Machining method for continuous variable-cross-section differential-thickness pipe expansion type part

Abstract

The invention provides a machining method for a continuous variable-cross-section differential-thickness pipe expansion part. The machining method comprises the steps that S1, a hot air expansion material is provided; s2, a thickening area, a transition area and a thinning area are divided, and a pipe blank is obtained; s3, the wall thickness of the thickening area and the wall thickness of the thinning area are adjusted; s4, the length L of a transition area in the pipe blank is adjusted, and L is larger than or equal to 100 * (a-b); s5, the pipe blank is preformed; s6, the preformed pipe blank is austenitized; s7, the thinning area and part of the transition area are expanded; and S8, the thickening area and the transition area are expanded, and the expansion degree of the thinning area is larger than the expansion degree of the transition area and larger than the expansion degree of the thickening area. According to the partition design, the limitation of a traditional uniform material is broken through, differentiation optimization is conducted according to the actual requirements of different parts of the part, the performance and reliability of the part are improved, light weight is achieved while the functional requirements are met, and the manufacturing cost is reduced. The composite material has a wide application prospect in the fields with high requirements on weight and strength, such as automobile manufacturing, aerospace and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of bulging processing, and specifically refers to a processing method for continuously variable cross-section and differential thickness tube bulging parts. Background Art

[0002] In the field of automobile manufacturing, hot gas bulging parts can achieve a tensile strength of 1500 - 2000 Mpa for parts by virtue of high-temperature austenitization and high-pressure gas bulging processes. At the same time, they have high rigidity and impact resistance, and can effectively cope with the complex stress conditions during the driving of the automobile.

[0003] However, currently commonly used ordinary hot gas bulging parts are mostly made of homogeneous thick plate materials, and there are many performance limitations. In terms of mechanical properties, when subjected to large external force impacts or in a complex stress environment, they are extremely prone to deformation or even damage, making it difficult to ensure the safety of key parts of the automobile. Therefore, at present, the industry usually adopts the method of installing additional reinforcement plates to improve their strength. However, on the one hand, this not only increases additional costs and processing procedures, but also runs counter to the current industry requirements for lightweighting. Specifically, in terms of the lightweighting effect, it can only achieve a weight reduction of about 10% - 15%, making it difficult to meet the urgent needs of the modern automobile industry for lightweighting.

[0004] Moreover, ordinary hot gas bulging parts are mostly applied to parts with relatively low requirements for material strength and lightweighting, such as the automobile chassis, door frame interior trim parts, non-load-bearing functional components, and non-critical connecting parts, and lack the optimization ability for special requirements or complex working conditions.

[0005] With the development of the automobile industry, the requirements for safety performance in key parts of the automobile structure, such as A-pillars, B-pillars, and anti-collision beams, are constantly increasing. Especially for automobiles with a body structure without B-pillars, more stringent standards for the safety and functionality of these parts are put forward. Therefore, due to the above performance defects, ordinary hot gas bulging parts are prominent in disadvantages when applied to key parts and cannot meet the actual needs. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problems in the prior art and provide a processing method for continuously variable cross-section and differential thickness tube bulging parts.

[0007] To solve the above technical problems, the present invention provides a processing method for a continuously variable cross-section and variable thickness tube bulging part, which includes: Step S1, providing a hot gas bulging material; Step S2, dividing a thickening area, a transition area, and a thinning area on the hot gas bulging material to obtain a tube blank, wherein the transition area is arranged between the thickening area and the thinning area; Step S3, performing a simulation stress test on the tube blank, and adjusting the wall thicknesses of the thickening area and the thinning area according to the test results, and making the thickness of the transition area uniformly transition between the thickening area and the thinning area, wherein the thickness a of the thickening area > the thickness b of the thinning area; Step S4, adjusting the length L of the transition area in the tube blank to make L≥100×(a - b); Step S5, performing pre-forming processing on the tube blank; Step S6, austenitizing the pre-formed tube blank; Step S7, performing a first pressurized gas bulging process on the austenitized tube blank under a first bulging pressure until the thinning area and part of the transition area are bulged; Step S8, performing a second pressurized gas bulging process on the deformed tube blank under a second bulging pressure until the thickening area and the transition area are bulged, wherein the bulging degree of the thinning area > the bulging degree of the transition area > the bulging degree of the thickening area, and completing the processing process of the target bulging part.

[0008] In an embodiment of the present invention, the processing method for a continuously variable cross-section and variable thickness tube bulging part further includes Step S9, quenching the target bulging part, and then performing water cooling treatment under the condition that the cooling rate is 30~40°C / s to make the austenite structure of the tube blank transform into a martensite structure.

[0009] In an embodiment of the present invention, the processing method for a continuously variable cross-section and variable thickness tube bulging part further includes Step S10, performing post-processing on the water-cooled part, and the post-processing includes cutting, grinding and trimming, welding, and surface treatment processing in sequence.

[0010] In an embodiment of the present invention, the processing method for a continuously variable cross-section and variable thickness tube bulging part further includes Step S11, performing quality inspection on the part, and the quality inspection includes one or more of part dimension inspection, surface quality inspection, welding defect inspection, bending resistance and energy absorption inspection.

[0011] In an embodiment of the present invention, Step S3 is specifically: calculating the performance of the tube blank through finite element simulation to obtain the upper limit of the stress value in the stress concentration area inside the tube blank, determining the thickness distribution of the thickening area, the transition area, and the thinning area after bulging through the upper limit of the stress value and the physical properties of the hot gas bulging material, iteratively calculating the actual thicknesses of the thickening area, the transition area, and the thinning area according to the thickness distribution, and then adjusting the thickness of the tube blank according to the actual thickness.

[0012] In an embodiment of the present invention, step S5 is specifically as follows: Place the tube blank in a preforming die, and then apply pressure to the tube blank until it completely fits the preforming die.

[0013] In an embodiment of the present invention, step S6 is specifically as follows: Gradually heat the preformed tube blank within a temperature range of 930 - 950 °C, with a heating time of 110 - 330 s and a heat preservation time of 150 - 180 s.

[0014] In an embodiment of the present invention, in step S7, place the austenitized tube blank in a bulging die, and fill the interior of the bulging die with high-pressure inert gas to the first bulging pressure, where the first bulging pressure is 20 - 35 MPa.

[0015] In an embodiment of the present invention, in step S8, uniformly increase the ambient air pressure of the tube blank from the first bulging pressure to the second bulging pressure, where the second bulging pressure is 35 - 70 MPa, and the pressure holding time is 8 - 15 s.

[0016] The above technical solution of the present invention has the following advantages compared with the prior art: The processing method of the continuously variable cross-section and variable thickness tube bulging part of the present invention divides and processes the hot gas bulging material before bulging, enabling the tube blank to integrate multiple functions during actual use, achieving a high combination of functions such as lightweight and high strength and a complex cross-section layout. Furthermore, it improves the use effect on the premise of expanding its applicable scenarios. Compared with the current conventional part bulging process, this application has the advantages of strong functionality, low cost, high integration level, ability to improve automotive performance, and wide application range, providing new development ideas and directions for this industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention in conjunction with the drawings.

[0018] Figure 1 is a flowchart of the processing method of the continuously variable cross-section and variable thickness tube bulging part in the preferred embodiment of the present invention; Figure 2 is a schematic structural diagram of the tube blank after completing step S3 in the preferred embodiment of the present invention; Figure 3 is a comparison structural diagram before and after bulging of the deformed tube blank in the preferred embodiment of the present invention.

[0019] Explanation of the reference numerals in the drawings: 100, thickening area; 200, transition area; 300, thinning area. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0021] Embodiment 1:

[0022] See Figure 1 As shown, this embodiment provides a processing method for a continuously variable cross-section and variable thickness tube bulging part, which is used to provide a part that can simultaneously meet high strength and light weight. Specifically, before actual processing and preparation, it is necessary to comprehensively consider various factors such as the application scenario, performance requirements, and manufacturing feasibility of the part, and clarify the various performance indicators required for the target part, such as strength, stiffness, impact resistance, and light weight. Then, the following steps are carried out according to the above parameters: Step S1: Provide a hot gas bulging material; in this embodiment, according to the performance requirements and application scenario of the part, the hot gas bulging material is preferably aluminum alloy to ensure that its chemical composition, mechanical properties and other indicators meet the design requirements. In different embodiments, it can also be configured as 22MnB5 steel and other composite materials, and the present invention does not make specific limitations on this.

[0023] Step S2: Divide the thickening area 100, the transition area 200, and the thinning area 300 on the hot gas bulging material to obtain a tube blank. Among them, the transition area 200 is arranged between the thickening area 100 and the thinning area 300; among them, the thickening area 100 significantly improves the overall strength of the hot gas bulging material by increasing the material thickness or optimizing the internal structure, so that it can withstand greater external forces and complex stresses. In key parts such as the A-pillar, B-pillar, and anti-collision beam of the automobile structure, it bears large external forces such as collision impact force and vehicle body load. By setting the thickening area 100 in these corresponding areas, the material can have higher tensile strength and yield strength. The transition area 200 is located between the thickening area 100 and the thinning area 300, and its key role is to ensure that the stress can be evenly distributed during the thickness gradient change of the material, effectively reducing the risk of stress concentration; the thinning area 300 is mainly set in the parts where the part is less stressed, and it realizes the light weight goal of the product by reasonably reducing the material thickness, reducing the overall weight without affecting the key performance.

[0024] The thickening region 100, the transition region 200, and the thinning region 300 do not work independently, but cooperate with each other and act synergistically. The thickening region 100 provides strength guarantee for key parts, the thinning region 300 achieves the lightweight goal, and the transition region 200 ensures a smooth transition between the two, enabling the material properties to be reasonably distributed throughout the part. This zoned design breaks the limitations of traditional uniform materials and optimizes differently according to the actual needs of different parts of the part. It not only improves the performance and reliability of the part, but also achieves lightweight while meeting the functional requirements, and has broad application prospects in fields such as automotive manufacturing and aerospace that have high requirements for weight and strength.

[0025] Step S3: Perform a simulation stress test on the tube blank, and adjust the wall thickness of the thickening region 100 and the thinning region 300 according to the test results, and make the thickness of the transition region 200 transition smoothly between the thickening region 100 and the thinning region 300, where the thickness a of the thickening region 100 > the thickness b of the thinning region 300; Furthermore, step S3 of this embodiment is specifically: calculating the performance of the tube blank through finite element simulation to obtain the upper limit of the stress value in the stress concentration region inside the tube blank, determining the thickness distribution of the thickening region 100, the transition region 200, and the thinning region 300 after bulging through the upper limit of the stress value and the physical properties of the hot gas bulging material, iteratively calculating the actual thicknesses of the thickening region 100, the transition region 200, and the thinning region 300 according to the thickness distribution, and then adjusting the thickness of the tube blank according to the actual thickness.

[0026] Among them, finite element simulation calculation can highly restore the mechanical behavior of the tube blank under complex working conditions. By simulating actual stress scenarios such as collision and vibration, the stress concentration region inside the tube blank can be accurately captured, and the upper limit of the stress value can be obtained. Based on this, the potential failure risks of the part, such as the crack initiation position and fatigue life, can be predicted in advance. According to the upper limit of the stress value and the physical properties of the hot gas bulging material such as elastic modulus and yield strength, the thickness distribution of each region after bulging is scientifically determined.

[0027] The transition region 200 transitions smoothly between the thickening region 100 and the thinning region 300, effectively eliminating stress mutation. The actual thickness determined by iterative calculation can control the stress gradient change within an ideal range. Specifically, iterative calculation and actual adjustment are performed according to the thickness distribution to form a closed-loop optimization process. Each simulation result can be fed back to the design link to dynamically correct the thickness of each region. Optimizing the design through simulation in advance can reduce the trial-and-error cost in actual production and improve the processing efficiency. Specifically, the structure of the tube blank after completing step S3 in this embodiment is shown in Figure 2 as shown.

[0028] Step S4: Adjust the length L of the transition zone 200 in the tube blank so that L ≥ 100×(a - b); when the length L of the transition zone 200 is ≥ 100×(a - b), the change in material thickness is more gradual. During the stress application process, the stress can be gradually transmitted and dispersed along the longer transition zone 200, avoiding a sharp increase in stress caused by sudden thickness changes, reducing the stress concentration coefficient, making the part more stable in a complex stress environment, reducing the risk of fatigue crack generation, and extending the service life of the part. Especially during the bulging process, the longer transition zone provides sufficient space for the plastic deformation of the material during the hot gas bulging process. In the bulging process, the material can flow and extend more uniformly, preventing local excessive deformation or rupture and ensuring the forming quality of the part.

[0029] Step S5: Perform pre-forming processing on the tube blank; in this embodiment, step S5 is specifically: place the tube blank in a pre-forming die, and then apply pressure to the tube blank until it completely fits the pre-forming die. Specifically, placing the tube blank in the pre-forming die and applying pressure to make it fit can use the precise cavity contour of the die to constrain the forming of the tube blank. The high-precision design of the die enables effective control of the deformation and dimensional changes of each part of the tube blank during the pressure application process, thus ensuring that the shape and size of each part after pre-forming are highly consistent. This lays a good foundation for the subsequent hot gas bulging process, reduces the accuracy deviation of the final product caused by the initial shape difference, and significantly improves the product qualification rate.

[0030] Step S6: Austenitize the pre-formed tube blank; in this embodiment, step S6 is specifically: gradually heat the pre-formed tube blank in the temperature range of 930 - 950°C, with a heating time of 110 s and a holding time of 150 s. Specifically, performing gradual heating and holding treatment in the temperature range of 930°C can promote the full transformation of the original structures such as ferrite and pearlite in the tube blank into austenite. Gradual heating avoids excessive internal thermal stress in the material caused by sudden temperature rise, making the tissue transformation more uniform. After this austenitizing treatment, the martensite structure formed by the subsequent cooling of the material has high strength and high hardness characteristics.

[0031] Step S7: Perform the first pressurized gas bulging process on the austenitized tube blank under the first bulging pressure until the thinning area and part of the transition area are bulged. Specifically, in step S7 of this embodiment, the austenitized tube blank is placed in a bulging mold, and high-pressure inert gas is filled into the bulging mold to the first bulging pressure, and the first bulging pressure is 20 MPa. Further, this step specifically causes the thinning area 300 and part of the transition area 200 to bulge preferentially, which can precisely control the deformation area and degree of the material. With the preset first bulging pressure of 20 MPa, it is possible to ensure the expected thinning effect in the thinning area 300 while preventing the thickening area 100 from participating in deformation prematurely, ensuring that the thickness distribution of each area meets the design requirements. Furthermore, the step-by-step bulging strategy, first bulging the thinning area 300 and part of the transition area 200, enables the material to gradually adapt to the deformation process. Compared with one-time overall bulging, it can effectively reduce stress concentration.

[0032] Step S8: Perform the second pressurized gas bulging process on the deformed tube blank under the second bulging pressure until the thickening area and the transition area are bulged, where the bulging degree of the thinning area > the bulging degree of the transition area > the bulging degree of the thickening area, completing the processing of the target bulged part. Specifically, in step S8 of this embodiment, the ambient air pressure of the tube blank is uniformly increased from the first bulging pressure to the second bulging pressure, the second bulging pressure is 70 MPa, and the pressure holding time is 15 s. Specifically, by uniformly increasing the pressure from 20 MPa to 70 MPa, the thickening area 100 and the transition area 200 are bulged step by step in sequence, and the difference in the bulging degree of each area is clarified, which can precisely shape the final shape of the part. The relatively high second bulging pressure (70 MPa) and the reasonable pressure holding time (15 s) can promote further plastic deformation of the material in the high-temperature austenite state and refine the grain structure. Specifically, in this embodiment, the comparison diagram of the tube blank structure before and after bulging is shown in Figure 3 as shown.

[0033] This embodiment further includes step S9: Quench the target bulged part, and then perform water cooling treatment under the condition that the cooling rate is 30 °C / s to transform the austenite structure of the tube blank into a martensite structure. During the quenching process, rapid cooling inhibits the precipitation of carbides, making carbon atoms supersaturated and solid-solved in the iron lattice to form fine and uniform martensite laths or needles. Then, rapid water cooling can quickly transform the austenite structure into a martensite structure, and martensite has the characteristics of high strength and high hardness.

[0034] Further, this embodiment further includes step S10: Perform post-processing on the water-cooled part. The post-processing includes cutting, grinding and trimming, welding, and surface treatment processing in sequence to adapt to different part requirements.

[0035] Further, this embodiment further includes step S11 of performing quality inspection on the parts. The quality inspection includes one or more of part dimension inspection, surface quality inspection, welding defect inspection, bending resistance and energy absorption inspection, and the present invention does not make specific limitations thereto.

[0036] Embodiment Two:

[0037] This embodiment provides another processing method for continuously variable cross-section and variable-thickness tube bulging parts. Its main implementation steps and principles are the same as those of Embodiment One, and will not be elaborated here too much. Only some parameter settings in this embodiment are the same as those in Embodiment One, specifically: Step S1: Provide a hot gas bulging material; Step S2: Divide the thickening area, transition area, and thinning area on the hot gas bulging material to obtain a tube blank. Among them, the transition area is arranged between the thickening area and the thinning area; Step S3: Perform a simulation stress test on the tube blank, and adjust the wall thickness of the thickening area and the thinning area according to the test results, and make the thickness of the transition area transition evenly between the thickening area and the thinning area. Among them, the thickness a of the thickening area > the thickness b of the thinning area; Step S4: Adjust the length L of the transition area in the tube blank so that L≥100×(a - b); Step S5: Perform preforming processing on the tube blank; Step S6: Austenitize the preformed tube blank; Further, step S6 is specifically: Gradually heat the preformed tube blank within the temperature range of 930 - 950°C, the heating time is 330s, and the holding time is 180s. In different implementation manners, the heating time and the holding time can be adaptively adjusted according to actual usage requirements, and the present invention does not make specific limitations thereto.

[0038] Step S7: Perform the first pressurized gas bulging processing on the austenitized tube blank under the first bulging pressure until the thinning area and part of the transition area are bulged; Further, in step S7, place the austenitized tube blank in a bulging mold, and fill high-pressure inert gas into the interior of the bulging mold to the first bulging pressure. The first bulging pressure is 35MPa. In different implementation manners, the first bulging pressure can be adaptively adjusted according to actual usage requirements, and the present invention does not make specific limitations thereto.

[0039] Step S8: Under the second bulging pressure, perform a second pressurized air bulging process on the deformed tube blank until the thickened area and the transition area are bulged. Among them, the bulging degree of the thinned area > the bulging degree of the transition area > the bulging degree of the thickened area, and the processing of the target bulged part is completed. Further, in step S8, the ambient air pressure of the tube blank is uniformly increased from the first bulging pressure to the second bulging pressure. The second bulging pressure is 70 MPa, and the pressure holding time is 15 s. In different embodiments, the second bulging pressure and its pressure holding time can be adaptively adjusted according to actual usage requirements, and the present invention does not make specific limitations thereto.

[0040] In summary, for the continuous variable cross-section and variable thickness tube bulging part processing method of the present invention, by dividing the hot air bulging material into regions and processing them separately before bulging, the tube blank can integrate multiple functions during actual use, achieving a high combination of functions such as lightweight and high strength, as well as complex cross-section layouts. Furthermore, on the premise of expanding its applicable scenarios, the usage effect is improved. Compared with the current conventional part bulging process, this application has the advantages of strong functionality, low cost, high integration level, ability to improve vehicle performance, and wide application range, providing new development ideas and directions for this industry.

[0041] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A processing method for a tube bulging part with continuously variable cross-section and different wall thicknesses, characterized in that: Including: Step S1: Provide a hot gas expansion type material; Step S2: Divide a thickening zone, a transition zone, and a thinning zone on the hot gas expansion type material to obtain a tube blank, wherein the transition zone is arranged between the thickening zone and the thinning zone; Step S3: Conduct a simulation stress test on the tube blank, and adjust the wall thickness of the thickening zone and the thinning zone according to the test results, and make the thickness of the transition zone transition uniformly between the thickening zone and the thinning zone, wherein the thickness a of the thickening zone > the thickness b of the thinning zone; Step S4: Adjust the length L of the transition zone in the tube blank so that L≥100×(a - b); Step S5: Conduct preforming processing on the tube blank; Step S6: Austenitize the preformed tube blank; Step S7: Conduct the first pressurized gas expansion processing on the austenitized tube blank under the first expansion pressure until the thinning zone and part of the transition zone are expanded; Step S8: Conduct the second pressurized gas expansion processing on the deformed tube blank under the second expansion pressure until the thickening zone and the transition zone are expanded, wherein the expansion degree of the thinning zone > the expansion degree of the transition zone > the expansion degree of the thickening zone, and complete the processing of the target expanded part.

2. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 1, characterized in that: The processing method for the continuously variable cross-section and different-thickness tube expanded part further includes Step S9: Quench the target expanded part, and then conduct water cooling treatment under the condition that the cooling rate is 30 - 40°C / s to make the austenite structure of the tube blank transform into a martensite structure.

3. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 2, wherein: The processing method for the continuously variable cross-section and different-thickness tube expanded part further includes Step S10: Conduct post-processing on the water-cooled part, and the post-processing includes cutting, grinding and trimming, welding, and surface treatment processing in sequence.

4. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 3, characterized in that: The processing method for the continuously variable cross-section and different-thickness tube expanded part further includes Step S11: Conduct quality inspection on the part, and the quality inspection includes one or more of part dimension inspection, surface quality inspection, welding defect inspection, bending resistance and energy absorption inspection.

5. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 1, characterized in that: Step S3 is specifically: Calculate the performance of the tube blank through finite element simulation to obtain the upper limit of the stress value in the stress concentration area inside the tube blank, determine the thickness distribution of the thickening zone, the transition zone, and the thinning zone after expansion through the upper limit of the stress value and the physical properties of the hot gas expansion type material, iteratively calculate the actual thickness of the thickening zone, the transition zone, and the thinning zone according to the thickness distribution, and then adjust the thickness of the tube blank according to the actual thickness.

6. The processing method of the continuously variable cross-section and different-thickness tube bulging part according to claim 1, wherein: Step S5 is specifically: Place the tube blank in a preforming die, and then apply pressure to the tube blank until it completely fits the preforming die.

7. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 1, wherein: Step S6 is specifically: Gradually heat the preformed tube blank in the temperature range of 930 - 950°C, the heating time is 110 - 330 s, and the heat preservation time is 150 - 180 s.

8. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 1, characterized in that: In Step S7, place the austenitized tube blank in a gas expansion die, and fill high-pressure inert gas into the gas expansion die to the first expansion pressure to conduct the first pressurized gas expansion processing, and the first expansion pressure is 20 - 35 MPa.

9. The processing method of the continuously variable cross-section and variable thickness tube bulging part according to claim 1, characterized in that: In step S8, the ambient air pressure of the tube blank is uniformly increased from the first bulging pressure to the second bulging pressure, where the second bulging pressure is 35 - 70 MPa and the pressure holding time is 8 - 15 s.

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