Electric arc additive remanufacturing method for hot forging die of automobile half shaft

Abstract

The invention discloses an automobile half shaft hot forging die electric arc additive remanufacturing method, and relates to the technical field of hot forging die electric arc additive remanufacturing, and the method comprises the following steps: S1, determining a heat equilibrium state temperature field through the heat flux density of finite element analysis so as to determine a hot forging die area for electric arc additive remanufacturing; s2, an accurate reverse digital model is established for a hot forging die failure area, numerical control machining is facilitated, and an optimal electric arc additive remanufacturing path is planned for the model; s3, the to-be-welded hot forging die and the welding material are subjected to pre-welding pretreatment; s4, optimal additive manufacturing process parameters of the KT835 welding material and the YD557 welding material are found out, and electric arc additive remanufacturing is conducted on the pretreated hot forging die according to the planned path; and S5, post-processing is conducted on the hot forging die, a model with the qualified size is obtained, the remanufacturing process is simplified, the remanufacturing area is divided through accurate heat balance analysis, and the labor cost and the machining cost are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of hot forging die additive remanufacturing, and in particular to an arc additive remanufacturing method for a hot forging die of an automobile half-axle. Background Art

[0002] During the manufacturing process of automobile half shafts as key transmission components, hot forging dies often face harsh working environments, resulting in frequent wear and thermal fatigue failure, which affects the life and production efficiency of hot forging dies. Traditional hot forging die repair methods, such as manual surfacing and thermal spraying technology, can extend the service life of hot forging dies to a certain extent, but they usually cannot meet the performance standards of new dies, and the accuracy and consistency of repair are difficult to guarantee. Especially when dealing with complex three-dimensional cavities and fine structures of hot forging dies, traditional methods are more limited and it is difficult to achieve high-quality and high-precision repair effects. The low cost, high efficiency, and flexible selection of repair areas and additive manufacturing materials of electric arc additive manufacturing (WAAM) technology provide new possibilities for hot forging die repair. However, the traditional method first removes the failure area by air planing or machining, and then removes the model by three-dimensional scanning and compares it with the standard mold to determine the arc additive remanufacturing area. The process is complicated and the precision of the remanufactured mold is not high. There is no set of guiding theories to remove the failure layer of hot forging dies, which makes it impossible to remanufacture hot forging dies by arc additive in batches. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an arc additive remanufacturing method for a hot forging die of an automobile half-axle, so as to solve the deficiencies of the prior art.

[0004] The object of the present invention is achieved through the following technical solution: A method for arc additive remanufacturing of a hot forging die for an automobile half-axle, comprising the following steps:

[0005] S1. Determine the thermal equilibrium temperature field through the heat flux density of finite element analysis, so as to determine the failure area of ​​the hot forging die for arc additive remanufacturing;

[0006] S2. Establish an accurate reverse digital model of the hot forging die failure area to facilitate CNC machining and plan the best arc additive remanufacturing path for the model;

[0007] S3, pre-treating the hot forging die and welding materials for arc additive remanufacturing;

[0008] S4. Find out the optimal additive manufacturing process parameters of KT835 welding materials and YD557 welding materials, and perform arc additive manufacturing on the pre-treated hot forging die according to the planned path; KT835 welding materials are used as the base material to enhance the plastic deformation ability of the hot forging die, and YD557 is used as the surface strengthening layer material to form a double metal layer structure. Through arc additive manufacturing technology, ensure that the surface of the hot forging die has excellent wear resistance and thermal fatigue resistance;

[0009] S5. Post-process the hot forging die to obtain a model with qualified dimensions.

[0010] Furthermore, in step S1, the arc additive remanufacturing area is divided by the 540°C isotherm under the thermal equilibrium temperature field to ensure the removal of the fatigue stress layer exceeding 510 MPa on the surface of the hot forging die.

[0011] Further, in step S2, the path planning of arc additive manufacturing includes the following steps:

[0012] S21. For the failure area of ​​the hot forging die, a reverse digital model is established using MATLAB and 3D software, and the failure area of ​​the hot forging die is removed by CNC machining using computer-aided manufacturing software CAM to ensure that there are no defects such as cracks on the surface of the hot forging die after machining, thereby obtaining the H13 steel hot forging die substrate to be manufactured by arc additive manufacturing;

[0013] S22. Use the principle of central axis transformation to perform adaptive path planning on the digital model to ensure uniform filling and gap-free arc additive layers. Use offline encoded paths to effectively fill any given cross-sectional geometry on the surface of the hot forging die and reduce the heat-affected zone and internal stress.

[0014] Furthermore, in step S3, a strict hot forging die surface treatment procedure is implemented to remove impurities on the hot forging die, and then the hot forging die is preheated to 400°C as a whole to optimize welding conditions; then the hot forging die is wrapped with insulation material to maintain the preheating state of the hot forging die to ensure that the temperature of the hot forging model cavity area to be remanufactured is not lower than 320°C, creating a good thermal environment for subsequent arc additive manufacturing and preventing stress concentration caused by sudden temperature changes.

[0015] Furthermore, the yield strength σ of KT835 welding material s Greater than or equal to 1156.5MPa, YD557 welding wire is specially designed for surface strengthening layer 9, and its mechanical properties include: yield strength ≥867.6MPa, tensile strength ≥1186.2MPa, elongation ≥6.1% and section shrinkage ≥3%.

[0016] Furthermore, the average height of the base layer is 22 mm, and the average height of the surface strengthening layer is 8 mm.

[0017] Further, the carbon equivalent of H13 steel is 1.682%, the carbon equivalent of the base layer material KT835 is 2.205%, and the carbon equivalent of the strengthening layer material YD557 is 3.359%.

[0018] Furthermore, in step S4, the Taguchi design method is used to perform microstructure analysis, microhardness test and wear performance test on the single-pass single-layer and single-pass multi-layer processes of KT835 welding wire and YD557 welding wire, and the arc additive manufacturing parameters are optimized. For KT835 welding material, the determined process parameters are: welding voltage U=21.5V, wire feeding speed Vs=4.5m / min, deposition speed Vc=12mm / s; for YD557 welding material, the optimized parameter range is: U=19.5-20.5V, Vs=5m / min, Vc=12mm / s.

[0019] Furthermore, in step S4, when the hot forging die base is arc-additively remanufactured, after completing the arc-additive manufacturing of the 6 mm base layer, the oxide scale and welding slag on the surface of the base layer are removed, and ultrasonic impact is performed on it. During the impact, the impact gun moves back and forth on the surface at a uniform speed, and then the YD557 welding wire is used to perform arc-additive manufacturing of the surface strengthening layer, wherein the path selected is from the inside to the outside for layer-by-layer additive manufacturing.

[0020] Further, in step S5, after completing the arc additive manufacturing, the workpiece is heated to 850°C and kept warm for 2.5 hours. After taking out the sample, it is immediately oil-cooled to room temperature, heated to 560°C again and kept warm for 2.5 hours, and air-cooled to complete the heat treatment. At this time, most of the residual austenite in the mold body is transformed into martensite, and the internal stress of the martensite is eliminated. At this time, the hardness of the surfacing part is higher than the hardness of the mold body. The hot forging die is post-processed, including machining, cutting off flash, and grinding burrs to obtain a hot forging die that meets standard dimensions.

[0021] The beneficial effects of the present invention are:

[0022] 1. Provide a method for quickly removing the failure layer of the hot forging die, simplify the remanufacturing process, divide the remanufacturing area through accurate thermal balance analysis, and reduce labor and machining costs.

[0023] 2. The selection of bimetallic layer materials and the optimization of process parameters significantly improve the comprehensive performance of the hot forging die, optimize the heat affected zone control and thermal stress distribution, and extend the service life.

[0024] 3. Efficient path planning and precise control improve the accuracy of hot forging die remanufacturing, realize efficient and high-quality hot forging die batch remanufacturing, and improve production efficiency.

[0025] 4. The specific heat treatment process effectively improves the microstructure, enhances the wear resistance and overall mechanical properties of the hot forging die, is suitable for the long-life, low-cost manufacturing of curved cavity hot forging dies, and provides a practical solution for the efficient remanufacturing of automotive half-axle hot forging dies. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1A schematic diagram of a half-section of a hot forging die in an arc additive remanufacturing method of a hot forging die for an automobile half-axle according to the present invention;

[0027] Figure 2 The arc additive remanufacturing area division determined by the 540°C isotherm in the thermal equilibrium temperature field is shown for the present invention;

[0028] Figure 3 A three-dimensional model for remanufacturing of the hot forging die of the present invention and arc additive remanufacturing path planning;

[0029] Figure 4 It is a two-dimensional structure of a double metal layer after the arc additive manufacturing process of the present invention;

[0030] Figure 5 This is a process flow chart of arc additive remanufacturing of the lower die of the hot forging die of the present invention;

[0031] In the figure, 1-upper die, 2-lower die, 3-workpiece, 4-digital model of arc additive remanufacturing area, 5-path planning of digital model of arc additive remanufacturing, 6-lower die after CNC machining, 7-H13 steel hot forging die substrate, 8-base layer, 9-strengthening layer. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0033] Embodiment 1

[0034] like Figures 1 to 5 As shown, Figure 1 The upper die 1 and the lower die 2 of the hot end die are molded together to form a workpiece (automobile half shaft). An arc additive remanufacturing method for a hot forging die of an automobile half shaft comprises the following steps:

[0035] S1. Determine the thermal equilibrium temperature field through the heat flux density of finite element analysis, so as to determine the failure area of ​​the hot forging die for arc additive remanufacturing; provide a method for quickly removing the failure layer of the hot forging die, determine the 540℃ isothermal curve to divide the mold additive remanufacturing area by comparing the temperature field and stress field in the thermal equilibrium state, and use computer-aided manufacturing software (CAM) to remove the failure area of ​​the hot forging die above 540℃, and design the best arc additive remanufacturing path according to the digital model; simplify the traditional process steps of first removing the failure area of ​​the hot forging die and then three-dimensionally scanning the failed hot forging die;

[0036] S2. Establish an accurate reverse digital model of the hot forging die failure area to facilitate CNC machining and plan the best arc additive manufacturing path for the model. When planning and designing the strengthening layer path, reserve an additional 4mm of machining allowance;

[0037] S3, pre-treating the hot forging die and welding materials to be welded;

[0038] S4. Find out the optimal additive manufacturing process parameters for KT835 welding materials and YD557 welding materials, and perform arc additive remanufacturing on the pre-treated hot forging die according to the planned path; KT835 welding materials are used as the base material to enhance the plastic deformation ability of the hot forging die, and YD557 is used as the surface strengthening layer material to form a bimetallic layer structure. Through arc additive manufacturing technology, the surface of the hot forging die is ensured to have excellent wear resistance and thermal fatigue resistance. The base layer uses low-alloy heat-resistant steel KT835 welding wire to enhance the toughness and heat resistance of the matrix, and the surface strengthening layer uses high-wear-resistant flux-cored wire YD557, which contains high-temperature alloy elements such as tungsten, molybdenum, and cobalt. Through precise arc additive manufacturing technology, strong carbon compounds are formed on the surface of the lower die to improve the wear resistance and thermal fatigue resistance of the hot forging die;

[0039] Among them, the optimal additive manufacturing process parameters for KT835 welding materials and YD557 welding materials ensure the formation of a uniform and defect-free surfacing layer on the surface of the hot forging die by precisely controlling key parameters such as welding voltage, wire feeding speed, and shielding gas flow rate; the Taguchi design method is used to optimize the parameters in the arc additive manufacturing process to obtain the best single-pass forming quality and multi-layer surfacing effect, ensuring a good metallurgical bond between the surfacing layer and the substrate; specifically, for KT835 welding materials, the determined process parameters are: welding voltage U = 21.5V, wire feeding speed Vs = 4.5m / min, deposition speed Vc = 12mm / s; for YD557 welding materials, the optimized parameter range is: U = 19.5-20.5V, Vs = 5m / min, Vc = 12mm / s;

[0040] S5. Post-process the hot forging die to obtain a model with qualified dimensions. In order to eliminate the internal stress generated during the arc additive manufacturing process and ensure the stability and service life of the remanufactured mold, a specific heat treatment process is designed, including preheating and tempering steps. The tempering temperature is set at 560°C, and the holding time is adjusted according to the material thickness to optimize the microstructure and improve the overall mechanical properties. The hot forging die that has completed arc additive remanufacturing is surface treated, including machining, grinding, cleaning, etc., to ensure that the surface is smooth and free of defects. Metallographic analysis, microhardness testing, friction and wear testing, and tensile performance testing are used to comprehensively evaluate the microstructure, hardness distribution, wear resistance, and comprehensive mechanical properties of the remanufactured mold to ensure that it meets actual production needs.

[0041] Embodiment 2

[0042] On the basis of the first embodiment, in step S1, the finite element analysis technology is used to accurately locate the temperature field in the thermal equilibrium state based on the heat flux density distribution of the hot forging die during the operation process, thereby dividing the arc additive remanufacturing area of ​​the hot forging die, ensuring that the parts that are subjected to excessive heat load and produce fatigue failure are effectively identified and located. In specific implementation, the failure area determination and preparatory processing stage includes:

[0043] 1. First, the working process of the hot forging die is simulated using finite element analysis software. After the hot forging die has gone through 20 working cycles, the heat flux density of the hot forging die enters a balanced state, and the thermal equilibrium temperature field and the corresponding stress distribution state inside the hot forging die are accurately identified;

[0044] 2. In view of the data in the material manual showing that the fatigue strength of H13 steel at 540°C is 510MPa, Figure 2 It can be seen that the 540℃ isothermal curve of the hot forging die no longer expands after 20 times, and the hot forging die enters a thermal equilibrium state. By comparing the temperature field area above 540℃ (height of about 28mm) and the stress field area above 510MPa (height of about 26.3mm), it is found that the area above the 540℃ isotherm can remove the fatigue stress layer failure area of ​​the hot forging die of 510MPa, and the 540℃ isotherm is established as the scientific basis for defining the arc additive remanufacturing area, ensuring the effective identification and isolation of the high-stress fatigue layer that needs to be removed.

[0045] Embodiment 3

[0046] In the second embodiment, in step S2, the path planning of arc additive manufacturing includes the following steps:

[0047] S21. For the failure area of ​​the hot forging die, a reverse digital model (such as Figure 3 The digital model of the arc additive remanufacturing area is obtained by using computer-aided manufacturing software CAM to remove the failure area of ​​the hot forging die by numerical control machining to ensure that there are no defects such as cracks on the surface of the hot forging die after machining, and the H13 steel hot forging die substrate to be manufactured by arc additive manufacturing is obtained. Figure 3 The lower die 6 after CNC machining;

[0048] S22, using the principle of medial axis transformation to perform adaptive path planning on the digital model, ensuring uniform filling and gap-free arc additive layers, using offline coded paths to effectively fill any given cross-sectional geometry on the hot forging die surface, reducing heat-affected zones and internal stresses, such as Figure 3 Digital model path planning for arc additive remanufacturing5.

[0049] Embodiment 4

[0050] In Example 3, in step S3, a strict hot forging die surface treatment procedure is implemented to remove impurities on the hot forging die, including but not limited to sand, oxide scale, oil stains, rust, burrs and casting defects, to ensure surface cleanliness, and then the hot forging die is preheated to 400°C as a whole to optimize welding conditions; then the hot forging die is wrapped with insulation material to maintain the preheating state of the hot forging die to ensure that the temperature of the hot forging model cavity area to be remanufactured is not lower than 320°C, to create a good thermal environment for subsequent arc additive manufacturing, and to prevent stress concentration caused by sudden temperature changes.

[0051] Embodiment 5

[0052] On the basis of the fourth embodiment, the selection of welding materials for the remanufacturing hot forging die and the optimization of arc additive manufacturing process parameters include:

[0053] 1. KT835 welding wire is selected as the base material 8 for arc additive remanufacturing of hot forging dies, mainly due to its low carbon characteristics and excellent compatibility with the H13 steel matrix; this characteristic not only prevents carbon migration, but also significantly reduces the risk of interface separation induced by thermal stress, and also provides the necessary toughness guarantee for the hot forging die by showing excellent plasticity (elongation δ ≥ 14.5%) and ductility (section reduction ψ ≥ 22%), effectively inhibiting the formation of cracks during service; it is worth noting that although the yield strength σ of KT835 is s At least 1156.5MPa, which is lower than H13 steel, but its excellent ductility successfully makes up for this strength difference, making it the preferred medium for connecting the hot forging die matrix and the surface strengthening layer; the Ni element contained in the KT835 welding wire, as a non-carbide forming element, can dissolve in α-Fe, thereby strengthening the matrix, refining the austenite grains, reducing overheating sensitivity, and playing a precipitation strengthening role, while improving the tempering stability of the steel. The Mn in it can dissolve in Fe3C to form compounds such as (FeMn3)C, further reducing overheating sensitivity and improving tempering stability;

[0054] 2. YD557 welding wire is specially designed for surface strengthening layer 9. Its mechanical performance indicators include yield strength ≥867.6MPa, tensile strength ≥1186.2MPa, elongation ≥6.1% and cross-sectional shrinkage ≥3%. Room temperature mechanical tests show that its ductility index is inferior to H13 steel and KT835. The unique advantage of YD557 comes from the fact that it is rich in high-temperature alloy elements such as W, Mo, and Co, which give the material excellent thermal fatigue resistance under high temperature conditions. The specific mechanism is: rapid cooling promotes the formation of martensitic structure and retained austenite. In the subsequent tempering process, alloy element carbides in the supersaturated martensite precipitate and transform into tempered martensite. This process is accompanied by the precipitation of solid-solution carbon in α-ferrite, forming a more stable organizational structure with a hardness of 645HV. Elements such as W, Cr, and Mo not only promote the formation of carbides, but also can replace Co and Fe to form solid solution strengthening, significantly improving wear resistance and reducing wear. Therefore, although the mechanical properties of YD557 are slightly insufficient at room temperature, its high temperature performance is excellent, which effectively improves the heat resistance and wear resistance of hot forging dies, ensuring reliability and long life under severe thermal conditions;

[0055] 3. In the selection of bimetallic layers, Figure 4 As shown, the average height of the base layer 8 (KT835) is about 6mm. Its high plasticity effectively alleviates the peak stress of the surface strengthening layer 9 (YD557) under thermal fatigue and mechanical load, and prevents damage to the H13 steel hot forging die substrate 7. The average height of the YD557 layer is 26mm. Although the mechanical properties at room temperature are relatively low, its unique composition design gives it good thermal stability and a gentle stress fracture curve, allowing the surface layer to maintain good comprehensive performance under high-temperature working conditions. Therefore, this double-layer material design not only realizes the gradual transition of material properties, but also optimizes the overall thermal stress distribution of the hot forging die, achieving the purpose of both reducing costs and increasing service life;

[0056] 4. In material selection and process optimization, the carbon equivalent of H13 steel is 1.682%, the carbon equivalent of the base material KT835 is 2.205%, and the carbon equivalent of the strengthening layer material YD557 is significantly increased to 3.359%, especially YD557 due to the additional addition of tungsten (W) and cobalt (Co) elements, resulting in an increase in its carbon equivalent and potential crack sensitivity. In view of this, YD557 requires more stringent preheating measures during arc additive manufacturing (AM) to prevent the formation of cracks in the process, which is attributed to the hardening and cracking tendency that may be caused by high content of alloying elements. To this end, the present invention proposes a set of preheating and temperature control strategies, using a box-type resistance heating furnace to pre-heat the substrate uniformly to 400°C to ensure that the material is in a suitable state before arc additive manufacturing. During the manufacturing process, the substrate temperature is maintained at not less than 250°C to stabilize the heat-affected zone and reduce the risk of cracks induced by thermal stress. In addition, in order to optimize the welding environment, a mixed gas of 80% argon (Ar) + 20% carbon dioxide (C02) is used as the protective atmosphere, aiming to protect the weld from contamination and improve the welding quality and integrity;

[0057] 5. Through the Taguchi design method, the arc additive manufacturing parameters are optimized through microstructure analysis, microhardness test and wear performance test. For KT835, the determined process parameters are: welding voltage U = 21.5V, wire feeding speed Vs = 4.5m / min, deposition speed Vc = 12mm / s; for YD557, the optimized parameter range is: U = 19.5-20.5V, Vs = 5m / min, Vc = 12mm / s.

[0058] Embodiment 6

[0059] On the basis of Example 5, when the hot forging die base body is remanufactured by arc additive manufacturing, after completing the arc additive manufacturing of the 6mm base layer, the oxide scale and welding slag on the surface of the base layer are removed, and ultrasonic impact is performed on it. During the impact, the impact gun moves back and forth on the surface at a uniform speed, and then YD557 is used to perform arc additive manufacturing of a surface strengthening layer of about 26mm. The path is selected to perform additive manufacturing layer by layer from the inside to the outside. Compared with other paths, the path sample shows excellent organizational properties, mechanical properties and wear properties in multi-pass multi-layer arc additive manufacturing, and has a lower average friction coefficient and wear amount;

[0060] After completing the arc additive manufacturing, the workpiece is heated to 850℃ and kept warm for 2.5h. After taking out the sample, it is immediately oil-cooled to room temperature, and then heated to 560℃ and kept warm for 2.5h and air-cooled to complete the heat treatment. After air-cooling to room temperature, most of the residual austenite in the mold body is transformed into martensite, and the internal stress of the martensite is eliminated. At this time, the hardness of the remanufacturing part is higher than the hardness of the mold body. The hot forging die is post-processed, including machining, cutting off the flash, and grinding the burrs to obtain a hot forging die that meets the standard size, such as Figure 1 Middle and lower mold 2.

[0061] In summary, using this set of hot forging die arc additive remanufacturing method, through simplified process flow and the use of innovative bimetallic layer materials, the surface hardness of the hot forging die is increased by 50HV compared with the H13 steel substrate, and the average friction coefficient is also optimized by 41.2%. This improvement greatly enhances the wear resistance of the hot forging die, and the service life of the hot forging die is significantly enhanced by more than 26%. This technical method not only effectively saves the consumption of original hot forging die materials and reduces the overall cost of the hot forging die, but also significantly extends the service life of the hot forging die.

Claims

1. An arc additive remanufacturing method for hot forging dies of automobile half shafts, characterized in that: The following steps are involved: S1. Determine the thermal equilibrium temperature field through the heat flux density of finite element analysis, so as to determine the failure area of ​​the hot forging die for arc additive remanufacturing; S2. Establish an accurate reverse digital model of the hot forging die failure area to facilitate CNC machining and plan the best arc additive remanufacturing path for the model; S3, pre-treating the hot forging die and welding materials to be welded; S4, find out the optimal additive manufacturing process parameters of KT835 welding materials and YD557 welding materials, and perform arc additive remanufacturing on the pretreated hot forging die according to the planned path; KT835 welding material is used as the base material to enhance the plastic deformation ability of the hot forging die. YD557 is used as the surface strengthening layer material to form a double metal layer structure. Through arc additive manufacturing technology, the hot forging die surface is ensured to have excellent wear resistance and thermal fatigue resistance. S5. Post-process the hot forging die to obtain a model with qualified dimensions.

2. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1 is characterized in that: In step S1, the arc additive remanufacturing area is divided by the 540°C isotherm under the thermal equilibrium temperature field to ensure the removal of the fatigue stress layer exceeding 510 MPa on the surface of the hot forging die.

3. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1 is characterized in that: In step S2, the path planning of arc additive manufacturing includes the following steps: S21. For the failure area of ​​the hot forging die, a reverse digital model is established using MATLAB and 3D software, and the failure area of ​​the hot forging die is removed by CNC machining using computer-aided manufacturing software CAM to ensure that there are no defects such as cracks on the surface of the hot forging die after machining, thereby obtaining the H13 steel hot forging die substrate to be manufactured by arc additive manufacturing; S22. Use the principle of medial axis transformation to perform adaptive path planning on the digital model to ensure uniform filling and gap-free arc additive layers. Use offline programming paths to effectively fill any given cross-sectional geometry on the surface of the hot forging die and reduce the heat-affected zone and internal stress.

4. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1 is characterized in that: In step S3, a strict hot forging die surface treatment procedure is implemented to remove impurities on the hot forging die, and then the hot forging die is preheated to 400°C as a whole to optimize welding conditions; then the hot forging die is wrapped with insulation material to maintain the preheating state of the hot forging die, ensuring that the temperature of the hot forging model cavity area to be surfacing is not lower than 320°C, creating a good thermal environment for subsequent arc additive manufacturing and preventing stress concentration caused by sudden temperature changes.

5. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1 is characterized in that: Yield strength σ of KT835 welding material s Greater than or equal to 1156.5MPa, YD557 welding wire is specially designed for surface strengthening layer 9, and its mechanical properties include: yield strength ≥867.6MPa, tensile strength ≥1186.2MPa, elongation ≥6.1% and section shrinkage ≥3%.

6. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 5 is characterized in that: The average height of the base layer is 6 mm, and the average height of the surface strengthening layer is 26 mm.

7. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 6 is characterized in that: The carbon equivalent of H13 steel is 1.682%, the carbon equivalent of the base material KT835 is 2.205%, and the carbon equivalent of the strengthening layer material YD557 is 3.359%.

8. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1 is characterized in that: In step S4, the arc additive manufacturing parameters are optimized through microstructure analysis, microhardness test and wear performance test by Taguchi design method. For KT835 welding material, the determined process parameters are: welding voltage U = 21.5V, wire feeding speed Vs = 4.5m / min, deposition speed Vc = 12mm / s; for YD557 welding material, the optimized parameter range is: U = 19.5-20.5V, Vs = 5m / min, Vc = 12mm / s.

9. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1, characterized in that: In step S4, when the hot forging die base is arc-added and remanufactured, after completing the arc additive manufacturing of the 6mm base layer, the oxide scale and welding slag on the surface of the base layer are removed, and ultrasonic impact is performed on it. The impact gun moves back and forth at a uniform speed on the surface, and then YD557 is used to perform arc additive manufacturing of a surface strengthening layer of about 26mm, wherein the path is selected from the inside to the outside for layer-by-layer additive manufacturing.

10. The arc additive remanufacturing method for hot forging dies of automobile half shafts according to claim 1, characterized in that: In step S5, after completing the arc additive remanufacturing, the workpiece is heated to 850°C and kept warm for 2.5 hours. After taking out the sample, it is immediately oil-cooled to room temperature, heated to 560°C again and kept warm for 2.5 hours, and air-cooled to complete the heat treatment. At this time, most of the residual austenite in the mold body is transformed into martensite, and the internal stress of the martensite is eliminated. At this time, the hardness of the remanufactured part is higher than the hardness of the mold body. The hot forging die is post-processed, including machining, cutting off flash, and grinding burrs to obtain a hot forging die that meets standard dimensions.

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