A stress relief method for powder metallurgical monolithic interstage casings

Abstract

Titanium alloy intermediate casing is the most complex structure in the turbofan engine and is one of the most important main load-bearing components. Powder metallurgy forming method can realize high precision, high performance and high quality of the whole manufacturing of the intermediate casing, but due to the complex structure, stress relief becomes one of the key links. The present application proposes a stress relief method for powder metallurgy whole intermediate casing, which carries out creative research from the following aspects: incremental fillet design of transition connection, symmetric sleeve processing removal method, whole tight-fitting type gradient high-temperature vacuum annealing method and high-frequency point impact stress relief method of transition connection, and realizes low stress control of powder metallurgy whole intermediate casing.

Description

Technical Field

[0001] This patent belongs to the field of manufacturing technology of thin-walled complex titanium alloy components, specifically involving a stress relief method for powder metallurgy integral intermediate casing. It can eliminate structural and forming internal stress while achieving high-precision forming of the integral intermediate casing, thereby improving the reliability of the integral intermediate casing. Background Technology

[0002] The intermediate casing, also known as the support casing, is the most complex casing-type component within a turbofan aero-engine and one of the engine's main load-bearing components. Intermediate casings typically exhibit two key characteristics: First, their structure is extremely complex. Located between the fan and outer bypass casing, they generally consist of an inner casing, an outer casing, a flow divider ring, and a load-bearing hollow support plate. The outer casing connects the fan casing and the outer bypass casing at the front and rear, respectively. The flow divider ring connects to the front mounting edge of the high-pressure compressor, dividing the fan airflow into inner and outer bypass airflow. The inner casing connects the central drive unit, the rear support point of the fan, and the front support point of the high-pressure compressor. Second, they experience extremely complex stresses. As a primary load-bearing component, the intermediate casing bears the aerodynamic loads during engine operation and the maneuvering loads during flight. Due to the numerous mounting edges, the number of loads acting on various parts is very large, making load calculations extremely complex.

[0003] Currently, there are two main traditional methods for manufacturing intermediate engine casings both domestically and internationally: one is the sheet metal forming + argon arc welding process, represented by Russia, and the other is the precision casting process, represented by the United States. Domestically, corresponding to these two schools of thought, there are also two manufacturing processes for intermediate engine casings. Intermediate engine casings for small and medium thrust turbofan engines generally use sheet metal forming + argon arc welding. A single intermediate engine casing has more than 300 welds, resulting in a very long welding cycle, low yield, low reliability, and frequent cracking failures. Intermediate engine casings for large thrust turbofan engines generally use precision casting. However, due to process limitations, some structures still need to be disassembled, and controlling casting defects is difficult, with minimum wall thickness requirements. Therefore, achieving high-precision, high-quality, and high-efficiency integrated manufacturing of intermediate engine casings using novel forming methods has always been a research hotspot in the engineering field. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of existing technologies and propose a stress relief method for integral intermediate casings made of powder metallurgy. This method can integrally form complex intermediate casing components for aero-engines, achieving high-precision forming while effectively solving the problem of internal stress control caused by integral forming of complex structures, thereby improving the reliability of the intermediate casing.

[0005] The technical solution of this invention is: a stress relief method for an integral intermediate casing in powder metallurgy, wherein the intermediate casing includes an inner casing, a flow divider ring, and an outer casing, comprising:

[0006] First, the intermediate casing structure is redesigned based on the characteristics of powder metallurgy forming. The transition connection between the hollow support plate and the inner casing, the flow ring and the outer casing is designed with progressively larger fillets from the inside to the outside.

[0007] The intermediate casing is manufactured using a near-net-shape powder metallurgy method, and the cladding is removed using symmetrical machining and electrolysis to obtain the intermediate casing blank; during the machining process, high-frequency impact stress relief treatment is performed at the transition connection.

[0008] The intermediate housing blank is subjected to integral clamping gradient high-temperature vacuum annealing to ensure that the stress of the intermediate housing is minimized.

[0009] Preferably, the fillet radius design values ​​for the transition connections between the hollow support plate and the inner casing, and between the flow divider ring and the outer casing are R3~R6, R6~R9, and R9~R12, respectively.

[0010] Preferably, the symmetrical machining method is as follows:

[0011] Assuming the number of hollow support plates is 2n, the intermediate housing casing is also divided into 2n blocks. Starting from any block, milling is performed to remove it, and the block is numbered as the first block. After the first block is removed, the (n+1)th block is processed symmetrically. Then the second block adjacent to the first block is processed, and the (n+2)th block is processed symmetrically, and so on, until the entire intermediate housing casing casing is processed and removed.

[0012] Preferably, the symmetrical machining has a allowance of 3-5 mm.

[0013] Preferably, the integral clamping gradient high-temperature vacuum annealing of the intermediate casing blank includes:

[0014] Using tooling, an outward force is applied from the inside of the inner casing, and an inward force is applied from the outside of the outer casing to tightly clamp the entire intermediate casing. It is then placed in a vacuum annealing furnace for gradient vacuum annealing, with a vacuum level requirement better than 1*10⁻⁶. -3 Pa, the temperature is raised from room temperature to 600-650℃, held for 120-240 minutes, after which the temperature is raised to 750-850℃, held for 60-120 minutes, after which the temperature is lowered to 600-650℃, held for another 120-240 minutes, and finally cooled to below 100℃ before being removed from the furnace.

[0015] Preferably, the tooling includes a chassis, an inner support ring, and an outer clamping ring; the chassis is the basic component of the tooling and also the transmission component, the intermediate housing is placed on the chassis, and the inner support ring and the outer clamping ring are connected to the chassis via connecting rods; the inner support ring acts on the inner housing, applying an outward force to the intermediate housing, and the outer clamping ring acts on the outer housing, applying an inward force to the intermediate housing; both the inner support ring and the outer clamping ring adopt a semi-circular arc design and are connected by screws to ensure that the outward and inward forces acting on the intermediate housing are adjustable.

[0016] Preferably, the tooling is made of the same grade of titanium alloy as the intermediate housing.

[0017] Preferably, the outer diameter of the inner support ring is equal to the inner diameter of the inner casing, and the angle of each semicircle is 160-175°; the inner diameter of the outer clamping ring is equal to the outer diameter of the outer casing, and the angle of each semicircle is 150-165°.

[0018] Preferably, between the roughing and finishing processes, the intermediate casing transition connection is subjected to high-frequency impact stress relief treatment.

[0019] Preferably, the impact head is driven to impact the rounded corner of the transition connection at a frequency of 5,000 to 10,000 times per second, acting simultaneously on the transition connections of all hollow support plates. The diameter of the impact head is 0.5 to 1 mm, the traveling speed along the transition connection is 1 to 3 mm / s, and the action time is 30 to 90 minutes.

[0020] The beneficial effects of this invention compared with the prior art are as follows: The intermediate casing prepared by this invention solves the problem of new microcracks appearing during the forming and processing of the earliest intermediate casing components. No new cracks were generated throughout the entire product process, and it successfully passed all fluorescent surface quality tests and X-ray internal quality tests. The stress level was found to be very low when the stress was detected by an X-ray diffraction stress meter, which improved the reliability of the intermediate casing components. This has played a strong role in promoting the development of the next generation of aero engines and has also laid the material and process technology foundation for the development of higher-performance aero engines required for my country's future aviation weapons and equipment. Attached Figure Description

[0021] Figure 1 This is a structural diagram of the intermediate casing;

[0022] Figure 2 Schematic diagram of clamping annealing fixture Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] This invention provides a stress relief method for an integral intermediate housing made of powder metallurgy. First, the intermediate housing structure is redesigned based on the characteristics of powder metallurgy forming, with adjustments and optimizations made to certain positions. Then, the intermediate housing is manufactured using a near-net-shape powder metallurgy forming method. The main processes include intermediate housing casing design, manufacturing, assembly and welding, powder loading and degassing, sealing welding, and hot isostatic pressing. After hot isostatic pressing, the casing is removed using symmetrical machining and electrolysis to obtain the intermediate housing blank. The intermediate housing blank undergoes integral clamping gradient high-temperature vacuum annealing, and high-frequency impact stress relief treatment is performed at the transition joints during processing to ensure that the stress in the intermediate housing is minimized. Details are as follows:

[0025] Step 1: Prepare the intermediate casing blank using powder metallurgy; specifically, this includes the following steps:

[0026] Step (1.1) involves redesigning the intermediate casing structure based on the characteristics of powder metallurgy forming, and adjusting and optimizing some positions.

[0027] like Figure 1 As shown, the intermediate casing is a multi-layered complex component, generally consisting of an inner casing, a flow divider ring, and an outer casing from the inside out, with varying numbers of hollow support plates evenly distributed circumferentially. The hollow support plates pass through the inner casing, flow divider ring, and outer casing, and the corresponding transition joints are the most prone to stress concentration. Through simulation calculations, under the premise of controlling weight, the transition joints are designed with progressively increasing fillet radii from the inside out. The fillet radii design values ​​for the hollow support plates and inner casing, and for the flow divider ring and outer casing, are R3~R6, R6~R9, and R9~R12, respectively.

[0028] Step (1.2): Design the intermediate casing forming sleeve according to the optimized intermediate casing structure. A typical intermediate casing structure includes multiple layers from the inside to the outside, such as the inner casing, the flow divider ring and the outer casing, and different numbers of hollow support plates are evenly distributed in the circumference.

[0029] Step (1.3): Process the intermediate casing casing according to the casing design drawing in step (1.2). The casing casing mainly includes the inner casing forming casing, the outer casing forming casing, the hollow support plate forming casing, the diverter ring forming casing, the positioning block, the casing upper cover, the casing lower cover, and the auxiliary fixing components. The material is 20# steel or high temperature alloy.

[0030] In step (1.4), the intermediate casing sleeve parts obtained in step (1.3) are assembled and welded. Titanium alloy spherical powder is loaded into the intermediate casing sleeve through the reserved powder loading hole. The powder is compacted by tapping and vibration. Finally, the reserved degassing steel pipe is welded on to obtain a complete intermediate casing sleeve.

[0031] In step (1.5), the complete intermediate casing from step (1.4) is placed into the resistance furnace, the degassing steel pipe is connected to the vacuum unit, and a vacuum is drawn at high temperature. After degassing is completed, the steel pipe is sealed and welded. Finally, the sealed intermediate casing is placed into a hot isostatic press for hot isostatic pressing treatment.

[0032] In step (1.6), after hot isostatic pressing, most of the cladding of the intermediate housing is removed by machining. The principle of removing the cladding is to expose the titanium alloy surface where there is room for further machining, and to leave a 3-5mm allowance according to the product dimensions for areas that will not be machined further, to ensure that the intermediate housing product is not damaged.

[0033] After hot isostatic pressing, the steel or high-temperature alloy cladding and titanium alloy intermediate housing have diffused and bonded under high temperature and pressure, requiring destructive removal methods. Machining is the most effective removal method, but a certain allowance must be left to avoid damaging the intermediate housing product; this allowance is generally controlled within 3-5mm. During machining, the stress state of the component is dynamically changing, and symmetrical removal is used to control the stress state. If the number of hollow support plates is 2n, then the intermediate housing cladding is also divided into 2n pieces. Milling is started from any one piece, numbered as piece 1. After machining, piece n+1 is symmetrically machined, then piece 2 adjacent to piece 1 is machined, and so on, symmetrically machining piece n+2, until the entire intermediate housing cladding is removed.

[0034] Step (1.7) involves removing the remaining casing on the intermediate casing product by electrolytic removal to obtain a titanium alloy intermediate casing blank.

[0035] Step 2: Perform finishing, annealing, and high-frequency impact stress relief treatment on the intermediate casing blank.

[0036] To improve the roughness of the unmachined surfaces of the intermediate housing, the intermediate housing blank first needs to undergo a flow-type finishing process.

[0037] After finishing, the powder metallurgy integral intermediate casing blank undergoes integral clamping gradient high-temperature vacuum annealing, with specialized tooling designed, such as... Figure 2 As shown, an outward force is applied from the inside of the inner casing, and an inward force is applied from the outside of the outer casing to tightly clamp the entire intermediate casing. It is then placed in a vacuum annealing furnace for gradient vacuum annealing, with a vacuum level requirement better than 1*10⁻⁶. - 3 Pa, the temperature is raised from room temperature to 600-650℃, held for 120-240 minutes, after which the temperature is raised to 750-850℃, held for 60-120 minutes, after which the temperature is lowered to 600-650℃, held for another 120-240 minutes, and finally cooled to below 100℃ before being removed from the furnace.

[0038] The earliest intermediate casing manufactured using powder metallurgy employed a simple high-temperature annealing process. However, microcracks appeared during the final processing. Extensive testing revealed that the microstructure of titanium alloys obtained through powder metallurgy differs from that of traditional forging and casting processes. Due to variations in particle boundaries and internal deformation, stabilization treatment at a lower temperature followed by full annealing at a higher temperature and then further stabilization is necessary for better annealing results. X-ray stress testing showed that, compared to simple annealing, gradient high-temperature annealing reduced the internal stress at the same location in the intermediate casing blank by 5% to 15%.

[0039] To eliminate the influence of different material linear expansion coefficients on annealing, the special tooling is made of the same grade of titanium alloy as the intermediate housing. The tooling mainly consists of three parts: a base, an inner support ring, and an outer clamping ring. The base is the foundation and transmission component of the tooling. The intermediate housing is placed on the base, and the inner support ring and outer clamping ring are connected to the base via connecting rods. The inner support ring acts on the inner housing, applying an outward force to the intermediate housing, while the outer clamping ring acts on the outer housing, applying an inward force to the intermediate housing. Both the inner support ring and the outer clamping ring adopt a semi-circular arc design to ensure adjustable outward and inward forces acting on the intermediate housing. The outer diameter of the inner support ring arc is equal to the inner diameter of the inner housing, with each semi-circular arc angle of 160–175°. The two semi-circular arcs are connected as one unit by a screw. The inner diameter of the outer clamping ring is equal to the outer diameter of the outer housing, with each semi-circular arc angle of 150–165°. The two semi-circular arcs are connected as one unit on the outer side by a screw.

[0040] Only after the intermediate housing has undergone annealing can machining begin. Between the roughing and finishing processes, high-frequency impact stress relief is applied to the transition joints of the intermediate housing. These transition joints are where stress is most concentrated throughout the entire intermediate housing. A designed device utilizes high-density energy to drive an impact head, impacting the rounded corners of the transition joints at a frequency of 5000–10000 times per second. The number of workstations equals the number of hollow support plates, ensuring that the transition joints of all hollow support plates are affected simultaneously. The impact head diameter is 0.5–1 mm, its travel speed along the transition joint is 1–3 mm / s, and the impact time is 30–90 minutes. This high-frequency impact induces micro-plastic deformation at the transition joints, thereby reducing internal stress and ensuring the stability and reliability of subsequent processes.

[0041] Example 1

[0042] A new type of turbofan engine serves as the power plant for my country's new fighter jet. It is made of TA15 titanium alloy and has a three-layer structure from the inside out. The inner layer is a K-shaped inner casing, the middle layer has a semi-enclosed V-shaped flow divider ring, and the outer casing has three mounting edges and over 30 protrusions of different shapes, with 10 hollow support plates evenly distributed. The thickness varies; the V-shaped flow divider ring is the thinnest at only 1.2 mm, the hollow support plates are 1.5 mm thick, and most other components are around 2 mm thick. Taking the intermediate casing of this engine as an example, this paper describes the stress relief method for a powder metallurgy integral intermediate casing.

[0043] (1) The intermediate casing structure was redesigned based on the characteristics of powder metallurgy forming, and some positions were adjusted and optimized. The hollow support plate passes through the inner casing, the flow divider ring and the outer casing. The corresponding transition connection is the most prone to stress concentration. Through simulation calculation, the transition connection is designed with progressively increasing fillets from the inside to the outside. The fillet design values ​​for the hollow support plate and the inner casing, and the flow divider ring and the outer casing are R6, R9 and R12, respectively.

[0044] (2) Based on the optimized intermediate casing structure, the intermediate casing forming sleeve is designed. A typical intermediate casing structure includes multiple layers from the inside to the outside, such as the inner casing, the flow divider ring and the outer casing, and different numbers of hollow support plates are evenly distributed in the circumferential direction.

[0045] (3) Processing intermediate casing sleeve, mainly including inner casing forming sleeve, outer casing forming sleeve, hollow support plate forming sleeve, diverter ring forming sleeve, positioning block, sleeve upper cover, sleeve lower cover and auxiliary fixing components, all of which are made of 20# steel.

[0046] (4) Assemble and weld the various parts of the intermediate casing sleeve obtained by processing. Put titanium alloy spherical powder into the intermediate casing sleeve through the reserved powder filling hole. Use knocking and vibration to compact the powder. Finally, weld the reserved degassing steel pipe to obtain a complete intermediate casing sleeve.

[0047] (5) Place the complete intermediate casing sleeve into the resistance furnace, connect the degassing steel pipe to the vacuum unit, and evacuate at high temperature. After degassing, seal the steel pipe. Finally, place the sealed intermediate casing sleeve into a hot isostatic press for hot isostatic pressing treatment. The degassing temperature is 800℃, and the vacuum degree is better than 5*10. -3 The vacuuming time is 8 hours; the process parameters for hot isostatic pressing are: temperature 920℃, pressure 140MPa, and time 4 hours.

[0048] (6) After hot isostatic pressing, most of the cladding on the intermediate housing is removed by machining. Machining is the most effective way to remove the cladding, but a certain allowance of 5mm must be left in order not to damage the intermediate housing product. During the machining process, the stress state of the component is dynamically changing, and stress state control is achieved by symmetrical removal. If there are 10 hollow support plates, the intermediate housing cladding is also divided into 10 pieces. Milling is performed starting from any piece, numbered as piece 1. After machining, piece 6 is machined symmetrically, then piece 2 is machined adjacent to piece 1, and piece 7 is machined symmetrically, and so on, until the cladding of all 10 pieces of the intermediate housing is removed. Then, the remaining cladding on the intermediate housing product is removed by electrolytic removal.

[0049] (7) First, the titanium alloy intermediate housing blank is finished. After finishing, the powder metallurgy integral intermediate housing is subjected to integral clamping gradient high-temperature vacuum annealing. A special tooling for TA15 titanium alloy is designed, with the intermediate housing placed on the chassis. The inner support ring and outer clamping ring are also connected to the chassis via connecting rods. An outward force is applied from the inside of the inner housing, and an inward force is applied from the outside of the outer housing to clamp the entire intermediate housing. Then, it is placed in a vacuum annealing furnace for gradient vacuum annealing, with a vacuum level requirement better than 1*10. -3Pa, the temperature is raised from room temperature to 600℃, held for 180 minutes, then raised to 800℃ and held for 90 minutes, then cooled to 600℃ and held for another 180 minutes, and finally cooled to below 100℃ before being removed from the furnace.

[0050] After annealing, the intermediate casing blank undergoes rough machining, followed by high-frequency impact treatment at the transition joint. The transition joint is the location of highest stress concentration within the entire intermediate casing. A specialized device is designed to utilize high-density energy to drive impact heads at a frequency of 8000 times per second to impact the rounded corners of the transition joint. The device uses 10 impact heads simultaneously acting on the transition rounded corners of 10 hollow support plates. The impact head diameter is 0.8 mm, the travel speed is 2 mm / s, and the action time is 60 minutes, inducing micro-plastic deformation at the transition joint to reduce internal stress. Finally, the intermediate casing blank undergoes finishing machining and subsequent processing steps to obtain the final intermediate casing component.

[0051] The room temperature mechanical properties, high temperature mechanical properties, and creep rupture properties of the formed intermediate casing were tested according to GB / T228, GB / T4338, and GB / T2039, respectively. The room temperature mechanical properties showed yield strengths of 926 MPa, 921 MPa, and 925 MPa; tensile strengths of 995 MPa, 994 MPa, and 996 MPa; elongation of 17.0%, 19.0%, and 18.5%; and reduction of area of ​​37%, 46%, and 46%. The tensile strengths at 500℃ were 652 MPa, 632 MPa, and 641 MPa. The creep rupture properties at 500℃ and 470 MPa remained intact for 60 hours. The annealed intermediate casing underwent X-ray inspection according to GJB 1187A and was judged according to ASTM E1320. The X-ray inspection results showed no porosity, looseness, or inclusions. The overall performance of the intermediate casing formed by hot isostatic pressing reaches the level of forgings, with high material properties and high internal quality.

[0052] Four fluorescence tests were performed on the intermediate casing components: after annealing, after high-frequency impact treatment, after finishing, and after all processes were completed. The fluorescence tests were conducted according to GJB 2367A, and no surface cracks were found in any of the tests. After the high-frequency multi-point impact treatment, the intermediate casing underwent one X-ray diffraction stress test, mainly testing the stress at the transition connection of the support plates. All 10 support plates were tested, with 13 test points taken from the inside to the outside of each support plate, covering all locations. The test results for support plate No. 1 are shown in Table 1, and the results for the other support plates are similar. It can be seen that the residual stress at the transition connection of the support plates is very small, and the stress state of the entire intermediate casing is well controlled.

[0053] Table 1. Stress test results of support plate No. 1

[0054]

[0055]

[0056] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A method for stress relief of an integral intermediate casing in powder metallurgy, wherein the intermediate casing comprises an inner casing, a flow divider ring, and an outer casing, characterized in that... include: First, the intermediate casing structure is redesigned based on the characteristics of powder metallurgy forming. The transition connection between the hollow support plate and the inner casing, the flow divider ring and the outer casing is designed with progressively increasing fillets from the inside to the outside. The fillet design values ​​for the transition connection between the hollow support plate and the inner casing, the flow divider ring and the outer casing are R3~R6, R6~R9 and R9~R12, respectively. The intermediate casing is manufactured using a near-net-shape powder metallurgy method, and the cladding is removed using symmetrical machining and electrolysis to obtain the intermediate casing blank; during the machining process, high-frequency impact stress relief treatment is performed at the transition connection. The intermediate housing blank is subjected to integral clamping gradient high-temperature vacuum annealing to ensure that the stress of the intermediate housing is minimized. The overall clamping gradient high-temperature vacuum annealing of the intermediate casing blank includes: Using tooling, an outward force is applied from the inside of the inner casing, and an inward force is applied from the outside of the outer casing to tightly clamp the entire intermediate casing. It is then placed in a vacuum annealing furnace for gradient vacuum annealing, with a vacuum level requirement better than 1*10⁻⁶. -3 Pa, the temperature is raised from room temperature to 600-650℃, held for 120-240 minutes, after which the temperature is raised to 750-850℃, held for 60-120 minutes, after which the temperature is lowered to 600-650℃, held for another 120-240 minutes, and finally cooled to below 100℃ before being removed from the furnace.

2. The stress relief method for a powder metallurgy integral intermediate casing according to claim 1, characterized in that: The symmetrical machining method is as follows: Assuming the number of hollow support plates is 2n, the intermediate housing casing is also divided into 2n blocks. Starting from any block, milling is performed to remove it, and the block is numbered as the first block. After the first block is finished, the (n+1)th block is machined symmetrically. Then the second block adjacent to the first block is machined, and the (n+2)th block is machined symmetrically after the first block is finished, and so on, until the entire intermediate housing casing casing is machined and removed.

3. The stress relief method for a powder metallurgy integral intermediate casing according to claim 1, characterized in that: The symmetrical machining process leaves a margin of 3-5mm.

4. The stress relief method for a powder metallurgy integral intermediate casing according to claim 1, characterized in that: The tooling includes a chassis, an inner support ring, and an outer clamping ring. The chassis is the basic component of the tooling and also the transmission component. The intermediate housing is placed on the chassis. The inner support ring and the outer clamping ring are connected to the chassis via connecting rods. The inner support ring acts on the inner housing, applying an outward force to the intermediate housing, while the outer clamping ring acts on the outer housing, applying an inward force to the intermediate housing. Both the inner support ring and the outer clamping ring adopt a semi-circular arc design and are connected by screws to ensure that the outward and inward forces acting on the intermediate housing are adjustable.

5. The stress relief method for a powder metallurgy integral intermediate casing according to claim 1, characterized in that: The tooling is made of the same grade of titanium alloy as the intermediate casing.

6. The stress relief method for a powder metallurgy integral intermediate casing according to claim 4, characterized in that: The outer diameter of the inner support ring is equal to the inner diameter of the inner casing, and the angle of each semicircle is 160-175°; the inner diameter of the outer clamping ring is equal to the outer diameter of the outer casing, and the angle of each semicircle is 150-165°.

7. The stress relief method for a powder metallurgy integral intermediate casing according to claim 1, characterized in that: Between the roughing and finishing processes, the intermediate casing transition connection is subjected to high-frequency impact stress relief treatment.

8. The stress relief method for a powder metallurgy integral intermediate casing according to claim 1, characterized in that: The impact head is driven to impact the rounded corner of the transition connection at a frequency of 5,000 to 10,000 times per second, and acts simultaneously on the transition connection of all hollow support plates. The diameter of the impact head is 0.5 to 1 mm, the traveling speed along the transition connection is 1 to 3 mm / s, and the action time is 30 to 90 minutes.

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