Cold extrusion strengthening device and method for non-circular hole slotted lining

Abstract

The invention belongs to the technical field of part surface treatment, and particularly relates to a non-circular hole slotted lining cold extrusion strengthening device and method. Comprising a slotted bushing (1), an extrusion head (2), a nose top cap (3), a high-strength bolt (4), a nut (5) and a base (6), the slotted bushing (1) is mounted in a non-circular hole of a part (7) to be reinforced, the extrusion head (2) is mounted in the slotted bushing (1), the nose top cap (3) is mounted at the bottom end of the extrusion head (2), the nut (5) is fixed on the base (6), and the high-strength bolt (4) sequentially penetrates through the extrusion head (2) and the nose top cap (3) to be fixedly connected with the nut (5), so that the base (6) is attached to the nose top cap (3). The method mainly aims at strengthening requirements of non-circular holes, and can realize cold extrusion strengthening of slotted bushings of non-circular holes such as turbine disc air-entraining holes so as to prolong the fatigue life of the slotted bushings; and the stress point of the extrusion head can be accurately controlled through bolt driving, so that the strengthening effect of a fatigue weak area is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology for parts, and specifically relates to a cold extrusion strengthening device and method for non-circular hole slotted bushings. Background Technology

[0002] Currently, high-pressure compressor discs are subjected to centrifugal loads, vibration loads, and temperature during service. Areas such as bleed holes exhibit significant stress concentration, making them prone to fatigue crack initiation. Under complex loads, these cracks can propagate, potentially leading to disc failure and jeopardizing engine service safety. Therefore, long-life connection processes must be implemented in engine design and manufacturing to prevent initial cracks at fastening holes and slow crack propagation, which is crucial for improving engine lifespan. Hole extrusion strengthening technology is the most effective method for improving hole structure. It involves continuously and uniformly extruding the hole with a mandrel (or mandrel + bushing) with a certain interference fit, creating an elastic-plastic deformation layer around the hole. After hole extrusion strengthening, a deep residual compressive stress layer greater than 1 mm is generated at the hole edge. Based on strain hardening, deformed structures are introduced, and the residual compressive stress value of the hole wall is reduced. Through these strengthening mechanisms, the fatigue strength of the hole structure can be significantly improved. This technology has been widely used in circular holes such as aircraft and engine bolt holes, but research on non-circular holes such as bleed holes is still limited. Therefore, there is an urgent need for a technology that can strengthen non-circular holes through extrusion.

[0003] Patent CN202011447830.0 discloses a process for strengthening assembly holes using a slotted mandrel through cold extrusion. It proposes using a slotted mandrel to strengthen the assembly holes through cold extrusion, aiming to achieve reusability of the mandrel, improve extrusion efficiency, and increase the extrusion volume. Patent CN202411326151.6 discloses a device and method for strengthening holes by cold extrusion of a slotted bushing. It proposes that the insertion length of the mandrel can be precisely adjusted using a distance adjustment component and a distance measuring assembly, making it applicable to cold extrusion strengthening of holes of different depths. This allows for loading of hole walls at different depths without causing impact damage to the machine body, providing versatility for cold extrusion. However, the above methods for strengthening holes by cold extrusion of slotted bushings have limitations; they can only strengthen circular holes and cannot meet the requirements for strengthening non-circular holes such as turbine disk bleed holes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a cold extrusion strengthening device and method for non-circular hole slotted bushings, so as to solve the strengthening requirements for non-circular holes such as air vents, and to complete the cold extrusion strengthening of non-circular hole slotted bushings.

[0005] To solve the above technical problems, the present invention adopts the following technical solution: a cold extrusion strengthening device for a non-circular hole slit bushing, comprising a slit bushing 1, an extrusion head 2, a nose cap 3, a high-strength bolt 4, a nut 5, and a base 6; the slit bushing 1 is installed inside the non-circular hole of the workpiece 7 to be strengthened, the extrusion head 2 is installed inside the slit bushing 1, the nose cap 3 is installed at the bottom end of the extrusion head 2, the nut 5 is fixed on the base 6, and the high-strength bolt 4 passes through the extrusion head 2 and the nose cap 3 in sequence and is fixedly connected to the nut 5, so that the base 6 and the nose cap 3 fit together.

[0006] The slit bushing 1, when opened, has a shape consistent with the non-circular hole of the part 7 to be reinforced, and has a slit with a width of no more than 2mm. The slit direction should be non-fatigue weak direction, and there should be a curl at the tail with a length of no more than 1mm.

[0007] The slotted bushing 1 is made of 1 / 4 or full hard stainless steel strip, with a strip thickness between 0.15 and 0.6 mm.

[0008] The preparation method of the slotted bushing 1 is as follows: after the inner surface of the steel strip is sandblasted, a layer of tightly bonded lubricant is applied by spraying or rolling. After heat curing, it is plastically formed into the required shape and size.

[0009] The extrusion head 2 has the same shape as the non-circular hole of the part to be strengthened 7, and has a taper of 1:40 to 1:2.

[0010] The small end of the extrusion head 2 is smaller than the size of the non-circular hole minus double the bushing thickness, and the large end is larger than the size of the non-circular hole minus double the bushing thickness. The extra size is the interference, which should be between 0.05 and 0.50 mm.

[0011] The extrusion head 2 is made of high-strength steel.

[0012] The base 6 has a hole with the same shape and size as the nut 5 to restrict its rotation during the extrusion process.

[0013] The nose cap 3 has a barrel-shaped structure with a hole at the center of the bottom end face, through which the high-strength bolt 4 is connected to the nut 5.

[0014] The method for cold extrusion strengthening of non-circular hole slotted bushings using the above-mentioned cold extrusion strengthening device is characterized by the following strengthening steps: 1) Fix the part 7 to be strengthened on the fixture, with the curled end of the slotted bushing 1 in front, and slowly push it into the small end of the extrusion head 2. Push the extrusion head 2 equipped with the slotted bushing 1, with the small end in front, into the non-circular hole of the part 7 to be strengthened. 2) Assemble the nose cap 3 and the extrusion head 2 with high-strength bolts 4 and nuts 5, and fix them on the base 6, so that the base 6 and the nose cap 3 fit together. 3) At the same time, slowly twist all the high-strength bolts 4 (generally 1 to 4 depending on the shape of the non-circular hole to be strengthened), so that the extrusion head 2 slowly moves downward to open the bushing, and at the same time, the non-circular hole to be strengthened undergoes plastic deformation until the extrusion head passes through the hole to be strengthened. 4) Slowly remove the slotted bushing 1 from the non-curled side and mill the reinforcing hole to the final size.

[0015] Compared with the prior art, the present invention has the following advantages: The present invention is mainly aimed at the strengthening needs of non-circular holes, and can realize the cold extrusion strengthening of slotted bushings such as turbine disk air vents to improve their fatigue life; the bolt drive can precisely control the force point of the extrusion head to ensure the strengthening effect of fatigue weak areas. Attached Figure Description

[0016] Figure 1 This is a structural diagram of the tooling of the present invention; Figure 2 For non-circular holes to be reinforced; Figure 3 Schematic diagram of a non-circular hole slotted bushing; Figure 4 Schematic diagram of the extrusion head Figure 5 This is a schematic diagram of a non-circular hole after reinforcement. Figure 6 To enhance the distribution of residual stress deep within the post-hole layer.

[0017] Among them: 1-slotted bushing, 2-extrusion head, 3-nose cap, 4-high-strength bolt, 5-nut, 6-base, 7-part to be reinforced. Detailed Implementation The present invention will now be described in detail with reference to the accompanying drawings and specific examples. The main steps are as follows: A cold extrusion strengthening device for non-circular hole slotted bushings, such as Figure 1 As shown, the assembly includes a slotted bushing 1, an extrusion head 2, a nose cap 3, a high-strength bolt 4, a nut 5, and a base 6. The slotted bushing 1 is installed inside the non-circular hole of the workpiece 7 to be strengthened. The extrusion head 2 is installed inside the slotted bushing 1. The nose cap 3 is installed at the bottom end of the extrusion head 2. The nut 5 is fixed to the base 6. The high-strength bolt 4 passes through the extrusion head 2 and the nose cap 3 in sequence and is fixedly connected to the nut 5, so that the base 6 fits snugly against the nose cap 3. In this example, the workpiece to be strengthened is a high-temperature alloy elliptical hole. The initial hole's minor axis length L is 7mm, the major axis length M is 21mm, and the hole diameter is 4mm. The specific shape and dimensions are as follows. Figure 2 As shown.

[0018] The slit bushing 1, after being opened, has a shape consistent with the non-circular hole of the component 7 to be reinforced, and has a slit with a width of no more than 2 mm. The slit direction is in the minor axis direction, and there is a curl at the tail with a length of no more than 1 mm. Figure 3As shown, the material of the slotted bushing 1 is a full-hardness stainless steel strip with a thickness of 0.3mm. The preparation method of the slotted bushing 1 is as follows: after sandblasting the inner surface of the steel strip, a layer of tightly bonded lubricant is applied by spraying or roller coating. After heat curing, it is plastically formed into its final shape and size. The extrusion head 2 is made of 300M high-strength steel, and its shape is an ellipse consistent with the non-circular hole of the part to be strengthened 7, with a taper of 1:20. The short axis of the small end is 6.2mm, and the long axis is 19.2mm. Both dimensions are smaller than the dimensions of the non-circular hole minus double the bushing thickness (short axis is 6.4mm, long axis is 19.4mm). The short axis of the large end is 6.7mm, and the long axis is 19.7mm. Both dimensions are larger than the dimensions of the non-circular hole minus double the bushing thickness (short axis is 6.4mm, long axis is 19.4mm). The extra 0.3mm is the interference fit, as shown in the figure. Figure 4 As shown; the extrusion head 2 and the nose cap 3 are connected by a high-strength bolt 4; the nut 5 is fixed to the base 6, and the base 6 has a hole with the same shape and size as the nut 5 to restrict its rotation during the extrusion process. The nose cap 3 has a barrel-shaped structure with a hole at the center of its bottom end face, through which the high-strength bolt 4 is connected to the nut 5.

[0019] The cold extrusion strengthening method for non-circular hole slotted bushings using the aforementioned cold extrusion strengthening device comprises the following strengthening steps: 1) Fix the part 7 to be strengthened on the fixture, with the curled end of the slotted bushing 1 in front, and slowly push it into the small end of the extrusion head 2. Push the extrusion head 2 equipped with the slotted bushing 1, with the small end in front, into the non-circular hole of the part 7 to be strengthened, until the slotted bushing 1 and the extrusion head 2 are both in the non-circular hole and it is difficult to push them forward. 2) Bolt holes are present at both ends of the extrusion head, such as... Figure 2 As shown, bolt holes are also present at the corresponding positions of the nose cap 3. The nose cap 3 is assembled with the extrusion head 2 by two high-strength bolts 4 and nuts 5, and fixed to the base 6, so that the base 6 and the nose cap 3 fit together. 3) Simultaneously, slowly twist the two high-strength bolts 4, causing the extrusion head 2 to slowly move downwards, opening the bushing, and causing the non-circular hole to be strengthened to undergo plastic deformation until the extrusion head passes through the hole to be strengthened. The rotation speed of the two high-strength bolts 4 must be consistent, and the difference in the number of twists must not exceed half a turn.

[0020] 4) Slowly remove the slotted bushing 1 from the non-curled side. After compression, a slot left by the slotted bushing 1 remains on the inner wall of the non-circular hole. The short axis undergoes plastic deformation to 7.25 mm, and the long axis undergoes plastic deformation to 21.25 mm, as detailed below. Figure 5 As shown by the dashed line. Finally, the reinforced non-circular hole is milled to the final hole size, an elliptical hole with a minor axis length of 8mm and a major axis length of 22mm.

[0021] Furthermore, to verify the strengthening effect, a finite element analysis was performed on the residual stress after strengthening, and the residual stress distribution in the four directions (ABCD) of the inner hole before and after strengthening was obtained as follows: Figure 6 As shown, after strengthening, large residual compressive stresses are introduced in all directions of the inner hole, and the depth of residual compressive stresses in the fatigue weak areas that need to be strengthened is more than 1.5 mm.

[0022] The embodiments described above are merely preferred embodiments of the present invention, and not an exhaustive list of all possible implementations of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A cold extrusion strengthening device for non-circular hole slotted bushings, characterized in that; It includes a slotted bushing (1), an extrusion head (2), a nose cap (3), a high-strength bolt (4), a nut (5), and a base (6); the slotted bushing (1) is installed inside the non-circular hole of the part to be reinforced (7), the extrusion head (2) is installed inside the slotted bushing (1), the nose cap (3) is installed at the bottom of the extrusion head (2), the nut (5) is fixed on the base (6), and the high-strength bolt (4) passes through the extrusion head (2), the nose cap (3), and the nut (5) in sequence to fix and connect, so that the base (6) fits against the nose cap (3).

2. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The slit bushing (1) has a shape consistent with the non-circular hole of the part to be reinforced (7) after being opened, and there is a slit with a width of no more than 2mm. The slit direction should be non-fatigue weak direction, and there is a curl at the tail with a length of no more than 1mm.

3. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The material of the slotted bushing (1) is 1 / 4 or full hard stainless steel strip, and the thickness of the steel strip is between 0.15 and 0.6 mm.

4. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The preparation method of the slotted bushing (1) is as follows: after the inner surface of the steel strip is sandblasted, a layer of tightly bonded lubricant is applied by spraying or rolling. After heat curing, it is plastically formed into the required shape and size.

5. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The extrusion head (2) has the same shape as the non-circular hole of the part to be strengthened (7) and has a taper of 1:40 to 1:

2.

6. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The small end of the extrusion head (2) is smaller than the size of the non-circular hole minus double the bushing thickness, and the large end is larger than the size of the non-circular hole minus double the bushing thickness. The extra size is the interference, which should be between 0.05 and 0.50 mm.

7. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The extrusion head (2) is made of high-strength steel.

8. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The base (6) has a hole with the same shape and size as the nut (5) to restrict its rotation during the extrusion process.

9. The cold extrusion strengthening device for non-circular hole slotted bushings according to claim 1, characterized in that; The nose cap (3) has a barrel-shaped structure with a hole at the center of the bottom end face. The high-strength bolt (4) is connected to the nut (5) through the hole.

10. The method for cold extrusion strengthening of non-circular hole slotted bushings using the cold extrusion strengthening device according to any one of claims 1-9, characterized in that, The enhancement steps are as follows: 1) Fix the part to be strengthened (7) on the fixture, with the curled end of the slit bushing (1) in front, slowly push it into the small end of the extrusion head (2), and push the extrusion head (2) equipped with the slit bushing (1) with the small end in front into the non-circular hole of the part to be strengthened (7). 2) The nose cap (3) and the extrusion head (2) are assembled by high-strength bolts (4) and nuts (5) and fixed on the base (6), so that the base (6) and the nose cap (3) fit together; 3) At the same time, slowly twist all the high-strength bolts (4) to make the extrusion head (2) slowly move downward to open the bushing, and at the same time make the non-circular hole to be strengthened plastically deformed until the extrusion head passes through the hole to be strengthened; 4) Slowly remove the slotted bushing (1) from the non-curled side and mill the reinforcing hole to the final size.

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