A combined forming process suitable for hollow and complex cross-section aluminum profiles

Abstract

The present application relates to the technical field of metal profile processing, in particular to a combined forming process suitable for hollow and complex cross-section aluminum profiles and a roller device suitable for the process, the present application provides a combined forming process, which decomposes the cross-section of the target profile into several semi-finished plate materials without hollow closed shape and at most two corners; the alloy base material is cut into a strip after rolling, and the width of the strip is the same as the corresponding cross-section profile development size; the strip is gradually formed into a semi-finished profile strip by multi-pass progressive rolling through multiple roller combinations, and the inclination angle of each group of lower rollers increases gradually along the feeding direction; the semi-finished profile strip can be cooled or directly adjusted to a butt joint attitude and then spliced into a complete profile by friction stir welding. The present application combines the strip strategy with the progressive rolling forming, improves the uniformity of the profile organization, reduces the forming energy consumption and the mold load, and is suitable for the preparation of large cross-section complex aluminum profiles.

Description

Technical Field

[0001] This invention relates to the field of metal profile processing technology, specifically to a combined forming process applicable to hollow and complex cross-section aluminum profiles. Background Technology

[0002] Currently, the mainstream process for producing aluminum alloy profiles (especially hollow profiles) in the industry is hot extrusion forming. Its typical process is as follows: 1. Ingot heating: Heating a cylindrical aluminum alloy ingot to 450℃-500℃. 2. Extrusion deformation: Under the high pressure of the extruder, the hot aluminum ingot flows out through a die (such as a planar flow divider die). 3. Flow divider welding: For hollow profiles, the metal flow is divided by flow dividers and then re-converges in the welding chamber under high temperature and pressure to form a hollow cross-section.

[0003] Although hot extrusion technology is mature, it faces significant bottlenecks in the manufacturing of high-performance, large-section profiles. First, due to the complex deformation path of the material and the poor uniformity of the substrate structure, the substrate needs to undergo multi-directional flow splitting and welding during the extrusion process, resulting in repeated local plastic deformation, which can easily lead to uneven grain orientation and performance distribution. Second, in the high-temperature, high-pressure, and high-friction molding process, the mold is subjected to extreme working conditions, resulting in high maintenance and replacement costs. Third, in large-scale pressing processes, the material undergoes repeated plastic deformation and welding at high temperatures, resulting in high energy consumption and significant ineffective deformation power consumption. Summary of the Invention

[0004] The purpose of this invention is to provide a combined forming process suitable for hollow and complex cross-section aluminum profiles, so as to solve the technical problems of poor microstructure uniformity, short mold life, high energy consumption and limited preparation of large cross sections caused by the complex material deformation path in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0006] A combined forming process suitable for hollow and complex cross-section aluminum profiles includes the following steps:

[0007] S100. Based on the preset cross-sectional shape of the target profile, determine the target cross-sectional outline of several semi-finished plates. The semi-finished plates are connected end to end to form the entire target profile. The cross-section of the semi-finished plates does not contain a hollow closed shape and has at most two corners.

[0008] S200. The alloy substrate is preheated and rolled into a plate with a fixed thickness and length. The plate is then cut into several strips, wherein the width of each strip is the same as the unfolded dimension of the corresponding target cross-sectional profile.

[0009] S300. The strips are passed sequentially through the corresponding roller combination, and each strip is rolled into a semi-finished profile slit that matches the cross-sectional shape through a continuous roll forming process.

[0010] Furthermore, it also includes the following steps: S400, adjusting each of the semi-finished profiles to a preset butt joint posture according to the cross-sectional shape of the target profile, and using friction stir welding to weld along the weld seam between each of the semi-finished profiles, so that each of the semi-finished profiles is welded into a profile with the complete cross-sectional shape of the target profile.

[0011] Furthermore, step S200 also includes multiple rolling processes, in which the rolling angle of the strip is increased sequentially until the strip matches the semi-finished sheet material.

[0012] Furthermore, during the rolling processes of two adjacent groups, the increase in the bending deformation of the strip does not exceed the allowable bending deformation of the strip material.

[0013] In each rolling bend, the two side edges of the strip are successively formed with a first bending angle, a second bending angle, and an Nth bending angle, and the sum of the bending deformation of the strip in each pass is equal to the bending angle of the two side edges of the semi-finished profile.

[0014] Furthermore, along the feeding direction of the strip, the first bending angle, the second bending angle, and the Nth bending angle increase in a non-equal arithmetic progression.

[0015] Furthermore, in adjacent rolling processes, the difference in bending angle is no greater than 35°.

[0016] Furthermore, in step S400, the welding sequence of the friction stir welding is as follows: first, weld one or more welds located in the central area of ​​the cross-section of the target profile in each of the semi-finished profile slits, and then weld the welds located in the outer area.

[0017] Furthermore, step S400 also includes post-weld heat treatment of the welded profile; the post-weld heat treatment includes solution treatment and aging treatment; the solution treatment temperature is 520℃~550℃, the holding time is 0.5h~2h, followed by quenching and cooling; the aging treatment temperature is 160℃~200℃, the holding time is 6h~12h.

[0018] To ensure the continuity of rolling, the present invention further provides a rolling mill device suitable for combined forming processes of hollow and complex cross-section aluminum profiles, comprising: a frame;

[0019] Several sets of roll assemblies are arranged sequentially on the frame along the strip feeding direction. Each set of roll assemblies includes an upper roll and a lower roll that are vertically opposite to each other on the upper and lower sides of the strip.

[0020] The upper roller is an active drive roller, which is pressed on the upper surface of the strip and is used to apply a pressing force to the strip in the direction of the lower roller and drive the strip to be fed in its own longitudinal direction.

[0021] The lower roller includes a first roller and a second roller respectively disposed on both sides of the strip width direction. The first roller and the second roller are both arranged in an inclined posture relative to the horizontal direction, and are used to apply bending deformation to the two side edges of the strip during the longitudinal feeding of the strip.

[0022] Along the feeding direction of the strip, the inclination angles of the first roller and the second roller gradually increase, so that the bending deformation of the two sides of the strip increases gradually as it passes through each set of lower rollers, thereby bending the two sides of the strip to a preset target angle through multiple progressive bending passes.

[0023] Furthermore, the upper roller is sequentially arranged between the first roller and the second roller in each group along the delivery direction of the strip.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention decomposes the cross-section of the target profile so that the cross-section of each semi-finished sheet does not contain a hollow closed shape and has at most two corners, thereby simplifying the cross-sectional complexity of individual components. This allows for unidirectional and progressive plastic deformation through roll forming, with a single metal flow path. This avoids the problems of disordered grain orientation and uneven performance distribution caused by the multi-directional flow and repeated welding of metal in traditional extrusion processes, which is conducive to obtaining profile products with uniform structure and consistent performance.

[0026] This invention uses friction stir welding as a welding method. The welding process does not involve the complex flow after the base material is melted as a whole, which can effectively avoid defects such as porosity, hot cracking and burn-through that are common in aluminum alloy fusion welding. Furthermore, the welding sequence of first the central area and then the periphery helps to optimize the heat input distribution and stress accumulation path during the welding process, and reduce welding deformation and residual stress.

[0027] This invention employs a configuration with multiple sets of lower rolls having progressively increasing inclination angles. Through multiple passes of progressive bending, the edge of the strip is gradually bent to the target angle. The increase in bending deformation between adjacent passes is controlled within the allowable bending deformation of the material. The sum of the deformation in each pass equals the target angle, effectively avoiding forming defects such as edge cracks, wrinkles, or excessive springback caused by excessive bending in a single pass. This ensures the yield and dimensional accuracy of the roll forming process. Attached Figure Description

[0028] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of Embodiment 1 of the combined molding process of the present invention.

[0030] Figure 2 This is a schematic flowchart of Embodiment 2 of the combined molding process of the present invention.

[0031] Figure 3 This is a schematic diagram of a set of rollers according to the present invention.

[0032] Figure 4 This is a schematic diagram showing the gradual increase in the tilt angle of the lower roll in a multi-roll combination.

[0033] Figure 5 A schematic diagram showing the butt joint posture of each semi-finished profile before it is slit and welded.

[0034] The reference numerals in the figure are as follows:

[0035] 1-Strip; 2-Roller assembly; 3-Semi-finished sheet material; 4-Tip; 5-Agitator head;

[0036] 201 - Upper roll; 202 - Lower roll;

[0037] 2021 - First roller; 2022 - Second roller. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] This invention first rationally divides the target profile, which has a hollow or complex cross-section, into several semi-finished sheets with a closed cross-section that does not contain a hollow core and has at most two corners. These semi-finished sheets are then connected end to end to form the cross-sectional outline of the entire target profile. Each sheet is then rolled into a semi-finished profile strip of the corresponding shape using a continuous roll forming process. Finally, the strips are welded together using friction stir welding to form a complete profile.

[0040] This invention provides a combined forming process suitable for hollow and complex cross-section aluminum profiles, comprising the following steps:

[0041] S100. Based on the preset cross-sectional shape of the target profile, determine the target cross-sectional outline of several semi-finished panels. The semi-finished panels are connected end to end to form the entire target profile. The cross-section of the semi-finished panels does not contain a hollow closed shape and has at most two corners.

[0042] S200. The alloy substrate is preheated and rolled into a plate with a fixed thickness and length. The plate is then cut into several strips, wherein the width of the strips is the same as the unfolded dimension of the corresponding target cross-sectional profile.

[0043] S300: The strips are passed through the corresponding roller combination in sequence, and each strip is rolled into a semi-finished profile that matches the cross-sectional shape through continuous roll forming process.

[0044] In the above steps, the present invention first decomposes the cross section of the target profile so that the cross section of each semi-finished plate does not have a hollow closed shape and has at most two corners, so as to simplify the cross section complexity of a single component, enabling it to achieve unidirectional and progressive plastic deformation by roll forming. The metal flow path is single, avoiding the problems of disordered grain orientation and uneven performance distribution caused by the need for multi-directional flow and repeated welding of metal in traditional extrusion processes, and obtaining profile products with uniform structure and consistent performance.

[0045] The core of the decomposition step is to "decompose" the cross-sectional shape of the target profile to ensure that the semi-finished panels are connected end to end to form the entire target profile. That is, the outlines of each semi-finished panel on the cross-section are connected end to end to form the complete cross-sectional outline of the target profile.

[0046] Its decomposition method has two limitations:

[0047] Firstly, the cross-section does not contain a hollow closed shape. The cross-section of each semi-finished sheet is open and not closed, thus avoiding the problem of mold failure or molding difficulties caused by the formation of a closed cross-section during subsequent roll forming.

[0048] Secondly, the cross-sectional shape can be set as needed according to the forming shape and stress state. The specific shape can be determined in advance by simulation, experiment and other methods, which ensures that the cross-sectional shape of each semi-finished board is simple enough to be reliably processed by roll forming process.

[0049] The above decomposition method transforms the originally extremely difficult hollow and complex cross-section profiles, which were originally very difficult to extrude or bend as a whole, into the forming problem of several sheet metal components with simple cross-sectional shapes, thereby reducing the difficulty of the process.

[0050] In the heat treatment step S200, the alloy substrate is preferably an aluminum alloy substrate. Aluminum alloys have good rolling and welding properties, making them ideal materials for manufacturing lightweight profiles.

[0051] The purpose of preheating is to improve the plasticity of the alloy substrate, reduce the deformation resistance during subsequent rolling, and help eliminate residual stress inside the substrate. The rolling process prepares the substrate into plates with a fixed thickness and length, ensuring that each strip has a consistent thickness and good plate quality. The plates are then cut into several strips according to preset dimensions.

[0052] The width of the strip is the same as the unfolded dimension of the corresponding target cross-sectional profile. The "unfolded dimension" refers to the width of the semi-finished sheet material after unfolding the target cross-sectional profile along its length into a straight line. Ensuring that the strip width matches the unfolded dimension is to guarantee that the profile dimensions of each strip after roll forming accurately match the target cross-sectional profile, avoiding problems such as misalignment or excessive gaps during welding due to dimensional deviations.

[0053] In step S300, continuous roll forming (also known as roll bending or roll forming) is a cold metal forming process that uses multiple rollers to apply controllable and continuous pressure to the profile, causing the material to gradually undergo permanent plastic deformation as it passes through the machine until it reaches the desired shape. Compared with processes such as stamping or bending, roll forming has significant advantages such as progressive loading, impact-free forming, and continuous production capability.

[0054] The present invention further discloses a method and software tool for determining a preset cross-sectional shape, including digital modeling of the cross-sectional shape, determination of the cross-sectional decomposition strategy, and calculation of the unfolded dimensions.

[0055] The core of digital modeling of cross-sectional shape lies in using computer-aided design (CAD) software to accurately model the complete cross-section of the target profile and complete the decomposition into each semi-finished sheet.

[0056] Specifically, designers first create a complete cross-sectional sketch of the target profile in a common 3D CAD software platform (such as Dassault SolidWorks or Autodesk Inventor). To improve design efficiency, aluminum profile-specific plugins—such as the FRAMEpro CAD plugin—can be loaded into the aforementioned CAD environments. Alternatively, a pre-developed industrial aluminum profile library can be utilized in the SolidWorks welding plugin tool. This library covers various cross-sectional sizes of light-load, medium-load, and heavy-load aluminum alloy profiles, as well as general-purpose aluminum alloy profiles, which designers can directly access without having to draw from scratch.

[0057] For non-standard profiles that do not have a standard cross-section, designers can directly draw a custom section sketch in SolidWorks or Inventor. After drawing, the software's mass property lookup or dedicated section property calculation plugin can be used to automatically calculate the geometric parameters of the section, such as area, perimeter, and moment of inertia.

[0058] Furthermore, specialized aluminum alloy section design and analysis tools—such as the RSECTION program—can be used. This tool supports custom sections and imports them into finite element analysis software such as RFEM / RSTAB for structural verification, and effective section properties can be considered according to standards such as EN1999-1-1. There are also specialized reverse engineering software programs for aluminum profile sections in China (such as version V1.0 developed by Hangzhou Zhufeng Technology Co., Ltd.), which can reverse engineer section data from existing profile samples.

[0059] The determination of the cross-sectional decomposition strategy is the focus of this invention. The basic principle of decomposition has been clarified in the aforementioned step S100: the cross-section of each semi-finished plate does not contain a hollow closed shape and has at most two corners.

[0060] This decomposition process is essentially a topological segmentation of the cross-sectional profile. In CAD software, designers use specific points (such as inflection points and branch points) on the target cross-sectional profile as segmentation nodes to "cut" and "unfold" the closed profile into several open profile segments, each corresponding to the cross-sectional shape of a semi-finished sheet material. The selection of segmentation nodes needs to comprehensively consider the following factors: Welding accessibility: The segmentation line should be selected in a location easily accessible to friction stir welding tools to avoid welds located inside narrow cavities; Stress distribution: The weld location should avoid high-stress areas during the profile's service life; Forming feasibility: The shape of each segment after unfolding should be achievable through roll forming.

[0061] Finally, the calculation of the unfolded dimensions is involved. In this invention, the width of each semi-finished sheet is defined as equal to the unfolded dimension of the corresponding target cross-sectional profile. This is the straight line length of the profile curve after it has been "straightened" along its length. This calculation can be performed directly in CAD software using the "measurement" tool to obtain the curve length, or automatically output by a cross-sectional property calculation plugin.

[0062] Furthermore, in the specific process, it includes, for example Figure 1 Example 1 shown and as follows Figure 2 Example 2 is shown, wherein the difference between Example 2 and Example 1 is that Example 1 does not weld directly, but cools to room temperature first.

[0063] In Example 1, after roll forming, the material is first cooled to room temperature, which allows the residual stress inside the slits to be fully released and the elastic rebound to stabilize. After cooling, the slits are packaged according to the same cross-sectional shape, which facilitates precise alignment on the welding fixture, resulting in uniform weld gaps and minimal misalignment, which is beneficial to the consistency of welding quality in friction stir welding.

[0064] Example 1 is suitable for applications with strict requirements on the dimensional tolerances of finished profiles (such as rail transit vehicle bodies and aerospace structural components). Furthermore, slits of different cross-sectional shapes can be cooled, stacked, and temporarily stored independently. The production line can continuously roll-form slits of various specifications and classify them for inventory, then flexibly assemble and weld them according to order requirements, significantly improving production flexibility.

[0065] The present invention further provides an embodiment 2, in which steps S100 to S300 are exactly the same, except that the semi-finished profiles are slit and welded directly without cooling.

[0066] S400. According to the cross-sectional shape of the target profile, each semi-finished profile is slit and adjusted to the preset butt joint posture. Friction stir welding is used to weld along the weld seam between each semi-finished profile slit, so that each semi-finished profile slit is welded into a profile with the complete cross-sectional shape of the target profile.

[0067] This invention uses friction stir welding as a welding method. The welding process does not involve the complex flow after the base material is melted as a whole, which can effectively avoid defects such as porosity, hot cracking and burn-through that are common in aluminum alloy fusion welding. Furthermore, the welding sequence of first the central area and then the periphery helps to optimize the heat input distribution and stress accumulation path during the welding process, and reduce welding deformation and residual stress.

[0068] Meanwhile, the slitting temperature remains relatively high after roll forming, eliminating the energy consumption of cooling to room temperature and then reheating before direct welding. This significantly reduces energy consumption, especially in the production of large profiles. Furthermore, because this invention employs friction stir welding, the plastic flow of the material is significantly affected by temperature. The high initial temperature of the hot slitting process allows the material around the stirring head to soften more easily during welding, enhancing its fluidity. This facilitates thorough mixing of the weld metal, reducing defects such as voids and incomplete welds, and improving the mechanical properties of the joint.

[0069] In Example 2, the slits are welded in a hot state. The temperature field of the slits is superimposed with the heat input generated by friction stir welding to form a gentler temperature gradient. The cooling process after welding tends to shrink synchronously, which can effectively reduce the peak value of residual tensile stress, reduce welding deformation and warping, and make it easier to ensure the straightness of the profile.

[0070] Compared to Example 1, Example 2 eliminates the waiting and transfer time for cooling and re-clamping, making it suitable for mass production of single-variety profiles on assembly lines.

[0071] In practical applications, the most suitable implementation plan can be selected based on factors such as the precision requirements of the target profile, production scale, and energy costs.

[0072] In a preferred embodiment of the present invention, step S300 includes multiple rolling processes, that is, the strip passes through the rollers sequentially along its longitudinal direction, and the strip is gradually shaped into the target shape through multiple progressive bending passes.

[0073] During the bending process, aluminum alloy materials undergo both elastic and plastic deformation. After the mold is unloaded, the elastic deformation disappears, and the final forming angle of the workpiece deviates from the target angle; this phenomenon is called springback. Using multi-pass progressive bending and over-bending allows for control of smaller deformation amounts in each pass, enabling the material to gradually enter the plastic deformation range. This avoids excessive bending in a single pass, which could lead to cracks at the edges of the strip, and effectively compensates for springback through the cumulative deformation of multiple passes.

[0074] From a mechanical perspective, through the cumulative effect of multiple passes, the bending angle at the edge of the strip gradually increases from the initial 0° to the target angle. This progressive loading method keeps the deformation of the material within a small range in each pass, avoiding defects such as cracks and wrinkles caused by stress concentration and excessive plastic deformation.

[0075] During two adjacent rolling processes, the increase in bending deformation of the strip does not exceed the allowable bending deformation of the strip material. This is because each aluminum alloy material has its own plastic forming limit. If the bending deformation in a single pass exceeds the allowable bending deformation of the material, cracks or even breakage will occur at the edge of the strip. Therefore, this invention further limits the bending deformation constraint conditions. By controlling the increase in deformation in each pass to not exceed the allowable value, it ensures that the material remains within a safe plastic deformation range throughout the entire forming process.

[0076] Specifically, the two edges of the strip form a first bending angle, a second bending angle, ..., a Nth bending angle in each bending pass, and the sum of the bending deformation of the strip in each pass equals the preset target angle. This ensures that the cumulative effect of the multi-pass progressive bending exactly meets the target forming requirements, preventing incomplete forming due to insufficient cumulative deformation or over-forming due to excessive cumulative deformation.

[0077] N is chosen from positive integers.

[0078] Along the feeding direction of the strip, the first bending angle, the second bending angle, and the Nth bending angle increase in a non-arithmic manner. By precisely controlling the increment of the rolling tilt angle, the amount of bending deformation of the strip can be precisely controlled. Along the feeding direction of the strip, the tilt angle of each rolling process can increase in either an arithmetic progression or a non-arithmic progression. The specific increment method can be determined comprehensively based on factors such as the mechanical properties of the strip material, the target bending angle, and the number of passes.

[0079] In adjacent rolling processes, the difference in bending angle shall not exceed 35°.

[0080] For example, if the rolling process is repeated three times and the finished product has a tilt angle of 75°, the tilt angle of the first rolling is from 0° to 15°, the tilt angle of the second rolling is from 15° to 50°, and the tilt angle of the last rolling is from 50° to 75°.

[0081] Using a smaller tilt angle in the initial rolling pass helps the strip edges smoothly enter the plastic deformation state, avoiding excessive deformation in the initial pass. Using a larger tilt angle in the middle passes ensures the strip edges reach the required final bending angle. A smaller tilt angle is used at the end to prevent material springback.

[0082] Specifically, the present invention also includes step S400, a welding step: according to the cross-sectional shape of the target profile, each semi-finished profile is slit and adjusted to a preset butt joint posture, and friction stir welding is used to weld along the weld seam between each semi-finished profile slit, so that each semi-finished profile slit is welded into a profile with the complete cross-sectional shape of the target profile.

[0083] This step connects the separately formed strips into a single unit using friction stir welding. As a solid-state joining technology, friction stir welding does not involve the overall melting and complex flow of the base material, thus effectively avoiding defects common in aluminum alloy fusion welding, such as porosity, hot cracking, and burn-through. Furthermore, the welding temperature of friction stir welding is relatively low, resulting in relatively small residual stress and deformation after welding, which helps ensure the dimensional accuracy of the final profile.

[0084] In a preferred embodiment of the present invention, the welding sequence of friction stir welding is as follows: first, weld one or more welds located in the central region of the target profile section in each semi-finished profile slit, and then weld the welds located in the peripheral region. The welding sequence has a significant impact on the residual stress and residual deformation of the welded parts, and optimizing the welding sequence can effectively control welding deformation.

[0085] Welding can be done from left to right or from right to left, but in this invention, the main approach is to weld from the center outwards in order to effectively control the heat input distribution and stress accumulation during the welding process.

[0086] Specifically, welding the central area first creates a preliminary rigid framework for the profile cross-section, providing sufficient structural rigidity for subsequent welding of the outer perimeter seams and thus reducing welding deformation. When welding the outer perimeter seams later, since the connection in the central area is already complete, the overall rigidity of the profile is enhanced, and the stress and deformation generated by the outer perimeter welding are constrained, making it less likely for the profile to twist or warp as a whole.

[0087] In addition, the welding sequence of center first and then periphery is conducive to the uniform dissipation of heat generated during the welding process, avoiding excessive heat accumulation in local areas, which can lead to coarsening of the structure or deterioration of performance.

[0088] In a preferred embodiment of the present invention, step S400 further includes post-weld heat treatment of the welded profile. Post-weld heat treatment includes solution treatment and aging treatment. After friction stir welding of aluminum alloys, the microstructure and mechanical properties of the weld zone and heat-affected zone often undergo certain changes. Strengthening phases may dissolve or coarsen in the weld area, leading to a decrease in joint strength. Through post-weld solution treatment combined with aging heat treatment, strengthening phases can be re-precipitated in the weld zone, restoring or even improving the mechanical properties of the joint.

[0089] Specifically, the solution treatment temperature is 520℃~550℃, the holding time is 0.5h~2h, followed by quenching and cooling. The purpose of solution treatment is to redissolve the coarse precipitates in the weld zone and heat-affected zone into the aluminum matrix, forming a supersaturated solid solution. The temperature range of 520℃~550℃ is suitable for most heat-treatable wrought aluminum alloys, ensuring sufficient dissolution of the strengthening phase without causing excessive grain coarsening or localized melting. Holding time of 0.5h~2h is sufficient for sufficient and uniform diffusion of solute atoms; excessive time may lead to grain growth. The purpose of quenching and cooling is to retain the supersaturated solid solution from the high temperature to room temperature, creating conditions for subsequent aging precipitation.

[0090] The aging treatment temperature is 160℃~200℃, and the holding time is 6h~12h. The purpose of aging treatment is to induce the precipitation of solute atoms in the supersaturated solid solution as fine and dispersed strengthening phases, thereby significantly improving the strength and hardness of the joint. 160℃~200℃ is the optimal aging temperature range for most aluminum alloys. Holding at this temperature for 6h~12h allows the strengthening phases to fully precipitate and reach the peak aging state, achieving the best strengthening effect.

[0091] Compared with existing technologies, the friction stir welding method used in this invention has three major advantages:

[0092] 1. Reduce energy consumption

[0093] Extrusion welding involves heating an entire aluminum alloy ingot (weighing several tons) to 450°C-500°C and maintaining this high temperature during extrusion. Simultaneously, the extruder must provide pressure of hundreds of megapascals to force the metal through the die with intense shear deformation. A significant amount of electrical and thermal energy is wasted on ineffective deformation and overall heat preservation. The friction stir welding method disclosed in this invention utilizes localized solid-phase heat. During welding, heat is generated solely through high-speed friction between the stirring head and the weld interface, raising the local weld temperature to 60%-80% of the aluminum alloy's melting point (approximately 400°C-480°C). Heat input is highly concentrated along the weld line, resulting in an extremely narrow heat-affected zone, and no overall heat preservation is required.

[0094] The process of this invention avoids repeated heating of the whole ingot and huge extrusion back pressure, and the overall energy consumption can usually be reduced by 30% to 50%, which is especially suitable for the preparation of large cross-section profiles.

[0095] 2. Improved splicing quality

[0096] In the extrusion welding process, within the flow separation welding chamber, the metal undergoes "separation, flow around, and convergence." At the convergence interface, the metal flow direction is chaotic, easily forming "weld lines" or "flow separation marks," resulting in significant differences in grain orientation in this region and mechanical properties (such as elongation and fatigue resistance) that are significantly lower than those of the substrate. At high temperatures, the oxide film on the surface of the aluminum ingot is brought into the welding chamber. If the welding pressure is insufficient, it is very easy to form a latent defect of "unwelded (oxide inclusions)."

[0097] The friction stir welding disclosed in this invention belongs to a solid-state forging process. The strong mechanical mixing action of the stirring head causes dynamic recrystallization in the weld zone, forming dense, equiaxed, and fine recrystallized grains (usually finer than the matrix grains). The weld strength coefficient can reach 70% to 90% of the base material, and the fatigue performance is excellent. At the same time, since the material does not melt, common defects in fusion welding such as porosity, hot cracking, and burn-through are completely avoided. The mechanical stirring force of the stirring head can effectively break up and disperse the oxide film distributed on the surface, making the weld quality more reliable.

[0098] 3. Mold requirements have decreased.

[0099] Extrusion welding production of hollow or complex cross-section profiles requires the use of a flow-dividing combination die (the upper die has flow-dividing holes, and the lower die has a welding chamber for material discharge). This die is subjected to extreme working conditions of 500°C high temperature, extremely high internal pressure, and severe friction.

[0100] During splicing and welding, the mold only needs to withstand bending stress at room temperature / medium-high temperature, without having to withstand 500℃ high temperature and high pressure. Ordinary mold steel or cemented carbide rolls are sufficient. The mold wears slowly and is easy to maintain, which greatly reduces the manufacturing difficulty and replacement frequency of the core tooling.

[0101] This process is applicable to the preparation of materials such as plates, strips, pipes, and profiles (I-beams, angle steel, etc.), and can be performed using any rolling mill. However, with existing rolling mills, there is a lack of continuity between the rolling rolls. During the rolling process, the strip needs to be fed into the equipment multiple times. Between each feeding and output, the heat generated during the rolling process is easily transferred, resulting in uneven heating and cooling of the strip during each rolling, discontinuous stress changes, and thus strength differences within the same strip.

[0102] To address this problem, the present invention also provides a rolling mill device suitable for the combined forming process of the above-mentioned hollow and complex cross-section aluminum profiles.

[0103] like Figure 3 refer to Figure 5 As shown, the rolling mill device includes a frame and several sets of rolling mill assemblies 2 arranged sequentially on the frame along the feeding direction of the strip 1. Each set of rolling mill assemblies 2 includes an upper rolling mill 201 and a lower rolling mill 202 arranged vertically opposite to each other on the upper and lower sides of the strip 1.

[0104] The upper roller 201 is a driven roller, pressed against the upper surface of the strip 1, and is used to apply a pressing force to the strip 1 in the direction of the lower roller 202 and drive the strip 1 to feed along its own longitudinal direction. The upper roller 201 is driven by a servo motor through a reducer. The servo motor is electrically connected to a controller, and the rotational speed of the upper roller 201 can be adjusted in real time according to the feeding speed of the strip. The surface of the upper roller 201 is provided with knurling or annular grooves to increase the friction between it and the upper surface of the strip 1, ensuring reliable transmission of driving force.

[0105] The lower roller 202 includes a first roller 2021 and a second roller 2022 respectively disposed on both sides of the strip width direction. Both the first roller 2021 and the second roller 2022 are arranged at an angle relative to the horizontal direction, used to apply bending deformation to the two side edges of the strip 1 during longitudinal feeding. Both the first roller 2021 and the second roller 2022 are mounted on the frame via bearing seats and their tilt angle relative to the frame can be adjusted. The tilt angle adjustment of each roller can be achieved through a screw and nut mechanism or a hydraulic cylinder, and after adjustment, it is fixed by a locking device.

[0106] Along the feeding direction of strip 1, the tilt angle of the first roller 2021 and the second roller 2022 increases successively, so that the bending deformation of the two sides of strip 1 increases successively as it passes through each set of lower rollers 202. Thus, the two sides of strip are bent to the preset target angle through multiple progressive bending passes, and finally a semi-finished board 3 is formed.

[0107] The lower rollers 202 of this rolling device are continuously arranged, which can ensure the continuity of the strip 1 in the preparation process to the greatest extent. The upper rollers 201 can connect end to end when the strip passes through the adjacent lower rollers 202, so that the strip 1 does not need to be transferred by other means, and the continuity is strong.

[0108] The following provides a detailed description of the specific structure and operation of roll assembly 2:

[0109] The roll assembly 2 includes an upper roll 201 and a lower roll 202 vertically opposite to each other on the upper and lower sides of the strip. The upper roll 201 presses against the upper surface of the strip and is an active drive roll used to apply a pressing force to the strip in the direction of the lower roll 202 and drive the strip to feed in its own longitudinal direction. As an active drive roll, the upper roll 201 is usually driven to rotate by a motor through a reduction gear, and the friction between it and the upper surface of the strip drives the strip to move forward. The upper roll 201 also applies a downward pressing force to the strip to ensure that the strip maintains a stable position and posture when passing through the roll assembly 2, and to prevent the strip from shifting or warping during bending.

[0110] The distance between adjacent roll combinations 2 is less than the length of strip 1.

[0111] It should be noted that the "tilted posture" of the first roller 2021 and the second roller 2022 refers to the fact that their rotation axes are at a certain angle relative to both the horizontal and vertical directions, thereby generating an oblique bending force at the edge of the strip, causing the edge of the strip to gradually bend upwards or downwards. This tilted roller design is a common method for achieving edge bending of sheet metal in roll forming, but the control of its tilt angle and the coordination between multiple passes are the same as the angle control in the above-mentioned process.

[0112] To reduce the impact of heat loss on the strip, the present invention further optimizes the configuration of the roll assembly 2. The upper roll 201 is sequentially arranged between the first roller 2021 and the second roller 2022 of each group along the delivery direction of the strip 1. The upper roll 201 acts as the active drive roller to continuously drive the strip to be fed longitudinally, while the first roller 2021 and the second roller 2022 of the lower roll 202 are passively rotated (i.e., driven rollers) as the strip is fed. Their inclined arrangement causes rolling contact between the rollers and the edge of the strip. While rolling, a bending force is applied to the edge of the strip. At this time, the heat is concentrated in the bent part of the strip 1, and the rolling part is in the center of the strip, which helps to reduce local heat loss of the strip and thus ensure the consistency of the strip during the pressing process.

[0113] Meanwhile, rolling contact occurs at the center of the strip, resulting in lower frictional resistance, which helps reduce scratches and wear on the strip surface, while ensuring the smooth transmission of bending force.

[0114] The hollow and complex cross-section aluminum profiles (usually long straight profiles) involved in this invention are preferably produced by gantry-type friction stir welding equipment.

[0115] This invention further discloses the specific structure of friction stir welding, such as... Figure 4 As shown, the device includes a stirring head 5, which has a tip 4 for applying heat. The stirring head 5 is mounted on the spindle via a clamping device. The clamping device typically includes a clamping head, a heat dissipation pipe, and other components. The heat dissipation pipe is hollow and has multiple heat dissipation grooves to facilitate heat dissipation from the stirring head during the welding process.

[0116] In this invention, the position of the semi-finished sheet material 3 needs to be fixed first, and then welding is performed using a stirring head 5. For aluminum alloy sheets of different thicknesses, a stirring head 5 of appropriate specifications must be selected. For example, for 3mm thick aluminum alloy, a high-quality stirring head can achieve a stable welding life of up to 1500m and a welding speed of up to 3m / min.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application 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 of the technical features. All such modifications or substitutions should be covered within the protection scope of this application, and should not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A combined forming process suitable for hollow and complex cross-section aluminum profiles, characterized in that, Includes the following steps: S100. Based on the preset cross-sectional shape of the target profile, determine the target cross-sectional outline of several semi-finished plates. The semi-finished plates are connected end to end to form the entire target profile. The cross-section of the semi-finished plates does not contain a hollow closed shape and has at most two corners. S200. The alloy substrate is preheated and rolled into a plate with a fixed thickness and length. The plate is then cut into several strips, wherein the width of each strip is the same as the unfolded dimension of the corresponding target cross-sectional profile. S300. The strips are passed sequentially through the corresponding roller combination, and each strip is rolled into a semi-finished profile slit that matches the cross-sectional shape through a continuous roll forming process.

2. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 1, characterized in that, The method also includes the following steps: S400, adjusting each of the semi-finished profiles into a preset butt joint position according to the cross-sectional shape of the target profile, and using friction stir welding to weld along the weld seam between each of the semi-finished profiles, so that each of the semi-finished profiles is welded into a profile with the complete cross-sectional shape of the target profile.

3. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 1, characterized in that, In step S200, multiple rolling processes are also included. In each rolling process, the roll angle of the strip is increased sequentially until the strip matches the semi-finished sheet material.

4. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 3, characterized in that, During two adjacent rolling processes, the increase in bending deformation of the strip does not exceed the allowable bending deformation of the strip material. In each rolling bend, the two side edges of the strip are successively formed with a first bending angle, a second bending angle, and an Nth bending angle, and the sum of the bending deformation of the strip in each pass is equal to the bending angle of the two side edges of the semi-finished profile.

5. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 4, characterized in that, Along the feeding direction of the strip, the first bending angle, the second bending angle, and the Nth bending angle increase in a non-equal arithmetic progression.

6. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 5, characterized in that, In adjacent rolling processes, the difference in bending angle is no greater than 35°.

7. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 1, characterized in that, In step S400, the welding sequence of friction stir welding is as follows: first, weld one or more welds located in the central area of ​​the cross-section of the target profile in each of the semi-finished profile strips, and then weld the welds located in the outer area.

8. The combined forming process for hollow and complex cross-section aluminum profiles according to claim 6, characterized in that, Step S400 further includes post-weld heat treatment of the welded profile; the post-weld heat treatment includes solution treatment and aging treatment; the solution treatment temperature is 520℃~550℃, the holding time is 0.5h~2h, followed by quenching and cooling; the aging treatment temperature is 160℃~200℃, the holding time is 6h~12h.

9. A rolling mill device suitable for a combined forming process of hollow and complex cross-section aluminum profiles as described in any one of claims 1-9, characterized in that, include: frame; Several sets of roller assemblies (2) are arranged sequentially on the frame along the feeding direction of the strip (1). Each set of roller assemblies (2) includes an upper roller (201) and a lower roller (202) arranged opposite to each other on the upper and lower sides of the strip (1) in the vertical direction. The upper roller (201) is an active drive roller, which is pressed on the upper surface of the strip (1) and is used to apply a pressing force to the strip (1) in the direction of the lower roller (202) and drive the strip (1) to be fed in its own longitudinal direction. The lower roller (202) includes a first roller (2021) and a second roller (2022) respectively disposed on both sides of the strip width direction. The first roller (2021) and the second roller (2022) are both arranged in an inclined posture relative to the horizontal direction, and are used to apply bending deformation to the two side edges of the strip (1) respectively during the longitudinal feeding of the strip (1). Along the feeding direction of the strip (1), the tilt angles of the first roller (2021) and the second roller (2022) gradually increase, so that the bending deformation of the two sides of the strip (1) increases gradually as it passes through each set of lower rollers (202), thereby bending the two sides of the strip (1) to a preset target angle through multiple progressive bending passes.

10. A rolling mill apparatus according to claim 9, characterized in that, The upper roller (201) is arranged sequentially between the first roller (2021) and the second roller (2022) of each group along the delivery direction of the strip (1).

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