Hot bath forming process method of integrated annular zinc-based coating part

Abstract

The invention belongs to the technical field of steel machining, and particularly relates to a hot bath forming process method of an integrated annular zinc-based coating part. Zinc-based coating hot forming steel has the advantages of cost and performance under the environment of light weight, cost reduction and efficiency improvement in the automobile industry, meanwhile, an integrated annular product has a remarkable effect in automobile light weight, however, due to the material characteristics of the zinc-based coating hot forming steel, a bare board and an aluminum-silicon coating hot forming stamping process cannot be referred to, and the cost is greatly reduced. The LMIE phenomenon can exist in direct hot forming of a zinc-based coating material, and the service performance of parts can be seriously affected when microcracks are larger than 10 micrometers. Therefore, the hot bath forming process is adopted for the zinc-based coating annular part, the problem of the LMIE phenomenon existing in the hot forming process of a zinc-based coating material is solved, meanwhile, the zinc-based coating annular part is applied to an automobile body, the prospect requirement for automobile light weight is met, the performance can be improved, cost can be reduced, and the application prospect is wide. The method has great economic value and social benefit in the automobile industry.

Description

Technical Field

[0001] The invention belongs to the technical field of steel processing, and in particular relates to a hot bath forming process method for an integrated annular zinc-based coating component. Background Art

[0002] In recent years, China's automobile industry has developed rapidly, and the rapid development of the new energy vehicle market is one of the main driving forces for the growth of industry revenue. Automobile lightweighting is a relatively complex project, which needs to take into account multiple factors such as collision performance, stiffness, and strength. Hot-formed steel can meet both lightweight and performance requirements. On the premise of ensuring the performance of the whole vehicle, high-strength or even ultra-high-strength hot-formed steel is used to achieve part thinning, design a more reasonable and better body structure, and strengthen process improvements to minimize the weight of the whole vehicle.

[0003] The most commonly used hot-formed steels are uncoated materials and coated materials. The most widely used coating material is aluminum-silicon coating. Zinc-based coating materials are less used because there is a problem of liquid metal induced brittleness (LMIE) during the hot forming process, which causes cracking or delayed cracking during the forming process of parts. In order to solve this phenomenon, Voestalpine currently uses an indirect hot forming method to produce zinc-based coated parts, which increases costs. However, the hot bath forming process of zinc-based coating materials has been successfully developed. This process uses a direct forming method to transfer the heated austenitized sheet to a hot bath mold for stamping. The cost of zinc-based coating materials is lower than that of aluminum-silicon materials, and the anti-corrosion performance is better than that of aluminum-silicon coating materials. The hot bath forming process effectively solves the LMIE phenomenon of zinc-based coating materials.

[0004] With the implementation of the 25% small offset collision regulations of the China Insurance Automotive Safety Index (C-IASI), and the difficulty of traditional body structures to meet high collision ratings and lightweight vehicles. In recent years, the industry has seen the emergence of one-piece hot-formed annular technology products, which have become a hot topic for research by automobile companies. In hot-formed annular products, bare plate materials have poor corrosion resistance, and after forming, high-frequency shot blasting is required to remove the thick oxide scale on the surface, which has a great impact on the profile size of the annular product. In the welding process of aluminum-silicon materials, the strength of the weld will be reduced due to the influence of aluminum elements, so the aluminum element in the coating needs to be removed. Zinc-based coating materials have been used in hot bath forming, and can be welded by wire welding or self-melting welding, which reduces costs, zinc-based coating materials have good corrosion resistance, and hot bath forming technology effectively solves the LMIE phenomenon. Annular zinc-based coating material parts are an important development trend in the future.

[0005] CN114714045A discloses a method for preparing an uncoated integrated door knocker, using uncoated hot-formed steel, through blanking, welding, oxygen-free heating austenitization, hot stamping, cutting and subsequent preparation of surface coating, to prepare an integrated door knocker. The method of the present invention can solve the problem that the deformation of ultra-thin plate materials is difficult to control by shot blasting and the corrosion resistance of bare plate materials is poor. However, the material involved in this patent is an uncoated material, and after hot forming, stamping and cutting, it is necessary to prepare a surface coating, which further increases the process and cost.

[0006] CN117259985B discloses a laser welded door ring and production process, which uses galvanized sheet materials and bare sheet materials, laser welding and patch plate spot welding, and laser shot blasting after hot forming to obtain an integrated door ring. The invention realizes welding between different materials, meets the corrosion resistance requirements of the lower body, and reduces costs and market demand. The door rings prepared from different materials involved in this patent have a bare sheet material on the upper body, which has poor corrosion resistance, and only meets the corrosion resistance requirements on the lower body.

[0007] CN118616892A discloses a production process for a composite door ring for automobiles, which uses raw materials including bare plates and aluminum-silicon coated plates, laser welding between different materials, and the last weld is completed by spot welding overlap to connect the door ring pieces, the patch plate uses non-coated materials and spot welding is performed directly after the last weld is completed, the annular piece is placed in a heating furnace for heating and austenitization, and then placed in a hot forming mold for stamping, and a composite door ring is obtained after laser treatment, and the welding between different materials is achieved by the present invention, and the patch plate uses the same material as the vehicle body, which optimizes the production process, improves production efficiency and reduces energy consumption. However, some materials and patch plates in this patent are made of non-coated materials, and there are coating defects between the patch plate and the substrate in the subsequent coating, and the corrosion resistance is poor.

[0008] Currently, the raw materials used are bare plates, aluminum-silicon coatings, and composite (partial bare plates and partial coated plates) materials, which are hot stamped after welding and spot welding to obtain one-piece annular products. After the bare plate material product is formed, a large amount of oxide scale is present on the surface, so high-frequency shot blasting is required. However, due to the large size of annular products, it is difficult to control the product surface size after high-frequency shot blasting, and the corrosion resistance of bare plate materials is poor. After welding, the weld strength of aluminum-silicon coating materials is weaker than that of the parent material. In order to improve the weld strength, it is necessary to reduce the influence of aluminum elements in the weld, so a stripping process is required during the welding process, which increases costs during the production process. Summary of the invention

[0009] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0010] The present invention provides a hot bath forming process for an integrated annular zinc-based coating component. The process comprises the following steps: heating and austenitizing an annular zinc-based coating blank that has been welded, and then transferring the blank to a water bath mold and stamping the blank under the action of a press to obtain an annular component product of an integrated zinc-based coating material. The component product reduces the weight of the vehicle body and improves the corrosion resistance of the component product. The LMIE phenomenon generated during the direct hot forming process of the zinc-based coating material is effectively solved, the excellent performance and dimensional accuracy control of the product are ensured, and the problem of the influence of the aluminum element during the welding process of the aluminum-silicon coating material is solved, thereby achieving cost reduction and efficiency improvement.

[0011] The present invention provides a hot bath forming process method for an integrated annular zinc-based coating component, comprising the following steps:

[0012] S1: heating the annular sheet to obtain an austenitized annular sheet; the annular sheet is subjected to substrate laser welding and patch plate spot welding before heating; the heating temperature is 860-910°C, the heating time T1 is 300-610s, T1=t*115+150; wherein t is the maximum material thickness value in the annular sheet blank, in mm;

[0013] S2: The austenitized annular sheet obtained in the step S1 is subjected to hydraulic and hot bath stamping forming and pressure holding in a mold to obtain an annular part; the austenitized annular sheet is immersed in hot water during forming and pressure holding, and the temperature before forming is maintained at 450-650°C; the pressure of the pressure holding is 800-2000T, and the pressure holding time T2=t*3+1; wherein t is the maximum material thickness value in the annular sheet blank, in mm;

[0014] S3: laser blasting and shot blasting the annular part after forming and pressure holding in step S2 to obtain an integrated annular product.

[0015] Preferably, the material of the annular sheet is galvanized hot-formed steel with a tensile strength of 500-2000 MPa, and the thickness of the coating is 65-85 g / m 2 .

[0016] Preferably, before the patch plate is spot-welded, the thickness of the annular sheet in the base plate and patch plate regions are both 0.8-3.0 mm.

[0017] Preferably, the material thickness of the patch plate after spot welding is 0.8-6.0 mm.

[0018] Preferably, in step S1, heating is performed by isothermal heating or gradient heating.

[0019] Preferably, in step S2, hot water and a heating rod are installed in the lower mold box of the mold during forming and pressure holding, and the temperature is maintained at 70-100°C.

[0020] Specifically, the hot bath forming process method of the above-mentioned one-piece annular zinc-based coated parts mainly solves the performance problems of low material utilization, heavy overall weight and material differences caused by traditional welding in annular products, and solves the LMIE phenomenon problem that occurs in the traditional hot forming stamping process of zinc-based coated plates. The specific implementation method or operation steps are as follows:

[0021] S11: The material taking robot transfers the annular pieces after butt welding and spot welding to the furnace body for heating and austenitizing;

[0022] S12: The austenitized annular sheet is transferred to a designed support rack in the mold by using a loading robot;

[0023] S13: Under the action of the hydraulic press, the upper mold is pressed down to contact the sheet, and then is further fitted with the lower mold to complete the hot bath stamping forming of the annular sheet;

[0024] S14: After the pressure holding is completed, the unloading robot takes out the annular parts. After laser blasting and shot blasting, the parts are obtained as one-piece annular products with qualified performance and size.

[0025] The welding described in step S11 refers to splicing different sheets of annular parts into a whole through laser welding technology. After the splicing is completed, the patch plate is spot welded in the required area of ​​the annular parts to obtain the required annular blank. Because the forming temperature is lower than that of the traditional process, the Mn element content in the sheet matrix component is increased to improve the hardenability of the material. The annular sheet is heated by isothermal or gradient heating for austenitization, the heating temperature range is 860-910℃, and the heating time range is 300-610s.

[0026] The heating time is: T1=t*115+150; t is the maximum material thickness value in the blank, and the maximum value of T1 is 610s.

[0027] In step S12, the lower mold box is filled with hot water, and the annular mold forming rod should be immersed in the hot water of the lower mold box, and the hot water level is 0-300mm above the lower mold forming rod, and the liquid level cannot exceed the top of the bracket. After the austenitized annular sheet is immersed in hot water, a layer of air film insulation layer will be formed on the surface of the sheet in the hot water, and the heat transfer rate between the sheet and the hot water will be greatly reduced. The temperature of the sheet before forming is maintained between 450-650°C, ensuring that the temperature of the sheet before forming is above the martensite start transformation temperature, while reducing the content of liquid zinc in the coating, avoiding the LMIE phenomenon of the part during the forming process.

[0028] In step S13, the annular sheet is formed in the mold, wherein the temperature of the hot water in the lower mold box is 70-100°C, and during the hot bath forming process, the annular sheet needs to be completely immersed in the hot water for 8-16 seconds, and the holding pressure is between 800-2000T. The annular sheet will begin to deform after contacting the upper mold, and at the moment of complete mold closing, the air film formed on the surface of the sheet will be destroyed, the heat exchange coefficient between the sheet and the hot water will be greatly improved, and it will fit the mold to achieve rapid quenching, and finally transform into a martensitic structure.

[0029] The holding time is: T2 = t*3 + 1. t is the maximum thickness of the blank, and the maximum value of T2 is 16s.

[0030] The mechanical properties of the formed parts in step S14 are as follows: tensile strength is 1000-2150MPa, yield strength is 950-1500MPa, elongation after fracture is ≥5%, and coating thickness is between 15-30 microns. The microcracks of the parts after forming are all below 10μm, which meets the standards of BMW and Volkswagen for microcracks of galvanized sheets, and the ring product size test is qualified.

[0031] The present invention also provides a component prepared by the hot bath forming process of the above-mentioned integrated annular zinc-based coating component.

[0032] Preferably, the tensile strength of the component is 1000-2150 MPa, the yield strength is 950-1500 MPa, and the elongation after fracture is ≥5%.

[0033] Preferably, the coating thickness of the component is 15-30 μm.

[0034] Preferably, the microcracks of the component after forming are less than 10 μm.

[0035] The technical solution of the present invention has the following advantages over the prior art:

[0036] The present invention can adopt a hot bath forming process to produce annular zinc-based coating material parts. The single-part blanks of the annular product are integrated together through the welding technology, which reduces the weight of the vehicle body and improves the production efficiency of the parts. The galvanized annular product can reduce the welding cost during welding, and the part performance meets the requirements, the surface size is qualified, and the corrosion resistance is improved, which effectively solves the problem of LMIE phenomenon occurring in the hot forming process of the zinc-based coating material. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a hot bath process flow chart of the present invention;

[0038] Figure 2 It is the drawing of the ring-shaped blank in the present invention;

[0039] Figure 3 It is the microstructure diagram of microcracks in the coating in the present invention;

[0040] Figure 4 This is the microstructure diagram of the coating thickness in the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0042] Example 1

[0043] In this embodiment, the hot bath forming and stamping experiment of the annular galvanized sheet parts is carried out according to the process method of the present invention. The material thickness of each area of ​​the annular sheet is A: 2.1mm, B: 1.9mm, C: 2.0mm, D: 1.0mm, E: 1.6mm, and the thickness of the patch plate is patch plate 1 (B): 1.1mm, patch plate 2 (C): 1.4mm, and the materials are all galvanized hot-formed steel sheets. The sheets in each area of ​​the annular sheet are laser welded, and the patch plates are spot welded in areas B and C after the welding is completed. After the spot welding is completed, they are transferred to a roller hearth furnace for heating. The temperature of the roller hearth furnace is set to 900℃, and the temperature is kept for 8 minutes to complete austenitization. After the austenitization is completed, it is transferred to the mold support frame by a manipulator, and the hydraulic press is used to close the mold. The holding pressure is 1200T and the holding time is 10s. The lower die forming rod is immersed in hot water with a temperature of 90-95°C. During the stamping process, the blank begins to deform after contacting the upper die and enters the hot water from the air medium. A uniform vapor film will form on the surface of the annular blank in the hot water. The cooling speed of the blank can be controlled under the action of the hot water and the vapor film. When the mold is fully closed, the vapor film on the surface is destroyed, and the heat transfer rate between the annular component and the hot water is accelerated. Under the joint action of the mold, the product is quenched to obtain a zinc-based hot-formed annular component product, which simultaneously shortens the holding time and improves the production rhythm.

[0044] Example 2

[0045] In this embodiment, the hot bath forming and stamping experiment of the annular galvanized sheet parts is carried out according to the process method of the present invention. The material thickness of each area of ​​the annular sheet is A: 2.1mm, B: 1.9mm, C: 2.0mm, D: 1.0mm, E: 1.6mm, and the thickness of the patch plate is patch plate 1 (B): 1.1mm, patch plate 2 (C): 1.4mm, and the materials are all galvanized hot-formed steel sheets. The sheets in each area of ​​the annular sheet are laser welded, and the patch plates are spot welded in areas B and C after the welding is completed. After the spot welding is completed, they are transferred to the roller hearth furnace for heating. The temperature of the roller hearth furnace is set to 890℃, and the heating time is 8min to complete the austenitization. After the austenitization is completed, it is transferred to the support rack in the mold by a manipulator, and the hydraulic press is used to close the mold. The holding pressure is 1200T and the holding time is 10s. The lower die forming rod is immersed in hot water with a temperature of 90-95°C. During the stamping process, the blank begins to deform after contacting the upper die and enters the hot water from the air medium. A uniform vapor film will form on the surface of the annular blank in the hot water. The hot water and the vapor film can control the cooling rate of the blank. When the mold is fully closed, the surface vapor film is destroyed, and the heat transfer rate between the annular component and the hot water is accelerated. Under the joint action of the mold, the product is quenched to obtain a zinc-based hot-formed annular component product, which simultaneously shortens the holding time and improves the production rhythm.

[0046] Example 3

[0047] In this embodiment, the hot bath forming and stamping experiment of the annular galvanized sheet parts is carried out according to the process method of the present invention. The thickness of each area of ​​the annular sheet is A: 2.1mm, B: 1.9mm, C: 2.0mm, D: 1.0mm, E: 1.6mm, and the thickness of the patch plate is patch plate 1 (B): 1.1mm, patch plate 2 (C): 1.4mm, and the materials are all galvanized hot-formed steel sheets. The sheets in each area of ​​the annular sheet are laser welded, and the patch plates are spot welded in areas B and C after the welding is completed. After the spot welding is completed, they are transferred to a roller hearth furnace for heating. The roller hearth furnace temperature is set to 900°C, the heating time is 7min, the holding pressure is 1200T, the holding time is 10s, and the hot water temperature is 90-95°C.

[0048] Example 4

[0049] In this embodiment, the hot bath forming and stamping experiment of the annular galvanized sheet parts is carried out according to the process method of the present invention. The material thickness of each area of ​​the annular sheet is A: 2.1mm, B: 1.9mm, C: 2.0mm, D: 1.0mm, E: 1.6mm, and the thickness of the patch plate is patch plate 1 (B): 1.1mm, patch plate 2 (C): 1.4mm, and the materials are all galvanized hot-formed steel sheets. The sheets in each area of ​​the annular sheet are laser welded, and the patch plates are spot welded in areas B and C after the welding is completed. After the spot welding is completed, they are transferred to the roller bottom furnace for heating. The roller bottom furnace temperature is set to 890℃, and the heating time is 7min to complete austenitization. After the austenitization is completed, it is transferred to the mold support frame by a manipulator, and the hydraulic press is used for mold closing. The holding pressure is 1200T, the holding time is 10s, and the hot water temperature is 90-95℃.

[0050] Comparative Example 1

[0051] In this comparative example, a direct hot stamping experiment of annular galvanized sheet parts was carried out according to the process method of the present invention. The material thickness of each area of ​​the annular sheet is A: 2.1mm, B: 1.9mm, C: 2.0mm, D: 1.0mm, E: 1.6mm, and the thickness of the patch plate is patch plate 1 (B): 1.1mm, patch plate 2 (C): 1.4mm, and the materials are all galvanized hot-formed steel sheets. The sheets of each area of ​​the annular sheet are laser welded, and the patch plates are spot welded in areas B and C after the welding is completed. After the spot welding is completed, they are transferred to a roller hearth furnace for heating. The temperature of the roller hearth furnace is set to 900℃, and the heating time is 8min to complete austenitization. After austenitization is completed, it is transferred to a traditional mold by a manipulator for direct stamping. The mold temperature is 700-800℃. After completing the mold closing pressure quenching, the annular parts are obtained. The pressure holding pressure is 1200T and the pressure holding time is 10s.

[0052] Comparative Example 2

[0053] In this embodiment, a direct hot stamping experiment of annular galvanized sheet parts is carried out according to the process method of the present invention. The material thickness of each area of ​​the annular sheet is A: 2.1mm, B: 1.9mm, C: 2.0mm, D: 1.0mm, E: 1.6mm, and the thickness of the patch plate is patch plate 1 (B): 1.1mm, patch plate 2 (C): 1.4mm, and the materials are all galvanized hot-formed steel sheets. The sheets of each area of ​​the annular sheet are laser welded, and the patch plates are spot welded in areas B and C after the welding is completed. After the spot welding is completed, they are transferred to a roller furnace for heating. The temperature of the roller furnace is set to 890℃, and the heating time is 8min to complete austenitization. After the austenitization is completed, it is transferred to the mold by a manipulator for direct stamping. The mold temperature is 700-800℃. After the mold closing pressure quenching is completed, the annular parts are obtained. The pressure holding pressure is 1200T and the pressure holding time is 10s.

[0054] Effect evaluation 1

[0055] Table 1 Hot bath forming parameters and results of various embodiments of the present invention and comparative examples

[0056]

[0057] Zinc-based hot-formed steel has both cost and performance advantages in the context of lightweighting and cost reduction and efficiency improvement in the automotive industry. At the same time, one-piece annular products play a significant role in lightweighting of automobiles. However, due to the material properties of zinc-based hot-formed steel, it is impossible to refer to the bare plate and aluminum-silicon coated hot-forming stamping process. The parts prepared by the zinc-based coating material under the direct hot forming process have LMIE phenomenon, which seriously affects the performance. Therefore, the present invention is aimed at the hot forming process of zinc-based coating annular parts, and uses a hot bath forming process to solve the LMIE phenomenon problem of zinc-based coating materials during the hot forming process. At the same time, the zinc-based coating annular parts are used on the body to meet a prospective demand for lightweighting of automobiles and can bring performance improvement and cost reduction, which has great economic value and social benefits in the automotive industry.

[0058] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A hot bath forming process for an integrated annular zinc-based coating component, characterized in that: The steps include: S1: heating the annular sheet to obtain an austenitized annular sheet; the annular sheet is subjected to substrate laser welding and patch plate spot welding before heating; the heating temperature is 860-910°C, the heating time T1 is 300-610s, T1=t*115+150; wherein t is the maximum material thickness value in the annular sheet blank; S2: The austenitized annular sheet obtained in step S1 is subjected to hydraulic and hot bath stamping and pressure holding in a mold to obtain an annular part; the austenitized annular sheet is immersed in hot water during forming and pressure holding, and the temperature before forming is maintained at 450-650°C; the pressure of the pressure holding is 800-2000T, and the pressure holding time T2=t*3+1; wherein t is the maximum material thickness value in the annular sheet blank; S3: laser blasting and shot blasting the annular part after forming and pressure holding in step S2 to obtain an integrated annular product.

2. The hot bath forming process of the one-piece annular zinc-based coating component according to claim 1, characterized in that: The material of the annular sheet is galvanized hot-formed steel with a tensile strength of 500-2500 MPa, and the thickness of the coating is 65-85 g / m 2 .

3. The hot bath forming process of the one-piece annular zinc-based coating component according to claim 1, characterized in that: Before the patch plate is spot-welded, the thickness of the annular sheet in the base plate and patch plate regions is 0.8-3.0 mm.

4. The hot bath forming process of the one-piece annular zinc-based coating component according to claim 3, characterized in that: The material thickness of the area after spot welding between the substrate and the patch plate is 0.8-6.0 mm.

5. The hot bath forming process of the one-piece annular zinc-based coating component according to claim 1, characterized in that: In the step S1, heating is performed by isothermal heating or gradient heating.

6. The hot bath forming process of the one-piece annular zinc-based coating component according to claim 1, characterized in that: In step S2, during forming and pressure holding, hot water is contained in the lower mold box of the mold and the temperature of the hot water is maintained at 70-100°C.

7. A component manufactured by a hot bath forming process of the one-piece annular zinc-based coating component according to any one of claims 1 to 6.

8. The component according to claim 7, characterized in that The tensile strength of the component is 1000-2150MPa, the yield strength is 950-1500MPa, and the elongation after fracture is ≥5%.

9. The component according to claim 7, characterized in that The coating thickness of the component is 15-30 μm.

10. The component according to claim 7, characterized in that The microcracks of the component after forming are less than 10 μm.

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