Multi-blank extrusion device and large fine-grain rod manufacturing method

Abstract

The application discloses a multi-billet extrusion device and a large-size fine-grain rod manufacturing method. The device comprises an extrusion assembly, an upper die assembly and a lower die assembly. The extrusion assembly comprises multiple extrusion channels with consistent extension direction, cross-sectional shape and size. The upper die assembly comprises a welding chamber communicating with the multiple extrusion channels. The lower die assembly comprises a shearing channel communicating with the welding chamber. The shearing channel is provided with a shearing section for twice equal-channel-angle extrusion to refine the grains, and is provided with an extrusion channel with the same cross-sectional shape and size as the extrusion channel. The large-size fine-grain rod manufacturing method is to extrude multiple initial rods with the same cross section through the extrusion device to obtain rods with the same cross section as the initial billets and increased length and refined grains, cut the rods and then load them into the extrusion channel for re-extrusion to obtain longer rods and refined grains. After multiple passes of extrusion, the large-size fine-grain rods can be obtained.

Description

Technical Field

[0001] This invention relates to the technical field of metal multi-bulb extrusion, specifically to a multi-bulb extrusion apparatus and a method for manufacturing large fine-grained bars. Background Technology

[0002] Equal Channel Corner Extrusion (ECAP) refines the grain size of a material without altering its cross-sectional area or shape. The extrusion channel consists of two channels at a specific angle, both with identical cross-sections. The extruded blank moves from the upper extrusion punch into the die channel, pushing it downwards into the corner. This causes the blank to accumulate shear strain, increasing dislocation density and triggering dynamic recrystallization, thereby refining the grain size and improving strength, toughness, yield strength, and plasticity. However, traditional ECAP processes can only process small cylindrical or prismatic materials, limiting their application. Furthermore, in multi-pass ECAP processes, excessively long blanks can lead to problems such as difficulty in fitting into the die, excessive extrusion pressure due to friction, blank double-drum instability, and punch instability. The length of the finished product must be trimmed at both ends before proceeding to the next ECAP pass, resulting in increasingly shorter finished products with very small individual lengths. In addition, when preparing large bars using traditional hot extrusion processes, the uneven metal flow, low deformation in the central region, and insufficient recrystallization driving force make it almost impossible to avoid the formation of coarse grains. Meanwhile, the finished forgings have extremely strict requirements on the grain size of the raw material billet, which makes the preparation of large fine-grained bars a difficult problem in the industry. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention provides a multi-bulb extrusion device and a method for manufacturing large fine-grained rods, solving the problems of being unable to break through the upper limit of the manufacturing size of fine-grained rods and the uneven grain refinement of large rods.

[0004] According to a first aspect of the present invention, a multi-bulb extrusion apparatus includes: An extrusion assembly includes multiple extrusion channels with the same extension direction, cross-sectional shape, and size, the extrusion channels being used to extrude multiple billets; The upper die assembly includes a welding chamber, which is connected to a plurality of extrusion channels, and the welding chamber is used to weld together a plurality of the billets; The lower die assembly includes a shearing channel communicating with the welding chamber. The shearing channel includes two shearing sections for performing two equal-channel corner extrusions to refine the grains of the multiple welded billets. The other end of the shearing channel away from the welding chamber is provided with an extrusion channel. The extrusion channel has the same cross-sectional shape and size as the extrusion channel.

[0005] A multi-bulb extrusion apparatus according to an embodiment of the present invention has at least the following beneficial effects: This invention utilizes a multi-bulb extrusion apparatus designed with identical cross-sectional shapes and dimensions for both the extrusion and compression channels. This design results in bars produced after extrusion with the same cross-sectional shape and dimensions as the initial billet loaded into the compression channels, but with increased length. By repeatedly loading the produced bars into the compression channels for multiple extrusion passes, the product length can be extended, overcoming the length-to-diameter ratio limitations of traditional extrusion processes. Furthermore, the addition of two equal-channel angular compression shear channels within the multi-bulb extrusion apparatus significantly refines the grain size, effectively reducing the number of extrusion passes and improving production efficiency. Simultaneously, each extrusion pass refines the billet, achieving equivalent strain accumulation through repeated extrusion passes, thus avoiding the problem of uneven grain refinement encountered in hot extrusion processes when producing large-sized bars.

[0006] According to some embodiments of the present invention, the two shear segments have the same bending angle and opposite bending directions, and the bending angle φ of the two shear segments satisfies the following relationship: 90°≤φ≤150°.

[0007] According to some embodiments of the present invention, the bending angle φ of the two sheared segments satisfies: φ=120°.

[0008] A method for manufacturing large fine-grained rods according to a second aspect of the present invention, applicable to the above-mentioned multi-bulb extrusion apparatus, the manufacturing method comprising: Prepare multiple billets with cross-sectional shapes and dimensions identical to the multiple extrusion channels; Multiple billets are extruded through the multi-bill extrusion device to obtain intermediate bars with unchanged cross-section but increased length; After the intermediate bar stock is trimmed or cut, it is loaded into multiple extrusion channels along with bars of the same size for multi-bill extrusion. Repeat the previous step to perform multiple extrusion welding until a large fine-grained bar with an aspect ratio and cumulative equivalent strain that meet the manufacturing requirements is obtained.

[0009] According to some embodiments of the present invention, the step of trimming or slitting the intermediate bar stock and then loading it into multiple extrusion channels for multi-billet extrusion along with bars of the same size includes: The head and tail of the intermediate bar are removed and trimmed, and the length-to-diameter ratio of the intermediate bar is measured. If the length-to-diameter ratio of the intermediate bar does not exceed the limit threshold, the head and tail are cut off and trimmed, and then a bar of the same size is added for multi-bill extrusion. If the length-to-diameter ratio of the intermediate bar exceeds the limit threshold, the intermediate bar is split into two pieces, and a bar of the same size as the split intermediate bar is added for multi-bill extrusion.

[0010] According to some embodiments of the present invention, the limit threshold is 5.

[0011] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 A cross-sectional view of an embodiment of a multi-bill extrusion device provided by the present invention; Figure 2 A side view of an embodiment of a multi-bill extrusion apparatus provided by the present invention; Figure 3 This invention provides a multi-bulb extrusion device. Figure 2 A cross-sectional view of the embodiment shown; Figure 4 A cross-sectional view of the shearing channel of a multi-bill extrusion device provided by the present invention; Figure 5 Side views of two embodiments of a multi-bill extrusion apparatus provided by the present invention; Figure 6 A schematic flowchart of an embodiment of a method for manufacturing large fine-grained rods provided by the present invention; Figure 7 This is a flowchart illustrating step S300 of a method for manufacturing large fine-grained rods provided by the present invention.

[0013] Icon labels: Extrusion assembly 100; Extrusion channel 110; Billet 120; Upper mold assembly 200; Welding chamber 210; Lower die assembly 300; shearing channel 310; shearing section 311; extrusion channel 320. Detailed Implementation

[0014] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0015] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0016] In the description of this invention, "multiple" refers to two or more. The use of "first" and "second" is for distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features or their sequential relationship.

[0017] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are some embodiments of the present invention, not all embodiments.

[0019] Equal Channel Corner Extrusion (ECAP) refines the grain size of a material without altering its cross-sectional area or shape. The extrusion channel consists of two channels at a specific angle, both with identical cross-sections. The extruded blank moves from the upper extrusion punch into the die channel, pushing it downwards into the corner. This causes the blank to accumulate shear strain, increasing dislocation density and triggering dynamic recrystallization, thereby refining the grain size and improving strength, toughness, yield strength, and plasticity. However, traditional ECAP processes can only process small cylindrical or prismatic materials, limiting their application. Furthermore, in multi-pass ECAP processes, excessively long blanks can lead to problems such as difficulty in fitting into the die, excessive extrusion pressure due to friction, blank double-drum instability, and punch instability. The length of the finished product must be trimmed at both ends before proceeding to the next ECAP pass, resulting in increasingly shorter finished products with very small individual lengths. In addition, when preparing large bars using traditional hot extrusion processes, the uneven metal flow, low deformation in the central region, and insufficient recrystallization driving force make it almost impossible to avoid the formation of coarse grains. Meanwhile, the finished forgings have extremely strict requirements on the grain size of the raw material billet, which makes the preparation of large fine-grained bars a difficult problem in the industry.

[0020] To address the aforementioned problems, this invention provides a multi-bulb extrusion device and a method for manufacturing large fine-grained rods, which can effectively solve the problems of being unable to break through the upper limit of fine-grained rod manufacturing size and uneven grain refinement in large rods.

[0021] refer to Figures 1 to 7 The following are embodiments of the multi-bulb extrusion apparatus and the method for manufacturing large fine-grained bars of the present invention: Reference Figure 1 An embodiment of the present invention provides a multi-bill extrusion device, comprising an extrusion assembly 100, an upper die assembly 200, and a lower die assembly 300.

[0022] Reference Figure 1 , Figure 2 and Figure 3 The extrusion assembly 100 includes multiple extrusion channels 110 with the same extension direction, cross-sectional shape, and size. The extrusion channels 110 are used to extrude multiple billets 120 respectively. The upper die assembly 200 includes a welding chamber 210, which is connected to the multiple extrusion channels 110. The welding chamber 210 is used to weld the multiple billets 120 together. The lower die assembly 300 includes a shearing channel 310 connected to the welding chamber 210. The shearing channel 310 includes two shearing sections 311 for two equal-channel angle extrusions to refine the grains of the welded multiple billets 120. The other end of the shearing channel 310 away from the welding chamber 210 is provided with an extrusion channel 320, which has the same cross-sectional shape and size as the extrusion channel 110.

[0023] Reference Figure 4 According to some embodiments of the present invention, the two shearing segments 311 have the same bending angle and opposite bending directions. The bending angle φ of the two shearing segments 311 satisfies the following relationship: 90°≤φ≤150°. Preferably, the bending angle φ of the two shearing segments 311 satisfies: φ=120°. By designing the bending angle of the two shearing segments 311, the flow resistance of the billet 120 is kept small and a strong shearing effect is generated.

[0024] To achieve the desired effect, this invention designs a multi-bulb extrusion device with identical cross-sectional shapes and dimensions for the extrusion channel 320 and the extrusion channel 110. This results in a bar produced after extrusion with the same cross-sectional shape and dimensions as the initial billet 120 loaded into the extrusion channel 110, but with increased length. The resulting bar is then repeatedly loaded into the extrusion channel 110 as billet 120 for multiple extrusion passes, thereby extending the product length and overcoming the aspect ratio limitation of bar manufacturing in the ECAP process. Simultaneously, the addition of a shear channel 310 with two equal-channel corner extrusion passes in the multi-bulb extrusion device significantly refines the grains, effectively reducing the number of extrusion passes, improving production efficiency, and reducing material waste caused by trimming the ends. Furthermore, the billet 120 is refined during each extrusion pass, and equivalent strain accumulation is achieved through multiple repeated extrusion passes, avoiding the problem of uneven grain refinement in the hot extrusion process when preparing large-size bars.

[0025] The following are two embodiments of a multi-bill extrusion apparatus.

[0026] Example 1 Reference Figure 2 and Figure 3 In this embodiment, the multi-bill extrusion device includes an extrusion assembly 100, an upper die assembly 200, and a lower die assembly 300. The extrusion assembly 100 includes two extrusion channels 110 with the same extension direction, cross-sectional shape, and size. The extrusion channels 110 are used to extrude two billets 120 respectively. The upper die assembly 200 includes a welding chamber 210, which communicates with the two extrusion channels 110 and is used to weld the two billets 120 together. The lower die assembly 300 includes a shearing channel 310 that communicates with the welding chamber 210. 310 includes two shearing sections 311 with two equal-channel corner extrusions. The bending angle of the shearing section 311 is 120°. The other end of the shearing channel 310 away from the welding chamber 210 is provided with an extrusion channel 320. The extrusion channel 320 has the same cross-sectional shape and size as the extrusion channel 110. Two billets 120 with the same shape and size are loaded into the two extrusion channels 110. After the two billets 120 are welded in the welding chamber 210, they are refined through the shearing channel 310 and extruded through the extrusion channel 320 to obtain a bar with unchanged cross-section and increased length.

[0027] After the rod is obtained, it is repeatedly extruded through the extrusion channel 110. If the aspect ratio exceeds the limit threshold, it is split and then extruded again. During the repeated extrusion process, equivalent strain is accumulated and the grains are refined until two rods with aspect ratios close to but not exceeding the limit threshold are extruded through the multi-bill 120 to obtain a large fine-grained rod that breaks through the aspect ratio limit threshold.

[0028] Example 2 Reference Figure 5In this embodiment, the multi-bill extrusion device includes an extrusion assembly 100, an upper die assembly 200, and a lower die assembly 300. The extrusion assembly 100 includes three extrusion channels 110 with the same extension direction, cross-sectional shape, and size. The extrusion channels 110 are used to extrude three billets 120 respectively. The upper die assembly 200 includes a welding chamber 210, which communicates with the three extrusion channels 110 and is used to weld the three billets 120 together. The lower die assembly 300 includes a shearing channel 310 that communicates with the welding chamber 210. 310 includes two shearing sections 311 with equal channel angle extrusion at both ends. The bending angle of the shearing section 311 is 120°. The other end of the shearing channel 310 away from the welding chamber 210 is provided with an extrusion channel 320. The extrusion channel 320 has the same cross-sectional shape and size as the extrusion channel 110. Three billets 120 with the same shape and size are loaded into the three extrusion channels 110. After the three billets 120 are welded in the welding chamber 210, they are refined by grain refinement through the shearing channel 310 and extruded through the extrusion channel 320 to obtain a bar with unchanged cross-section and increased length.

[0029] After the rod is obtained, it is repeatedly extruded through the extrusion channel 110. If the aspect ratio exceeds the limit threshold, it is cut and then extruded again. During the repeated extrusion process, equivalent strain is accumulated and the grains are refined until two rods with aspect ratios close to but not exceeding the limit threshold are extruded through the multi-bill 120 to obtain a large fine-grained rod that breaks through the aspect ratio limit threshold.

[0030] Reference Figure 6 The present invention also proposes a method for manufacturing large fine-grained rods, applicable to the aforementioned multi-bulb extrusion apparatus, the manufacturing method comprising: Step S100: Prepare multiple billets 120 with the same cross-sectional shape and size as the multiple extrusion channels 110; Step S200: Extruding multiple billets 120 through a multi-bill extrusion device to obtain intermediate bars with unchanged cross-section but increased length; Step S300: After trimming or slitting the intermediate bar stock, it is loaded into multiple extrusion channels 110 along with bar stock of the same size for multi-bill extrusion 120. Step S400: Repeat the previous step to perform multiple extrusion welding until a large fine-grained bar with an aspect ratio and cumulative equivalent strain that meet the manufacturing requirements is obtained.

[0031] In step S100, multiple blanks 120 with the same cross-sectional shape and size are prepared and adapted to the extrusion channel 110 so that they can serve as the initial blanks for extrusion. The multiple blanks 120 form the basis for extruding large fine-grained rods.

[0032] In step S200, multiple billets 120 are welded at high temperature in welding chamber 210 and then enter shearing channel 310. The grains of billet 120 are refined by two equal channel angle extrusions in shearing channel 310 to improve the comprehensive mechanical properties of the bar.

[0033] Reference Figure 7 According to some embodiments of the present invention, in step S300, after the intermediate bar stock is cut or slit, it is loaded into multiple extrusion channels 110 along with bars of the same size for multi-bulb extrusion 120, including: Step S310: Trim the head and tail of the intermediate bar stock and measure the length-to-diameter ratio of the intermediate bar stock; Step S320: If the length-to-diameter ratio of the intermediate bar does not exceed the limit threshold, the head and tail are cut off and trimmed, and then a bar of the same size is added for multi-bill 120 extrusion. Step S330: If the length-to-diameter ratio of the intermediate bar exceeds the limit threshold, the intermediate bar is split into two pieces, and a bar of the same size as the split intermediate bar is added for multi-bill 120 extrusion.

[0034] In this invention, the length-to-diameter ratio limit of the intermediate bar stock is 5, meaning its length cannot exceed 5 times its diameter. Bar stock blanks 120 with excessively large length-to-diameter ratios have the following defects in the ECAP process: due to poor straightness or cylindricity, when loaded into the extrusion channel 110, the tail end is easily stuck at the entrance and cannot be automatically aligned; the pressure of the extrusion device increases, which in severe cases can cause the punch to become unstable or the die to crack; double-drum deformation occurs in the extrusion channel 110, creating a sealed space to contain gas. As filling proceeds, the gas enters the microcracks on the surface of the blank 120. These cracks are welded together when passing through the die, forming bubbles on the product surface, or failing to weld through the die hole and forming peeling.

[0035] In summary, when the bar stock is used as billet 120 in the ECAP process, there is a limit threshold for the aspect ratio. If this threshold is exceeded, it will affect the preparation process of large fine-grained bars.

[0036] Therefore, in steps S310 to S330, the length of the intermediate bar needs to be measured during the multiple repeated extrusion process to obtain the length-to-diameter ratio of the intermediate bar. The intermediate bar above the limit threshold is cut to avoid it being too long and unable to perform the extrusion process normally. The intermediate bar below the limit threshold does not need to be cut, and only the head and tail are trimmed to adjust the shape.

[0037] In step S400, a large fine-grained bar with increased length is obtained by adding a bar of the same shape and size and extruding it together with the intermediate bar. At the same time, during the extrusion process, the grains are refined by the shear channel 310. The equivalent strain in the multiple repeated extrusions accumulates continuously, thereby obtaining an extruded bar with uniform material and excellent mechanical properties.

[0038] The following are two embodiments of a method for manufacturing large fine-grained rods.

[0039] Example 3 This embodiment corresponds to the multi-bulb extrusion device shown in Embodiment 1. Two extrusion channels 110 are provided, each with a diameter of Ф205mm. The extrusion channel 320 has a diameter of Ф200mm. The extrusion channels 110 are configured with a reasonable diameter allowance to accommodate deviations in the straightness and cylindricity of the billet. A welding chamber 210 and a shearing channel 310 connect the extrusion channels 110 and 320. The shearing channel 310 has a diameter of Ф200mm and a rotation angle of 120°. The initial billet 120 is a Ф200mm round bar with a length L1 = 650mm. After the first extrusion pass, the two Ф200*650 round bars are welded together in the welding chamber 210 of the upper die and extruded from the lower die to become Ф200 round bars, with a cut length L2 = 960mm. After obtaining two Ф200*960 round bars, they are extruded a second time to obtain Ф200 round bars, which are then cut to a length of L3=1350mm. Since the length-to-diameter ratio of the Ф200*1350 round bar is greater than 5, it is cut into two round bars of L4=650mm each. These are then extruded a third time to produce Ф200mm round bars, which are then cut to a length of L5=960mm. Finally, the two Ф200*960mm round bars are extruded a fourth time to produce Ф200 round bars, which are then cut to a length of L6=1400mm.

[0040] In this embodiment, after welding and S-shaped channel corner extrusion in four extrusion processes, a large single aluminum alloy fine-grained rod with a length-to-diameter ratio of 7 (Ф200*1400) and a weight of 118kg is obtained.

[0041] In a single-pass extrusion process, the extrusion ratio λ=2, so the equivalent strain in the upper die assembly 200 is ε1=ln(λ)=0.693. In the S-shaped equal-channel angular extrusion process of the lower die assembly 300, after two 120° S-shaped equal-channel angular extrusions, the equivalent strain ε2=0.647*2=1.294. For a single-pass extrusion in a multi-bill extrusion device, the sum of the material equivalent strains is 1.99. The cumulative equivalent strain of multi-pass extrusion is a multiple of the number of extrusions; for example, after 4 extrusions, the cumulative equivalent strain becomes 4*1.99=7.96.

[0042] Example 4 This embodiment corresponds to the multi-bulb extrusion device shown in Embodiment 2. There are three extrusion channels 110, each with a diameter of Ф205mm. The extrusion channel 320 has a diameter of Ф200mm. The extrusion channels 110 are designed with a reasonable diameter allowance to accommodate deviations in the straightness and cylindricity of the billet. A welding chamber 210 and a shearing channel 310 connect the extrusion channels 110 and 320. The shearing channel 310 has a diameter of Ф200mm and a rotation angle of 120°. The initial billet 120 is a Ф200mm round bar with a length of 650mm. After the first extrusion pass, the three Ф200*650 round bars are welded together in the welding chamber 210 of the upper die and extruded from the lower die to become Ф200 round bars, with a cut length of 1500mm. Because the length-to-diameter ratio of the Ф200*1500 round bar is greater than 5, the round bar is cut into two 700mm round bars, and a round bar of the same size produced by another extrusion process is added for the second extrusion, extruding a Ф200mm round bar, which is then cut to a length of 1650mm. The Ф200*1650 round bar is then cut into two 800mm round bars, and a round bar of the same size produced by another extrusion process is added for the third extrusion, extruding a Ф200mm round bar, which is then cut to a length of 1900mm. The Ф200*1900 round bar is then cut into two 800mm round bars, and a round bar of the same size produced by another extrusion process is added for the fourth extrusion, extruding a Ф200mm round bar, which is then cut to a length of 1900mm.

[0043] In this embodiment, after welding and S-shaped channel corner extrusion in four extrusion processes, a large single aluminum alloy fine-grained rod with a length-to-diameter ratio of Ф200*2200 and a weight of 186kg is obtained.

[0044] In a single-pass extrusion process, the extrusion ratio λ=3, so the equivalent strain in the upper die assembly 200 is ε1=ln(λ)=1.1. In the S-shaped equal-channel angular extrusion process of the lower die assembly 300, after two 120° S-shaped equal-channel angular extrusions, the equivalent strain ε2=0.647*2=1.294. The sum of the material's equivalent strain in a single-pass extrusion is 2.39. After four extrusions, the cumulative equivalent strain is 4*2.39=9.56.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A multi-bill extrusion device, characterized in that, include: An extrusion assembly includes multiple extrusion channels with the same extension direction, cross-sectional shape, and size, the extrusion channels being used to extrude multiple billets; The upper die assembly includes a welding chamber, which is connected to a plurality of extrusion channels, and the welding chamber is used to weld together a plurality of the billets; The lower die assembly includes a shearing channel communicating with the welding chamber. The shearing channel includes two shearing sections for performing two equal-channel corner extrusions to refine the grains of the multiple welded billets. The other end of the shearing channel away from the welding chamber is provided with an extrusion channel. The extrusion channel has the same cross-sectional shape and size as the extrusion channel.

2. The multi-bulb extrusion device according to claim 1, characterized in that: The two shear segments have the same bending angle and opposite bending directions. The bending angle φ between the two shear segments satisfies the following relationship: 90°≤φ≤150°.

3. The multi-bulb extrusion device according to claim 2, characterized in that: The bending angle φ between the two sheared segments satisfies: φ=120°.

4. A method for manufacturing large fine-grained rods, characterized in that, The manufacturing method, applicable to the multi-bulb extrusion apparatus as described in any one of claims 1 to 3, comprises: Prepare multiple billets with cross-sectional shapes and dimensions identical to the multiple extrusion channels; Multiple billets are extruded through the multi-bill extrusion device to obtain intermediate bars with unchanged cross-section but increased length; After the intermediate bar stock is trimmed or cut, it is loaded into multiple extrusion channels along with bars of the same size for multi-bill extrusion. Repeat the previous step to perform multiple extrusion welding until a large fine-grained bar with an aspect ratio and cumulative equivalent strain that meet the manufacturing requirements is obtained.

5. The method for manufacturing large fine-grained rods according to claim 4, characterized in that, The process of trimming or slitting the intermediate bar stock, and then loading it into multiple extrusion channels along with bars of the same size for multi-bulk extrusion, includes: The head and tail of the intermediate bar are removed and trimmed, and the length-to-diameter ratio of the intermediate bar is measured. If the length-to-diameter ratio of the intermediate bar does not exceed the limit threshold, the head and tail are cut off and trimmed, and then a bar of the same size is added for multi-bill extrusion. If the length-to-diameter ratio of the intermediate bar exceeds the limit threshold, the intermediate bar is split into two pieces, and a bar of the same size as the split intermediate bar is added for multi-bill extrusion.

6. The method for manufacturing large fine-grained rods according to claim 5, characterized in that: The limit threshold is 5.

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