A method of manufacturing an aircraft duct

Abstract

The application provides a preparation method of an aviation conduit, comprising the following steps: extruding, rolling, drawing and heat treating a metal blank to obtain the aviation conduit; the wall thickness tolerance of the extruded product is 5% of the wall thickness of the metal blank. The method provided by the application can improve the wall thickness size precision of the aviation conduit from 1+ / -0.08 mm specified in the national standard to 1+ / -0.03 (wall thickness+ / -3%) mm, and the inner and outer surface quality reaches the requirement of the aviation conduit; and the application solves the problems of frequent breakage, core sticking and difficult core head drawing production in the drawing process of the 6061 alloy pipe with a wall thickness of less than 1 mm.

Description

Technical Field

[0001] This invention belongs to the field of aviation tubing technology, and particularly relates to a method for preparing aviation ducts. Background Technology

[0002] In recent years, with my country's investment in the aviation industry, thin-walled tubes, which are the lifeblood of aircraft, such as fuel, hydraulic, and environmental control systems, have also undergone new changes. The new 6061 high-precision thin-walled tube has significantly improved in both dimensional accuracy and overall performance compared to previous thin-walled tubes. However, the production process of this high-precision thin-walled tube faces the problem of difficulty in pulling the tube with the mandrel, which seriously affects the accuracy of the tube wall thickness and makes mass production difficult. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for preparing an aviation conduit, which can improve the wall thickness accuracy of aviation conduit drawing.

[0004] This invention provides a method for preparing an aviation duct, comprising:

[0005] Metal blanks are extruded, rolled, and drawn to obtain aviation conduits;

[0006] The wall thickness tolerance of the extruded product is ±4 to 6% of the wall thickness of the extruded metal blank.

[0007] Preferably, the metal blank is composed of 6-series aluminum alloy.

[0008] Preferably, the diameter of the metal blank is 45-55 mm and the wall thickness is 3-7 mm.

[0009] Preferably, the rolling process includes:

[0010] The rolling process is performed in two stages, one rolling and one rolling.

[0011] The wall thickness of the product after one rolling process is 2-4 mm;

[0012] The wall thickness of the product after the second rolling is 1 to 1.3 mm.

[0013] Preferably, the wall thickness tolerance of the rolled product is ±3 to 5% mm.

[0014] Preferably, the pulling method includes:

[0015] First perform air pulling, then pull the core head;

[0016] The diameter of the product after air stretching is 21-23 mm.

[0017] Preferably, the core used in the core-pulling process is a tapered rod with a taper of 1 to 3 degrees.

[0018] Preferably, the length of the core used in the core pulling process is 15-25mm; the working belt length of the core is 1-4mm.

[0019] Preferably, the working strip length of the drawing die used in the core head drawing process is 4 to 6 mm.

[0020] Preferably, the wall thickness tolerance of the aviation duct is ±0.02 to 0.05 mm.

[0021] The method provided by this invention can improve the wall thickness accuracy of aerospace ducts from the national standard of 1±0.08mm to 1±0.03 (wall thickness ±3%)mm, and the inner and outer surface quality meets the requirements of aerospace ducts; moreover, this invention solves the problem of frequent breakage and core sticking (e.g., during the drawing process of 6061 alloy tubes with a wall thickness ≤1mm) Figure 1 and Figure 2 (As shown), there are problems such as difficulties in the production of core head drawing. Attached Figure Description

[0022] Figure 1 Images showing the pipe breaking during the pulling process;

[0023] Figure 2 Images showing the tube core sticking together during the drawing process;

[0024] Figure 3 This is a schematic diagram of the core-head pulling process;

[0025] Figure 4 Schematic diagram and photograph of the chip head structure in the prior art;

[0026] Figure 5 The diagram and photographs are of the core head structure in the embodiments of the present invention;

[0027] Figure 6 This is a schematic diagram of the drawing die structure in an embodiment of the present invention;

[0028] Figure 7 Image of the aviation duct prepared in Example 5 of this invention;

[0029] Figure 8 Image of the aviation duct prepared in Example 4 of this invention;

[0030] Figure 9 Image of the aviation duct prepared in Example 4 of the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing an aviation duct, comprising:

[0033] Metal blanks are extruded, rolled, and drawn to obtain aviation conduits.

[0034] This invention involves blanking metal blanks on an extruder without lubrication, reducing the wall and diameter of the blanks by a high-speed cold rolling mill, and finally drawing and annealing the blanks on a chain-type drawing machine.

[0035] In this invention, the composition of the metal blank is preferably aluminum alloy, more preferably 6-series aluminum alloy, and most preferably 6061 aluminum alloy.

[0036] The present invention does not impose any special restrictions on the source of the metal blank. The metal blank with the required composition can be obtained by casting methods well known to those skilled in the art, or by commercially available castings with the above composition.

[0037] In this invention, the diameter of the metal blank is preferably 45-55 mm, more preferably 48-52 mm, and most preferably 50 mm; the wall thickness is preferably 3-7 mm, more preferably 4-6 mm, and most preferably 5 mm.

[0038] In this invention, the extrusion process preferably employs a non-lubricated forward extrusion process; the extrusion temperature is preferably 470–500°C, more preferably 480–490°C, and most preferably 485°C; the extrusion speed is preferably 2.0–3.0 m / min, more preferably 2.2–2.8 m / min, and most preferably 2.4–2.6 m / min; the extrusion cylinder temperature during the extrusion process is preferably 440–450°C, and more preferably 445°C.

[0039] In this invention, in order to ensure that the wall thickness accuracy of the final product meets the requirement of ±0.03mm, the wall thickness tolerance after extrusion is preferably ±T×(4~6%), more preferably T×(4.5~5.5%), and most preferably T×5%, where T is the wall thickness of the extruded metal blank. It is preferable to ensure the above-mentioned wall thickness tolerance after extrusion by processing with an ingot casting machine and adjusting the center of the equipment. For example, if the specification of the extruded metal blank is φ45*5mm, the wall thickness tolerance after extrusion is 5±0.25mm.

[0040] In this invention, the process after extrusion and before rolling preferably includes rolling annealing.

[0041] In this invention, a box-type annealing furnace is preferably used for annealing during the rolling annealing process; the rolling annealing temperature is preferably 350-390℃, more preferably 360-380℃, and most preferably 370℃; the rolling annealing time is preferably 1-3h, more preferably 1.5-2.5h, and most preferably 2h; a suitable rolling annealing time can be adopted according to the furnace loading.

[0042] In this invention, the rolling process preferably includes:

[0043] Single rolling and double rolling.

[0044] In this invention, the diameter of the product obtained after the first rolling is preferably 35-40 mm, more preferably 36-38 mm; the wall thickness is preferably 2-4 mm, more preferably 3 mm. In this invention, the diameter of the product obtained after the second rolling is preferably 25-30 mm, more preferably 26-28 mm, and most preferably 27 mm; the wall thickness is preferably 1-1.3 mm, more preferably 1.1-1.2 mm, and most preferably 1.15 mm.

[0045] In this invention, a periodic two-roll cold rolling mill is preferably used in the primary rolling process, and the feed rate is preferably 4-5 mm. In this invention, a periodic cold rolling mill is preferably used in the secondary rolling process, and the feed rate is preferably 1.0-1.5 mm.

[0046] In this invention, a two-roll cold rolling mill is preferably used in the rolling process, and the rolling feed rate is preferably ≤5mm to ensure the wall thickness accuracy of the product. In this invention, the wall thickness tolerance of the rolled product is preferably ±3~5%mm, more preferably ±3.5~4.5%mm, and most preferably ±4%mm. For example, if the rolled product specification is φ27*1.15mm, the wall thickness tolerance is 1.15±0.04mm.

[0047] In this invention, the wall thickness accuracy of the product after extrusion and rolling has not yet reached the requirement of 1±0.03mm, and further improvement of the wall thickness accuracy is required through drawing.

[0048] In this invention, the drawing method preferably includes:

[0049] First, perform air pulling, then pull the core head.

[0050] In this invention, the air pull is preferably a two-stage air pull.

[0051] In this invention, a hydraulic drawing machine is preferably used during the air drawing process, and slow drawing is preferred. The drawing speed of the air drawing is preferably 0.6 to 0.8 m / s, and more preferably 0.7 m / s.

[0052] In this invention, the diameter of the product obtained after air stretching is preferably 21-23 mm, more preferably 22 mm.

[0053] In this invention, the process after the empty pull and before the core head is pulled preferably includes:

[0054] Perform drawing and annealing.

[0055] In this invention, the drawing annealing process preferably uses a box-type annealing furnace, the drawing annealing temperature is preferably 350-400℃, more preferably 360-390℃, and most preferably 370-380℃; the drawing annealing time is preferably 1.5-2.5h, more preferably 1.8-2.2h, and most preferably 2h.

[0056] In this invention, the wall thickness is reduced by using a drawing die to reduce the diameter and by limiting the amount of inner diameter reduction by the mandrel. Figure 3 As shown; during the drawing process with a mandrel, the diameter must also be reduced at the same time as the wall thickness in each pass; otherwise, reducing only the wall thickness without reducing the diameter will result in the mandrel not being able to be inserted and the drawing process not being able to proceed. That is, before each drawing pass, the diameter of the mandrel must be smaller than the inner diameter of the tube blank so that the mandrel can be smoothly inserted into the tube blank.

[0057] In this invention, the tube is rolled twice and then drawn in two passes to a diameter of φ22mm. After the air drawing, the wall thickness of the product increases slightly, reaching approximately 1.20mm. The final cold deformation is about 23%. When using existing mandrel drawing technology, the friction between the mandrel and the inner surface is high during production, and the product wall is thin, making it prone to breakage. However, the wall thickness in this case is relatively ideal, achieving a wall thickness accuracy of 1±0.03mm.

[0058] This invention analyzes the breakage situation. Inspection of the outer surface of the pipe revealed no abnormalities. The main causes are as follows: 1) Excessive product deformation: Larger deformation requires greater pulling force, resulting in greater tensile stress on the pipe's cross-section. When this stress exceeds the pipe's strength limit, breakage occurs. 2) The mandrel is positioned too far forward: During production, the mandrel working surface and the drawing die working surface must correspond. However, due to the mandrel working surface being too long and the drawing die working surface being too short (2-3mm), alignment is difficult, causing the mandrel to be positioned too far forward. After the pipe is pulled out of the die hole, the inner wall remains in contact with the mandrel working surface, resulting in a thin finished pipe wall and breakage.

[0059] In this invention, the grain size of the aerospace conduit must be no greater than Grade 1. Large deformation is a crucial prerequisite for ensuring grain refinement, necessitating research into the drawing tools and processes. This invention reveals that the final wall thickness of the tube is determined by the gap between the sizing zone of the drawing die and the working zone of the drawing mandrel. Larger dimensions of both zones result in more stable tube deformation and higher wall thickness accuracy. When the working zone of the drawing die is 2–3 mm, the effective length of the working zone of the mandrel is also 2–3 mm, achieving a wall thickness accuracy of 1 ± 0.03 mm. To address the problem of misalignment between the mandrel and the drawing die during the drawing process, leading to the mandrel being too far forward, this invention redesigns the drawing die and the drawing mandrel.

[0060] In this invention, the core head used in the core drawing process is preferably a tapered rod; the taper of the tapered rod is preferably 1 to 3°, more preferably 1.5 to 2.5°, and most preferably 2°; the length of the core head is preferably 15 to 25 mm, more preferably 18 to 22 mm, and most preferably 20 mm; the working belt length of the core head is preferably 1 to 4 mm, and more preferably 2 to 3 mm.

[0061] This invention, through research, has discovered that the actual working length of the mandrel does not need to be too long to guarantee the wall thickness tolerance of the product. In this invention, to facilitate the smooth insertion of the mandrel into the tube blank and reduce damage to the inner surface of the product, the shape of the mandrel has been changed from the original cylindrical shape (e.g., ...). Figure 4 As shown) optimized into a tapered rod with a taper of 2° (e.g. Figure 5 As shown in the figure, the overall length of the core tip has also been shortened from 50mm to 20mm.

[0062] In this invention, the working strip length of the drawing die used in the core drawing process is preferably 4 to 6 mm, more preferably 4.5 to 5.5 mm, and most preferably 5 mm.

[0063] In this invention, the structural schematic diagram of the drawing die is shown below. Figure 6 As shown in the figure, (a) is a conical mold, (b) is an arc-shaped mold, I is a lubricating belt, II is a compression belt, III is a sizing belt, and IV is an outlet belt.

[0064] In this invention, the main function of the sizing band of the drawing die is to ensure that the product obtains stable and accurate dimensions. To reduce friction during mandrel drawing, the length of the working band of the drawing die is shorter than during idle drawing. This is to address the issue of excessive mandrel length, as a long working band during drawing with a cylindrical mandrel results in a longer actual mandrel length during the drawing process. In this invention, the length of the working band is optimized from 50mm to 1mm-4mm. The length of the working band is not limited by the drawing die, and the friction during drawing is not significantly affected by the drawing die. Appropriately lengthening the working band of the drawing die facilitates the matching between the mandrel and the drawing die, improving the dimensional accuracy and surface finish of the product. Therefore, the working band of the drawing die is lengthened from 2mm to 5mm.

[0065] In this invention, during the core-head drawing process, it is preferable to immerse the product to be drawn in lubricating oil to fully lubricate the inner and outer surfaces of the tube, and then hoist the lubricated product onto the feeding machine to complete the core-head drawing operation one by one.

[0066] In this invention, during the core drawing process, the drawing speed is preferably 0.4 to 0.6 m / s, more preferably 0.5 m / s.

[0067] In this invention, the diameter of the product obtained after drawing the core head is preferably 18-22 mm, more preferably 19-21 mm, and most preferably 20 mm; the wall thickness is preferably 0.8-1.2 mm, more preferably 0.9-1.1 mm, and most preferably 1.0 mm.

[0068] In this invention, the process after drawing preferably further includes:

[0069] The drawn product is then subjected to heat treatment.

[0070] In this invention, the heat treatment preferably includes:

[0071] One or more of the following: quenching treatment, quenching and aging treatment and / or finished product annealing treatment.

[0072] Those skilled in the art can select different heat treatment methods based on the desired final state of the product.

[0073] In this invention, the diameter of the aviation duct is preferably 15-25 mm, more preferably 18-22 mm, and most preferably 20 mm; the wall thickness is preferably 0.5-1.5 mm, more preferably 0.8-1.2 mm, and most preferably 1 mm; the wall thickness tolerance is preferably ±0.02-0.05 mm, and more preferably ±0.03 mm.

[0074] The key to this invention lies in controlling the wall thickness accuracy of the extruded blank to ±5%; it employs a novel drawing mandrel structure design, including a conical structure and working band size design; and a new drawing die with a sizing band width used in conjunction with the novel mandrel. The conical design of the novel drawing mandrel facilitates material insertion and improves the inner surface quality of the tube; the combined use of the novel drawing mandrel and die can improve the tolerance accuracy of 1mm wall thickness aluminum alloy products to 1±0.03mm (±3%), with a smooth, undamaged surface quality, meeting aerospace requirements; the drawing operation of this invention is simple and safe, easy to produce and debug, saves production time, and can be extended to the production of other specifications.

[0075] The metal ingots used in the following embodiments of the present invention are 6061 aluminum alloys provided by Southwest Aluminum (Group) Co., Ltd.; the pictures, dimensions, and schematic diagrams of the drawing tools (drawing dies, drawing mandrels, etc.) used are as follows. Figure 5 and Figure 6 As shown.

[0076] Example 1

[0077] Metal ingots are extruded without lubrication on an extrusion press, then the wall and diameter are reduced by a high-speed cold rolling mill. The resulting blank with a mandrel is drawn through the same drawing die but with different working zones to form the aerospace guide tube. The specific process parameters are as follows:

[0078] Extrusion process parameters:

[0079]

[0080] Rolling process parameters:

[0081]

[0082] Process parameters for air-pull:

[0083] Rolling specifications (mm) Air pull (mm) Pulling speed (m / s) Pulling and annealing 26*1.2 23*1.2 0.7 350～400℃ / (1.5～2.5h)

[0084] The process parameters for core-head drawing are shown in Table 1.

[0085] Examples 2 to 5

[0086] The aviation conduit was prepared according to the method of Example 1. The difference from Example 1 is that the process parameters for drawing the core tip are shown in Table 1.

[0087] Table 1. Process parameters for preparing the core tip of the aerospace duct in the embodiments of the present invention.

[0088]

[0089] In the embodiments of this invention, under the premise of using the same drawing die, drawing was performed with mandrels of different working strip lengths. The wall thickness deviation of the prepared aerospace ducts was tested according to the standard GJB2379A-2015, and the test results are shown in Table 1. It can be seen that when the working strip of the mandrel is 1mm, the maximum wall thickness deviation is 1±0.05mm; when the working strip size of the mandrel is 4-5mm, the wall thickness is 1±0.02mm, but when the length is 5mm, a slight "drawing streak" defect appears on the surface of the tube (e.g., Figure 7 , Figure 8 and Figure 9 As shown, the inner surface quality of the pipes is generally good. Therefore, with the combination of the new conical mandrel and the new drawing die, high-quality aviation conduits can be produced.

[0090] The key to this invention lies in controlling the wall thickness accuracy of the extruded blank to ±5%; it employs a novel drawing mandrel structure design, including a conical structure and working band size design; and a new drawing die with a sizing band width used in conjunction with the novel mandrel. The conical design of the novel drawing mandrel facilitates material insertion and improves the inner surface quality of the tube; the combined use of the novel drawing mandrel and die can improve the tolerance accuracy of 1mm wall thickness aluminum alloy products to 1±0.03mm (±3%), with a smooth, undamaged surface quality, meeting aerospace requirements; the drawing operation of this invention is simple and safe, easy to produce and debug, saves production time, and can be extended to the production of other specifications.

[0091] While the invention has been described and illustrated with reference to specific embodiments thereof, such description and illustration are not intended to limit the invention. It will be readily understood by those skilled in the art that various changes may be made to suit particular circumstances, materials, compositions, substances, methods, or processes to the objectives, spirit, and scope of this application without departing from the true spirit and scope of the invention as defined by the appended claims. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a particular order, it should be understood that these operations may be combined, subdivided, or reordered to form equivalent methods without departing from the teachings of the invention. Therefore, unless specifically indicated herein, the order and grouping of operations are not a limitation of this application.

Claims

1. A method for preparing an aviation duct, comprising: Metal blanks are extruded, rolled, and drawn to obtain aviation conduits; The wall thickness tolerance of the extruded product is ±4~6% of the wall thickness of the extruded metal blank; The rolling process includes: The rolling process is performed in two stages, one rolling and one rolling. The wall thickness of the product after one rolling process is 2~4mm; The wall thickness of the product after the second rolling is 1~1.3mm; The pulling method includes: First, perform two rounds of empty pulling, then perform core head pulling; The diameter of the product after air stretching is 21~23mm; The core used in the core-head drawing process is a tapered rod with a taper of 1~3°; the core length used in the core-head drawing process is 15~25mm; and the working strip length of the core is 1~4mm. The wall thickness accuracy of the aviation duct is 1±0.03mm; The working strip length of the drawing die used in the core drawing process is 4~6mm.

2. The method according to claim 1, characterized in that, The metal blank is composed of 6-series aluminum alloy.

3. The method according to claim 1, characterized in that, The diameter of the metal blank is 45~55mm and the wall thickness is 3~7mm.

4. The method according to claim 1, characterized in that, The wall thickness tolerance of the rolled product is ±3~5%.

5. The method according to claim 1, characterized in that, The wall thickness tolerance of the aviation duct is ±0.02~0.05mm.

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