Precise forming process of multi-cell body variable cross-section metal pipe fitting and metal pipe fitting

Abstract

The invention relates to the technical field of metal plastic processing and advanced manufacturing, in particular to a precise forming process of a multi-cell-body variable-cross-section metal pipe fitting and the metal pipe fitting. The precise forming process comprises the following steps: heating a multi-cell body blank to a preset thermoplastic forming temperature interval; the heated multi-cell body blank is placed in a lower die cavity with the final shape of the target component; in the first stage, gas with first set pressure is inflated into each independent cavity in the multi-cell body blank through the multi-channel inflation valve system; controlling the upper die to move downwards under the support of internal gas pressure; in the descending process of the second stage, the internal pressure of each cavity is controlled to reach second set pressure in real time; and after the mold is completely closed, entering a mold locking and pressure maintaining stage. The metal tubular structural member is of a multi-cell body structure, the section shape and size of the metal tubular structural member change continuously in the axis direction, and the design and manufacturing requirements of an integrated, high-performance and light-weight vehicle body structure are met.

Description

Technical Field

[0001] This application relates to the fields of metal plastic processing and advanced manufacturing technology, and more specifically, to a precision forming process for multicellular variable cross-section metal pipe fittings and the metal pipe fittings themselves. Background Technology

[0002] As automotive body structures evolve towards lightweight, high safety, and integrated design, the forms of structural components are becoming increasingly complex. For body structural tubular beams, the mainstream applications in the industry are currently steel and aluminum tubular beams. Steel tubular beams, due to their high strength and large mass, are often hollow structures. However, for aluminum structural components, because their strength and density are lower than steel, aluminum tubular beams used in car bodies are all multi-cell extruded profiles.

[0003] Currently, the main process for manufacturing multi-cavity aluminum tubular beams for automotive bodies is "extrusion + secondary bending." Extrusion involves passing a heated aluminum rod through a die with a fixed cross-sectional shape to obtain a straight, multi-celled profile with a uniform cross-section. This method cannot directly produce components with varying cross-sectional shape or size along their length. Secondary bending / forming involves plastically bending the extruded profile with a uniform cross-section into a bending or forming die to adapt to the assembly space. This process has two inherent drawbacks: First, it cannot achieve variable cross-section design; the final product cross-section is identical to the initial extrusion cross-section. It cannot optimize the cross-sectional shape and wall thickness according to the actual stress state (optimal force transmission path) in different sections of the structure, limiting further improvements in structural performance. Second, it results in poor forming quality and low yield: during bending or overall pressure bending, the complex ribs (cell walls) within the multi-cavity structure exhibit highly uncoordinated material flow, easily leading to defects such as localized wrinkles, collapses, cracks, or cross-sectional distortion. This results in poor forming accuracy for long, multi-cavity, small-bending-radius complex components, which can severely impact service performance.

[0004] Therefore, the industry urgently needs to develop a new process that can achieve precision forming of multi-cavity metal tubes with continuous variable cross-section along the axis, in order to solve the problem of material flow control and meet the design and manufacturing needs of integrated, high-performance, and lightweight vehicle body structures. Summary of the Invention

[0005] The purpose of this application is to provide a precision forming process for multicellular variable cross-section metal tubular components and the metal tubular components themselves, so as to form metal tubular structural components with multicellular structures and continuously changing cross-sectional shape and size along the axial direction, thereby meeting the design and manufacturing requirements of integrated, high-performance, and lightweight vehicle body structures.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a precision forming process suitable for multicellular variable cross-section metal tubular components, comprising: Select a suitable multicellular preform according to the material requirements of the target component, and heat the multicellular preform to a preset thermoplastic forming temperature range; The heated multicellular blank is placed into the lower mold cavity with the final shape of the target component. The upper mold reserves space that matches the initial cross section of the blank. Each channel of the multi-channel air-filling valve system establishes an independent and sealed fluid pressure channel with each independent chamber inside the multicellular blank. In the first stage, gas at a first set pressure is injected into each independent chamber inside the multi-cell blank through the multi-channel gas filling valve system; under the support of the internal gas pressure, the upper die is controlled to move downward to perform the first stage forging of the multi-cell blank to complete 60% bending deformation and preliminary cross-sectional compression. In the second stage, the upper mold continues to descend for final mold closing. During the descent in the second stage, the internal pressure of each chamber is controlled in real time to the second set pressure. After the mold is fully closed, it enters the mold locking and pressure holding stage; After the pressure holding period is completed, the internal pressure of each chamber is released in sequence, the mold is opened, and the formed target component is taken out.

[0007] Secondly, this application provides a multicellular variable cross-section metal pipe fitting, which is manufactured using a precision forming process for multicellular variable cross-section metal pipe fittings.

[0008] The embodiments of this application have the following technical effects: This application creatively integrates "multi-stage die forging with external molds" with "multi-stage independent control of internal multi-chamber pressure," forming a collaborative control mechanism linking the internal and external systems. The external mold provides the main shape constraint and primary deformation force, while the internal pressure acts as "flexible support" and "stress flow control." Its distribution and timing are active process parameters, not passive results. The first-stage pressure focuses on suppressing overall instability and macroscopic wrinkling; the second-stage pressure focuses on promoting material microflow, filling complex features, and preventing microscopic defects. This temporal differentiation of pressure strategies is the core of this method's precise control. A multi-channel valve system enables independent pressure control of each independent chamber, solving the problem of uneven internal support in multicellular structures. This is a prerequisite for this method to be applicable to the forming of complex multicellular structures (such as twin-cell, triple-cell, and higher), fundamentally different from traditional single-chamber pneumatic bulging. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0010] Figure 1 This is a schematic flowchart of a precision forming process for multicellular variable cross-section metal tubular components provided in an embodiment of this application; Figure 2 This is a schematic diagram of the forming of a dual-chamber tube provided in an embodiment of this application; Figure 3 This is a schematic diagram of the cross-section and wall thickness of the dual-chamber pipe fitting provided in the embodiments of this application; Figure 4 This is a schematic diagram of the forming of a three-chambered tube according to an embodiment of this application; Figure 5 This is a schematic diagram of the cross-section of the pipe fittings and the wall thickness of the three chambers provided in the embodiments of this application. Detailed Implementation

[0011] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of this application, including various details to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0012] Figure 1 This is a schematic flowchart of a precision forming process for multicellular variable cross-section metal tubular components provided in this application embodiment. This embodiment is applicable to the integrated forming of lightweight vehicle body structural components (such as anti-collision beams, longitudinal beams, sill beams, battery pack frames, etc.) with high requirements for lightweighting, such as aluminum alloys and magnesium alloys. Figure 1 The process shown includes: S110. Select a suitable multicellular blank according to the material requirements of the target component, and heat the multicellular blank to a preset thermoplastic forming temperature range.

[0013] The material of the multicellular preform is aluminum alloy, and the thermoplastic forming temperature range is 400°C to 500°C.

[0014] Optionally, depending on the material requirements of the target component (e.g., 6000 series or 7000 series aluminum alloys), an extruded multicellular straight tube of the corresponding grade can be selected as the blank. Based on the material's plastic deformation characteristics, the blank is heated to its optimal thermoplastic forming temperature range, ensuring uniform temperature distribution. In one example, a uniform cross-section triple-cell rectangular tube extruded from 6082 aluminum alloy is used as the blank; see [reference needed]. Figure 1 The cross-section contains two vertical stiffeners, forming four independent chambers A, B, and C. The multicellular billet is 1500 mm long and is uniformly heated to 450 ± 10°C in an electric resistance furnace. The mold cavity has a variable cross-section design with a spatially curved shape and a cross-sectional height that gradually decreases from the middle to both ends.

[0015] S120. The heated multicellular blank is placed into the lower mold cavity with the final shape of the target component. The upper mold reserves space that matches the initial cross section of the blank. Each channel of the multi-channel air-filling valve system establishes an independent and sealed fluid pressure channel with each independent chamber inside the multicellular blank.

[0016] Connect the specially designed multi-channel inflation valve system to the end of the billet or a preset interface to ensure that the multi-channel inflation valve system can establish an independent, sealed fluid pressure channel with each independent chamber (cell) inside the billet.

[0017] S130. In the first stage, gas at a first set pressure is injected into each independent chamber inside the multi-cell blank through the multi-channel gas filling valve system; under the support of the internal gas pressure, the upper die is controlled to move downward to perform the first stage forging of the multi-cell blank, so as to complete 60% bending deformation and preliminary cross-sectional compression.

[0018] The first stage is the preforming stage. Based on the material flow control requirements of the preforming stage, a gas (such as N2, Ar, or other inert gases) at a certain pressure is injected into different chambers of the billet through a multi-channel valve system to support the cells, establishing a preset pressure distribution for the first stage. The pressure values ​​of different chambers can be differentiated according to their location, target deformation amount, and the need to suppress defects (such as concavity), and are not uniform. Optionally, the first preset pressure for each independent chamber is determined according to the following formula: ; Among them, P i1 σ is the first set pressure (MPa) of the i-th chamber in the first stage; s (T) is the yield strength of the multicellular preform at the current temperature T, obtained through a high-temperature tensile test, i.e., tensile performance testing is performed at different strain rates within the target forming temperature range. Alternatively, it can be determined by referring to a material heat deformation data table or through testing. A 0i A fiLet be the initial cross-sectional area and the target cross-sectional area (mm²) of the i-th chamber, respectively. The pipe fitting is composed of multiple chambers, each of which is supplied with air at different pressures. Calculating the required pressure for each chamber requires obtaining the initial cross-sectional area and the corresponding target cross-sectional area after forming. The initial and target cross-sectional areas can be obtained through measurement and calculation, or through three-dimensional geometric modeling and simulation. t is the wall thickness (mm) of the outer pipe fitting. Figure 2 This is a schematic diagram of the forming process of a dual-chamber pipe fitting provided in an embodiment of this application. The diagram shows the entire process of a multicellular preform becoming a preform in the first stage, and then becoming a formed body (i.e., the target component) in the second stage. The pipe fitting includes two chambers, and the first set pressures are P... a1 and P b1 The second set pressure is P a2 and P b2 . Figure 4 This is a schematic diagram of a three-chambered pipe fitting provided in an embodiment of this application. The pipe fitting includes three chambers, and the first set pressures are P... a1 P b1 P c1 The second set pressure is P. a2 P b2 P c2 . Figure 3 This is a schematic diagram of the cross-section and wall thickness of the dual-chamber pipe fitting provided in the embodiments of this application. Figure 5 This is a schematic diagram showing the cross-sections and wall thicknesses of the pipe fittings for the three chambers provided in this embodiment. The wall thickness t is labeled. R bend It is the bending radius of the pipe fitting. After the pipe fitting is bent, its shape resembles an arc, which is the radius of the arc.

[0019] Figure 2 In the process, by taking the two ends of the pipe fitting and the midpoint where the downward pressure is greatest, the bending radius of the pipe fitting can be calculated. K1 and K2 are empirical coefficients that can be adjusted. Optionally, by means of pipe fitting simulation or pre-experimentation, the appropriate initial cross-sectional area and target cross-sectional area of ​​the i-th chamber, as well as the yield strength and bending radius, can be obtained, thereby calculating the first set pressure.

[0020] Optionally, the first set pressure of the first cell in the multicellular blank is 1.8 MPa, the first set pressure of the second cell is 2.2 MPa, and the first set pressure of the third cell is 2.0 MPa; in the first stage, the upper die descends at a speed of 5 mm / s to complete 60% bending deformation and preliminary cross-sectional compression.

[0021] This step combines the plastic flow characteristics of the material at high temperatures with the requirements for geometric deformation. By adjusting the pressure differences between the chambers, it guides the initial flow of the multi-cell wall material, suppressing wrinkling and collapse. The material must not collapse or buckle after the first pre-deformation step; the forming process will be controlled in the second stage.

[0022] The main purpose of the first stage is to induce a significant degree of overall bending or initial change in the cross-section of the billet, while utilizing internal differential pressure support to initially control the flow trend of the multi-cell wall material and prevent local instability.

[0023] S140. In the second stage, the upper mold is controlled to continue descending for final mold closing. During the descent in the second stage, the internal pressure of each chamber is controlled in real time to the second set pressure.

[0024] During the second stage of downward movement, the internal pressure of each chamber is adjusted synchronously and in real time to the second set pressure. The pressure distribution strategy in the second stage is different from that in the first stage. It aims to precisely control the material filling of each corner of the mold cavity at the final forging moment, especially complex feature areas such as the variable cross-section transition zone and rounded corners, and further balance the stress between each cell wall to avoid cracking or excessive thinning.

[0025] The second set pressure for each independent chamber is determined according to the following formula: ; ; Among them, S actual (t) is the mold-fitting distance (mm) between the pipe fitting with wall thickness t and the mold. It can be extracted by combining the mold design drawing with simulation, or by cutting the pipe blank after testing and fitting it to the mold to obtain the mold-fitting distance. Alternatively, a displacement sensor can be installed inside the pipe fitting for real-time monitoring during the test. The significance lies in the fact that during the forming process of pipe fittings (such as forging and stamping), in order to ensure that the metal can be smoothly filled, avoid defects, and guarantee the life of the mold, it is necessary to design a key clearance or fitting distance between the pipe fitting and the mold cavity or punch. target This is the maximum distance (mm) between the target fitting and the mold; σ b (T) is the tensile strength (MPa) at temperature T; α is the minimum fillet radius (mm) of the cross-section of the i-th chamber of the pipe fitting, which can be extracted using a 3D model. i ,β i These are the correction coefficients for the i-th chamber. It is the second set pressure change ratio of the i-th chamber; It is the second set pressure of the i-th chamber in the pipe fitting with wall thickness t in the second stage.

[0026] Optionally, the second set pressure of the first cell in the multicellular preform is stabilized at 8.0 MPa, the second set pressure of the second cell is stabilized at 7.5 MPa, and the second set pressure of the third cell is stabilized at 7.8 MPa; in the second stage, the upper mold continues to descend at a speed of 15 mm / s for final mold closing. This pressure increase path aims to strengthen the material filling of the thinner areas at both ends and balance the stress in the middle area.

[0027] This step synchronizes the pressure increase with the mold descent process, achieving coordinated control of "pressure-displacement", which is especially suitable for variable cross-section transition areas and fillets, avoiding cracking and excessive thinning.

[0028] In a specific implementation, simulation analysis is first required. By adjusting factors such as forming temperature T and internal pressure, appropriate experimental parameters are explored. Then, experimental prefabrication is carried out, and the correlation coefficient is appropriately adjusted by comparing and analyzing with the mold.

[0029] S150. After the mold is fully closed, it enters the mold locking and pressure holding stage.

[0030] After the mold is fully closed, the mold-locking and pressure-holding stage begins. During this stage, the internal pressure of each chamber is maintained at a certain level. The holding pressure is generally 70% to 90% of the second set pressure, and the holding time is typically 5 to 30 seconds, depending on the material properties and the component dimensions. Pressure holding allows the material to undergo sufficient creep and stress relaxation under continuous pressure, stabilizing the component shape, improving dimensional accuracy and mechanical properties. The shape stabilization effect caused by material creep during the pressure holding stage can be described using a creep model.

[0031] in, Creep strain rate characterizes the deformation rate of a material under high temperature and constant stress. Relevant performance parameters can be obtained by testing the high-temperature creep performance of pipe fitting materials. The strain generated during material flow should be within the creep strain range.

[0032] A c σ is a material property constant related to the microscopic mechanisms of creep (such as diffusion and dislocation movement); σ is the external stress on the material, which can be set through creep performance testing; n c is the stress exponent, reflecting the sensitivity of the creep strain rate to stress changes; Q is the creep activation energy, a thermodynamic parameter describing the ease or difficulty of the creep process; R: universal gas constant (common value is 8.314 J / (mol)). K); T is the thermodynamic temperature (K).

[0033] By testing and analyzing the high-temperature creep properties of the material itself, we can further explore the material flow of the pipe after it is formed.

[0034] S160. After the pressure holding is completed, release the internal pressure of each chamber in sequence, open the mold, and take out the formed target component.

[0035] Specifically, after mold closing, pressure is maintained for 10 seconds. After depressurization and mold opening, an integrated sill beam component with a clear outline, no stiffener wrinkles or cracks, and a smooth cross-section transition is obtained. Measurements show that the wall thickness reduction rate in key areas is less than 15%, far lower than the localized thinning of over 25% often seen in traditional processes.

[0036] This application also provides a multicellular variable cross-section metal pipe fitting, which is manufactured using the aforementioned precision forming process for multicellular variable cross-section metal pipe fittings.

[0037] This application creatively integrates "multi-stage die forging with external molds" with "multi-stage independent control of internal multi-chamber pressure," forming a collaborative control mechanism linking the internal and external systems. The external mold provides the main shape constraint and primary deformation force, while the internal pressure acts as "flexible support" and "stress flow control." Its distribution and timing are active process parameters, not passive results. The first-stage pressure focuses on suppressing overall instability and macroscopic wrinkling; the second-stage pressure focuses on promoting material microflow, filling complex features, and preventing microscopic defects. This temporal differentiation of pressure strategies is the core of this method's precise control. A multi-channel valve system enables independent pressure control of each independent chamber, solving the problem of uneven internal support in multicellular structures. This is a prerequisite for this method to be applicable to the forming of complex multicellular structures (such as twin-cell, triple-cell, and higher), fundamentally different from traditional single-chamber pneumatic bulging.

[0038] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this application can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this application can be achieved, and this is not limited herein.

[0039] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A precision forming process suitable for multicellular variable cross-section metal tubular fittings, characterized in that, include: Select a suitable multicellular preform according to the material requirements of the target component, and heat the multicellular preform to a preset thermoplastic forming temperature range; The heated multicellular blank is placed into the lower mold cavity with the final shape of the target component. The upper mold reserves space that matches the initial cross section of the blank. Each channel of the multi-channel air-filling valve system establishes an independent and sealed fluid pressure channel with each independent chamber inside the multicellular blank. In the first stage, gas at a first set pressure is injected into each independent chamber inside the multi-cell blank through the multi-channel gas filling valve system; under the support of the internal gas pressure, the upper die is controlled to move downward to perform the first stage forging of the multi-cell blank to complete 60% bending deformation and preliminary cross-sectional compression. In the second stage, the upper mold continues to descend for final mold closing. During the descent in the second stage, the internal pressure of each chamber is controlled in real time to the second set pressure. After the mold is fully closed, it enters the mold locking and pressure holding stage; After the pressure holding period is completed, the internal pressure of each chamber is released in sequence, the mold is opened, and the formed target component is taken out.

2. The precision forming process for multicellular variable cross-section metal tubular fittings according to claim 1, characterized in that, The material of the multicellular blank is aluminum alloy, and the thermoplastic forming temperature range is 400°C to 500°C.

3. The precision forming process for multicellular variable cross-section metal tubular fittings according to claim 2, characterized in that, The initial set pressure for each independent chamber is determined according to the following formula: ； Among them, P i1 σ is the first set pressure of the i-th chamber in the first stage; s (T) is the yield strength of the multicellular billet at the current temperature T; A 0i A fi Let be the initial cross-sectional area and the target cross-sectional area of ​​the i-th chamber, respectively; t is the wall thickness of the outer pipe fitting; R bend K1 and K2 are the bending radius of the pipe fitting; K1 and K2 are empirical coefficients.

4. The precision forming process for multicellular variable cross-section metal tubular fittings according to claim 3, characterized in that, The first set pressure of the first cell in the multicellular billet is 1.8 MPa, the first set pressure of the second cell is 2.2 MPa, and the first set pressure of the third cell is 2.0 MPa. In the first stage, the upper mold descends at a speed of 5 mm / s.

5. The precision forming process for multicellular variable cross-section metal tubular fittings according to claim 4, characterized in that, The second set pressure for each independent chamber is determined according to the following formula: ； ； Among them, S actual (t) is the contact distance between the pipe fitting with wall thickness t and the mold; S target σ is the maximum distance of the target template; b (T) is the tensile strength (MPa) at temperature T; It is the minimum fillet radius of the i-th chamber cross-section of the pipe fitting; α i ,β i These are the correction coefficients for the i-th chamber; It is the second set pressure change ratio of the i-th chamber; It is the second set pressure of the i-th chamber in the pipe fitting with wall thickness t in the second stage.

6. The precision forming process for multicellular variable cross-section metal tubular components according to claim 5, characterized in that, In the multicellular billet, the second set pressure of the first cell is stabilized at 8.0 MPa, the second set pressure of the second cell is stabilized at 7.5 MPa, and the second set pressure of the third cell is stabilized at 7.8 MPa; In the second stage, the upper mold continues to descend at a speed of 15 mm / s for final mold closing.

7. The precision forming process for multicellular variable cross-section metal tubular fittings according to claim 6, characterized in that, The pressure holding time is 10 seconds.

8. A multicellular variable cross-section metal pipe fitting, characterized in that, The metal pipe fitting is manufactured using the precision forming process of the multicellular variable cross-section metal pipe fitting provided in any one of claims 1-7.

Images