Hollow motor shaft and processing method thereof

Abstract

The invention discloses a hollow motor shaft and a processing method thereof. A spline shaft end and a tail shaft end of the hollow motor shaft are respectively formed by die forging; the spline shaft end, the middle shaft tube and the tail shaft end are sequentially welded into a whole through rotary friction welding or laser-arc hybrid welding; a spline shaft end cooling oil way and a tail shaft end cooling oil way are arranged at the axis of the spline shaft end and the axis of the tail shaft end respectively. The spline shaft end cooling oil way, the tail shaft end cooling oil way and the middle shaft pipe cavity form a cooling oil way for direct shaft system oil injection. The hollow motor shaft is divided into three sections, the wall thickness of the motor shaft is uniform, and the size is easy to control; the spline shaft end and the tail shaft end are formed through die forging, an uninterrupted streamline structure is obtained, the structure is compact, and the size is easy to control; the welding position avoids the welding at the abrupt change part of the cross section and avoids a stress concentration point, so that the safety is higher; the technical threshold and the production cost are low; and effective and uniform cooling of the motor shaft is realized through a cooling oil path of direct shaft system oil injection.

Description

Technical Field

[0001] This invention belongs to the technical field of automotive motor equipment, specifically relating to a hollow motor shaft and its processing method. Background Technology

[0002] The motor shaft is a crucial component of the motor in an automotive transmission system. It drives the rotor within the motor, transmitting torque and bearing loads to achieve the conversion between electrical and mechanical energy. It also connects to the output shafts of the reducer and differential, thereby controlling the vehicle's operation. It is a key component determining the vehicle's driving performance and operational stability, characterized by high speed, high transmission ratio, and high torque.

[0003] When an electric motor is in use, the torque transmitted at the shaft center is relatively small. In order to reasonably distribute and bear the motor shaft loads such as torque, moment of force, and bending moment, and to optimize the structure and reduce the weight of parts, existing motor shafts mostly use hollow motor shafts instead of traditional solid shafts. For example, patent document CN111106707A discloses a hollow motor shaft suitable for new energy vehicles.

[0004] The machining of automotive motor shafts is a complex process involving multiple technical challenges. Existing hollow motor shafts mostly employ rotary forging. For example, patent document CN113477857A discloses a method for forming a hollow motor shaft, which involves first preparing a bar into a tube blank; performing initial heat treatment on the tube blank to obtain a tube of the required length; pre-machining the outer diameter of the tube; then rotary forging the tube to obtain a hollow rotor shaft blank with varying diameter and multiple steps; and finally, performing a first machining, a second heat treatment, and a second machining on the hollow rotor shaft blank to form the hollow rotor shaft.

[0005] However, rotary forging requires continuous feeding during the process, and the stability of the feeding is easily affected by the operator's skill and physical strength, resulting in unstable processing quality. The hollow rotor shaft blanks formed by rotary forging have uneven wall thickness, are difficult to control in terms of size, affect dynamic balance, and reduce service life. Moreover, rotary forging requires specialized equipment, the feeding device has a complex structure, requires a large investment, and the process of processing motor shafts with large diameter variations and many steps is very difficult. Summary of the Invention

[0006] To address the problems of uneven wall thickness, difficulty in dimensional control, complex structure, and high production cost in existing motor shaft manufacturing technologies, this invention provides a hollow motor shaft and its manufacturing method. It employs a combination of die forging and rotary friction welding or laser arc welding. Die forging offers precise dimensional control, is a mature technology, and has low production costs. Rotary friction welding or laser arc welding provides high welding quality and production efficiency, and can weld different materials and large wall thicknesses.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The present invention discloses a hollow motor shaft, wherein the spline shaft end and the tail shaft end are respectively formed by die forging; the spline shaft end, the intermediate shaft tube and the tail shaft end are sequentially welded into a whole by rotary friction welding or laser arc hybrid welding; a spline shaft end cooling oil passage and a tail shaft end cooling oil passage are respectively provided at the shaft center of the spline shaft end and the tail shaft end; the tail shaft end cooling oil passage, the spline shaft end cooling oil passage and the intermediate shaft tube cavity constitute a cooling oil passage for direct shaft system oil spraying.

[0008] Preferably, a motor shaft welding pad extending from the spline shaft end is provided on the inner side of the welding position between the spline shaft end and the intermediate shaft tube; and a motor shaft welding pad extending from the tail shaft end is provided on the inner side of the welding position between the tail shaft end and the intermediate shaft tube.

[0009] The intermediate shaft tube, spline shaft end, and tail shaft end can be made of different materials. Preferably, the intermediate shaft tube is made of a high-temperature resistant alloy, such as 20CrMnTi or 42CrMo; the spline shaft end and tail shaft end are made of the high-temperature resistant alloy 20CrMnTi. 20CrMnTi has advantages such as low raw material cost, excellent forgeability, weldability, and machinability, and good overall material strength.

[0010] A method for processing a hollow motor shaft according to the present invention includes the following steps: S1, obtaining a blank that meets the requirements of the motor shaft and preheating it; S2, transferring the preheated blank to a corresponding mold and forming it by mechanical forging to obtain forging blanks for the spline shaft end and the tail shaft end respectively; S3, heat-treating the forging blanks for the spline shaft end and the tail shaft end, as well as the tube blank of the intermediate shaft tube; S4, machining the intermediate shaft tube, the spline shaft end, and the tail shaft end to obtain their respective required dimensions; and machining the spline shaft end at the shaft center of the spline shaft end and the tail shaft end respectively. Cooling oil circuit and tail shaft end cooling oil circuit; S5, using rotary friction welding or laser arc hybrid welding, weld the spline shaft end, intermediate shaft tube and tail shaft end into one piece in sequence; S6, perform high-frequency annealing on the weld seam of the motor shaft; S7, use machining to remove the radial flash of friction welding or the excess height of laser arc hybrid welding, and finish machine the hollow motor shaft to the finished size; S8, perform carburizing and quenching on the hollow motor shaft; clean the hollow motor shaft; S9, temper the hollow motor shaft; S10, perform shot blasting on the tempered hollow motor shaft to obtain the finished product.

[0011] Preferably, in step S3, the heat treatment is as follows: the forging blanks of the spline shaft end and the tail shaft end, as well as the tube blank of the intermediate shaft tube, are subjected to residual heat normalizing treatment at 800-950°C and cooled in air at a cooling rate of 0.5-5°C / s.

[0012] Preferably, in step S6, the high-frequency annealing is performed by heating the welding positions of the tail shaft end and the intermediate shaft tube, and the welding positions of the spline shaft end and the intermediate shaft tube to 720-850°C and holding them at that temperature, with the heating rate controlled at 10-20°C / s and the holding time being 2-2.5 min per millimeter of effective thickness, and then cooling them to room temperature in air.

[0013] Preferably, in step S8, the carburizing and quenching process involves heating the hollow motor shaft to 800–950°C, controlling the heating rate at 3–5°C / s, holding it at that temperature for 5–8 hours, and then cooling it to room temperature in quenching oil.

[0014] Preferably, in step S9, the tempering is performed by heating the hollow motor shaft to 150-250°C for tempering, controlling the heating rate at 4-20°C / s, holding the temperature for 1-3 hours, and then cooling it in air.

[0015] Compared with the prior art, the present invention has the following advantages: This invention divides the hollow motor shaft into three sections, each made of a different suitable material or machined into a shape with special requirements. The motor shaft has a uniform wall thickness and its dimensions are easy to control. The spline shaft end and tail shaft end are formed by die forging, resulting in a continuous streamline structure with dense structure and easy dimensional control. Welding is avoided at points of abrupt changes in cross-section, thus avoiding stress concentration points and improving safety. The invention has low technical barriers and low production costs. Effective and uniform cooling of the motor shaft is achieved through a direct shaft system oil spray cooling oil circuit. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the hollow motor shaft of the present invention; Figure 2 This is a schematic diagram of the welding positions and cooling oil circuit of the hollow motor shaft; Figure 3 This is a schematic diagram of the welding gasket for a hollow motor shaft; In the diagram: 1-Intermediate shaft tube, 2-Splined shaft end, 3-Tail shaft end, 4-Welding position between tail shaft end and intermediate shaft tube, 5-Welding position between splined shaft end and intermediate shaft tube, 6-Motor shaft welding gasket, 7-Splined shaft end cooling oil passage, 8-Tail shaft end cooling oil passage. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. These descriptions of the embodiments are intended to help understand the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0018] As attached Figures 1-3As shown, a hollow motor shaft has a splined shaft end 2 and a tail shaft end 3 formed by die forging. The splined shaft end 2, the intermediate shaft tube 1, and the tail shaft end 3 are sequentially welded into a single unit using rotary friction welding or laser-arc hybrid welding. A splined shaft end cooling oil passage 7 and a tail shaft end cooling oil passage 8 are respectively provided at the axial center of the splined shaft end 2 and the tail shaft end 3. The splined shaft end cooling oil passage 7, the tail shaft end cooling oil passage 8, and the cavity of the intermediate shaft tube 1 form a direct shaft system oil spray cooling oil passage to achieve effective and uniform cooling of the motor shaft.

[0019] Preferably, a motor shaft welding pad 6 extending from the spline shaft end 2 is provided on the inner side of the welding position between the spline shaft end 2 and the intermediate shaft tube 1; a motor shaft welding pad 6 extending from the tail shaft end 3 is provided on the inner side of the welding position between the tail shaft end 3 and the intermediate shaft tube 1; when rotary friction welding is used, the motor shaft welding pad 6 can prevent burrs from forming on the inner side of the motor shaft; when laser-arc hybrid welding is used, the motor shaft welding pad 6 can prevent welding defects such as bottom humps from forming at the weld root, thus ensuring welding quality.

[0020] The intermediate shaft tube 1, spline shaft end 2, and tail shaft end 3 can be made of different materials. Preferably, the intermediate shaft tube 1 is made of a high-temperature resistant alloy, such as 20CrMnTi or 42CrMo; the spline shaft end 2 and tail shaft end 3 are made of the high-temperature resistant alloy 20CrMnTi; 20CrMnTi has advantages such as low raw material cost, excellent forgeability, weldability, and machinability, and good overall material strength.

[0021] Example 1 A method for machining a hollow motor shaft includes the following steps: S1, Obtain the blank that meets the requirements of the motor shaft and preheat it; S2, the preheated billet is transferred to the corresponding mold and mechanically forged to obtain forged billets of spline shaft end 2 and tail shaft end 3 respectively; S3, the forging blanks of spline shaft end 2 and tail shaft end are subjected to residual heat normalizing treatment at 900℃ and air cooling at a cooling rate of 4.5℃ / s; the tube blank of intermediate shaft tube 1 is subjected to residual heat normalizing treatment at 900℃ and air cooling at a cooling rate of 2.0℃ / s. S4. Machining is performed on the intermediate shaft tube 1, spline shaft end 2, and tail shaft end 3 to obtain their respective required dimensions; cooling oil passages for the spline shaft end and tail shaft end are machined at the shaft center of the spline shaft end 2 and tail shaft end 3 respectively; the motor shaft welding gasket 6 of the spline shaft end 2 and tail shaft end 3 is also machined to the required length. S5, using rotary friction welding or laser-arc hybrid welding, sequentially welds the spline shaft end 2, intermediate shaft tube 1 and tail shaft end 3 into one piece; S6. After rotary friction welding or laser-arc hybrid welding, the motor shaft weld is subjected to high-frequency annealing: heated to 800℃ and held at a temperature of 15℃ / s, with a holding time of 2 minutes per millimeter of effective thickness, and then cooled to room temperature in air. S7 uses machining to remove radial flash from friction welding or excess height from laser-arc composite welding, and precision-machines the hollow motor shaft to the finished size; S8. Heat the hollow motor shaft to 870℃ for carburizing and quenching, with the heating rate controlled at 4℃ / s and held for 6 hours. Cool it to room temperature in quenching oil. Clean the hollow motor shaft. S9, heat the hollow motor shaft to 200℃ for tempering, control the heating rate at 10℃ / s, hold for 2 hours, and then cool in air; S10 involves shot blasting the tempered hollow motor shaft to obtain the finished product.

[0022] When using rotary friction welding, the spline shaft end 2, intermediate shaft tube 1, and tail shaft end 3 are transferred to the rotary friction welding machine in pairs. The end faces are tightly fitted together, and the two end faces rotate relative to each other and generate heat through friction. When the temperature of the mating surface reaches the temperature required for friction welding, the rotation of the two shaft ends stops rapidly, and axial pressure is further applied to cause plastic deformation of the mating surface and weld the spline shaft end 2, intermediate shaft tube 1, and tail shaft end 3 into one piece.

[0023] When rotary friction welding applies axial pressure to cause plastic deformation of the mating surfaces, burrs are generated on both the inner and outer walls of the weld. The burrs on the outer wall can be removed by machining, but the uneven burrs on the inner wall can affect the dynamic balance of the motor shaft during high-speed rotation. To eliminate this effect, this invention processes motor shaft welding gaskets 6 on the inner side of the junction between the spline shaft end and the tail shaft end and the intermediate shaft tube. This prevents the burrs from extending along the inner wall of the weld, thus generating burrs only on the outer wall of the motor shaft. After machining away the outer wall burrs, it helps ensure the dynamic balance of the motor shaft during high-speed rotation.

[0024] When using laser-arc hybrid welding, the spline shaft end 2, intermediate shaft tube 1, and tail shaft end 3 are transferred to the laser welding machine rotary table, with their end faces tightly fitted. As the fixture rotates, the laser welding machine generates a laser beam, while the arc welding machine ignites an electric arc to weld the tail shaft end to the intermediate shaft tube at welding position 4 and the spline shaft end to the intermediate shaft tube at welding position 5. Conventional laser-arc hybrid welding produces a single-pass, full-penetration, double-sided weld. Due to the imbalance of the interaction forces between the laser and the arc, surface tension, molten pool gravity, and plasma recoil force, the molten pool experiences unbalanced forces during welding, easily leading to welding defects such as root humps at the weld root. Root humps manifest as continuous or intermittent root drooping or a pearl-chain-like appearance. The motor shaft welding pad 6 stabilizes the weld pool, preventing root humps. It also eliminates the need to consider weld burn-through defects, allowing for increased welding power, ensuring full weld penetration, and improving overall welding quality.

[0025] The hollow motor shaft of the present invention has the following advantages: 1. Replacing a solid motor shaft of the same size with a welded hollow structure can reduce weight by about 12%. For example, a solid motor shaft weighs 2001g, while a welded hollow structure reduces weight by 239.57g.

[0026] 2. Because of the support of the motor shaft welding liner, there will be no defects such as burrs from friction welding or root humps from laser arc composite welding inside the cavity, making it easier to ensure the dynamic balance performance of the motor at high speeds and ensuring high product consistency. 3. The processing method of this invention can significantly reduce equipment processing costs. Without a motor shaft welding pad, laser welding requires high-end equipment, such as the German EMAG or TRUMPF laser welding equipment used by Tesla, which is expensive but has stable performance. With a motor shaft welding pad, the laser welding power can be increased. With the support of the welding pad, there is no need to worry about burn-through or other problems. Domestic equipment can be used, reducing equipment costs. Even if the laser beam quality is occasionally unstable, high power can be used to avoid welding defects such as incomplete fusion.

Claims

1. A hollow motor shaft, characterized in that, The spline shaft end (2) and tail shaft end (3) are formed by die forging respectively; the spline shaft end (2), intermediate shaft tube (1) and tail shaft end (3) are sequentially welded into one piece by rotary friction welding or laser arc composite welding; a spline shaft end cooling oil passage (7) and a tail shaft end cooling oil passage (8) are respectively provided at the axial center of the spline shaft end (2) and the tail shaft end (3); the spline shaft end cooling oil passage (7), the tail shaft end cooling oil passage (8) and the cavity of the intermediate shaft tube (1) form a cooling oil passage for direct shaft system oil spraying.

2. The hollow motor shaft according to claim 1, characterized in that, On the inner side of the welding position between the spline shaft end (2) and the intermediate shaft tube (1), a motor shaft welding pad (6) extending from the spline shaft end is provided; on the inner side of the welding position between the tail shaft end (3) and the intermediate shaft tube (1), a motor shaft welding pad (6) extending from the tail shaft end is provided.

3. The hollow motor shaft according to claim 1, characterized in that, The intermediate shaft tube (1) is one of the high-temperature resistant alloys 20CrMnTi and 42CrMo; the spline shaft end (2) and the tail shaft end (3) are high-temperature resistant alloys 20CrMnTi.

4. A method for machining a hollow motor shaft as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Obtain the blank that meets the requirements of the motor shaft and preheat it; S2. Transfer the preheated blank to the corresponding mold and form it by mechanical forging to obtain the forging blanks of the spline shaft end and the tail shaft end respectively; S3. Heat treat the forging blanks of the spline shaft end and the tail shaft end, as well as the tube blank of the intermediate shaft tube; S4. Machin the intermediate shaft tube, the spline shaft end, and the tail shaft end to obtain their respective required dimensions; Machining is used to machine the cooling oil channels of the spline shaft end and the tail shaft end at the shaft center respectively; S5. Weld the spline shaft end, the intermediate shaft tube, and the tail shaft end into one piece in sequence by rotary friction welding or laser arc hybrid welding; S6. Perform high-frequency annealing on the weld of the motor shaft; S7. Machining is used to remove the radial flash of friction welding or the excess height of laser arc hybrid welding, and the hollow motor shaft is precision machined to the finished size; S8, Carburize and quench the hollow motor shaft; clean the hollow motor shaft; S9, Temper the hollow motor shaft; S10, Shot blast the tempered hollow motor shaft to obtain the finished product.

5. The machining method for a hollow motor shaft according to claim 4, characterized in that, In step S3, the heat treatment is as follows: the forging blanks of the spline shaft end and the tail shaft end, as well as the tube blank of the intermediate shaft tube, are subjected to residual heat normalizing treatment at 800-950°C and cooled in air at a cooling rate of 0.5-5°C / s.

6. The machining method for a hollow motor shaft according to claim 4, characterized in that, In step S6, the high-frequency annealing is as follows: the welding positions of the tail shaft end and the intermediate shaft tube, and the welding positions of the spline shaft end and the intermediate shaft tube are heated to 720-850°C and held at that temperature. The heating rate is controlled at 10-20°C / s, and the holding time is 2-2.5 min per millimeter of effective thickness. Then, the temperature is cooled to room temperature in air.

7. The machining method for a hollow motor shaft according to claim 4, characterized in that, In step S8, the carburizing and quenching process involves heating the hollow motor shaft to 800–950°C, controlling the heating rate at 3–5°C / s, holding it at that temperature for 5–8 hours, and then cooling it to room temperature in quenching oil.

8. The machining method for a hollow motor shaft according to claim 4, characterized in that, In step S9, the tempering is performed by heating the hollow motor shaft to 150-250°C for tempering, controlling the heating rate at 4-20°C / s, holding it at that temperature for 1-3 hours, and then cooling it in air.

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