Split self-tightening spline shaft hot extrusion die suitable for difficult-to-deform metal

Abstract

The application discloses a split self-tightening spline shaft hot extrusion die suitable for difficult deformation metal, and belongs to the technical field of metal precision hot extrusion dies. The die comprises an outer die sleeve, a middle die core seat, a lower end forming die, an upper end punch and a plurality of split spline inserts; a radial insert mounting hole is formed in the side wall of the middle die core seat, the split spline insert is embedded in the hole, and the outer side of the split spline insert is a wedge-shaped pressure bearing surface; a corresponding wedge-shaped limiting groove is arranged on the inner wall of the outer die sleeve, and the wedge-shaped surface applies a radial pre-tightening force to the split spline insert when the outer die sleeve is axially sleeved; the lower end forming die and the upper end punch are respectively arranged at the two ends of the middle die core seat, and the three are coaxially arranged. The wedge-shaped self-tightening structure is used to realize bolt-free fastening of the spline insert, the pre-tightening force is stronger when the bulging force is greater under the extrusion condition, the radial support stiffness of the die is greatly improved, the high deformation resistance hot extrusion scene of the difficult deformation metal is adapted, the split inserts can be replaced individually, and the use cost of the die is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of precision hot extrusion forming mold technology for metals, and in particular to a split hot extrusion mold for spline shafts of difficult-to-deform metals such as titanium alloys and high-temperature alloys. Background Technology

[0002] Difficult-to-deform metals, such as titanium alloys and nickel-based superalloys, are widely used in transmission components in aerospace, new energy vehicles, and high-end equipment manufacturing due to their excellent properties such as high specific strength, high temperature resistance, and corrosion resistance. As a core transmission component, the forming quality of the spline shaft directly affects the load-bearing capacity and service life of the transmission system.

[0003] Currently, the machining of difficult-to-deform metal spline shafts mainly employs cutting processes such as milling and grinding, resulting in low material utilization, long production cycles, and the cutting process cutting off the metal fiber flow lines, reducing the mechanical properties of the parts. Hot extrusion forming of spline shafts can achieve near-net-shape forming, preserving the complete metal flow lines and improving part strength; however, existing hot extrusion dies still have many shortcomings: Firstly, the spline teeth of an integral spline mold are integrated with the mold body. Once the spline teeth are worn or broken, the entire mold needs to be scrapped, resulting in high manufacturing costs and long replacement cycles. Secondly, existing split spline molds mostly use bolts to radially lock the spline inserts. Under the high temperature and high deformation resistance extrusion conditions of difficult-to-deform metals, the bolts are subjected to thermal stress and alternating loads for a long time, which can easily lead to loosening and fracture failure. In addition, the support stiffness of the bolt connection is limited, and the spline inserts are prone to radial retraction, resulting in insufficient spline tooth filling and dimensional deviation. Third, the existing molds mostly use cylindrical surface stops for positioning in the upper and lower forming sections and the middle section. Under high temperature, the mold is prone to coaxiality deviation after thermal expansion, which affects the forming accuracy of the spline shaft. In addition, the demolding resistance is large, and the problem of sticking and tearing is easy to occur. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of poor fixing reliability, insufficient support stiffness, and low forming accuracy of spline inserts in existing spline extrusion dies for difficult-to-deform metals. It provides a split self-tightening hot extrusion die for spline shafts suitable for difficult-to-deform metals. The spline inserts are boltless fastened through a wedge-shaped self-tightening structure, and self-reinforcing pre-tightening is achieved by utilizing the reaction of extrusion force, which greatly improves the load-bearing capacity and forming accuracy of the die.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A split self-tightening hot extrusion die for a difficult-to-deform metal spline shaft includes an outer die sleeve, a die core middle section seat, a lower forming die, an upper punch, and several split spline inserts. The mold core middle section seat is located in the middle of the mold, and has an axially penetrating middle section forming cavity inside. The side wall of the mold core middle section seat is evenly provided with several radially penetrating insert mounting holes along the circumference. The split spline inserts are fitted into the insert mounting holes one by one. The inner side of the split spline insert is provided with spline forming teeth that extend into the middle forming cavity. The outer side wall of the split spline insert is a wedge-shaped pressure bearing surface that is wider on the outside and narrower on the inside. The outer mold sleeve is coaxially sleeved on the outside of the middle section of the mold core. The inner wall of the outer mold sleeve is provided with wedge-shaped limiting grooves that correspond one-to-one with the split spline inserts. The inclination angle of the groove wall of the wedge-shaped limiting groove matches the inclination angle of the wedge-shaped bearing surface. When the outer mold sleeve is installed in place axially downwards, the groove wall of the wedge-shaped limiting groove squeezes the wedge-shaped bearing surface, causing each split spline insert to tighten radially inwards, applying radial preload to the spline forming teeth. The lower forming mold is detachably positioned and installed at the lower end of the middle section of the mold core. The lower forming mold has a first shaft end cavity with a top opening inside. The first shaft end cavity and the middle section forming cavity are coaxially arranged. The upper punch is movably disposed above the middle section seat of the die core. The upper punch has a second shaft end cavity with a bottom opening inside. The second shaft end cavity is coaxially disposed with the middle section forming cavity.

[0006] Furthermore, the angle between the wedge-shaped bearing surface and the mold axis is 3°~5°, and the radial preload stroke of the single split spline insert is 0.2~0.5mm. This angle range takes into account both the preload amplification effect and the ease of disassembly and assembly, avoiding insufficient preload due to an excessively small angle, or jamming during demolding due to an excessively large angle.

[0007] Furthermore, the surface of the spline forming teeth of the split spline insert has a gradually decreasing draft angle of 0.5° to 1° along the demolding direction, and the chamfer at the tip of the spline forming teeth is R0.2 to R0.5 mm. The gradually decreasing draft angle can reduce the demolding resistance after hot extrusion of difficult-to-deform metals, and the chamfer at the tip of the teeth can avoid tooth breakage caused by stress concentration, thereby improving the service life of the insert.

[0008] Furthermore, a limiting step is provided at the inner opening of the insert mounting hole, and a retaining edge is provided at the inner end of the split spline insert to cooperate with the limiting step. When the retaining edge is in contact with the limiting step, the tooth surface of the spline forming tooth smoothly connects with the inner wall of the middle forming cavity. The limiting step can prevent the split spline insert from extending excessively into the cavity, ensuring the dimensional accuracy of the spline tooth.

[0009] Furthermore, the lower end of the mold core middle section seat is provided with a lower positioning cone surface, and the top of the lower forming mold is provided with an upper positioning ring groove that matches the lower positioning cone surface. The mold core middle section seat and the lower forming mold achieve radial coaxial positioning through the cone surface engagement. The cone surface positioning has an automatic centering effect, which can offset the influence of thermal expansion deformation on coaxiality and improve molding accuracy.

[0010] Furthermore, the upper end of the middle section of the mold core is provided with an upper guide cone surface, and the bottom of the upper punch is provided with a lower guide ring groove that is adapted to the upper guide cone surface. When the upper punch moves down to close the mold, it achieves coaxial alignment with the middle section of the mold core through the cone surface guidance.

[0011] Furthermore, the bottom of the outer mold sleeve is integrally connected to a base flange, and the base flange is provided with several mounting through holes evenly distributed along the circumference for fixing the mold as a whole to the extrusion equipment worktable.

[0012] Furthermore, the inner bottom center of the first shaft end cavity is provided with an upwardly protruding lower shaft hole boss, and the inner top center of the second shaft end cavity is provided with a downwardly protruding upper shaft hole boss. Both the lower and upper shaft hole bosses are coaxially arranged with the middle forming cavity. The shaft hole bosses can directly form the center hole of the shaft end during extrusion, reducing subsequent machining processes.

[0013] Furthermore, the upper end of the inner wall of the middle section of the mold core is provided with a mold opening angle of 1° to 1.5°. The mold opening angle expands outward along the demolding direction to assist demolding and reduce the viscous resistance between the workpiece and the mold wall.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. The wedge-shaped self-tightening spline insert structure eliminates the need for bolt locking, achieving radial pre-tightening solely through the axial fitting of the outer mold sleeve. During extrusion, the expansion force of the difficult-to-deform metal on the cavity pushes the spline insert outward, while the wedge-shaped limiting groove further increases the clamping force on the insert, creating a self-reinforcing effect of "the greater the expansion force, the stronger the pre-tightening force." This fundamentally solves the problem of bolt fixation failure under high temperature and high load conditions, significantly improving the radial support stiffness of the mold and adapting to the high deformation resistance hot extrusion conditions of difficult-to-deform metals.

[0015] 2. The split spline insert can be disassembled and replaced individually, eliminating the need to scrap the entire mold, which greatly reduces mold maintenance costs and shortens production downtime. At the same time, by replacing inserts with different tooth depths, it can be adapted to the production of spline shafts of different specifications, improving the versatility of the mold.

[0016] 3. The upper and lower molds and the middle mold all adopt conical stop positioning, which has the characteristic of automatic centering. It can compensate for the dimensional deviation caused by high temperature thermal expansion deformation, ensure the coaxiality of the three cavities, and improve the forming accuracy of the spline shaft.

[0017] 4. The spline forming teeth are set with a gradual draft angle, which, together with the opening angle of the middle mold, effectively reduces the demolding resistance after hot extrusion of difficult-to-deform metals, reduces defects such as sticking and tearing, and improves the surface quality of the finished product. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the overall axial cross-sectional structure of the mold described in this invention; Figure 2 This is a top sectional view of the assembly of the mold core middle section seat and the split spline insert; Figure 3 A schematic diagram of the radial cross-section structure of the split spline insert; Figure 4 This is a three-dimensional structural diagram of the lower forming mold; Figure 5 This is a three-dimensional structural diagram of the upper punch die; Figure 6 This is a schematic diagram of the three-dimensional structure of the outer mold sleeve in axial section. Figure 7 for Figure 1 A magnified schematic diagram of the wedge fit at point A.

[0019] Explanation of reference numerals in the attached figures: 1-Outer mold sleeve; 11-Wedge-shaped limiting groove; 12-Inner cavity of sleeve; 13-Top guide opening; 2-Mold core middle section seat; 21-Middle section forming cavity; 22-Insert mounting hole; 23-Limiting step; 24-Lower end positioning cone surface; 25-Upper end guide cone surface; 26-Mold opening angle; 3-Lower end forming mold; 31-First shaft end cavity; 32-Upper end positioning ring groove; 33-Lower boss of shaft hole; 4-Upper punch; 41-Second shaft end cavity; 42-Lower guide ring groove; 43-Upper boss of shaft hole; 5-Separate spline insert; 51-Wedge-shaped bearing surface; 52-Spline forming teeth; 53-Side guard; 54-Demolding bevel; 6-Base flange; 61-Mounting through hole. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a split self-tightening hot extrusion die for spline shafts suitable for difficult-to-deform metals. It is mainly used for hot extrusion forming of TC4 titanium alloy spline shafts. The whole is made of hot work die steel and includes an outer die sleeve 1, a die core middle section seat 2, a lower forming die 3, an upper punch 4, and 8 split spline inserts 5.

[0022] The mold core middle section seat 2 is a cylindrical structure located in the middle of the mold. Its interior has a cylindrical middle section forming cavity 21 that runs through the center along the axis, serving as the forming body for the spline section of the spline shaft. The side wall of the mold core middle section seat 2 has eight radially through insert mounting holes 22 evenly distributed along the circumference. Each insert mounting hole 22 corresponds to the installation of a split spline insert 5.

[0023] Combination Figure 2 and Figure 3 As shown, the split spline insert 5 is an elongated structure that extends along the mold axis, and its length matches the length of the middle forming cavity 21. The inner side of the split spline insert 5 is provided with spline forming teeth 52 that extend into the middle forming cavity 21, and the tooth profile parameters of the spline forming teeth 52 are consistent with the spline parameters of the target spline shaft; the outer wall of the split spline insert 5 is a wedge-shaped bearing surface 51 that is wider on the outside and narrower on the inside, that is, the circumferential width of the insert gradually increases from the inside to the outside along the radial direction of the mold.

[0024] A limiting step 23 is provided at the inner opening of the insert mounting hole 22, and an outwardly extending flange 53 is provided at the inner end of the split spline insert 5. When the split spline insert 5 is inserted into the insert mounting hole 22 from the outside of the mold core middle section seat 2, the flange 53 can fit with the limiting step 23 to restrict the inward displacement of the insert, ensuring that the tooth surface of the spline forming tooth 52 is smoothly connected to the inner wall of the middle section forming cavity 21, and avoiding steps that affect the forming quality.

[0025] like Figure 6 and Figure 7 As shown, the outer mold sleeve 1 is a cylindrical structure, coaxially fitted outside the middle section seat 2 of the mold core, and its interior is the sleeve cavity 12. The inner wall of the outer mold sleeve 1 has eight axially extending wedge-shaped limiting grooves 11 along its circumferential direction. The positions of the wedge-shaped limiting grooves 11 correspond one-to-one with the split spline inserts 5, and the inclination angle of the groove wall of the wedge-shaped limiting grooves 11 perfectly matches the inclination angle of the wedge-shaped bearing surface 51. In this embodiment, the angle between the wedge-shaped bearing surface 51 and the mold axis is 4°, and the radial preload stroke of a single split spline insert 5 is 0.3 mm.

[0026] When the outer mold sleeve 1 is axially fitted from above onto the outside of the mold core middle section seat 2, the groove wall of the wedge-shaped limiting groove 11 gradually fits against the wedge-shaped bearing surface 51. As the fitting stroke increases, a radially inward compressive force is applied to the split spline insert 5, causing all inserts to tighten inward synchronously, forming an initial preload. During the extrusion molding process, the high-temperature titanium alloy billet expands outward under pressure, applying a radially outward force to the spline forming teeth 52. This force pushes the split spline insert 5 outward to press against the wedge-shaped limiting groove 11. Due to the self-locking characteristics of the wedge-shaped surface, the outer mold sleeve 1 generates a greater reverse clamping force on the insert, thereby achieving self-reinforcement of the preload and ensuring that the spline teeth maintain stable positional accuracy under high deformation resistance.

[0027] The lower forming mold 3 is detachably positioned and installed at the lower end of the middle section seat 2 of the mold core. Figure 4 As shown, the lower forming mold 3 has a cylindrical structure with a first shaft end cavity 31 with a top opening inside, used to form the lower shaft section of the spline shaft. The lower end of the mold core middle section seat 2 has a lower positioning conical surface 24, and the top of the lower forming mold 3 has an annular upper positioning ring groove 32. The inner sidewall of the upper positioning ring groove 32 is a conical surface, which is perfectly matched with the lower positioning conical surface 24. During assembly, the lower end of the mold core middle section seat 2 is inserted into the upper positioning ring groove 32. Through the conical surface fit, automatic centering is achieved, ensuring the coaxiality of the first shaft end cavity 31 and the middle forming cavity 21. At the same time, the conical surface fit can compensate for thermal expansion deformation under high temperature and avoid interference jamming problems that occur with cylindrical surface positioning.

[0028] The upper punch 4 is movably positioned above the middle section seat 2 of the die core, connected to the slider of the extrusion equipment, and can reciprocate axially. Figure 5 As shown, the upper die 4 has a second shaft end cavity 41 with a bottom opening for forming the upper shaft section of the spline shaft. The upper end of the mold core middle section seat 2 has an upper guide cone surface 25, and the bottom of the upper die 4 has a lower guide ring groove 42. The inner wall of the lower guide ring groove 42 is a cone surface, which matches the upper guide cone surface 25. When the upper die 4 moves downward to close the mold, it automatically aligns with the mold core middle section seat 2 through the cone surface guidance, ensuring the coaxiality of the second shaft end cavity 41 and the middle section forming cavity 21.

[0029] In this embodiment, the inner bottom center of the first shaft end cavity 31 is provided with an upwardly protruding lower boss 33 of the shaft hole, and the inner top center of the second shaft end cavity 41 is provided with a downwardly protruding upper boss 43 of the shaft hole. Both bosses are coaxial with the middle section forming cavity 21, and the central process holes can be formed directly at both ends of the spline shaft during the extrusion process, eliminating the need for subsequent drilling processes.

[0030] The surface of the spline forming teeth 52 of the split spline insert 5 has a 0.8° gradient demolding slope 54 along the demolding direction, and the tooth tip is rounded with an R0.3mm radius. At the same time, the upper end of the inner wall of the mold core middle section seat 2 has a 1.2° mold opening slope 26, which expands outward along the demolding direction. The combination of these two features can significantly reduce the demolding resistance after hot extrusion of titanium alloy and reduce surface scratches and sticking to the mold.

[0031] The bottom of the outer mold sleeve 1 is integrally connected to a disc-shaped base flange 6. The base flange 6 has 6 mounting through holes 61 evenly opened along the circumference. The mold can be fixed on the worktable of the extruder by bolts.

[0032] To facilitate understanding of the present invention, the assembly and operation process in conjunction with this embodiment is described below: 1. Mold assembly: First, place the lower forming mold 3 on the extruder worktable positioning seat. Then, install the mold core middle section seat 2 on the top of the lower forming mold 3 by aligning the lower positioning cone surface 24 with the upper positioning ring groove 32. Select the corresponding specification of split spline insert 5 according to the parameters of the target spline and insert them one by one into the insert mounting holes 22 from the outside of the mold core middle section seat 2. Then, install the outer mold sleeve 1 axially from above, aligning the wedge-shaped limiting groove 11 with the split spline insert 5. Press the outer mold sleeve 1 down until the base flange 6 fits against the worktable. Tighten the base flange 6 with bolts to complete the pre-tightening assembly. Finally, install the upper punch 4 on the extruder slide block and align it with the mold core middle section seat 2.

[0033] 2. Extrusion molding: The TC4 titanium alloy billet heated to the forging temperature is placed into the middle forming cavity 21. The extruder slide drives the upper die 4 to move down and close the die. The billet undergoes plastic deformation under triaxial compressive stress, filling the first shaft end cavity 31, the middle forming cavity 21 and the second shaft end cavity 41 respectively, and simultaneously forming the lower shaft section, spline section and upper shaft section. During the extrusion process, the expansion force of the billet is transmitted to the outer die sleeve 1 through the split spline insert 5. The wedge structure makes the preload increase with the expansion force, ensuring the forming accuracy of the spline teeth.

[0034] 3. Demolding and Part Removal: After extrusion, the upper die 4 moves upward to reset, and the outer die sleeve 1 is lifted upward to release the radial preload. Then, the middle section seat 2 of the die core and the formed workpiece are removed in sequence to complete one production cycle. When a split spline insert 5 is worn or broken, only the corresponding insert needs to be disassembled and replaced individually, without scrapping the entire die.

[0035] 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, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A split-type self-tightening hot extrusion die for difficult-to-deform metals, characterized in that, Includes outer mold sleeve, mold core middle section seat, lower forming mold, upper punch, and several split spline inserts; The mold core middle section seat is located in the middle of the mold, and has an axially penetrating middle section forming cavity inside. The side wall of the mold core middle section seat is evenly provided with several radially penetrating insert mounting holes along the circumference. The split spline inserts are fitted into the insert mounting holes one by one. The inner side of the split spline insert is provided with spline forming teeth that extend into the middle forming cavity. The outer side wall of the split spline insert is a wedge-shaped pressure bearing surface that is wider on the outside and narrower on the inside. The outer mold sleeve is coaxially sleeved on the outside of the middle section of the mold core. The inner wall of the outer mold sleeve is provided with wedge-shaped limiting grooves that correspond one-to-one with the split spline inserts. The inclination angle of the groove wall of the wedge-shaped limiting groove matches the inclination angle of the wedge-shaped bearing surface. When the outer mold sleeve is installed in place axially downwards, the groove wall of the wedge-shaped limiting groove squeezes the wedge-shaped bearing surface, causing each split spline insert to tighten radially inwards, applying radial preload to the spline forming teeth. The lower forming mold is detachably positioned and installed at the lower end of the middle section of the mold core. The lower forming mold has a first shaft end cavity with a top opening inside. The first shaft end cavity and the middle section forming cavity are coaxially arranged. The upper punch is movably disposed above the middle section seat of the die core. The upper punch has a second shaft end cavity with a bottom opening inside. The second shaft end cavity is coaxially disposed with the middle section forming cavity.

2. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The angle between the wedge-shaped bearing surface and the mold axis is 3°~5°, and the radial preload stroke of the single split spline insert is 0.2~0.5mm.

3. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The surface of the spline forming teeth of the split spline insert has a gradually changing draft angle of 0.5° to 1° along the demolding direction, and the chamfer of the tooth tip of the spline forming teeth is R0.2 to R0.5 mm.

4. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The inner opening of the mounting hole of the insert is provided with a limiting step, and the inner end of the split spline insert is provided with a retaining edge that cooperates with the limiting step. When the retaining edge is in contact with the limiting step, the tooth surface of the spline forming tooth is smoothly connected to the inner wall of the middle forming cavity.

5. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The lower end of the mold core middle section seat is provided with a lower end positioning cone surface, and the top of the lower end forming mold is provided with an upper end positioning ring groove that matches the lower end positioning cone surface. The mold core middle section seat and the lower end forming mold achieve radial coaxial positioning through the cone surface cooperation.

6. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The upper end of the middle section of the mold core is provided with an upper guide cone surface, and the bottom of the upper punch is provided with a lower guide ring groove that is adapted to the upper guide cone surface. When the upper punch moves down to close the mold, it achieves coaxial alignment with the middle section of the mold core through the cone surface guidance.

7. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The bottom of the outer mold sleeve is integrally connected to a base flange, and the base flange has several mounting through holes evenly distributed along its circumference.

8. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The first shaft end cavity has an upwardly protruding lower shaft hole boss at the center of its inner bottom, and the second shaft end cavity has a downwardly protruding upper shaft hole boss at the center of its inner top. Both the lower shaft hole boss and the upper shaft hole boss are coaxially arranged with the middle section forming cavity.

9. The split self-tightening spline shaft hot extrusion die for difficult-to-deform metals according to claim 1, characterized in that, The upper end of the inner wall of the middle section of the mold core is provided with a mold opening angle of 1° to 1.5°, which expands outward along the demolding direction.

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