A fine high ring anti-cracking sintering method by laser selective pre-strengthening

Abstract

The application provides a fine high ring anti-cracking sintering method through laser selective pre-strengthening, which comprises the following steps: firstly, pressing powder for preparing a fine high ring into a green body with a fine high ring shape; then, strengthening the green body through laser scanning under an argon protective atmosphere; firstly, scanning the inner and outer edges of the lower port and the upper port of the green body and scanning a plurality of elementary line regions uniformly distributed in the circumferential direction of the inner wall curved surface of the green body in the axial direction by using point laser scanning, so that the green body powder is micro-melted and rapidly cooled to form a strengthened ring and a plurality of reinforcing ribs; then, scanning the inner wall curved surface and the outer wall curved surface of the green body by using line laser scanning, and the scanning intensity and the scanning temperature of the line laser are both lower than those of the point laser; finally, gradient sintering the green body by using a vacuum sintering furnace, and the sintering density temperature is higher than the scanning temperature of the point laser, and argon is used for atmosphere protection during sintering. The application strengthens the structural strength of the fine high ring green body through laser pre-strengthening, reduces the cracking problem of the fine high ring during sintering, and improves the yield of the fine high ring.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal powder processing, and particularly relates to a fine high ring anti-cracking sintering method with laser selected area pre-strengthening. BACKGROUND

[0002] With the development of servo motors, mechanical assembly and the like, the use of fine high ring-shaped parts is also more and more. For example, the fine high radiation ring used by servo motors and stepping motors, the radial ring used by hollow cup motors, the fine tube of ferro-cobalt magnetically conductive, the titanium fine ring used in engines and the like. The demand for fine high ring-shaped parts in various industries is exceptionally huge, among which the demand for permanent magnet materials providing magnetic field in motors is also more and more, and the fine high radiation ring servo motor has higher stability and durability than the spliced servo motor. However, the fine high ring (the height is greater than 20 mm, the outer diameter is less than 10 mm, and the wall thickness is less than 3 mm) has inconsistent inner and outer ring wall shrinkage rates (especially the fine high radiation ring of neodymium iron boron material) in the sintering stage, and the green body strength is low, the self-weight effect is significant, and in the traditional vacuum sintering forming, the ring body stress is huge, so that the green body is prone to longitudinal bending deformation (banana effect occurs when the gas in the powder body overflows unevenly during heating, and lateral bending occurs), the ring body middle part is prone to radial cracking (the inner and outer ring wall shrinkage rates are different during sintering, and cracking occurs at the maximum torque in the green body), and the port edge is prone to collapse (stress concentration easily occurs at the edge of the green body port, leading to collapse cracking). Therefore, the yield of the fine high ring is not high, and thus how to improve the cracking problem of the fine high ring product becomes the top priority.

[0003] The traditional schemes for improving the cracking problem of the sintered fine high ring include: one forming method by cold isostatic pressing or a large pressure press to improve the forming density; a method of removing the stress in the green body by changing the sintering curve; a method of preventing lateral bending by supporting the green body with a support; and a method of using a composite powder of cast ingot and spun ribbon to enhance the mechanical strength of the green body for neodymium iron boron material. Although these schemes are effective, they still have the following defects: the schemes of improving the green body density and optimizing the sintering curve have limited anti-cracking effect; the use of a complex sintering support will introduce contact point stress and produce new defects; and the use of the composite powder of spun ribbon and cast ingot to enhance the mechanical strength will introduce alpha-Fe (a crystal structure form of iron element, which will seriously affect the magnetic performance of the neodymium iron boron material), and alpha-Fe is not easy to remove. Therefore, a more effective method for improving the cracking problem of the sintered fine high ring is needed. SUMMARY

[0004] The purpose of the present application is to provide a fine high ring anti-cracking sintering method with laser selected area pre-strengthening, which can improve the yield of the fine high ring by pre-strengthening the structural strength of the fine high ring green body with laser and reducing the cracking problem of the fine high ring during sintering.

[0005] To achieve the above object, the solution of the present application is to provide a laser selective pre-strengthening fine high ring anti-cracking sintering method, comprising the following steps:

[0006] S1, the powder for preparing the fine high ring is pressed into a green body in the shape of a fine high ring;

[0007] S2, the green body is strengthened by laser scanning under an argon protective atmosphere, including two steps of strengthening scanning and partition scanning:

[0008] S2.1, strengthening scanning: the inner and outer edges of the lower port and the upper port of the green body are scanned by point laser, and a plurality of element line regions uniformly distributed in the circumferential direction of the inner wall curved surface of the green body are scanned by axial scanning, so that the green body powder is micro-melted and rapidly cooled to form a strengthening ring and a plurality of reinforcing ribs;

[0009] S2.2, partition scanning: the inner wall curved surface and the outer wall curved surface of the green body are scanned by line laser, and the scanning intensity and the scanning temperature of the line laser are lower than those of the point laser in step S2.1;

[0010] S3, the green body is gradient sintered by using a vacuum sintering furnace, and the sintering density temperature is higher than the scanning temperature of the point laser in step S2.1, and argon is used for atmosphere protection during sintering.

[0011] Further, in step S1, the prepared fine high ring is a neodymium iron boron radiation ring, and the powder is neodymium iron boron powder; in step S2.1, the scanning intensity of the point laser is 1000cps-2000cps, and the scanning temperature is 1000±10℃; in step 2.2, the scanning intensity of the line laser is 500-1000cps, and the scanning temperature is 850℃-900℃; in step S3, the sintering density temperature is 1050℃.

[0012] Further, in step S2, the scanning intensity, scanning temperature and molten pool splash size of the laser are monitored by using a plasma spectrum monitoring device, an infrared thermal imager and a molten pool high-speed camera device respectively during laser scanning, if the intensity is ≥5000cps, a neodymium-rich phase evaporation alarm is issued; if the scanning temperature reaches 0.6 times the melting point of neodymium iron boron, an alarm is issued and the laser scanning is stopped; if the observed splash size is >5μm, an alarm is issued and the laser power is reduced.

[0013] Further, in step S1, the neodymium iron boron ingots and the neodymium iron boron ribbon produced by the casting furnace and the ribbon furnace respectively are hydrogen broken, the hydrogen broken powders produced by the casting furnace and the ribbon furnace are mixed according to the designed proportion, then the fine powder of 3-4μm is ground by using an air flow mill, which is the powder for preparing the neodymium iron boron radiation ring, then the green body is prepared by rotating orientation pressing and cold isostatic pressing.

[0014] Further, in step S2, after each point laser scanning of ≤1mm length and line laser scanning of ≤1mm arc length, the scanned area is cooled by argon for 10s, the argon flow rate is 15m / s, and the laser scanning and argon cooling are continuously performed.

[0015] Further, in step S2.2, the outer wall surface and the inner wall surface of the green body are each divided into multiple regions along the circumference, and the scanning interval time of the regions in the same radial direction of the inner wall surface and the outer wall surface is ≥5min.

[0016] Further, in step S2.2, the outer wall surface and the inner wall surface of the green body are each divided into four regions along the circumference, and the arc length of each region is ≥2mm.

[0017] Further, in step S2.1, the green body is first fixed, the point laser is first sequentially scanned from the outer edge region and the inner edge region of the lower port of the green body, then axially scanned from the lower to the upper of a single line region of the inner wall surface of the green body, then sequentially scanned from the inner edge and the outer edge regions of the upper port of the green body, and then the green body is circumferentially rotated, the point laser skips the scanning of the upper and lower port edge regions, completes the scanning of the next single line region, and repeats the step to complete the scanning of all single line regions.

[0018] Further, in step S2.2, the laser length of the line laser is aligned with the height of the green body, the position of the line laser is fixed during scanning, and the circumferential rotation of the green body completes the laser scanning of the inner and outer wall surfaces of the green body; and when scanning the outer wall surface of the green body, the scanning direction of the line laser is along the circumferential tangent direction of the outer ring of the green body; when scanning the inner wall surface of the green body, the emitter of the line laser is located at the center position of the inner ring of the green body, and has an included angle with the central axis of the green body.

[0019] Further, in step S1, the thin high ring is a radial ring, a multi-stage ring or a radial ring, and the powder for preparing the thin high ring is a neodymium iron boron, stainless steel, hard alloy or ceramic powder.

[0020] After the above scheme is used, the application has the following beneficial effects:

[0021] 1. The application creatively introduces a laser selective pre-strengthening step in the traditional powder metallurgy process. By scanning the laser on the multiple elementary line areas of the key port edge and inner wall curve of the green body, micro-melting of the green body powder occurs, followed by rapid cooling, so that a strengthening framework is formed in the key area of the green body, significantly enhancing the overall structural strength and stiffness of the green body during sintering. Among them, the micro-melting of the port edge forms a strengthening ring, which can resist edge collapse and provide a "pinching" effect, while the elementary line areas scanned axially form reinforcing ribs, which can resist longitudinal bending. The strengthening framework can effectively resist the huge internal stress generated by the weight of the green body and the inconsistent shrinkage of the inner and outer walls, thereby fundamentally inhibiting the longitudinal bending, middle radial cracking and port edge collapse defects that easily occur during sintering, greatly improving the yield of the fine high ring.

[0022] 2. For permanent magnet materials such as neodymium iron boron, by strictly limiting the scanning area to the non-magnetic orientation sensitive area, i.e. not scanning the middle area between the inner and outer edges of the port, which is a magnetic orientation sensitive area, the laser heat affected zone is completely avoided, ensuring the final magnetic properties of the product while significantly improving the strength of the green body and preventing cracking.

[0023] 3. The green body accumulates internal stress during pressing, and during the strengthening scan, the strengthening framework and the surrounding un-strengthened green body main body will have a significant internal stress concentration due to the large difference in shrinkage rate and modulus. During subsequent sintering, micro-cracks or even cracks may occur due to internal stress concentration. The application further uses a line laser to perform zoned scanning on the inner and outer wall curves of the green body after the strengthening scan. Zoned scanning can increase the strength of the green body surface, while releasing the internal stress concentration generated during pressing and strengthening scanning, avoiding cracks during sintering, and further improving the yield.

[0024] 4. The technical solution of the application is not limited to a specific ring structure (which can be applied to radial rings, multi-stage rings, radial rings, etc.) or material (which can be applied to neodymium iron boron, stainless steel, hard alloy, ceramic, etc.). By adjusting the laser parameters and sintering curve according to the melting point and sintering characteristics of different materials, it can be widely applied to solve the common problem of sintering cracking of fine high ring-shaped parts in multiple technical fields. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A perspective view of the application for strengthening scanning;

[0026] Figure 2 A top view of the application for zoned scanning;

[0027] Figure 3 A schematic view of the application for scanning the inner wall curve of the green body;

[0028] Figure 4 Method flowchart of the present application.

[0029] Label description:

[0030] 1, green body; 2, reinforcing ring; 3, reinforcing rib; 4, point laser emitter; 5, line laser emitter. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application, and the range of the present application includes two end values.

[0032] As shown in Figures 1-4 The present application provides a fine high ring anti-cracking sintering method by laser selective pre-strengthening, comprising the following steps:

[0033] S1, pressing the powder for preparing the fine high ring into a fine high ring-shaped green body 1. The fine high ring can be a radiation ring, a multi-stage ring or a radial ring of various materials (including neodymium iron boron, stainless steel, hard alloy, ceramic, etc.), and the following will be described by taking a neodymium iron boron radiation ring as an example.

[0034] Specifically, the powder for preparing the neodymium iron boron radiation ring can be obtained by hydrogen crushing of neodymium iron boron ingots and neodymium iron boron strip cast pieces produced by a casting furnace and a strip casting furnace respectively. The hydrogen crushed powders produced by the casting furnace and the strip casting furnace are mixed in a designed ratio, which can be 1:20, and then a gas flow mill is used to grind fine powder of 3-4 μm.

[0035] Optionally, after the magnetic powder ground by the gas flow mill is pressed by rotation orientation, the density of the green body is improved by using a traditional cold isostatic pressing method.

[0036] S2, laser scanning strengthening of the green body under an argon protection atmosphere.

[0037] Specifically, the green body 1 is first fixed by a ceramic clamp in an argon cabin, and the clamping force is 10-50 N. The clamping force should not be too large to damage the green body. Then, a standard block is used to calibrate the focal length of the laser, and then argon is started, with a flow rate of 30 L / min for 5 min. Finally, the laser is started for scanning, including two steps of strengthening scanning and partition scanning.

[0038] S2.1, strengthening scanning: as shown in Figure 1As shown, the lower port inner and outer edge areas of the green body are scanned by the point laser to slightly melt the green body powder, and then rapidly cooled to form a reinforcing ring 2, which can resist edge collapse and provide a "pinch" effect. In addition to the edge area of the green body port, the green body inner wall curved surface is also scanned in the axial direction to form multiple reinforcing ribs 3, preferably eight reinforcing ribs 3, which can resist longitudinal bending. Thus, the reinforcing ring 2 and the reinforcing ribs 3 form a reinforcing framework of the green body, which can effectively resist the huge internal stress caused by the weight of the green body and the inconsistent shrinkage of the inner and outer walls, thereby fundamentally inhibiting the longitudinal bending, middle radial cracking and edge collapse defects that easily occur during the sintering process, and greatly improving the yield of the fine high ring.

[0039] Specifically, the sequence of the reinforcing scanning can be as follows: the green body is first fixed, the emitter 4 of the point laser moves to sequentially scan the outer edge area and the inner edge area of the lower port of the green body, then scans a single line area of the inner wall curved surface of the green body from bottom to top, then sequentially scans the inner edge and outer edge areas of the upper port of the green body, and then the green body is rotated by 45° in the circumferential direction. The point laser skips the scanning of the edge areas of the upper and lower ports and completes the scanning of the next single line area. This step is repeated to complete the scanning of all single line areas.

[0040] It should be noted that the scanning temperature of the point laser should not be higher than the densification temperature during subsequent sintering, which is controlled at 1000±10℃. The scanning temperature should also not be higher than the threshold temperature, which is set at 0.6 times the melting point of neodymium iron boron. If the scanning temperature reaches this threshold, it will affect the neodymium iron boron radiation ring. An infrared thermal imager can be used to monitor the scanning temperature in real time, and an alarm will be triggered and the point laser will automatically shut down when the scanning temperature reaches or exceeds the threshold.

[0041] The scanning intensity of the point laser should also not be too high, otherwise it will cause the evaporation of the neodymium-rich phase. In the neodymium iron boron radiation ring, neodymium exists in the form of local enrichment, which is called "neodymium-rich phase". If the scanning intensity is too high, it will easily cause a large amount of neodymium evaporation, i.e. neodymium-rich phase evaporation. Excessive evaporation of neodymium will result in insufficient neodymium element content in the final formed part, changing the local properties of the material, and forming defects such as pores, splashes and un-melted. The scanning intensity of the point laser can be monitored by an ion plasma spectrum monitoring device by monitoring the intensity of the neodymium element characteristic spectrum line (wavelength 521nm). The scanning intensity of the point laser is generally controlled at 1000cps-2000cps, where cps is the number of photons received per second at a wavelength of 521nm. If the intensity is ≥5000cps, an alarm for neodymium-rich phase evaporation will be triggered.

[0042] In addition to the strength and temperature monitoring, a high-speed camera (frame rate of 10kfps) can be used to monitor the size of the molten pool splashes. If the observed splash size is >5pm, an alarm is issued and the laser power is reduced. Splashing is a phenomenon in which liquid metal droplets in the molten pool are ejected at high speed. Large splashes not only cause material loss (leading to holes) in the current processing area, but also cause adhesion and increased roughness on the formed surface, and even damage the powder layer below. A stable molten pool is the key to obtaining a dense, uniform, and smooth formed part. Therefore, molten pool splashing monitoring is needed.

[0043] In addition, the area after scanning also needs to be cooled during scanning. Specifically, argon gas can be used for cooling. After completing a 1mm long point laser scanning (the scanning length cannot exceed 1mm), the area scanned by the laser is cooled for 10s using argon gas with a flow rate of 15m / s. Laser scanning and argon cooling need to be continuous.

[0044] S2.2, partition scanning: line laser is used to scan the inner wall surface and outer wall surface of the green body 1, which can increase the strength of the green body surface, release the internal stress concentration generated during pressing and strengthening scanning, avoid cracks during sintering, and further improve the yield.

[0045] As shown in Figure 2 , the laser length of the line laser is aligned with the height of the blank. During scanning, the position of the line laser is fixed, and the green body rotates circumferentially to complete the laser scanning of the inner and outer wall surfaces of the green body. The order of scanning the inner and outer wall surfaces of the green body by the line laser has no restriction. However, when scanning the outer wall surface of the green body, the scanning direction of the line laser is along the circumferential tangent direction of the outer ring of the green body to avoid direct laser radiation causing local cracking of the green body, leading to powder spattering. Strengthening scanning can also use this scanning method when scanning the edge area of the sintered green body port to avoid powder spattering. When scanning the inner wall surface of the green body, the emitter of the line laser is located at the center of the inner ring of the green body, as shown in Figure 3 , and the emitter 5 of the line laser has an angle of about 5° with the axis, i.e. the emitter 5 of the line laser is inclined to avoid direct laser radiation causing powder spattering.

[0046] The outer wall surface and the inner wall surface of the green body are each divided into multiple regions along the circumferential direction, as shown in Figure 2 . The outer wall surface and the inner wall surface are each divided into four regions along the circumferential direction, which are the first, second, third, and fourth regions in counterclockwise direction, i.e. the green body rotates counterclockwise so that the line laser scans the first, second, third, and fourth regions in turn. The arc length of each region needs to be ≥2mm, and the scanning interval time of the inner wall surface and the outer wall surface in the same radial region needs to be ≥5min to prevent heat accumulation.

[0047] In the partition scanning, the same forced cooling by argon gas, and the monitoring of scanning intensity, temperature and spatter are required, and the operation process is the same as that of the reinforcing scanning. However, the scanning intensity and temperature of the linear laser should be lower than those in the reinforcing scanning in step S2.1, the scanning intensity is 500-1000 cps, and the scanning temperature is 850-900℃.

[0048] S3, gradient sintering of the green body is performed using a vacuum sintering furnace, the sintering density temperature is higher than the scanning temperature of the point laser in step S2.1, and the sintering density temperature can be 1050℃, and argon gas is used for atmosphere protection during sintering.

[0049] Specifically, the gradient sintering includes a low-speed debinding section, a multi-stage heat preservation and relaxation section, a controlled temperature rising sintering section, and a slow cooling section. The multi-stage heat preservation and relaxation section and the slow cooling section can effectively release the thermal stress and sintering stress introduced by the laser, further eliminate micro defects, and ensure excellent comprehensive performance of the product. If necessary, hot isostatic pressing (HIP) can be performed to further eliminate micro defects.

[0050] The yield of the traditional preparation of the neodymium iron boron radiation ring is only 50%, and after testing, the yield of the neodymium iron boron radiation ring prepared by the above method can be increased to more than 80%, which significantly reduces the production cost. Moreover, the process parameters of the above preparation method are only taken as an example of the neodymium iron boron radiation ring, if other materials are used to prepare ring structures, only the melting point and sintering characteristics of different materials need to be adjusted to adjust the laser parameters and sintering curve, which can be widely applied, and solves the common problem of sintering cracking of thin high ring-shaped parts in multiple technical fields.

[0051] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0052] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser-selective pre-strengthened fine high-strength ring anti-cracking sintering method, characterized in that, Includes the following steps: S1. Press the powder for preparing fine high-ring shapes into a green body in the shape of fine high-ring shapes; S2. Strengthening the green compact by laser scanning under an argon protective atmosphere, including two steps: strengthening scanning and zone scanning: S2.1 Strengthening Scan: The inner and outer edges of the lower port and the inner and outer edges of the upper port of the green blank are scanned by point laser, as well as the area of ​​multiple generatrices evenly distributed in the circumferential direction of the inner wall curved surface of the green blank, so that the green blank powder is micro-melted and rapidly cooled to form a strengthening ring and multiple reinforcing ribs. S2.2 Partition scanning: Line laser is used to scan the inner and outer curved surfaces of the green blank, and the scanning intensity and scanning temperature of the line laser are lower than those of the point laser in step S2.

1. S3. Gradient sintering of the green billet is performed using a vacuum sintering furnace. The densification temperature of the sintering is higher than the scanning temperature of the laser in step S2.

1. Argon gas is used for atmosphere protection during sintering.

2. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 1, characterized in that: In step S1, the prepared fine high-density ring is a neodymium iron boron radiating ring, and the powder is neodymium iron boron powder; in step S2.1, the scanning intensity of the point laser is 1000cps-2000cps, and the scanning temperature is 1000±10℃; in step S2.2, the scanning intensity of the line laser is 500-1000cps, and the scanning temperature is 850℃-900℃; in step S3, the sintering densification temperature is 1050℃.

3. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 2, characterized in that: In step S2, while the laser is scanning, the scanning intensity, scanning temperature and molten pool spatter size are monitored by a plasma spectral monitoring device, an infrared thermal imager and a high-speed camera for the molten pool, respectively. If the intensity is ≥5000cps, an alarm for neodymium-rich phase evaporation is issued; if the scanning temperature reaches 0.6 times the melting point of neodymium iron boron, an alarm is issued and the laser scanning is stopped; if the observed spatter size is >5μm, an alarm is issued and the laser power is reduced.

4. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 2, characterized in that: In step S1, the NdFeB ingots and NdFeB strips produced by the ingot casting furnace and the strip spinning furnace respectively are subjected to hydrogen crushing. The hydrogen crushed powder produced by the ingot casting furnace and the strip spinning furnace is mixed according to the design ratio, and then the powder is ground into fine powder of 3μm-4μm by air jet mill. This powder is used to prepare NdFeB radiation rings. After being rotated and oriented, it is then pressed into green blanks by cold isostatic pressing.

5. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 1, characterized in that: In step S2, after each point laser scan with a length of ≤1mm and a line laser scan with an arc length of ≤1mm is completed, the area scanned by the laser is cooled by argon gas for 10s, with an argon gas flow rate of 15m / s, and the laser scanning and argon gas cooling are performed continuously.

6. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 1, characterized in that: In step S2.2, the outer and inner curved surfaces of the green blank are each divided into multiple regions along the circumference, and the scanning interval between the inner and outer curved surfaces in the same radial region is ≥5 min.

7. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 6, characterized in that: In step S2.2, the outer and inner curved surfaces of the green blank are each divided into four regions along the circumference, and the arc length of each region is ≥2mm.

8. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 1, characterized in that: In step S2.1, the green blank is first fixed, and the point laser moves to scan the outer edge area and inner edge area of ​​the lower port of the green blank in sequence. Then, it scans a generatrix area of ​​the inner wall curved surface of the green blank from bottom to top. Next, it scans the inner edge and outer edge area of ​​the upper port of the green blank in sequence. Then, the green blank rotates circumferentially, and the point laser skips the step of scanning the edge areas of the upper and lower ports to complete the scanning of the next generatrix area. This step is repeated to complete the scanning of all generatrix areas.

9. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings by laser sintering as described in claim 1, characterized in that: In step S2.2, the laser length of the line laser is aligned with the height of the billet. During scanning, the position of the line laser is fixed, and the billet rotates circumferentially to complete the laser scanning of the inner and outer walls of the billet. When scanning the outer curved surface of the billet, the scanning direction of the line laser is along the circumferential tangent direction of the outer ring of the billet. When scanning the inner curved surface of the billet, the emitter of the line laser is located at the center of the inner ring of the billet and has an angle with the central axis of the billet.

10. The laser selective pre-strengthening method for preventing cracking of fine high-strength rings as described in claim 1, characterized in that: In step S1, the fine high-growth ring is a radial ring, a multi-level ring, or a radial ring, and the powder used to prepare the fine high-growth ring is neodymium iron boron, stainless steel, cemented carbide, or ceramic powder.

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