceway and inner circle of the ring after step S4 are finely ground. The total fine grinding allowance is controlled to be 3-5μm. Only the micro-deformation layer on the surface of the ring is removed to avoid grinding through the compound white bright layer. The final ring surface retains a white bright layer of ≥5μm to ensure the rust prevention effect. In this embodiment, the models of grinding wheels and grinding machines selected for fine grinding are shown in Table 1, and the grinding machine parameters are shown in Table 2. Table 1 Grinding part Grinding wheel model Compatible with grinding machines outer circle of bearing 1A1 600×40×37 CBN120 VJ 7 3MK2220 CNC cylindrical grinding machine bearing inner raceway 11V9 50×32×10 CBN180 VK 6 3MK1420 CNC Grooving Grinding Machine Table 2 Parameter categories CNC cylindrical grinding machine CNC channel grinding machine Grinding wheel linear velocity 45-50m / s 25-30m / s Workpiece rotation speed 150-200r / min 80-120r / min Fine grinding feed rate 0.007mm 0.007mm Grinding speed 1μ / s 1μ / s Polishing amount 0.001mm 0.001mm Polishing delay 5s 5s S6 Post-processing: After fine grinding, the bearing ring is ultrasonically cleaned with a cleaning agent to thoroughly remove grinding debris and residual grinding fluid from the surface of the ring. After cleaning, it is dried with hot air to ensure that the surface of the ring is clean and dry. Within 30 minutes after drying, the ring is immersed in environmentally friendly rust-preventive oil for sealing treatment. The immersion time is 10-15 minutes to allow the rust-preventive oil to fully fill the micro gaps on the surface of the ring and form an oil film protective layer. After immersion, the excess rust-preventive oil is drained, and the bearing ring processing is completed.

[0030] Second Embodiment

[0031] A composite machining method for salt spray resistant and rust-resistant cross roller bearings for robots includes the following steps: S1 Pretreatment: GCr15 bearing steel is used for hot forging to effectively remove defects such as porosity, looseness and segregation in the billet, and to form a dense internal metal structure to form a bearing ring blank. S2 Rough Machining and Heat Treatment: The bearing ring blank obtained in step S1 is rough turned and finish turned. Rough turning removes most of the machining allowance, and finish turning ensures the basic dimensional accuracy of the ring's shape and inner hole, leaving a reasonable finishing allowance for subsequent grinding (0.15-0.20mm allowance for outer diameter and inner raceway). After finish turning, a vacuum quenching and low-temperature tempering combined heat treatment process is used. The composite heat treatment process is as follows: First, quenching is performed in a vacuum environment at a temperature of 840-860℃. The holding time is set according to the wall thickness of the ring, i.e., the ring wall thickness is 10-90mm and the holding time is 60-90min. The quenching cooling medium is high-speed nitrogen to ensure uniform cooling of the ring and avoid quenching deformation. Then, three low-temperature tempering processes are performed at a temperature of 160-180℃, with each tempering holding time of 120min. After tempering, the ring is cooled to room temperature in the furnace. S3 Semi-finish grinding: The bearing ring after heat treatment in step S2 is semi-finish ground on the outer circle and raceway. The surface roughness Ra of the ring after semi-finish grinding is controlled to be ≤0.8μm. A machining allowance of 0.015-0.025mm is reserved. The machining allowance includes the deformation allowance after QPQ treatment and the allowance for subsequent fine grinding. S4 QPQ treatment: The rings after semi-fine grinding in step S3 are subjected to QPQ salt bath nitriding and oxidation composite treatment. S41: Ultrasonic degreasing is used at a temperature of 65-85℃ for 20-25 minutes to thoroughly remove cutting fluid, oil, and dust from the surface of the raceway. After degreasing, hot air drying is performed at a temperature of 80-110℃ for 10-15 minutes to ensure that there is no moisture residue on the surface of the raceway and to avoid pinholes and bubbles during the nitriding process. S42 Salt Bath Nitriding: The pretreated rings are placed in a nitriding salt bath furnace. The nitriding temperature is controlled at 560-580℃ and the nitriding time is 110-130min. Through the penetration and diffusion of nitrogen atoms, a dense compound layer is formed on the surface of the rings. S43 Salt Bath Oxidation: After nitriding, the ring is transferred into an oxidation salt bath furnace. The oxidation temperature is controlled at 380-395℃ and the oxidation time is 25-40 minutes. A thin and dense oxide film is formed on the surface of the compound layer to improve the rust prevention performance. In step S42, the thickness of the compound layer is 11-16 μm; in step S43, the thickness of the oxide film is 110-130 μm. S5 Fine grinding: The outer circle, raceway and inner circle of the ring after step S4 are finely ground. The total fine grinding allowance is controlled to be 3-5μm. Only the micro-deformation layer on the surface of the ring is removed to avoid grinding through the compound white bright layer. The final ring surface retains a white bright layer of ≥5μm to ensure the rust prevention effect. S51 Grinding allowance allocation: The machining allowance for the outer diameter of the ring after step S4 is controlled to be 0.02-0.05mm, and the machining allowance for the inner raceway of the ring is controlled to be 0.01-0.03mm; S52: The grinding process is combined with a high-performance fully synthetic metalworking fluid to avoid grinding heat during the grinding process, which may cause micro-deformation of the ring, and at the same time prevent grinding debris from scratching the surface of the ring. S53 Grinding wheel selection: Select a suitable grinding wheel and grinding machine based on the outer diameter and inner raceway of the raceway; the selected grinding wheel and grinding machine models should be consistent with those used in Example 1; S54 Grinding parameters: Select parameters for both cylindrical grinding machines and grooved grinding machines. The parameters include grinding wheel linear speed, workpiece rotation speed, fine grinding feed rate, fine grinding speed, finishing grinding amount and finishing grinding delay, which are consistent with the parameters of the grinding machine used in Example 1. S55: Select the appropriate processing technology to complete the fine grinding; S6 Post-processing: After fine grinding, the bearing ring is ultrasonically cleaned with a cleaning agent to thoroughly remove grinding debris and residual grinding fluid from the surface of the ring. After cleaning, it is dried with hot air to ensure that the surface of the ring is clean and dry. Within 30 minutes after drying, the ring is immersed in environmentally friendly rust-preventive oil for sealing treatment. The immersion time is 10-15 minutes to allow the rust-preventive oil to fully fill the micro gaps on the surface of the ring and form an oil film protective layer. After immersion, the excess rust-preventive oil is drained, and the bearing ring processing is completed.

[0032] Third Embodiment

[0033] A composite machining method for salt spray resistant and rust-resistant cross roller bearings for robots includes the following steps: S1 Pretreatment: GCr15 bearing steel is used for hot forging to effectively remove defects such as porosity, looseness and segregation in the billet, and to form a dense internal metal structure to form a bearing ring blank. S2 Rough Machining and Heat Treatment: The bearing ring blank obtained in step S1 is rough turned and finish turned. Rough turning removes most of the machining allowance, and finish turning ensures the basic dimensional accuracy of the ring's shape and inner hole, leaving a reasonable finishing allowance for subsequent grinding (0.15-0.20mm allowance for outer diameter and inner raceway). After finish turning, a vacuum quenching and low-temperature tempering combined heat treatment process is used. The composite heat treatment process is as follows: First, quenching is performed in a vacuum environment at a temperature of 840-860℃. The holding time is set according to the wall thickness of the ring, i.e., the ring wall thickness is 10-90mm and the holding time is 60-90min. The quenching cooling medium is high-speed nitrogen to ensure uniform cooling of the ring and avoid quenching deformation. Then, three low-temperature tempering processes are performed at a temperature of 160-180℃, with each tempering holding time of 120min. After tempering, the ring is cooled to room temperature in the furnace. S3 Semi-finish grinding: The bearing ring after heat treatment in step S2 is semi-finish ground on the outer circle and raceway. The surface roughness Ra of the ring after semi-finish grinding is controlled to be ≤0.8μm. A machining allowance of 0.015-0.025mm is reserved. The machining allowance includes the deformation allowance after QPQ treatment and the allowance for subsequent fine grinding. S4 QPQ treatment: The rings after semi-fine grinding in step S3 are subjected to QPQ salt bath nitriding and oxidation composite treatment. S41: Ultrasonic degreasing is used at a temperature of 65-85℃ for 20-25 minutes to thoroughly remove cutting fluid, oil, and dust from the surface of the raceway. After degreasing, hot air drying is performed at a temperature of 80-110℃ for 10-15 minutes to ensure that there is no moisture residue on the surface of the raceway and to avoid pinholes and bubbles during the nitriding process. S42 Salt Bath Nitriding: The pretreated rings are placed in a nitriding salt bath furnace. The nitriding temperature is controlled at 560-580℃ and the nitriding time is 110-130min. Through the penetration and diffusion of nitrogen atoms, a dense compound layer is formed on the surface of the rings. S43 Salt Bath Oxidation: After nitriding, the ring is transferred into an oxidation salt bath furnace. The oxidation temperature is controlled at 380-395℃ and the oxidation time is 25-40 minutes. A thin and dense oxide film is formed on the surface of the compound layer to improve the rust prevention performance. In step S42, the thickness of the compound layer is 11-16 μm; in step S43, the thickness of the oxide film is 110-130 μm. S5 Fine grinding: The outer circle, raceway and inner circle of the ring after step S4 are finely ground. The total fine grinding allowance is controlled to be 3-5μm. Only the micro-deformation layer on the surface of the ring is removed to avoid grinding through the compound white bright layer. The final ring surface retains a white bright layer of ≥5μm to ensure the rust prevention effect. S51 Grinding allowance allocation: The machining allowance for the outer diameter of the ring after step S4 is controlled to be 0.02-0.05mm, and the machining allowance for the inner raceway of the ring is controlled to be 0.01-0.03mm; S52: The grinding process is combined with a high-performance fully synthetic metalworking fluid to avoid grinding heat during the grinding process, which may cause micro-deformation of the ring, and at the same time prevent grinding debris from scratching the surface of the ring. S53 Grinding wheel selection: Select a suitable grinding wheel and grinding machine based on the outer diameter of the raceway and the inner raceway of the raceway. The model of the selected grinding wheel and grinding machine should be the same as that of the grinding wheel and grinding machine used in Example 1. S54 Grinding parameters: Select parameters for both cylindrical grinding machines and grooved grinding machines. The parameters include grinding wheel linear speed, workpiece rotation speed, fine grinding feed rate, fine grinding speed, finishing grinding amount and finishing grinding delay, which are consistent with the parameters of the grinding machine used in Example 1. S55: Select the appropriate processing technology to complete the fine grinding; S551 Grinding Wheel Dressing: Diamond single-point dressing pen, correction amount 6μ / time, dressing speed adapted to grinding wheel linear speed, ensuring smooth grinding surface and improving grinding accuracy; S552: The external cylindrical grinding uses an electromagnetic centerless chuck, and the raceway grinding uses a floating support chuck. The clamping runout is ≤1μ, which avoids clamping stress from causing deformation of the ring and local grinding through the QPQ anti-rust layer during grinding. S553: ​​Grinding wheel spindle vibration value: ≤1.5μ, to prevent grinding marks caused by grinding wheel vibration during grinding and to ensure the surface quality of the bearing ring.

[0034] S6 Post-processing: After fine grinding, the bearing ring is ultrasonically cleaned with a cleaning agent to thoroughly remove grinding debris and residual grinding fluid from the surface of the ring. After cleaning, it is dried with hot air to ensure that the surface of the ring is clean and dry. Within 30 minutes after drying, the ring is immersed in environmentally friendly rust-preventive oil for sealing treatment. The immersion time is 10-15 minutes to allow the rust-preventive oil to fully fill the micro gaps on the surface of the ring and form an oil film protective layer. After immersion, the excess rust-preventive oil is drained, and the bearing ring processing is completed.

[0035] Testing was conducted using national standard physical and chemical testing instruments. (1) The bearing rings prepared by this method were tested with a stylus roughness tester according to GB / T6062 and the surface roughness Ra≤0.2μm. The roundness tester and bearing-specific rotational accuracy tester were used to verify that all the accuracy requirements met the P4 level rotational accuracy requirements.

[0036] (2) The bearing bonding force is tested by the pull-out adhesion tester (GB / T5210) and is ≥50N / mm². The bonding force is much higher than the physical bonding of the electroplated layer. There is no risk of coating peeling during the high-frequency rotation and vibration of the robot joint.

[0037] (3) Salt spray test: According to GB / T10125, the neutral salt spray test chamber is used for testing. The existing conventional rust prevention method (ordinary rust-preventive oil) for bearings fails to prevent rust in salt spray for about 2 hours. The salt spray rust prevention effect of such bearings after electroplating and reprocessing is about 15 hours. The rust prevention effect of bearings processed by this process is ≥120 hours, and the salt spray performance is improved by more than 8 times, which fully meets the long-term use requirements of special working conditions such as marine climate and high humidity.

[0038] (4) The bearing rings are tested in a high and low temperature test chamber and an inductive micrometer. The dimensional deformation is ≤4μ in the temperature range of -40℃ to 80℃, and the dimensional stability is excellent.

[0039] The above description is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A composite machining method for salt spray resistance and high rust prevention of cross roller bearings for robots, characterized in that, Includes the following steps: S1 Pre-treatment: GCr15 bearing steel is used for hot forging to form bearing ring blanks; S2 Rough machining and heat treatment: The bearing ring blank obtained in step S1 is rough machined and finish machined. After finish machining, it is treated by a combination of vacuum quenching and low temperature tempering heat treatment process. After rough turning and finish turning, a allowance of 0.15-0.20mm should be left for the outer diameter and inner raceway of the bearing ring; S3 Semi-finish grinding: The bearing rings after heat treatment in step S2 are semi-finish ground on the outer diameter and raceway. After semi-finish grinding, the surface roughness Ra of the ring should be controlled to be ≤0.8μm, with a machining allowance of 0.015-0.025mm. S4 QPQ treatment: The rings after semi-fine grinding in step S3 are subjected to QPQ salt bath nitriding and oxidation composite treatment. The QPQ salt bath nitriding and oxidation combined treatment in step S4 includes the following steps: S41: Ultrasonic degreasing is used at a temperature of 65-85℃ for 20-25 minutes to thoroughly remove cutting fluid, oil, and dust from the surface of the raceway. After degreasing, hot air drying is performed at a temperature of 80-110℃ for 10-15 minutes to ensure that there is no moisture residue on the surface of the raceway and to avoid pinholes and bubbles during the nitriding process. S42 Salt Bath Nitriding: The pretreated rings are placed in a nitriding salt bath furnace. The nitriding temperature is controlled at 560-580℃ and the nitriding time is 110-130min. Through the penetration and diffusion of nitrogen atoms, a dense compound layer is formed on the surface of the rings. S43 Salt Bath Oxidation: After nitriding, the ring is transferred into an oxidation salt bath furnace. The oxidation temperature is controlled at 380-395℃ and the oxidation time is 25-40 minutes. A thin and dense oxide film is formed on the surface of the compound layer to improve the rust prevention performance. In step S42, the thickness of the compound layer is 11-16 μm; in step S43, the thickness of the oxide film is 110-130 μm. S5 Fine grinding: The outer circle, raceway and inner circle of the ring processed in step S4 are finely ground, and the total fine grinding allowance is controlled to be 3-5μm. The fine grinding process in step S5 includes the following steps: S51 Grinding allowance allocation: The machining allowance for the outer diameter of the ring after step S4 is controlled to be 0.02-0.05mm, and the machining allowance for the inner raceway of the ring is controlled to be 0.01-0.03mm; S52: The grinding process is combined with a high-performance fully synthetic metalworking fluid to avoid grinding heat during the grinding process, which may cause micro-deformation of the ring, and at the same time prevent grinding debris from scratching the surface of the ring. S53 Grinding Wheel Selection: Select the appropriate grinding wheel and grinding machine based on the outer diameter and inner raceway of the raceway; S54 Grinding Parameters: Select parameters for external cylindrical grinding machines and grooved grinding machines respectively. The parameters include grinding wheel linear speed, workpiece rotation speed, fine grinding feed, fine grinding speed, finishing grinding amount and finishing grinding delay. S55: Select the appropriate processing technology to complete the fine grinding; S551 Grinding Wheel Dressing: Diamond single-point dressing pen, correction amount 6μ / time, dressing speed adapted to grinding wheel linear speed, ensuring smooth grinding surface and improving grinding accuracy; S552: The external cylindrical grinding uses an electromagnetic centerless chuck, and the raceway grinding uses a floating support chuck. The clamping runout is ≤1μ, which avoids the deformation of the ring caused by clamping stress and the local grinding through of the QPQ anti-rust layer during grinding. S553: ​​Grinding wheel spindle vibration value ≤1.5μ, to prevent grinding marks caused by grinding wheel vibration during grinding and to ensure the surface quality of the ring; S6 Post-processing: After fine grinding, the bearing ring is ultrasonically cleaned with a cleaning agent and then dried with hot air. After drying, the bearing ring is immersed in environmentally friendly rust-preventive oil for sealing treatment, so that the rust-preventive oil fully fills the micro gaps on the surface of the bearing ring and forms an oil film protective layer. After immersion, the excess rust-preventive oil is drained, and the bearing ring processing is completed.

2. The method for composite processing of a robot-specific crossed roller bearing with high salt spray resistance and rust prevention according to claim 1, characterized in that, The composite heat treatment process in step S2 is as follows: first, quenching is performed in a vacuum environment, and the holding time is 60-90 min, depending on the wall thickness of the ring, which is 10-90 mm; then, three low-temperature temperings are performed, with a tempering temperature of 160-180℃ and a holding time of 120 min for each tempering. After tempering, the ring is cooled to room temperature in the furnace.

3. The method for composite processing of robot-specific crossed roller bearings with high salt spray resistance and rust prevention according to claim 2, characterized in that, The quenching temperature is 840-860℃, and the quenching cooling medium is high-speed nitrogen.

4. The method for composite processing of a robot-specific crossed roller bearing with high salt spray resistance and rust prevention according to claim 1, characterized in that, In step S6, the sealing treatment time is within 30 minutes after drying, and the soaking time is 10-15 minutes.