A surface strengthening device for shaft-type workpieces and its application

Abstract

This invention relates to the field of workpiece processing, specifically to a surface strengthening device for shaft-type workpieces and its application. The two ends of the shaft-type workpiece are fixed to a clamping and rotating system, so that a portion of the workpiece surface to be strengthened is encased in a graphite electrode, and then the other portion is contacted by a copper guide wheel. A circuit is formed under the action of a pulsed current, allowing current to flow through the workpiece. Because the copper guide wheel and the circumferential surface of the shaft-type workpiece have line contact, the current density is high, and the generated Joule heat rapidly raises the contact surface to the quenching temperature. Simultaneously, rotating the workpiece achieves the effect of alternating heating and cooling of the entire surface. By adjusting process parameters such as the applied pulsed current, rotation speed, and time interval, surface strengthening treatment of large or complex shaft-type workpieces can be achieved, ultimately enabling the workpiece to simultaneously achieve higher hardness, wear resistance, and impact toughness.

Description

Technical Field

[0001] This invention relates to the field of workpiece processing, and specifically to a surface strengthening device for shaft-type workpieces and its application. Background Technology

[0002] For complex and large shaft-type workpieces, such as the half-shaft of an integrated cast bridge housing with relatively poor surface properties, improving the performance of the half-shaft has a significant impact on the overall service life of the bridge housing. Some methods for improving the surface of complex workpieces, such as mechanical hardening (e.g., rolling, shot peening), chemical plating, magnetron sputtering, electroplating / brush plating, electrical discharge / vapor deposition, brazing, thermal spraying, and surface carburizing / nitriding, are limited by the process. These methods can often only treat an extremely thin surface layer on the workpiece, and the process is complex, time-consuming, and labor-intensive. Because the material of the integrated cast bridge housing is a large, complex, or irregularly shaped material, its half-shaft is larger and more complex than the half-shafts of other workpieces. Existing technologies make it difficult to perform quenching treatment only on the half-shaft of the bridge housing or selectively on a localized surface. Furthermore, existing technologies (induction hardening, laser surface hardening) will cause the following problems when quenching the surface of the half-shaft: First, due to equipment power limitations or low heating rates, the quenching depth is too shallow, resulting in insufficient hardened layer depth and inadequate strengthening of the half-shaft; second, during surface quenching, the uneven speed of the half-shaft during rotation or movement leads to uneven heat treatment, ultimately resulting in incomplete surface strengthening; third, after quenching, the surface of the half-shaft may solidify, significantly reducing the surface quality of the workpiece and increasing subsequent processing costs; fourth, while quenching increases the hardness of the half-shaft, it also reduces its toughness, meaning it is difficult to simultaneously improve the hardness, wear resistance, and toughness of the half-shaft. Therefore, how to perform quenching treatment on complex and large shaft workpieces or selectively on local surfaces to control the depth of the hardened layer and surface quality, so as to simultaneously improve the hardness, wear resistance, fatigue strength and toughness of shaft workpieces, is a technical problem that urgently needs to be solved. Summary of the Invention

[0003] To solve the above-mentioned technical problems, the present invention provides a surface strengthening device for shaft-type workpieces, comprising: a base 1, a power control system 2, a worktable 3, a clamping and rotating system 4, a graphite electrode 5, and a copper guide wheel 6. The power control system 2 is located on the base 1 and is used to control the pulse current output and the opening and movement of the clamping and rotating system 4, the graphite electrode 5, and the copper guide wheel 6. The worktable 3 is located above the power control system 2. The clamping and rotating system 4 is placed on the worktable 3 and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system 2 is connected to the graphite electrode 5 and the copper guide wheel 6. The graphite electrode 5 is placed at the front end of the worktable 3, and the copper guide wheel electrode 6 is located at the rear end of the worktable 3. The graphite electrode 5 is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel 6 is a copper wheel that can rotate freely.

[0004] This invention also provides the application of a surface strengthening device for shaft-type workpieces in the field of surface strengthening. Its preparation method includes: turning on the surface strengthening device for shaft-type workpieces; fixing both ends of the shaft-type workpiece to the clamping and rotating system 4; adjusting the positions of the graphite electrode 5 and the copper guide wheel 6 to ensure close contact with the first circumferential surface to be processed on the shaft-type workpiece; turning on the power control system 2 to perform uniform rotation and pulse current processing on the shaft-type workpiece. The pulse current processing is as follows: pulse current 3KA-12KA, voltage 16-25V, frequency 0.5-200Hz, discharge time 5-500s; the rotation line of the shaft-type workpiece... At a speed of 5-100 mm / s, the copper guide wheel 6 moves relative to the shaft workpiece under the rotation of the shaft workpiece, and pulse current heating and air cooling treatment (hereinafter referred to as pulse current quenching treatment) are alternately performed on the surface of the shaft workpiece. After the first circumferential surface of the shaft workpiece is completed by pulse current quenching treatment, it is cooled at room temperature for 30-300 seconds. Then, the next circumferential surface of the shaft workpiece is subjected to pulse current quenching treatment in the same way as the first circumferential surface of the shaft workpiece. After the above process is completed, the entire shaft workpiece is finally processed and the shaft workpiece after pulse current quenching treatment is obtained.

[0005] Furthermore, the shaft-type workpiece is shaped as one of a half-shaft, crankshaft, stepped shaft, or hollow shaft; and is made of one of ductile iron, cast steel, forged steel, or titanium alloy.

[0006] Furthermore, the ductile iron is one of QT400-15, QT450-10, QT500-7, and QT600-3.

[0007] Furthermore, the cast steel is one of ZG200-400, ZG230-450, ZG270-500, ZG310-570, and ZG340-640.

[0008] Furthermore, the forged steel is one of 35CrMo, 20Cr, 38SiMnMo, 37SiMn, and 20CrMnTi.

[0009] Furthermore, the titanium alloy is one of TC4, TC6, TC11, and TC17. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating the application of the surface strengthening device for shaft-type workpieces according to the present invention.

[0011] Figure 2 A cross-sectional view of the main components of the surface strengthening device for shaft-type workpieces of the present invention;

[0012] Figure 3 This is an optical micrograph of the hardened layer of bridge shell 1 in Example 1;

[0013] Figure 4 Examples 1(a) and (b) show the optical microstructure comparison of the surfaces of the QT600-3 ductile iron bridge housing half-shaft and bridge housing half-shaft 1, respectively. Detailed Implementation

[0014] A surface strengthening device for shaft-type workpieces includes: a base 1, a power control system 2, a worktable 3, a clamping and rotating system 4, a graphite electrode 5, and a copper guide wheel 6. The power control system 2 is located on the base 1 and is used to control the pulse current output and the opening and movement of the clamping and rotating system 4, the graphite electrode 5, and the copper guide wheel 6. The worktable 3 is located above the power control system 2. The clamping and rotating system 4 is placed on the worktable 3 and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system 2 is connected to the graphite electrode 5 and the copper guide wheel 6. The graphite electrode 5 is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel 6 is a copper wheel that can rotate freely.

[0015] Example 1

[0016] The surface strengthening device for shaft-type workpieces is activated. The two ends of the QT600-3 ductile iron bridge housing half-shaft (hereinafter referred to as the half-shaft) are fixed on the clamping and rotating system 4. The positions of the graphite electrode 5 and the copper guide wheel 6 are adjusted to ensure close contact with the first circumferential surface to be machined on the half-shaft. The power control system 2 is turned on to perform uniform rotation and pulse current treatment on the half-shaft. The pulse current treatment is as follows: pulse current of 5KA, voltage of 18V, frequency of 100Hz, discharge time of 40s, and the rotational linear velocity of the half-shaft is 5mm / s. Driven by the rotation of the half-shaft, the copper guide wheel 6 moves relative to the half-shaft, alternately performing pulse current heating and air cooling treatment (i.e., pulse current quenching treatment) on the surface of the half-shaft. After the first circumferential surface of the half-shaft has completed the pulse current quenching treatment, it is cooled at room temperature for 60s. Then, the next circumferential surface of the half-shaft is subjected to pulse current quenching treatment in the same manner as the first circumferential surface. Following the above process, the entire bridge housing half-shaft is finally machined, resulting in the bridge housing half-shaft 1 after pulse current quenching treatment. Microstructural characterization and mechanical property analysis were performed on the bridge housing half-shaft 1 after pulse current quenching treatment. Figure 3 The optical microstructure of the hardened layer shows that the depth of the hardened layer in bridge housing half-shaft 1 is 0.98 mm. Figure 4 It can be seen that: the surface microstructure of the QT600-3 ductile iron bridge housing half shaft ( Figure 4 Compared to (a), where the surface microstructure is composed of ferrite and pearlite,... Figure 4 (b) The surface microstructure of the bridge housing half-shaft 1 is homogeneous.

[0017] The surface of bridge housing half-shaft 1 is harder than that of QT600-3 ductile iron bridge housing half-shaft due to its uniform and fine martensite and ferrite with a higher proportion of dislocations (compared to the unmachined bridge housing half-shaft). However, the core structure of bridge housing half-shaft 1 is the same as that of QT600-3 ductile iron bridge housing half-shaft (its surface and core structures are the same). Therefore, bridge housing half-shaft 1 forms a structure with a hard surface and a soft core. The surface structure of bridge housing half-shaft 1 is composed of fine and uniform martensite, ferrite with a greater number of dislocations, and the adjustable and controllable depth of the hardened layer, as well as the synergistic regulation of the hard surface and soft core, all contribute to the differentiated stepped structure and microstructure of bridge housing half-shaft 1. Ultimately, bridge housing half-shaft 1 simultaneously possesses higher hardness, wear resistance, and impact toughness, breaking through the technical bottleneck of the difficulty in simultaneously improving the hardness, wear resistance, and impact toughness of existing bridge housing half-shafts.

[0018] Table 1 Comparison of Mechanical Properties of QT600-3 Ductile Iron Bridge Housing and Bridge Housing 1

[0019] Example 2

[0020] Activate the surface strengthening device for shaft-type workpieces. Fix both ends of the QT600-3 ductile iron bridge housing half-shaft (hereinafter referred to as the half-shaft) onto the clamping and rotating system 4. Adjust the positions of the graphite electrode 5 and the copper guide wheel 6 to ensure close contact with the first circumferential surface to be machined on the half-shaft. Turn on the power control system 2 to perform uniform rotation and pulse current processing on the half-shaft. The pulse current processing is as follows: pulse current of 8KA, voltage of 20V, frequency of 120Hz, discharge time of 20s, and to make the half-shaft rotate at a uniform speed with a linear rotational speed of 10mm / s. Driven by the rotation of the half shaft, the copper guide wheel 6 moves relative to the half shaft, and the half shaft surface is alternately subjected to pulse current heating and air cooling treatment (i.e. pulse current quenching treatment). After the first circumferential surface of the half shaft is completed by pulse current quenching treatment, it is cooled at room temperature for 90 seconds. Then, the next circumferential surface of the half shaft is subjected to pulse current quenching treatment in the same way as the first circumferential surface of the half shaft. After the above process is completed, the entire bridge housing half shaft is finally processed, and the bridge housing half shaft 2 after pulse current quenching treatment is obtained. Compared to the surface microstructure of QT600-3 ductile iron bridge housing half-shaft (which consists of ferrite and pearlite), the surface microstructure of bridge housing half-shaft 2 is uniform and fine martensite and ferrite with a higher dislocation ratio (the dislocation ratio is higher than that of the unmachined bridge housing half-shaft). Therefore, the surface of bridge housing half-shaft 2 is harder than that of QT600-3 ductile iron bridge housing half-shaft. However, the core microstructure of bridge housing half-shaft 2 is the same as that of QT600-3 ductile iron bridge housing half-shaft (its surface and core microstructures are the same). The surface microstructure of bridge housing half-shaft 2, composed of fine and uniform martensite and ferrite with a greater number of dislocations, along with the adjustable and controllable hardened layer depth and the synergistic regulation of a hard surface and a soft core, results in a differentiated stepped structure and microstructure. The hardened layer depth of bridge housing half-shaft 2 is 3.11 mm, and bridge housing half-shaft 2 exhibits higher hardness, wear resistance, and impact toughness. This breakthrough overcomes the technical bottleneck of simultaneously improving the hardness, wear resistance, and impact toughness of axle housing half-shafts in existing technologies.

[0021] Table 2 Mechanical properties of ductile iron materials before and after surface electro-pulse quenching

[0022]

[0023] Example 3

[0024] Activate the surface strengthening device for shaft-type workpieces. Fix both ends of the ZG310-570 cast steel bridge housing half-shaft (hereinafter referred to as the half-shaft) onto the clamping and rotating system 4. Adjust the positions of the graphite electrode 5 and the copper guide wheel 6 to ensure close contact with the first circumferential surface to be machined on the half-shaft. Turn on the power control system 2 to perform uniform rotation and pulse current processing on the half-shaft. The pulse current processing is as follows: pulse current of 4KA, voltage of 16V, frequency of 80Hz, discharge time of 34s, and to make the half-shaft rotate at a uniform speed with a linear rotational speed of 6mm / s. Driven by the rotation of the half shaft, the copper guide wheel 6 moves relative to the half shaft, and the half shaft surface is alternately subjected to pulse current heating and air cooling treatment (i.e. pulse current quenching treatment). After the first circumferential surface of the half shaft is completed by pulse current quenching treatment, it is cooled at room temperature for 45 seconds. Then, the next circumferential surface of the half shaft is subjected to pulse current quenching treatment in the same way as the first circumferential surface of the half shaft. After the above process is completed, the entire bridge housing half shaft is finally processed, and the bridge housing half shaft 3 after pulse current quenching treatment is obtained. Compared to the surface microstructure of the ZG310-570 cast steel axle housing half-shaft (which is ferrite + pearlite), the surface microstructure of axle housing half-shaft 3 is uniform and fine martensite and retained austenite, with a hardened layer depth of 0.58 mm. Therefore, the surface of axle housing half-shaft 3 is harder than that of the ZG310-570 cast steel axle housing. The core microstructure of axle housing half-shaft 3 and the ZG310-570 cast steel axle housing half-shaft (whose surface and core microstructures are the same) are both a mixed microstructure of ferrite + pearlite. The composition of fine and uniform martensite and retained austenite on the surface of axle housing half-shaft 3, the adjustable and controllable hardened layer depth, and the synergistic regulation of a hard surface and a soft core result in a differentiated stepped structure and microstructure of axle housing half-shaft 3. Ultimately, this allows axle housing half-shaft 3 to simultaneously possess higher hardness, wear resistance, and impact toughness, breaking through the technical bottleneck of simultaneously improving the hardness, wear resistance, and impact toughness of ZG310-570 cast steel axle housing half-shafts.

[0025] Table 2 Mechanical properties of ductile iron materials before and after surface electro-pulse quenching

[0026] Example 4

[0027] Activate the surface strengthening device for shaft-type workpieces. Fix both ends of the QT500-7 ductile iron crankshaft onto the clamping and rotating system 4. Adjust the positions of the graphite electrode 5 and the copper guide wheel 6 to ensure close contact with the first surface to be machined on the crankshaft journal. Turn on the power control system 2 to perform uniform rotation and pulse current treatment on the crankshaft. The pulse current treatment is as follows: pulse current of 4.5KA, voltage of 18.5V, frequency of 90Hz, and discharge time of 45s, ensuring uniform rotation of the crankshaft at a linear speed of 5.5mm / s. Driven by the rotation of the crankshaft, the copper guide wheel 6 moves relative to the crankshaft journal, alternately performing pulse current heating and air cooling treatment (i.e., pulse current quenching treatment) on the surface of the crankshaft journal. After the first journal surface of the crankshaft has completed the pulse current quenching treatment, cool it at room temperature for 30s. Then, perform pulse current quenching treatment on the next surface according to the same processing method as the first journal surface. Following the above process, the surface strengthening treatment of the entire stepped shaft is finally completed, resulting in the crankshaft 1 after pulse current quenching treatment.

[0028] Example 5

[0029] The surface strengthening device for shaft-type workpieces is activated. The two ends of the 20Cr steel gearbox stepped shaft are fixed to the clamping and rotating system 4. The positions of the graphite electrode 5 and the copper guide wheel 6 are adjusted to ensure close contact with the first surface of the stepped shaft to be processed. The power control system 2 is turned on to perform uniform rotation and pulse current treatment on the stepped shaft. The pulse current treatment is as follows: pulse current 5.5KA, voltage 19.5V, frequency 105Hz, discharge time 42s, ensuring uniform rotation of the stepped shaft at a linear speed of 6.5mm / s. Driven by the rotation of the stepped shaft, the copper guide wheel 6 moves relative to the stepped shaft, alternately performing pulse current heating and air cooling treatment (i.e., pulse current quenching) on ​​the surface of the stepped shaft. After the first surface of the stepped shaft has completed pulse current quenching, it is cooled at room temperature for 80s. The next surface is then subjected to pulse current quenching in the same manner as the first surface. Following this process, the surface strengthening treatment of the entire crankshaft journal is finally completed, resulting in the stepped shaft 1 after pulse current quenching.

[0030] Example 6

[0031] The surface strengthening device for shaft-type workpieces is activated. The two ends of the TC4 titanium alloy hollow shaft are fixed to the clamping and rotating system 4. The positions of the graphite electrode 5 and the copper guide wheel 6 are adjusted to ensure close contact with the first surface to be processed on the hollow shaft. The power control system 2 is turned on to perform uniform rotation and pulse current treatment on the hollow shaft. The pulse current treatment is as follows: pulse current 6.5KA, voltage 20.5V, frequency 110Hz, discharge time 50s, ensuring uniform rotation of the hollow shaft at a linear speed of 8mm / s. Driven by the rotation of the hollow shaft, the copper guide wheel 6 moves relative to the hollow shaft, alternately performing pulse current heating and air cooling treatment (i.e., pulse current quenching) on ​​the surface of the hollow shaft. After the first surface of the hollow shaft completes the pulse current quenching treatment, it is cooled to room temperature for 80s. The next surface is then subjected to pulse current quenching treatment in the same manner as the first surface. Following this process, the surface strengthening treatment of the entire hollow shaft is finally completed, resulting in the hollow shaft 1 after pulse current quenching treatment.

[0032] Comparative Example 1

[0033] This comparative example is taken from Luo Dan's master's thesis at Hunan University, "Research on Laser Multi-pass Quenching Process of QT600-3 Ductile Iron Surface", published in November 2013. In this comparative example, QT600-3 ductile iron was subjected to single-pass laser surface quenching. Under the action of lasers with different powers of 1300-1700W, the maximum hardened layer depth was 1.16mm and the maximum surface hardness was 60HRC.

[0034] The hardened layer depth of QT600-3 after treatment in Example 1 was 0.98 mm, and the hardness after quenching was 716 HBW, which is equivalent to 63.8 HRC in Rockwell hardness. According to existing technology reports, the greater the hardened layer depth, the greater the surface hardness should be. Compared with Comparative Example 1, the hardened layer depth of Comparative Example 1 was larger, but the hardness obtained by Example 1 of this invention was indeed higher than that obtained by Comparative Example 1. Therefore, compared with Comparative Example 1, Example 1 of this invention achieved an unexpectedly significant improvement in technical effect. In addition, Example 1, which did not disclose the technical effects of high wear resistance and toughness, also achieved technical effects.

[0035] Comparative Example 2

[0036] This comparative example is taken from "Research on Induction Hardening Performance of Ductile Cast Iron for Automotive Parts" published by the Technical Center of China FAW Group Corporation in the journal "Automotive Technology and Materials" in 2013. In this comparative example, QT600-3 ductile cast iron was subjected to induction heating quenching. After induction hardening at 60kW, the maximum surface hardness was 62.5HRC, and the hardened layer depth was between 3-3.5mm.

[0037] In all embodiments of the present invention, the hardened layer depth obtained in Embodiment 1 is the shallowest, at 0.98 mm, and the hardness after quenching is 716 HBW, which is equivalent to 63.8 HRC after Rockwell hardness conversion. According to prior art reports, the greater the hardened layer depth, the greater the surface hardness should be. Compared with Comparative Example 2, the hardened layer depth of Comparative Example 2 is much greater than that of Embodiment 1, but the result is that the hardness obtained in Embodiment 1 is higher than that obtained in Comparative Example 2. Therefore, compared with Comparative Example 2, Embodiment 1 of the present invention achieves an unexpectedly significant improvement in technical effect.

[0038] In summary, compared with existing technologies, this invention enables the processing of irregular or large-sized shaft-like workpieces, simplifies the process, and reduces costs. Through the synergistic control of the device and process parameters, it forms a fine and uniform martensite surface structure, ferrite with a high dislocation ratio or α phase (titanium alloy) with more dislocations, adjustable and controllable hardened layer depth, and a stepped differential structure and microstructure with a hard surface and soft core. Ultimately, this results in workpieces with higher hardness, wear resistance, and impact toughness. Even with a shallow hardened layer depth, it still achieves superior hardness, wear resistance, and impact toughness compared to existing technologies, resulting in unexpectedly significant improvements. Furthermore, the material obtained in Example 1 (not disclosed in the comparative example) also exhibits high wear resistance and toughness.

[0039] This invention achieves pulsed current heating and air cooling (pulse current quenching) of large, complex, and irregularly shaped shaft-like workpieces through the synergistic control of the sample to be processed, the device, the process, and the process parameters. This ensures line contact between the copper guide wheel and the circumferential surface of the shaft-like workpiece, solving the technical problem of difficulty in quenching the surface of large, complex shaft-like workpieces or selectively quenching arbitrary local surfaces. This invention enables the austenitic phase transformation of ferrite in steel workpieces, forming uniform and fine martensite and ferrite with a greater number of dislocations, adjustable and controllable hardened layer depth, a hard surface and soft core, and a fine-grain strengthening effect through synergistic control. This not only hardens the material surface, forms fine grains and a stepped microstructure, and has a larger and more tortuous crystal surface area, effectively hindering crack propagation and improving the material's resistance to fracture during deformation, but also, while the surface hardens, the core retains its initial toughness, resulting in higher hardness, wear resistance, and impact toughness, significantly improving the overall material properties. Yes, it can cause the α-phase in titanium alloy workpieces to undergo an α→β phase transformation. Through the synergistic regulation of multiple aspects, including the formation of uniform, fine martensite and a greater number of dislocations in the α-phase, adjustable and controllable hardened layer depth, a hard surface and soft core, and the effect of fine-grain strengthening, it not only hardens the material surface, forms fine grains and a stepped microstructure, and has a larger and more tortuous crystal surface area, effectively hindering crack propagation and improving the material's resistance to fracture during deformation, but also, while the surface is hardened, the core retains its initial structure with good toughness. It also exhibits higher hardness, wear resistance, and impact toughness, significantly improving the overall performance of the material. Furthermore, compared to laser surface hardening and induction heating surface hardening, it offers a wider controllable range of hardened layers, better surface quality, and superior performance. Existing technologies have difficulty in performing quenching treatment on large, complex, and irregularly shaped shaft workpieces. Even when quenching the workpiece surface, it is difficult to simultaneously improve the workpiece's hardness, wear resistance, and toughness. Compared with existing technologies, this invention can perform surface quenching on both simple and large, complex shaft workpieces, simplifies the process, increases the processing speed, and achieves higher workpiece hardness even when the hardened layer depth is lower than that of existing technologies. Moreover, this invention can simultaneously achieve high toughness and wear resistance.

[0040] In summary, this invention utilizes the synergistic control of shaft-type workpieces with surface strengthening devices, processes, and process parameters, and only within the scope of protection of the claims of this invention can the hardness, wear resistance, and toughness of shaft-type workpieces be improved simultaneously.

Claims

1. A surface strengthening method for a QT600-3 ductile iron bridge housing half-shaft, characterized in that: The method includes: turning on the surface strengthening device for shaft workpieces, fixing both ends of the QT600-3 ductile iron bridge housing half shaft on the clamping and rotating system (4), adjusting the position of the graphite electrode (5) and the copper guide wheel (6) to make close contact with the first circumferential surface to be processed of the half shaft; turning on the power control system (2) to perform uniform rotation and pulse current treatment on the half shaft, wherein the pulse current treatment is: pulse current is 5KA, voltage is 18V, frequency is 100Hz, discharge time is 40s, and the rotational linear speed of the half shaft is 5mm / s; under the rotation of the half shaft, the copper guide wheel (6) moves relative to the half shaft, and pulse current heating and air cooling are alternately performed on the surface of the half shaft. After the first circumferential surface of the half shaft is completed by pulse current quenching treatment, it is cooled at room temperature for 60s, and the next circumferential surface of the half shaft is subjected to pulse current quenching treatment according to the processing method of the first circumferential surface of the half shaft. After the above process is completed, the entire bridge housing half shaft is finally processed, and the bridge housing half shaft 1 after pulse current quenching treatment is obtained. Microstructural characterization and mechanical property analysis were performed on the bridge housing half-shaft 1. The hardened layer depth of bridge housing half-shaft 1 was 0.98 mm. The surface microstructure of bridge housing half-shaft 1 consisted of uniform and fine martensite and ferrite with a high proportion of dislocations. Bridge housing half-shaft 1 formed a structure with a hard surface and a soft core. The surface microstructure of bridge housing half-shaft 1, composed of fine and uniform martensite and ferrite with a higher number of dislocations, along with the adjustable and controllable hardened layer depth and the synergistic effect of a hard surface and soft core, resulted in a differentiated stepped structure and microstructure of bridge housing half-shaft 1. Ultimately, bridge housing half-shaft 1 simultaneously possessed higher hardness, wear resistance, and impact toughness. The surface hardness of bridge housing half-shaft 1 was 716 HBW, and the impact toughness was 8.95 J / cm. 2 ; The surface strengthening device for shaft-type workpieces includes: a base (1), a power control system (2), a worktable (3), a clamping and rotating system (4), a graphite electrode (5), and a copper guide wheel (6). The power control system (2) is located on the base (1) and is used to control the output of pulse current and the opening and movement of the clamping and rotating system (4), the graphite electrode (5), and the copper guide wheel (6). The worktable (3) is located above the power control system (2). The clamping and rotating system (4) is placed on the worktable (3) and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system (2) is connected to the graphite electrode (5) and the copper guide wheel (6). The graphite electrode (5) is placed at the front end of the worktable (3), and the copper guide wheel (6) is located at the rear end of the worktable (3). The graphite electrode (5) is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel (6) is a copper wheel that can rotate freely.

2. A surface strengthening method for a QT600-3 ductile iron bridge housing half-shaft, characterized in that: The method includes: turning on the surface strengthening device for shaft workpieces, fixing both ends of the QT600-3 ductile iron bridge housing half shaft on the clamping and rotating system (4), adjusting the position of the graphite electrode (5) and the copper guide wheel (6) to make close contact with the first circumferential surface to be processed of the half shaft; turning on the power control system (2) to perform uniform rotation and pulse current treatment on the half shaft, wherein the pulse current treatment is: the pulse current is 8KA, the voltage is 20V, the frequency is 120Hz, the discharge time is 20s, and the half shaft rotates at a uniform speed, with the rotational linear speed of the half shaft being 10mm / s; under the rotation of the half shaft, the copper guide wheel 6 moves relative to the half shaft, and the half shaft surface is alternately subjected to pulse current heating and air cooling treatment; after the first circumferential surface of the half shaft is completed by pulse current quenching treatment, it is cooled at room temperature for 90s, and the next circumferential surface of the half shaft is subjected to pulse current quenching treatment according to the processing method of the first circumferential surface of the half shaft; after completing the processing of the entire bridge housing half shaft according to the above process, the bridge housing half shaft 2 after pulse current quenching treatment is obtained. The surface microstructure of the bridge housing half-shaft 2 consists of uniform, fine martensite and ferrite with a high proportion of dislocations. The combination of fine, uniform martensite, ferrite with a greater number of dislocations, the adjustable and controllable hardened layer depth, and the synergistic effect of a hard surface and soft core results in a differentiated stepped structure and microstructure for the bridge housing half-shaft 2. The hardened layer depth of the bridge housing half-shaft 2 is 3.11 mm, giving it higher hardness, wear resistance, and impact toughness. The surface hardness of the bridge housing half-shaft 1 is 738 HBW, and its impact toughness is 6.53 J / cm². 2 ; The surface strengthening device for shaft-type workpieces includes: a base (1), a power control system (2), a worktable (3), a clamping and rotating system (4), a graphite electrode (5), and a copper guide wheel (6). The power control system (2) is located on the base (1) and is used to control the output of pulse current and the opening and movement of the clamping and rotating system (4), the graphite electrode (5), and the copper guide wheel (6). The worktable (3) is located above the power control system (2). The clamping and rotating system (4) is placed on the worktable (3) and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system (2) is connected to the graphite electrode (5) and the copper guide wheel (6). The graphite electrode (5) is placed at the front end of the worktable (3), and the copper guide wheel (6) is located at the rear end of the worktable (3). The graphite electrode (5) is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel (6) is a copper wheel that can rotate freely.

3. A surface strengthening method for ZG310-570 cast steel bridge housing half-shaft, characterized in that: The method includes: turning on the surface strengthening device for shaft workpieces, fixing both ends of the ZG310-570 cast steel bridge housing half shaft on the clamping and rotating system (4), adjusting the position of the graphite electrode (5) and the copper guide wheel (6) to make close contact with the first circumferential surface to be processed of the half shaft; turning on the power control system (2) to perform uniform rotation and pulse current treatment on the half shaft, wherein the pulse current treatment is: the pulse current is 4KA, the voltage is 16V, the frequency is 80Hz, the discharge time is 34s, and the half shaft rotates at a uniform speed, with a rotational linear velocity of 6mm / s; under the rotation of the half shaft, the copper guide wheel 6 moves relative to the half shaft, and the half shaft surface is alternately subjected to pulse current heating and air cooling treatment. After the first circumferential surface of the half shaft is completed by pulse current quenching treatment, it is cooled at room temperature for 45s, and the next circumferential surface of the half shaft is subjected to pulse current quenching treatment according to the processing method of the first circumferential surface of the half shaft. After the above process is completed, the entire bridge housing half shaft is finally processed, and the bridge housing half shaft 3 after pulse current quenching treatment is obtained. The surface microstructure of the bridge housing half-shaft 3 consists of fine and uniform martensite and retained austenite. The adjustable and controllable depth of the hardened layer and the synergistic regulation of a hard surface and a soft core result in a differentiated stepped structure and microstructure for the bridge housing half-shaft 3. This gives the bridge housing half-shaft 3 higher hardness, wear resistance, and impact toughness. The surface hardness of the bridge housing half-shaft 3 is 654 HBW; the impact toughness is 17.56 J / cm². 2 ; The surface strengthening device for shaft-type workpieces includes: a base (1), a power control system (2), a worktable (3), a clamping and rotating system (4), a graphite electrode (5), and a copper guide wheel (6). The power control system (2) is located on the base (1) and is used to control the output of pulse current and the opening and movement of the clamping and rotating system (4), the graphite electrode (5), and the copper guide wheel (6). The worktable (3) is located above the power control system (2). The clamping and rotating system (4) is placed on the worktable (3) and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system (2) is connected to the graphite electrode (5) and the copper guide wheel (6). The graphite electrode (5) is placed at the front end of the worktable (3), and the copper guide wheel (6) is located at the rear end of the worktable (3). The graphite electrode (5) is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel (6) is a copper wheel that can rotate freely.

4. A surface strengthening method for a QT500-7 ductile iron crankshaft, characterized in that: The method includes: turning on the surface strengthening device for shaft workpieces, fixing both ends of the QT500-7 ductile iron crankshaft on the clamping and rotating system (4), adjusting the position of the graphite electrode (5) and the copper guide wheel (6) to make close contact with the first surface to be processed of the crankshaft journal; turning on the power control system (2) to rotate the crankshaft at a constant speed and perform pulse current treatment, wherein the pulse current treatment is: the pulse current is 4.5KA, the voltage is 18.5V, the frequency is 90Hz, the discharge time is 45s, and the crankshaft rotates at a constant speed, with a rotational linear velocity of 5.5mm / s; under the rotation of the crankshaft, the copper guide wheel 6 moves relative to the crankshaft journal, and pulse current heating and air cooling are alternately performed on the surface of the crankshaft journal. After the first journal surface of the crankshaft is completed by pulse current quenching treatment, it is cooled at room temperature for 30s, and then the next surface is subjected to pulse current quenching treatment according to the processing method of the first journal surface of the crankshaft. Following the above process, the surface strengthening treatment of the entire stepped shaft is finally completed, and the crankshaft 1 after pulse current quenching treatment is obtained. The surface strengthening device for shaft-type workpieces includes: a base (1), a power control system (2), a worktable (3), a clamping and rotating system (4), a graphite electrode (5), and a copper guide wheel (6). The power control system (2) is located on the base (1) and is used to control the output of pulse current and the opening and movement of the clamping and rotating system (4), the graphite electrode (5), and the copper guide wheel (6). The worktable (3) is located above the power control system (2). The clamping and rotating system (4) is placed on the worktable (3) and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system (2) is connected to the graphite electrode (5) and the copper guide wheel (6). The graphite electrode (5) is placed at the front end of the worktable (3), and the copper guide wheel (6) is located at the rear end of the worktable (3). The graphite electrode (5) is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel (6) is a copper wheel that can rotate freely.

5. A surface strengthening method for a 20Cr steel gearbox stepped shaft, characterized in that: The method includes: turning on the surface strengthening device for shaft workpieces, fixing both ends of the 20Cr steel gearbox stepped shaft on the clamping and rotating system (4), adjusting the position of the graphite electrode (5) and the copper guide wheel (6) to make close contact with the first surface to be processed of the stepped shaft; turning on the power control system (2) to rotate the stepped shaft at a constant speed and perform pulse current treatment, wherein the pulse current treatment is: the pulse current is 5.5KA, the voltage is 19.5V, the frequency is 105Hz, the discharge time is 42s, and the stepped shaft rotates at a constant speed, with a rotational linear velocity of 6.5mm / s; under the rotation of the stepped shaft, the copper guide wheel 6 moves relative to the stepped shaft, and pulse current heating and air cooling are alternately performed on the surface of the stepped shaft. After the first surface of the stepped shaft has completed the pulse current quenching treatment, it is cooled at room temperature for 80s, and then the next surface is subjected to pulse current quenching treatment according to the processing method of the first surface of the stepped shaft. Following the above process, the surface strengthening treatment of the entire crankshaft journal is finally completed, and the stepped shaft 1 after pulse current quenching treatment is obtained. The surface strengthening device for shaft-type workpieces includes: a base (1), a power control system (2), a worktable (3), a clamping and rotating system (4), a graphite electrode (5), and a copper guide wheel (6). The power control system (2) is located on the base (1) and is used to control the output of pulse current and the opening and movement of the clamping and rotating system (4), the graphite electrode (5), and the copper guide wheel (6). The worktable (3) is located above the power control system (2). The clamping and rotating system (4) is placed on the worktable (3) and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system (2) is connected to the graphite electrode (5) and the copper guide wheel (6). The graphite electrode (5) is placed at the front end of the worktable (3), and the copper guide wheel (6) is located at the rear end of the worktable (3). The graphite electrode (5) is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel (6) is a copper wheel that can rotate freely.

6. A surface strengthening method for a TC4 titanium alloy hollow shaft, characterized in that: The method includes: turning on the surface strengthening device for shaft workpieces, fixing both ends of the TC4 titanium alloy hollow shaft on the clamping and rotating system (4), adjusting the position of the graphite electrode (5) and the copper guide wheel (6) to make close contact with the first surface to be processed of the hollow shaft; turning on the power control system (2) to perform uniform rotation and pulse current treatment on the hollow shaft, wherein the pulse current treatment is: the pulse current is 6.5KA, the voltage is 20.5V, the frequency is 110Hz, the discharge time is 50s, and the hollow shaft rotates at a uniform speed, with a rotational linear velocity of 8mm / s; under the rotation of the hollow shaft, the copper guide wheel 6 moves relative to the hollow shaft, and pulse current heating and air cooling are alternately performed on the surface of the hollow shaft. After the first surface of the hollow shaft has completed the pulse current quenching treatment, it is cooled at room temperature for 80s, and then the next surface is subjected to pulse current quenching treatment according to the processing method of the first surface of the hollow shaft. Following the above process, the surface strengthening treatment of the entire hollow shaft is finally completed, and the hollow shaft 1 after pulse current quenching treatment is obtained. The surface strengthening device for shaft-type workpieces includes: a base (1), a power control system (2), a worktable (3), a clamping and rotating system (4), a graphite electrode (5), and a copper guide wheel (6). The power control system (2) is located on the base (1) and is used to control the output of pulse current and the opening and movement of the clamping and rotating system (4), the graphite electrode (5), and the copper guide wheel (6). The worktable (3) is located above the power control system (2). The clamping and rotating system (4) is placed on the worktable (3) and is used to clamp and fix the workpiece and adjust the workpiece to move up and down and rotate. The power control system (2) is connected to the graphite electrode (5) and the copper guide wheel (6). The graphite electrode (5) is placed at the front end of the worktable (3), and the copper guide wheel (6) is located at the rear end of the worktable (3). The graphite electrode (5) is a semi-circular groove electrode formed by stacking multiple graphite blocks, which can cover the surface of the workpiece. The copper guide wheel (6) is a copper wheel that can rotate freely.

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