Composite machining method of hollow rotating shaft

Abstract

The application discloses a kind of composite processing methods of hollow rotating shaft, including rotating shaft blank using hot piercing, straightening, spheroidizing annealing, phosphorus saponification process obtains first forming piece;The right part of first forming piece is reduced in diameter;The left part of second forming piece is formed into stepped shaft;The middle part of third forming piece is formed into long key groove;Fourth forming piece is treated using spheroidizing annealing, phosphorus saponification, and the right part of fourth forming piece is formed into internal spline on the inner side;Fifth forming piece is formed into shaft shoulder;Sixth forming piece is formed into hollow rotating shaft blank using isothermal normalizing.The first through hole is formed in rotating shaft blank by hot piercing, then the material is directionally flowed in each process using cold extrusion to gradually shape the characteristics, and the second through hole, stepped shaft, long key groove, internal spline and shaft shoulder are sequentially formed, so that the shape characteristics formed in the previous process are not damaged in the subsequent process, and the integrated processing of complex shape hollow rotating shaft is realized.

Description

Technical Field

[0001] This invention relates to the field of new energy vehicle power motor technology, specifically to a composite processing method for a hollow rotating shaft. Background Technology

[0002] According to materials mechanics analysis, when a shaft transmits torque, the outermost part of the shaft has a greater effect on transmitting effective torque, viewed from the radial section. Therefore, when a shaft needs to transmit a large torque, a larger shaft diameter is desired. Using a hollow shaft can reduce its weight. Hollow motor shafts have many advantages, such as being lightweight, having good heat dissipation performance, and low noise and vibration, and have gradually replaced solid motor shafts as the mainstream in the market.

[0003] Hollow shafts can be manufactured through processes such as forging and cold extrusion. Cold extrusion is an advanced manufacturing technology that applies pressure to metal material at room temperature using a die, causing it to plastically deform and form shaft-like parts. Based on the plastic deformation characteristics of metal, the die guides the material flow direction, and the processes mainly include: forward extrusion where the metal flow direction is consistent with the punch movement; reverse extrusion where the metal flow direction is opposite to the punch movement; composite extrusion combining forward and reverse extrusion; and radial extrusion where the metal flow direction is perpendicular to the punch movement. In the process of cold extrusion machining shaft parts with complex shapes, the material flow direction at each step determines whether stress concentration occurs in the formed part and the rate of material scrap during secondary processing.

[0004] like Figure 8a and Figure 8b As shown, a hollow shaft for a new energy vehicle motor has a complex shape and is placed inside the motor housing. Specifically, the left side of the hollow shaft is a fixing part 1, with a stepped shaft 11 formed on its outer surface for mates with a bearing. The middle part of the hollow shaft is a mounting part 2, with a long keyway 6 formed on its outer surface for mounting a flat key, thus fixing a silicon steel sheet to the outer surface of the mounting part 2 and stabilizing the motor's magnetic field. The right side of the hollow shaft is an output part 3, with a shoulder 32 formed on its outer surface. This shoulder 32 restricts the axial movement of the silicon steel sheet and the axial movement of the hollow shaft relative to the motor housing, ensuring the stability of the hollow shaft and silicon steel sheet within the motor. The inner surface of the output part 3 of the hollow shaft has an internal spline 31, which mates with the external spline of the differential's input shaft or the external spline of the drive shaft to transmit the motor's torque.

[0005] The inventors of this application discovered during the cold extrusion process of hollow shafts with complex shapes that the material flow during the cold extrusion process of long keyways and internal splines can easily cause slight changes in the dimensions of the hollow shaft, increasing stress concentration in the long keyways and internal splines of the hollow shaft blank, reducing the dimensional accuracy of the hollow shaft blank, reducing the material utilization rate of secondary machining, increasing the machining allowance, and increasing the processing cost of hollow shafts with complex shapes. Summary of the Invention

[0006] To solve the above problems, this invention provides a composite machining method for hollow rotating shafts, the specific technical solution of which is as follows:

[0007] Composite processing methods include:

[0008] Step 1: The round steel is cut to form a shaft blank. The shaft blank is then heat-pierced along the axial direction to form a through hole to obtain the first formed part.

[0009] Step 2: The right side of the first molded part is reduced in diameter by cold extrusion to obtain a second molded part with a second through hole;

[0010] Step 3: The left side of the second molded part is cold-extruded to form a stepped shaft to obtain the third molded part;

[0011] Step 4: The middle part of the third molded part is cold-extruded to form a long keyway to obtain the fourth molded part;

[0012] Step 5: The right side of the fourth molded part is cold-extruded to form an internal spline on the side of the second through hole to obtain the fifth molded part;

[0013] Step 6: The fifth molded part is cold-extruded axially to form a shoulder, thus obtaining the sixth molded part;

[0014] Step 7: The sixth forming part is formed into a hollow rotating shaft blank using isothermal normalizing.

[0015] Preferably, in step 1, the hot piercing process for the shaft blank is as follows: heating the shaft blank to the hot piercing processing temperature to obtain a heated shaft; and sending the heated shaft into a piercing machine to form a first through hole.

[0016] Preferably, the diameter of the first through hole is greater than the diameter of the second through hole; the length of the shaft blank is less than the length of the hollow shaft blank.

[0017] Preferably, the first molded part is surface treated by straightening, spheroidizing annealing, and phosphating. The spheroidizing annealing process is as follows: the working temperature of the heating furnace is raised to 750℃~770℃, the holding time in the heating furnace is 2~3h, and the heating furnace is cooled to 500℃-550℃ and then air-cooled.

[0018] Preferably, in step 2, the inner diameter of the second through hole is smaller than the inner diameter of the first through hole, the axial direction of the second through hole is consistent with the axial direction of the first through hole, and the right diameter of the second molded part is smaller than the right diameter of the first molded part; in step 2, the cold extrusion die includes a core rod disposed inside the first through hole and a diameter reduction die disposed on the outer side of the first molded part. During the diameter reduction process, the core rod applies a supporting force to part of the inner side of the first through hole, and the diameter reduction die applies pressure and performs positive work to the right outer side of the first molded part. This pressure is perpendicular to the axial direction of the first molded part until the second molded part is formed.

[0019] Preferably, in step 3, the outer diameter of the stepped shaft gradually decreases from the middle of the third molded part to the left side of the third molded part, and the outer diameter of the stepped shaft is smaller than the middle diameter of the third molded part. The axial direction of the stepped shaft is consistent with the axial direction of the third molded part. In step 3, the cold extrusion die also includes a stepped shaft die disposed on the outer side of the second molded part. During the forming of the stepped shaft, the core rod applies a supporting force to the inner side of the first through hole, and the stepped shaft die applies pressure and performs positive work on the outer side of the left side of the second molded part. This pressure is perpendicular to the axial direction of the second molded part until the third molded part is formed.

[0020] Preferably, in step 4, the length direction of the long keyway is consistent with the axial direction of the first through hole and the second through hole, the long keyway is symmetrical about the axis of the middle part of the fourth molded part, and the long keyway is formed in the middle part of the fourth molded part; in step 4, the cold extrusion die also includes a keyway die disposed on the outer side of the third molded part, during the forming of the long keyway, the core rod applies a supporting force to the inner side of the first through hole, and the keyway die applies pressure and performs positive work to the middle part of the third molded part, the pressure being parallel to the axial direction of the third molded part, until the fourth molded part is formed.

[0021] Preferably, in step 5, the length direction of the internal spline is consistent with the axial direction of the second through hole, and the root circle diameter of the internal spline is larger than the inner diameter of the second through hole; in step 5, the cold extrusion die includes an internal spline die disposed inside the second through hole, and during the internal spline forming process, the internal spline die applies pressure to the second through hole, the pressure is consistent with the axial direction of the second through hole, or the component of the pressure is consistent with the axial direction of the second through hole, until the fifth molded part is formed; the fourth molded part is first surface treated by spheroidizing annealing and phosphating, and then the internal spline is formed.

[0022] Preferably, in step 6, the shoulder is formed on the outer side of the right part of the sixth forming part, the axial direction of the shoulder is consistent with the axial direction of the stepped shaft, and the diameter of the shoulder is larger than the middle diameter of the sixth forming part; in step 6, the cold extrusion die also includes a shoulder die A and a shoulder die B disposed on the outer side of the fifth forming part. Both shoulder die A and shoulder die B are dies that coincide with the outer side of the fifth forming part. Shoulder die A and shoulder die B are connected at the maximum diameter of the shoulder. During the forming process of the shoulder, the core rod applies a supporting force to the inner side of the first through hole. Shoulder die A, core rod and shoulder die B are relatively close to each other along the axial direction and converge at the maximum diameter of the shoulder until the sixth forming part is formed.

[0023] Preferably, in step 7, the isothermal normalizing process is as follows: the internal temperature of the heating furnace is raised to 910℃-930℃, the holding time is selected according to the maximum wall thickness of the sixth forming part for holding in the heating furnace, the internal temperature of the heating furnace is reduced to 600℃-650℃, the holding time is 1h-2h in the heating furnace, and the heating furnace is opened for air cooling to room temperature to form a hollow rotating shaft blank.

[0024] As can be seen from the above technical solution, the present invention has the following beneficial effects:

[0025] This invention forms a first through hole by hot piercing a shaft blank. During cold extrusion, material on the right side of the first forming part flows to the first through hole to form a second through hole. Material on the left side of the second forming part flows to both axial ends to form a stepped shaft without affecting the size of the second through hole. Material on the outer side of the middle part of the third forming part flows to the right axial end of the middle part to form a long keyway without affecting the size of the second through hole and the stepped shaft. Material on the inner side of the right part of the fourth forming part flows to the right axial end of the right part to form an internal spline without affecting the size of the second through hole, the stepped shaft, and the long keyway. Material on the outer side of the right part of the fifth forming part flows radially outward to form a shoulder without affecting the inner diameter of the second through hole, the diameter of the stepped shaft, the width of the long keyway, and the shape of the internal spline. This process forms the shape of a hollow shaft blank, reduces stress concentration, improves material utilization in subsequent machining, and reduces machining allowance. Attached Figure Description

[0026] Figure 1 This is a flowchart of a composite processing method;

[0027] Figure 2 This is a cross-sectional view of the first molded part embodiment;

[0028] Figure 3 This is a cross-sectional view of the second molded part embodiment;

[0029] Figure 4 This is a schematic diagram of the structure of the third molding part embodiment;

[0030] Figure 5This is a schematic diagram of the structure of the fourth molding part embodiment;

[0031] Figure 6 This is a cross-sectional view of the fifth molded part embodiment;

[0032] Figure 7 This is a schematic diagram of the structure of the sixth molding part embodiment;

[0033] Figure 8a This is a schematic diagram of the hollow rotating shaft blank structure;

[0034] Figure 8b This is a sectional view of a hollow rotating shaft blank.

[0035] In the figure: 1. Fixing part; 11. Stepped shaft; 2. Mounting part; 3. Output part; 31. Internal spline; 32. Shaft shoulder; 4. First through hole; 5. Second through hole; 6. Long keyway. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0038] like Figure 8a and Figure 8b As shown, the composite machining method is used to process the hollow shaft in the motor of a new energy vehicle. The hollow shaft has a complex shape and includes a fixing part 1, a mounting part 2 and an output part 3 along the axial direction from the left end to the right end. According to the description in the background art, the fixing part 1 is used to fix the bearing, the mounting part 2 is used to install the silicon steel sheet, and the output part 3 is used to output the motor torque.

[0039] like Figure 1 As shown, one embodiment of the composite processing method has the following steps:

[0040] like Figure 2As shown, S1: round steel is cut to form a shaft blank, and the shaft blank is hot-pierced along the axial direction to form a through hole 4 to obtain a first formed part. The first formed part is surface treated by straightening, spheroidizing annealing and phosphating.

[0041] Specifically, round steel is cut to the length of the hollow shaft to obtain a shaft blank. The length of the shaft blank is less than the length of the hollow shaft blank. During the cold extrusion process, the diameter of the shaft blank is reduced while its axial length is increased, and the material flows along the axial direction. Secondly, hot piercing softens the metal at high temperature, which can significantly reduce the deformation resistance when forming the first through hole 4. Its single-pass deformation rate is much greater than that of cold extrusion, which can reduce the number of piercing passes, thereby reducing the time to form the first through hole 4 and improving the forming efficiency of the first through hole 4. Furthermore, rapid cooling after hot piercing can refine the grains and improve the fatigue strength of the shaft blank.

[0042] Secondly, during hot piercing, due to high-temperature plastic deformation and cooling contraction, round steel is prone to defects such as bending and excessive ovality. Hot straightening utilizes the high temperature of the first formed part to reduce its resistance to plastic deformation, avoiding surface cracks during the straightening process. Subsequently, hot straightening corrects the deformation of the first formed part through external pressure and thermal expansion and contraction. The straightness of the corrected first formed part is ≤1mm / m, reducing the risk of further straightening during subsequent cold extrusion processing and increasing surface cracking. Furthermore, during the spheroidizing annealing process of the hot-pierced first formed part, heating dissolves the internal lamellar carbides, forming groove-like defects. Incompletely dissolved carbide fragments are then treated... As the nucleation core, carbon atoms diffuse and uniformly deposit on its surface, forming a uniform spherical structure by evenly distributing spherical carbides. This reduces stress concentration in the first molded part, lowers its hardness, improves its plasticity, and prevents cracks from occurring during subsequent cold extrusion. Secondly, the phosphating and saponification process is a surface treatment technology that combines phosphating and saponification. It is mainly used for lubrication treatment before metal processing. The main steps include: degreasing, pickling, water washing, phosphating treatment with phosphating solution, saponification treatment with saponification solution, drying, and coating with a corrosion-resistant coating. Through the synergistic effect of chemical conversion and lubrication film, it reduces the surface roughness of the first molded part, improves its surface quality, thereby reducing wear on the mold and improving its cold working performance.

[0043] Therefore, the straightness of the first molded part is ≤1mm / m, forming a uniform spheroidized structure and a lubricating film, thus improving its cold working performance.

[0044] like Figure 3 As shown, S2: The right side of the first molded part is reduced in diameter by cold extrusion to obtain a second molded part with a second through hole 5.

[0045] Specifically, the first forming part is subjected to cold extrusion to apply pressure to its right side, causing the material on the right side to flow axially towards both ends and towards the first flow on the right side, reducing its radial dimension on the outer side, reducing the inner diameter of the first through hole 4 to form the second through hole 5, and increasing its axial dimension. The first forming part uses a diameter reduction method to reduce the outer diameter of its right side and the inner diameter of the first through hole 4 on the right side to form the second through hole 5, making the right diameter of the first forming part smaller than the middle diameter, and the second through hole 5 smaller than the first through hole 4, thus forming a conical structure to prepare for subsequent cold extrusion processes. During cold extrusion, pressure is applied to the outer side of the first forming part simultaneously. The pressure on the left and middle sides is used to fine-tune its outer diameter to make it equal to the diameter of the fixed part 1 and the output part 3 of the hollow rotating shaft blank, while the pressure on the right side is used to axially compress it, making its outer diameter smaller than the middle diameter. The portion of the first through hole 4 on the right side moves radially with the right side of the first forming part, thus forming the second through hole 5.

[0046] Therefore, the first molded part is formed into a second molded part with a second through hole 5 by reducing the diameter. The compression rate when the inventor of this application performs this step is 30%.

[0047] Combination Figure 4 As shown, S3: The left side of the second molded part is formed by cold extrusion molding of the stepped shaft 11 to obtain the third molded part.

[0048] Specifically, the outer diameter of the left side of the second molded part is the same. Only the left side is subjected to pressure in the vertical axial direction, without applying deformation pressure to the first through hole 4 located on the left side. This causes the material on the left side of the second molded part to flow axially towards both ends to reduce its radial dimension, but without reducing the inner diameter of the first through hole 4 located on the left side. Secondly, the pressure applied to the second molded part does different work at different positions, which causes the left side of the second molded part to form a stepped shaft 11 with different diameters. The diameter of the stepped shaft 11 increases discontinuously from the left end to the right end, thereby enabling the placement of a bearing and applying radial limit to the bearing.

[0049] Therefore, the second molded part is formed by cold extrusion to form a stepped shaft 11 with different outer diameters, and the inner diameter of the first through hole 4 of the first molded part is equal to the inner diameter of the first through hole 4 of the second molded part, so that the left part of the third molded part is a stepped shaft 11 and the diameter of the right part is smaller than the diameter of the middle part.

[0050] Combination Figure 5 As shown, S4: The fourth part is obtained by cold extrusion forming a long keyway 6 in the middle of the third part.

[0051] Specifically, pressure is applied to the outer sides of the left and middle parts of the third molded part in the direction of the axis. The radial projection of this pressure is the radial projection of the long keyway 6. During the pressure application, the material in the long keyway 6 flows radially, increasing the diameter of the outer side of the middle part of the third molded part. When the cold extrusion die for forming the long keyway 6 is completely closed, the excess material in the middle part of the third molded part flows axially, increasing the axial length of the third molded part. This ensures the dimensional accuracy of the stepped shaft 11 and the second through hole 5 formed by the third molded part, while simultaneously forming the long keyway 6 to obtain the fourth molded part, thereby ensuring the shape and dimensional accuracy of the fourth molded part.

[0052] Secondly, the third molding part is symmetrically formed with long keyways 6 along the axis to obtain the fourth molding part, and silicon steel sheets are installed on its outer surface, so that the symmetrical long keyways 6 can transmit torque to the silicon steel sheets equally, thereby improving the transmission effect of the fourth molding part.

[0053] Combination Figure 6 As shown, S5: The fourth molded part is treated by spheroidizing annealing and phosphating saponification. The right side of the fourth molded part is cold-extruded to form an internal spline 31 on the side of the second through hole 5 to obtain the fifth molded part.

[0054] Specifically, the fourth forming part uses spheroidizing annealing to reduce stress concentration and avoid cracks during subsequent cold extrusion. Phosphating is used to improve the lubrication of the outer surface and improve the cold extrusion processing capability. The processes of spheroidizing annealing and phosphating are the same as those in S1 to achieve the same treatment effect.

[0055] Secondly, the inner side of the second through hole 5 is subjected to pressure from the vertical axis outward, while the outer diameter of the right part of the fourth forming part remains unchanged. This causes the material on the inner side of the second through hole 5 to flow axially to the right part of the fifth forming part, and to flow radially from the tooth root to the tooth tip of the inner spline 31, thereby ensuring the diameter of the right part of the fifth forming part and the dimensional accuracy of the inner spline 31. The right part of the inner spline 31 forms a fit with the outer spline of the reducer input shaft, thereby transmitting torque.

[0056] Combination Figure 7 As shown, S6: The fifth part is formed by cold extrusion along the axial direction to form a shoulder 32 to obtain the sixth part.

[0057] Specifically, the two ends of the fifth forming part are squeezed, thereby reducing its length. During this process, the inner side of the first through hole 4, the inner side of the inner spline 31, the outer side of the stepped shaft 11, the outer side of the middle part, and part of the outer side of the right part of the fifth forming part are all constrained so that their dimensions do not change. This allows the material to flow radially to the left end of the right part of the fifth forming part that connects to the middle part, forming a shoulder 32. The diameter of the shoulder 32 is larger than the diameter of the middle part, while ensuring that the other dimensions of the sixth forming part meet the processing requirements.

[0058] Secondly, the shaft shoulder 32 of the sixth molded part can apply axial limiting to the silicon steel sheet mounted on the middle portion and the bearing mounted on the right portion.

[0059] Further, in S7: the sixth molded part is subjected to isothermal normalizing to obtain a hollow rotating shaft blank.

[0060] Specifically, isothermal normalizing is a heat treatment process that achieves grain refinement and structure homogenization by precisely controlling the cooling process. During the isothermal normalizing of the sixth molded part, its original structure is completely austenitized to eliminate defects such as coarse grains caused by cold extrusion; the austenite grains are cooled to the pearlite transformation region to promote grain refinement, then the structure is subjected to isothermal treatment to complete the ferrite + pearlite transformation, so as to increase the grain size grade and obtain the hollow rotating shaft blank, thereby improving the mechanical properties of the hollow rotating shaft and further prolonging the service life thereof.

[0061] Secondly, it is known from common knowledge in the art that the hollow rotating shaft blank further needs subsequent processes such as rough and fine turning, fine milling of key grooves, heat treatment and finish machining to further improve the dimensional accuracy, so as to form a finished hollow rotating shaft.

[0062] Further, in step S1, the processing step of hot piercing for the rotating shaft blank is: heating the rotating shaft blank to a hot piercing processing temperature to obtain a heated rotating shaft; feeding the heated rotating shaft into a piercing machine for piercing to form a first through hole 4.

[0063] Specifically, the rotating shaft blank is heated to 1000°C-1200°C to improve its plastic deformation capability, and then placed into a three-roll skew piercing mill. The three-roll skew piercing mill is a skew piercing type in which three rolls are arranged in a "product" shape at an angle of 120°, and the three rolls drive the rotating shaft blank to move close to the plug to perform piercing.

[0064] Wherein, the three-roll skew piercing mill forms a "closed" annular pass by three driving rolls and one plug. When the rotating shaft blank is placed between the three rolls, since it is always compressed in three directions and the ellipticity of the annular pass is small, cracking generally does not occur at the center of the rotating shaft blank, so that high inner surface quality of the first through hole 4 is obtained, and the dimensional accuracy of the first through hole 4 is improved.

[0065] Further, the diameter of the first through hole 4 is larger than the diameter of the second through hole 5; the length of the rotating shaft blank is smaller than the length of the hollow rotating shaft blank.

[0066] Specifically, a first through hole 4 is formed inside the first molded part, which in turn forms a sidewall. The right part of the first molded part flows radially towards the axis, and the material of the sidewall located on the right part flows towards the axis, so that the diameter of the right part of the second molded part is smaller than the diameter of the middle part, and the inner diameter of the second through hole 5 of the second molded part is smaller than the inner diameter of the first through hole 4. Secondly, during the cold extrusion process, the material of the shaft blank moves along both ends of the axis, thereby increasing its axial length. Therefore, the length of the hollow shaft blank is equal to the length of the shaft blank plus the length increased during the cold extrusion process.

[0067] Furthermore, the spheroidizing annealing process involves: raising the working temperature of the heating furnace to 750℃~770℃, holding the furnace at that temperature for 2~3 hours, and then cooling the furnace to 500℃-550℃ before air cooling.

[0068] Specifically, the furnace heats the swivel blank to 750℃~770℃, causing some of the internal carbides to dissolve and spheroidize, thus preventing excessive austenite formation. When the temperature of the swivel blank is below 750℃, the lamellar carbides in the microstructure cannot completely dissolve. The undissolved carbides hinder the formation of spheroidization nuclei, resulting in the presence of long strip-shaped or chain-shaped carbides in the microstructure, increasing work hardening properties and making the workpiece prone to surface cracks during subsequent cold extrusion. When the temperature of the swivel blank is above 770℃, excessive austenite formation occurs in the microstructure, forming coarse lamellar pearlite after cooling. At the same time, carbon-rich austenite is prone to forming martensite or bainite, reducing the plastic deformation performance of the swivel blank. During cold extrusion, local stress concentration easily occurs, leading to cracks and affecting surface quality.

[0069] Secondly, the heating furnace holds the first formed part at a temperature range of 750℃ to 770℃ for 2 to 3 hours, allowing the carbides to become fully spheroidized and ensuring that the carbon atoms in the core diffuse sufficiently, eliminating the difference in microstructure between the surface and the core caused by the temperature gradient. When the holding time is less than 2 hours, the spheroidization of the shaft blank is insufficient, and undissolved layered carbides remain in the ferrite matrix, forming a mixed microstructure of pearlite and spheroidized carbides, reducing its plastic deformation capacity, reducing its material fluidity, increasing surface hardness, and thus reducing its cold extrusion processing performance. When the holding time is greater than 3 hours, the carbides inside the shaft blank accumulate excessively, and the austenite grains continue to grow at high temperatures, reducing the tensile strength of the hollow shaft blank. At the same time, for every additional hour of holding, the energy consumption cost increases by 18%-25%, increasing the processing cost.

[0070] Furthermore, in S2, the inner diameter of the second through hole 5 is smaller than the inner diameter of the first through hole 4, the axial direction of the second through hole 5 is consistent with the axial direction of the first through hole 4, and the right diameter of the second molded part is smaller than the right diameter of the first molded part; in S2, the cold extrusion die includes a core rod disposed inside the first through hole 4 and a diameter reduction die disposed on the outer side of the first molded part. During the diameter reduction process, the core rod applies a supporting force to part of the inner side of the first through hole 4, and the diameter reduction die applies pressure to the right outer side of the first molded part and performs positive work. This pressure is perpendicular to the axial direction of the first molded part until the second molded part is formed.

[0071] Specifically, during the process of machining the right side of the first forming part using the diameter reduction die, the material located on the right side of the first forming part flows radially synchronously, so that the outer and inner sides of the right side remain coaxial during the diameter reduction process, thereby making the second through hole 5 coaxial with the outer side of the right side, and thus making the second through hole 5 coaxial with the outer side of the middle part of the second forming part and the first through hole 4.

[0072] Secondly, the core rod in the cold extrusion die is a round rod with the same diameter as the inner diameter of the first through hole 4, and the top of the round rod near the right end forms a cone. The diameter of the second through hole 5 is within the range of the cross-sectional diameter of the cone. The diameter reduction die is divided into a left section and a right section. The left section can wrap around the left and middle parts of the second molded part, and the inner diameter of the left section is equal to the diameter of the left and middle parts of the second molded part. The left end of the right section is fixedly connected to the right end of the left section. The inner diameter of the left end of the right section gradually decreases until it is the same as the diameter of the right part of the second molded part, and the inclination of the outer side of the left end of the right section is the same as the inclination of the outer side of the top end of the core rod. During the diameter reduction process, the round rod is inserted into the first through hole 4 until the top end is completely located on the right section. At this time, the inner side of the left end of the right section of the diameter reduction mold is parallel to the outer side of the top end. The first forming part is placed in the diameter reduction mold. The diameter reduction mold is radially merged under the action of the press. The inner side of the left section is used to finely adjust the diameter of the left and middle parts of the first forming part. The outer side of the core rod is used to finely adjust the inner side size of the first through hole 4. The inner side of the right section radially presses the right part of the first forming part until the right part of the second forming part is formed. The outer side of the left end of the right part of the second forming part is a smooth curved surface connected to the middle part, and the outer side of the right end is a curved surface with a constant diameter, so that the dimensions of the first through hole 4 and the second through hole 5 of the second forming part are the same as the dimensions of the first through hole 4 and the second through hole 5 of the hollow rotating shaft blank.

[0073] Furthermore, in S3, the outer diameter of the stepped shaft 11 gradually decreases from the middle of the third molded part to the left side of the third molded part, and the outer diameter of the stepped shaft 11 is smaller than the middle diameter of the third molded part. The axial direction of the stepped shaft 11 is consistent with the axial direction of the third molded part. In S3, the cold extrusion die also includes a stepped shaft die disposed on the outer side of the second molded part. During the forming process of the stepped shaft 11, the core rod applies a supporting force to the inner side of the first through hole 4, and the stepped shaft die applies pressure and performs positive work on the outer side of the left part of the second molded part. This pressure is perpendicular to the axial direction of the second molded part until the third molded part is formed.

[0074] Specifically, the diameter of the stepped shaft 11 produced by the inventor of this application is 35.8mm and 45.8mm from the left end to the right end, respectively. The diameter of the mounting part 2 of the hollow rotating shaft is 48.8mm. Thus, the stepped shaft 11 gradually decreases in size, forming a mounting position for placing the bearing and a limiting structure for restricting the axial movement of the bearing. During the processing of the left part of the second molded part by the stepped shaft mold, the material of the left part flows radially synchronously towards the axis, so that the stepped shaft 11 remains cylindrical during the molding process. This ensures that the stepped shaft 11 of the third molded part is coaxial with the middle part, thereby preventing eccentric rotation and noise during the rotation of the third molded part.

[0075] Secondly, the protrusion dimensions on the inner side of the stepped shaft mold change from left to right. The inner diameter of the protrusion is the same as the diameter of the stepped shaft 11, the middle diameter of the third forming part, and the right diameter of the third forming part, respectively. During the forming process of the stepped shaft 11, the core rod is inserted into the first through hole 4 axially. The outer side of its round part coincides with the inner side of the first through hole 4, and the outer side of its top end coincides with the transition inclined surface from the first through hole 4 to the second through hole 5. This ensures that during the process of the stepped shaft mold extruding the second forming part, the middle and right dimensions of the second forming part do not change. Only the left part of the second forming part is formed by radial extrusion of the protrusion of the stepped shaft mold to form the stepped shaft 11. The material at this position flows axially, thereby increasing the length of the third forming part, making the length of the third forming part greater than that of the second forming part. There is no material waste during this process, reducing the material waste rate. At the same time, the dimensions of the stepped shaft 11 of the third forming part are the same as the dimensions of the stepped shaft 11 of the hollow rotating shaft blank.

[0076] Furthermore, in S4, the length direction of the long keyway 6 is consistent with the axial direction of the first through hole 4 and the second through hole 5. The long keyway 6 is symmetrical about the axis of the middle part of the fourth molded part, and the long keyway 6 is formed in the middle part of the fourth molded part. In S4, the cold extrusion die also includes a keyway die disposed on the outer side of the third molded part. During the forming of the long keyway 6, the mandrel applies a supporting force to the inner side of the first through hole 4, and the keyway die applies pressure and performs positive work on the middle part of the third molded part. This pressure is parallel to the axial direction of the third molded part until the fourth molded part is formed.

[0077] Specifically, the outer surface of the fourth molded part has symmetrically distributed elongated keyways 6, with the line of symmetry being the axis of the fourth molding. A silicon steel sheet is installed in the middle of the fourth molded part, and the silicon steel sheet and the elongated keyways 6 form a fit, so that the elongated keyways 6 can apply a pair of pressures of the same magnitude but opposite directions to the silicon steel sheet through the flat key. The lines of action of these pressures are all tangents to the fourth molded part, and the perpendicular lines of the lines of action of these pressures are on the same straight line, and this straight line intersects the axis of the fourth molded part perpendicularly. This makes the lever arms of the paired torques applied by the fourth molded part to the silicon steel sheet on the same straight line, thereby avoiding uneven stress on one side of the silicon steel sheet, which could lead to local plastic deformation or fatigue failure, and reducing stress concentration.

[0078] Secondly, the inner surface of the keyway mold has axisymmetrically distributed protrusions, the axis of symmetry of which is the axis of the keyway mold. The length direction of the protrusion is consistent with the axis of the keyway mold, and the protrusion size is the same as the depth of the long keyway 6. The diameter of the non-protruding part of the inner surface of the middle end of the keyway mold is the same as the diameter of the middle part of the third forming part. During the forming process of the long keyway 6, the press drives the mandrel to insert into the first through hole 4 to apply support force to the inner surface of the first through hole 4, preventing the material from flowing radially into the first through hole 4 and affecting its size. At the same time, the press drives the keyway mold to extrude. The keyway mold for the third forming part moves from the left end to the right end along the axis of the third forming part. Its movement direction is consistent with the axis direction and the axes of the two coincide. During the movement, the inner side protrusion of the keyway mold squeezes the middle side of the third forming part, thereby forming an axisymmetrically distributed long keyway 6. The length of the long keyway 6 is the same as the movement distance of the inner side protrusion relative to the third forming part. Thus, the length of the long keyway 6 can be controlled by controlling the movement distance of the keyway mold relative to the third forming part. At the same time, the size of the long keyway 6 of the fourth forming part is the same as the size of the long keyway 6 of the hollow rotating shaft blank.

[0079] Furthermore, in S5, the length direction of the internal spline 31 is consistent with the axial direction of the second through hole 5, and the root circle diameter of the internal spline 31 is larger than the inner diameter of the second through hole 5; in S5, the cold extrusion die includes an internal spline die disposed inside the second through hole 5. During the forming process of the internal spline 31, the internal spline die applies pressure to the second through hole 5, which is consistent with the axial direction of the second through hole 5, or the component of the pressure is consistent with the axial direction of the second through hole 5, until the fifth formed part is formed.

[0080] Specifically, an internal spline 31 is formed on the inner right side of the fifth molded part. The size of the internal spline 31 is the same as that of the internal spline 31 of the hollow shaft blank. The internal spline 31 of the hollow shaft blank is used to match the external spline of the external input shaft. The length direction of the internal spline 31 is consistent with the right axial direction of the fifth molded part, and the axis of the internal spline 31 coincides with the axis of the fifth molded part and the axis of the second through hole 5. This ensures that there will be no eccentric rotation during the output torque process of the fifth molded part, thereby reducing noise during the rotation process and improving the service life of the fifth molded part.

[0081] Secondly, the internal spline mold forms an external spline that matches the internal spline 31 of the fifth molded part. The length direction and axis of the external spline are the same as those of the internal spline 31. Secondly, the internal spline mold forms a cavity to house the right side of the fourth / fifth molded part. The inner diameter of the cavity's inner surface is the same as the diameter of the right side, thus constraining the diameter of the right side of the fourth molded part and preventing material located in the second through hole 5 from flowing radially towards the right side of the fourth molded part during the molding of the internal spline 31, thereby increasing its right diameter. During the process, the press drives the internal spline mold to move from the left end to the right end of the fourth forming part, with the direction of movement consistent with the axial direction of the fourth forming part. During this movement, the external spline formed by the internal spline mold presses against the inner side of the second through hole 5. This pressure acts on the side of the second through hole 5, and the line of action of the pressure or the line of action of the pressure component is consistent with the length direction of the second through hole 5. This results in the length direction of the formed internal spline 31 being consistent with the length direction of the second through hole 5. Simultaneously, the cavity formed by the internal spline mold allows material to flow axially, increasing the axial length of the right side of the fifth forming part. The dimensions of the internal spline 31 of the fifth forming part are the same as the dimensions of the internal spline 31 of the hollow rotating shaft blank.

[0082] Furthermore, in S6, the shoulder 32 is formed on the outer side of the right part of the sixth forming part. The axial direction of the shoulder 32 is consistent with the axial direction of the stepped shaft 11, and the diameter of the shoulder 32 is larger than the middle diameter of the sixth forming part. In S6, the cold extrusion die also includes a shoulder die A and a shoulder die B disposed on the outer side of the fifth forming part. Both the shoulder die A and the shoulder die B are dies that coincide with the outer side of the fifth forming part. The shoulder die A and the shoulder die B are connected at the maximum diameter of the shoulder 32. During the forming process of the shoulder 32, the core rod applies a supporting force to the inner side of the first through hole 4. The shoulder die A, the core rod and the shoulder die B approach each other along the axial direction and converge at the maximum diameter of the shoulder 32 until the sixth forming part is formed.

[0083] Specifically, the right side of the sixth forming part is connected to the middle part, and the connecting end of the right side of the sixth forming part forms a shoulder 32. The maximum diameter of the shoulder 32 is larger than the diameter of the middle part of the sixth forming part, and its size is the same as that of the shoulder 32 of the hollow rotating shaft blank. It can restrict the silicon steel sheet and the bearing installed on the right side of the sixth forming part from moving axially.

[0084] Secondly, the inner side of the left end of shoulder mold A coincides with the outer side of the middle part of the fifth forming part, and the inner diameter of the right side of its right end gradually increases to form a limiting surface A, which coincides with the left side of shoulder 32; the inner side of the right end of shoulder mold B coincides with the outer side of the right part of the fifth forming part, and the inner diameter of the left side of its left end gradually increases to form a limiting surface B, which coincides with the right side of shoulder 32. During the forming of shoulder 32, the right end of shoulder mold A and the left end of shoulder mold B approach each other until they are spliced. The inner diameter of the splicing position is the maximum diameter of shoulder 32, so that the material flows axially to shoulder mold A and shoulder mold B. In the forming of shoulder 32, the cold extrusion mold also includes a mandrel and an outer spline mold matching the inner spline 31. The mandrel is inserted into the first through hole 4 with shoulder mold A, and the outer spline mold is inserted into the inner spline 31 with shoulder mold B, to prevent the material from flowing radially to the first through hole 4 and the inner spline 31, and to ensure the dimensional accuracy of both.

[0085] Furthermore, the isothermal normalizing process steps are as follows: the internal temperature of the heating furnace is raised to 910℃-930℃, the holding time is selected according to the maximum wall thickness of the sixth forming part, the internal temperature of the heating furnace is reduced to 600℃-650℃, the holding time in the heating furnace is 1h-2h, the heating furnace is opened for air cooling to room temperature to form a hollow rotating shaft blank.

[0086] Specifically, when the sixth forming part is placed in the heating furnace, if the internal temperature of the heating furnace is less than 910℃, the work-hardened structure remaining from cold extrusion will not be fully dissolved, resulting in incomplete austenitization of the internal structure of the hollow shaft blank. During the subsequent cooling process, a mixed-grain structure will be formed, with disordered grain levels and uneven hardness distribution. If the internal temperature of the heating furnace is greater than 930℃, the internal structure of the hollow shaft blank will coarsen, its hardness will decrease, and its strength and toughness will deteriorate, making it prone to brittleness during subsequent carburizing or quenching. The maximum wall thickness of the sixth forming part is the wall thickness of the mounting part 2. The holding time is generally calculated as 1.5-2 times the wall thickness. If the holding time is too short, the austenite composition of the internal structure of the hollow shaft blank will be uneven, and undissolved carbides will remain. If the holding time is too long, the grains will grow excessively, resulting in coarsening.

[0087] The heating furnace is then cooled to 600℃-650℃, either with the furnace or by opening the furnace. This promotes the decomposition of austenite into fine lamellar pearlite, balancing the strength and plasticity of the hollow shaft blank and improving its mechanical properties. When the temperature is below 600℃, the austenite transforms into bainite or martensite, resulting in excessive hardness and reduced mechanical properties. When the temperature is above 650℃, coarse lamellar pearlite forms, leading to a decrease in strength. Furthermore, if the holding time is less than 1 hour, the austenite is not fully decomposed, and the remaining untransformed austenite forms hard phases such as martensite during subsequent air cooling, resulting in excessive hardness and affecting subsequent processing. If the holding time is greater than 2 hours, carbides aggregate or grains coarsen in the microstructure, reducing the fatigue strength of the hollow shaft blank. After air cooling, the sixth forming part is formed into a hollow shaft blank. The hollow shaft blank undergoes secondary machining to achieve high material utilization and low machining allowance, resulting in the finished hollow shaft.

[0088] In another embodiment, the composite processing method includes: cutting round steel into a shaft blank, forming a first through hole along the axial direction of the shaft blank using hot piercing to obtain a first formed part, the hot piercing processing step of the shaft blank is as follows: S1: heating the shaft blank to the hot piercing processing temperature to obtain a heated shaft, feeding the heated shaft into a piercing machine to form a first through hole, the diameter of the first through hole being larger than the diameter of the second through hole; the length of the shaft blank being smaller than the length of the hollow shaft blank, the first formed part undergoing surface treatment using straightening, spheroidizing annealing, and phosphating, the spheroidizing annealing processing step being as follows: the working temperature of the heating furnace is raised to 750°C, the holding time in the heating furnace is 2 hours, the heating furnace is cooled to 500°C and then air-cooled; the right side of the first formed part is reduced in diameter using cold extrusion to obtain a second formed part with a second through hole.

[0089] S2: The left side of the second molded part is cold-extruded to form a stepped shaft to obtain a third molded part. The inner diameter of the second through hole is smaller than the inner diameter of the first through hole, and the axial direction of the second through hole is consistent with the axial direction of the first through hole. The right diameter of the second molded part is smaller than the right diameter of the first molded part. In step 2, the cold extrusion die includes a core rod disposed inside the first through hole and a diameter reduction die disposed on the outer side of the first molded part. During the diameter reduction process, the core rod applies a supporting force to part of the inner side of the first through hole, and the diameter reduction die applies pressure and performs positive work to the right outer side of the first molded part. This pressure is perpendicular to the axial direction of the first molded part until the second molded part is formed.

[0090] S3: The middle part of the third molded part is cold-extruded to form a long keyway to obtain the fourth molded part. The outer diameter of the stepped shaft gradually decreases from the middle part of the third molded part to the left part of the third molded part. The outer diameter of the stepped shaft is smaller than the middle diameter of the third molded part. The axial direction of the stepped shaft is consistent with the axial direction of the third molded part. In step 3, the cold extrusion die also includes a stepped shaft die set on the outer side of the second molded part. During the forming of the stepped shaft, the core rod applies a supporting force to the inner side of the first through hole. The stepped shaft die applies pressure and performs positive work on the outer side of the left part of the second molded part. This pressure is perpendicular to the axial direction of the second molded part until the third molded part is formed.

[0091] S4: The right side of the fourth molded part is cold-extruded to form an internal spline on the side of the second through hole to obtain the fifth molded part. The length direction of the long keyway is consistent with the axial direction of the first through hole and the second through hole. The long keyway is symmetrical about the axis of the middle part of the fourth molded part. The long keyway is formed in the middle part of the fourth molded part. In step 4, the cold extrusion die also includes a keyway die set on the outer side of the third molded part. During the forming of the long keyway, the core rod applies a supporting force to the inner side of the first through hole, and the keyway die applies pressure to the middle part of the third molded part and does positive work. This pressure is parallel to the axial direction of the third molded part until the fourth molded part is formed.

[0092] S5: The fifth forming part is formed by cold extrusion along the axial direction to form a shoulder, resulting in the sixth forming part. The length direction of the internal spline is consistent with the axial direction of the second through hole, and the root circle diameter of the internal spline is larger than the inner diameter of the second through hole. In step 5, the cold extrusion die includes an internal spline die set inside the second through hole. During the forming of the internal spline, the internal spline die applies pressure to the second through hole. The pressure is consistent with the axial direction of the second through hole, or the component of the pressure is consistent with the axial direction of the second through hole, until the fifth forming part is formed. The fourth forming part is first surface treated by spheroidizing annealing and phosphating, and then the internal spline is formed.

[0093] S6: The sixth forming part is formed by isothermal normalizing to form a hollow rotating shaft blank. The shoulder is formed on the outer side of the right part of the sixth forming part. The axial direction of the shoulder is consistent with the axial direction of the stepped shaft. The diameter of the shoulder is larger than the middle diameter of the sixth forming part. In step 6, the cold extrusion die also includes a shoulder die A and a shoulder die B set on the outer side of the fifth forming part. Both shoulder die A and shoulder die B are dies that coincide with the outer side of the fifth forming part. Shoulder die A and shoulder die B are connected at the maximum diameter of the shoulder. During the forming of the shoulder, the core rod applies a supporting force to the inner side of the first through hole. Shoulder die A, core rod and shoulder die B are relatively close to each other along the axial direction and meet at the maximum diameter of the shoulder until the sixth forming part is formed.

[0094] S7: The isothermal normalizing process is as follows: the internal temperature of the heating furnace is raised to 910℃, the holding time is selected according to the maximum wall thickness of the sixth forming part, the internal temperature of the heating furnace is reduced to 600℃, the holding time is 1 hour, the heating furnace is opened for air cooling to room temperature to form a hollow rotating shaft blank.

[0095] In another embodiment, the composite processing method includes: cutting round steel into a shaft blank, forming a first through hole along the axial direction of the shaft blank using hot piercing to obtain a first formed part, the hot piercing processing step of the shaft blank is as follows: S1: heating the shaft blank to the hot piercing processing temperature to obtain a heated shaft, feeding the heated shaft into a piercing machine to form a first through hole, the diameter of the first through hole being larger than the diameter of the second through hole; the length of the shaft blank being smaller than the length of the hollow shaft blank, the first formed part undergoing surface treatment using straightening, spheroidizing annealing, and phosphating, the spheroidizing annealing processing step being as follows: the working temperature of the heating furnace is raised to 760°C, the holding time in the heating furnace is 2.5h, the heating furnace is cooled to 525°C and then air-cooled; the right part of the first formed part is reduced in diameter using cold extrusion to obtain a second formed part with a second through hole.

[0096] S2: The left side of the second molded part is cold-extruded to form a stepped shaft to obtain a third molded part. The inner diameter of the second through hole is smaller than the inner diameter of the first through hole, and the axial direction of the second through hole is consistent with the axial direction of the first through hole. The right diameter of the second molded part is smaller than the right diameter of the first molded part. In step 2, the cold extrusion die includes a core rod disposed inside the first through hole and a diameter reduction die disposed on the outer side of the first molded part. During the diameter reduction process, the core rod applies a supporting force to part of the inner side of the first through hole, and the diameter reduction die applies pressure and performs positive work to the right outer side of the first molded part. This pressure is perpendicular to the axial direction of the first molded part until the second molded part is formed.

[0097] S3: The middle part of the third molded part is cold-extruded to form a long keyway to obtain the fourth molded part. The outer diameter of the stepped shaft gradually decreases from the middle part of the third molded part to the left part of the third molded part. The outer diameter of the stepped shaft is smaller than the middle diameter of the third molded part. The axial direction of the stepped shaft is consistent with the axial direction of the third molded part. In step 3, the cold extrusion die also includes a stepped shaft die set on the outer side of the second molded part. During the forming of the stepped shaft, the core rod applies a supporting force to the inner side of the first through hole. The stepped shaft die applies pressure and performs positive work on the outer side of the left part of the second molded part. This pressure is perpendicular to the axial direction of the second molded part until the third molded part is formed.

[0098] S4: The right side of the fourth molded part is cold-extruded to form an internal spline on the side of the second through hole to obtain the fifth molded part. The length direction of the long keyway is consistent with the axial direction of the first through hole and the second through hole. The long keyway is symmetrical about the axis of the middle part of the fourth molded part. The long keyway is formed in the middle part of the fourth molded part. In step 4, the cold extrusion die also includes a keyway die set on the outer side of the third molded part. During the forming of the long keyway, the core rod applies a supporting force to the inner side of the first through hole, and the keyway die applies pressure to the middle part of the third molded part and does positive work. This pressure is parallel to the axial direction of the third molded part until the fourth molded part is formed.

[0099] S5: The fifth forming part is formed by cold extrusion along the axial direction to form a shoulder, resulting in the sixth forming part. The length direction of the internal spline is consistent with the axial direction of the second through hole, and the root circle diameter of the internal spline is larger than the inner diameter of the second through hole. In step 5, the cold extrusion die includes an internal spline die set inside the second through hole. During the forming of the internal spline, the internal spline die applies pressure to the second through hole. The pressure is consistent with the axial direction of the second through hole, or the component of the pressure is consistent with the axial direction of the second through hole, until the fifth forming part is formed. The fourth forming part is first surface treated by spheroidizing annealing and phosphating, and then the internal spline is formed.

[0100] S6: The sixth forming part is formed by isothermal normalizing to form a hollow rotating shaft blank. The shoulder is formed on the outer side of the right part of the sixth forming part. The axial direction of the shoulder is consistent with the axial direction of the stepped shaft. The diameter of the shoulder is larger than the middle diameter of the sixth forming part. In step 6, the cold extrusion die also includes a shoulder die A and a shoulder die B set on the outer side of the fifth forming part. Both shoulder die A and shoulder die B are dies that coincide with the outer side of the fifth forming part. Shoulder die A and shoulder die B are connected at the maximum diameter of the shoulder. During the forming of the shoulder, the core rod applies a supporting force to the inner side of the first through hole. Shoulder die A, core rod and shoulder die B are relatively close to each other along the axial direction and meet at the maximum diameter of the shoulder until the sixth forming part is formed.

[0101] S7: The isothermal normalizing process is as follows: the internal temperature of the heating furnace is raised to 920℃, the holding time is selected according to the maximum wall thickness of the sixth forming part, the internal temperature of the heating furnace is reduced to 625℃, the holding time in the heating furnace is 1.5h, the heating furnace is opened for air cooling to room temperature to form a hollow rotating shaft blank.

[0102] In another embodiment, the composite processing method includes: cutting round steel into a shaft blank, forming a first through hole along the axial direction of the shaft blank using hot piercing to obtain a first formed part, the hot piercing processing step of the shaft blank is as follows: S1: heating the shaft blank to the hot piercing processing temperature to obtain a heated shaft, feeding the heated shaft into a piercing machine to form a first through hole, the diameter of the first through hole being larger than the diameter of the second through hole; the length of the shaft blank being smaller than the length of the hollow shaft blank, the first formed part undergoing surface treatment using straightening, spheroidizing annealing, and phosphating, the spheroidizing annealing processing step being as follows: the working temperature of the heating furnace is raised to 770°C, the holding time in the heating furnace is 3 hours, the heating furnace is cooled to 550°C and then air-cooled; the right part of the first formed part is reduced in diameter using cold extrusion to obtain a second formed part with a second through hole.

[0103] S2: The left side of the second molded part is cold-extruded to form a stepped shaft to obtain a third molded part. The inner diameter of the second through hole is smaller than the inner diameter of the first through hole, and the axial direction of the second through hole is consistent with the axial direction of the first through hole. The right diameter of the second molded part is smaller than the right diameter of the first molded part. In step 2, the cold extrusion die includes a core rod disposed inside the first through hole and a diameter reduction die disposed on the outer side of the first molded part. During the diameter reduction process, the core rod applies a supporting force to part of the inner side of the first through hole, and the diameter reduction die applies pressure and performs positive work to the right outer side of the first molded part. This pressure is perpendicular to the axial direction of the first molded part until the second molded part is formed.

[0104] S3: The middle part of the third molded part is cold-extruded to form a long keyway to obtain the fourth molded part. The outer diameter of the stepped shaft gradually decreases from the middle part of the third molded part to the left part of the third molded part. The outer diameter of the stepped shaft is smaller than the middle diameter of the third molded part. The axial direction of the stepped shaft is consistent with the axial direction of the third molded part. In step 3, the cold extrusion die also includes a stepped shaft die set on the outer side of the second molded part. During the forming of the stepped shaft, the core rod applies a supporting force to the inner side of the first through hole. The stepped shaft die applies pressure and performs positive work on the outer side of the left part of the second molded part. This pressure is perpendicular to the axial direction of the second molded part until the third molded part is formed.

[0105] S4: The right side of the fourth molded part is cold-extruded to form an internal spline on the side of the second through hole to obtain the fifth molded part. The length direction of the long keyway is consistent with the axial direction of the first through hole and the second through hole. The long keyway is symmetrical about the axis of the middle part of the fourth molded part. The long keyway is formed in the middle part of the fourth molded part. In step 4, the cold extrusion die also includes a keyway die set on the outer side of the third molded part. During the forming of the long keyway, the core rod applies a supporting force to the inner side of the first through hole, and the keyway die applies pressure to the middle part of the third molded part and does positive work. This pressure is parallel to the axial direction of the third molded part until the fourth molded part is formed.

[0106] S5: The fifth forming part is formed by cold extrusion along the axial direction to form a shoulder, resulting in the sixth forming part. The length direction of the internal spline is consistent with the axial direction of the second through hole, and the root circle diameter of the internal spline is larger than the inner diameter of the second through hole. In step 5, the cold extrusion die includes an internal spline die set inside the second through hole. During the forming of the internal spline, the internal spline die applies pressure to the second through hole. The pressure is consistent with the axial direction of the second through hole, or the component of the pressure is consistent with the axial direction of the second through hole, until the fifth forming part is formed. The fourth forming part is first surface treated by spheroidizing annealing and phosphating, and then the internal spline is formed.

[0107] S6: The sixth forming part is formed by isothermal normalizing to form a hollow rotating shaft blank. The shoulder is formed on the outer side of the right part of the sixth forming part. The axial direction of the shoulder is consistent with the axial direction of the stepped shaft. The diameter of the shoulder is larger than the middle diameter of the sixth forming part. In step 6, the cold extrusion die also includes a shoulder die A and a shoulder die B set on the outer side of the fifth forming part. Both shoulder die A and shoulder die B are dies that coincide with the outer side of the fifth forming part. Shoulder die A and shoulder die B are connected at the maximum diameter of the shoulder. During the forming of the shoulder, the core rod applies a supporting force to the inner side of the first through hole. Shoulder die A, core rod and shoulder die B are relatively close to each other along the axial direction and meet at the maximum diameter of the shoulder until the sixth forming part is formed.

[0108] S7: The isothermal normalizing process is as follows: the internal temperature of the heating furnace is raised to 930℃, the holding time is selected according to the maximum wall thickness of the sixth forming part, the internal temperature of the heating furnace is reduced to 650℃, the holding time in the heating furnace is 2 hours, the heating furnace is opened for air cooling to room temperature to form a hollow rotating shaft blank.

[0109] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0110] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A composite machining method for a hollow rotating shaft, the hollow rotating shaft comprising a fixing part (1), a mounting part (2), and an output part (3), characterized in that, include: S1: Round steel is cut to form a shaft blank, and the shaft blank is hot-pierced along the axial direction to form a through first hole (4) to obtain the first formed part; S2: The right side of the first molded part is reduced in diameter by cold extrusion to obtain a second molded part with a second through hole (5); in S2, the inner diameter of the second through hole (5) is smaller than the inner diameter of the first through hole (4), the axial direction of the second through hole (5) is consistent with the axial direction of the first through hole (4), and the right diameter of the second molded part is smaller than the right diameter of the first molded part. S3: The left side of the second molded part is cold-extruded to form a stepped shaft (11) to obtain the third molded part; S4: The fourth part is obtained by cold extrusion forming a long keyway (6) in the middle of the third part; S5: The right side of the fourth molded part is cold-extruded to form an internal spline (31) on the side of the second through hole (5) to obtain the fifth molded part; S6: The fifth part is formed by cold extrusion along the axial direction to form a shoulder (32) to obtain the sixth part; S7: The sixth forming part uses isothermal normalizing to form a hollow rotating shaft blank; In S2, the cold extrusion die includes a core rod disposed inside the first through hole (4) and a diameter reduction die disposed on the outer side of the first molded part. During the diameter reduction process, the core rod applies a supporting force to a portion of the inner side of the first through hole (4), and the diameter reduction die applies pressure to the right outer side of the first molded part and performs positive work. This pressure is perpendicular to the axial direction of the first molded part until the second molded part is formed. In S3, the outer diameter of the stepped shaft (11) gradually decreases from the middle of the third molded part to the left of the third molded part, and the outer diameter of the stepped shaft (11) is smaller than the middle diameter of the third molded part. The axial direction of the stepped shaft (11) is consistent with the axial direction of the third molded part. In S3, the cold extrusion die also includes a stepped shaft die disposed on the outer side of the second molded part. During the forming of the stepped shaft (11), the core rod applies a supporting force to the inner side of the first through hole (4), and the stepped shaft die applies pressure to the left outer side of the second molded part and performs positive work. This pressure is perpendicular to the axial direction of the second molded part until the third molded part is formed. In S4, the length direction of the long keyway (6) is consistent with the axial direction of the first through hole (4) and the second through hole (5). The long keyway (6) is symmetrical about the axis of the middle part of the fourth molded part. The long keyway (6) is formed in the middle part of the fourth molded part. In S4, the cold extrusion die also includes a keyway die disposed on the outer side of the third forming part. During the forming of the long keyway (6), the core rod applies a supporting force to the inner side of the first through hole (4), and the keyway die applies pressure to the middle part of the third forming part and performs positive work. This pressure is parallel to the axial direction of the third forming part until the fourth forming part is formed.

2. The composite processing method according to claim 1, characterized in that: In S1, the hot piercing process of the shaft blank is as follows: heating the shaft blank to the hot piercing processing temperature to obtain a heated shaft; sending the heated shaft into a piercing machine to form the first through hole (4).

3. The composite processing method according to claim 2, characterized in that: The diameter of the first through hole (4) is greater than the diameter of the second through hole (5); the length of the shaft blank is less than the length of the hollow shaft blank.

4. The composite processing method according to claim 3, characterized in that: The first molded part is surface treated by straightening, spheroidizing annealing and phosphating. The spheroidizing annealing process is as follows: the working temperature of the heating furnace is raised to 750℃~770℃, the heating furnace is kept warm for 2~3 hours, and the heating furnace is cooled to 500℃-550℃ and then air-cooled.

5. The composite processing method according to claim 1, characterized in that: In S5, the length direction of the internal spline (31) is consistent with the axial direction of the second through hole (5), and the root circle diameter of the internal spline (31) is larger than the inner diameter of the second through hole (5). In S5, the cold extrusion die includes an internal spline die disposed inside the second through hole (5). During the forming of the internal spline (31), the internal spline die applies pressure to the second through hole (5). The pressure is consistent with the axial direction of the second through hole (5), or the component of the pressure is consistent with the axial direction of the second through hole (5), until the fifth formed part is formed. In S5, the fourth molded part is first surface treated with spheroidizing annealing and phosphating saponification, and then the internal spline is formed.

6. The composite processing method according to claim 1, characterized in that: In S6, the shoulder (32) is formed on the outer side of the right part of the sixth molded part, the axial direction of the shoulder (32) is consistent with the axial direction of the stepped shaft (11), and the diameter of the shoulder (32) is larger than the middle diameter of the sixth molded part; In S6, the cold extrusion die also includes a shoulder die A and a shoulder die B disposed on the outer side of the fifth molded part. Both the shoulder die A and the shoulder die B are dies that coincide with the outer side of the fifth molded part. The shoulder die A and the shoulder die B are connected at the maximum diameter of the shoulder (32). During the process of forming the shoulder (32), the core rod applies a supporting force to the inner side of the first through hole (4). The shoulder die A, the core rod and the shoulder die B are relatively close to each other along the axial direction and converge at the maximum diameter of the shoulder (32) until the sixth molded part is formed.

7. The composite processing method according to claim 1, characterized in that: In S7, the isothermal normalizing process is as follows: the internal temperature of the heating furnace is raised to 910℃-930℃, the holding time is selected according to the maximum wall thickness of the sixth forming part for holding in the heating furnace, the internal temperature of the heating furnace is reduced to 600℃-650℃, the holding time in the heating furnace is 1h-2h, and the heating furnace is opened for air cooling to room temperature to form a hollow rotating shaft blank.

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