Manufacturing method of heavy-duty gear with high-hardness gradient outer teeth and high-precision inner and outer teeth

Abstract

The invention discloses a manufacturing method of a heavy-duty gear with high-hardness gradient outer teeth and high-precision inner and outer teeth, which combines the requirements of high hardness and high precision of the heavy-duty gear, adopts a gas / liquid composite permeating agent, high carbon potential carburizing and 100% strong carburizing process to improve the basic carbon content of a carburizing layer, and then adopts strengthening measures of quenching, cold treatment and low-temperature tempering to improve the hardness of the gear. And the hardening layer depth with high hardness and more gentle gradient is obtained. The heavy-duty gear manufactured through the method has the advantages of being high in hardness, precision and bearing capacity, high in machining efficiency and low in machining cost, and is worthy of application and popularization.

Description

Technical Field

[0001] This invention relates to the field of gear processing technology, and in particular to a method for manufacturing heavy-duty gears with high hardness gradient external teeth and high precision internal and external teeth. Background Technology

[0002] To meet the requirements of new high-power-density integrated transmission devices, heavy-duty spline gears are made of high-quality steels such as 18Cr2Ni2MoNbA and 25CrNi2MoVE to ensure that excessive wear or damage will not occur under long-term high-load operation. Technical requirements: The hardened layer depth (carburized and quenched hardened layer) of this series of gears is required to be 1.5~1.8mm (before grinding); the hardness value within 1.0mm of the tooth surface is ≥698HV (before grinding, Rockwell hardness conversion value is 60HRC); the hardness of non-carburized parts is 35~49HRC; the spline major diameter tolerance and axial circumferential runout are both ≤0.02mm; and the gear and spline accuracy is grade 6.

[0003] Based on an average hardened layer depth of 1.65mm, using traditional gas carburizing technology, the depth of the carburized layer with a hardness ≥698HV is approximately 0.8mm, making it difficult to achieve the requirement of ≥1.0mm. Furthermore, during the gas carburizing diffusion period, due to reverse decarburization and surface porosity, the hardness within 0.3mm of the carburized layer surface often falls below 698HV. This series of gears has extremely high requirements for spline diameter tolerance and axial circumferential runout. Theoretically, the only economical and efficient machining method is broaching, but to ensure high tooth surface hardness, the gears can only undergo low-temperature tempering after carburizing and quenching. In this state, the hardness of the non-carburized parts of the gear reaches 44~48HRC, far exceeding the requirement of ≤40HRC for the broached parts of a one-time spline broach. A hardness of 44~48HRC can be achieved by hardened tooth surface broaching or wire EDM splines, but this suffers from low machining efficiency and poor machining accuracy, resulting in the inability to simultaneously meet the requirements for spline diameter tolerance, axial circumferential runout, and gear and spline accuracy. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications, which is simple to manufacture, has high processing efficiency, and low processing costs.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is: a method for manufacturing heavy-duty gears with high hardness gradient external teeth and high precision internal and external teeth, comprising the following steps:

[0006] Step 1: Mix the carburizing agent and methanol to prepare a composite liquid carburizing agent and add it to the storage tank; clean the surface of the gear workpiece to be carburized, removing dust, oil stains, and cutting fluid, and after drying, load it into the carburizing material frame;

[0007] Step 2: Set the flow rates of the main percolating agent (propane) and the composite liquid percolating agent in the auxiliary system of the controlled atmosphere multi-purpose furnace;

[0008] Step 3: Set the carburizing process parameters. Introduce the composite liquid carburizing agent at a temperature of 820℃. After 30~35 minutes, raise the temperature to 930℃ for carburizing. The strong carburizing potential is 1.25%, the strong carburizing time is 100%, and after carburizing to a depth of 1.65mm, turn off the composite liquid carburizing agent and transfer the part from the heating furnace to the cooling chamber.

[0009] Step 4: Carburize the gear workpiece. After carburizing, cool it to ≤100℃ and then temper it at high temperature. After tempering, remove it from the furnace and air cool it. Then turn the gear workpiece into a machine to remove the excess carburized layer from the inner hole and the end face of the inner hole. Then turn it into a quenching process.

[0010] Step 5: Quench the gear workpiece;

[0011] Step Six: Clean the quenched gear workpiece and then transfer it to a liquid nitrogen cryogenic chamber for cold treatment;

[0012] Step 7: After the gear workpiece has returned to room temperature under natural conditions, it should be subjected to low-temperature tempering treatment immediately, followed by furnace cooling or air cooling after the heat preservation is completed.

[0013] Step 8: Perform induction tempering on the inner hole of the gear workpiece;

[0014] Step 9: Install and fix the gear workpiece on the centering platform, install and adjust the inductor and its position; use the three-stage heating method; after the three-stage heating is completed for 10~12 seconds, cool the workpiece with water or aqueous solution and then blow it dry with compressed air. Remove the gear workpiece from the centering platform and continue the induction tempering of the next piece.

[0015] Step 10: Transfer the gear workpiece to the machining center, finish machine the end face and inner hole, then use a double-center broach with large and small diameters and vertical broaching to machine the internal spline, and then grind the external teeth with the small diameter of the internal spline as the reference.

[0016] In the manufacturing method of the above-mentioned high-hardness gradient external gear and high-precision internal and external gear heavy-duty gear, in step one, BH-5 penetration catalyst and methanol are mixed at a volume ratio of 1:10 to prepare a composite liquid penetration agent.

[0017] In the above-mentioned method for manufacturing high-hardness gradient external gears and high-precision internal and external gear heavy-duty gears, in step two, the main permeation agent propane flow rate is 0.20 m³ / s. 3 / h, the flow rate of the composite liquid permeating agent is 5ml / min.

[0018] In the above-mentioned method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications, the high-temperature tempering and heat preservation parameters in step four are 650℃×240min.

[0019] In the above-mentioned method for manufacturing high-hardness gradient external gears and high-precision internal and external gear heavy-duty gears, in step five, the quenching equipment is a controllable atmosphere multi-purpose furnace or a vacuum furnace, the quenching holding parameters are 830℃×60min, the cooling medium is rapid quenching oil, and the oil temperature is 60℃.

[0020] In the manufacturing method of the above-mentioned high-hardness gradient external gear and high-precision internal and external gear heavy-duty gear, in step six, the cooling rate is controlled at 1.5~2.5℃ / min, and the cold treatment insulation parameters are -120℃×120min.

[0021] In the above-mentioned method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications, in step eight, the induction tempering equipment is a multi-functional CNC medium-frequency induction heating machine tool, with an induction frequency of 8000KZ and a rotation speed of 30r / min. The outer diameter of the induction coil and the single-sided gap between the inner diameter of the workpiece are 4~8mm.

[0022] In the manufacturing method of the above-mentioned high-hardness gradient external gear and high-precision internal and external gear heavy-duty gear, in step nine, during the three-stage heating process, the first stage uses 25~35KW power to heat for 25~30s to bring the temperature of the inner hole of the workpiece to 480~520℃; heating is stopped for 5s to allow the heat to diffuse, and then heated with 20~25KW power for 12~15s to bring the temperature of the inner hole of the workpiece back to 480~520℃; heating is stopped for 8s to allow the heat to diffuse, and then heated with 20~25KW power for 12~15s to bring the temperature of the inner hole of the workpiece back to 480~520℃.

[0023] 9. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, in step ten, the major diameter tolerance of the spline and the axial circumferential runout are both ≤0.02mm, and the precision of the gear and spline both reach grade 6.

[0024] The above-mentioned method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty gears results in gears with a surface hardness ≥62HRC, a stable hardness of ≥60HRC at 1.1mm from the surface of the diffusion layer, a matrix hardness of 46±2HRC, and a hardness of 35~40HRC in the inner hole of the spline to be machined and within 12mm from the surface of the inner hole.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. The surface hardness of gear workpieces treated with this process is increased by more than 2 HRC compared with traditional processes, and the diffusion layer can reach a hardness of 60 HRC, which is more than 0.3 mm deeper than traditional processes, thus greatly improving the load-bearing capacity and wear resistance of gears.

[0027] 2. The grade of martensite, carbide, and core structure of the gear workpiece treated by this process is ≤2, which is better than the ≤3 grade of the traditional process. The residual austenite content is controlled from 20~30% to 8~12% with optimal comprehensive performance and microstructure by adopting the measures of high temperature tempering after carburizing and cold treatment.

[0028] 3. The induction heating program is set through high-precision temperature measurement. The induction heating process is fully CNC controlled. The three-stage heating method can stably control the hardness of the inner hole and the area within 12mm from the inner hole surface (about 4mm for the single-stage heating method) to be 35~40HRC. At this hardness, a 6-level precision spline can be formed in one broaching operation. The broaching spline time is ≤3min, which reduces the processing time by more than 3 hours compared with the original wire cutting solution, greatly improving production efficiency and reducing production costs. At the same time, the broached spline can ensure that the gear major diameter tolerance and axial circumferential runout are both ≤0.02mm. Attached Figure Description

[0029] Figure 1 A schematic diagram showing the area where hardness needs to be adjusted for heavy-duty splined gears.

[0030] Figure 2 This is a comparison diagram of the hardness gradient of the carburized layer treated by the present invention and the conventional process. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] Step 1: Mix BH-5 carburizing agent and methanol at a volume ratio of 1:10 to prepare a composite liquid carburizing agent and add it to the storage tank; clean the surface of the 18Cr2Ni2MoNbA steel gear workpiece to be carburized, removing dust, oil stains, cutting fluid, etc., and after drying, load it into the carburizing material frame.

[0034] Step 2: Set the main percolator propane flow rate to 0.20 m³ / h in the controlled atmosphere multi-purpose furnace auxiliary system. 3 / h, set the flow rate of the composite liquid permeabilizer to 5ml / min.

[0035] Step 3: Set the carburizing process parameters in the Carb-O-Prof software. Introduce the composite liquid carburizing agent at 820℃. After 30~35 minutes, raise the temperature to 930℃ for carburizing. The strong carburizing potential is 1.25%, and the strong carburizing time is 100%. After carburizing to a depth of 1.65mm, turn off the composite liquid carburizing agent and transfer the part from the heating furnace to the cooling chamber.

[0036] Step 4: Carburize the gear workpiece. After carburizing, cool it to ≤100℃ and then temper it at high temperature. The high temperature tempering holding parameters are 650℃×240min. After tempering, remove it from the furnace and air cool it. Then, turn the gear workpiece into a machine to remove the excess carburized layer from the inner hole, inner hole end face, etc., and then proceed to the quenching process.

[0037] Step 5: Quench the gear workpiece using a controlled atmosphere multi-purpose furnace. The quenching holding parameters are 830℃×60min, and the cooling medium is rapid quenching oil at a temperature of 60℃.

[0038] Step 6: Clean the quenched gear workpiece, then transfer it to a liquid nitrogen cryogenic chamber for cold treatment. The cooling rate is controlled at 1.5~2.5℃ / min, and the cold treatment holding parameters are -120℃×120min.

[0039] Step 7: After the gear workpiece has returned to room temperature under natural conditions, it should be subjected to low-temperature tempering treatment immediately. The low-temperature tempering holding parameters are 150℃×240min, and furnace cooling is performed after the holding is completed.

[0040] Step 8: Perform induction tempering on the inner hole of the gear workpiece (the spline part to be machined). The equipment is a multi-functional CNC medium frequency induction heating machine tool. The induction frequency is set to 8000KZ, the rotation speed is 30r / min, and the outer diameter of the induction coil and the single-sided gap between the inner hole of the workpiece are 4mm.

[0041] Step Nine: Install and fix the gear workpiece on the centering platform, and install and adjust the inductor and its position. Use a three-stage heating method: In the first stage, heat with 25KW power for 25~30s to bring the inner hole temperature of the workpiece to 480~500℃; stop heating for 5s to allow the heat to dissipate, then heat with 20KW power for 12~15s to bring the inner hole temperature of the workpiece back to 480~500℃; stop heating for 8s to allow the heat to dissipate, then heat with 20KW power for 12~15s to bring the inner hole temperature of the workpiece back to 480~500℃; after the three-stage heating is completed for 10~12s, cool the workpiece with an aqueous solution and then dry it with compressed air. Remove the gear workpiece from the centering platform and continue with the induction tempering of the next piece.

[0042] Step 10: Transfer the gear workpiece to the machining center. After finishing the end face and inner hole, use a double-centering broach with large and small diameters and a vertical broaching method to machine the internal spline. Then, grind the external teeth with the small diameter of the internal spline as the reference. The large diameter tolerance of the spline and the axial circumferential runout are both ≤0.02mm. The accuracy of the gear and spline are both grade 6 or higher.

[0043] Example 2

[0044] Step 1: Mix BH-5 carburizing agent and methanol at a volume ratio of 1:10 to prepare a composite liquid carburizing agent and add it to the storage tank; clean the surface of the 25CrNi2MoVE steel gear workpiece to be carburized, removing dust, oil stains, cutting fluid, etc., and after drying, load it into the carburizing material frame.

[0045] Step 2: Set the main percolator propane flow rate to 0.20 m³ / h in the controlled atmosphere multi-purpose furnace auxiliary system. 3 / h, set the flow rate of the composite liquid permeabilizer to 5ml / min.

[0046] Step 3: Set the carburizing process parameters in the Carb-O-Prof software. Introduce the composite liquid carburizing agent at 820℃. After 30~35 minutes, raise the temperature to 930℃ for carburizing. The strong carburizing potential is 1.25%, and the strong carburizing time is 100%. After carburizing to a depth of 1.65mm, turn off the composite liquid carburizing agent and transfer the part from the heating furnace to the cooling chamber.

[0047] Step 4: Carburize the gear workpiece. After carburizing, cool it to ≤100℃ and then temper it at high temperature. The high temperature tempering holding parameters are 650℃×240min. After tempering, remove it from the furnace and air cool it. Then, turn the gear workpiece into a machine to remove the excess carburized layer from the inner hole, inner hole end face, etc., and then proceed to the quenching process.

[0048] Step 5: Quench the gear workpiece using a vacuum furnace. The quenching temperature is 830℃ for 60 minutes, and the cooling medium is rapid quenching oil at a temperature of 60℃.

[0049] Step 6: Clean the quenched gear workpiece, then transfer it to a liquid nitrogen cryogenic chamber for cold treatment. The cooling rate is controlled at 1.5~2.5℃ / min, and the cold treatment holding parameters are -120℃×120min.

[0050] Step 7: After the gear workpiece has returned to room temperature under natural conditions, it should be subjected to low-temperature tempering treatment immediately. The low-temperature tempering holding parameters are 150℃×240min, and furnace cooling is performed after the holding is completed.

[0051] Step 8: Perform induction tempering on the inner hole of the gear workpiece. The equipment is a multi-functional CNC medium-frequency induction heating machine tool. The induction frequency is set to 8000KZ, the rotation speed is 30r / min, and the outer diameter of the induction coil and the single-sided gap between the inner hole of the workpiece are 8mm.

[0052] Step Nine: Install and fix the gear workpiece on the centering platform, and install and adjust the inductor and its position. Use a three-stage heating method: In the first stage, heat with 35KW power for 25-30 seconds to bring the inner hole temperature of the workpiece to 500-520℃; stop heating for 5 seconds to allow the heat to dissipate, then heat with 25KW power for 12-15 seconds to bring the inner hole temperature of the workpiece back to 500-520℃; stop heating for 8 seconds to allow the heat to dissipate, then heat with 25KW power for 12-15 seconds to bring the inner hole temperature of the workpiece back to 500-520℃; after the three-stage heating is completed for 10-12 seconds, cool the workpiece with an aqueous solution and then dry it with compressed air. Remove the gear workpiece from the centering platform and continue with the induction tempering of the next piece.

[0053] Step 10: Transfer the gear workpiece to the machining center. After finishing the end face and inner hole, use a double-centering broach with large and small diameters and a vertical broaching method to machine the internal spline. Then, grind the external teeth with the small diameter of the internal spline as the reference. The large diameter tolerance of the spline and the axial circumferential runout are both ≤0.02mm. The accuracy of the gear and spline are both grade 6 or higher.

[0054] like Figure 1 As shown, Figure 1 In the diagram, A represents the gear reinforcement area, and B represents the induction tempering area. For example... Figure 2 As shown, the gear workpieces obtained in Examples 1 and 2 have a tooth surface hardness ≥62HRC, a hardness of 698HV (60HRC) or higher at a distance of 1.1mm from the surface of the diffusion layer, a matrix hardness of 46±2HRC, a hardness of 35~40HRC in the inner hole of the spline to be machined and within 12mm from the surface of the inner hole, a martensite grade ≤2, a carbide grade ≤2, a core structure grade ≤2, and a retained austenite content of 8~12%.

Claims

1. A method for manufacturing a heavy-duty gear with high-hardness gradient external teeth and high-precision internal and external teeth, characterized in that, Includes the following steps: Step 1: Mix the carburizing agent and methanol to prepare a composite liquid carburizing agent and add it to the storage tank; clean the surface of the gear workpiece to be carburized, removing dust, oil stains, and cutting fluid, and after drying, load it into the carburizing material frame; Step 2: Set the flow rates of the main percolating agent (propane) and the composite liquid percolating agent in the auxiliary system of the controlled atmosphere multi-purpose furnace; Step 3: Set the carburizing process parameters. Introduce the composite liquid carburizing agent at a temperature of 820℃. After 30~35 minutes, raise the temperature to 930℃ for carburizing. The strong carburizing potential is 1.25%, the strong carburizing time is 100%, and after carburizing to a depth of 1.65mm, turn off the composite liquid carburizing agent and transfer the part from the heating furnace to the cooling chamber. Step 4: Carburize the gear workpiece. After carburizing, cool it to ≤100℃ and then temper it at high temperature. After tempering, remove it from the furnace and air cool it. Then turn the gear workpiece into a machine to remove the excess carburized layer from the inner hole and the end face of the inner hole. Then turn it into a quenching process. Step 5: Quench the gear workpiece; Step Six: Clean the quenched gear workpiece and then transfer it to a liquid nitrogen cryogenic chamber for cold treatment; Step 7: After the gear workpiece has returned to room temperature under natural conditions, it should be subjected to low-temperature tempering treatment immediately, followed by furnace cooling or air cooling after the heat preservation is completed. Step 8: Perform induction tempering on the inner hole of the gear workpiece; Step 9: Install and fix the gear workpiece on the centering platform, install and adjust the inductor and its position; use the three-stage heating method; after the three-stage heating is completed for 10~12 seconds, cool the workpiece with water or aqueous solution and then blow it dry with compressed air. Remove the gear workpiece from the centering platform and continue the induction tempering of the next piece. Step 10: Transfer the gear workpiece to the machining center, finish machine the end face and inner hole, then use a double-center broach with large and small diameters and vertical broaching to machine the internal spline, and then grind the external teeth with the small diameter of the internal spline as the reference.

2. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step one, BH-5 penetration catalyst and methanol are mixed at a volume ratio of 1:10 to prepare a composite liquid penetration agent.

3. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step two, the flow rate of the main permeation agent, propane, is 0.20 m³ / h. 3 / h, the flow rate of the composite liquid permeating agent is 5ml / min.

4. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step four, the high-temperature tempering and heat preservation parameters are 650℃ × 240min.

5. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step five, the quenching equipment is a controllable atmosphere multi-purpose furnace or a vacuum furnace, the quenching holding parameters are 830℃×60min, the cooling medium is rapid quenching oil, and the oil temperature is 60℃.

6. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step six, the cooling rate is controlled at 1.5~2.5℃ / min, and the cold treatment insulation parameters are -120℃×120min.

7. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step eight, the induction tempering equipment is a multi-functional CNC medium-frequency induction heating machine tool, with an induction frequency of 8000KZ, a rotation speed of 30r / min, and a single-sided gap of 4~8mm between the outer diameter of the induction coil and the inner hole of the workpiece.

8. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step nine, during the three-stage heating process, the first stage uses 25-35KW power to heat for 25-30 seconds until the inner hole temperature of the workpiece reaches 480-520℃; heating is stopped for 5 seconds to allow the heat to diffuse, and then heated again with 20-25KW power for 12-15 seconds until the inner hole temperature of the workpiece reaches 480-520℃ again; heating is stopped for 8 seconds to allow the heat to diffuse, and then heated again with 20-25KW power for 12-15 seconds until the inner hole temperature of the workpiece reaches 480-520℃ again.

9. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, In step ten, the major diameter tolerance of the spline and the axial circumferential runout are both ≤0.02mm, and the accuracy of both the gear and the spline reaches grade 6.

10. The method for manufacturing high-hardness gradient external gears and high-precision internal and external gears for heavy-duty applications according to claim 1, characterized in that, The final gear has a surface hardness of ≥62HRC, a stable hardness of ≥60HRC at 1.1mm from the surface of the diffusion layer, a matrix hardness of 46±2HRC, and a hardness of 35~40HRC in the inner hole of the spline to be machined and within 12mm from the surface of the inner hole.

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