A short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan

Abstract

This invention discloses a short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan, comprising the following steps: S1, pre-formation of the pre-formed billet; S2, pre-forming of the blind-hole inner flange: using a blind-hole inner flange forming die ring, which is installed on the anvil of a forging press, the cylindrical forging billet is pre-formed to form the blind-hole inner flange, completing the inner hole pre-forming and blind-hole inner flange blank reservation simultaneously in one operation; S3, eight-sided material distribution; S4, initial elongation of the cylinder; S5, die forging of the outer flange and transition large fillet: designing and manufacturing an automatic turntable mechanism, a positioning outer die, and an integrated forming inner die for the inner fillet of the outer flange. Under the action of the press, the integrated forming inner die for the inner fillet of the outer flange performs die forging on the inner hole of the upper end of the forging billet, simultaneously forming the outer flange and the transition large fillet at the inner hole of the outer flange on the upper part of the forging billet in one operation; S6, elongation and finishing of the cylinder. The forging process of this invention has fewer forging passes, higher forming accuracy, longer die life, and lower forging manufacturing cost.

Description

Technical Field

[0001] This invention relates to the field of large forging manufacturing technology, specifically to a short-process near-net-shape forging process for a large thin-walled hollow fan main shaft. Background Technology

[0002] As offshore wind power develops towards higher power outputs of 10 MW+, the main shaft of wind turbines is trending towards larger size, thinner walls, and higher strength and toughness (materials such as Q460NE and 34CrNiMo6). Traditional forging processes suffer from the following prominent problems: First, it involves multiple firing cycles and high energy consumption: conventional processes require 5 to 6 firing cycles, and repeated heating leads to oxidation loss of 4% to 6%, resulting in high energy consumption and high carbon emissions.

[0003] Secondly, the forming accuracy is low: the transition area between the outer flange and the cylinder relies on manual grinding, resulting in poor consistency of the rounded corners, and UT testing is prone to folding or insufficient filling.

[0004] Third, blind hole forming is difficult: the flange inside the lower blind hole needs to be punched through before sealing the bottom, which is a complicated process and the bottom welding risk is high.

[0005] Fourth, the die life is short: the stacked die forging of the outer flange is subjected to uneven axial heat transfer (hot on top and cold on the bottom) under high temperature impact, which leads to inconsistent radial expansion of the outer ring of each layer, resulting in interlayer misalignment, steps or even circumferential cracks. The die life is usually less than 30 pieces. Frequent die replacement not only increases costs, but also affects the continuity and efficiency of production.

[0006] Therefore, there is an urgent need for a short-process near-net-shape forming process for forging the main shaft of large thin-walled hollow fans, which features fewer forging passes, precise forming, long die life, and intelligent thermal management. This process would allow the forgings to closely approximate the shape and size of the final product, thereby reducing subsequent machining, improving material utilization and production efficiency, and lowering manufacturing costs. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a short-process, near-net-shape forging process for large, thin-walled hollow fan main shafts. This process aims to achieve full forging in 3-4 heat treatments through highly integrated operations. Combined with a specialized die structure and an innovative heat equalization device, it simultaneously improves forming accuracy and die reliability while reducing forging manufacturing costs. The specific technical solution is as follows: A short-process near-net-shape forging process for a large thin-walled hollow fan main shaft is disclosed. The forging structure of the thin-walled hollow fan main shaft includes an upper outer flange, a variable cross-section thin-walled cylinder, and a lower blind hole inner flange, which are integrally connected from top to bottom. The inner hole of the outer flange is provided with a large transition fillet, and the connection between the outer flange and the outer circle of the cylinder is also provided with a large transition fillet. The short-process near-net-shape forging process includes the following steps: S1. Precast billet preparation: A large continuously cast round billet is used, which is then upset and drawn in sequence to obtain a preliminary cylindrical forging billet; S2. Pre-forming of blind hole inner flange: Using a blind hole inner flange forming die ring, which is installed on the anvil of the forging press, the cylindrical forging blank is pre-formed into a blind hole inner flange; the inner cavity of the blind hole inner flange forming die ring is designed as follows: the lower half is a straight hole and the upper half is a tapered hole; during forming, the lower part of the cylindrical forging blank is placed in the blind hole inner flange forming die ring, first upsetting, and then punching with a short punch; the stroke of the short punch is controlled so that the punching process does not penetrate through, and the bottom blank is retained to directly form the blank of the lower blind hole inner flange, thereby completing the inner hole pre-forming and blind hole inner flange blank reservation in one operation; S3, Eight-sided material distribution: The short punch is left in the forging billet without being removed. A special material distribution pressure head is used to lay the forging billet flat. At the outer circle position where the outer flange of the forging billet is adjacent to the cylinder, the forging billet is divided into at least eight equal parts in the circumference and pressure is applied to each part, thereby pressing out a material distribution groove along the circumference. S4. Initial drawing of the cylinder: Remove the short punch from the inner hole of the forging billet, replace it with a long mandrel, and draw the thickened part of the cylinder. S5. Die forging of outer flange and transition large fillet: Design and manufacture an automatic turntable mechanism, a positioning outer die, and an inner die for integral forming of the inner fillet of the outer flange. Fix the positioning outer die on the automatic turntable mechanism. Place the cylindrical part of the forging blank into the inner cavity of the positioning outer die. The lower step of the outer circle of the upper part of the forging blank, which belongs to the outer flange, is in contact with the upper end face of the positioning outer die. Using the inner die for integral forming of the inner fillet of the outer flange, under the action of the press, the inner die for integral forming of the inner fillet of the outer flange performs die forging on the inner hole part of the upper end of the forging blank, and simultaneously forms the transition large fillet at the inner hole of the outer flange and the outer flange at the upper part of the forging blank in one go. S6. Lengthening and finishing of the cylinder: The formed forging is moved to the free forging station, and a long mandrel is inserted into the inner hole to lengthen and finish the thin-walled cylinder section in the middle to achieve the target size and ensure the parallelism and perpendicularity of the flanges at both ends.

[0008] Preferably, the upper part of the blind hole inner flange forming die ring has a tapered hole with a single-sided 45° (total tapered angle 90°).

[0009] Preferably, the continuously cast round billet is a continuously cast round billet with a diameter of more than 1 meter, and the material of the continuously cast round billet is Q460NE.

[0010] Preferably, the heating cycles of the short-process near-net-shape forging process are arranged as follows: First heating: The continuously cast round billet is heated to the initial forging temperature, and the pre-formed billet preparation in step S1 and the blind hole inner flange prefabrication in step S2 are completed in sequence. Second heating: The forging billet obtained in step S2 is reheated to the initial forging temperature, and the eight-sided material distribution in step S3 and the initial elongation of the cylinder in step S4 are completed in sequence. Third heating: The forging billet obtained in step S4 is reheated to the initial forging temperature to complete the die forging of the outer flange and transition large fillet in step S5; Fourth heating: The forging billet obtained in step S5 is reheated to the initial forging temperature to complete the cylinder drawing and finishing in step S6.

[0011] Preferably, the furnace exit temperature of the first furnace pass is 1150 ± 20℃, and the final forging temperature is ≥900℃; the furnace exit temperature of the second furnace pass is 1180 ± 20℃, and the final forging temperature is ≥920℃; the furnace exit temperature of the third furnace pass is 1150 ± 20℃, and the final forging temperature is ≥900℃; and the furnace exit temperature of the fourth furnace pass is 1120 ± 20℃, and the final forging temperature is ≥900℃.

[0012] In this invention, the main shaft of the large thin-walled hollow fan is normalized after forging to refine the grains and eliminate residual stress.

[0013] Preferably, the cross-sectional shape of the material distribution groove is V-shaped, and the bottom of the groove is provided with rounded corners. The side of the V-shaped material distribution groove near the outer flange is perpendicular to the axis of the cylinder.

[0014] In this invention, the inner mold for integral forming of the outer flange inner rounded corner includes a clamping flange section, a transition large rounded corner section, a straight neck section, and a tapered guide section that are integrally connected from top to bottom.

[0015] Preferably, the inner mold for integrally forming the inner rounded corner of the outer flange adopts a double-fan-shaped block structure with symmetrical left and right sides instead of a whole circular inner mold. This, combined with an automatic turntable mechanism, achieves indexing rotation and pressure application, forming a complete transitional large rounded corner at the inner hole of the outer flange of the forging. This "rotationally symmetrical local die forging" process significantly reduces forging pressure, breaking down the challenge of one-time forming using an ultra-large press into multiple local forming processes that can be completed by a medium-sized press. This significantly lowers the equipment investment threshold and manufacturing costs.

[0016] Preferably, the positioning outer mold includes a leaking plate assembly composed of a number of leaking plates stacked and connected vertically, with adjacent leaking plates positioned and engaged by positioning stops, and the inner hole of the uppermost leaking plate having a large transition radius.

[0017] By setting up a stacked structure for the die plate, it can flexibly adapt to the forging of spindles of different lengths, enhancing the versatility of the process. More importantly, it greatly reduces the maintenance cost of the mold. When individual die plates are damaged, they only need to be replaced individually, reducing the maintenance cost of replacing conventional integral die plates.

[0018] To address the problem of interlayer deformation and cracking caused by uneven axial heat transfer in the stacked mold trays, this invention further includes a mold temperature balancing anti-cracking device on the mold tray assembly of the positioning outer mold. This device is used to maintain a uniform temperature between the upper and lower parts of the mold and reduce the tendency of uneven deformation and cracking of the mold trays. The mold temperature balancing anti-cracking device includes a number of high thermal conductivity strips vertically arranged on the outer circle of the mold tray assembly and evenly spaced along the circumference; a number of thermally conductive grooves radially opened between adjacent upper and lower mold trays and evenly spaced along the circumference; and high thermal conductivity sheets installed in the thermally conductive grooves and connected to the high thermal conductivity strips at corresponding positions.

[0019] Preferably, in the drain plate assembly, the outer circles of the uppermost and lowermost drain plates are larger than the outer circles of the other drain plates, and an installation groove is formed on the outer circle of the drain plate in the vertical direction. The upper and lower ends of the high thermal conductivity strip are embedded in the installation groove and are pressed and fixed by screws and elastic washers. The high thermal conductivity strip is connected to the high thermal conductivity sheet by screws and elastic washers.

[0020] The high thermal conductivity strip is embedded in the mounting groove at both ends and pressed together with screws and elastic washers, ensuring thermal contact while allowing for thermal expansion and slippage. The outer end of the high thermal conductivity sheet has an L-shaped bend to form a large-area contact with the high thermal conductivity strip. A receiving groove is formed on the outer circumference of the drain plate, and the L-shaped bend of the high thermal conductivity sheet is placed in the receiving groove.

[0021] Preferably, the high thermal conductivity strip and the high thermal conductivity sheet are made of chromium zirconium copper or oxygen-free copper, and the high thermal conductivity strip has a waist-shaped hole for the screw to pass through.

[0022] As a further improvement, an annular groove is provided between the upper and lower adjacent drain plates and near the inner hole of the drain plate, and an annular high thermal conductivity gasket is embedded in the annular groove.

[0023] The working principle of the temperature balancing crack prevention device is as follows: During the third forging of the outer flange, heat is mainly transferred from the bottom of the forging to the upper layer of the mold plate, resulting in a significantly higher temperature in the upper layer than in the lower layer. In traditional laminated structures, due to poor thermal conductivity in the air gaps between layers, the radial expansion of the upper outer ring is much greater than that of the lower layer, generating shear stress and causing cracking. This invention uses high thermal conductivity strips and heat-conducting sheets to form a low thermal resistance axial thermal bridge, rapidly conducting heat from the upper layer downwards, significantly reducing the axial temperature difference, and making the thermal expansion of each layer of the mold plate more uniform, fundamentally eliminating uneven deformation and cracking tendencies. The specific implementation process is as follows: During forging, more heat is transferred from the high-temperature forging to the upper layer of the rotating die assembly, resulting in uneven temperature between the upper and lower molds. The heat from each layer is quickly collected by the high thermal conductivity sheet. With the upper layer having a higher temperature and the lower layer having a lower temperature, the heat is conducted downwards through the axial "thermal highway" of the high thermal conductivity strip, and diffused circumferentially through the annular high thermal conductivity gasket. This quickly equalizes the temperature field of the entire rotating die assembly in the axial and circumferential directions, making the thermal expansion of each layer of the die synchronized. This fundamentally suppresses problems such as interlayer misalignment and microcrack initiation caused by thermal stress, and significantly improves the reliability and lifespan of the mold under rotating working conditions.

[0024] Furthermore, an annular high thermal conductivity gasket is embedded between the upper and lower adjacent drain plates and near the inner hole. After secondary precision machining, the annular high thermal conductivity gasket is coplanar with the end face of the drain plate, which can rapidly diffuse the local heat from the heat-conducting sheet along the circumference, realize the circumferential temperature balance of the inner wall area, and prevent the inner hole edge from generating circumferential cracks due to local overheating.

[0025] The beneficial effects of this invention are: First, the present invention provides a short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan. Through processes such as "pre-fabrication of blind hole inner flange" and "eight-sided material distribution", materials are precisely pre-allocated, and then precisely formed by die forging. This significantly reduces machining allowance and increases material utilization to over 65%. Through process integration, the traditional 5-6 forging cycles are reduced to 4 forging cycles, reducing energy consumption per piece by over 25% and reducing oxidation loss by 1.5%.

[0026] Secondly, the present invention provides a short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan. By adopting a blind-hole inner flange forming die ring and combining it with a "bottom-punching" process, subsequent bottom-sealing welding can be avoided, thus eliminating internal defect sources.

[0027] Third, the present invention provides a short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan. The mold temperature balancing anti-crack device forms a three-dimensional thermal equilibrium network through high thermal conductivity strips, thermal conductive sheets, and annular washers, achieving dual temperature control in both the axial and circumferential directions. This can effectively suppress thermal cracking of the stacked slotted disc and increase the mold service life by more than double.

[0028] Fourth, the present invention provides a short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan. Through the "eight-sided material distribution" groove prefabrication process and the "rotationally symmetrical local die forging" process, the forging pressure is greatly reduced. The problem of requiring one-time forming with an ultra-large press is decomposed into multiple local forming processes that can be completed by a medium-sized press, which can significantly reduce the equipment investment threshold and manufacturing cost. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to the present invention. Figure 2 This is a structural schematic diagram of a forged thin-walled hollow fan main shaft forging. Figure 3 This is a schematic diagram of step S1 in a short-process near-net-shape forging process for a large thin-walled hollow fan main shaft according to the present invention. Figure 4 This is a schematic diagram of step S2, which involves die forging using a blind hole inner flange forming die ring, in a short-process near-net-shape forming forging process for the main shaft of a large thin-walled hollow fan according to the present invention. Figure 5 This is a schematic diagram of step S3 in a short-process near-net-shape forging process for a large thin-walled hollow fan main shaft according to the present invention. Figure 6 This is a schematic diagram of step S4 in a short-process near-net-shape forging process for a large thin-walled hollow fan main shaft according to the present invention. Figure 7 This is a schematic diagram of the forming process in step S5 of a short-process near-net-shape forming forging process for a large thin-walled hollow fan main shaft according to the present invention, in which an automatic turntable mechanism, a positioning outer mold, and an inner mold for integral forming of the outer flange inner rounded corner are used for die forging. Figure 8 This is a schematic diagram of step S6 in a short-process near-net-shape forging process for a large thin-walled hollow fan main shaft according to the present invention. Figure 9 Is Figure 7 Based on the above, a schematic diagram of a further improved structure for the leaky disc assembly is provided.

[0030] In the diagram: 1. Thin-walled hollow fan main shaft forging; 2. Outer flange; 3. Variable cross-section thin-walled cylinder; 4. Blind hole inner flange; 5. Transition large fillet; 6. Blind hole inner flange forming mold ring; 7. Straight hole; 8. Tapered hole; 9. Short punch; 10. Material distribution groove; 11. Long mandrel; 12. Automatic turntable mechanism; 13. Positioning outer mold; 14. Outer flange inner fillet integral forming inner mold; 15. Squeegee; 16. Squeegee assembly; 17. Positioning stop; 18. Mold temperature upper and lower balancing anti-crack device; 19. High thermal conductivity strip; 20. Thermal conductivity groove; 21. High thermal conductivity sheet; 22. Mounting groove; 23. Screw; 24. Elastic washer; 25. L-shaped bend; 26. Storage groove; 27. Waist-shaped hole; 28. Annular groove; 29. ​​Annular high thermal conductivity washer. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0032] like Figures 1 to 9 The illustration shows an embodiment of a short-process near-net-shape forging process for a large thin-walled hollow fan main shaft according to the present invention. The structure of the thin-walled hollow fan main shaft forging 1 includes an upper outer flange 2, a variable cross-section thin-walled cylinder 3, and a lower blind hole inner flange 4, which are integrally connected from top to bottom. A transition large fillet 5 is provided at the inner hole of the outer flange 2, and a transition large fillet 5 is provided at the connection between the outer flange 2 and the outer circle of the cylinder. The short-process near-net-shape forging process includes the following steps: S1. Precast billet preparation: A large continuously cast round billet is used, which is then upset and drawn in sequence to obtain a preliminary cylindrical forging billet; S2. Pre-forming of the blind hole inner flange: Using the blind hole inner flange forming die ring 6, which is installed on the anvil of the forging press, the cylindrical forging blank is pre-formed into the blind hole inner flange 4. The inner cavity of the blind hole inner flange forming die ring 6 is designed as follows: the lower half is a straight hole 7 and the upper half is a tapered hole 8. During forming, the lower part of the cylindrical forging blank is placed in the blind hole inner flange forming die ring 6, and upsetting is performed first, followed by punching with a short punch 9. The stroke of the short punch 9 is controlled so that the punching process does not penetrate through, and the bottom blank is retained to directly form the blank of the lower blind hole inner flange 4, thereby completing the inner hole pre-forming and the blank retention of the blind hole inner flange 4 in one operation. S3, Eight-sided material distribution: The short punch 9 is retained in the forging billet and not removed. A special material distribution pressure head is used to lay the forging billet flat. At the outer circle position of the outer flange 2 of the forging billet adjacent to the cylinder, the forging billet is divided into at least eight equal parts in the circumference and pressure is applied to each part, thereby pressing out a material distribution groove 10 in the circumference. S4. Initial drawing of the cylinder: Remove the short punch 9 from the inner hole of the forging billet, replace it with the long mandrel 11, and draw the thickened part of the cylinder. S5. Die forging of outer flange and transition large fillet: Design and manufacture an automatic turntable mechanism 12, a positioning outer mold 13, and an inner mold 14 for integral forming of outer flange inner fillet. Fix the positioning outer mold 13 on the automatic turntable mechanism 12. Place the cylindrical part of the forging blank into the inner cavity of the positioning outer mold 13. The lower step of the outer circle of the upper part of the forging blank, which belongs to the outer flange 2, is in contact with the upper end face of the positioning outer mold 13. Using the inner mold 14 for integral forming of outer flange inner fillet, under the action of the press, the inner mold 14 for integral forming of outer flange inner fillet performs die forging on the inner hole part of the upper end of the forging blank, and simultaneously forms the outer flange 2 and the transition large fillet 5 at the inner hole of the outer flange 2 at the upper part of the forging blank. S6. Lengthening and finishing of the cylinder: The formed forging is moved to the free forging station. A long mandrel 11 is inserted into the inner hole to lengthen and finish the three parts of the thin-walled cylinder in the middle to achieve the target size and ensure the parallelism and perpendicularity of the flanges at both ends.

[0033] Preferably, the upper part of the tapered hole 8 of the blind hole inner flange forming die ring 6 is a tapered hole with a single-sided 45° (total cone angle 90°).

[0034] Preferably, the continuously cast round billet is a continuously cast round billet with a diameter of more than 1 meter, and the material of the continuously cast round billet is Q460NE.

[0035] Preferably, the heating cycles of the short-process near-net-shape forging process are arranged as follows: First heating: The continuously cast round billet is heated to the initial forging temperature, and the pre-formed billet preparation in step S1 and the prefabrication of blind hole inner flange 4 in step S2 are completed in sequence. Second heating: The forging billet obtained in step S2 is reheated to the initial forging temperature, and the eight-sided material distribution in step S3 and the initial elongation of the cylinder in step S4 are completed in sequence. Third heating: The forging billet obtained in step S4 is reheated to the initial forging temperature to complete the die forging of the outer flange 2 and the transition large fillet 5 in step S5; Fourth heating: The forging billet obtained in step S5 is reheated to the initial forging temperature to complete the cylinder drawing and finishing in step S6.

[0036] Preferably, the furnace exit temperature of the first furnace pass is 1150 ± 20℃, and the final forging temperature is ≥900℃; the furnace exit temperature of the second furnace pass is 1180 ± 20℃, and the final forging temperature is ≥920℃; the furnace exit temperature of the third furnace pass is 1150 ± 20℃, and the final forging temperature is ≥900℃; and the furnace exit temperature of the fourth furnace pass is 1120 ± 20℃, and the final forging temperature is ≥900℃.

[0037] In this embodiment, the large thin-walled hollow fan main shaft forging 1 is normalized after forging to refine the grains and eliminate residual stress.

[0038] Preferably, the cross-sectional shape of the material distribution groove 10 is V-shaped, and the bottom of the groove is provided with rounded corners. The side of the V-shaped material distribution groove 10 near the outer flange 2 is perpendicular to the axis of the cylinder.

[0039] In this embodiment, the inner mold 14, which is integrally formed with the inner rounded corner of the outer flange, includes a clamping flange section, a transition large rounded corner section, a straight neck section, and a tapered guide section that are integrally connected from top to bottom.

[0040] Preferably, the inner mold 14, which is integrally formed with rounded inner corners of the outer flange, adopts a double-fan-shaped block structure with symmetrical left and right sides instead of a whole circular inner mold. This, combined with the automatic turntable mechanism 12, enables indexing and rotational pressure application, forming a complete transition rounded corner 5 at the inner hole of the outer flange 2 of the forging. This "rotationally symmetrical local die forging" process significantly reduces forging pressure, breaking down the challenge of one-time forming using an ultra-large press into multiple local forming processes that can be completed by a medium-sized press. This significantly lowers the equipment investment threshold and manufacturing costs.

[0041] Preferably, the positioning outer mold 13 includes a drain plate assembly 16 composed of a number of drain plates 15 stacked and connected vertically. The upper and lower adjacent drain plates 15 are positioned and fitted together by positioning stops 17, and the inner hole of the uppermost drain plate 15 is provided with a transition large rounded corner 5.

[0042] By setting the overlapping structure of the slotted plate 15, it can flexibly adapt to the forging of spindles of different lengths and specifications, enhancing the versatility of the process. More importantly, it greatly reduces the maintenance cost of the mold. When individual slotted plates 15 are damaged, they only need to be replaced individually, reducing the maintenance cost of replacing conventional integral slotted plates.

[0043] To address the interlayer deformation and cracking problem caused by uneven axial heat transfer in the stacked slotted discs 15, this embodiment further includes a mold temperature balancing anti-cracking device 18 on the slotted disc assembly 16 of the positioning outer mold 13. This device is used to maintain a uniform temperature between the upper and lower parts of the mold and reduce the tendency of uneven deformation and cracking of the slotted discs 15. The mold temperature balancing anti-cracking device 18 includes a number of high thermal conductivity strips 19 vertically arranged on the outer circle of the slotted disc assembly 16 and evenly spaced along the circumference; a number of thermally conductive grooves 20 radially opened between adjacent upper and lower slotted discs 15 and evenly spaced along the circumference; and high thermal conductivity sheets 21 installed in the thermally conductive grooves 20 and connected to the high thermal conductivity strips 19 at corresponding positions.

[0044] Preferably, in the drain plate assembly 16, the outer circles of the uppermost drain plate 15 and the lowermost drain plate 15 are larger than the outer circles of the other drain plates 15, and an installation groove 22 is formed on the outer circle of the drain plate 15 in the vertical direction. The upper and lower ends of the high thermal conductivity strip 19 are embedded in the installation groove 22 and are pressed and fixed by screws 23 and elastic washers 24. The high thermal conductivity strip 19 is connected to the high thermal conductivity sheet 21 by screws 23 and elastic washers 24.

[0045] The high thermal conductivity strip 19 is embedded in the mounting groove 22 at its upper and lower ends and is pressed together by screws 23 and elastic washers 24, ensuring thermal contact while allowing for thermal expansion and slippage. The outer end of the high thermal conductivity sheet 21 is provided with an L-shaped bend 25 to form a large-area contact with the high thermal conductivity strip 19. A receiving groove 26 is provided on the outer circumference of the drain plate 15, and the L-shaped bend 25 of the high thermal conductivity sheet 21 is placed in the receiving groove 26.

[0046] Preferably, the high thermal conductivity strip 19 and the high thermal conductivity sheet 21 are made of chromium zirconium copper or oxygen-free copper, and the high thermal conductivity strip 19 has an oblong hole 27 for passing through the screw 23.

[0047] As a further improvement, an annular groove 28 is provided between the upper and lower adjacent drain plates 15 and near the inner hole of the drain plate 15, and an annular high thermal conductivity gasket 29 is embedded in the annular groove 28.

[0048] The working principle of the temperature balancing anti-cracking device 18 is as follows: During the third forging of the outer flange 2, heat is mainly transferred from the bottom of the forging to the upper layer of the mold plate assembly 16, resulting in a significantly higher temperature in the upper layer than in the lower layer. In traditional laminated structures, due to the poor thermal conductivity of the air gaps between layers, the radial expansion of the outer ring of the upper layer is much greater than that of the lower layer, generating shear stress and causing cracking. In this embodiment, a low thermal resistance axial thermal bridge is formed by the high thermal conductivity strip 19 and the high thermal conductivity sheet 21 in the thermal groove 20, which quickly conducts the heat from the upper layer downwards, significantly reducing the axial temperature difference and making the thermal expansion of each layer of the mold plate 15 more uniform, fundamentally eliminating uneven deformation and cracking tendency. The specific implementation process is as follows: During forging, more heat is transferred from the high-temperature forging to the upper layer of the rotating mold assembly 16, resulting in uneven temperature between the upper and lower molds. The heat from each layer is quickly collected by the high thermal conductivity sheet 21. When the upper layer has a high temperature and the lower layer has a low temperature, the heat is conducted downward through the axial "thermal highway" of the high thermal conductivity strip 19, and diffused circumferentially through the annular high thermal conductivity gasket 29. This quickly equalizes the temperature field of the entire rotating mold assembly 16 in the axial and circumferential directions, so that the thermal expansion of each layer of the mold 15 is synchronized. This fundamentally suppresses problems such as interlayer misalignment and microcrack initiation caused by thermal stress, and significantly improves the reliability and lifespan of the mold in the rotating working state.

[0049] Furthermore, an annular high thermal conductivity gasket 29 is embedded between the upper and lower adjacent drain plates 15 and near the inner hole. After secondary precision machining, the annular high thermal conductivity gasket 29 is coplanar with the end face of the drain plate 15, which can rapidly diffuse the local heat from the high thermal conductivity sheet 21 along the circumference, realize the circumferential temperature balance of the inner wall area, and prevent the inner hole edge from generating circumferential cracks due to local overheating.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan, characterized in that, The structure of the thin-walled hollow fan main shaft forging includes an upper outer flange, a variable cross-section thin-walled cylinder, and a lower blind hole inner flange, which are integrally connected from top to bottom. The inner hole of the outer flange is provided with a large transition fillet, and the connection between the outer flange and the outer circle of the cylinder is also provided with a large transition fillet. The short-process near-net-shape forging process includes the following steps: S1. Precast billet preparation: A large continuously cast round billet is used, which is then upset and drawn to obtain a preliminary cylindrical forging billet. S2. Pre-forming of blind hole inner flange: Using a blind hole inner flange forming die ring, which is installed on the anvil of the forging press, the cylindrical forging blank is pre-formed into a blind hole inner flange; the inner cavity of the blind hole inner flange forming die ring is designed as follows: the lower half is a straight hole and the upper half is a tapered hole; during forming, the lower part of the cylindrical forging blank is placed in the blind hole inner flange forming die ring, first upsetting, and then punching with a short punch; the stroke of the short punch is controlled so that the punching process does not penetrate through, and the bottom blank is retained to directly form the blank of the lower blind hole inner flange, thereby completing the inner hole pre-forming and blind hole inner flange blank reservation in one operation; S3, Eight-sided material distribution: The short punch is left in the forging billet without being removed. A special material distribution pressure head is used to lay the forging billet flat. At the outer circle position where the outer flange of the forging billet is adjacent to the cylinder, the forging billet is divided into at least eight equal parts in the circumference and pressure is applied to each part, thereby pressing out a material distribution groove along the circumference. S4. Initial drawing of the cylinder: Remove the short punch from the inner hole of the forging billet, replace it with a long mandrel, and draw the thickened part of the cylinder. S5. Die forging of outer flange and transition large fillet: Design and manufacture an automatic turntable mechanism, a positioning outer die, and an inner die for integral forming of the inner fillet of the outer flange. Fix the positioning outer die on the automatic turntable mechanism. Place the cylindrical part of the forging blank into the inner cavity of the positioning outer die. The lower step of the outer circle of the upper part of the forging blank, which belongs to the outer flange, is in contact with the upper end face of the positioning outer die. Using the inner die for integral forming of the inner fillet of the outer flange, under the action of the press, the inner die for integral forming of the inner fillet of the outer flange performs die forging on the inner hole part of the upper end of the forging blank, and simultaneously forms the transition large fillet at the inner hole of the outer flange and the outer flange at the upper part of the forging blank in one go. S6. Lengthening and finishing of the cylinder: The formed forging is moved to the free forging station, and a long mandrel is inserted into the inner hole to lengthen and finish the thin-walled cylinder section in the middle to achieve the target size and ensure the parallelism and perpendicularity of the flanges at both ends. The material distribution groove has a V-shaped cross-section and a rounded bottom. The side of the V-shaped material distribution groove near the outer flange is perpendicular to the axis of the cylinder. The positioning outer mold includes a drain plate assembly composed of several drain plates that are stacked and connected vertically. The adjacent drain plates are positioned and fitted by a positioning stop. The inner hole of the uppermost drain plate is provided with a large transition rounded corner.

2. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 1, characterized in that, The continuously cast round billet is a continuously cast round billet with a diameter of more than 1 meter, and the material of the continuously cast round billet is Q460NE.

3. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 1, characterized in that, The heating sequence for the short-process near-net-shape forging process is arranged as follows: First heating: The continuously cast round billet is heated to the initial forging temperature, and the pre-formed billet preparation in step S1 and the blind hole inner flange prefabrication in step S2 are completed in sequence. Second heating: The forging billet obtained in step S2 is reheated to the initial forging temperature, and the eight-sided material distribution in step S3 and the initial elongation of the cylinder in step S4 are completed in sequence. Third heating: The forging billet obtained in step S4 is reheated to the initial forging temperature to complete the die forging of the outer flange and transition large fillet in step S5; Fourth heating: The forging billet obtained in step S5 is reheated to the initial forging temperature to complete the cylinder drawing and finishing in step S6.

4. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 3, characterized in that, The furnace exit temperature of the first furnace firing is 1150 ± 20℃, and the final forging temperature is ≥900℃; the furnace exit temperature of the second furnace firing is 1180 ± 20℃, and the final forging temperature is ≥920℃; the furnace exit temperature of the third furnace firing is 1150 ± 20℃, and the final forging temperature is ≥900℃; the furnace exit temperature of the fourth furnace firing is 1120 ± 20℃, and the final forging temperature is ≥900℃.

5. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 1, characterized in that, The inner mold for the outer flange with rounded inner corners includes a clamping flange section, a transition large rounded corner section, a straight neck section, and a tapered guide section that are connected from top to bottom.

6. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 1, characterized in that, The mold temperature balancing anti-crack device is also provided on the mold locating outer mold assemblies to maintain the temperature balance between the upper and lower parts of the mold and reduce the tendency of uneven deformation and cracking of the mold assemblies. The mold temperature balancing anti-crack device includes a number of high thermal conductivity strips that are vertically arranged on the outer circle of the mold assemblies and evenly spaced along the circumference, a number of thermal conductivity grooves that are radially opened between the upper and lower adjacent mold assemblies and evenly spaced along the circumference, and high thermal conductivity sheets that are installed in the thermal conductivity grooves and connected to the high thermal conductivity strips at the corresponding positions.

7. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 6, characterized in that, In the drain plate assembly, the outer circles of the uppermost and lowermost drain plates are larger than the outer circles of the other drain plates, and an installation groove is formed on the outer circle of the drain plate in the vertical direction. The upper and lower ends of the high thermal conductivity strip are embedded in the installation groove and are pressed and fixed by screws and elastic washers. The high thermal conductivity strip is connected to the high thermal conductivity sheet by screws and elastic washers.

8. The short-process near-net-shape forging process for the main shaft of a large thin-walled hollow fan according to claim 6, characterized in that, An annular groove is provided between the upper and lower adjacent drain plates and near the inner hole of the drain plate, and an annular high thermal conductivity gasket is embedded in the annular groove.

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