Hollow shaft forging method

Abstract

The invention relates to a hollow shaft forging method. The method comprises the following steps: a blanking procedure: providing a blank; the blank is heated to the temperature within a first preset temperature range and subjected to heat preservation for a first preset time period, the heated blank is transferred to a mold subjected to first preheating operation, and one or more times of upsetting and drawing-out operation are carried out on the blank to obtain a pre-forged piece; and a finish forging process: performing one-heating two-step operation on the pre-forged piece to obtain a final forged piece, including heating the pre-forged piece to a temperature within a second preset temperature range during the one-heating period and preserving heat for a second preset time period, and transferring the heated pre-forged piece to a mold subjected to second preheating operation and performing the two steps to obtain the final forged piece, the two working steps comprise a first working step and a second working step, the first working step enables a first upper punch of the die to press downwards so as to complete forging of the outer contour of the hollow shaft piece, and the second working step enables a second upper punch of the die to press downwards so as to complete forging of the inner contour of the hollow shaft piece.

Description

Technical Field

[0001] The present invention relates to the field of machining and manufacturing, and more particularly to a forging method for a hollow shaft part. Background Art

[0002] In the mechanical field, hollow shaft parts are very common parts. For some large-sized hollow shaft parts (especially those with relatively complex configurations), their machining and manufacturing pose extremely strict requirements on equipment and process control. For example, in a high-bypass turbofan engine, as the bypass ratio of a commercial engine increases, the engine performance increases, and the requirements for reliability and economy also increase. As the configuration size of parts increases and the structure gradually becomes complex, the performance requirements for compressor disk parts increase. Therefore, the performance of parts also places higher requirements on the performance of forgings.

[0003] Currently, in domestic narrow-body airliner engines and military aircraft, the fan shaft forgings usually use C250 steel, and the main processes used are a combined process of open die forging and impression die forging to form the large end and the rod part of the fan shaft forging respectively. The fan shaft of a commercial wide-body airliner engine has a trumpet-shaped hollow structure, with a total length of about 860 mm (millimeters), a maximum outer diameter of about 430 mm at the large end, a minimum inner diameter of about 110 mm at the small end, and an overall wall thickness of about 10 - 50 mm. In order to reduce the weight of wide-body airliner engines, the fan shafts of internationally advanced wide-body engines use titanium alloys, such as Ti-6Al-4V alloy. For wide-body airliner engines, using Ti-6Al-4V alloy instead of C250 alloy can reduce the weight of the fan shaft by about 50%.

[0004] However, for hollow shaft parts with complex configurations, such as fan shafts, they are long in length, large at one end and small at the other end, in a trumpet shape, and have a relatively thick conical wall. Their die forging has extremely strict requirements for equipment, forging temperature, and time control. Moreover, the hot plasticity of Ti-6Al-4V alloy is lower than that of C250, and overly severe deformation will result in too deep surface cracks. Higher requirements are put forward for the heat preservation and lubrication of the billet during the die forging process. The plastic deformation of titanium alloy is worse than that of stainless steel, and the metal fluidity is poor, which may cause uneven deformation of the material along the axial direction, instability at the over-deformed areas, and inability to recrystallize at the under-deformed areas, resulting in poor or unqualified performance consistency. The complexity of the configuration may also cause uneven deformation in each area of the forging or the appearance of deformation dead zones in local positions, leading to unqualified mechanical properties and microstructures.

[0005] Therefore, there is a need in the art for a forging method for shaft parts to improve the deformation uniformity. Summary of the Invention

[0006] To solve the above problems existing in the prior art, the present invention provides a forging method for a hollow shaft member, including: a blanking process: providing a blank; a pre-forging process: heating the blank to a temperature within a first predetermined temperature range and holding for a first predetermined period, and transferring the heated blank to a die that has undergone a first preheating operation and performing one or more upsetting and drawing operations on the blank to obtain a pre-forged part; and a final forging process: performing a 1-fire 2-step operation on the pre-forged part to obtain a final forging, including heating the pre-forged part to a temperature within a second predetermined temperature range and holding for a second predetermined period during 1 fire, and transferring the heated pre-forged part to the die that has undergone a second preheating operation and performing 2 steps, the 2 steps including a first step and a second step, the first step pressing down a first upper punch of the die to complete the forging of the outer contour of the hollow shaft member, and the second step pressing down a second upper punch of the die to complete the forging of the inner contour of the hollow shaft member.

[0007] In one or more embodiments of the present invention, the above forging method for a hollow shaft member further includes performing one or more re-forging processes before the pre-forging process, each re-forging process heating the blank to a temperature within a third predetermined temperature range and holding for a third predetermined period and performing one or more upsetting and drawing operations on the blank.

[0008] In one or more embodiments of the present invention, the above forging method for a hollow shaft member further includes performing a heat treatment process after the final forging process, the heat treatment process performing homogenization heat treatment and / or annealing heat treatment on the final forging.

[0009] In one or more embodiments of the present invention, the above forging method for a hollow shaft member further includes machining the shaft member after one or more of the pre-forging process, the final forging process, and the heat treatment process.

[0010] In one or more embodiments of the present invention, the hollow shaft member is in a trumpet shape.

[0011] In one or more embodiments of the present invention, the hollow shaft member is made of a lightweight material.

[0012] In a preferred embodiment of the present invention, the lightweight material is a Ti-6Al-4V alloy.

[0013] In one or more embodiments of the present invention, the first predetermined temperature range is 940 - 990 °C, the first predetermined period is 270 - 390 minutes, and the first preheating operation heats the die to a temperature greater than or equal to 250 °C.

[0014] In one or more embodiments of the present invention, the second predetermined temperature range is 940 - 990 °C, the second predetermined time period is 270 - 390 minutes, and the second preheating operation heats the die to a temperature greater than or equal to 300 °C.

[0015] In one or more embodiments of the present invention, the third predetermined temperature range is 940 - 990 °C, and the third predetermined time period is 280 - 400 minutes for cold material or 140 - 260 minutes for hot material.

[0016] In one or more embodiments of the present invention, the homogenization heat treatment raises the temperature of the final forging to 940 - 990 °C and holds for 60 - 66 minutes, and then water cooling is performed; the annealing heat treatment raises the temperature of the final forging to 650 - 750 °C and holds for 120 - 132 minutes, and then air cooling is performed.

[0017] In one or more embodiments of the present invention, the first upper punch presses down at a speed of 5 - 15 mm / s, while the second upper punch presses down at a speed of 5 - 10 mm / s.

[0018] In another aspect of the present invention, a hollow shaft part forged by the above method is provided.

[0019] These and other features and aspects of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To be able to understand the present invention in detail, a more specific description of the present invention briefly outlined above can be obtained by referring to the embodiments. Some embodiments are shown in the accompanying drawings. For the sake of facilitating understanding, the same reference numerals have been used as much as possible to label the same elements common to the drawings. However, it should be noted that the drawings only show typical embodiments of the present invention and should not be regarded as limiting the scope of the present invention, because the present invention allows other equivalent embodiments. In the drawings:

[0021] Figure 1 A flowchart of an exemplary method for forging a hollow shaft part according to an embodiment of the present invention is shown.

[0022] Figure 2 A cross-sectional view of an exemplary pre-forging according to an embodiment of the present invention is shown.

[0023] Figure 3 A partial cross-sectional view of an exemplary final forging according to an embodiment of the present invention is shown.

[0024] Figure 4 The distribution of the mechanical properties of a shaft part manufactured by using the method for forging a hollow shaft part according to an embodiment of the present invention is shown.

[0025] Figure 5 The high-magnification microstructural photograph of a shaft manufactured by using a forging method of a hollow shaft according to an embodiment of the present invention is shown.

[0026] Figure 6 The mechanical properties and microstructural photographs at different positions of the body of a shaft manufactured by using a forging method of a hollow shaft according to an embodiment of the present invention are shown.

[0027] It can be expected that the elements in one embodiment of the present invention can be advantageously applied to other embodiments without further elaboration. Detailed Description of the Invention

[0028] The following describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, those skilled in the art should understand that the present invention can be implemented without some or all of these specific details. Therefore, the present invention is not limited by the specific embodiments disclosed below. On the other hand, well-known processes or procedures are not specifically described to avoid unnecessarily obscuring the present invention.

[0029] In addition, it can also be understood that the various embodiments shown in the drawings are illustrative, and the drawings are not necessarily drawn to scale.

[0030] The present invention uses specific terms to describe the embodiments of the present invention. Such as "one embodiment", "an embodiment", and / or "some embodiments" mean a certain feature, structure, or characteristic related to at least one embodiment of the present invention. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more at different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the present invention can be appropriately combined.

[0031] In this document, unless otherwise specified, the technical terms or scientific terms used in the claims and the specification should have the ordinary meaning understood by those of ordinary skill in the technical field to which the present invention belongs. The "first", "second", and similar terms used in the specification and claims of the present invention do not indicate any order, quantity, or importance, but are only used to distinguish different components. The terms such as "comprising" or "including" mean that the elements or objects appearing before "comprising" or "including" cover the elements or objects listed after "comprising" or "including" and their equivalent elements, and do not exclude other elements or objects. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections. In addition, in this document, the use of terms such as "about" or "approximately" means within the range of ±10% of the nominal value.

[0032] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0033] One or more embodiments of the present invention relate to a forging method for a hollow shaft member. Referring to Figure 1 , an exemplary forging method 100 for a hollow shaft member may include a blanking process 110 for providing a blank. The forging method 100 for a hollow shaft member may further include a pre-forging process 130 for heating the blank to a temperature within a first predetermined temperature range and holding for a first predetermined period of time, and transferring the heated blank to a die that has been subjected to a first pre-heating operation and performing one or more upsetting and drawing operations on the blank to obtain a pre-forged part. The forging method 100 for a hollow shaft member may further include a finish-forging process 140 for performing a one-fire-two-step operation on the pre-forged part to obtain a finish-forged part. The finish-forging process 140 may include heating the pre-forged part to a temperature within a second predetermined temperature range and holding for a second predetermined period of time during one fire, and transferring the heated pre-forged part to a die that has been subjected to a second pre-heating operation and performing two steps, the two steps including a first step and a second step. In the first step, the first upper punch of the die is pressed down to complete the forging of the outer contour of the hollow shaft member, and in the second step, the second upper punch of the die is pressed down to complete the forging of the inner contour of the hollow shaft member.

[0034] The one-fire-two-step operation in the finish-forging process of the present invention reduces the deformation instability region and the deformation dead zone, and improves the deformation uniformity of each region of the forging. Moreover, compared with the one-burn-one-forge operation of the prior art, the one-fire-two-step can reduce the idle burning. In addition, the one-fire-two-step can also reduce the amount of material used.

[0035] Taking the manufacture of an aeroengine fan shaft as an example, the large open end of the fan shaft has a large deformation, while the small closed end has a small deformation. If the number of fires is designed too small, it is difficult to ensure the deformation amount or the deformation uniformity at the large open end. If the number of fires is designed too large, it is easy to form a clear crystal structure after idle burning at the small closed end. Adopting the one-fire-two-step operation can enable the large open end to obtain sufficient deformation, while the small closed end is not subjected to multiple idle burnings, that is, under the condition of ensuring that the small closed end is only idly burned once, sufficient and uniform deformation can be achieved at the large open end. In addition, adopting the one-fire-two-step operation can save about 100 kilograms of material for the manufacture of each fan shaft.

[0036] The hollow shaft member of the present invention can be made of a lightweight material (such as suitable for use in an aircraft). The lightweight material may include titanium alloy, aluminum alloy, and / or carbon fiber composite material, etc., such as Ti-6Al-4V alloy.

[0037] In the forging method 100 of the hollow shaft part of the present invention, the temperature value or temperature range to which the forging should be raised and the required heat preservation duration can be determined according to the size of the shaft part to be forged. For example, the first predetermined temperature range during the pre-forging process 130 can be 940 - 990 °C, the first predetermined time period for heat preservation can be 270 - 390 minutes, and the first preheating operation can heat the die to a temperature greater than or equal to 250 °C. In addition, the second predetermined temperature range during the final forging process 140 can be 940 - 990 °C, the second predetermined time period for heat preservation can be 270 - 390 minutes, and the second preheating operation can heat the die to a temperature greater than or equal to 300 °C. In addition, the transfer time for transferring the blank and / or pre-forging to the die can be less than or equal to 60 seconds, for example, less than 45 seconds.

[0038] In the 1-fire 2-step operation, the first upper punch of the die can be pressed down at a speed of 5 - 15 mm / s in the first step, while the second upper punch of the die can be pressed down at a speed of 5 - 10 mm / s in the second step. During this period, the lower die (also called the chassis) of the die can remain stationary.

[0039] Return to reference Figure 1 Optionally, the forging method 100 of the hollow shaft part can include a red-forging process (also called a blank-making process) 120. The red-forging process 120 can be performed before the pre-forging process 130 and can be performed one or more times. Each red-forging process 120 can heat the blank to a temperature within a third predetermined temperature range and keep it warm for a third predetermined time period, and perform one or more upsetting and drawing operations on the blank. Herein, the blank after red-forging can be called a rough blank. Similarly, the temperature value or temperature range to which the forging should be raised and the required heat preservation duration can be determined according to the size of the shaft part to be forged. In the example, the third predetermined temperature range can be 940 - 990 °C. In addition, in the example of using cold material, the third predetermined time period for heat preservation can be 280 - 400 minutes. While in the example of using hot material, the third predetermined time period can be 140 - 260 minutes.

[0040] The execution of the red-forging process can provide a preformed rough blank, promoting the uniformity of forging deformation, enabling the forging to have better dimensional accuracy and surface flatness during the deformation process, so that the deformation is more in line with the predetermined model.

[0041] Further, the forging method 100 of the hollow shaft member may optionally include a heat treatment process 150. The heat treatment process 150 may be performed after the final forging process 140. The heat treatment process 150 may include homogenization heat treatment and / or annealing heat treatment. In one example, the homogenization heat treatment may heat the final forging to 940 - 990 °C and hold for 60 - 66 minutes, and then perform water cooling. In one example, the annealing heat treatment may heat the final forging to 650 - 750 °C and hold for 120 - 132 minutes, and then perform air cooling.

[0042] The execution of the heat treatment process can eliminate forging stress, improve the mechanical properties of the material and the uniformity of property distribution.

[0043] In addition, after each process of the present invention (for example, one or more of the blanking process 110, the pre-forging process 130, the final forging process 140, and the heat treatment process 150), the shaft member can be machined to make the blank / forging of the shaft member meet the final part design and usage requirements. For example, after the pre-forging process 130, a positioning hole can be machined. In an embodiment, the machining can be rough machining or finish machining, and includes but is not limited to: chamfering, milling, drilling, threading, boring, cutting, grinding and other operations.

[0044] The present invention can also further ensure the deformation uniformity of the forging body through numerical simulation optimization. For large-size hollow shaft members, a suitable preform can be one of the keys to ensuring the success of shaft member forging. The requirements for the volume distribution of the shaft member material in the forging process should be aimed at complete cavity filling, no flow defects, and uniform deformation of each part, determine the corresponding relationship between the final forging cavity and the shape and size of the blank, so as to design the optimal blank shape and size combination, further ensuring the deformation uniformity of the forging, as well as the product performance and flaw detection level.

[0045] Exemplary Embodiment

[0046] Next, taking the forging process of an aero-engine fan shaft as an example, the performance of the shaft member forged according to the method of the present invention will be described in detail.

[0047] (1) Blanking: Provide a Ti-6Al-4V alloy bar with a diameter of 330 mm as the blank. The specific chemical composition includes: 6.58% Al, 4.4% V, 0.19% Fe, 0.022% C, 0.22% O, B < 0.001%, Y < 0.001%, H < 0.002%, and the balance is Ti.

[0048] (2) Reducing forging: Perform reducing forging in 2 heats. In each heat of reducing forging, heat the blank bar to 950 ± 10 °C and hold, and perform multiple upsetting and drawing operations on the blank bar. The diameter of the obtained cylindrical blank is 330 ± 10 mm.

[0049] (3) Pre-forging: Heat the blank to 950 ± 10 °C and hold for 270 - 390 minutes. At the same time, heat the die to a temperature of ≥ 250 °C. Transfer the heated blank to the heated die within a transfer time of ≤ 60 seconds and perform multiple upsetting and drawing operations on the blank. The large end diameter of the obtained pre-forged part is 330 ± 5 mm, and the small end diameter is 160 ± 3 mm, as shown in, for example, Figure 2 shown.

[0050] (4) Finish-forging: Heat the pre-forged part to 950 ± 10 °C and hold for 270 - 390 minutes. At the same time, heat the die to a temperature of ≥ 300 °C. Transfer the heated pre-forged part to the heated die within a transfer time of ≤ 60 seconds and perform the first and second working steps. The downward pressing speed of the upper punch used in the first working step is 10 mm / s, and the downward pressing speed of the upper punch used in the second working step is 7 mm / s. The obtained finish-forged part is shown in, for example, Figure 3 shown (after machining).

[0051] (5) Heat treatment: Includes homogenization heat treatment and annealing heat treatment. During the homogenization heat treatment, heat the forging to 960 ± 10 °C and hold for 60 - 66 minutes, then perform water cooling. During the annealing heat treatment, heat the forging to 700 ± 6 °C and hold for 120 - 132 minutes, then perform air cooling.

[0052] The inventor conducted performance tests on the obtained fan shaft. In the forging body of the fan shaft, the inventor took 4 circumferential (also known as chordal) specimens, 3 radial specimens, and 6 axial specimens from different positions, a total of 13 specimens. Perform mechanical property tests on these specimens at room temperature and high temperature (300 °C). The obtained average value and standard deviation results are shown in Table 1 below. Table 1: Mechanical properties of the shaft body Test Temperature Tensile Strength (MPa) Yield Strength (MPa) Elongation (%) Reduction of Area (%) Measured Mean ± Standard Deviation Room Temperature 1021±15 930±15 15±1 36±2 Reference Value Room Temperature 900-1160 ≥830 ≥9 ≥25 Measured Mean ± Standard Deviation 300℃ 704±18 578±13 17±2 51±2 Reference Value 300℃ ≥650 ≥530 ≥9 ≥35

[0053] In addition, Figure 4 the small figure (a) in shows the tensile strength (also known as the tensile strength) and yield strength of each of the 13 specimens at room temperature. Figure 4 The small figure (b) in shows the tensile strength and yield strength of each of the 13 specimens at a high temperature of 300 °C. Combining the sampling positions, it can be seen from Figure 4 the mechanical property distribution in the shaft body. Figure 5 shows the high-magnification microstructural photograph (×500 times) of the obtained shaft part. Figure 6 shows the mechanical properties and microstructural photographs (×100 times) of different positions of the obtained shaft body.

[0054] From Table 1 and Figure 4-6 It can be seen that the mechanical properties and microstructure of the body of the hollow shaft obtained by the forging method according to the present invention can meet the design requirements while having a low standard deviation and good stability.

[0055] The inventor also performed flaw detection tests on the obtained shaft parts. Specifically, through the water immersion zonal flaw detection method for large-sized forgings, water immersion flaw detection was carried out on 10 detection surfaces of the fan shaft forging. The results were as follows: the highest noise level was Φ0.8 - 10 dB, and no recorded display signals were found during the detection process, so the detection was qualified. This indicates that there are no defects in the obtained forgings within the detection range, and the structure has a high degree of uniformity.

[0056] It should be noted that, in order to simplify the description of the present application and thus help in the understanding of one or more embodiments, in the previous description of the embodiments of the present application, sometimes multiple features are merged into one embodiment, drawing, or description thereof. However, this disclosure method does not mean that the features required by the subject matter of the present application are more than those mentioned in the claims. In fact, the features of the embodiments can be fewer than all the features of the single embodiment disclosed above.

[0057] During the specific description of these embodiments, for the sake of concise description, it is impossible for this specification to describe all the features of the actual embodiments in detail. It should be understood that in the actual implementation process of any one of the embodiments, in order to achieve the specific goals of the developer and to meet system-related or business-related restrictions, various specific decisions are often made, and these will also vary from one embodiment to another. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in the present invention, some design, manufacturing, or production changes based on the technical content disclosed in the present invention are just conventional technical means and should not be understood as the content of the present invention being insufficient.

[0058] Although the present application has been described with reference to the current specific embodiments, those skilled in the art should recognize that the above embodiments are illustrative rather than restrictive, and various equivalent changes or substitutions can be made without departing from the spirit of the present application. Therefore, as long as the changes and modifications to the above embodiments are within the scope of the spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A forging method for a hollow shaft part, characterized in that, it includes the following processes: Blank cutting process (110): Provide a blank; Pre-forging process (130): Heat the blank to a temperature within a first predetermined temperature range and hold for a first predetermined period, and transfer the heated blank to a die that has undergone a first preheating operation and perform one or more upsetting and drawing operations on the blank to obtain a pre-forged part; And Final forging process (140): Perform a 1-fire 2-step operation on the pre-forged part to obtain a final forging, including heating the pre-forged part to a temperature within a second predetermined temperature range and holding for a second predetermined period during 1 fire, and transferring the heated pre-forged part to the die that has undergone a second preheating operation and performing 2 steps, the 2 steps including a first step and a second step, the first step pressing down the first upper punch of the die to complete the forging of the outer contour of the hollow shaft part, and the second step pressing down the second upper punch of the die to complete the forging of the inner contour of the hollow shaft part.

2. The forging method for a hollow shaft part according to claim 1, characterized in that, it further includes performing one or more re-forging processes (120) before the pre-forging process (130), each re-forging process (120) heating the blank to a temperature within a third predetermined temperature range and holding for a third predetermined period and performing one or more upsetting and drawing operations on the blank.

3. The forging method for a hollow shaft part according to claim 1, characterized in that, it further includes performing a heat treatment process (150) after the final forging process (140), the heat treatment process (150) performing homogenization heat treatment and / or annealing heat treatment on the final forging.

4. The forging method for a hollow shaft part according to claim 1, characterized in that, it further includes machining the shaft part after one or more of the pre-forging process (130), the final forging process (140), and the heat treatment process (150).

5. The forging method for a hollow shaft part according to claim 1, characterized in that, the hollow shaft part is in a trumpet shape.

6. The forging method for a hollow shaft part according to claim 1, characterized in that, the hollow shaft part is made of a lightweight material.

7. The forging method for a hollow shaft part according to claim 6, characterized in that, the lightweight material is a Ti-6Al-4V alloy.

8. The forging method for a hollow shaft part according to claim 1, characterized in that, the first predetermined temperature range is 940 - 990 °C, the first predetermined period is 270 - 390 minutes, and the first preheating operation heats the die to a temperature greater than or equal to 250 °C.

9. The forging method for a hollow shaft part according to claim 1, characterized in that, the second predetermined temperature range is 940 - 990 °C, the second predetermined period is 270 - 390 minutes, and the second preheating operation heats the die to a temperature greater than or equal to 300 °C.

10. The forging method for a hollow shaft part according to claim 2, characterized in that, The third predetermined temperature range is 940 - 990 °C, and the third predetermined time period is 280 - 400 minutes for cold materials or 140 - 260 minutes for hot materials.

11. The forging method of a hollow shaft part according to claim 3, characterized in that, In the homogenization heat treatment, the final forging is heated to 940 - 990 °C and held for 60 - 66 minutes, and then water-cooled; in the annealing heat treatment, the final forging is heated to 650 - 750 °C and held for 120 - 132 minutes, and then air-cooled.

12. The forging method of a hollow shaft part according to claim 1, characterized in that, The first upper punch presses down at a speed of 5 - 15 mm / s, while the second upper punch presses down at a speed of 5 - 10 mm / s.

13. A hollow shaft part forged by using the method according to any one of claims 1 - 12.

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