Near-net forming extrusion die for stepped shaft forgings

Abstract

The utility model belongs to the technical field of metal plastic forming, and particularly discloses a near-net forming extrusion die for stepped shaft forgings, which comprises a first die core, a die front seat, a second die core and a die rear seat. A second sizing hole with a cylindrical inner wall is formed in the second die core in the axis direction in a penetrating mode, the first sizing hole and the second sizing hole are coaxially formed, and the diameter of the end face of the second sizing hole is smaller than that of the end face of the first sizing hole. The die disclosed by the utility model can extrude blanks into two-stage stepped shaft forgings in one heating number, the obtained forgings are smooth in outer wall, complete in streamline and high in dimensional accuracy, the uniformity and the material utilization rate of the forgings are improved, and the die is suitable for producing the stepped shaft forgings.

Description

Technical Field

[0001] The utility model relates to the technical field of metal plastic forming, in particular to a near-net-shape extrusion die for step-type shaft forgings. Background Art

[0002] To ensure high-performance forming of shaft forgings, different forming methods are used depending on the complexity of the shape, size, and product performance requirements of the shaft forgings. Common forming methods for shaft forgings include die forging, open forging, and extrusion.

[0003] Shaft forgings formed by die forging usually have large flash and low material utilization. Shaft forgings formed by free forging are prone to defects such as surface dents, end depressions, and surface cracks, resulting in poor surface quality of the forgings. Large machining allowances need to be reserved, and the material utilization is also low. For step-type shaft forgings, multiple forgings are required, which are prone to recrystallization, coarse grains, mixed crystals and other defects. Therefore, the forming efficiency of the forgings is low, the production cost is high, and it is not conducive to the production of high-performance forgings. The extrusion process has higher material utilization and forming accuracy, higher deformation plasticity and forming limit of the billet, and small machining allowance. It has certain advantages for forming some shaft forgings with larger deformation. Therefore, the extrusion process is gradually adopted in the manufacture of some shaft forgings.

[0004] Extruded shaft forgings are typically cylindrical bars of constant diameter or single-step shaft forgings. Chinese utility model patent application number 201721698312.X discloses a reverse extrusion die for long shaft forgings, comprising a lower die sleeve, an ejector block, an extrusion belt, and an extrusion barrel. The extrusion belt and extrusion barrel are detachably connected to produce single-step shaft forgings. Shaft forgings extruded from this die have a simple shape and cannot produce shaft forgings with two steps, making them difficult to apply to the extrusion molding of precision stepped shaft forgings. Utility Model Content

[0005] In order to solve the above deficiencies in the prior art, the present invention aims to provide a near-net-shape extrusion die for stepped shaft forgings, which can form shaft forgings with two steps at one time through an extrusion process.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a step-type shaft forging near-net-shape forming extrusion die includes a first die core, a die front seat, a second die core, and a die back seat; a first sizing hole with a cylindrical inner wall is opened through the interior of the first die core along the axial direction; a second cavity is opened through the interior of the die front seat in the axial direction, and the first die core is detachably installed in the second cavity; a second sizing hole with a cylindrical inner wall is opened through the interior of the second die core along the axial direction, the first sizing hole and the second sizing hole are coaxially arranged, and the end face diameter of the second sizing hole is smaller than the end face diameter of the first sizing hole; the die back seat is detachably coaxially arranged at one end of the die front seat close to the extrusion side, a fourth cavity with a cylindrical inner wall is opened through the interior of the die back seat in the axial direction, and the second die core is detachably installed at one end of the fourth cavity close to the extrusion side.

[0007] As a limitation of the present invention: the near-net-shape extrusion die for the stepped shaft forgings also includes a die ring, whose external shape is adapted to the shape of the inner wall of the second cavity, and the die ring can be detachably installed in the second cavity; a first cavity is opened through the inside of the die ring along the axial direction, the shape of the inner wall of the first cavity is adapted to the external shape of the first mold core, and the first mold core can be detachably installed in the first cavity.

[0008] As a definition of the present utility model: a first inlet hole is coaxially opened at one end of the first sizing hole close to the extrusion side, and a first outlet hole is coaxially opened at one end of the first sizing hole close to the extrusion side; the inner wall of the first inlet hole is a conical surface with the bottom surface facing the extrusion side, and the inner wall of the first outlet hole is a conical surface with the bottom surface facing the extrusion side, and the diameters of the first inlet hole close to the extrusion side and the first outlet hole close to the extrusion side are the same as the diameter of the first sizing hole.

[0009] As a definition of the present utility model: a first transition hole is coaxially opened between the first sizing hole and the first entry hole, the inner wall of the first transition hole is a conical surface with the bottom surface facing the extrusion side, the end face diameter close to the extrusion side is larger than the end face diameter close to the extrusion side, and the diameter of the first transition hole close to the extrusion side is the same as the diameter of the first sizing hole.

[0010] As a definition of the present utility model: a second inlet hole is coaxially opened at one end of the second sizing hole close to the extrusion side, and a second outlet hole is coaxially opened at one end of the second sizing hole close to the extrusion side; the inner wall of the second inlet hole is a conical surface with the bottom surface facing the extrusion side, and the inner wall of the second outlet hole is a conical surface with the bottom surface facing the extrusion side, and the diameters of the second inlet hole close to the extrusion side and the second outlet hole close to the extrusion side are the same as the diameter of the second sizing hole.

[0011] As a limitation of the present invention: a second transition hole is coaxially provided between the second sizing hole and the second entry hole, the inner wall of the second transition hole is a conical surface with the bottom surface facing the extrusion side, the diameter of the end face close to the extrusion side is larger than the diameter of the end face close to the extrusion side, and the diameter of the second transition hole close to the extrusion side is the same as the diameter of the second sizing hole.

[0012] As a definition of the present utility model: a third inlet hole is coaxially opened at one end of the first cavity close to the extrusion side, and a support platform is coaxially fixedly set at one end of the first cavity close to the extrusion side; the shape of the third inlet hole is a conical surface with the bottom surface facing the extrusion side, and its cross-sectional diameter away from the extrusion side is the same as the cross-sectional diameter of the first cavity; a third cavity with a cylindrical shape is opened through the interior of the support platform in the axial direction, and its diameter is smaller than the diameter of the first cavity and larger than the diameter of the first sizing hole.

[0013] As a limitation of the present invention: a transverse slot is fixedly provided at the bottom of the front mold seat along the circumferential direction, and a longitudinal slot is fixedly provided at the bottom of the rear mold seat along the axial direction. The front mold seat and the rear mold seat are detachably connected to the base for placing the front mold seat and the rear mold seat through the transverse slot and the longitudinal slot respectively.

[0014] As a limitation of the present invention: a first hanging bolt is fixedly provided on the upper portion of the mold front seat, and a second hanging bolt is fixedly provided on the upper portion of the mold rear seat.

[0015] Due to the adoption of the above-mentioned technical solution, the beneficial effect achieved by the present invention compared with the prior art is that by providing a first sizing hole and a second sizing hole with successively decreasing end face diameters in the shaft forging extrusion die, the blank can be extruded into a stepped shaft forging with different diameters at one time, thus achieving one-shot extrusion forming of a two-stage stepped shaft forging. Since the structure of the inlet area of ​​the die core is a conical surface, it can be adapted to the structure of the blank, and a transition area with a rounded structure is provided in the die core, making it easier for the blank to enter the die. The outer wall of the resulting forging is smooth, streamlined, and has high dimensional accuracy. Therefore, the uniformity of the forging is improved, the processing volume is reduced, and it is beneficial to improve material utilization, thereby achieving high-performance forming of stepped shaft forgings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 This is a schematic structural diagram of an embodiment of the present utility model;

[0018] Figure 2 This is a schematic structural diagram of the first mold core according to an embodiment of the present utility model;

[0019] Figure 3 This is a cross-sectional view of the first mold core of an embodiment of the present utility model;

[0020] Figure 4 This is a cross-sectional view of the second mold core of an embodiment of the present utility model;

[0021] Figure 5 This is a schematic structural diagram of the mold ring according to an embodiment of the present utility model;

[0022] Figure 6 This is a cross-sectional view of a die ring according to an embodiment of the present invention;

[0023] Figure 7 This is a structural diagram of the front seat of the utility model embodiment;

[0024] Figure 8 This is a cross-sectional view of the front seat of the embodiment of the utility model;

[0025] Figure 9 This is a structural diagram of the first mold core, mold ring, mold front seat, and mold rear seat in an assembled state according to an embodiment of the present utility model;

[0026] Figure 10 This is a cross-sectional view of the first mold core, mold ring, mold front seat, and mold rear seat in an assembled state according to an embodiment of the present utility model;

[0027] Figure 11 This is a structural diagram of the base of an embodiment of the utility model;

[0028] Figure 12 This is a schematic structural diagram of the blank of an embodiment of the utility model;

[0029] Figure 13 A schematic structural diagram of a stepped shaft produced according to an embodiment of the present utility model;

[0030] Figure 14 This is a schematic structural diagram of the working position of the utility model in the extrusion process;

[0031] Figure 15 This is a cross-sectional view of the utility model at the working position during the extrusion process.

[0032] In the figure: 1-first mold core, 11-first inlet hole, 12-first transition hole, 13-first calibrating hole, 14-first outlet hole,

[0033] 2-die ring, 21-first cavity, 22-support platform, 23-third entry hole, 24-third cavity,

[0034] 3-mold front seat, 31-first hanging bolt, 32-second cavity, 33-horizontal slot,

[0035] 4-mold back seat, 41-second hanging bolt, 42-second mold core, 43-longitudinal slot, 44-second entry hole, 45-second transition hole, 46-second calibrating hole, 47-second exit hole, 48-fourth cavity,

[0036] 5-base, 51-horizontal boss, 52-longitudinal boss,

[0037] 6-retaining wall, 7-extrusion pad, 8-glass pad, 9-stepped shaft,

[0038] 10-blank, 101-head, 102-transition part, 103-body,

[0039] 111-die, 222-extrusion cylinder, 333-extrusion rod. DETAILED DESCRIPTION

[0040] The preferred embodiment of the present invention will be described below with reference to the accompanying drawings. It should be understood that the step-type shaft forging near-net-shape extrusion die described herein is a preferred embodiment and is only used to illustrate and explain the present invention and does not constitute a limitation of the present invention.

[0041] The directional terms or positional relationships such as "up", "down", "left" and "right" described in the present invention are based on the directional relationships in the drawings of the present invention specification and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the content protected by the present invention.

[0042] The structural diagram of the blank 10 required for producing the stepped shaft 9 in this embodiment is as follows Figure 12 As shown, it includes a head 101, a transition portion 102, and a body 103. The shape of the head 101 and the body 103 are both cylindrical, the diameter of the head 101 is smaller than the diameter of the body 103, and the diameter of the head 101 is smaller than the diameter of the first calibrating hole 13, and the difference between them is preferably 5mm. The shape of the transition portion 102 is a conical surface with the bottom surface facing the body 103, and the cone angle α1' is preferably 80°. Since the blank 10 has the above structure, it can smoothly enter the extrusion die. The structural schematic diagram of the produced stepped shaft 9 is shown as follows Figure 13 As shown, it consists of three segments with different diameters, which are d1, d2 and d3 with successively larger diameters.

[0043] like Figure 1 As shown, a step-type shaft forging near-net-shape extrusion die has one end for the extrusion side and the other end for the extrusion side, including a first die core 1, a die front seat 3, a second die core 42, and a die back seat 4 that are hollow and coaxially arranged. It should be noted that the embodiment of the present invention is Figures 1 to 11In the figure, the right side is the intrusion side and the left side is the extrusion side.

[0044] like Figure 2 and Figure 3 As shown, the outer shape of the first mold core 1 is cylindrical, and a first sizing hole 13 with a cylindrical inner wall is provided inside the mold core along the axial direction. A first inlet hole 11 is coaxially provided at one end of the first sizing hole 13 close to the inlet side, and a first outlet hole 14 is coaxially provided at one end of the first sizing hole 13 close to the extrusion side. The inner wall of the first inlet hole 11 is a conical surface with the bottom facing the inlet side, and its top angle is α1, preferably 100°. The billet 10 is extruded into the mold by the extruder from this area; the inner wall of the first outlet hole 14 is a conical surface with the bottom facing the extrusion side. The diameters of the first inlet hole 11 close to the extrusion side and the first outlet hole 14 close to the inlet side are the same as the diameter of the first sizing hole 13, which is beneficial to improving the flatness of the surface of the billet 10.

[0045] Furthermore, to ensure smooth passage of the blank 10 from the inlet side into the sizing zone, a first transition hole 12 is coaxially disposed between the first sizing hole 13 and the first entry hole 11. The inner wall of the first transition hole 12 is a curved conical surface with its bottom facing the inlet side. The diameter of the end surface near the inlet side is larger than that near the extrusion side, and its sidewalls exhibit rounded corners in a cross-sectional view. The diameter of the first transition hole 12 near the extrusion side is the same as that of the first sizing hole 13, which helps improve the surface smoothness of the blank 10.

[0046] In other possible cases, only a first calibrating hole 13 with a cylindrical inner wall is opened through the interior of the first mold core 1 along the axial direction, and the blank 10 can enter the first mold core 1 from the extrusion side for preliminary processing.

[0047] The outer shape of the mold front seat 3 is cylindrical, and a second cavity 32 is opened through it in the axial direction. The shape of the inner wall of the second cavity 32 is adapted to the shape of the outer side of the first mold core 1 and has the same size, which is cylindrical; the first mold core 1 can be detachably installed in the second cavity 32, so the first mold core 1 and the mold front seat 3 can be assembled into an integrated structure.

[0048] like Figure 9 and Figure 10 As shown, the outer shape of the mold back seat 4 is cylindrical, and it is detachably coaxially arranged at the end of the mold front seat 3 close to the extrusion side. A fourth cavity 48 with a cylindrical inner wall is opened through the axial direction of the mold back seat 4, and the second mold core 42 is fixedly installed at the end close to the extrusion side. Figure 4 As shown, a second calibrating hole 46 with a cylindrical inner wall is opened inside the second mold core 42 along the axial direction. The first calibrating hole 13 and the second calibrating hole 46 are coaxially arranged. The end face diameter of the second calibrating hole 46 is smaller than the end face diameter of the first calibrating hole 13. When the blank 10 passes through the first calibrating hole 13 and the second calibrating hole 46 in sequence, as shown in FIG. Figure 13 As shown, the outer contour of the blank 10 is extruded into a stepped shaft member 9 with different diameters, wherein the end face diameter of the second calibrating hole 46 is equal to d1, the end face diameter of the first calibrating hole 13 is equal to d2, and the diameter of the cylindrical blank 10 is equal to d3.

[0049] A second inlet hole 44 is coaxially disposed at one end of the second calibrating hole 46, which is closer to the inlet side, and a second outlet hole 47 is coaxially disposed at the other end of the second calibrating hole 46, which is closer to the extrusion side. The inner wall of the second inlet hole 44 is a conical surface with its bottom facing the inlet side, while the inner wall of the second outlet hole 47 is a conical surface with its bottom facing the extrusion side. The diameters of the second inlet hole 44, closer to the extrusion side, and the second outlet hole 47, closer to the inlet side, are both the same as the diameter of the second calibrating hole 46, which helps to improve the surface smoothness of the blank 10.

[0050] Furthermore, in order to allow the blank 10 to smoothly enter the sizing zone from the extrusion side, a second transition hole 45 is coaxially arranged between the second sizing hole 46 and the second entry hole 44. The inner wall of the second transition hole 45 is a conical surface with the bottom surface facing the extrusion side. The side wall has rounded corners in the cross-sectional view, and the end face diameter close to the extrusion side is larger than the end face diameter close to the extrusion side. The diameter of the second transition hole close to the extrusion side is the same as the diameter of the second sizing hole, which is beneficial to improving the flatness of the surface of the blank 10.

[0051] In other possible cases, the second mold core 42 is provided with only a second calibrating hole 46 with a cylindrical inner wall along the axial direction, and the blank 10 can enter the second mold core 42 from the extrusion side for secondary processing.

[0052] Furthermore, if Figure 5 and Figure 6 As shown, the near-net-shape extrusion die for stepped shaft forgings also includes a die ring 2, whose external shape is a conical surface with the bottom facing the extrusion side, and the top angle is β, preferably 12°. A first cavity 21 is opened inside the die ring 2 along the axial direction, and the inner wall of the first cavity 21 is a cylinder with the same diameter as the outer diameter of the first mold core 1. The first mold core 1 is installed in the first cavity 21, so the first mold core 1 and the die ring 2 can be assembled into an integrated structure.

[0053] Inside the die ring 2, from the inlet side to the extrusion side, there are coaxially arranged third inlet hole 23, first cavity 21, and support platform 22. The third inlet hole 23 is in the shape of a conical surface with the bottom surface facing the inlet side, and its top angle is α2, which is greater than α1, and α2 is preferably 120°. In addition, the cross-sectional diameter of the third inlet hole 23 away from the inlet side is the same as the diameter of the first cavity 21, which is conducive to maintaining the flatness of the surface of the blank 10. The support platform 22 is used to support the first mold core 1 placed in the first cavity 21, and the interior of the support platform 22 has a third cylindrical cavity 24, whose diameter is smaller than the diameters of the first cavity 21 and the fourth cavity 48, so that the blank 10 can move smoothly inside the mold.

[0054] like Figure 7 and Figure 8 As shown, the front mold seat 3 has a cylindrical exterior shape, with a second cavity 32 extending through it along its axis. The inner wall of the second cavity 32 is a conical surface with its bottom facing the intrusion side, and its top angle is β', preferably 12°. The second cavity 32 matches the exterior shape and dimensions of the mold ring 2. The mold ring 2 is installed in the second cavity 32, thus forming a single integrated structure with the first mold core 1, mold ring 2, and front mold seat 3.

[0055] like Figure 11 As shown, in order to better fix the cylindrical front die seat 3 and the rear die seat 4 on the extruder, the extruder includes a "U"-shaped base 5, whose axial length is equal to the sum of the axial lengths of the front die seat 3 and the rear die seat 4. The front die seat 3 and the rear die seat 4 can be placed on the base 5. Specifically, a transverse boss 51 is fixedly provided on the base 5 along the circumference, and a transverse groove 33 is fixedly provided on the bottom of the front die seat 3 along the circumference, the size of which is compatible with the transverse boss 51. The front die seat 3 and the base 5 are detachably connected via the transverse groove 33 and the transverse boss 51. A longitudinal boss 52 is fixedly provided on the base 5 along the axial direction, and a longitudinal groove 43 is fixedly provided on the bottom of the rear die seat 4 along the axial direction, the size of which is compatible with the longitudinal boss 52. The rear die seat 4 and the base 5 are detachably connected via the longitudinal groove 43 and the longitudinal boss 52.

[0056] like Figure 1 As shown, the extruder also includes a square plate-shaped retaining wall 6 fixedly connected to the base 5, which is fixedly arranged at the end of the die back seat 4 away from the extrusion side and is used to support the billet 10 during the extrusion process. Figure 10 As shown, a first hanging bolt 31 is fixedly provided on the upper portion of the mold front seat 3, and a second hanging bolt 41 is fixedly provided on the upper portion of the mold rear seat 4, both of which are used to provide force points for the lifting device.

[0057] Since the first sizing hole 13 and the second sizing hole 46 with successively decreasing end diameters are provided in the shaft forging extrusion die, the blank 10 can be extruded into a stepped shaft forging with different diameters at one time, thus achieving the one-shot extrusion forming of a two-stage stepped shaft forging. By setting the structure of the die core inlet area to a conical surface, it can be adapted to the structure of the head 101 and the transition part 102 of the blank 10, and a transition area with a rounded corner structure is provided in the die core, so that the process of the blank 10 entering the die is smoother, and the outer wall of the resulting stepped shaft 9 is smooth, the streamline is complete, and the dimensional accuracy is high. Therefore, the uniformity of the stepped shaft 9 is improved, the processing amount is reduced, which is conducive to improving the material utilization rate and achieving high-performance forming of stepped shaft forgings.

[0058] The process of producing the stepped shaft 9 by using the above-mentioned step-type shaft forging near-net-shape extrusion die is as follows: Figure 14 and Figure 15 As shown, after high-temperature treatment, the blank 10 is loaded into the cylindrical extrusion barrel 222. The extruder's pressure system then causes the extrusion rod 333 to push the extrusion pad 7 and the blank 10 toward the die assembly 111. When the blank 10 is in close contact with the glass pad 8 coaxially positioned near the extrusion side of the first mold core 1, the extruder's high-pressure system is activated. After the metal of the blank 10 is roughened, it is sequentially extruded into the first mold core 1 and the second mold core 42, forming a stepped shaft 9 with different diameters.

[0059] The glass mat 8 is a hollow platform. The outer wall of the portion away from the extrusion side is shaped to match the inner wall of the first entry hole 11, forming a conical surface with its bottom facing the extrusion side. The angle of the conical surface is the same as the angle α1 of the conical surface of the first entry hole 11. The diameter of the end face of the hollow structure away from the extrusion side is between the diameter of the first calibrating hole 13 and the diameter of the end face of the first entry hole 11 near the extrusion side. The diameter of the end face of the hollow structure away from the extrusion side is the same as the diameter of the end face of the hollow structure near the extrusion side. The outer wall of the portion of the glass mat 8 near the extrusion side is cylindrical, with a diameter identical to the diameter of the cylindrical cavity within the extrusion barrel 222 for placing the blank 10. The glass mat 8 is also removably coaxially disposed on the inner wall of the first entry hole 11 near the extrusion side and the inner wall of the cylindrical cavity of the extrusion barrel 222 near the first entry hole 11.

[0060] When the blank 10 is extruded to a length of 210 mm, the extrusion is ended, the extrusion cylinder 222 and the extrusion rod 333 retreat, driving the extrusion pad 7, the stepped shaft 9 and the first mold core 1 to retreat at the same time, and then the stepped shaft 9 is taken out, and the extrusion process is ended.

Claims

1. A step-type near-net-shape extrusion die for shaft forgings, characterized by: It includes a first mold core, a mold front seat, a second mold core, and a mold back seat; A first calibrating hole with a cylindrical inner wall is formed inside the first mold core along the axial direction; A second cavity is provided through the mold front seat in the axial direction, and the first mold core is detachably installed in the second cavity; A second calibrating hole with a cylindrical inner wall is formed inside the second mold core along the axial direction, the first calibrating hole and the second calibrating hole are coaxially arranged, and the end face diameter of the second calibrating hole is smaller than the end face diameter of the first calibrating hole; The mold rear seat is detachably coaxially arranged at one end of the mold front seat close to the extrusion side. A fourth cavity with a cylindrical inner wall is opened through the axial direction of the mold rear seat. The second mold core is detachably installed at one end of the fourth cavity close to the extrusion side.

2. The step-type near-net-shape extrusion die for shaft forgings according to claim 1, characterized in that: The body also includes a mold ring, the outer shape of which matches the shape of the inner wall of the second cavity, and the mold ring is detachably installed in the second cavity; A first cavity is formed inside the mold ring along the axial direction. The shape of the inner wall of the first cavity matches the outer shape of the first mold core. The first mold core is detachably installed in the first cavity.

3. The step-type near-net-shape extrusion die for shaft forgings according to claim 2, characterized in that: A first inlet hole is coaxially formed at one end of the first sizing hole close to the extrusion side, and a first outlet hole is coaxially formed at one end of the first sizing hole close to the extrusion side. The inner wall of the first inlet hole is a conical surface with the bottom facing the extrusion side, and the inner wall of the first outlet hole is a conical surface with the bottom facing the extrusion side. The diameters of the first inlet hole close to the extrusion side and the first outlet hole close to the extrusion side are the same as the diameter of the first sizing hole.

4. The step-type near-net-shape extrusion die for shaft forgings according to claim 3, characterized in that: A first transition hole is coaxially provided between the first sizing hole and the first entry hole. The inner wall of the first transition hole is a conical surface with the bottom facing the extrusion side. The diameter of the end face close to the extrusion side is larger than the diameter of the end face close to the extrusion side. The diameter of the first transition hole close to the extrusion side is the same as the diameter of the first sizing hole.

5. The step-type near-net-shape extrusion die for shaft forgings according to claim 4, characterized in that: A second inlet hole is coaxially formed at one end of the second sizing hole close to the extrusion side, and a second outlet hole is coaxially formed at one end of the second sizing hole close to the extrusion side. The inner wall of the second inlet hole is a conical surface with the bottom facing the extrusion side, and the inner wall of the second outlet hole is a conical surface with the bottom facing the extrusion side. The diameters of the second inlet hole close to the extrusion side and the second outlet hole close to the extrusion side are the same as the diameter of the second sizing hole.

6. The near-net-shape extrusion die for stepped shaft forgings according to claim 5, characterized in that: A second transition hole is coaxially provided between the second sizing hole and the second entry hole. The inner wall of the second transition hole is a conical surface with the bottom facing the extrusion side. The diameter of the end face close to the extrusion side is larger than the diameter of the end face close to the extrusion side. The diameter of the second transition hole close to the extrusion side is the same as the diameter of the second sizing hole.

7. The near-net-shape extrusion die for stepped shaft forgings according to claim 6, characterized in that: A third inlet hole is coaxially opened at one end of the first cavity close to the extrusion side, and a support platform is coaxially fixedly provided at one end of the first cavity close to the extrusion side; The third inlet hole is in the shape of a conical surface with its bottom surface facing the inlet side, and its cross-sectional diameter away from the inlet side is the same as the cross-sectional diameter of the first cavity; A third cylindrical cavity is provided through the inner axial direction of the support platform, and the diameter of the third cavity is smaller than that of the first cavity and larger than that of the first calibrating hole.

8. The step-type near-net-shape extrusion die for shaft forgings according to claim 7, characterized in that: The bottom of the mold front seat is fixed with a transverse slot along the circumferential direction, and the bottom of the mold rear seat is fixed with a longitudinal slot along the axial direction. The mold front seat and the mold rear seat are detachably connected to the base for placing the mold front seat and the mold rear seat through the transverse slot and the longitudinal slot respectively.

9. The near-net-shape extrusion die for stepped shaft forgings according to any one of claims 1 to 8, characterized in that: A first hanging bolt is fixedly provided on the upper portion of the mold front seat, and a second hanging bolt is fixedly provided on the upper portion of the mold rear seat.

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