Point rail forging die with pre-tightening function

Abstract

The point rail forging die with the pre-tightening function comprises an upper die base, a lower die base, a guide sleeve, a guide column, an upper die sleeve, an upper die core, a lower die sleeve and a lower die core, the upper die base is horizontally arranged, and the guide sleeve is vertically installed at the bottom of the upper die base in an interference fit mode; the lower die base is horizontally arranged, and a guide column is vertically installed on the top of the lower die base in an interference fit mode. The guide columns and the guide sleeves are arranged at diagonal positions, and a guide function is realized; an upper die base is fixedly mounted at the bottom of the upper die sleeve; an upper die core is mounted at the bottom of the upper die base in an interference fit manner; a lower die base is fixedly mounted at the top of the lower die sleeve; a lower die core is mounted at the top of the lower die base in an interference fit manner; an upper cavity is designed at the bottom of the upper die core according to the forge piece shape; the top of the lower die core is provided with a lower cavity according to the shape of a forge piece. A pre-tightening assembly structural form is adopted, so that the internal stress of the die in the forming process is reduced to a certain extent, and the service life of the die is prolonged.

Description

Technical Field

[0001] The utility model belongs to the technical field of metal stamping and forging dies for operating and transporting railway turnouts without cutting, and particularly relates to a pre-tightened heart rail forging die. Background Art

[0002] The center rail is a crucial component of railway frogs. Conventional center rail forging dies utilize cores made entirely of cast high-manganese steel, forged high-manganese steel, or alloy steel. This excessive forming force can lead to localized stress in the mold, causing wear, deformation, and even damage. This significantly shortens the mold's lifespan, impacting production efficiency and product quality. Therefore, designing a structure that reduces mold stress is crucial for railway frog center rail production. To address this, the following improved technical solution is proposed. Utility Model Content

[0003] The technical problem solved by the utility model is to provide a pre-tightened heart rail forging die, which adopts a pre-tightened assembly structure to reduce the internal stress of the die during the forming process to a certain extent and increase the service life of the die.

[0004] The technical solution adopted by the utility model is a pre-tightened heart rail forging die, which comprises an upper die base, a lower die base, a guide sleeve, a guide column, an upper die sleeve, an upper die core, a lower die sleeve and a lower die core.

[0005] The upper die base is arranged horizontally, and the guide sleeve is installed in a vertical interference fit at the bottom of the upper die base.

[0006] The lower die base is arranged horizontally, and the top of the lower die base is provided with a guide post for vertical interference fit installation.

[0007] The guide pins and guide sleeves are arranged at diagonal positions and are used to realize the guiding function of the mold.

[0008] The upper die base is fixedly installed on the bottom of the upper die sleeve, and the upper die core is installed on the bottom of the upper die base through interference fit.

[0009] The lower die base is fixedly installed on the top of the lower die sleeve, and the lower die core is installed on the top of the lower die base through interference fit.

[0010] The bottom of the upper die core is designed with an upper cavity according to the shape of the forging; the top of the lower die core is designed with a lower cavity according to the shape of the forging.

[0011] Among the above technical solutions, as the preferred technical solution of the present invention, the guide sleeve is installed through interference fit with the upper die base through the stepped hole; the guide post is installed through interference fit with the lower die base through the through hole.

[0012] In the main technical solution, as the preferred technical solution of the present utility model: the upper die sleeve is fixedly connected to the upper die base by keys and screws; the lower die sleeve is fixedly connected to the lower die base by keys and screws.

[0013] Among the main technical solutions, as the preferred technical solution of the present invention: a lower groove is provided at the bottom of the upper mold sleeve, and the lower groove is used to install the upper mold core; an upper groove is provided at the top of the lower mold sleeve, and the upper groove is used to install the lower mold core 8; the dimensions of the upper and lower grooves in the width direction are 0.5mm~0.8mm smaller than the width of the upper and lower mold cores 6 and 8, that is, the single-sided interference is between 0.25mm~0.4mm.

[0014] In the above technical solution, as a further improvement of the present invention, the edges of the bottom surfaces of the upper and lower grooves are designed with chamfers at the positions where they contact the upper and lower mold cores to avoid the occurrence of stress concentration.

[0015] Among the aforementioned technical solutions, as the preferred technical solution of the present invention: the chamfer is a rounded corner.

[0016] In the main technical solution, as a further improvement of the present invention: the upper mold core and the upper mold sleeve are aligned front, back, top and bottom, and the lower mold core and the lower mold sleeve are aligned front, back, top and bottom, and the allowable error is less than or equal to ±0.5mm.

[0017] In the above technical solution, as a further improvement of the present invention, the equivalent stress between the mold core and the mold sleeve is 1 / 2 to 1 / 3 of the yield stress of the materials of both.

[0018] In the above technical solution, as a further improvement of the present invention: the width of the mold core is 2 to 2.5 times the width of the upper and lower mold cavities.

[0019] In the above technical solution, as a further improvement of the present invention: the mold core and the mold sleeve are installed with interference fit so that the pre-tightening force generated by the mold core is used to reduce the stress of the mold core; the width of the square groove in the mold sleeve is 1 / 3 to 1 / 4 of the overall width of the mold sleeve, and the depth of the square groove is 1 / 2 to 1 / 3 of the overall depth of the mold sleeve.

[0020] The advantages of this utility model compared with the prior art are:

[0021] 1. The utility model is generally assembled by interference fit pre-tightening, which can reduce the internal stress of the mold during the forming process to a certain extent and increase the service life of the mold, which is of great significance for the production of railway switch point rails.

[0022] 2. A mold sleeve is provided outside the mold core of the utility model. The mold core and the mold sleeve are installed in an interference fit manner. After installation, a certain amount of pre-tightening force is generated between the mold core and the mold sleeve to reduce the stress of the mold core.

[0023] 3. The width of the upper and lower grooves of the utility model is 0.5mm to 0.8mm smaller than the width of the upper and lower mold cores, that is, the single-sided interference is 0.25mm to 0.4mm. The specific value is determined by the stress on the mold core during the forming process and has certain versatility.

[0024] 4. The contact position between the upper and lower mold cores of the utility model is designed with chamfers to avoid stress concentration.

[0025] 5. The setting of various parameters of the utility model can further fully ensure the internal stress of the mold during the forging process of the center rail according to actual needs, thereby increasing the service life of the mold.

[0026] 6. Through simulation comparison of the embodiments, the present invention found that the equivalent stress on the heart rail forging die with pre-tightening force is significantly lower than that on the heart rail forging die without pre-tightening force. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a three-dimensional diagram of the utility model;

[0028] Figure 2 This is a three-dimensional diagram of the assembly of the upper mold core and the upper mold sleeve of the utility model;

[0029] Figure 3 This is a three-dimensional diagram of the assembly of the lower mold core and the lower mold sleeve of the utility model;

[0030] In the figure: 1-upper die base, 2-lower die base, 3-guide sleeve, 4-guide pillar, 5-upper die sleeve, 6-upper die core, 7-lower die sleeve, 8-lower die core. DETAILED DESCRIPTION

[0031] The following is a combination of the appended examples of the present invention Figure 1-3 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0032] (like Figure 1 (As shown) A pre-tightened heart rail forging die comprises an upper die base 1, a lower die base 2, a guide sleeve 3, a guide column 4, an upper die sleeve 5, an upper die core 6, a lower die sleeve 7, and a lower die core 8.

[0033] The upper die base 1 is horizontally positioned, with a guide sleeve 3 installed vertically and interference-fitted at its bottom. The lower die base 2 is horizontally positioned, with a guide post 4 installed vertically and interference-fitted at its top. This interference fit creates a preload force to reduce stress.

[0034] The guide pins 4 and guide sleeves 3 are arranged in diagonal positions and are used to realize the guiding function of the mold. Compared with the four-corner setting of the guiding function, the diagonal setting can save the space occupied by the mold, making the overall structure of the mold more compact, which is conducive to improving production efficiency and equipment utilization. The diagonal setting can ensure the precise positioning of the mold during the mold closing process, reduce the errors caused by inaccurate positioning, and improve the processing accuracy of the product. The contact area and friction path of the diagonally arranged guide pins and sleeves are optimized during the opening and closing process of the mold, which helps to reduce friction and wear, thereby extending the service life of the guide pins and sleeves. Since the diagonal setting improves the wear resistance of the guide pins and sleeves, the frequency of replacement due to wear is reduced, thereby reducing the maintenance cost of the mold. The diagonally arranged guide pins and sleeves are relatively simple to install, without the need for complicated positioning and debugging processes, which helps to shorten the installation cycle and debugging time of the mold.

[0035] The upper mold base 1 is fixedly installed on the bottom of the upper mold sleeve 5, and the upper mold core 6 is installed on the bottom of the upper mold base 1 by interference fit; a mold sleeve is provided on the outside of the mold core, and the mold core and the mold sleeve are installed in an interference fit manner. After installation, a certain amount of pre-tightening force is generated between the mold core and the mold sleeve to reduce the stress of the mold core.

[0036] Similarly: the lower mold base 2 is fixedly installed on the top of the lower mold sleeve 7, and the lower mold core 8 is installed on the top of the lower mold base 2 by interference fit; a mold sleeve is provided on the outside of the mold core, and the mold core and the mold sleeve are installed in an interference fit manner. After installation, a certain amount of pre-tightening force is generated between the mold core and the mold sleeve to reduce the stress of the mold core.

[0037] The upper die core 6 has an upper die cavity at the bottom according to the shape of the forging, and the lower die core 8 has a lower die cavity at the top according to the shape of the forging. The upper die cavity and the lower die cavity are used together to forge the forging.

[0038] In the above embodiment, as a preferred embodiment of the present utility model: the guide sleeve 3 is installed through an interference fit with the upper die base 1 through a stepped hole; the guide column 4 is installed through an interference fit with the lower die base 2 through a through hole.

[0039] It should be noted that the interference fit utilizes the elasticity of the material to expand and deform the hole so that it fits over the shaft. When the hole is restored, a clamping force is generated on the shaft. This tightening force makes the connection between the guide sleeve and the upper die seat more secure, capable of withstanding greater shock and vibration, and improving the overall stability of the mold. The interference fit can ensure the precise positioning of the guide sleeve in the upper die seat and reduce errors caused by inaccurate positioning, which is crucial to the precision of the mold and the processing quality of the product. Compared with other connection methods, such as key connections or pin connections, the interference fit reduces the number of parts and simplifies the mold structure, which helps to reduce manufacturing costs and improve production efficiency. The interference fit generates a lot of pressure between the mating surfaces. During operation, the load is transmitted by the friction generated by the clamping force. This friction helps to reduce wear on the mating surfaces and extend the service life of the mold.

[0040] The stepped hole design provides multiple positioning surfaces, making the guide sleeve more accurately and securely positioned in the upper die holder. This multiple positioning mechanism helps reduce loosening caused by vibration or impact, thereby enhancing the strength and stability of the connection. The stepped hole design helps maintain coaxiality between the guide sleeve and the upper die holder, which is critical to the mold's guiding function and the product's processing quality. Maintaining coaxiality can reduce vibration and noise caused by eccentricity, improving the stability and durability of the mold. The stepped hole design ensures a more even distribution of stress on the mating surfaces. This optimized stress distribution helps reduce the risk of fatigue cracks and fractures caused by stress concentration, thereby increasing the service life of the mold. During mold operation, the stepped hole design can enhance the guide sleeve's resistance to impact loads. By dispersing and transmitting impact energy, the stepped hole helps protect the mold from damage and extend its service life.

[0041] As for through-hole assembly, the through-hole design simplifies the structure of the lower die base, eliminating the need for additional complex structures to accommodate or secure the guide pins. This streamlined design not only reduces machining difficulty but also improves production efficiency. Through-hole machining is relatively easy and can be achieved through conventional machining methods such as drilling and boring, without the need for specialized equipment or processes. This reduces production costs and improves machining accuracy.

[0042] In the main embodiment, as a preferred embodiment of the present utility model: the upper die sleeve 5 is fixedly connected to the upper die base 1 by keys and screws; the lower die sleeve 7 is fixedly connected to the lower die base 2 by keys and screws.

[0043] It should be noted that the dual fixing method of key and screw provides dual fixation between the mold sleeve and the mold base. The key connection achieves axial positioning and torque transmission through the close fit of the side of the key and the keyway; while the screw connection provides additional radial and axial fixing force through the locking effect of the thread. This dual fixing method significantly improves the strength and stability of the connection. The key connection ensures the relative position accuracy between the mold sleeve and the mold base through the precise fit of the keyway and key. This is crucial for the guiding function of the mold and the processing quality of the product. The key connection generally has high rigidity and can resist deformation or offset caused by external forces, thereby maintaining the overall stability and positioning accuracy of the mold. The key and screw fixing method helps to disperse stress between the mold sleeve and the mold base, reducing the risk of fatigue cracks or fractures caused by stress concentration. This helps to extend the service life of the mold.

[0044] In the main embodiment, as a preferred embodiment of the present utility model: the upper die sleeve 5 is provided with a lower groove at the bottom, and the lower groove is used to install the upper die core 6; the lower die sleeve 7 is provided with an upper groove at the top, and the upper groove is used to install the lower die core 8; the dimensions of the upper and lower grooves in the width direction are 0.5mm to 0.8mm smaller than the width of the upper and lower die cores (6, 8), that is, the unilateral interference is 0.25mm to 0.4mm. It should be noted that: the specific value is determined by the stress exerted on the die core during the forming process.

[0045] In the above embodiment, as a further improved embodiment of the present invention, the edges of the bottom surfaces of the upper and lower grooves are designed with chamfers at the positions where they contact the upper and lower mold cores (6, 8) to avoid the occurrence of stress concentration.

[0046] Furthermore, chamfering eliminates sharp corners, reduces the direct contact area between the mold and the part, and reduces the risk of scratches caused by friction or collision. During mold design and manufacturing, chamfering helps reduce the accumulation of machining errors and improves both mold manufacturing accuracy and part machining precision. For molds and parts that require a tight fit, chamfering improves contact between mating surfaces and enhances fit quality. Chamfering can make mold and part assembly smoother, reducing assembly difficulty and time. During mold maintenance and repair, chamfering reduces the risk of damage from disassembly and assembly, lowering maintenance costs.

[0047] In the aforementioned embodiment, as a preferred embodiment of the present utility model: the chamfer is a rounded corner.

[0048] When rounded corners are preferred: rounded corners can disperse stress more effectively than chamfers, reducing the risk of fatigue cracks and fractures caused by stress concentration. The rounded corner design makes the contact surface smoother and reduces stress concentration points caused by sharp corners. Rounded corners have no sharp edges, so they are less likely to scratch users or objects in contact with them during use, improving the safety and reliability of the product. Although the processing of rounded corners may be relatively complicated, in some cases, such as when using high-precision processing equipment such as CNC machine tools, the processing efficiency of rounded corners is not lower than chamfers, and may even be higher. In addition, the processing accuracy of rounded corners is also easier to control. The rounded corner design reduces the risk of damage caused by stress concentration and scratches, thereby reducing the maintenance cost of the product.

[0049] In the main embodiment, as a further improved embodiment of the present utility model: the front, rear, top and bottom of the upper mold core 6 and the upper mold sleeve 5 are aligned and flush, and the front, rear, top and bottom of the lower mold core 8 and the lower mold sleeve 7 are aligned and flush, and the allowable error is less than or equal to ±0.5mm.

[0050] It should be noted that strict control of the alignment error between the mold core and mold sleeve ensures precise positioning of the mold during the mold closing process. This precise positioning helps reduce processing errors caused by mold misalignment and improves the dimensional and shape accuracy of the product. High-precision mold positioning ensures greater product consistency, maintaining high consistency in both the product's external dimensions and internal structure, meeting stringent customer requirements. Precise alignment between the mold core and mold sleeve reduces friction and collision between them, thereby reducing mold wear. This helps extend the mold's lifespan and lowers production costs. Precise alignment enhances mold stability during operation. A stable mold can better withstand vibration and impact, reducing processing defects caused by mold movement. High-precision mold positioning reduces adjustment time during production. Operators no longer need to frequently adjust the mold's position and angle, thereby improving production efficiency. Precise alignment reduces scrap caused by mold misalignment. This not only reduces production costs but also improves production efficiency. The high-precision mold design enables it to adapt to the production needs of a variety of products. By replacing different mold cores and mold sleeves, product transitions and upgrades can be easily achieved. When market demand changes, high-precision molds can quickly respond and adjust production plans to meet the diverse needs of customers.

[0051] In the aforementioned embodiment, as a further improved embodiment of the present invention, the equivalent stress between the mold core and the mold sleeve is 1 / 2 to 1 / 3 of the yield stress of the materials of both.

[0052] In the aforementioned embodiment, as a further improved embodiment of the present invention, the width of the mold core is 2 to 2.5 times the width of the upper and lower mold cavities.

[0053] In the aforementioned embodiment, as a further improved embodiment of the present invention: the mold core and the mold sleeve are installed with interference fit so that the preload force generated by the mold core is used to reduce the stress of the mold core; the width of the square groove in the mold sleeve is 1 / 3 to 1 / 4 of the overall width of the mold sleeve, and the depth of the square groove is 1 / 2 to 1 / 3 of the overall depth of the mold sleeve.

[0054] Regarding the aforementioned parameter limitations, the working principle of the present invention is as follows: Both the punch and die of the present invention are composed of a die sleeve and a die core. The die sleeve and die core utilize an interference fit to generate an appropriate preload, which can offset some of the pressure exerted by the blank on the die during forging, ultimately achieving the goal of reducing internal stress in the die. The preloaded die structure proposed in the present invention effectively increases the strength of the die core and improves the service life of the die.

[0055] In specific implementation, the outer dimensions of the upper die sleeve 5 are 770 mm × 820 mm × 350 mm, the inner cavity depth is 182 mm, the weight is 1410 kg, and the material is 5CrNiMo.

[0056] The outer dimensions of the upper mold core 6 are 270mm×820mm×182mm, the internal cavity depth is 40mm, the weight is 248.61kg, and the material used is H-13.

[0057] After installation, the upper mold core 6 is aligned with the upper plane of the upper mold sleeve 5 with an error of 0.3 mm. The single-side interference of the upper mold core 6 and the upper mold sleeve 5 is 0.3 mm, and thermal assembly is adopted.

[0058] The outer dimensions of the lower die sleeve 7 are 770mm×1100mm×350mm, the internal cavity depth is 182mm, the weight is 1856.4kg, and the material is 5CrNiMo.

[0059] The outer dimensions of the lower mold core 8 are 270mm×1100mm×182mm, the internal cavity depth is 90mm, the weight is 318kg, and the material used is H-13.

[0060] After installation, the end faces of the lower die core and the lower die sleeve are aligned with each other, with an error of no more than 0.2mm. The lower die core and the lower die sleeve are interference fit, with a single-side interference of 0.3mm, and thermal assembly is adopted.

[0061] Through simulation analysis of the embodiment mold, the final simulation results show that the overall stress level of the upper mold core is not high, and the equivalent stress in most areas is about 300 MPa. There is stress concentration in some areas, among which the maximum equivalent stress is at the outer bevel of the upper mold core and the center of the cavity, and the maximum equivalent stress does not exceed 500 MPa. The stress level in most areas of the lower mold core is relatively low, about 300 MPa, and there is stress concentration in some areas, among which the maximum equivalent stress is at the outer bevel of the lower mold core and the center of the cavity, and the maximum equivalent stress does not exceed 500 MPa. Overall, the stress levels of the upper and lower mold cores are relatively low, and the stress in most areas is 300 MPa. The areas with the maximum equivalent stress are at the outer bevel of the upper and lower mold cores and the center of the cavity, and the maximum equivalent stress does not exceed 500 MPa.

[0062] At the same time, a forming force simulation analysis was performed on another comparative embodiment. This embodiment is a mold without preload. The simulation found that the stress level in most areas of the upper and lower mold cores is relatively large, at about 600 MPa. There is stress concentration in the central part of the cavity, and the equivalent stress in the central part of the cavity reaches 800 MPa.

[0063] Through simulation comparison of the embodiments, it is found that the equivalent stress on the heart rail forging die with preload is significantly lower than that on the heart rail forging die without preload.

[0064] The relevant work flow of this utility model:

[0065] Step 1. Assemble the mold: The mold core and mold sleeve are assembled by interference fitting. Using thermal assembly, the mold sleeve is heated at high temperature and the mold core is installed after heating. The single-sided interference between the mold core and the mold sleeve is 0.3mm. After the mold sleeve is cooled, the stress on the outer surface of the mold core is about 300MPa.

[0066] Step 2: Forging process: Heat the blank and use a robotic arm to feed the blank into the lower mold cavity. The anvil of the free forging press presses down on the upper pad, causing the blank to be compressed and deformed, filling the cavity.

[0067] Step 3: End of forging: After forging is complete, the blank is fully filled. The overall stress level of the core is not high. The equivalent stress in most areas of the cavity is around 300 MPa. There is stress concentration in some areas, with the maximum equivalent stress occurring in the center of the cavity, which does not exceed 500 MPa.

[0068] In summary, the interference preload design proposed in this patent effectively reduces the impact of forming forces on the mold, improving the mold's service life and the quality of the railway frog rail. This design is feasible in actual production and can bring technological innovation and significant economic benefits to railway frog rail manufacturers.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications and equivalent replacements made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

[0070] It should be understood that although this specification is described according to one embodiment, this embodiment does not only include one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in this embodiment can also be appropriately arranged and combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A pre-tightened mandrel forging die, characterized in that: It comprises an upper die base (1), a lower die base (2), a guide sleeve (3), a guide post (4), an upper die sleeve (5), an upper die core (6), a lower die sleeve (7), and a lower die core (8); The upper die base (1) is arranged horizontally, and the bottom of the upper die base (1) is vertically interference-fitted with a guide sleeve (3); The lower die base (2) is arranged horizontally, and the top of the lower die base (2) is vertically interference-fitted with a guide column (4); The guide pillar (4) and the guide sleeve (3) are arranged at diagonal positions and are used to realize the guiding function of the mold; The upper die base (1) is fixedly mounted on the bottom of the upper die sleeve (5), and the upper die core (6) is installed on the bottom of the upper die base (1) in an interference fit; The lower die base (2) is fixedly mounted on the top of the lower die sleeve (7), and the lower die core (8) is installed on the top of the lower die base (2) in an interference fit; The bottom of the upper die core (6) is designed with an upper die cavity according to the shape of the forging; the top of the lower die core (8) is designed with a lower die cavity according to the shape of the forging.

2. The pre-tightened mandrel forging die according to claim 1, characterized in that: The guide sleeve (3) is installed through interference fit with the upper die base (1) via a stepped hole; and the guide post (4) is installed through interference fit with the lower die base (2) via a through hole.

3. The pre-tightened mandrel forging die according to claim 1, characterized in that: The upper die sleeve (5) is fixedly connected to the upper die base (1) via keys and screws; the lower die sleeve (7) is fixedly connected to the lower die base (2) via keys and screws.

4. The pre-tightened mandrel forging die according to claim 1, characterized in that: The upper die sleeve (5) has a lower groove at the bottom, and the lower groove is used to install the upper die core (6); the lower die sleeve (7) has an upper groove at the top, and the upper groove is used to install the lower die core (8); the width of the upper and lower grooves is 0.5mm to 0.8mm smaller than the width of the upper and lower die cores (6, 8), that is, the single-sided interference is 0.25mm to 0.4mm.

5. The pre-tightened mandrel forging die according to claim 4, characterized in that: The edges of the bottom surfaces of the upper and lower grooves are designed with chamfers at positions where they contact the upper and lower mold cores (6, 8) to avoid stress concentration.

6. The pre-tightened mandrel forging die according to claim 5, characterized in that: The chamfer is a rounded corner.

7. The pre-tightened mandrel forging die according to claim 1, characterized in that: The upper mold core (6) and the upper mold sleeve (5) are aligned in front, back, top and bottom, and the lower mold core (8) and the lower mold sleeve (7) are aligned in front, back, top and bottom, and the allowable error is less than or equal to ±0.5mm.

8. The pre-tightened mandrel forging die according to claim 1, characterized in that: The equivalent stress between the mold core and the mold sleeve is 1 / 2 to 1 / 3 of the yield stress of the materials of both.

9. The pre-tightened mandrel forging die according to claim 1, characterized in that: The width of the mold core is 2 to 2.5 times the width of the upper and lower cavities.

10. The pre-tightened mandrel forging die according to claim 4, characterized in that: The interference fit between the mold core and the mold sleeve allows the preload force generated by the mold core to reduce the stress of the mold core. The width of the square groove in the mold sleeve is 1 / 3 to 1 / 4 of the overall width of the mold sleeve, and the depth of the square groove is 1 / 2 to 1 / 3 of the overall depth of the mold sleeve.

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