Tooth die for straight bevel gear of differential mechanism on warm precision forging of electric screw press

Abstract

The invention provides a tooth die for a straight bevel gear of a differential mechanism on warm-precision forging of an electric screw press. The tooth die comprises a prestress guide die sleeve, a pressure-bearing transition cushion block, a die core and an ejector rod, an inner hole is formed in the prestress guide die sleeve and comprises a first part, a second part, a third part and a fourth part which are arranged in sequence and have different inner diameters; the pressure-bearing transition cushion block is arranged in the first part, the pressure-bearing transition cushion block comprises an inner-layer cushion block and an outer-layer cushion block which are nested together, and a first central through hole is formed in the inner-layer cushion block; the core mold is arranged in the second part and the third part, a nitriding layer and a PVD reinforcing layer are further sequentially arranged on the outer surface of the core mold, a second center through hole is further formed in the core mold, the second center through hole and the first center through hole are coaxially formed, and the hole diameters of the second center through hole and the first center through hole are different; the ejector rod is arranged in the first center through hole and the second center through hole in a sliding mode. The anti-impact cable is good in anti-impact performance and long in service life.

Description

Technical Field

[0001] This application relates to the technical field of temperature precision forging gear dies for electric screw presses, and particularly to gear dies used for differential straight bevel gears in temperature precision forging of electric screw presses. Background Technology

[0002] In automotive transmission systems, the differential straight bevel gear, as a core component for power transmission and differential function, directly affects the vehicle's transmission efficiency, operational stability, and service life due to its manufacturing precision and mechanical properties. Currently, the industry commonly employs warm forging technology for the precision forming of differential straight bevel gears. This process is widely used in mass production because it effectively improves the plastic flow of metal materials, reduces forming resistance, and minimizes subsequent machining operations. The basic and core step of this process involves placing the blank into the gear die of a warm forging using an electric screw press, where it undergoes high-temperature and high-pressure impact forming several times per minute, sometimes even dozens of times. Existing technologies typically use 3Cr2W8V or 4Cr3Mo2MnVNbB die steel for warm forging using electric screw presses, employing an integral structural design. While these two types of die steel possess certain high-temperature strength, hardness, and wear resistance, exhibiting good performance under normal and medium-low temperature forming conditions, the die must withstand prolonged exposure to high temperatures (typically 800-950℃), high-frequency impact loads, and intense friction during the hot precision forging of differential straight bevel gears. The working conditions are extremely harsh. Long-term production practice has verified that the service life of disposable precision forging dies using the aforementioned materials and structures is typically only around 7000-9000 pieces. After this service life, the toothed portion of the cavity will inevitably experience various forms of failure, such as localized wear, collapse deformation, or cracking. Sometimes, even premature failure due to temperature stress or abnormal press overload can occur, leading to abnormal cracking of the die. Summary of the Invention

[0003] This application aims to address the technical problem in the prior art where tooth dies used in the warm precision forging of electric screw presses are prone to failure due to localized wear, collapse deformation, cracking, or abnormal cracking caused by temperature stress or abnormal overload of the press, resulting in a short service life. It proposes a tooth die for the differential straight bevel gear in the warm precision forging of an electric screw press, which effectively improves its resistance to impact damage, reduces deformation during use, and extends the service life of the tooth die.

[0004] To achieve the above objectives, this application adopts the following technical solution:

[0005] The tooth die for the differential straight bevel gear on the electric screw press for hot precision forging includes a prestressed guide die sleeve, a pressure-bearing transition pad, a die core, and an ejector rod.

[0006] The prestressed guide sleeve has an inner hole, which includes a first part, a second part, a third part and a fourth part arranged in sequence with different inner diameters;

[0007] The pressure-bearing transition pad is disposed within the first part and is clearance-fitted with the first part; the pressure-bearing transition pad includes an inner pad and an outer pad nested together, and the inner pad is provided with a first central through hole;

[0008] The core mold is disposed within the second part and the third part, and a water-based graphite layer is provided between the core mold and the third part. A nitriding layer and a PVD reinforcing layer are also sequentially provided on the outer surface of the core mold. The core mold is also provided with a second central through hole, which is coaxially arranged with the first central through hole but has a different diameter.

[0009] The push rod is slidably disposed within the first central through hole and the second central through hole.

[0010] Furthermore, the tooth mold also includes a positioning key, and a keyway adapted to the positioning key is provided at one end of the prestressed guide mold sleeve near the first part, and the positioning key is engaged in the keyway.

[0011] Furthermore, the end of the fourth part that is furthest from the third part is a circular arc guide end, and the lead of the circular arc guide end is greater than 25mm.

[0012] Furthermore, the inner and outer pads are interference fit, with an interference coefficient of 0.3% to 0.35%.

[0013] Furthermore, the inner pad is made of Cr12MoV material, and the outer pad is made of 4Cr5MoSiV1 material.

[0014] Furthermore, the core mold is made of 4Cr3Mo2MnVNbB mold steel.

[0015] Furthermore, the core mold and the second part are in a clearance fit, and the core mold and the third part are in an interference fit, wherein the interference coefficient is 0.20% to 0.23%.

[0016] Furthermore, the nitrided layer has a thickness of <0.2mm and a hardness of 950HV-1000HV; the PVD reinforcing layer has a thickness of 0.3um-0.5um and a hardness of 2600HV-2800HV.

[0017] Furthermore, the second part has a positioning reference with an inner convex or outer concave shape on its side wall, and the outer side wall of the core mold has a positioning surface that matches the positioning reference. The positioning surface and the positioning reference cooperate with each other to position and limit the core mold and the second part.

[0018] Furthermore, the push rod includes a fifth part and a sixth part with different outer diameters. The outer diameter of the fifth part is adapted to the inner diameter of the first central through hole so that the fifth part can be slidably inserted into the first central through hole. The outer diameter of the sixth part is adapted to the inner diameter of the second central through hole so that the sixth part can be slidably inserted into the second central through hole. The axial length of the fifth part is less than the axial length of the first central through hole.

[0019] Furthermore, the preparation method of the core mold is as follows: the base material is processed into the cavity using a high-speed milling machine and then precision polished to obtain a semi-finished product with a surface roughness of Ra0.4; the semi-finished product is ultrasonically cleaned and dried and then placed in a PVD strengthening device for ion nitriding treatment to obtain a nitrided layer, and then PVD strengthening treatment to obtain a PVD strengthening layer.

[0020] The beneficial effects of this application are:

[0021] This application, by employing a separate design of the pressure-bearing transition pad and the mold core, combined with a prestressed guide sleeve structure, effectively eliminates the risk of plastic deformation or even cracking of the tooth mold under triaxial compressive stress. The pressure-bearing transition pad is made of Cr12MoV material for the inner layer and 4Cr5MoSiV1 material for the outer layer, and is manufactured by interlocking the inner and outer pads together. This ensures that the inner pad has a high elastic modulus and that the prestress is greater than or close to the compressive stress during the downward phase of use, thus essentially eliminating the risk of pad cracking failure under alternating stress conditions. It further reduces the possibility of mold plastic deformation or even cracking caused by localized stress concentration within the tooth mold. This effectively improves its impact resistance, slows down deformation during use, and extends the service life of the tooth mold. Furthermore, the separate design of the pressure-bearing transition pad and the mold core allows for individual replacement of damaged parts while the remaining parts can continue to be used, significantly reducing mold material costs.

[0022] This application effectively improves the wear resistance of the core mold surface by setting a nitrided layer with a hardness of 950HV-1000HV and a thickness of <0.2mm and a PVD reinforcing layer with a hardness of 2600HV-2800HV and a thickness of 0.3um-0.5um on the core mold surface, thereby enhancing the service life of the core mold.

[0023] This application sets the port edge of the fourth part as an arc guide structure with a lead greater than 25mm. During use, it can ensure smooth alignment even if there is slight misalignment during the mold closing process, and will not cause damage to the mold guide part due to radial shear caused by excessive clearance of the machine tool guide rail, resulting in reduced or excessive guiding accuracy.

[0024] This application, by setting a water-based graphite layer between the core mold and the third part, can effectively prevent the inner wall of the third part from being damaged when replacing the core mold, and can also reduce the pressure of ejecting the core mold and improve the convenience of core mold replacement. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic cross-sectional view of the tooth mold provided in the embodiments of this application;

[0027] Figure 2 A schematic cross-sectional view of the prestressed guide sleeve provided in the embodiments of this application;

[0028] Figure 3 A top view of the prestressed guide sleeve provided in the embodiments of this application;

[0029] Figure 4 A top view of the pressure-bearing transition pad provided in an embodiment of this application;

[0030] Figure 5 This is a top view of the core mold structure provided in an embodiment of this application;

[0031] Figure 6 A schematic diagram of the top rod cross-section provided in an embodiment of this application.

[0032] Explanation of symbols in the diagram:

[0033] Prestressed guide mold sleeve 1, first part 1-1, second part 1-2, third part 1-3, fourth part 1-4, keyway 1-5, positioning datum 1-6, pressure-bearing transition pad 2, inner pad 2-1, outer pad 2-2, first central through hole 2-3, mold core 3, second central through hole 3-1, positioning cut surface 3-2, ejector pin 4, fifth part 4-1, sixth part 4-2, positioning key 5. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0035] This application provides a tooth die for a differential straight bevel gear on a hot forging machine using an electric screw press, such as... Figure 1 As shown, it includes a prestressed guide mold sleeve 1, a pressure-bearing transition pad 2, a mold core 3, a push rod 4, and a positioning key 5;

[0036] The prestressed guide sleeve 1 is made of 4Cr5MoSiV1 material, and after heat treatment, its viscosity is HRC46-49. For example... Figure 2 and 3 As shown, the prestressed guide sleeve 1 has an inner hole, which includes a first part 1-1, a second part 1-2, a third part 1-3, and a fourth part 1-4 arranged sequentially with different inner diameters. In some embodiments, the inner diameter of the first part 1-1 is 180 mm, the inner diameter of the second part 1-2 is 120 mm, the inner diameter of the third part 1-3 is 110 mm, and the inner diameter of the fourth part 1-4 is 150 mm. In actual applications, the specific inner diameter of each part is not limited to the dimensions disclosed above, and those skilled in the art can make appropriate adjustments according to actual needs.

[0037] The pressure-bearing transition pad 2 is disposed within the first part 1-1 and is clearance-fitted with the first part 1-1; for example Figure 4 As shown, the pressure-bearing transition pad 2 adopts a combined prestressed structure, comprising an inner pad 2-1 and an outer pad 2-2 nested together. The inner pad 2-1 is made of Cr12MoV material with a hardness of HRC 58-62; the outer pad 2-2, serving as the outer prestressing ring, is made of 4Cr5MoSiV1 material with a hardness of HRC 44-47. The inner pad 2-1 and the outer pad 2-2 are nested with an interference fit, with an interference coefficient of 0.3% to 0.35%. During preparation, the outer pad 2-2 is first heated to 400℃ in a resistance furnace and held for 20-30 minutes before being removed from the furnace. Then, the inner pad 2-1 and the outer pad 2-2 are nested together and cooled to room temperature for later use. The inner pad 2-1 has a first central through hole 2-3 for assembling the top rod 4.

[0038] The core mold 3 is disposed within the second part 1-2 and the third part 1-3. A water-based graphite layer (not shown in the figure) is provided between the core mold 3 and the third part 1-3. A nitrided layer (not shown in the figure) and a PVD reinforcing layer (not shown in the figure) are also sequentially provided on the outer surface of the core mold 3. The nitrided layer has a thickness <0.2 mm and a hardness of 950 HV-1000 HV; the PVD reinforcing layer has a thickness of 0.3 μm-0.5 μm and a hardness of 2600 HV-2800 HV. Figure 5 As shown, the core mold 3 is also provided with a second central through hole 3-1, which is coaxially arranged with the first central through hole 2-3 but has a different diameter;

[0039] The preparation method of the core mold 3 is as follows: the 4Cr3Mo2MnVNbB matrix material is processed into the cavity by a high-speed milling machine and then precision polished to obtain a semi-finished product with a surface roughness of Ra0.4; the semi-finished product is ultrasonically cleaned and dried and then placed in a PVD strengthening equipment for ion nitriding treatment to obtain a nitrided layer, and then PVD strengthening treatment to obtain a PVD strengthening layer. The bonding force between the PVD strengthening layer and the semi-finished product is F1 grade.

[0040] The process of assembling the core mold 3 into the second part 1-2 and the third part 1-3 of the prestressed guide mold sleeve 1 is as follows: A water-based graphite stock solution is evenly applied to the outer surface of the core mold 3 at the position corresponding to the third part 1-3, and then dried for later use. Next, a layer of water-based graphite stock solution is also applied to the inner wall of the third part 1-3, and then the core mold 3 is placed in a resistance furnace and heated to 350–380°C, held for 30 minutes, and then removed from the furnace. Finally, the core mold 3 is assembled into the second part 1-2 and the third part 1-3 of the prestressed guide mold sleeve 1. The core mold 3 and the second part 1-2 have a clearance fit, while the core mold 3 and the third part 1-3 have an interference fit, with an interference coefficient of 0.20%–0.23%.

[0041] The push rod 4 is slidably disposed within the first central through hole 2-3 and the second central through hole 3-1. For example... Figure 6As shown, the ejector rod 4 includes a fifth part 4-1 and a sixth part 4-2 with different outer diameters. The connection between the fifth part 4-1 and the sixth part 4-2 is a rounded transition. This design prevents localized stress concentration at the sharp corner of the diameter change when the ejector rod is under stress, thus preventing fatigue cracks. The outer diameter of the fifth part 4-1 is adapted to the inner diameter of the first central through hole 2-3 so that the fifth part can slide into the first central through hole 2-3. The outer diameter of the sixth part 4-2 is adapted to the inner diameter of the second central through hole 3-1 so that the sixth part 4-2 can slide into the second central through hole 3-1. The axial length of the fifth part 4-1 is less than the axial length of the first central through hole 2-3. This ensures that when the forging prepared by the tooth mold is ejected during use, the fifth part 4-1 of the ejector rod 4 is completely within the first central through hole 2-3, thus no longer subject to external forces. In some embodiments, the axial length of the fifth portion 4-1 is 0.5 mm smaller than the axial length of the first central through hole 2-3.

[0042] The prestressed guide sleeve 1 has a keyway 1-5 at one end near the first part 1-1, which is adapted to the positioning key 5. The positioning key 5 is engaged in the keyway 1-5. During the assembly of the gear mold and the mold frame, the gapless positioning key 5 precisely matches the reference positioning keyway on the upper mold cylinder of the mold frame, which can completely eliminate the positioning difficulties of traditional multi-stage keyway positioning and the excessive cumulative error caused by it. This improves the positioning accuracy of the gear mold.

[0043] In this embodiment, the tooth mold is designed and assembled above the mold frame. The blank to be deformed is positioned using the lower cavity mold. Under triaxial compressive stress, it can resist the high-temperature tempering and softening of the mold cavity surface matrix material caused by the contact between the high-temperature deformable material and the tooth mold cavity. The tooth mold cavity surface has good wear resistance, and the final failure mode of the tooth mold is only manifested as a fine fatigue crack at the transition point of the cavity at the bottom of the tooth mold cavity. This greatly improves the service life of the tooth mold.

[0044] In some embodiments, the end of the fourth part 1-4 furthest from the third part 1-3 is an arc-shaped guide end with a lead greater than 25mm. That is, the port of the fourth part 1-4 furthest from the third part 1-3 is set with an arc transition. A lead greater than 25mm means that when the die descends to the surface of the die cavity and just contacts the bar stock to be processed, the arc-shaped guide end is inserted into the lower cavity of the outer mold by more than 5mm. Subsequently, as the die continues to descend to the dead point, the entire lead is greater than 25mm. During this process, the bar stock is compressed and deformed, and the guide rigidity is sufficient to overcome the various irregularities of the deformed material and the harmful horizontal forces caused by different lubrication conditions, ensuring complete filling of the die cavity. This design ensures smooth alignment even with slight misalignment during mold closing, preventing radial shearing damage to the guide portion caused by excessive machine tool guide clearance, thus avoiding reduced or out-of-tolerance guiding accuracy.

[0045] In some embodiments, the second part 1-2 has an inwardly protruding positioning reference 1-6 on its sidewall, and the inner sidewall of the positioning reference 1-6 is flush with the inner sidewall of the third part 1-3. The outer sidewall of the core mold 3 has a positioning cut surface 3-2 that is adapted to the positioning reference 1-6. During assembly, the positioning cut surface 3-2 and the positioning reference 1-6 cooperate with each other to position and limit the core mold 3 and the second part 1-2.

[0046] The foregoing has provided a detailed description of a gear mold for a differential straight bevel gear in a hot forging process using an electric screw press, as provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this application; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A gear die for a differential straight bevel gear in a hot precision forging process using an electric screw press, characterized in that: Includes prestressed guide sleeve, pressure-bearing transition pad, mold core and ejector pin; The prestressed guide sleeve has an inner hole, which includes a first part, a second part, a third part and a fourth part arranged in sequence with different inner diameters; The pressure-bearing transition pad is disposed within the first part. The pressure-bearing transition pad includes an inner pad and an outer pad nested together. The inner pad is provided with a first central through hole. The core mold is disposed within the second part and the third part, and a water-based graphite layer is provided between the core mold and the third part. A nitriding layer and a PVD reinforcing layer are also sequentially provided on the outer surface of the core mold. The core mold is also provided with a second central through hole, which is coaxially arranged with the first central through hole but has a different diameter. The push rod is slidably disposed within the first central through hole and the second central through hole.

2. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The tooth mold also includes a positioning key. The prestressed guide mold sleeve has a keyway at one end near the first part that is adapted to the positioning key, and the positioning key is engaged in the keyway.

3. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The end of the fourth part furthest from the third part is a circular arc guide end, and the lead of the circular arc guide end is greater than 2. 5 mm.

4. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The inner and outer pads are interference fit, with an interference coefficient of 0.3% to 0.35%.

5. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The inner pad is made of Cr12MoV material, and the outer pad is made of 4Cr5MoSiV1 material.

6. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The core mold is made of 4Cr3Mo2MnVNbB mold steel.

7. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The core mold and the second part are clearance fit, and the core mold and the third part are interference fit, wherein the interference coefficient is 0.20% to 0.23%.

8. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The nitrided layer has a thickness of <0.2mm and a hardness of 950HV-1000HV; the PVD reinforcing layer has a thickness of 0.3um-0.5um and a hardness of 2600HV-2800HV.

9. The gear die for a differential straight bevel gear on a hot precision forging machine using an electric screw press as described in claim 1, characterized in that: The second part has a positioning reference with an inner convex or outer concave shape on its side wall, and the outer side wall of the core mold has a positioning surface that matches the positioning reference. The positioning surface and the positioning reference cooperate with each other to position and limit the core mold and the second part.

10. The gear die for a differential straight bevel gear on a hot forging machine using an electric screw press as described in claim 1, characterized in that: The push rod includes a fifth part and a sixth part with different outer diameters. The outer diameter of the fifth part is adapted to the inner diameter of the first central through hole so that the fifth part can be slidably inserted into the first central through hole. The outer diameter of the sixth part is adapted to the inner diameter of the second central through hole so that the sixth part can be slidably inserted into the second central through hole.

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