A method for forming a head of a GH350 alloy bolt

Abstract

The application discloses a GH350 alloy bolt head forming processing method, the longitudinal section of the alloy bolt is T-shaped, and the bolt head comprises a vertical stud and a head with a cylindrical head arranged at the top end of the stud; the processing method of the head is to pre-adopt a laser beam to realize local precise heating and softening, and then adopt an induction heating mode to perform hot heading forming. By adopting the processing method, after pre-heating and softening treatment, induction heating treatment is performed, the induction heating area can be reduced, the heating temperature can be reduced, the deformation strengthening is greater than recrystallization due to the low heating temperature, the hardness of the head is improved, the heading part is soft, the forming performance is good in the heating state, the forming performance of the head is ensured, the product qualified rate is effectively improved, and in particular, the GH350 alloy material bolt with a stud blank diameter of 6-12 mm provides a new processing mode, and can be popularized and applied in the field of aviation engine GH350 bolt processing and manufacturing.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for aero-engine bolts, specifically to a method for forming the head of a GH350 alloy bolt. Background Technology

[0002] In recent years, with the rapid development of science and technology and the continuous upgrading of my country's aerospace equipment, the performance requirements have become increasingly stringent, which in turn has led to higher requirements for fastener materials. In particular, the requirements for the service temperature, strength and corrosion resistance of high-temperature alloy materials for fasteners have gradually increased, which has placed higher demands on fasteners used in aerospace equipment.

[0003] GH350 alloy is a typical high-temperature alloy material with dual composite strengthening through cold work hardening and age hardening. After cold work hardening, the room temperature tensile strength is about 1200-1300 MPa and the hardness can reach above 38 HRC. After age hardening, the room temperature tensile strength is above 1580 MPa, and the high temperature tensile strength at 730℃ is as high as 1200 MPa. The maximum service temperature of this alloy can reach 760℃.

[0004] Due to its excellent high-temperature and high-strength properties, and stable microstructure and properties below 760℃, GH350 alloy has gradually replaced GH159 alloy, which has a temperature resistance of only 600℃, in the field of aero-engines, and has been widely adopted. However, the fact that GH350 alloy achieves its high strength through cold work hardening and age hardening also presents significant challenges to the upsetting of bolt heads.

[0005] The product structure of GH350 bolts is as follows: Figure 1 and Figure 2 As shown, the bolt has a stud portion and a head with a cylindrical tip at the top of the stud. The manufacturing process involves using cold-worked raw material, followed by hot upsetting of the head → aging → machining → radius rolling → thread rolling. The GH350 alloy raw material is in a cold-worked state, with a hardness typically between 38 and 40 HRC. Due to the high hardness of the raw material, the head must be formed by hot upsetting after heating, a process known in the industry as hot upsetting. For a GH350 bolt with a diameter of d, the heating area is as follows... Figure 3 As shown.

[0006] Induction coil heating is commonly used in hot upsetting. If the heating temperature is too high, recrystallization will occur, and the work hardening effect of the alloy will partially or completely disappear, leading to varying degrees of hardness reduction. Furthermore, due to the long transition zone of induction heating, the hardness of the area below the head support surface will also decrease. After subsequent aging, the hardness of the bolt head and the hardness of the support surface below the head will be lower than the hardness of other areas, i.e., the hardness of the raw material. Ultimately, the reduced head hardness leads to a decrease in the load-bearing capacity of the head, resulting in the bolt tensile force failing to meet the specified value due to the weakness of the head. If the heating temperature is too low, the upsetting performance will be poor, and deformation strengthening will occur during the upsetting process, increasing the head hardness and further deteriorating the forming performance, resulting in upsetting defects such as folds, cracks, fissures, and tucks.

[0007] The hardness of the bolt head after hot upsetting is essentially a combined result of the recrystallization and deformation strengthening processes. Higher heating temperatures facilitate forming, but recrystallization outweighs deformation strengthening, leading to a decrease in the head hardness after hot upsetting. Conversely, lower heating temperatures make forming more difficult, but deformation strengthening outweighs recrystallization, resulting in an increase in the head hardness after hot upsetting. Therefore, the challenge of induction heating hot upsetting of GH350 alloy lies in the difficulty of precisely controlling the heating temperature and heating length. Thus, to meet the requirements of high-temperature and high-strength bolts in aerospace equipment connection systems, this paper proposes a different method for forming GH350 alloy bolt heads than existing technologies, to better meet these requirements. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to address the problems existing in the background art, and thus provide a head forming processing method. By using this processing method, through preheating and softening treatment, the technical problems such as the easy reduction of hardness in the bolt head and the R position under the head, making it difficult to upset and form, which are common in the existing induction heating hot upsetting method, are effectively solved. Thus, the processed products can meet the usage requirements of GH350 alloy bolts. Specifically, it is a GH350 alloy bolt head forming processing method.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for forming the head of a GH350 alloy bolt, wherein the longitudinal section of the alloy bolt is T-shaped, including a vertically arranged stud and a head with a cylindrical head disposed at the top of the stud. The head is processed by first using a laser beam to achieve localized and precise heating and softening, and then using induction heating to hot-forge the head. Specifically, it includes the following steps: S1. Turning: The GH350 bar stock is turned to obtain a semi-finished upset bar billet; S2. Laser heating: The head end of the upset billet is locally heated using a laser beam; S3. Upsetting: After laser heating, the upsetting bar blank is locally heated at the heating end using a high-frequency induction heater, and then placed in a special mold for hot upsetting to form a semi-finished bolt with a cylindrical head.

[0010] Furthermore, in the GH350 alloy bolt head forming processing method of the present invention, during the laser heating process in step S2, the length of the heating area of ​​the laser beam is set to L1mm, where L1mm is the material length for forming the bolt head. L1 can also be the length of the heated area of ​​the bolt head under traditional induction heating, set to Lmm, minus the length of the transition area, set to L2mm, i.e., L1=L-L2. Finally, the laser beam is used to heat the L1 length area. Through laser beam heating, the material end of the head is pre-softened. The power of the laser beam is 300-500W, and the heating time is 15-20 seconds.

[0011] Furthermore, in the GH350 alloy bolt head forming processing method described in this invention, during the upsetting process in step S3, the length of the laser beam heating area is determined to be L1 mm based on the material used for the head of the alloy bolt. By pre-softening the material end of the head, the L2 mm length transition area caused by the traditional induction heating method can be avoided. The length of L2 is 2-3 mm. After the laser beam is pre-softened, the high-frequency induction heating length during bolt upsetting is determined to be L1 mm, where L1 = L - L2. Then, a high-frequency induction heater is used to heat the material end of the head. The heating temperature of the high-frequency induction heater is 900-930℃.

[0012] Furthermore, in the GH350 alloy bolt head forming processing method described in this invention, during the upsetting process in step S3, the special mold is a hot upsetting mold. After being heated by high frequency, the upsetting bar blank in the hot upsetting mold is hot upsetting by a hot upsetting machine to form a semi-finished bolt with a cylindrical head.

[0013] Furthermore, in the GH350 alloy bolt head forming processing method described in this invention, the stud blank diameter φ of the alloy bolt is 6-12mm.

[0014] The GH350 alloy bolt head forming method described in this invention offers several advantages over existing technologies. Firstly, pre-heating with a laser beam for precise localization and softening, followed by hot upsetting using conventional induction heating, not only shortens the induction heating length and lowers the heating temperature, thus increasing bolt head hardness, but also improves its forming performance, ensuring a full head shape and preventing upsetting defects such as folds, cracks, fissures, and tucks. Compared to induction coil heating, laser beam heating offers advantages such as precise heating length control and a smaller transition zone.

[0015] In summary, the processing method described in this invention, which involves preheating and softening followed by induction heating, not only reduces the induction heating area but also lowers the heating temperature. Due to the lower heating temperature, deformation strengthening exceeds recrystallization, increasing the head hardness. The upset portion itself is relatively soft, resulting in good formability under heating conditions, thus ensuring the head's formability and effectively improving the product qualification rate. In particular, it provides a new processing method for GH350 bolts made of high-temperature alloy material with a stud blank diameter of 6-12mm, and can be widely applied in the manufacturing of GH350 bolts for aero-engines. Attached Figure Description

[0016] The present invention will now be described in further detail with reference to the accompanying drawings.

[0017] Figure 1 This is a schematic diagram of the GH350 bolt product structure. Figure 1 ; Figure 2 This is a schematic diagram of the GH350 bolt product structure. Figure 2 ; Figure 3 This is a schematic diagram of a length region structure heated using existing induction heating methods; Figure 4 This is a schematic diagram of the structure of the heating region using the heating method described in this invention. Detailed Implementation

[0018] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0019] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness or purpose of the invention, should still fall within the scope of the disclosed technical content. Furthermore, the terms "upper," "lower," "left," and "right" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connection" and "provided with" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] It should be noted that the term "comprising" or any other variation is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0022] like Figure 4 As shown, the present invention provides a method for forming the head of a GH350 alloy bolt. The longitudinal section of the alloy bolt is T-shaped, including a vertically arranged stud and a head with a cylindrical head at the top of the stud. The stud blank diameter φ of the alloy bolt is 6-12mm. The head is processed by pre-heating and softening the bolt locally with a laser beam, and then hot-forging the head using induction heating. The specific steps include: S1. Turning: The GH350 bar stock is turned to obtain a semi-finished upset bar billet; S2. Laser heating: The head end of the upset bar blank is locally heated using a laser beam. Specifically, the heating area of ​​the laser beam is set to L1mm, where L1mm is the length of the material used for forming the bolt head. L1 can also be the length of the heated area of ​​the bolt head under traditional induction heating, set to Lmm, minus the length of the transition area, set to L2mm, i.e., L1=L-L2. Finally, the laser beam is used to heat the L1 length area. Through laser beam heating, the head end of the material is pre-softened. The power of the laser beam is 300-500W, and the heating time is 15-20 seconds.

[0023] S3. Upsetting: After laser heating, the upset bar blank is locally heated at the heating end using a high-frequency induction heater, and then placed in a special mold for hot upsetting, thus forming a semi-finished bolt with a cylindrical head. Specifically, the upsetting method involves determining the heating area length of the laser beam to be L1 mm based on the material used for the head of the alloy bolt. By pre-softening the material end of the head, the L2 mm transition area caused by traditional induction heating can be avoided. The length of L2 is 2-3 mm. After pre-softening with the laser beam, the high-frequency induction heating length during bolt upsetting is determined to be L1 mm, where L1 = L - L2. Then, a high-frequency induction heater is used to heat the material end of the head at a temperature of 900-930℃. The special mold is a hot upsetting mold. After high-frequency heating, the upset bar blank within the hot upsetting mold is hot-upset using a hot upsetting machine, thus forming a semi-finished bolt with a cylindrical head. In specific applications, the power and heating time parameters used in laser heating need to be adjusted according to the blank diameter and heating length. This method is mainly applicable to bolt blanks with a diameter of φ6-12mm, and the laser heating power is controlled between 300-500W, with a heating time of 15-20 seconds. Example

[0024] This embodiment uses a twelve-angle precision bolt with a machining specification of MJ8×1 and a material of GH350 as an example. In order to improve the head hardness of the GH350 alloy bolt, the specific machining method includes the following steps: S1 Turning: Turn the bar stock to the required size billet, Φ9×50mm, to obtain a semi-finished upset billet; S2 laser heating: One end of the upturned billet after turning is locally heated by a laser beam, with a heating length of 19±0.2mm; the power of the laser beam is 400W, and the heating time is 15 seconds; through laser beam heating, the length of its softened area can reach 19-20mm. S3 upsetting: One end of the billet is locally heated using a high-frequency induction heater. The local heating length is 19mm. The heating method follows the existing process, and the heating temperature is controlled at 900-930℃. Then, it is placed in a special mold for hot upsetting to form a semi-finished bolt with a cylindrical head. S4 Test: The hardness of the bolt at a point 1mm below the radius (R) and 1mm inward from the shank edge was tested. The hardness was 490 HV, while the hardness of the raw material was 480 HV. Therefore, the processing method described in this invention has the advantage of increasing the hardness of the bolt head at the R position. If the traditional upsetting method is used, the local heating length is 22mm, and the hardness at this point 1mm below the radius (R) and 1mm inward from the shank edge after upsetting is 20-50 HV lower than the hardness of the raw material.

[0025] Using the processing method described in this embodiment, a laser beam is used to preheat the area of ​​the head upsetting material with a length L1 of 19mm to achieve softening. Since the length of the head upsetting material has already softened, induction heating is then performed on this softened basis. At this time, the length of induction heating is smaller than the length of heating directly using an induction heater. When using direct induction heating, the length is L=19mm. Since the length of the head upsetting material of 19mm has already softened, induction heating is then performed on this softened basis. At this time, the length L1 of induction heating can be controlled by subtracting the size L2 of the induction heating transition zone from L, that is, L1=L-L2. Because of the reduced length, the heating temperature during hot upsetting can also be appropriately reduced. For example, when hot upsetting is performed using the commonly used induction heating method, the heating temperature is usually 970-1000℃ to ensure the forming performance of the head. However, by using laser beam preheating for softening and then using the commonly used induction heating, the induction heating temperature can be reduced to 900-930℃. Due to the lower heating temperature, the deformation strengthening is greater than the recrystallization, the head hardness is increased, and the upsetting part itself is relatively soft, resulting in good forming performance under heating, thus ensuring the forming performance of the head.

[0026] Therefore, based on the commonly used induction heating mode, when using a laser beam to achieve localized and precise heating and softening before using induction heating for hot upsetting of the head, the induction heating length can be appropriately shortened and the heating temperature reduced. This can improve the hardness of the bolt head and enhance the bolt head forming performance, ensuring a full head shape and avoiding upsetting defects such as folds, cracks, crazing, and tucks.

[0027] In summary, the processing method described in this invention, which involves preheating and softening followed by induction heating, not only reduces the induction heating area but also lowers the heating temperature. Due to the lower heating temperature, deformation strengthening exceeds recrystallization, increasing the head hardness. The upset portion itself is relatively soft, resulting in good formability under heating conditions, thus ensuring the head's formability and effectively improving the product qualification rate. In particular, it provides a new processing method for GH350 bolts made of high-temperature alloy material with a stud blank diameter of 6-12mm, and can be widely applied in the manufacturing of GH350 bolts for aero-engines.

[0028] Other aspects of this invention that are not detailed herein are all conventional techniques known to those skilled in the art.

[0029] The scope of protection of this invention is not limited to the technical solutions disclosed in the specific embodiments. The above description is only a preferred embodiment of this invention and does not limit this invention. Any minor modifications, equivalent substitutions and improvements made based on the technical solutions of this invention should be included within the scope of protection of the technical solutions of this invention.

Claims

1. A method for forming the head of a GH350 alloy bolt, wherein the longitudinal section of the alloy bolt is T-shaped, comprising a vertically arranged stud and a head with a cylindrical head disposed at the top of the stud, characterized in that: The head processing method involves pre-heating and softening the head locally using a laser beam, followed by hot upsetting of the head using induction heating. Specifically, it includes the following steps: S1. Turning: The GH350 bar stock is turned to obtain a semi-finished upset bar billet; S2. Laser heating: The head end of the upset bar blank is locally heated by a laser beam. The power of the laser beam is 300-500W and the heating time is 15-20 seconds. The length L1mm of the heated area of ​​the laser beam is the length of the material used for forming the bolt head. Alternatively, L1 is determined by subtracting the length L2mm of the transition area from the length Lmm of the heated area of ​​the bolt head under traditional induction heating. S3. Upsetting: The upsetting bar blank after laser heating is locally heated at the heating end using a high-frequency induction heater at a temperature of 900-930℃. Then it is placed in a special mold for hot upsetting to form a semi-finished bolt with a cylindrical head.

2. The method for forming the head of a GH350 alloy bolt according to claim 1, characterized in that: In the upsetting process of step S3, the length of the heating area of ​​the laser beam is determined to be L1 mm according to the material of the head of the alloy bolt. By pre-softening the material end of the head, the L2 mm length transition area caused by the traditional induction heating method can be avoided. The length of L2 is 2-3 mm. After the laser beam is pre-softened, the high-frequency induction heating length L1 mm during bolt upsetting is determined, where L1 = L - L2.

3. The method for forming the head of a GH350 alloy bolt according to claim 2, characterized in that: In the upsetting process of step S3, the special mold is a hot upsetting mold. After being heated by high frequency, the upsetting bar blank in the hot upsetting mold is hot upsetting by a hot upsetting machine to form a semi-finished bolt with a cylindrical head.

4. The method for forming the head of a GH350 alloy bolt according to claim 3, characterized in that: The diameter φ of the stud blank of the alloy bolt is 6 to 12 mm.

Images