A method of processing a tapered tube and a supporting core

Abstract

The application discloses a kind of conical pipe processing method and supporting core, belong to machining technical field.The method includes: prefabricated straight pipe material;Supporting core is made of soft material, its outer diameter is greater than the inner hole of straight pipe material to form interference fit;Supporting core is inserted into one end of straight pipe material;The end portion inserted with supporting core is carried out rotary swaging and is formed conical surface;Remove supporting core;Conical surface is finished.The supporting core is made of soft material with Brinell hardness ≤30HBW, and symmetrical guide conical surface is provided at both ends thereof.The supporting core with soft interference fit supports the inner wall and forms a guide during rotary swaging, and can be easily removed by turning after processing, effectively solves the problem that slender conical pipe parts cannot be turned due to insufficient tool rigidity, and significantly improves the machining precision and the qualified rate.

Description

Technical Field

[0001] This invention belongs to the field of machining technology, specifically relating to a machining method and a special support core for machining slender tapered tube parts. Background Technology

[0002] The nozzle component at the air inlet of an aero-engine inlet temperature sensor is typically a slender tapered tube with a tapered end. These components are characterized by a large length-to-diameter ratio and a small end aperture. In traditional machining, the tapered surface is usually machined by turning. However, due to the slender shape and small end aperture, the excessive overhang of the turning tool leads to insufficient rigidity, causing vibration and tool deflection during machining. This not only makes it difficult to guarantee the dimensional accuracy and surface quality of the tapered surface but may even prevent machining altogether.

[0003] To address the forming challenges of such slender tubular components, existing technologies have attempted to employ rotary forging processes. For instance, Chinese patent application CN117696808A discloses a method for processing a steering inner tube, which uses a rigid mandrel as an internal support during rotary forging to prevent material collapse. However, the rigid mandrel in this solution is suitable for parts with fully removable molds. For tapered tubes with one closed end or a tapered inner diameter, the rigid mandrel is difficult to remove after forming and may even scratch the inner wall. Furthermore, the rigid mandrel and the tube are typically fitted with a clearance, which cannot provide precise guidance and alignment during rotary forging, making it difficult to meet high coaxiality requirements.

[0004] Therefore, there is an urgent need for a tapered tube processing method and a dedicated support core that can provide support, guidance, and easy removal. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a processing method and a special support core that can effectively solve the processing problems of slender tapered tubes, ensure the forming quality of the tapered surface, and improve processing efficiency and pass rate.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for machining tapered tubes, comprising the following steps: Prefabricated straight tube material: The bar stock is processed into straight tube material by turning the outer diameter and wire cutting the inner hole. The outer diameter and inner diameter are consistent with the non-tapered section of the tapered tube part to be processed. The total length of the straight tube material is greater than the design length of the tapered tube part to be processed. Preparation of the support core: The support core is made of soft material, and the outer diameter of the support core is larger than the inner diameter of the straight tube material to form an interference fit; Install the support core: Insert the support core into one end of the straight tube; since the outer diameter of the support core is larger than the inner diameter of the tube, forming an interference fit, the support core is inserted to its maximum outer diameter and is stuck at the end of the tube. At this time, the guide cone part of the support core enters the tube, and the main body is exposed at the end of the tube; this installation state allows the guide cone part that enters the tube to provide inner wall support during the subsequent rotary forging process, while the exposed main body plays a guiding role; Rotary forging: The end of the tube with the inserted support core is rotary forged to form the desired conical surface. During the rotary forging process, the support core provides support and guidance for the inner wall of the tube. Remove the support core: The support core located inside the pipe is removed by mechanical processing; Finishing: The tapered surface is finished to obtain the tapered tube part with the final dimensions and surface quality.

[0008] Preferably, the soft material is a metallic material with a Brinell hardness ≤30HBW.

[0009] Preferably, the soft material is aluminum or an aluminum alloy.

[0010] Preferably, the outer diameter of the support core is 0.1mm-0.5mm larger than the inner diameter of the straight tube.

[0011] Preferably, the supporting core has a symmetrical structure at both ends, with guide cones at both ends, and the cone angle of the guide cones is 170°-178°.

[0012] Preferably, the length of the supporting core is greater than the axial length of the cone surface to be formed.

[0013] Preferably, the method further includes an annealing treatment of the straight tube material.

[0014] Preferably, the annealing process is vacuum annealing, with an annealing temperature of 800℃-900℃ and a holding time of 1-3 hours.

[0015] Preferably, the method for removing the support core located inside the tube is by turning.

[0016] The present invention also provides a support core for the above-described processing method. The support core is made of a soft material with a Brinell hardness ≤30HBW, and its outer diameter is configured to form an interference fit with the inner hole of the tube to be processed. Symmetrical guide cones are provided at both ends of the support core. Preferably, the cone angle of the guide cones is 170°-178°.

[0017] Beneficial effects: Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses a soft material to make a support core, which forms an interference fit with the inner hole of the tube. During rotary forging, it can closely adhere to the inner wall of the tube, providing uniform support force and effectively preventing abnormal material collapse during tapered surface forming. The symmetrical guide tapered surface design at both ends of the support core plays a guiding role during rotary forging, ensuring that the formed tapered surface remains coaxial with the center line of the tube, significantly improving machining accuracy. The choice of soft material allows the support core to be easily removed by simple turning after fulfilling its support function, perfectly solving the problem of difficult demolding of rigid mandrels. It is especially suitable for tapered tube parts with a reduced diameter at one end or a complex structure.

[0018] This invention organically combines annealing, soft support core, and rotary forging process to form a complete solution for machining slender tapered tubes, successfully overcoming the problem that traditional turning cannot solve. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the tapered tube component according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the straight pipe material in an embodiment of the present invention; Figure 3 This is a schematic diagram of the supporting core structure in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the usage state of the support core inserted into the tube in an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the tube after rotary forging in an embodiment of the present invention.

[0020] In the figure: 1-tapered tube part; 2-straight tube material; 3-support core; 31-guide cone surface; 4-forming cone surface. Detailed Implementation

[0021] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0022] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Example 1 This invention provides a method for machining a tapered tube and a supporting core. This embodiment uses the machining of an intake air temperature sensor nozzle for a certain type of aero-engine as an example to describe the machining method and the supporting core in detail. The part is a slender tapered tube structure with a total length of 80mm, a tapered surface length of 15mm at one end, a small end inner diameter of Φ10mm, and a large end inner diameter of Φ12mm. The material is 1Cr18Ni9Ti stainless steel. The machining method includes the following steps: Step 1: Prefabrication of straight pipe materials This step prefabricates the bar stock into straight tube stock, and the outer diameter and inner diameter of the resulting straight tube stock are consistent with the dimensions of the non-tapered section of the tapered tube part to be processed.

[0024] Specifically, select 1Cr18Ni9Ti bars of suitable diameter and machine the outer diameter to Φ. mm, internal hole machined to Φ using wire EDM. mm, processed into straight pipe material 2, with a total length of mm. mm (10mm longer than the finished product), such as Figure 2 As shown.

[0025] Step 2: Preparation of the support core This step uses a soft material with a Brinell hardness ≤30HBW to make the support core, wherein the outer diameter of the support core 3 is larger than the inner diameter of the straight tube 2 obtained in step one, so as to form an interference fit. In this embodiment, the soft material is preferably aluminum or aluminum alloy; the outer diameter of the support core 3 is 0.1mm-0.5mm larger than the inner diameter of the straight tube.

[0026] Specifically, aluminum alloy bars of grade 6061 are used and processed into shapes such as... Figure 3 The supporting core 3 is shown. The outer diameter of the supporting core 3 is Φ. mm (0.4 mm larger than the inner diameter of the pipe Φ12.2 mm, forming an interference fit), total length 38±0.5 mm, with symmetrical guide cone surfaces 31 at both ends, the cone angle of the guide cone surface 31 is 170°-178°; wherein the cone angle of the guide cone surface 31 is preferably 176°, and the cone surface length is 5 mm.

[0027] Step 3: Annealing This step involves annealing the straight tube material, specifically vacuum annealing, with the annealing temperature set at 800℃-900℃ and the holding time at 1-3 hours.

[0028] Specifically, the straight tube material processed in step one is placed in a vacuum furnace for annealing. The vacuum level is ≤0.1 Pa. The furnace temperature is raised to 850℃ and held for 1.5 hours. Then, it is pulled out of the heating tank and air-cooled to below 70℃ before the vacuum pump is turned off. This step aims to eliminate the stress from wire EDM processing, improve the material's plasticity, and prepare it for subsequent rotary forging.

[0029] Step 4: Install the support core The support core 3 prepared in step two is inserted into the heat-treated straight tube 2 from one end. Because the outer diameter of the support core (Φ12.6mm) is larger than the inner diameter of the tube (Φ12.2mm), an interference fit is formed, so the support core cannot be completely inserted into the tube. Guided by the guide cone 31 (cone angle 176°), the support core is inserted to its maximum outer diameter and then stopped by the end of the tube. At this point, only the guide cone portion enters the tube, while the main body of the support core protrudes from the end of the tube. Figure 4 As shown. Since the support core 3 has a symmetrical structure at both ends, there is no need to distinguish the direction during installation. This installation state ensures that during the subsequent rotary forging process: the exposed main body of the support core plays a guiding role, ensuring that the conical surface is coaxial with the center line of the tube; the guide conical surface part that enters the tube fits tightly with the inner wall of the tube, providing support for rotary forging.

[0030] Step 5: Rotary forging This step involves rotary forging the end of the tube containing the support core to form a conical surface.

[0031] Specifically, the tube with the inserting support core is clamped on a rotary forging machine, and the end with the inserting core is rotary forged to form a conical surface. During the rotary forging process, the guide cone portion entering the tube provides support to the inner wall of the tube, preventing the material from collapsing inward; simultaneously, the exposed main body of the support core, guided by the rotary forging die, acts as a guide, directing the material flow and ensuring that the formed cone surface 4 remains coaxial with the centerline of the tube. After rotary forging, this end is formed into the desired conical surface, such as... Figure 5 As shown.

[0032] Step Six: Remove the support core This step removes the support core located inside the tube. Specifically, the forged workpiece is clamped on a lathe, and the support core inside the tube is completely removed by turning. Since the support core material is soft aluminum alloy (Brinell hardness ≤30HBW), the turning process is easy and will not damage the inner wall of the tube.

[0033] Step 7: Finishing This step involves finishing the formed conical surface. Specifically, the conical surface is precision turned and polished. Simultaneously, the total length of the tube is turned to the design dimension of 66±0.1mm, and the end opening of the conical surface is chamfered, ultimately obtaining a qualified conical tube part 1, as shown below. Figure 1 As shown.

[0034] Testing revealed that the tapered tube parts machined in this embodiment have a coaxiality of ≤0.05mm between the tapered surface and the centerline, and a surface roughness Ra ≤1.6μm, fully meeting the design requirements. Using this method, the machining pass rate of these parts increased from 0% (unable to be turned) to over 95%.

[0035] Example 2 This embodiment is basically the same as Embodiment 1, except that: In step two, the support core is made of pure aluminum rod (with a Brinell hardness of about 25HBW) as a soft material, with an outer diameter of Φ12.5mm and an interference of 0.3mm; the cone angle of the guide cone surfaces at both ends of the support core is 172°.

[0036] In step four, during the installation of the support core, due to the interference fit, the support core is inserted to its maximum outer diameter and is stuck at the end of the pipe, with only the guide cone part entering the pipe.

[0037] In step five, the rotary forging parameters are adjusted to: spindle speed 320 r / min, feed rate 600 mm / min.

[0038] The processing effect is comparable to that of Example 1, and the cone surface forming quality is good.

[0039] Example 3 This embodiment is used to process a slender tapered tube part made of 316L stainless steel, with an inner diameter of Φ15mm.

[0040] In step two, the support core is made of 6061 aluminum alloy with a Brinell hardness of approximately 28 HBW, which meets the requirement of ≤30 HBW. The outer diameter of the support core is Φ15.4 mm, which is 0.4 mm larger than the inner diameter of the tube (Φ15 mm). This interference of 0.4 mm is within the range of 0.1 mm to 0.5 mm. The cone angle of the guide cone surfaces at both ends of the support core is 175°, which is within the range of 170° to 178°.

[0041] In step three, the annealing process is vacuum annealing, with the annealing temperature adjusted to 880℃ (within the range of 800℃-900℃) and held for 2 hours (within the range of 1-3 hours).

[0042] In step four, during the installation of the support core, due to the interference fit, the support core is inserted to its maximum outer diameter and is stuck at the end of the pipe, with only the guide cone part entering the pipe.

[0043] The processing results are good, and the accuracy of the conical surface forming meets the requirements.

[0044] Example 4 This embodiment is basically the same as Embodiment 1, except that: In step two, the outer diameter of the support core is Φ12.3mm, which is 0.1mm larger than the inner diameter of the tube (Φ12.2mm); the cone angle of the guide cone surfaces at both ends of the support core is 170°.

[0045] In step three, the annealing temperature is 800℃ and the holding time is 1 hour.

[0046] Processing results: The conical surface forming quality is good, and the coaxiality is ≤0.08mm, which meets the design requirements.

[0047] Example 5 This embodiment is basically the same as Embodiment 1, except that: In step two, the outer diameter of the support core is Φ12.7mm, which is 0.5mm larger than the inner diameter of the tube (Φ12.2mm); the cone angle of the guide cone surfaces at both ends of the support core is 178°.

[0048] In step three, the annealing temperature is 900℃ and the holding time is 3 hours.

[0049] Processing results: The conical surface forming quality is good, and the coaxiality is ≤0.06mm, which meets the design requirements.

[0050] Comparative Example 1 This comparative example is basically the same as Example 1, except that: in step two, the support core is not installed, and the straight tube material is directly subjected to rotary forging.

[0051] Results: During the rotary forging process, the end of the tube collapsed severely, resulting in a noticeable indentation inside the formed conical surface. Furthermore, the conical surface was significantly misaligned with the centerline of the tube, rendering the part unusable. This indicates that a conical surface cannot be formed without a supporting core.

[0052] Comparative Example 2 This comparative example is basically the same as Example 1, except that: in step two, a rigid steel mandrel is used as a support, and the mandrel and the inner hole of the tube are in clearance fit (Φ12.2mm / Φ12.1mm), instead of the soft material and interference fit support core required by this invention.

[0053] Results: During the rotary forging process, due to the clearance fit, the mandrel could not provide effective support, and the inner wall of the conical surface still showed slight collapse. After rotary forging, the mandrel was stuck inside due to the shrinkage of the tube end. Since both the steel mandrel and the tube were rigid materials, the shrinkage of the tube end after rotary forging generated a clamping force, making it impossible to remove the mandrel. Forcibly removing it would damage the inner wall, resulting in the scrapping of the part.

[0054] Comparative Example 3 This comparative example is basically the same as Example 1, except that: in step two, the outer diameter of the support core is Φ12.25mm, which is 0.05mm larger than the inner diameter of the tube (Φ12.2mm) and smaller than the lower limit of the difference between the outer diameter of the support core and the inner diameter of the straight tube (0.1mm).

[0055] Results: During rotary forging, due to insufficient interference, the support core did not fit tightly against the inner wall of the tube, failing to provide effective support. Slight collapse occurred on the inner wall of the conical surface, and coaxiality exceeded tolerance. This indicates that an interference of less than 0.1 mm cannot guarantee processing quality.

[0056] Comparative Example 4 This comparative example is basically the same as Example 1, except that: in step two, the cone angle of the guide cone surface of the supporting core is 165°, which is less than the lower limit of the cone angle of 170°.

[0057] Results: During rotary forging, due to an excessively small guide cone angle, the material flow was not adequately guided, resulting in misalignment between the formed cone surface and the centerline of the tube, leading to excessive coaxiality. This indicates that a guide cone angle less than 170° cannot guarantee the coaxiality requirement.

[0058] Comparative Example 5 This comparative example is basically the same as Example 1, except that the annealing temperature in step three is 750°C, which is lower than the lower limit of the annealing temperature of 800°C.

[0059] Results: During rotary forging, due to insufficient material plasticity, micro-cracks appeared at the ends of the tubes, affecting product quality. This indicates that annealing temperatures below 800℃ cannot guarantee material plasticity.

[0060] The tapered tube processing method and support core provided in this invention can be widely used in the precision processing of slender tapered tube parts such as aero-engine sensor nozzles, hydraulic pipe joints, and instrument connecting pipes. It is especially suitable for difficult-to-machine materials such as stainless steel and titanium alloys, and has significant economic and social benefits.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for machining tapered tubes, characterized in that, Includes the following steps: Prefabricated straight pipe material, wherein the outer diameter and inner diameter of the straight pipe material are consistent with the dimensions of the non-tapered section of the tapered pipe part to be processed; The support core is made of a soft material, and the outer diameter of the support core is larger than the inner diameter of the straight tube to form an interference fit. Insert the support core into one end of the straight tube; The end of the tube with the inserted support core is forged by rotary forging to form a conical surface. Remove the support core located inside the pipe; The conical surface is then precision machined.

2. The tapered tube processing method according to claim 1, characterized in that, The Brinell hardness of the soft material is ≤30HBW.

3. The tapered tube processing method according to claim 2, characterized in that, The soft material is aluminum or an aluminum alloy.

4. The tapered tube processing method according to claim 1, characterized in that, The outer diameter of the support core is 0.1mm-0.5mm larger than the inner diameter of the straight tube.

5. The tapered tube processing method according to claim 1, characterized in that, The supporting core has a symmetrical structure at both ends, with guide cones at both ends, and the cone angle of the guide cones is 170°-178°.

6. The tapered tube processing method according to claim 1, characterized in that, It also includes the step of annealing the straight tube material.

7. The tapered tube processing method according to claim 6, characterized in that, The annealing process is vacuum annealing, with an annealing temperature of 800℃-900℃ and a holding time of 1-3 hours.

8. The tapered tube processing method according to claim 1, characterized in that, The method for removing the support core located inside the tube is by turning.

9. A support core for use in the tapered tube processing method according to any one of claims 1-8, characterized in that, The support core is made of a soft material with a Brinell hardness ≤30HBW, and its outer diameter is configured to form an interference fit with the inner hole of the tube to be processed. Symmetrical guide cone surfaces are provided at both ends.

10. The supporting core according to claim 9, characterized in that, The cone angle of the guide cone surface is 170°-178°.

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