Rolling device and method for multi-step incremental forming of ultrahigh-strength plate

Abstract

According to the rolling device and method for multi-step incremental forming of the ultra-high-strength plate, through cooperative finishing of laser local heating and a small fillet forming roller, the minimum forming fillet radius of the ultra-high-strength plate can be compressed to be smaller than or equal to 2T (T is the thickness of the plate) from R larger than or equal to 3T in traditional cold rolling; while the design freedom degree and the structural performance of the part are remarkably improved, the cold hardening high-strength state of a non-heating area is precisely kept, and the overall softening defect caused by a hot stamping process is thoroughly avoided; and as the forming force mainly acts on the local softening area, the required forming force is obviously reduced, and meanwhile, the springback of the softening area can be effectively inhibited, so that the size precision and the shape stability of the small fillet are ensured. The device serves as an independent unit and can be conveniently integrated at the tail end of an existing rolling line, subversive transformation of the whole production line is not needed, and high economical efficiency and practical value are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal plate plastic processing, in particular to a rolling device and method for multi-step progressive forming of ultra-high strength plates. Background Art

[0002] With the increasing demand for lightweighting and safety performance in automobiles, ultra-high-strength steel (UHSS), due to its superior strength-to-weight ratio and collision energy absorption properties, has become a core material for key vehicle body structural components. UHSS now accounts for over 35% of the body-in-white (BIW) structure and is widely used in key safety components such as A / B pillars, door anti-collision beams, and chassis reinforcements, making it a core material in modern automotive manufacturing. The rapid development of new energy vehicles has further promoted the use of UHSS. Currently, new energy battery packs are primarily made of aluminum alloy, but this lacks strength and is costly, further highlighting the advantages of UHSS's high strength, low cost, and lightweight performance. According to industry research, every 10% increase in the use of UHSS in the BIW can reduce the overall vehicle weight by 6%-8%, while significantly improving torsional rigidity and collision safety.

[0003] Roll forming, a mainstream process for efficiently producing long, uniform-section parts, is widely used in UHSS profile manufacturing due to its advantages of continuous production, high efficiency, and low cost. However, traditional cold rolling processes exhibit significant shortcomings when working with UHSS. These include high yield strength and low plasticity reserve, which can lead to significant springback and cracking during forming. Furthermore, due to limitations in material flow and springback control, the minimum stable fillet radius achievable with cold rolling typically must meet the requirement of R ≥ 3T (where T is the sheet thickness).

[0004] To overcome the limitations of small fillet forming, existing technologies typically use hot stamping: heating the sheet to austenitizing temperature before forming. While this can achieve small fillets with an R value of approximately 1T, it results in overall softening of the part, high energy consumption, and slow production cycles, making it unsuitable for continuous production of long parts. Therefore, achieving precise small fillet forming (R ≤ 2T) for UHSS while retaining the high efficiency of the roll forming process has become a common industry challenge hindering lightweight structural design. Summary of the Invention

[0005] In view of the above problems, a rolling device and method for multi-step progressive forming of ultra-high strength plates are proposed to overcome or at least partially solve the above problems, specifically comprising: A rolling device for multi-step progressive forming of ultra-high strength plates, comprising: The online laser heating modules are located on either side of the small-radius forming roller inlet and are configured to locally heat only the pre-formed radius area of ​​the moving sheet metal with a preset cross-sectional profile until the temperature reaches the sheet metal's plasticity-enhancing temperature window. The online laser heating modules include an infrared temperature measurement feedback unit and an MFSC4kW multi-mode continuous fiber laser. The laser head model of the MFSC4kW multi-mode continuous fiber laser is ZF-HH003A. The small-radius forming roller is located downstream of the online laser heating module and comprises: a flat contact area in contact with the unheated portion of the sheet; a small-radius curved surface matching the preformed rounded corner area, wherein the radius of the small-radius curved surface is 1T≤R≤2T, where T is the sheet thickness; and a smooth slope connecting the flat contact area and the small-radius curved surface, which is used to extrude the heated preformed rounded corner material into the small-radius curved cavity. Support rollers, located above the small-radius forming rollers, are used to support the plate with a preset cross-sectional profile during travel; A computer control system is used to control the parameters of the online laser heating module and the plate travel speed; wherein the online laser heating module parameters include laser spot diameter, laser power density, scanning speed and laser relative position.

[0006] Optionally, the plate is a 1.5 mm thick 1700 MPa ultra-high strength steel plate.

[0007] Optionally, the distance between the laser head and the plate is 200 mm.

[0008] Optionally, the smooth slope is a surface slope with a gradually changing curvature.

[0009] A rolling method for forming small-radius corners of ultra-high-strength plates, comprising: forming the ultra-high-strength sheet into a sheet with a preset cross-sectional profile; An online laser is used to locally heat the pre-formed fillet area of ​​a sheet with a preset cross-sectional profile until the temperature rises to the plastic enhancement temperature window of the sheet; The heated sheet material immediately enters the small-radius forming roller; The preset cross-sectional profile fillet radius R≥3T, where T is the thickness of the ultra-high strength plate.

[0010] Optionally, the online laser power is 1.5 kW, the laser spot shape is a rectangular spot adapted to the rounded corner area, and the size is 8 mm × 4 mm.

[0011] Optionally, the plasticity enhancement temperature window is 600°C-800°C.

[0012] Optionally, the method is implemented in the final forming pass or finishing pass of a multi-pass roll forming production line.

[0013] Optionally, the production line speed is 10m / min.

[0014] Optionally, the preset cross-sectional profile is a U-shaped cross-sectional profile with a fillet radius R ≥ 3T.

[0015] The embodiment of the present invention, through the coordinated finishing of local laser heating and small-radius forming rollers, can reduce the minimum forming radius of ultra-high-strength sheet metal from R ≥ 3T in traditional cold rolling to R ≤ 2T (T is the thickness of the steel plate). While significantly improving the design freedom and structural performance of the part, it accurately maintains the high-strength state of cold work hardening in the non-heating area, completely avoiding the overall softening defects caused by the hot stamping process. Moreover, because the forming force mainly acts on the local softening zone, the required forming force is significantly reduced, and the rebound of the softening zone can be effectively suppressed, ensuring the dimensional accuracy and shape stability of the small radius. Furthermore, the device provided by the embodiment of the present invention, as an independent unit, can be easily integrated into the end of an existing rolling line, eliminating the need for disruptive modifications to the entire production line, and has high economic and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the description of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 A schematic diagram of a rolling device for multi-step progressive forming of ultra-high strength plates provided by an embodiment of the present invention; Figure 2 A schematic cross-sectional view of a preformed plate provided in an embodiment of the present invention; Figure 3 A schematic diagram of a U-shaped member provided in an embodiment of the present invention; Figure 4 Schematic diagram of a small-radius forming roller and a support roller provided in an embodiment of the present invention; Figure 5 Schematic diagram of the contact between the small-radius forming roller and the formed part provided by an embodiment of the present invention; Figure 6 A schematic diagram of a conventional roll forming platform provided as a comparative example of the present invention; Figure 7 Schematic diagram of a small-radius forming roller and a support roller without a transition slope provided in a comparative example of the present invention; Figure 8 A flow chart of a rolling method for forming small fillets of ultra-high-strength plate materials provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It is apparent that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0019] Roll forming is a continuous, efficient sheet metal forming technology that uses multiple roller passes to gradually bend a metal strip to a specific cross-sectional shape. Roll forming boasts high efficiency, high material utilization, and the ability to form complex cross-sections. It is widely used in industries such as automotive manufacturing, construction, machinery, and aviation.

[0020] Ultra-high-strength steel (UHSS) with strengths exceeding 1500MPa, thanks to its exceptional lightweighting potential and safety performance, now accounts for over 35% of body-in-white (BIW) structures. Widely used in key safety components such as A / B pillars, door anti-collision beams, and chassis reinforcements, it has become a core material in modern automotive manufacturing. The rapid development of new energy vehicles has fueled the use of UHSS. Currently, new energy battery packs are primarily constructed of aluminum alloy, which suffers from low strength and high cost. This further highlights the advantages of UHSS, including high strength, low cost, and lightweighting.

[0021] To achieve small fillet formation in high-strength steel during roll forming, multiple sets of rollers are used to progressively form the sheet material, gradually reducing the radius of the bend during the forming process. However, this process is complex, increasing production costs. Furthermore, roll forming lines cannot achieve extremely small bend radiuses, such as r = 1 to 2t, for high-strength steel during the forming process. Furthermore, the forming material is mostly ultra-high-strength steel with a strength below 1500 MPa. Forming extremely small fillets in ultra-high-strength steel with a strength greater than 1500 MPa presents many challenges. Currently, roll forming lines can only achieve a fillet radius of 3-4 times the sheet thickness for ultra-high-strength steel (strength levels above 1500 MPa). Conventional roll forming processes are unable to achieve fillet radiuses of 2 times or less for ultra-high-strength steel (strength levels above 1500 MPa).

[0022] Roll-forming ultra-high-strength sheet metal with small fillets is a recognized industry challenge. Traditional approaches either sacrifice fillet radius or abandon roll-forming in favor of other processes (such as hot stamping). The present invention provides an in-line composite process combining "local heat treatment and local finishing" to address the technical bottleneck of existing roll-forming processes, which hinders the formation of small fillet radii (typically R ≥ 3T, where T is the sheet thickness) due to the poor formability and high springback of ultra-high-strength sheet metal, while maintaining the high efficiency of traditional roll-forming.

[0023] An embodiment of the present invention provides a rolling device for multi-step progressive forming of ultra-high-strength plates. The device can be arranged at the end of a rolling production line and can also be referred to as a rolling device for forming small rounded corners of ultra-high-strength plates. The device can specifically include: Online laser heating modules are respectively arranged on both sides of the small fillet forming roller inlet, and are configured to locally heat only the pre-formed fillet area of ​​the plate with a preset cross-sectional profile during movement until the temperature rises to the plastic enhancement temperature window of the plate; The small-radius forming roller is located downstream of the online laser heating module and comprises: a flat contact area in contact with the unheated portion of the sheet; a small-radius curved surface matching the preformed rounded corner area, wherein the radius of the small-radius curved surface is 1T≤R≤2T, where T is the sheet thickness; and a smooth slope connecting the flat contact area and the small-radius curved surface, which is used to extrude the heated preformed rounded corner material into the small-radius curved cavity. Support rollers, located above the small-radius forming rollers, are used to support the plate with a preset cross-sectional profile during travel; Computer control system is used to control the parameters of online laser heating module and the speed of plate movement.

[0024] In an embodiment of the present invention, the online laser heating module can be respectively arranged on both sides of the entrance of the small rounded corner forming roller to achieve rapid and precise local heating of the pre-formed rounded corner area, so that the temperature of the pre-formed rounded corner area is raised to the plasticity improvement temperature window of the material, while the rest of the part remains in a low temperature state.

[0025] At the same time, a small distance can be maintained between the online laser heating module and the small fillet forming roller to ensure that the pre-formed fillet area of ​​the sheet material can immediately enter the small fillet forming station after being heated to the plastic enhancement temperature window. The online laser heating module can be equipped with an infrared temperature measurement real-time feedback unit for real-time monitoring of whether the temperature of the pre-formed fillet area has reached the plastic enhancement temperature window. Once the temperature of the pre-formed fillet area has reached the plastic enhancement temperature window, the sheet material is transferred to the small fillet forming roller for forming.

[0026] In an embodiment of the present invention, a small-radius forming roller may include: a planar contact area that contacts the unheated portion of the sheet; a small-radius curved surface that matches the preformed fillet area; and a smooth slope connecting the planar contact area and the small-radius curved surface. The planar contact area can be used to constrain the position of the unheated area of ​​the sheet, preventing the entire sheet from shifting, while the small-radius curved surface (i.e., the mold cavity) is used to define the final shape of the target fillet, with the radius of the small-radius curved surface being 1T≤R≤2T (where T is the sheet thickness). The smooth slope connecting the planar contact area and the small-radius curved surface can be used to guide the heated and softened material toward the small-radius curved surface (i.e., the mold cavity). Progressive extrusion can prevent stress concentration that could cause wrinkling or cracking in the material.

[0027] It can be understood that when the plate enters the small-radius forming roller, the smooth slope first contacts and squeezes the pre-formed radius area, that is, the radius area that has been heated and softened, and squeezes the material toward and fills the small-radius curved mold cavity, thereby achieving a precise transition from large radius to small radius.

[0028] In an embodiment of the present invention, the plate may be a 1.5 mm thick 1700 MPa ultra-high strength steel plate.

[0029] Example 1: A 1.5 mm thick 1700 MPa ultra-high strength steel plate can be processed into a preform through the previous process. Figure 1 As shown, the preformed fillet area of ​​the preform 1 can be heated to 700°C by online laser heating modules 2 and 3; the steel plate is roll-formed using small fillet forming rollers 4, 5 and support rollers 6 according to a specially designed roller profile. Figure 2 , the preform 1 is bent to 90° at 7, and the fillet 9 is formed to R=2.0mm after rolling; the arrow in the figure indicates the direction of movement. Figure 2 As shown, the angle at 8 is 80°, and the radius of the fillet at 9 is R = 6mm (4T); the U-shaped part after forming is as follows Figure 3 As shown, the radius of the 10 fillet corners is R=2.0mm (≈1.3T), and the radius of the small fillet forming roller is R=2.0mm.

[0030] As comparative example 1: Figure 6 A 1700 MPa ultra-high-strength steel plate, also 1.5 mm thick, can be preformed into a preformed part similar to Example 1, namely, ultra-high-strength steel plate 14, by first passing through three sets of rollers: rollers 15, 16, and 17, rollers 18, 19, 20, and 21, and rollers 22, 23, 24, and 25. The ultra-high-strength steel plate 14 then passes through a fourth set of rollers: rollers 26, 27, 28, and 29, and a fifth set of rollers: rollers 30, 31, 32, and 33. The arrows in the figure indicate the direction of movement. The ultra-high-strength steel plate 14 has a corner radius of 6 mm (4T).

[0031] By comparison, when comparative example 1 attempted to form a fillet with R=2mm, the ultra-high-strength steel plate showed cracking and large springback at the fillet; while the ultra-high-strength steel plate formed using the device provided by the embodiment of the present invention had an R value measured between 1.9mm-2.1mm, without any cracking, and the material springback was also small, which can solve the problem of small fillet forming of ultra-high-strength steel plates that cannot be achieved by traditional processes.

[0032] In the embodiment of the present invention, the laser of the online laser heating module is an MFSC 4kW multimode continuous fiber laser with a laser head model of ZF-HH003A. Parameters such as the laser spot diameter, laser power density, scanning speed, and laser relative position can be adjusted according to actual needs.

[0033] In practical applications, the MFSC4kW multimode continuous fiber laser can be used to laser heat only the preformed fillet areas (e.g., the two inner corners of a U-shaped section) of a moving sheet. Specifically, the MFSC4kW multimode continuous fiber laser's beam spot covers the fillet surface, controlling the material temperature and raising the target area to the plasticity-enhancing temperature window, thereby reducing the yield strength of the material in the target area while avoiding heating other areas.

[0034] In an embodiment of the present invention, the smooth slope may be a curved slope with a gradually changing curvature.

[0035] It can be understood that the planar contact area of ​​the small-radius forming roller in the embodiment of the present invention can lock the position of the unheated part, and the curvature gradient slope can guide the heated softened material to flow along the normal gradient through continuous curvature changes, eliminating the stress concentration risk of traditional straight slopes, allowing the material to be evenly filled into the small-radius curved mold cavity, and achieving precision compression from R≥3T to the target R≤2T under low pressure.

[0036] In order to verify the effect of the smooth slope surface in the small-radius forming roller, the embodiment of the present invention also provides the following control experiment: Example 2: A 1.5 mm thick 1700 MGPa ultra-high strength steel plate heated by online laser is transferred to a small-radius forming roller and a support roller for forming, as shown in FIG. Figure 4 As shown, the 11 areas of the roller profile that contact the straight portion of the sheet are flat, while the 12 areas that contact the rounded corners are machined into small-radius curved surfaces that match the target small-radius corner R = 2.0mm (≈1.3T). A smoothly transitioning ramp surface 13 is provided between the flat and small-radius curved surfaces. As the sheet passes through, the ramp surface 13 of the small-radius forming roller first contacts and presses the heated and softened rounded corner area 9, "forcing" the material toward and filling the small-radius curved cavity, thereby achieving a precise transition from large to small rounded corners.

[0037] Comparative Example 2: Figure 7 As shown, a 1.5 mm thick 1700 MPa ultra-high strength steel plate that has been online laser heated using the same parameters as in Example 2 is transferred to a "mutated" small-radius forming roller 34 without a smooth slope for forming, that is, the roller profile is directly mutated from a plane to a curved surface with R=2 mm.

[0038] By comparison, the steel plate in Comparative Example 2 has no smooth slope to guide it, so the heated and softened material does not flow smoothly when being extruded, and slight wrinkling and piling appear on the inside of the fillet, resulting in poor surface quality. However, the steel plate material in Example 2 flows smoothly, and the inner and outer surfaces of the fillet are smooth, resulting in better quality.

[0039] Reference Figure 8 The embodiment of the present invention further provides a rolling method for forming small fillet of ultra-high strength plate, comprising: forming the ultra-high-strength sheet into a sheet with a preset cross-sectional profile; An online laser is used to locally heat the pre-formed fillet area of ​​a sheet with a preset cross-sectional profile until the temperature rises to the plastic enhancement temperature window of the high-strength sheet; The heated sheet material immediately enters the small radius forming roller.

[0040] The preset cross-sectional profile fillet radius R ≥ 3T, where T is the thickness of the ultra-high-strength plate. The online laser power can be 1.5 kW, the laser spot shape is a rectangular spot adapted to the fillet area, the size is 8 mm × 4 mm, and the distance between the laser head and the plate is 200 mm. The plastic enhancement temperature window also varies depending on the plate. Generally, the plastic enhancement temperature window of ultra-high-strength plate is 600°C-800°C. The production line speed can be 10 m / min. The method provided in the embodiment of the present invention can be implemented in the final forming pass or finishing pass of a multi-pass roll forming production line, that is, the ultra-high-strength plate material can be preliminarily formed into a cross-sectional profile preform with a larger fillet radius (R ≥ 3T, where T is the plate thickness) through the preceding roll forming pass. The specific process parameters can be shown in Table 1.

[0041] Production line speed (m / min) Laser power (kW) Spot shape Spot size Plate surface temperature (℃) Sheet thickness (mm) Material strength (Mpa) 10 1.5 rectangle 8mm×4mm 700±20℃ 1.5 1700 Table 1 In an embodiment of the present invention, the plate can first be preformed into a preset cross-sectional profile with a large fillet radius (R≥3T, T is the plate thickness), such as a U-shaped cross-section, by multiple rolling passes. Subsequently, at the end of the production line, an online laser is used to locally heat the preformed fillet area of ​​the moving plate with a rectangular spot, so that its surface temperature is raised to the plasticity improvement temperature window (such as 700±20°C). At this time, the yield strength of the fillet area decreases, while the area not heated by the laser maintains a cold high strength; the heated plate is immediately sent to the downstream small fillet forming roller, and the softened material is guided to fill the finishing mold cavity with R≤2T through the progressive extrusion of its curvature gradient surface slope, and the fillet radius is compressed from the initial R≥3T to the target R≤2T under low pressure, while suppressing springback.

[0042] The embodiment of the present application can compress the minimum forming fillet radius of the ultra-high strength plate from R≥3T (T is the thickness of the plate) of the traditional cold roller pressing to R≤2T by the synergistic finishing of the local laser heating and the small fillet forming roller, significantly improves the part design freedom and structural performance, accurately maintains the cold work hardening high strength state of the non-heating area, completely avoids the overall softening defects caused by the hot stamping process; and since the forming force mainly acts on the local softening area, the required forming force is significantly reduced, and the springback of the softening area can be effectively inhibited, ensuring the stability of the small fillet size precision and shape. The device provided by the embodiment of the present application is an independent unit, which is convenient to integrate at the end of the existing roller pressing line, and does not need to revolutionize the whole production line, which has high economic efficiency and practical value.

[0043] The above describes a roller pressing device and method for multi-step progressive forming of ultra-high strength plate, specific examples are applied to explain the principle and implementation mode of the present application, and the above embodiment is only used to help understand the method and core idea of the present application; meanwhile, for the general technical personnel in the field, the specific implementation mode and application range will be changed according to the idea of the present application, and the above description should not be understood as the limitation of the present application.

Claims

1. A rolling device for multi-step progressive forming of ultra-high strength plates, characterized in that: include: An online laser heating module, located on either side of the small-radius forming roller inlet, is configured to locally heat only the pre-formed radius area of ​​the advancing sheet material with a preset cross-sectional profile until the temperature reaches the sheet material's plasticity enhancement temperature window. The online laser heating module includes an infrared temperature measurement feedback unit and an MFSC4kW multi-mode continuous fiber laser. The laser head model of the MFSC4kW multi-mode continuous fiber laser is ZF-HH003A. A small fillet forming roller is located downstream of the online laser heating module, and comprises: a planar contact area in contact with the unheated portion of the plate; a small radius curved surface matching the preformed fillet area, wherein the radius of the small radius curved surface is 1T≤R≤2T, where T is the thickness of the plate; and a smooth slope connecting the planar contact area and the small radius curved surface, wherein the smooth slope is used to extrude the heated preformed fillet area material into the small radius curved surface mold cavity; A support roller, located above the small-radius forming roller, is used to support the plate with a preset cross-sectional profile during travel; A computer control system is used to control the parameters of the online laser heating module and the plate travel speed; wherein the online laser heating module parameters include laser spot diameter, laser power density, scanning speed and laser relative position.

2. The device according to claim 1, characterized in that The plate is a 1.5 mm thick 1700 MPa ultra-high strength steel plate.

3. The device according to claim 2, characterized in that The distance between the laser head and the plate is 200 mm.

4. The device according to claim 3, characterized in that The smooth slope is a curved slope with a gradually changing curvature.

5. A rolling method for forming small fillet of ultra-high strength plate, characterized in that: The method comprises: forming the ultra-high-strength sheet into a sheet with a preset cross-sectional profile; Locally heating the preformed fillet area of ​​the plate with the preset cross-sectional profile by using an online laser until the temperature rises to the plasticity improvement temperature window of the plate; The heated sheet material immediately enters the small radius forming roller; Wherein, the preset cross-sectional profile fillet radius R≥3T, where T is the thickness of the ultra-high strength plate.

6. The method according to claim 5, characterized in that The online laser power is 1.5 kW, and the laser spot shape is a rectangular spot adapted to the rounded corner area, with a size of 8 mm×4 mm.

7. The method according to claim 6, characterized in that The plasticity improvement temperature window is 600°C-800°C.

8. The method according to claim 7, characterized in that The method is implemented in the final forming pass or finishing pass of a multi-pass roll forming production line.

9. The method according to claim 8, characterized in that The production line speed is 10 m / min.

10. The method according to claim 9, characterized in that The preset cross-sectional profile is a U-shaped cross-sectional profile with a fillet radius R≥3T.

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