Lightweight hot stamping wheel composite forming manufacturing method

Abstract

The present application relates to the technical field of automobile wheel manufacturing technology, and particularly relates to a lightweight hot stamping wheel composite forming manufacturing method, comprising the following steps: S1, sequentially performing surface pretreatment on steel material, and forming a matching passivation protective layer; S2, feeding into a hot stamping die for processing to obtain a spoke and a rim blank with uniform structure; S3, performing composite quenching heat treatment to form a uniform martensite structure in the blank matrix; S4, performing surface cleaning on the quenched spoke and rim blank to remove the thin oxide layer generated in the heat treatment process; S5, annularly welding the spoke and the rim to form a wheel semi-finished product; S6, performing accurate secondary induction heating on the weld and the surrounding annealing area; S7, performing gradient accurate water cooling treatment to re-form a uniform and strengthened martensite structure in the weld and the surrounding area; and S8, obtaining a finished lightweight hot stamping wheel after quality inspection. The present application solves the technical problems that the weld strength cannot be accurately reinforced and the overall performance of the wheel is uneven.

Description

Technical Field

[0001] This invention relates to the field of automobile wheel manufacturing technology, and in particular to a lightweight hot stamping composite forming manufacturing method for wheels. Background Technology

[0002] The traditional method for manufacturing lightweight hot-stamped wheels involves first forming the spokes and rim separately using hot-formed steel sheets, then completing hot stamping and quenching heat treatment to ensure the strength of the wheel base, and finally welding the spokes and rim together using methods such as MIG welding and submerged arc welding to achieve a balance between lightweighting and structural integrity. This process has been widely used in the production of high-strength hot-formed steel wheels, and existing technologies mainly focus on optimizing aspects such as overall cooling of hot stamping and selection of welding methods.

[0003] However, the existing forming and manufacturing processes also have the following shortcomings in actual production:

[0004] On the one hand, the concentrated local heat input during the welding process, common welding methods such as MIG welding and submerged arc welding can cause local high temperature red-hot phenomena at the wheel weld joint. However, the hot-stamped wheel has already undergone quenching and strengthening treatment. The local high temperature at the joint will cause circumferential annealing in this area, which will transform the martensitic structure of the weld and surrounding area into pearlite and ferrite, resulting in a significant decrease in strength. Existing patents have not provided a precise solution to this local annealing problem, but only compensated by overall heat treatment, which can easily lead to uneven overall wheel performance.

[0005] On the other hand, existing technologies lack specific methods for post-weld strength compensation. Either no reinforcement is performed, making the weld area a weak point in the wheel structure, prone to cracks, fractures and other hidden dangers, or overall heating and quenching is used, which not only consumes a lot of energy, but also affects the dimensional accuracy of the wheel that has already been formed, making it impossible to achieve precise reinforcement of the annealed joint, and making it difficult to balance the weld strength and the overall forming quality of the wheel.

[0006] Therefore, it is necessary to design a lightweight hot stamping wheel composite forming manufacturing method that can accurately solve the problem of local annealing after welding and take into account both strength and forming accuracy. Summary of the Invention

[0007] To solve one of the aforementioned technical problems, the present invention provides a method for manufacturing lightweight hot-stamped wheel composite forming, comprising the following steps:

[0008] S1. The steel is subjected to surface pretreatment in sequence, including degreasing, pickling and passivation, to remove surface oxide scale, oil and impurities, to precisely control the surface roughness of the steel and to form a suitable passivation protective layer.

[0009] S2. The pretreated steel is subjected to quenching and tempering to obtain wheel spokes and rim blanks with uniform structure.

[0010] S3. After the heat treatment, the wheel spokes and rim blanks are cold-formed and then subjected to composite quenching heat treatment to form a uniform martensitic structure in the blank matrix, while reserving strength matching allowance for subsequent welding processes.

[0011] S4. Clean the surface of the quenched wheel spokes and rim blanks to remove the thin oxide layer generated during the heat treatment process.

[0012] S5. The spokes and rim are welded together in a circumferential direction to form a semi-finished wheel. During the welding process, the welding heat input and the expansion range of the annealing zone around the weld are controlled simultaneously.

[0013] S6. After welding, a ring-shaped heating coil with the same axis and size as the wheel weld is used to perform precise secondary induction heating on the weld and the surrounding annealing area, so that the annealing area can fully reach the austenitizing temperature range of the steel.

[0014] S7. After the secondary induction heating is completed, the heated area is immediately subjected to gradient precision water cooling treatment to allow the weld and surrounding area to reform a uniformly strengthened martensitic structure.

[0015] S8. After water cooling, the semi-finished wheel is shaped, polished and quality inspected. After passing the inspection, the finished lightweight hot stamped wheel is obtained.

[0016] Based on any of the above technical solutions, the following optimization is made: the surface pretreatment in step S1 includes a degreasing process, an acid pickling process, and a passivation process in sequence.

[0017] Based on any of the above technical solutions, a further optimization is made as follows: the welding process in step S5 is either MIG welding or submerged arc welding, and a symmetrical segmented welding method is adopted during the welding process. By controlling the matching relationship between welding speed and heat input, the weld penetration and the expansion range of the annealing zone are simultaneously controlled. The welding heat input, weld penetration, and target annealing zone width satisfy the following linkage relationship:

[0018] .

[0019] in, This refers to the welding heat input. The welding process matching correction factor has a value range of 1.1-1.6, which is determined according to the material grade of the hot-formed steel. Design the weld penetration depth; This is the melting depth weighting coefficient, with a value ranging from 0.6 to 0.8; The width of the preset target annealing area is matched with the effective heating width of the annular heating ring in step S6; This is the weighting coefficient for the annealing region, with a value ranging from 0.2 to 0.4; This refers to the welding speed.

[0020] Based on any of the above technical solutions, the following optimizations are made: The annular heating coil in step S6 is a concentric annular electric heating coil structure as in the prior art, coaxially positioned with the wheel weld. The effective heating width of the annular heating coil matches the preset target annealing area width in step S5, ensuring that the secondary induction heating only acts on the annealed area after welding, avoiding additional thermal impact on other hardened areas of the wheel. The annular heating coil uses multiple tightly wound turns, with the winding density adapted to the weld width. The number of turns and winding spacing of the annular heating coil can be flexibly adjusted according to the weld size and annealing area width of different wheel specifications. The heating power of the annular heating coil and the post-weld hardness loss, austenitization transformation requirements, and heating area parameters satisfy the following linkage relationship:

[0021] .

[0022] in, The rated heating power for the annular heating coil; The specific heat capacity under constant pressure for hot-formed steel is determined based on the steel grade. For the quality of steel in the weld and surrounding annealed area; The critical austenitization completion temperature of hot-formed steel is determined according to the steel material grade. This refers to the room temperature of the annealing zone after welding. The enthalpy change per unit volume of steel during martensitic transformation is determined based on the material properties of the steel. The Vickers hardness loss value of the annealed area after welding relative to the substrate is determined by the difference between the substrate hardness and the hardness of the annealed area after welding in step S3. The effective heating area of ​​the annealing zone; This refers to the induction heating and heat preservation time. The thermal efficiency of induction heating is set to 0.78-0.88, determined based on the number of turns of the annular heating coil. This is a temperature uniformity correction factor, with a value ranging from 0.92 to 0.98, determined based on the winding density of the annular heating coil.

[0023] Based on any of the above technical solutions, the following optimization is made: the target temperature of the secondary induction heating in step S6 is the austenitizing temperature range of the hot-formed steel. For the mainstream 22MnB5 hot-formed steel, the austenitizing temperature range is 880℃-950℃. During the heating process, an infrared full-circumferential temperature real-time monitoring module is used to collect the 360° full-circumferential real-time temperature of the weld heating area to ensure that the temperature uniformity of the full-circumferential heating area is controlled within ±15℃, without local overheating or underheating.

[0024] Based on any of the above technical solutions, the following optimizations are made: In step S7, the precise water cooling adopts a ring-shaped spray water cooling method. The spray coverage area corresponds exactly to the effective heating width of the ring-shaped heating circle in step S6, ensuring precise overlap between the water-cooled area and the secondary induction heating area, achieving comprehensive, dead-angle-free synchronous cooling of the heating area; deionized water is used as the cooling medium to avoid scale formation and corrosion risks caused by impurities in the water in the heating area; the water cooling process employs a spray design, with high-density spraying in the core area near the weld and low-density spraying in the surrounding transition area, forming a gradient cooling field that gradually decreases from the weld center to the periphery; the water cooling rate satisfies the following linkage relationship with the induction heating temperature field, the critical cooling rate of martensitic transformation, and the welding residual stress:

[0025] .

[0026] in, The water cooling rate of the core area of ​​the weld; The correction factor for the water cooling process is 0.75-1.15, and its value is determined according to the material of the hot-formed steel. This represents the peak temperature of the weld area after secondary induction heating. The martensitic transformation initiation temperature of hot-formed steel is determined according to the steel grade. The critical cooling rate for martensitic transformation of hot-formed steel is determined based on the material properties of the steel. The base cooling rate is set at 1.2 times the critical cooling rate for martensitic transformation. The peak value of the residual welding stress in the weld area is determined by the welding heat input in step S5.

[0027] Based on any of the above technical solutions, the following optimization is made: During the water cooling process, a constant temperature water tank and a closed-loop temperature control system are used to control the temperature of the water cooling medium. The temperature of the water cooling medium is kept constant at 15-25℃ to avoid fluctuations in the medium temperature due to ambient temperature and production rhythm, thus ensuring the stability and batch consistency of the quenching and cooling process.

[0028] Based on any of the above technical solutions, the following optimization is made: the inspection in step S8 includes dimensional accuracy inspection, non-destructive testing of weld strength, and appearance quality inspection in sequence; dimensional accuracy inspection controls the roundness, coaxiality, mounting surface dimensions, and geometric tolerances of the wheel to ensure the overall vehicle installation compatibility of the wheel; non-destructive testing of weld strength adopts a combination of ultrasonic testing and magnetic particle testing to detect defects inside and on the surface of the weld in the full circumference, and to verify the welding quality and secondary strengthening effect of the weld.

[0029] Based on any of the above technical solutions, a further optimization is made: the overall quenching heat treatment in step S3 adopts a composite cooling method combining oil cooling and air cooling. By controlling the quenching cooling rate, the martensitic transformation requirements of the steel are met, while reserving strength matching allowance for subsequent welding processes. The quenching cooling rate and the steel thickness and welding hardness loss pre-matching satisfy the following linkage relationship:

[0030] .

[0031] in, The cooling rate for overall quenching; This is a correction factor for the quenching process, with a value ranging from 1.25 to 1.65, determined based on the material of the hot-formed steel. This represents the original thickness of the hot-formed steel. A weighting coefficient is reserved for strength, with a value of 0.15-0.35, determined according to the wheel load-bearing requirements; The preset hardness loss value of the weld area after welding is matched with the process parameters of steps S5 and S6. This is the standard Vickers hardness value of the matrix in the quenched state for hot-formed steel, determined according to the steel material grade.

[0032] Based on any of the above technical solutions, the following optimization is made: In the hot stamping process of step S2, a hot stamping die with a closed-loop constant temperature control system is used. The die temperature is kept constant within the austenitizing insulation range of the hot-formed steel. For mainstream 22MnB5 hot-formed steel, the die temperature is kept constant between 880℃ and 950℃. At the same time, the stamping speed and holding time of the servo press are controlled to avoid forming defects such as cracking, wrinkling, and uneven thickness in the wheel spokes and rim blanks. This provides a regular blank structure for subsequent quenching and welding processes, and works synergistically with the quenching in step S3 and the welding in step S5 to improve the forming accuracy and overall quality of the wheel.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. This invention addresses the problem of martensitic transformation and significant strength reduction in the weld and surrounding areas of hot-stamped wheels due to concentrated local heat input during circumferential annealing. It employs a universal annular heating ring with a concentric ring structure, combined with a precise secondary induction heating process, to target the weld and surrounding annealed areas. This ensures the annealed area reaches the austenitizing temperature range of the steel. Combined with gradient precise water cooling, this allows the annealed area to reform a uniformly strengthened martensitic structure, reversing the strength loss caused by welding annealing, eliminating weak points in the weld, and avoiding additional thermal impact on other hardened areas of the wheel. This solves the technical problems of inaccurate weld strength reinforcement and uneven overall wheel performance in existing technologies, significantly improving the overall load-bearing capacity and service safety of the wheel.

[0035] 2. The collaborative process of precise control of welding heat input, precise heating of the annular heating ring, and gradient water cooling quenching constructed in this invention precisely defines the boundary of the annealing zone by quantitatively controlling the welding heat input, weld penetration, and target annealing zone width, providing a clear target range for the heating of the annular heating ring. The annular heating ring adopts a multi-turn tightly wound design, which can flexibly adjust the number of turns and the winding spacing according to different wheel specifications. Combined with the quantitative linkage between heating power and post-weld hardness loss and austenitization transformation requirements, it achieves differentiated precise heating based on the degree of annealing damage. Combined with annular spray gradient water cooling, it ensures complete martensite transformation to restore weld strength, and releases welding residual stress through gradient cooling, avoiding the generation of quenching microcracks. It simultaneously takes into account weld strength, wheel dimensional accuracy, and crack resistance, significantly improving the fatigue life of the wheel.

[0036] 3. In this invention, the surface pretreatment uses a combination of degreasing, pickling, and passivation processes to precisely control the surface roughness of the steel and achieve a positive correlation between the passivation layer thickness and roughness, taking into account both rust prevention and weldability, providing a high-quality substrate for subsequent hot stamping, quenching, and welding; the hot stamping process uses a closed-loop constant-temperature mold to precisely control the mold temperature and stamping parameters, avoiding defects in the blank forming and providing a regular structure for subsequent quenching and welding; the overall quenching heat treatment uses a composite cooling method of oil cooling and air cooling, and through quantitative linkage of cooling rate with steel thickness and welding hardness loss pre-matching, a strength matching margin is reserved for the welding process, achieving a precise match between the base strength and weld reinforcement. The entire process is interconnected, significantly improving the wheel forming quality and batch consistency.

[0037] 4. The universal annular heating coil in this invention can be adapted to the weld seams and annealing areas of different wheel specifications by adjusting the number of turns and the winding spacing. The linkage formula can dynamically match process parameters according to different steel materials and different degrees of annealing damage, without the need for repeated debugging for different products. It is suitable for the production of various specifications and grades of hot-formed steel. The process can be directly integrated into the back end of the existing welding production line without the need for large-scale modification of the main equipment, reducing process upgrade costs, conforming to the green and environmentally friendly industrial development trend, and taking into account both economic efficiency and environmental protection.

[0038] 5. This invention significantly improves production efficiency and product qualification rate through precise control of multiple stages: the synergy between constant temperature hot stamping dies and precise stamping parameters can avoid defects such as blank cracking, wrinkling, and uneven thickness, thereby improving the blank yield; the combination of symmetrical segmented welding and precise heat input control during the welding process reduces welding deformation and lowers the workload of subsequent shaping; the secondary induction heating uses infrared full-circumferential temperature real-time monitoring, which can promptly detect temperature anomalies and make closed-loop adjustments to prevent defective products from flowing into subsequent processes; the full-dimensional quality inspection system realizes closed-loop quality feedback for each process, and can optimize the preceding process parameters through inspection results, further improving the product qualification rate, reducing production losses and rework costs, and achieving efficient and stable large-scale production. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or components are generally identified by similar reference numerals. In the drawings, the elements or components are not necessarily drawn to scale.

[0040] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0041] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore merely examples and should not be used to limit the scope of protection of the present invention. The specific process of the present invention is as follows: Figure 1 As shown in the image.

[0042] Example 1: A method for manufacturing lightweight hot-stamped wheels using composite forming, comprising the following steps:

[0043] S1. Select lightweight hot-formed steel and perform surface pretreatment on the steel in sequence, including degreasing, pickling and passivation, to remove surface oxide scale, oil and impurities, accurately control the surface roughness of the steel and form a suitable passivation protective layer.

[0044] S2. The pretreated steel is fed into the existing matching hot stamping mold for quenching and tempering heat treatment to obtain wheel spokes and rim blanks with uniform structure.

[0045] S3. After the heat treatment, the wheel spokes and rim blanks are cold-formed and then subjected to a composite quenching heat treatment combining oil cooling and air cooling to form a uniform martensitic structure in the blank matrix, while reserving strength matching allowance for subsequent welding processes.

[0046] S4. Clean the surface of the quenched wheel spokes and rim blanks to remove the thin oxide layer generated during the heat treatment process, ensuring that the welding surface is clean, flat and tightly bonded.

[0047] S5. Use MIG welding or submerged arc welding to weld the wheel spokes and rim together in a circumferential direction to form a semi-finished wheel. During the welding process, control the welding heat input and the expansion range of the annealing zone around the weld simultaneously.

[0048] S6. After welding, a ring-shaped heating coil with the same axis as the wheel weld and its size is used to perform precise secondary induction heating on the weld and the surrounding annealing area, so that the annealing area can fully reach the austenitizing temperature range of the steel.

[0049] S7. After the secondary induction heating is completed, the heated area is immediately subjected to gradient precision water cooling treatment to allow the weld and surrounding area to reform a uniformly strengthened martensitic structure.

[0050] S8. After water cooling, the semi-finished wheel is shaped, polished and quality inspected. After passing the inspection, the finished lightweight hot stamped wheel is obtained.

[0051] The lightweight hot-formed steel selected in step S1 of this solution is a 1200MPa-2000MPa grade hot-formed steel commonly used in wheel manufacturing in this field, with the mainstream grade being 22MnB5; the parameter settings of the mold constant temperature control system, stamping speed, and holding time in step S2 all meet the general requirements of the industry; the composite quenching heat treatment process used in step S3 can precisely control the cooling rate by adjusting the air cooling speed and oil cooling immersion time; the annular heating coil and high-frequency induction heating equipment used in step S6, wherein the high-frequency induction heating equipment is a common local heat treatment equipment in this field; the annular spray water cooling equipment used in step S7 can precisely control the cooling rate by adjusting the spray pressure and flow rate.

[0052] The core concept of this technical solution is unique. Addressing the long-standing problem in the hot-stamped wheel manufacturing industry of localized annealing and irreversible strength loss due to welding, this solution utilizes a composite forming process: overall quenching strengthening of the base material, welding forming, and precise secondary quenching reinforcement of the weld seam. Step S3, the overall quenching heat treatment, provides stable basic load-bearing strength to the wheel base. Step S5, the simultaneous control of welding heat input and the annealing area, provides a controllable target area for the subsequent precise induction heating in Step S6, avoiding blind spots in subsequent strengthening caused by irregular expansion of the annealing area. Step S6, the annular heating coil adaptable secondary heating, precisely reheats the annealed area to the austenitizing temperature range, providing a basis for microstructural transformation in Step S7's water-cooling quenching. Step S7's gradient precise water cooling and Step S6's secondary induction heating form a closed-loop synergy of precise reheating and gradient quenching, achieving non-destructive strengthening of the weld seam and completely reversing the strength loss caused by welding annealing.

[0053] The various technical features work together to achieve the technical effect of no loss of base strength, precise reinforcement of weld strength, and uniform overall strength of the wheel, which is different from the conventional understanding of welding annealing of hot stamped wheels in existing technologies.

[0054] In existing technologies, the high-strength martensitic structure formed after quenching of hot-formed steel undergoes an irreversible tempering transformation due to welding heat input. This results in a 30%-50% decrease in hardness in the weld area compared to the matrix. Existing technologies can only mitigate the annealing effect by reducing welding heat input, failing to fundamentally restore strength and easily leading to welding defects such as incomplete welds and insufficient penetration. This solution, based on the principle of reversible solid-state phase transformation in metals, precisely heats the annealing area to above the austenitizing temperature using a ring-shaped heating coil, followed by rapid water cooling to complete the martensitic phase transformation. This enhances the strength of the weld area and eliminates weak points in the weld. Secondly, in existing wheel manufacturing technologies, the pretreatment, forming, quenching, welding, and post-treatment processes are all designed in isolation, with each process focusing only on its own indicators. This easily leads to problems such as unrecoverable defects in preceding processes and mismatches between subsequent processes and preceding processes. This solution constructs parameters that adapt pretreatment roughness to welding performance, welding annealing area to induction heating range, and matrix quenching strength to weld reinforcement effect. First, it achieves closed-loop control of the entire process by using the output parameters of the previous process as the input boundary of the next process. Second, it solves the problem of not being able to simultaneously achieve weld strength and crack resistance in existing technologies. In existing technologies, increasing the quenching cooling rate is required to improve weld strength, but too fast a cooling rate will cause a sharp increase in residual welding stress in the weld area, leading to quenching microcracks and significantly reducing wheel fatigue life. Conversely, reducing the cooling rate cannot guarantee martensitic transformation, and the strength cannot meet the standard. This solution adopts gradient water cooling, using a high cooling rate in the core area of ​​the weld to ensure martensitic transformation, and a decreasing cooling rate in the surrounding transition area to release residual welding stress, simultaneously achieving strength improvement, crack resistance optimization, and fatigue life extension. Third, this solution is based on the principle of local precision heating, and only induction heating is performed on the annealing area of ​​the weld. It has low energy consumption, and the heating and water cooling processes can be directly integrated into the back end of the existing welding production line without modifying the main equipment of the existing wheel production line, resulting in low modification costs.

[0055] Based on any of the above technical solutions, the following further optimization is made: the surface pretreatment in step S1 includes a degreasing process, an acid pickling process, and a passivation process in sequence;

[0056] The degreasing process adopts a weakly alkaline, phosphorus-free, environmentally friendly spray degreasing process, with the free alkalinity controlled at 8-15pt, the degreasing liquid temperature constantly controlled at 40-60℃, and the effective spray treatment time at 3-8 minutes, thoroughly removing rolling oil, rust-preventive oil, and organic oil stains from the steel surface. After degreasing, the steel is rinsed with 2-3 counter-current clean water rinses.

[0057] The pickling process uses hydrochloric acid pickling with added corrosion inhibitors. The acid mass fraction is controlled at 8%-15%, the pickling temperature is 20-40℃, and the effective treatment time is 2-6 minutes. This process thoroughly removes the hot-rolled oxide scale from the steel surface and precisely controls the surface roughness Ra of the steel after pickling to be in the range of 1.6-6.3μm. After pickling, the steel is rinsed with 2-3 countercurrent clean water rinses.

[0058] The passivation process employs an environmentally friendly silane passivation process, with the solid content of the passivating agent controlled at 5%-10%. A roller coating method is used to form the film. The passivation layer thickness is linearly and positively correlated with the surface roughness of the steel after pickling. When the surface roughness Ra is 1.6-3.2 μm, the passivation layer thickness is controlled at 0.5-1.5 μm; when the surface roughness Ra is 3.2-6.3 μm, the passivation layer thickness is controlled at 1.5-3.0 μm. After passivation, the steel is dried in hot air circulation at 60-80℃ for 2-5 minutes. After pretreatment, the steel surface is free of residual oil, oxide scale, and impurities.

[0059] In the degreasing process, the selection of a weakly alkaline, phosphorus-free degreasing agent conforms to the industry-standard requirements for degreasing treatment of automotive steel sheet surfaces. The range of free alkalinity is determined based on the product specifications of the degreasing agent and the degree of oil contamination on the steel surface. For conventionally stored and transported hot-formed steel raw materials, the free alkalinity is 8-12 pt, while for raw materials with heavy surface oil contamination, the free alkalinity is 12-15 pt. The range of degreasing solution temperature is determined based on the optimal activity temperature range of the degreasing agent. 40-60℃ is the conventional optimal activity range for phosphorus-free alkaline degreasing agents. When the temperature is below 40℃, the degreasing agent's activity is insufficient and cannot completely remove oil contamination. When the temperature is above 60℃, the degreasing agent is prone to volatilization and ineffectiveness, while also increasing energy consumption. The effective spray treatment time range is determined based on the uncoiling speed of the steel sheet. The faster the speed, the longer the treatment time should be to ensure thorough removal of oil contamination. Countercurrent rinsing with clean water can thoroughly remove residual degreasing agent from the steel surface, preventing alkaline residue from being carried into the subsequent pickling process and causing acid neutralization failure.

[0060] In the pickling process, hydrochloric acid pickling, compared to sulfuric acid pickling, can avoid excessive corrosion of the steel substrate, surface pitting defects, and hydrogen embrittlement risks, making it more suitable for the material characteristics of high-strength hot-formed steel. The mass fraction of hydrochloric acid is determined based on the thickness of the oxide scale on the steel surface; 12%-15% is used for thicker oxide scales, and 8%-12% for thinner oxide scales. The corrosion inhibitor used is a hexamethylenetetramine-based corrosion inhibitor commonly used in this field, with an addition amount of 0.1%-0.3%, determined according to the "Technical Specification for Application of Corrosion Inhibitors in Metal Pickling." This effectively inhibits excessive corrosion of the steel substrate while avoiding the risk of hydrogen embrittlement. The linkage adjustment of pickling temperature and treatment time allows for precise control of steel surface roughness. When lower surface roughness is required, a lower acid concentration and shorter treatment time are used; when higher surface roughness is required, a higher acid concentration and longer treatment time are used. This linkage method can stably control the surface roughness within the design range without the need for additional mechanical grinding. Countercurrent rinsing with clean water after pickling can thoroughly remove residual acid from the steel surface. The pH value of the rinsing water is controlled at 6-7 to avoid insufficient adhesion of the passivation film and the appearance of dark rust during subsequent storage due to residual acid.

[0061] In the passivation process, environmentally friendly silane passivating agent completely replaces traditional toxic chromate passivation, meeting the VOCs control and environmental protection requirements of the automotive industry. The range of solid content of the passivating agent is determined based on the target passivation layer thickness; the higher the solid content, the thicker the film. Roll coating is a common process for steel plate passivation in this field, and the film thickness can be precisely controlled by adjusting the roller coating pressure and roller speed to adapt to different surface roughnesses. The passivation layer thickness and surface roughness have a positive correlation linear adaptation rule: the rougher the surface, the deeper the micro-pits, requiring a thicker passivation layer to fill the pits and form a continuous and complete protective film to avoid blind spots in protection. Conversely, the rougher the surface, the thinner the passivation layer is required to avoid the passivation layer being too thick and affecting the conductivity during welding. This adaptation rule can balance the protective performance of the passivation layer with the compatibility of subsequent welding processes.

[0062] The temperature and time range for hot air drying are determined according to the curing specifications of silane passivating agent. A temperature range of 60-80℃ can ensure complete curing of the passivation film, while avoiding excessive temperature that could cause the passivation film to crack and pulverize.

[0063] The input-output relationship of the entire pretreatment process in this solution is clearly defined: the input of the degreasing process is hot-formed steel raw material, and the output is steel that has been cleaned and rinsed to remove oil stains; the input of the pickling process is degreased steel, and the output is steel with scale removed and controllable roughness; the input of the passivation process is pickled steel, and the output is steel with a suitable passivation layer that can be directly used for hot stamping.

[0064] This technical solution achieves pre-treatment coordination with the subsequent hot stamping, quenching, welding, and local strengthening processes. The degreasing process thoroughly removes organic oil, providing a core foundation for the uniformity of subsequent pickling and preventing uneven pickling and uncontrolled surface roughness caused by oil obstruction. It also reduces die wear during hot stamping, minimizing the risk of forming cracks and directly meeting the quality requirements of the hot stamping process. The precise surface roughness control during pickling is the core foundation for the thickness adaptation design of the passivation process. Simultaneously, it ensures uniform heat transfer on the steel surface during S3 overall quenching heat treatment, resulting in sufficient and consistent austenite transformation, improving the stability of the matrix strength, and also ensuring… During S5 welding, the welding surfaces of the spokes and rim fit tightly, resulting in uniform weld penetration. This provides stable preconditions for precise control of welding heat input and limitation of the annealing zone width. The linear adaptation design of roughness and passivation layer thickness in the passivation process not only achieves rust protection for the steel during storage and transportation after pretreatment and before hot stamping, but also inhibits excessive oxidation of the steel surface during heat treatment, significantly reducing the workload of the S4 surface cleaning process. Simultaneously, it ensures stable arc and uniform conductivity during welding, avoiding defects such as weld porosity and incomplete welds. These technical features are not independent but rather, through a complete chain design, provide a fundamental quality guarantee for the entire composite forming process.

[0065] This technical solution completely solves the technical problem of the inability to simultaneously achieve protective and weldable performance in existing pretreatment processes. In existing technologies, the passivation layer needs to be thickened to improve the rust resistance of steel. However, an excessively thick passivation layer can lead to increased contact resistance and arc instability during welding, causing defects such as porosity and incomplete welds. Conversely, thinning the passivation layer results in insufficient rust prevention, making the steel susceptible to secondary corrosion during storage and transportation. This solution proposes a linear adaptation rule that is positively correlated with the surface roughness of the steel. For surfaces with high roughness, the thickened passivation layer fills microscopic pits, forming a continuous and complete protective film with no blind spots. For surfaces with low roughness... First, by thinning the passivation layer to avoid affecting the welding conductivity, the optimal balance between rust prevention and welding performance is achieved. Second, the pretreatment process is integrated with subsequent processes, addressing the shortcomings of isolated pretreatment and subsequent processes in existing technologies. Existing pretreatment methods only focus on impurity removal, neglecting the impact on subsequent hot stamping, quenching, and welding processes, often resulting in incompatible steel surface conditions after pretreatment. This solution precisely controls the steel surface roughness through pickling, providing a foundation for passivation layer compatibility and improving the fit between the steel and the die during hot stamping, reducing forming costs. This solution eliminates cracking and wrinkling defects while ensuring uniform heat transfer on the steel surface and consistent matrix transformation during quenching. It also controls the weld gap within ±0.2mm, improving weld penetration uniformity. Thirdly, it significantly reduces the defect rate in hot stamping and the workload of subsequent processes. Existing technologies often suffer from insufficient pretreatment, leading to oxide scale and oil residue on the steel surface, resulting in defects such as indentations, pitting, and cracking during hot stamping, resulting in low blank yield. Furthermore, a thick oxide layer is easily formed after heat treatment, requiring extensive grinding and cleaning. This solution, through a combination of degreasing, pickling, and passivation, completely removes harmful impurities from the surface. The passivation layer inhibits oxidation during heat treatment, reducing the defect rate of hot stamping blanks and increasing the yield. It also reduces the workload of subsequent surface cleaning, significantly improving production efficiency. Fourth, existing technologies mostly use chromate passivation and sulfuric acid pickling processes, which have problems such as heavy metal pollution, large acid mist, and high risk of hydrogen embrittlement. This solution uses a phosphorus-free environmentally friendly degreasing agent, hydrochloric acid pickling, corrosion inhibitor, and silane chromium-free passivation process to avoid heavy metal pollution and the emission of toxic and harmful substances. At the same time, the addition of corrosion inhibitors can avoid the risk of hydrogen embrittlement during pickling, ensuring that the toughness of the hot-formed steel matrix is ​​not damaged, thus taking into account environmental protection, safety, and process effect.

[0066] Based on any of the above technical solutions, a further optimization is made as follows: the welding process in step S5 is either MIG welding or submerged arc welding, and a symmetrical segmented welding method is adopted during the welding process. By controlling the matching relationship between welding speed and heat input, the weld penetration and the expansion range of the annealing zone are simultaneously controlled. The welding heat input, weld penetration, and target annealing zone width satisfy the following linkage relationship:

[0067] ;

[0068] in, This refers to the welding heat input. The welding process matching correction factor has a value range of 1.1-1.6, which is determined according to the material grade of the hot-formed steel. Design the weld penetration depth; This is the melting depth weighting coefficient, with a value ranging from 0.6 to 0.8; The width of the preset target annealing area is matched with the effective heating width of the annular heating ring in step S6; This is the weighting coefficient for the annealing region, with a value ranging from 0.2 to 0.4; This refers to the welding speed.

[0069] This formula quantitatively correlates weld formation quality with the annealing zone range, enabling pre-coordination between the welding process and subsequent secondary induction heating. The algorithm features and the process features of segmented welding support each other, ensuring that the weld penetration depth meets the standard and the connection performance is reliable, while also accurately defining the expansion boundary of the annealing zone, providing a pre-construction foundation for the accuracy of subsequent secondary heating.

[0070] This solution employs a symmetrical segmented welding method, a common technique in wheel circumferential weld welding. For passenger car wheels with a diameter of 400mm-600mm, four symmetrical segments are used; for commercial vehicle wheels with a diameter of 600mm or more, six to eight symmetrical segments are used. This effectively counteracts welding thermal stress and controls weld roundness deformation. Welding process matching correction coefficient. Its core function is to correct the differences in welding thermal conductivity and weldability of hot-formed steels of different materials. The specific value selection rule is as follows: when using 1200MPa grade hot-formed steel, the steel has better weldability and higher thermal conductivity. The value is 1.1-1.3; when using the industry-standard 1500MPa grade 22MnB5 hot-formed steel, The value should be between 1.2 and 1.4. When using ultra-high strength hot-formed steel of 1800MPa or higher, the weldability of the steel is poor, requiring a higher heat input to ensure penetration depth. The value is set between 1.4 and 1.6, and this selection rule is determined entirely based on industry standards and the known properties of the material. Second, the melting depth weighting coefficient. Weighting coefficients of the annealing region The determination method is as follows: As a core safety component of the vehicle, the reliability of the weld connection of the automobile wheel is the top priority indicator. Weld penetration depth is a core parameter that determines the weld connection strength and fatigue resistance; therefore, the penetration depth weighting coefficient is... The weight of the annealing region is set at 0.6-0.8; the width of the annealing region is a boundary control indicator for subsequent local strengthening processes, and belongs to the second priority, therefore the weight coefficient of the annealing region is... Take auxiliary weights of 0.2-0.4, and strictly follow the... The weight allocation principle ensures the rigor and rationality of the formula calculation logic. This weight allocation rule is determined entirely based on industry-standard design specifications. Third: Weld penetration depth design. The width of the target annealing zone is determined based on the wheel's load-bearing capacity and the steel plate thickness, typically ranging from 70% to 100% of the steel plate thickness; The effective heating width of the annular heating ring in subsequent step S6 is completely consistent with that of the weld, typically taken as 3-5mm on each side, for a total width of 8-12mm; welding speed The speed is determined based on the normal travel speed range of the welding equipment, and is set to 300mm / min-800mm / min.

[0071] The input-output relationship of the linkage formula in this scheme is clearly defined: the input parameters are the hot-formed steel material grade, the designed weld penetration depth, the preset target annealing zone width, and the welding speed; the output parameter is the welding heat input, which can be directly converted into the welding current and voltage parameters of the welding equipment and used directly in welding production. Simultaneously, the symmetrical segmented welding process of this scheme and the quantitative control of the formula form a deep synergy. Segmented welding can effectively control the interpass temperature during the welding process, avoiding heat accumulation and irregular expansion of the annealing zone caused by continuous welding, ensuring that the actual annealing zone width perfectly matches the preset target width, further improving the stability and accuracy of the process.

[0072] This technical solution employs a quantitative linkage control method for weld penetration, annealing zone width, and welding heat input, achieving pre-coordination between welding quality and subsequent local strengthening processes. The algorithmic and technical features of this solution exhibit a strong interaction, rather than being a simple parameter superposition: the linkage formula provides precise quantitative parameter support for the segmented welding process, accurately calculating the optimal welding heat input based on different weld design requirements and the boundary requirements of subsequent strengthening processes, avoiding the blind setting of welding parameters based solely on experience in existing technologies; the segmented welding process characteristics provide a stable implementation platform for the formula, effectively controlling the interpass temperature and ensuring that the actual annealing zone width is completely consistent with the target width preset by the formula.

[0073] Meanwhile, the technical features of this solution include: the target annealing zone width for welding process control matches the effective heating width of the S6 annular heating ring, providing a preliminary boundary for the accuracy of subsequent secondary induction heating, and completely avoiding the strengthening blind zone or base material overheating damage caused by the mismatch between the annealing zone and the heating zone; precise control of welding heat input can prevent excessive expansion of the annealing zone, reduce the ineffective energy consumption of subsequent induction heating, and form a closed-loop synergy with the local strengthening processes of S6 and S7; the uniform weld penetration depth guaranteed by the welding process can improve the structural connection reliability of the wheel, and form a synergy with the base material quenching strengthening of S3 and the local reinforcement of the weld in S6-S7, jointly ensuring the overall load-bearing performance of the wheel.

[0074] This technical solution completely solves the technical problem of the inability to simultaneously achieve weld connection reliability and annealing zone control in existing hot-stamped wheel welding processes. In existing technologies, to ensure weld connection strength and penetration depth meet standards, the welding heat input needs to be increased. However, increased heat input leads to irregular expansion of the annealing zone around the weld, making subsequent local strengthening incomplete and easily resulting in weak areas. Conversely, reducing heat input can shrink the annealing zone, but this leads to insufficient weld penetration depth and decreased connection performance, failing to meet the wheel's load-bearing safety requirements. This solution constructs a quantitative linkage formula between welding heat input, weld penetration depth, and target annealing zone width, through a weighted system... The rational allocation of parameters, using weld penetration depth as the core control indicator and annealing zone width as the boundary control indicator, allows for precise limitation of the annealing zone's expansion boundary while ensuring the weld penetration depth fully meets design requirements and the connection performance is up to standard. Secondly, it achieves pre-coordination between the welding process and subsequent local strengthening processes. In existing technologies, heat treatment parameters are adjusted only after welding is completed, which can easily lead to mismatches between the heat treatment parameters and the annealing zone. This solution pre-sets the target annealing zone width during the welding process to match the width of the subsequent annular heating ring, and precisely controls the welding heat input through formulas, ensuring that the actual annealing zone width matches the weld penetration depth. The actual annealing area is completely consistent with the preset target, and the subsequent induction heating process can directly use the matching fixed parameters without repeated adjustments based on the welding results, greatly improving process stability and production efficiency. Third, it significantly reduces welding deformation and the workload of subsequent shaping processes. Existing technologies lack precise control over welding heat input, easily leading to uneven distribution of thermal stress during welding, resulting in significant roundness deformation of the wheel after welding, requiring numerous shaping processes for correction. This solution uses a symmetrical segmented welding method in conjunction with precise heat input control, enabling symmetrical release of thermal stress during welding, reducing the roundness deformation of the wheel after welding, and significantly reducing subsequent shaping processes. Fourth, it significantly improves the effect and energy efficiency of subsequent local strengthening processes. In existing technologies, the boundary of the welding annealing area is uncontrollable, and subsequent induction heating needs to expand the heating range to avoid strengthening blind spots, resulting in a large amount of ineffective energy consumption. At the same time, it is easy to cause additional thermal effects on the already quenched areas of the base material. This solution, by precisely controlling the boundary of the annealing area, makes the heating width of the annular heating ring perfectly match the annealing area, which can completely avoid strengthening blind spots and ineffective heating, improve the weld strengthening qualification rate, reduce induction heating energy consumption, and completely avoid thermal effects on the already quenched areas of the base material, thus ensuring the stability of the base material strength.

[0075] Based on any of the above technical solutions, the following optimizations are made: The annular heating coil in step S6 is a concentric annular electric heating coil structure as in the prior art, coaxially positioned with the wheel weld. The effective heating width of the annular heating coil matches the preset target annealing area width in step S5, ensuring that the secondary induction heating only acts on the annealed area after welding, avoiding additional thermal impact on other hardened areas of the wheel. The annular heating coil uses multiple tightly wound turns, with the winding density adapted to the weld width. The number of turns and winding spacing of the annular heating coil can be flexibly adjusted according to the weld size and annealing area width of different wheel specifications. The heating power of the annular heating coil and the post-weld hardness loss, austenitization transformation requirements, and heating area parameters satisfy the following linkage relationship:

[0076] ;

[0077] in, The rated heating power for the annular heating coil; The specific heat capacity under constant pressure for hot-formed steel is determined based on the steel grade. For the quality of steel in the weld and surrounding annealed area; The critical austenitization completion temperature of hot-formed steel is determined according to the steel material grade. This refers to the room temperature of the annealing zone after welding. The enthalpy change per unit volume of steel during martensitic transformation is determined based on the material properties of the steel. The Vickers hardness loss value of the annealed area after welding relative to the substrate is determined by the difference between the substrate hardness and the hardness of the annealed area after welding in step S3. The effective heating area of ​​the annealing zone; This refers to the induction heating and heat preservation time. The thermal efficiency of induction heating is set to 0.78-0.88, determined based on the number of turns of the annular heating coil. This is a temperature uniformity correction factor, with a value ranging from 0.92 to 0.98, determined based on the winding density of the annular heating coil.

[0078] This formula works in deep synergy with the design of the annular heating coil and the closed-loop temperature control mode. It connects the welding process parameters in step S5 with the water-cooling quenching parameters in step S7, quantitatively binding the hardness loss after welding with the induction heating power, and achieving differentiated and precise heating based on the degree of annealing.

[0079] The annular heating ring of this solution features a concentric annular structure design, determined according to the inductor design specifications for induction heating of annular workpieces. Its coaxial placement with the wheel weld ensures uniform heating throughout the weld circumference. The effective heating width perfectly matches the target annealing area width preset in step S5, ensuring that the eddy current field of induction heating is concentrated only in the annealing area, avoiding thermal impact on the surrounding substrate. The annular heating ring is tightly wound with multiple turns, using hollow copper tubing commonly used in induction heating in this field. Water cooling prevents the annular heating ring from overheating. The number of turns is typically 4-10 turns, and the winding density is typically 2-5 turns / cm, which can be flexibly adjusted according to the weld width and annealing area width to adapt to different wheel specifications.

[0080] Induction heating thermal efficiency in the formula The determination method of this coefficient: The core function of this coefficient is to correct for heat loss during induction heating, including radiative heat loss, conductive heat loss, and coil self-loss. The specific rule for its value is as follows: When the number of turns in the annular heating coil is 4-6, the coupling efficiency between the coil and the heating area is relatively low, and the heat loss is relatively large. The value should be between 0.78 and 0.82; when the number of turns in the annular heating coil is 6-10, the coupling efficiency between the coil and the heating area is high, and the heat loss is relatively small. The value ranges from 0.82 to 0.88, and this value is determined entirely based on industry standards.

[0081] Second, temperature uniformity correction coefficient The determination method of this coefficient: The core function of this coefficient is to correct the influence of the winding density of the annular heating coil on the temperature uniformity of the heating area. The higher the winding density, the more uniform the circumferential temperature distribution of the heating area, and the closer the correction coefficient is to 1. The specific value rule is: when the winding density of the annular heating coil is 2-3 turns / cm, the circumferential temperature uniformity is relatively low. The value should be between 0.92 and 0.95; when the winding density of the annular heating coil is 3-5 turns / cm, the circumferential temperature uniformity is relatively high. The value ranges from 0.95 to 0.98, and this value is determined according to industry-standard design specifications. Specific heat capacity under constant pressure for hot-formed steel. austenitizing critical final temperature Enthalpy change per unit volume during martensitic transformation The parameters are all determined based on the known physical properties of the corresponding grades of hot-formed steel in the steel materials heat treatment handbook, specifically for the mainstream 22MnB5 hot-formed steel. The value is 480 J / (kg·℃). The value is 880℃. The value is 650 J / cm³, all of which are known material parameters; the steel quality of the weld and surrounding annealed area. The Vickers hardness loss of the annealed zone relative to the substrate is determined directly based on the volume of the annealed zone and the density of the steel, with the steel density taken as a known value of 7.85 g / cm³. The hardness is determined by the difference between the standard hardness value of the matrix after quenching and the standard hardness value of the annealed region after welding, as shown in step S3. For 22MnB5 steel, the hardness of the quenched matrix is ​​approximately 450-500 HV, and the hardness of the annealed region is approximately 250-350 HV. The standard value is 100-250 HV, which represents the known hardness variation range of the material after welding; the effective heating area of ​​the annealing zone. The induction heating holding time is determined directly based on the perimeter of the wheel weld and the width of the annealing zone. The standard value is 3-10 seconds to ensure uniform temperature in the heating zone and sufficient austenitization; the room temperature of the annealing zone after welding. The ambient temperature in the production workshop is typically 20-25℃.

[0082] This technical solution, based on differential precision induction heating of weld hardness loss, achieves quantitative linkage between annealing damage and heating parameters. The linkage formula provides precise quantitative support for the structural design of the annular heating coil and the setting of heating parameters. By incorporating the post-weld hardness loss value into the heating power calculation formula, the heating power can be dynamically adjusted according to the actual annealing damage of the weld, completely avoiding the blindness of fixed-parameter heating in existing technologies. The annular concentric structure and multi-turn winding design of the annular heating coil provide a precise implementation vehicle for the formula, ensuring complete overlap between the heating area and the annealing area, and uniform and stable heating temperature.

[0083] Meanwhile, the effective heating width of the annular heating ring is perfectly matched with the width of the pre-set target annealing area for welding, achieving a seamless connection between welding and heating, and avoiding the strengthening blind zone or overheating of the substrate caused by the mismatch between the heating area and the annealing area.

[0084] This technical solution achieves differentiated and precise heating based on the degree of annealing damage, solving the core defect of fixed-parameter heating in existing technologies. Existing technologies for induction heating of the weld annealing zone all use general parameters of fixed power and fixed time, failing to consider the differences in the degree of weld annealing damage under different welding conditions. This easily leads to problems such as insufficient heating resulting in incomplete austenitization and subsequent quenching failing to restore strength, or overheating causing coarse grains, overburning, and deterioration of the matrix properties. This solution incorporates the hardness loss value after welding into the heating power calculation formula; the hardness loss value directly reflects the hardness loss value of the weld area. The greater the hardness loss due to annealing damage, the higher the heating power should be. This ensures that annealing areas with different levels of damage can accurately reach the Ac3 austenitization critical completion temperature, with temperature control error within ±10℃. This guarantees complete austenitization transformation while completely avoiding overheating damage. Secondly, it achieves precise local heating without any matrix damage, solving the technical problem that existing induction heating technology easily affects the matrix properties. The existing annular heating ring design tends to exceed the weld annealing area, causing additional thermal impact on the already hardened area of ​​the wheel matrix, leading to martensite degradation in the matrix. Tempering and strength reduction: This solution employs a ring-shaped heating coil structure coaxial with the weld, effectively matching the width of the pre-set annealing zone. This ensures that the eddy current field from induction heating is concentrated only in the annealing zone of the weld, without affecting the microstructure and properties of the surrounding hardened matrix, thus reducing additional matrix strength loss. Third, it significantly improves the weld strength recovery effect. Through precise austenitizing reheating, combined with subsequent gradient water cooling quenching, the strength of the weld area can be restored, even exceeding the original strength of the matrix, eliminating weak points in the weld and improving the overall load-bearing capacity of the wheel. Fourth, it significantly… This solution enhances the adaptability and versatility of the process, making it suitable for the production of hot-stamped wheels of all specifications. Existing technologies require the design and repeated debugging of ring heating coils and heating parameters for different wheel specifications, resulting in long process development cycles and high costs. The ring heating coil in this solution can be adapted to weld seams and annealing areas of different widths by adjusting the number of turns and the winding spacing. The linkage formula can match the heating power and holding time according to different steel materials, different degrees of annealing damage, and different wheel specifications, eliminating the need for repeated debugging for different products. This can significantly shorten the process development cycle of new products and reduce development costs.

[0085] Based on any of the above technical solutions, the following optimization is made: the target temperature of the secondary induction heating in step S6 is the austenitizing temperature range of the hot-formed steel. For the mainstream 22MnB5 hot-formed steel, the austenitizing temperature range is 880℃-950℃. During the heating process, an infrared full-circumferential temperature real-time monitoring module is used to collect the 360° full-circumferential real-time temperature of the weld heating area to ensure that the temperature uniformity of the full-circumferential heating area is controlled within ±15℃, without local overheating or underheating.

[0086] The target temperature range for the secondary induction heating in this scheme, i.e., the austenitizing temperature range of hot-formed steel, is determined based on the austenitizing transformation characteristics of the corresponding grade of hot-formed steel in the "Handbook of Heat Treatment of Steel Materials". For the mainstream 1500MPa grade 22MnB5 hot-formed steel in the industry, its Ac1 austenitizing initiation temperature is about 720℃, and its Ac3 austenitizing critical termination temperature is about 880℃. When the heating temperature is below 880℃, ferrite cannot be completely transformed into austenite, and subsequent quenching cannot form a uniform martensite structure, resulting in insufficient strength recovery. When the heating temperature is above 950℃, it will lead to coarse austenite grains, and after subsequent quenching, the martensite structure will be coarse, the toughness of the steel will decrease significantly, and even overheating defects may occur. Therefore, 880℃-950℃ is the optimal austenitizing temperature range for 22MnB5 steel. For other grades of hot-formed steel, the austenitizing temperature range can be adjusted according to the known Ac1 and Ac3 temperatures of the material.

[0087] The requirement of controlling the temperature uniformity within ±15℃ can ensure that the degree of austenitization transformation of the weld is consistent throughout the entire circumference, and that the circumferential hardness and strength are uniform after subsequent quenching. This avoids differences in circumferential performance caused by uneven temperature, and prevents alternating stress concentration when the wheel rotates.

[0088] The output signal of the real-time temperature monitoring module in this solution is directly connected to the closed-loop control system. When the temperature of a certain area exceeds the target range, the control system can dynamically adjust the heating power and circumferential heating distribution of the ring heating coil to correct the temperature deviation in a timely manner, ensuring that the temperature of the entire circumferential heating area is stable within the target range and that the temperature uniformity meets the requirements.

[0089] The input-output relationship of this solution is clear: the input is the real-time temperature data of the entire circumference of the heating area, and the output is the temperature over-limit alarm signal and the closed-loop control adjustment signal. It can be directly connected to the control system of existing induction heating equipment. The logic is clear and can be directly implemented. There are no logical breakpoints in the entire solution, and technical personnel in the relevant technical field can directly reproduce it.

[0090] This technical solution addresses the core requirements of secondary induction heating by combining precise definition of the austenitizing temperature range with real-time circumferential temperature monitoring, achieving full-process temperature uniformity control during the heating process. The precise definition of the austenitizing temperature range, in conjunction with the linkage formula, ensures that the calculated heating parameters accurately stabilize the temperature of the heating area within the target range, providing a core foundation for subsequent martensitic transformation. The real-time circumferential temperature monitoring module, in conjunction with the PID closed-loop temperature control mode, provides real-time feedback of circumferential temperature data in the heating area, dynamically adjusting the heating power and circumferential heating distribution of the annular heating coil to avoid localized overheating or underheating, ensuring circumferential temperature uniformity throughout the heating area.

[0091] Meanwhile, this solution works synergistically with the S7 water-cooling quenching process. A uniform and stable heating temperature is a prerequisite for the formation of a uniform martensitic structure by subsequent water cooling. This avoids differences in structure and strength fluctuations after quenching caused by uneven temperature, and provides a stable guarantee for the core strengthening effect of the weld area.

[0092] This technical solution solves the problem of uneven circumferential temperature in existing induction heating processes. Current induction heating technologies for wheel ring welds only use single-point temperature measurement to control the overall temperature, failing to monitor the temperature distribution across the entire circumference of the weld. This easily leads to problems of excessively high or low temperatures in certain circumferential areas, resulting in uneven circumferential strength distribution after quenching. This causes alternating stress concentration during wheel rotation, significantly reducing fatigue life. This solution, based on the requirement for uniform circumferential heating of the ring weld, employs a real-time circumferential infrared temperature monitoring module. This module enables real-time 360° circumferential temperature acquisition of the weld. Combined with a closed-loop control mode, it dynamically adjusts heating parameters, controlling the circumferential temperature uniformity of the heating area within ±15℃. This completely avoids the problems of localized overheating or underheating, fundamentally ensuring the uniformity of the weld's circumferential structure and strength.

[0093] This solution precisely defines the target heating temperature within the austenitizing temperature range, ensuring complete transformation of ferrite to austenite while avoiding coarse austenite grains. This provides a perfect temperature foundation for obtaining a uniform and fine martensite structure during subsequent quenching, simultaneously guaranteeing the strength and toughness of the weld area. Thirdly, it significantly improves the uniformity and strength stability of the weld structure after quenching. In existing technologies, uneven heating temperatures lead to large differences in martensite content in the weld area after quenching, with strength fluctuations exceeding ±80 HV and poor weld quality stability. This solution, through a combination of temperature uniformity control and range control, ensures the uniformity and strength stability of the weld after quenching. The region forms a uniform and fine martensitic structure, and the strength fluctuation range is controlled within ±30HV, which greatly improves the stability of weld strength and batch consistency. Fourth, in the existing technology, the temperature is only detected after heating is completed, which cannot detect temperature anomalies in real time during the heating process. This can easily lead to defective products entering the subsequent quenching process, resulting in waste of raw materials and time. The real-time temperature monitoring module of this solution can detect temperature anomalies in real time during the heating process and trigger an alarm. It can adjust parameters or stop the machine in time, which can improve the pass rate of the secondary heating process and completely prevent defective products from flowing into the subsequent process, thus greatly reducing production losses.

[0094] Based on any of the above technical solutions, the following optimizations are made: In step S7, the precise water cooling adopts a ring-shaped spray water cooling method. The spray coverage area corresponds exactly to the effective heating width of the ring-shaped heating circle in step S6, ensuring precise overlap between the water-cooled area and the secondary induction heating area, achieving comprehensive, dead-angle-free synchronous cooling of the heating area; deionized water is used as the cooling medium to avoid scale formation and corrosion risks caused by impurities in the water in the heating area; the water cooling process employs a spray design, with high-density spraying in the core area near the weld and low-density spraying in the surrounding transition area, forming a gradient cooling field that gradually decreases from the weld center to the periphery; the water cooling rate satisfies the following linkage relationship with the induction heating temperature field, the critical cooling rate of martensitic transformation, and the welding residual stress:

[0095] ;

[0096] in, The water cooling rate of the core area of ​​the weld; The correction factor for the water cooling process is 0.75-1.15, and its value is determined according to the material of the hot-formed steel. This represents the peak temperature of the weld area after secondary induction heating. The martensitic transformation initiation temperature of hot-formed steel is determined according to the steel grade. The critical cooling rate for martensitic transformation of hot-formed steel is determined based on the material properties of the steel. The base cooling rate is set at 1.2 times the critical cooling rate for martensitic transformation. The peak value of the residual welding stress in the weld area is determined by the welding heat input in step S5.

[0097] This formula works in deep synergy with the annular spray structure and layered spray design, and forms a full-chain logical linkage with the welding parameters in step S5 and the induction heating parameters in step S6, while taking into account the three core objectives of martensitic transformation, temperature field distribution, and residual stress control.

[0098] The spray coverage area of ​​this scheme corresponds to the effective heating width of the annular heating ring in step S6; the layered spray design adopts the partitioned spraying method commonly used in the field of spray cooling, with a high density of spray holes in the core area and a moderate density of spray holes in the transition area, and a gradient cooling field is formed by controlling the difference in the density of spray holes.

[0099] Water cooling process matching correction coefficient The determination method is as follows: The cooling process correction coefficient for local quenching of hot-formed steel is specified in the standard. The core function of this coefficient is to correct for the differences in martensitic transformation characteristics and hardenability of hot-formed steels of different materials. Specifically, the rule for its value is: when using 1200MPa grade hot-formed steel, the steel has better hardenability, and the required cooling rate is relatively lower. The value is 0.75-0.85; when using the industry-standard 1500MPa grade 22MnB5 hot-formed steel, The value ranges from 0.85 to 1.0; when using ultra-high strength hot-formed steel of grade 1800MPa or above, the steel has poor hardenability and requires a higher cooling rate to ensure martensitic transformation. The value ranges from 1.0 to 1.15, and this selection rule is determined entirely based on national standards and the known properties of the material. This is the martensitic transformation initiation temperature for hot-formed steel. Critical cooling rate for martensitic transformation All parameters are determined based on the known phase transformation characteristics of the corresponding grades of hot-formed steel in the "Handbook of Heat Treatment of Steel Materials". This applies to the mainstream 22MnB5 hot-formed steel. The value is 425℃. The value is 30℃ / s, all of which are known parameters of the material; the reference cooling rate. The value is set to 1.2 times the critical cooling rate for martensitic transformation, ensuring that the cooling rate consistently exceeds the critical cooling rate, avoiding the formation of non-martensitic structures such as pearlite and bainite, and ensuring the quenching and strengthening effect; the peak temperature of the weld area after secondary induction heating. The target temperature for secondary induction heating in step S6 is determined, typically ranging from 880℃ to 950℃; the peak value of welding residual stress in the weld area. The residual stress peak value is directly calculated from the welding heat input in step S5. The larger the welding heat input, the higher the residual stress peak value.

[0100] The input parameters for this solution are the material properties of hot-formed steel, the peak temperature of secondary induction heating, and the peak value of welding residual stress. The output parameter is the water cooling rate of the core area of ​​the weld. This output value can be directly converted into the pressure and flow parameters of the spraying equipment and used directly for water cooling production.

[0101] This technical solution employs a gradient water-cooling quenching method that considers the critical requirements for martensitic transformation, the distribution of the induction heating temperature field, and the control of welding residual stress, achieving a simultaneous improvement in weld strength and optimization of crack resistance. The linkage formula in this solution provides precise quantitative support for the gradient cooling design of layered spraying, incorporating the peak value of welding residual stress into the water-cooling rate calculation formula. This allows the cooling rate to be dynamically adjusted according to the magnitude of welding residual stress, balancing quenching strengthening and stress control. Furthermore, this solution's technical features include: connecting to the secondary induction heating process in S6, matching the spray coverage area with the effective heating width of the annular heating ring, and linking the water-cooling rate with the peak heating temperature, achieving a seamless connection between heating and cooling; connecting to the welding process in S5, linking the water-cooling rate with the peak value of welding residual stress, allowing for further release of welding residual stress through cooling rate adjustments, preventing quenching cracks; and synergizing with the overall quenching process in S3, ensuring consistent microstructure and properties between the weld area and the substrate, avoiding performance discontinuities between the substrate and the weld.

[0102] In existing technologies, to ensure complete martensitic transformation and improve strength in the weld region, rapid cooling exceeding the critical cooling rate for martensitic transformation is necessary. However, rapid cooling leads to a sudden drop in weld region temperature, resulting in the superposition of thermal and structural stresses, which significantly increases residual welding stress. This can easily trigger quenching microcracks and drastically reduce wheel fatigue life. Conversely, reducing the cooling rate can decrease stress, but it cannot meet the critical cooling rate for martensitic transformation, thus failing to achieve the required strength. This solution constructs a linkage formula between water cooling rate, critical martensitic transformation rate, and peak residual welding stress. Simultaneously, it employs a layered gradient spray design. The core weld region uses a high cooling rate to ensure it exceeds the critical cooling rate, achieving complete martensitic transformation and guaranteeing the required strength. The surrounding transition region uses a gradually decreasing cooling rate to slow the cooling process, providing a time window for the release of residual welding stress. This approach reduces residual welding stress while ensuring complete martensitic transformation and weld strength recovery. Furthermore, it achieves precise matching cooling with the induction heating region, completely avoiding any impact on the matrix properties. Existing rapid quenching processes are prone to causing quenching microcracks in the weld area. These microcracks can become fatigue crack sources during wheel service, significantly reducing the wheel's fatigue life. This solution, through the synergy of gradient cooling design and linkage formula, can avoid the generation of quenching microcracks, reduce the incidence of microcrack defects in the weld area, and, combined with effective control of welding residual stress, improve the fatigue life of the wheel weld, significantly enhancing the wheel's service safety and service life.

[0103] Based on any of the above technical solutions, the following optimization is made: During the water cooling process, a constant temperature water tank and a closed-loop temperature control system are used to control the temperature of the water cooling medium. The temperature of the water cooling medium is kept constant at 15-25℃ to avoid fluctuations in the medium temperature due to ambient temperature and production rhythm, thus ensuring the stability and batch consistency of the quenching and cooling process.

[0104] When the medium temperature is below 15℃, the temperature difference between the cooling medium and the heating area is too large, which will lead to an excessively fast cooling rate and a sudden increase in thermal stress in the weld area, making it very easy to cause quenching cracks. At the same time, it will significantly increase the cooling energy consumption of the chiller. When the medium temperature is above 25℃, the temperature difference between the cooling medium and the heating area is too small, which will lead to the actual cooling rate being lower than the critical cooling rate for martensite transformation. This will not be able to guarantee that austenite will completely transform into martensite, resulting in insufficient recovery of weld strength. In addition, excessively high medium temperature will easily cause condensation in the spray pipes, affecting the service life of the equipment. Therefore, 15-25℃ is the optimal temperature range that balances quenching effect, crack resistance, and energy consumption control.

[0105] This solution takes real-time temperature data of the water-cooling medium as input and outputs heating / cooling regulation signals for the chiller. It can achieve fully automatic closed-loop control of the medium temperature without manual intervention and can be directly adapted to the continuous production rhythm of existing wheel production lines. Regardless of changes in ambient temperature or production rhythm, it can ensure that the medium temperature remains stable within the target range.

[0106] The constant control of the water-cooling medium temperature and the linkage formula work together to ensure that the water cooling rate calculated by the formula can be stably achieved, avoiding deviations of the actual cooling rate from the design value due to fluctuations in the medium temperature, and ensuring the stability of the martensitic transformation. In conjunction with the layered spray gradient cooling design, the constant medium temperature can ensure the stable distribution of the gradient cooling field, avoiding the cooling gradient disorder caused by changes in the medium temperature, ensuring that the cooling rate decreases smoothly from the center of the weld to the periphery, and achieving the goal of stress control.

[0107] Meanwhile, the technical features of this solution work synergistically with the secondary induction heating process of S6. The constant temperature of the cooling medium ensures that the cooling process after heating is stable and controllable, avoiding insufficient austenitization transformation and uneven martensite structure caused by fluctuations in cooling conditions, thus providing a stable foundation for the core strengthening effect of the weld area.

[0108] This solution maintains a constant water-cooling medium temperature within the normal range of 15-25℃, eliminating the influence of ambient temperature and production rhythm on the cooling rate. It reduces the fluctuation range of weld strength between different batches of wheels, ensuring batch-to-batch consistency in product quality. This effectively avoids quenching cracks while ensuring sufficient martensitic transformation. In existing technologies, excessively low medium temperatures lead to excessively rapid cooling, causing a sudden increase in thermal stress in the weld area, which easily triggers quenching cracks. Excessively high medium temperatures result in insufficient cooling, failing to reach the critical cooling rate for martensitic transformation, preventing complete austenitization and resulting in substandard weld strength. Based on the CCT curve principle of martensitic transformation in hot-formed steel, this solution determines 15-25℃ as the optimal medium temperature range. Within this range, while ensuring the cooling rate consistently exceeds the critical cooling rate for martensitic transformation and guarantees complete martensitic transformation, the cooling thermal stress is controlled within the allowable stress range of the steel, completely avoiding quenching cracks. In principle, it simultaneously considers both quenching strengthening effect and crack resistance.

[0109] Example 2: Compared with Example 1, this example also includes the following technical features:

[0110] Based on any of the above technical solutions, the following optimization is made: the inspection in step S8 includes dimensional accuracy inspection, non-destructive testing of weld strength, and appearance quality inspection in sequence; dimensional accuracy inspection controls the roundness, coaxiality, mounting surface dimensions, and geometric tolerances of the wheel to ensure the overall vehicle installation compatibility of the wheel; non-destructive testing of weld strength adopts a combination of ultrasonic testing and magnetic particle testing to detect defects inside and on the surface of the weld in the full circumference, and to verify the welding quality and secondary strengthening effect of the weld.

[0111] All testing items, methods, and qualification standards comply with national mandatory standards and industry specifications for automotive wheel manufacturing in this field. All testing equipment used is commercially available standard equipment, with no special non-standard equipment requirements. This comprehensive testing system forms a one-to-one quality feedback loop with each process: dimensional accuracy testing corresponds to S2 hot stamping, S5 welding, and S8 shaping processes, allowing for optimization of parameters in preceding forming processes through test results; non-destructive testing of weld strength corresponds to S5 welding and S6-S7 secondary strengthening processes, allowing for optimization of parameters in welding, heating, and water cooling processes through test results; and appearance quality testing corresponds to S4 surface cleaning and S8 grinding processes, allowing for optimization of parameters in surface treatment processes through test results.

[0112] Based on any of the above technical solutions, a further optimization is made: the overall quenching heat treatment in step S3 adopts a composite cooling method combining oil cooling and air cooling. By controlling the quenching cooling rate, the martensitic transformation requirements of the steel are met, while reserving strength matching allowance for subsequent welding processes. The quenching cooling rate and the steel thickness and welding hardness loss pre-matching satisfy the following linkage relationship:

[0113] ;

[0114] in, The cooling rate for overall quenching; This is a correction factor for the quenching process, with a value ranging from 1.25 to 1.65, determined based on the material of the hot-formed steel. This represents the original thickness of the hot-formed steel. A weighting coefficient is reserved for strength, with a value of 0.15-0.35, determined according to the wheel load-bearing requirements; The preset hardness loss value of the weld area after welding is matched with the process parameters of steps S5 and S6. This is the standard Vickers hardness value of the matrix in the quenched state for hot-formed steel, determined according to the steel material grade.

[0115] This formula works in conjunction with the combined cooling process of oil cooling and air cooling to achieve pre-matching between the preceding overall quenching process and the subsequent welding and local strengthening processes. By reserving strength margin in advance, it solves the technical problem of uneven strength between the wheel base and the weld area in the existing technology.

[0116] This solution combines oil cooling and air cooling, allowing for precise control of the cooling rate by adjusting the airflow speed in the air cooling section and the immersion time in the oil cooling section. Compared to single water cooling or oil cooling, this combined cooling method achieves a wider range of precise control over the cooling rate, while avoiding the risks of deformation and cracking caused by single cooling methods. It is suitable for the quenching needs of hot-formed steel of different thicknesses and materials.

[0117] Quenching process correction factor The determination method is as follows: It is determined according to the quenching and cooling process correction coefficient specification for the corresponding grade of hot-formed steel. The core function of this coefficient is to correct the differences in hardenability and martensitic transformation characteristics of hot-formed steel of different materials. The specific value selection rule is as follows: When using 1200MPa grade hot-formed steel, the steel has good hardenability and the required cooling rate is relatively low. The value is 1.25-1.4; when using the industry-standard 1500MPa grade 22MnB5 hot-formed steel, The value should be between 1.4 and 1.55. When using ultra-high strength hot-formed steel of 1800MPa or higher, the steel has poor hardenability and requires a higher cooling rate to ensure complete martensite transformation. The value is between 1.55 and 1.65, and this value is determined entirely based on national standards and the known properties of materials.

[0118] Strength reserved weighting coefficient The determination method is as follows: It is determined based on the strength allowance requirements of wheels with different load-bearing levels. The core function of this coefficient is to adjust the allowance for the quenching strength of the base material, adapting to the load-bearing requirements of different wheels and the hardness loss during subsequent welding. Specifically, the value selection rule is as follows: For ordinary load-bearing wheels of passenger vehicles, the load-bearing requirements are relatively low, and the strength allowance weighting coefficient is [not specified]. The value ranges from 0.15 to 0.25; this is for heavy-duty commercial vehicle wheels and high-performance sports car wheels, which have high load-bearing requirements and a strength-reserved weighting coefficient. The value ranges from 0.25 to 0.35, and this value is determined entirely based on national standards and industry-standard design specifications. This refers to the original thickness of the hot-formed steel. The thickness is determined based on the wheel's design load-bearing requirements, typically ranging from 1.2mm to 6.0mm, which is the standard steel plate thickness range for wheel manufacturing in this field; the preset hardness loss value in the weld area after welding is also included. Matching the process parameters in steps S5 and S6, for mainstream 22MnB5 steel, the conventional value is 100-250 HV, which is the known hardness variation range of the material after welding; the standard quenched matrix Vickers hardness value of hot-formed steel. The hardness is determined based on the known quenching hardness value of the corresponding grade of hot-formed steel. For 22MnB5 steel, Values ​​range from 450 to 500 HV.

[0119] The pre-matching process design method of the overall quenching and subsequent welding and local strengthening in this technical solution achieves a precise match between the strength of the base material and the strengthening performance of the weld.

[0120] The algorithmic and technical features of this solution have a strong interactive relationship: the linkage formula provides precise quantitative support for the combined cooling process of oil cooling and air cooling, and introduces preset welding hardness loss values ​​and strength reserve weight coefficients, so that the quenching strength of the substrate can be dynamically adjusted according to the annealing loss of subsequent welding and the load-bearing requirements of the wheel, realizing the pre-matching of the pre-quenching and subsequent processes; the combined cooling method of oil cooling and air cooling can precisely adjust the cooling rate through the combination of air cooling and oil cooling, perfectly matching the calculated value of the formula. The two support each other and jointly realize the synchronous control of the basic strength of the substrate and the subsequent reinforcement allowance.

[0121] Meanwhile, the technical features of this solution include the hot stamping forming process in S2, which provides stable structural reinforcement for the formed blank and ensures the basic load-bearing performance of the base material; the welding process in S5, with a preset hardness loss value that matches the welding process parameters, provides a reasonable performance margin for welding annealing and reduces the incidence of welding cracks; and the local strengthening process in S6-S7, where the strength margin reserved in the base material can perfectly match the strength after secondary strengthening of the weld, avoiding performance discontinuity between the base material and the weld and achieving uniformity of the overall strength of the wheel.

[0122] This technical solution achieves uniform strength matching between the wheel substrate and the weld area, completely solving the technical problem of performance discontinuity between the substrate and weld in existing technologies. Existing technologies, such as integral quenching, only pursue the highest strength of the substrate itself, resulting in a fixed hardness of 450-500 HV after quenching. However, the hardness of the weld area drops to 250-350 HV after welding, and even with subsequent reinforcement, it can only recover to around 400 HV. This creates a significant strength discontinuity between the weld and the substrate. When the wheel is under stress, stress concentration occurs at locations of abrupt strength changes, becoming fatigue crack initiation points and significantly reducing the wheel's fatigue life. This solution establishes a linkage between the quenching cooling rate and the preset weld hardness loss. The formula, while ensuring the base strength meets the wheel load-bearing requirements, pre-reserves a strength margin to match the weld hardness loss, ensuring that the strength of the weld after secondary strengthening is completely matched with the base strength, with the strength difference controlled within ±20HV, thus completely eliminating strength discontinuity and stress concentration. Secondly, it simultaneously considers the basic load-bearing strength of the base and the compatibility with subsequent welding processes. In existing technologies, excessively fast quenching and cooling rates result in excessively high base strength and hardness, making cold cracking more likely during welding, while also increasing thermal stress and causing more significant annealing zone expansion. Conversely, excessively slow cooling rates lead to insufficient base strength, failing to meet the wheel load-bearing safety requirements. This solution is based on thermal... The principle of martensitic transformation in formed steel and the compatibility requirements of welding processes are addressed by precisely calculating the optimal quenching cooling rate using a linkage formula. Combined with a composite cooling method of oil and air cooling, this ensures the base material reaches its designed load-bearing strength while controlling the base material hardness within a reasonable range. This provides good process compatibility for welding, reducing the incidence of welding cracks and significantly improving the welding qualification rate. Thirdly, it significantly improves the overall structural stability and load-bearing capacity of the wheel. In existing technologies, the uneven strength between the base material and the weld easily leads to fatigue failure of the wheel under alternating loads. The load-bearing capacity and fatigue life of the wheel are limited by the weak points in the weld. This solution addresses the issue of uneven strength between the base material and the weld. The uniform matching design eliminates weak points and stress concentrations in the welds, which can improve the overall static load-bearing capacity and fatigue life of the wheel, and significantly improve the service safety and service life of the wheel. Fourth, in the existing technology, when developing new wheel products, the quenching, welding and heat treatment processes need to be designed separately and repeatedly debugged, resulting in a long process development cycle and high cost. The quenching parameters of this solution form a full-chain linkage with the subsequent welding, secondary heating and water cooling parameters. The process parameters of the whole process can be adjusted synchronously according to different wheel product specifications and load requirements, without the need for separate debugging for each process. This can shorten the process development cycle of new products by more than 50% and significantly reduce development costs.

[0123] Based on any of the above technical solutions, the following optimization is made: In the hot stamping process of step S2, a hot stamping die with a closed-loop constant temperature control system is used. The die temperature is kept constant within the austenitizing insulation range of the hot-formed steel. For mainstream 22MnB5 hot-formed steel, the die temperature is kept constant between 880℃ and 950℃. At the same time, the stamping speed and holding time of the servo press are controlled to avoid forming defects such as cracking, wrinkling, and uneven thickness in the wheel spokes and rim blanks. This provides a regular blank structure for subsequent quenching and welding processes, and works synergistically with the quenching in step S3 and the welding in step S5 to improve the forming accuracy and overall quality of the wheel.

[0124] The hot stamping die with closed-loop constant temperature control system in this solution adopts a die structure with heating tubes and temperature sensors commonly used in hot stamping in this field. Combined with an existing PID closed-loop constant temperature controller, the die temperature fluctuation can be controlled within ±20℃. The die temperature is kept constant within the austenitizing holding range of the hot-formed steel. For mainstream 22MnB5 hot-formed steel, this range is 880℃-950℃. The determination is based on the austenitizing forming characteristics of 22MnB5 steel. Within this temperature range, the steel is in a fully austenitized state, with the best plasticity and the lowest deformation resistance, which can achieve the best forming effect and avoid forming defects. At the same time, it can ensure that the steel is always in an austenitized state during the stamping process, providing a uniform microstructure for subsequent quenching. The determination of this temperature range is entirely based on national standards and known material properties.

[0125] This technical solution achieves pre-process coordination between blank forming quality and subsequent quenching and welding processes. The technical features of this solution have a strong synergistic effect with other technical features: precise control of the mold's constant temperature range avoids uneven blank forming thickness and surface defects caused by mold temperature fluctuations, while ensuring the blank remains within the austenitizing range during stamping, providing a uniformly structured blank for the subsequent S3 overall quenching heat treatment, ensuring a uniform matrix structure and stable strength after quenching; precise control of stamping speed and holding time avoids blank cracking and wrinkling caused by excessively fast stamping speeds, and blank temperature drop and decreased formability caused by excessively slow stamping speeds, ensuring the dimensional accuracy and structural regularity of the blank, providing a tightly fitting welding surface for the subsequent S5 welding process, and improving welding quality and weld formation stability.

[0126] Meanwhile, the technical features of this solution synergize with the surface pretreatment process of S1. The clean, defect-free steel surface, combined with the constant-temperature mold, can further reduce the incidence of forming defects and improve the yield of finished blanks. These interconnected technical features provide a high-quality blank foundation for the entire composite forming process.

[0127] This technical solution significantly reduces the forming defect rate of hot stamping blanks and improves the blank yield. In the existing technology, the mold temperature is prone to fluctuation with the production rhythm, and the stamping speed is not precisely matched, which easily leads to forming defects such as cracking, wrinkling, uneven thickness, and surface indentation in the blanks. The blank yield is low, and a large number of defective products need to be reworked or scrapped, resulting in serious waste of raw materials. This solution stabilizes the mold temperature in the austenitizing heat preservation range, and with the stamping speed and holding time adapted to the blank structure, it can ensure that the blank is formed in the optimal plasticity range, thereby reducing the blank forming defect rate, greatly improving the yield, and significantly reducing raw material waste and rework costs. In addition, it significantly improves the effect of subsequent overall quenching process and the stability of matrix strength. In the existing technology, uneven blank forming thickness and uneven microstructure caused by temperature drop during stamping will result in large strength fluctuations and poor microstructure uniformity of the matrix after quenching. The hardness difference at different locations of the same blank exceeds ±50HV, resulting in poor matrix strength stability. This solution, through constant temperature control of the mold and optimization of stamping parameters, can ensure uniform thickness of the blank after forming and uniform austenite microstructure throughout the entire area, providing a perfect microstructure foundation for subsequent quenching. This reduces the hardness fluctuation range of the matrix after quenching and greatly improves the microstructure uniformity, providing stable basic strength for the wheel matrix.

[0128] The above solution also effectively improves the quality and pass rate of subsequent welding processes. In existing technologies, the low dimensional accuracy of the blanks and the irregularity of the welding surfaces easily lead to excessive gaps between the welding surfaces of the spokes and rims during the welding process, resulting in welding defects such as incomplete welding, porosity, and incomplete penetration. This solution, through precise control of hot stamping parameters, can ensure the dimensional accuracy and flatness of the welding surfaces of the spokes and rim blanks, keeping the gap between the welding surfaces within ±0.2mm. This significantly improves the stability of the welding arc and the uniformity of the weld penetration, reducing the incidence of welding defects and increasing the weld pass rate.

[0129] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. For those skilled in the art, any alternative improvements or transformations made to the implementation of the present invention fall within the protection scope of the present invention.

[0130] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for manufacturing lightweight hot-stamped wheel composite forming, characterized in that, Includes the following steps: S1. The steel is subjected to surface pretreatment of degreasing, pickling and passivation in sequence to remove surface oxide scale, oil and impurities, accurately control the surface roughness of the steel and form a suitable passivation protective layer. S2. The pretreated steel is subjected to quenching and tempering to obtain wheel spokes and rim blanks with uniform structure. S3. After the heat treatment, the spoke and rim blanks are cold-formed and then subjected to composite quenching heat treatment to form a uniform martensitic structure in the blank matrix, while reserving strength matching allowance for subsequent welding processes. S4. Clean the surface of the quenched wheel spokes and rim blanks to remove the thin oxide layer generated during the heat treatment process. S5. The spokes and rim are welded together in a circumferential direction to form a semi-finished wheel. During the welding process, the welding heat input and the expansion range of the annealing area around the weld are controlled simultaneously. S6. After welding, the circumferential weld and the surrounding annealing area are subjected to precise secondary induction heating so that the annealing area fully reaches the austenitizing temperature range of the steel. S7. After the secondary induction heating is completed, the heated area is immediately subjected to gradient precision water cooling treatment to allow the weld and surrounding area to reform a uniformly strengthened martensitic structure. S8. After water cooling, the semi-finished wheel is shaped, polished and quality inspected. After passing the inspection, the finished lightweight hot stamped wheel is obtained.

2. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, The surface pretreatment in step S1 includes degreasing, pickling and passivation processes in sequence.

3. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, The welding process in step S5 is either MIG welding or submerged arc welding. A symmetrical segmented welding method is used during the welding process. By controlling the matching relationship between welding speed and heat input, the weld penetration and the expansion range of the annealing zone are simultaneously managed. The welding heat input, weld penetration, and target annealing zone width satisfy the following linkage relationship: ； in, This refers to the welding heat input. This is a welding process matching correction factor, with a value range of 1.1-1.6; Design the weld penetration depth; This is the melting depth weighting coefficient, with a value ranging from 0.6 to 0.8; The width of the preset target annealing area is matched with the effective heating width of the annular heating ring in step S6; This is the weighting coefficient for the annealing region, with a value ranging from 0.2 to 0.4; This refers to the welding speed.

4. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, In step S6, the annular heating ring is coaxially positioned with the wheel weld. The effective heating width of the annular heating ring matches the target annealing area width preset in step S5, ensuring that the secondary induction heating only acts on the annealed area after welding. The annular heating ring is tightly wound with multiple turns, and the winding density is adapted to the weld width. The heating power of the annular heating ring is linked to the hardness loss after welding, the austenitization transformation requirement, and the heating area parameters as follows: ； in, The rated heating power for the annular heating coil; The specific heat capacity under constant pressure for hot-formed steel; For the quality of steel in the weld and surrounding annealed area; The critical austenitization completion temperature for hot-formed steel; This refers to the room temperature of the annealing zone after welding. The enthalpy change per unit volume during the martensitic transformation of steel; The Vickers hardness loss value of the annealed area after welding relative to the substrate is determined by the difference between the substrate hardness and the hardness of the annealed area after welding in step S3. The effective heating area of ​​the annealing zone; This refers to the induction heating and heat preservation time. For induction heating thermal efficiency, the value is taken as 0.78-0.88; This is a temperature uniformity correction factor, with a value ranging from 0.92 to 0.

98.

5. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 4, characterized in that, In step S6, the target temperature for the secondary induction heating is the austenitizing temperature range of the hot-formed steel. For the mainstream 22MnB5 hot-formed steel, the austenitizing temperature range is 880℃-950℃. During the heating process, an infrared full-circumferential temperature real-time monitoring module is used to collect the temperature of the weld heating area in real time in 360° full circumference, ensuring that the temperature uniformity of the heating area is controlled within ±15℃.

6. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, The precise water cooling in step S7 adopts a ring-shaped spray water cooling method. The spray coverage area corresponds exactly to the effective heating width of the ring-shaped heating circle in step S6, providing all-round, dead-angle-free synchronous cooling of the heating area. The water cooling process uses a spray design, with high-density spraying in the core area near the weld and low-density spraying in the surrounding transition area, forming a gradient cooling field that gradually decreases from the center of the weld to the periphery. The water cooling rate is linked to the induction heating temperature field, the critical cooling rate of martensitic transformation, and the welding residual stress as follows: ； in, The water cooling rate of the core area of ​​the weld; This is a correction factor for the water cooling process, with a value ranging from 0.75 to 1.

15. This represents the peak temperature of the weld area after secondary induction heating. The martensitic transformation initiation temperature of hot-formed steel; The critical cooling rate for the martensitic transformation of hot-formed steel; The base cooling rate is set at 1.2 times the critical cooling rate for martensitic transformation. The peak value of the residual welding stress in the weld area is determined by the welding heat input in step S5.

7. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 6, characterized in that, During the water cooling process, a constant temperature water tank and a closed-loop temperature control system are used to control the temperature of the water cooling medium, which is kept constant at 15-25℃.

8. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, The inspection in step S8 includes dimensional accuracy inspection, non-destructive testing of weld strength, and appearance quality inspection. Dimensional accuracy inspection controls the roundness, coaxiality, mounting surface dimensions, and geometric tolerances of the wheel to ensure the wheel's fit with the vehicle. Non-destructive testing of weld strength uses a combination of ultrasonic testing and magnetic particle testing to detect defects inside and on the surface of the weld in the entire circumference, verifying the welding quality and secondary strengthening effect of the weld.

9. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, The overall quenching heat treatment in step S3 adopts a composite cooling method combining oil cooling and air cooling. By controlling the quenching cooling rate, the martensitic transformation requirements of the steel are met, while reserving strength matching allowance for subsequent welding processes. The quenching cooling rate, steel thickness, and welding hardness loss are pre-matched to satisfy the following linkage relationship: ； in, The cooling rate for overall quenching; This is a correction factor for the quenching process, with a value ranging from 1.25 to 1.

65. This represents the original thickness of the hot-formed steel. A weighting coefficient is reserved for intensity, with a value ranging from 0.15 to 0.35; The preset hardness loss value of the weld area after welding is matched with the process parameters of steps S5 and S6. This is the standard Vickers hardness value of the matrix in the quenched state for hot-formed steel.

10. The lightweight hot-stamped wheel composite forming manufacturing method according to claim 1, characterized in that, In the hot stamping process of step S2, a hot stamping die is used, and the die temperature is kept constant within the austenitizing heat preservation range of the hot-formed steel. For 22MnB5 hot-formed steel, the die temperature is kept constant between 880℃ and 950℃. At the same time, the stamping speed and holding time of the servo press are controlled to provide a regular blank structure for subsequent quenching and welding processes, which works in synergy with the quenching in step S3 and the welding in step S5.

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