Selective laser pre-strengthening thin and high ring anti-cracking sintering method

Abstract

The invention provides an anti-cracking sintering method for a selective laser pre-strengthening thin and high ring. The anti-cracking sintering method comprises the following steps: firstly, pressing powder for preparing the thin and high ring into a thin and high ring-shaped green body; then the green body is strengthened through laser scanning under the argon protective atmosphere, the inner edge and the outer edge of a lower port and the inner edge and the outer edge of an upper port of the green body are scanned through point laser, multiple plain line areas evenly distributed in the circumferential direction of the curved surface of the inner wall of the green body are scanned in the axial direction, green body powder is slightly melted and rapidly cooled, and a strengthening ring and multiple strengthening ribs are formed; scanning the inner wall curved surface and the outer wall curved surface of the green body by adopting line laser, wherein the scanning intensity and the scanning temperature of the line laser are lower than those of the point laser; and finally, a vacuum sintering furnace is used for carrying out gradient sintering on the green body, the sintering densification temperature is higher than the scanning temperature of point laser, and argon is used for atmosphere protection during sintering. The structural strength of the thin and high ring green body is pre-strengthened through laser, the cracking problem of the thin and high ring during sintering is reduced, and the yield of the thin and high ring is improved.

Description

Technical Field

[0001] This invention belongs to the field of metal powder processing technology, and specifically relates to a laser selective pre-strengthening method for fine high-ring anti-cracking sintering. Background Technology

[0002] With the development of servo motors and mechanical assembly, the application of thin, high-tight ring components is increasing. Examples include thin, high-tight radial rings used in servo motors and stepper motors, radial rings used in coreless motors, iron-cobalt magnetic tubes, and thin titanium rings used in engines. The demand for thin, high-tight ring components is enormous across various industries, with increasing demand for permanent magnet materials that provide magnetic fields in motors. Furthermore, servo motors with thin, high-tight radial rings offer higher stability and durability compared to modular servo motors. However, fine high-density rings (height greater than 20mm, outer diameter less than 10mm, wall thickness less than 3mm) suffer from inconsistent shrinkage rates between the inner and outer ring walls during the sintering stage (especially fine high-density radiation rings made of NdFeB material). Furthermore, the low strength of the green body and significant self-weight effect lead to enormous stress within the ring during traditional vacuum sintering. This results in problems such as longitudinal bending deformation (uneven gas overflow from the powder during heating, leading to a banana effect and lateral bending), radial cracking in the middle of the ring (different shrinkage rates between the inner and outer ring walls during sintering cause cracking at the point of maximum torque within the green body), and edge chipping (stress concentration easily occurs at the edge of the green body, leading to chipping). Consequently, the yield of fine high-density rings is low. Therefore, improving the cracking problem of fine high-density ring products is of paramount importance.

[0003] Traditional solutions to improve cracking in sintered fine high-density rings include: increasing the forming density through one-time forming using cold isostatic pressing or high-pressure presses; eliminating internal stress in the green body by modifying the sintering curve; using supports to prevent lateral bending; and for NdFeB materials, using composite powders made from ingots and strip casting to enhance the mechanical strength of the green body. While these solutions are effective, they have the following drawbacks: increasing green body density and optimizing the sintering curve have limited anti-cracking effects; using complex sintering supports introduces contact point stress, creating new defects; and using composite powders made from ingots and strip casting to enhance mechanical strength introduces α-Fe (a crystalline form of iron that severely affects the magnetic properties of NdFeB materials), which is difficult to remove. Therefore, a more effective method to improve cracking in sintered fine high-density rings is needed. Summary of the Invention

[0004] The purpose of this invention is to provide a laser selective pre-strengthening method for preventing cracking during the sintering of fine high-density rings. By laser pre-strengthening the structural strength of the fine high-density ring green blank, the cracking problem during the sintering of fine high-density rings is reduced, and the yield of fine high-density rings is improved.

[0005] To achieve the above objectives, the solution of the present invention is as follows: A laser selective pre-strengthening method for preventing cracking of fine high-strength rings during sintering is provided, comprising 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.

[0006] Further, in step S1, the prepared fine high-growth 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℃.

[0007] Furthermore, 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.

[0008] Further, 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 crushing 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.

[0009] Furthermore, in step S2, after each point laser scan of ≤1mm length and line laser scan of ≤1mm arc length is completed, the area scanned by the laser is cooled by argon gas for 10s, the gas flow rate of argon gas is 15m / s, and the laser scanning and argon cooling are performed continuously.

[0010] Furthermore, 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 time between the inner and outer curved surfaces in the same radial region is ≥5 min.

[0011] Furthermore, 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.

[0012] Furthermore, 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 is rotated 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.

[0013] Furthermore, 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.

[0014] Furthermore, 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.

[0015] After adopting the above solution, the beneficial effects of the present invention are as follows: 1. This invention creatively introduces a laser selective pre-strengthening step into the traditional powder metallurgy process. By scanning multiple generatrices evenly distributed on the critical port edges and inner curved surfaces of the green compact with a laser, micro-melting of the green compact powder is achieved. Rapid cooling then follows, forming a reinforcing skeleton in the critical areas of the green compact, significantly enhancing the overall structural strength and rigidity of the green compact during sintering. Specifically, the micro-melting at the port edges forms a reinforcing ring, which resists edge chipping and provides a "pinch" effect, while the axially scanned generatrices form reinforcing ribs, resisting longitudinal bending. This reinforcing skeleton effectively resists the enormous internal stress caused by the green compact's own weight and the inconsistent shrinkage of the inner and outer walls, fundamentally suppressing defects such as longitudinal bending, radial cracking in the center, and port edge chipping that are prone to occur during sintering, greatly improving the yield of fine, high-quality rings.

[0016] 2. For permanent magnet materials such as neodymium iron boron, by strictly limiting the scanning area to the non-magnetically orientation-sensitive region, that is, not scanning the middle region between the inner and outer edges of the port, which is a magnetically orientation-sensitive region, not scanning this region can significantly improve the green strength and prevent cracking, while completely avoiding the damage of laser thermal effects on the magnetic domain orientation of the main phase of the magnet, thus ensuring the final magnetic properties of the product.

[0017] 3. During the pressing process, the green body accumulates internal stress. Furthermore, during the point laser strengthening scan, significant internal stress concentration occurs between the strengthened framework and the surrounding unstrengthened green body due to the large difference in shrinkage rate and modulus. This stress concentration can lead to microcracks or even complete cracking during subsequent sintering. This application further utilizes a line laser to perform sectional scanning of the inner and outer curved surfaces of the green body after the strengthening scan. Sectional scanning increases the surface strength of the green body and releases the internal stress concentration generated during pressing and strengthening scans, preventing cracks during sintering and further improving the yield.

[0018] 4. The technical solution of this application is not limited to specific annular structures (applicable to radiating rings, multi-level rings, radial rings, etc.) or materials (applicable to neodymium iron boron, stainless steel, cemented carbide, ceramics, etc.). It can be widely applied by simply adjusting the laser parameters and sintering curves according to the melting point and sintering characteristics of different materials, thus solving the common problem of sintering cracking of fine and tall annular parts in multiple technical fields. Attached Figure Description

[0019] Figure 1 A three-dimensional view of the present invention obtained through enhanced scanning; Figure 2 Top view of the partitioned scanning of this invention; Figure 3 This is a schematic diagram of the scanning of the inner curved surface of the green body according to the present invention; Figure 4 This is a flowchart of the method of the present invention.

[0020] Label Explanation: 1. Green blank; 2. Reinforcing ring; 3. Reinforcing rib; 4. Point laser emitter; 5. Line laser emitter. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The scope value described in this invention includes two endpoint values.

[0022] like Figures 1-4As shown, this application provides a laser selective pre-strengthened fine high-gloss ring anti-cracking sintering method, comprising the following steps: S1. Press the powder for preparing fine high rings into a fine high ring green body 1. The fine high ring can be a radiating ring, multi-level ring or radial ring of various materials (including neodymium iron boron, stainless steel, cemented carbide, ceramics, etc.). The following explanation uses neodymium iron boron radiating ring as an example.

[0023] Specifically, the powder for preparing NdFeB radiant rings can be obtained by hydrogen crushing of NdFeB ingots and NdFeB strips produced by ingot casting furnace and strip spinning furnace respectively. The hydrogen crushed powders produced by ingot casting furnace and strip spinning furnace are mixed according to the designed ratio, which can be 1:20, and then ground into fine powder of 3μm-4μm by air jet mill.

[0024] Optionally, the magnetic powder milled by air jet milling is subjected to rotary orientation pressing, and then the density of the green body is increased by traditional cold isostatic pressing.

[0025] S2. The green body is strengthened by laser scanning under an argon protective atmosphere.

[0026] Specifically, the green blank 1 is first fixed in the argon chamber using a ceramic clamp with a clamping force of 10N-50N. The clamping force should not be too large to avoid damaging the green blank. Then, the laser focus is calibrated using a standard block. Next, the argon gas is started at a flow rate of 30L / min for 5 minutes. Finally, the laser is started for scanning, including two steps: enhanced scanning and zonal scanning. S2.1 Enhanced Scan: such as Figure 1 As shown, a point laser is used to scan the inner and outer edges of the lower and upper ports of the green blank, causing the green blank powder to slightly melt. This is followed by rapid cooling to form a reinforcing ring 2, which resists edge chipping and provides a "pinch" effect. In addition to the edge region of the green blank ports, multiple uniformly distributed generatrices on the circumferential surface of the inner wall of the green blank are scanned axially to form multiple reinforcing ribs 3, preferably eight ribs 3, which resist longitudinal bending. Thus, the reinforcing ring 2 and reinforcing ribs 3 form the reinforcing skeleton of the green blank, effectively resisting the enormous internal stress caused by the green blank's own weight and the inconsistent shrinkage of the inner and outer walls. This fundamentally suppresses defects that are prone to occur during sintering, such as longitudinal bending, radial cracking in the center, and edge chipping at the ports, greatly improving the yield of fine, high-quality rings.

[0027] Specifically, the enhanced scanning sequence can be as follows: the green blank is first fixed, and the emitter 4 of 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 line area of ​​the inner wall 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 is rotated 45° 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 line area. This step is repeated to complete the scanning of all line areas.

[0028] It is important to note that during point laser scanning, the scanning temperature must not exceed the densification temperature during subsequent sintering, and should be controlled at 1000±10℃. The scanning temperature also must not exceed the set threshold temperature, which is set to 0.6 times the melting point of NdFeB. If the scanning temperature reaches this threshold, it will affect the NdFeB radiation ring. An infrared thermal imager can be used to monitor the scanning temperature in real time. When the scanning temperature reaches or exceeds the threshold, an immediate warning will be issued, and the point laser will automatically stop. Furthermore, it is crucial to avoid scanning the central region between the inner and outer edges of the green blank. This region is magnetically orientation sensitive. Excluding this region significantly improves the green blank strength, prevents cracking, and completely avoids the damage to the magnetic domain orientation of the main phase of the magnet caused by laser thermal effects, thus ensuring the final magnetic properties of the product.

[0029] During point laser scanning, the scanning intensity cannot be too high, otherwise it will lead to the evaporation of the neodymium-rich phase. In the neodymium-iron-boron radiation ring, neodymium exists in a locally enriched form, which is the "neodymium-rich phase." If the scanning intensity is too high, it is easy to cause a large amount of neodymium to evaporate, which is the evaporation of the neodymium-rich phase. Excessive evaporation of neodymium will result in insufficient neodymium content in that area of ​​the final molded part, changing the local properties of the material and forming defects such as porosity, spatter, and lack of fusion. The scanning intensity of the point laser can be monitored by using plasma spectroscopy monitoring equipment to monitor the intensity of the characteristic spectral line of neodymium (wavelength of 521nm). Generally, the scanning intensity of the point laser is controlled at 1000cps-2000cps, where cps is the number of photons with a wavelength of 521nm received per second. If the intensity is ≥5000cps, an alarm for neodymium-rich phase evaporation will be issued.

[0030] In addition to intensity and temperature monitoring, a high-speed camera (10kfps) can be used to monitor the size of the molten pool spatter. If the observed spatter size is greater than 5μm, an alarm will be issued and the laser power will be reduced. Spatter is the phenomenon of liquid metal droplets being ejected from the molten pool at high speed. Large spatter can not only create material defects in the current processing area (leading to holes), but the flying metal particles can also cause adhesion, increased roughness, and even damage the powder coating of the next layer when they land on the already formed surface. A stable molten pool is the key to obtaining dense, uniform, and smooth formed parts. Therefore, molten pool spatter monitoring is necessary.

[0031] In addition, the scanned area needs to be cooled during the scanning process. Specifically, argon atmosphere can be used for cooling. After each 1mm long point laser scan (the scanning length cannot exceed 1mm), the scanned area should be cooled with argon for 10s. The argon flow rate is 15m / s, and laser scanning and argon cooling need to be continuous.

[0032] S2.2 Partition scanning: Line laser scanning is used to scan the inner and outer curved surfaces of the green blank 1, which can increase the strength of the green blank surface. At the same time, it can release the internal stress concentration generated during the pressing and strengthening scanning stages, avoid cracks during sintering, and further improve the yield.

[0033] like Figure 2 As shown, 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. There is no restriction on the order in which the line laser scans the inner and outer curved surfaces of the billet. However, when scanning the outer curved surface, the scanning direction of the line laser is along the tangent direction of the outer ring of the billet to avoid direct laser beams causing localized cracking and powder sputtering. This scanning method can also be used to avoid powder sputtering when intensifying scanning in the edge area of ​​the fired billet port. When scanning the inner curved surface, the emitter of the line laser is located at the center of the inner ring of the billet, as shown in the image. Figure 3 As shown, the emitter 5 of the line laser has an angle of about 5° with the axis, that is, the emitter 5 of the line laser is tilted to avoid the direct laser beam causing raw powder sputtering.

[0034] The outer and inner curved surfaces of the green blank are each divided into multiple regions along the circumference, such as... Figure 2 As shown, both the outer and inner curved surfaces are divided into four regions circumferentially, designated as regions ①, ②, ③, and ④ in a counter-clockwise direction. This means the green billet rotates counter-clockwise, allowing the line laser to scan regions ①, ②, ③, and ④ sequentially. The arc length of each region must be ≥2mm, and the scanning interval between the inner and outer curved surfaces in the same radial region must be ≥5min to prevent heat accumulation.

[0035] During partitioned scanning, forced cooling with argon gas is also required, along with monitoring of scanning intensity, temperature, and spatter. The operating procedure is the same as for enhanced scanning. However, the scanning intensity and temperature of the line laser should be lower than those of the enhanced scanning in step S2.1, with a scanning intensity of 500-1000 cps and a scanning temperature of 850℃-900℃.

[0036] S3. Gradient sintering of the green billet is performed using a vacuum sintering furnace. The densification temperature is higher than the scanning temperature of the laser in step S2.1. The densification temperature can be 1050℃. Argon gas is used for atmosphere protection during sintering.

[0037] Specifically, gradient sintering is employed, including a low-speed debinding section, a multi-stage holding and relaxation section, a controlled heating sintering section, and a slow cooling section. The multi-stage holding and relaxation section and the slow cooling section effectively release the thermal stress and sintering stress introduced by the laser, further eliminating micro-defects and ensuring excellent overall product performance. If necessary, hot isostatic pressing (HIP) can be performed to further eliminate micro-defects.

[0038] Traditional methods for preparing NdFeB radiating rings yield only 50% of the product. Testing has shown that the method described above can increase the yield to over 80%, significantly reducing production costs. Furthermore, the process parameters described above are only for NdFeB radiating rings; to prepare ring structures of other materials, simply adjusting the laser parameters and sintering curves according to the melting point and sintering characteristics of different materials allows for wide applicability, solving the common problem of sintering cracking in thin, tall ring components across multiple technical fields.

[0039] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0040] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded 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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