Composite strengthening process of force bearing hole and force bearing hole obtained through composite strengthening process

Abstract

The invention relates to a composite strengthening process of a bearing hole and the bearing hole obtained through the composite strengthening process. The composite strengthening technology of the force bearing hole comprises the steps that S1, the hole wall of the force bearing hole of a workpiece is strengthened through an extrusion strengthening technology; and S2, the force bearing hole edge of the workpiece obtained after the step S1 is completed is strengthened through the ultrasonic strengthening technology. According to the method, the residual compressive stress is introduced into the hole wall of the bearing hole through the extrusion strengthening process, initiation and extension of hole wall cracks are inhibited, and the fatigue life of the bearing hole is prolonged. On the basis of extrusion strengthening, the residual compressive stress is introduced to the hole edge of the bearing hole through the ultrasonic strengthening process, insufficient residual compressive stress of the hole edge is compensated, and the fatigue life of the bearing hole is further prolonged.

Description

Technical Field

[0001] This article relates to the fields of surface strengthening technology and fatigue resistance technology, and in particular to an extrusion-ultrasonic composite strengthening process for load-bearing holes and the load-bearing holes obtained therefrom. Background Technology

[0002] Numerous perforated components exist in shipbuilding, automotive, and aerospace industries, and these perforations are often load-bearing holes. Because the geometric strength of these holes is relatively weak, they are prone to fatigue failure under external forces. Especially in extreme service environments, load-bearing holes operate under high loads and high frequencies, making them more susceptible to early fatigue cracking. Statistics show that 70% of fatigue cracks in aircraft structures originate from load-bearing holes; therefore, improving the fatigue life of load-bearing holes is crucial for extending the service life of aerospace equipment.

[0003] To improve the fatigue performance of load-bearing holes, surface strengthening processes such as extrusion and bushing extrusion are used to introduce residual compressive stress into the hole walls. Surface residual compressive stress can resist external tensile stress and effectively inhibit crack initiation and propagation. Therefore, the introduction of surface residual compressive stress can effectively improve the fatigue life of load-bearing holes. However, the residual compressive stress at the hole edge is relatively low after extrusion, and material accumulation occurs at the hole opening. Stress concentration easily occurs at the chamfer of the hole edge, leading to the initiation and propagation of fatigue cracks at the hole edge. Ultrasonic strengthening processes can introduce residual compressive stress into the hole opening using a suitable tool head. The tool head vibrates at high frequency under the drive of an ultrasonic shank. The tool head impacts the hole edge, causing severe plastic deformation, thereby introducing residual compressive stress into the hole edge and compensating for the insufficient residual compressive stress at the hole edge. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0005] This application provides a composite strengthening process for load-bearing holes, which introduces residual compressive stress into the hole edge and hole wall to improve the surface integrity of the hole and further improve the fatigue life of the load-bearing hole.

[0006] To achieve the above objectives, this application provides a composite reinforcement process for load-bearing holes, comprising the following steps: S1: The wall of the load-bearing hole in the workpiece is strengthened by extrusion strengthening process; S2: The edge of the load-bearing hole in the workpiece in step S1 is strengthened by ultrasonic strengthening process.

[0007] In one exemplary embodiment, in step S1, the extrusion strengthening process is a mandrel extrusion process.

[0008] In one exemplary embodiment, step S1 includes: S11: Lubricate the surface of the borehole wall; S12: Provide an extrusion device, the extrusion device including a press, a mandrel and tooling; install the workpiece on the extrusion device, and center the bearing hole to ensure that the mandrel is coaxial with the bearing hole; S13: Start the extrusion device so that the mandrel passes through the bearing hole at a constant speed under the drive of the press, thereby strengthening the hole wall of the bearing hole.

[0009] In one exemplary embodiment, in step S11, a lubricant is applied to the surface of the borehole wall for lubrication.

[0010] In one exemplary embodiment, the lubricant includes, but is not limited to, glass paste, graphite, molybdenum disulfide, and mineral oil; preferably, it is molybdenum disulfide.

[0011] In one exemplary embodiment, the mandrel has a taper of 2° to 6° and a working section length of 7.5-15 mm.

[0012] In one exemplary embodiment, in step S13, the interference of the extrusion strengthening process is 1%-3%, and the extrusion speed is 0.1-1 mm / s.

[0013] In one exemplary embodiment, in step S1, the extrusion strengthening process may also be bushing extrusion, ball extrusion, or multi-energy field assisted extrusion.

[0014] In one exemplary embodiment, in step S2, the ultrasonic strengthening process is an ultrasonic rolling process.

[0015] In one exemplary embodiment, step S2 includes: S21: Install the extruded and strengthened workpiece on a machine tool and center the load-bearing hole; S22: A chamfering device is provided, which performs a chamfering operation on the opening of the load-bearing hole under the drive of a machine tool; S23: Switch the chamfering device to an ultrasonic rolling chamfering device. The ultrasonic rolling chamfering device includes a tool head, an ultrasonic shank, a wireless transmission device, and an ultrasonic generator. The tool head is first pressed down along the hole axis to the pre-pressing depth under the drive of the machine tool. Then the ultrasonic rolling chamfering device is started. The tool head rotates and vibrates at a constant speed under the drive of the ultrasonic shank to complete the strengthening of the hole edge of the load-bearing hole.

[0016] In an exemplary embodiment, in step S22, the chamfering device is a chamfering cutter, and the chamfering operation is that the chamfering cutter rotates under the drive of the machine tool and feeds vertically downward along the hole axis to complete the chamfering of the edge of the load-bearing hole.

[0017] In one exemplary embodiment, in step S23, the pre-compression depth is 5-50 μm and the rotation speed is 50-300 r / min.

[0018] In one exemplary embodiment, the tool head has an inclination angle α of 30° to 60° and a length of 20-60 mm.

[0019] In one exemplary embodiment, in step S23, the vibration frequency is 18kHz-22kHz, the amplitude is 5-15μm, and the vibration time is 3-12s.

[0020] In one exemplary embodiment, in step S2, the ultrasonic strengthening process can also be ultrasonic hammering, ultrasonic impact, or multi-energy field assisted ultrasonic strengthening, etc.

[0021] In one exemplary embodiment, the diameter of the load-bearing hole is 10mm-50mm and the thickness is 5mm-40mm.

[0022] In one exemplary embodiment, the material of the workpiece may be a soft or hard alloy, such as an aluminum alloy or a titanium alloy.

[0023] The second aspect of this application provides a load-bearing hole obtained through the above-described composite strengthening process.

[0024] A third aspect of this application provides a workpiece having the aforementioned load-bearing hole.

[0025] Compared with existing related technologies, this application has the following beneficial effects: (1) This application first introduces residual compressive stress into the hole wall of the load-bearing hole through extrusion strengthening process, which inhibits the initiation and propagation of hole wall cracks and improves the fatigue life of the load-bearing hole; (2) Based on extrusion strengthening, this application introduces residual compressive stress at the edge of the load-bearing hole through ultrasonic strengthening process to compensate for insufficient residual compressive stress at the edge of the hole and further improve the fatigue life of the load-bearing hole.

[0026] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the embodiments described in the description and the accompanying drawings. Attached Figure Description

[0027] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0028] Figure 1 This is a flowchart of the composite reinforcement process for the load-bearing holes in this application; Figure 2 This is a schematic diagram showing the distribution of residual compressive stress layer on the surface of the load-bearing hole after the composite strengthening process of the load-bearing hole in this application. Figure 3 This is a schematic diagram of the extrusion strengthening process of this application; Figure 4 This is a schematic diagram of the chamfering operation in this application; Figure 5 This is a schematic diagram of the ultrasonic rolling chamfering operation of this application; Figure 6 The number of fatigue cycles for different groups of load-bearing holes.

[0029] Figure label: 1-Cross-section of the workpiece after mandrel extrusion; 2-Residual compressive stress layer after mandrel extrusion; 3-Cross-section of the workpiece after ultrasonic rolling chamfering operation; 4-Residual compressive stress layer after ultrasonic rolling chamfering operation; 5-Mandrel; 6-Workpiece to be extruded by mandrel; 7-Chamfering tool; 8-Workpiece to be chamfered; 9-Tool head; 10-Workpiece to be ultrasonically rolled chamfered. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] The preferred embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely illustrative and is not intended to limit the scope and application of the present invention.

[0032] like Figure 1 As shown in the embodiment of this application, a composite reinforcement process for load-bearing holes includes the following steps: S1: The wall of the load-bearing hole is strengthened by extrusion strengthening process; S2: The edge of the load-bearing hole after step S1 is strengthened by ultrasonic strengthening process.

[0033] Figure 2 This diagram illustrates the distribution of residual compressive stress layer on the surface of the bearing hole after the composite strengthening process described in this application. First, this application employs an extrusion strengthening process to reinforce the hole wall, introducing a residual compressive stress layer of a certain thickness. Then, based on the extrusion strengthening process, an ultrasonic strengthening process is used to strengthen the hole edge, further introducing residual compressive stress into the hole edge to compensate for the insufficient residual compressive stress at the hole edge after extrusion. This results in a more uniform residual compressive stress on the bearing hole surface, further improving the fatigue life of the bearing hole.

[0034] In this embodiment of the application, in step S1, the extrusion strengthening process is a mandrel extrusion process.

[0035] like Figure 3 As shown, in step S1, the extrusion strengthening process includes the following steps: S11: Lubricate the surface of the bearing hole wall of the workpiece to be extruded; S12: Provide an extrusion device, which includes a press, a mandrel, and tooling; install the workpiece to be extruded on the extrusion device, align the bearing hole, and ensure that the mandrel is coaxial with the bearing hole; S13: Start the extrusion device so that the mandrel passes through the bearing hole at a constant speed under the drive of the press, thereby strengthening the wall of the bearing hole.

[0036] In this embodiment, step S11 requires applying a lubricant to the surface of the bearing hole wall of the workpiece to be extruded. The lubricant includes, but is not limited to, glass paste, graphite, molybdenum disulfide, and mineral oil; this application does not limit the type of lubricant. Given that molybdenum disulfide has excellent lubricating properties, mixing it with alcohol and applying it repeatedly to the hole wall can reduce extrusion friction and improve the surface quality of the hole wall after extrusion. Molybdenum disulfide is preferred as the lubricant.

[0037] In this embodiment of the application, the size of the mandrel can be designed according to the actual working conditions. The taper of the mandrel is 2° to 6° and the length of the working section is 7.5-15mm.

[0038] The parameters of the extrusion process can be controlled according to the actual working conditions. For example, extruding aluminum alloy workpieces requires a smaller interference fit, while extruding titanium alloy workpieces requires a larger interference fit. In the embodiments of this application, the interference fit of the extrusion strengthening process is 1%-3%, and the extrusion speed is 0.1-1 mm / s.

[0039] In a preferred embodiment of this application, the interference of the extrusion strengthening process is 1% or 2%, and the extrusion speed is 0.1 mm / s.

[0040] In the embodiments of this application, the extrusion strengthening process in step S1 can also be bushing extrusion, ball extrusion, and multi-energy field assisted extrusion, etc., and this application does not limit it.

[0041] In this embodiment of the application, the ultrasonic strengthening process in step S2 is an ultrasonic rolling process.

[0042] like Figures 4 to 5 As shown, in step S2, the ultrasonic strengthening process includes: S21: Mount the extrusion-strengthened workpiece on the machine tool and center the load-bearing holes to be ultrasonically strengthened to ensure uniform processing. S22: A chamfering device is provided, which performs a chamfering operation on the load-bearing hole under the drive of a machine tool to remove material accumulation at the edge of the hole and reduce stress concentration; S23: Switch the chamfering device to an ultrasonic rolling chamfering device, which includes a tool head, an ultrasonic shank, a wireless transmission device, and an ultrasonic generator; the tool head is first pressed down along the hole axis to the pre-pressing depth under the drive of the machine tool, and then the ultrasonic rolling chamfering device is started. The tool head rotates and vibrates at a uniform speed under the drive of the ultrasonic shank, completing the strengthening of the hole edge of the load-bearing hole (see...). Figure 4 ).

[0043] In this embodiment, the chamfering device is a chamfering cutter, and the chamfering operation involves the chamfering cutter rotating under the drive of the machine tool and vertically feeding downwards along the hole axis to chamfer the edge of the load-bearing hole (see...). Figure 5 ).

[0044] In this embodiment of the application, the chamfering device has an inclination angle α of 30° to 60°.

[0045] In this embodiment of the application, the size of the tool head can be designed according to the actual working conditions. The inclination angle of the tool head is 30° to 60° and the length is 20-60mm.

[0046] In step S23, the processing parameters of the ultrasonic rolling chamfering operation can be controlled according to the actual working conditions. For example, ultrasonic rolling of aluminum alloy workpieces requires a smaller amplitude, while ultrasonic rolling of titanium alloy workpieces requires a larger amplitude. In the embodiments of this application, the pre-pressing depth is 5-50 μm, the rotation speed is 50-300 r / min, the vibration frequency is 18 kHz-22 kHz, the amplitude is 5-15 μm, and the vibration time is 3-12 s.

[0047] In the embodiments of this application, the ultrasonic strengthening process can also be ultrasonic hammering, ultrasonic impact, ultrasonic rolling, and multi-energy field assisted ultrasonic strengthening, etc., and the present invention does not limit it.

[0048] The following section selects 7050 aluminum alloy as the research object, and strengthens the workpiece using the composite strengthening process and the mandrel extrusion strengthening process alone, as described in the embodiments of this application. Fatigue tests are then performed on the workpieces before and after strengthening, with an ultimate stress of 178 MPa. The cycle count of the workpieces after different treatment processes is compared to verify the strengthening effect of the composite strengthening process of this application.

[0049] The workpieces are categorized into three groups: Group 1 consists of unstrengthened workpieces; Groups 2 and 4 consist of workpieces processed only using the mandrel extrusion process; and Groups 3 and 5 consist of workpieces strengthened using the composite strengthening process described in this application. In the extrusion process, the mandrel has a front taper of 2°, a rear taper of 2°, and a working section length of 15mm. In the ultrasonic strengthening process, the tool head tilt angle α is 45°, the tool head length is 25mm, the pre-pressure speed is 100rpm, the vibration frequency is 18kHz, and the vibration time is 3s. In each group, the bearing hole diameter is 20mm and the thickness is 15mm. Specific processing parameters are shown in Table 1 below, and the test results are shown in [Table 1]. Figure 6 .

[0050] Table 1 Grouping by different processing techniques Figure 6 The fatigue cycle counts for different groups are given. The figure shows that the fatigue cycle counts for groups 2, 3, 4, and 5 are all higher than that of group 1, indicating that the fatigue life of the workpiece's load-bearing holes is improved after strengthening through the strengthening process. Comparing groups 2 and 3, and groups 4 and 5, it is clear that group 3 has a higher cycle count than group 2, while group 5 has a higher cycle count than group 4. This indicates that the fatigue life of the workpiece strengthened using the composite strengthening process of this application embodiment is higher than that of the workpiece strengthened using only the mandrel extrusion process. The ultrasonic rolling process can further improve the fatigue life of the load-bearing holes based on the mandrel extrusion process. Comparing groups 3 and 5, it is clear that group 5 has a higher cycle count than group 3, indicating that appropriately increasing the strengthening parameters can further improve the fatigue life of the load-bearing holes.

[0051] In summary, the composite strengthening process of hole wall extrusion strengthening and hole edge ultrasonic strengthening provided in this application embodiment first strengthens the hole wall of the load-bearing hole by mandrel extrusion, and then strengthens the hole edge of the load-bearing hole by ultrasonic rolling strengthening on the basis of extrusion strengthening, which compensates for the insufficient residual compressive stress on the hole edge of the load-bearing hole after extrusion, making the residual compressive stress on the hole surface more uniform and further improving the fatigue life of the load-bearing hole.

[0052] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, various substitutions or modifications can be made to these described structures without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., refers to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in the embodiments or examples of the present invention.

[0053] Although embodiments of the invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the scope defined by the appended claims.

Claims

1. A composite strengthening process of a load-bearing hole, comprising the following steps: S1: strengthening the hole wall of the load-bearing hole of a workpiece by an extrusion strengthening process; S2: strengthening the hole edge of the load-bearing hole of the workpiece in step S1 by an ultrasonic strengthening process; In step S2, the ultrasonic strengthening process is an ultrasonic rolling process, comprising: S21: centering the load-bearing hole by installing the workpiece after extrusion strengthening on a machine tool; S22: providing a chamfering device, which is driven by the machine tool to perform chamfering operation on the hole edge of the load-bearing hole; S23: switching the chamfering device to an ultrasonic rolling chamfering device, which comprises a tool head, an ultrasonic tool holder, a wireless transmission device and an ultrasonic generator; the tool head is first pressed downward to a pre-pressing depth along the hole axis under the drive of the machine tool, and then the ultrasonic rolling chamfering device is started, the tool head rotates and vibrates at a constant speed under the drive of the ultrasonic tool holder, and the hole edge strengthening of the load-bearing hole is completed.

2. The composite stiffening process of force holes according to claim 1, wherein, In step S1, the extrusion strengthening process is a mandrel extrusion process, comprising: S11: lubricating the surface of the hole wall of the load-bearing hole; S12: providing an extrusion device, which comprises a press, a mandrel and a tooling; the workpiece is installed on the extrusion device, the load-bearing hole is centered, and the mandrel is ensured to be coaxial with the load-bearing hole; S13: starting the extrusion device, and the mandrel is driven by the press to uniformly pass through the load-bearing hole, and the hole wall strengthening of the load-bearing hole is completed.

3. The process for composite reinforcement of force holes as claimed in claim 2 wherein, In step S11, the surface of the hole wall of the load-bearing hole is coated with a lubricant for lubrication; Optionally, the lubricant is glass paste, graphite, molybdenum disulfide or mineral oil.

4. The process for composite reinforcement of force holes as claimed in claim 2 wherein, The taper of the mandrel is 2° to 6°, and the working section length is 7.5-15mm.

5. The process for composite reinforcement of force holes as claimed in claim 2 wherein, In step S13, the interference amount of the extrusion strengthening process is 1%-3%, and the extrusion speed is 0.1-1mm / s.

6. The composite stiffening process of force holes according to any one of claims 1 to 5, wherein, In step S22, the chamfering device is a chamfering cutter, and the chamfering operation is that the chamfering cutter rotates and vertically feeds downward along the hole axis under the drive of the machine tool to complete the chamfering of the hole edge of the load-bearing hole.

7. The composite stiffening process of force holes according to any one of claims 1 to 5, wherein, In step S23, the inclination angle α of the tool head is 30° to 60°, and the length is 20-60mm; and / or In step S23, the pre-pressing depth is 5-50μm, and the rotating speed is 50-300r / min; and / or In step S23, the vibration frequency is 18kHz-22kHz, the amplitude is 5-15μm, and the vibration time is 3-12s.

8. The composite stiffening process of force holes according to any one of claims 1 to 5, wherein, In step S1, the extrusion strengthening process can also be bushing extrusion, ball extrusion or multi-energy field assisted extrusion; and / or In step S2, the ultrasonic strengthening process can also be ultrasonic hammering, ultrasonic impact or multi-energy field assisted ultrasonic strengthening; and / or The diameter of the load-bearing hole is 10mm-50mm, and the thickness is 5mm-40mm. 9.A load-bearing hole obtained by the composite strengthening process of a load-bearing hole according to any one of claims 1 to 8.

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