A laser selective melting precision repair method for worn brake discs

Abstract

This invention discloses a laser selective melting precision repair method for worn brake discs, belonging to the field of brake disc repair. The method includes: machining and grinding the area to be repaired on the brake disc to form a flat base surface; clamping and positioning the brake disc in a selective laser melting device; preheating the brake disc to 200℃ and maintaining this temperature; laying 24CrNiMo alloy powder on the area to be repaired; and performing layer-by-layer printing repair using process parameters of laser power 120-140W, scanning speed 900-1000mm / s, and powder thickness 0.02mm, with a checkerboard scanning path; performing stress-relieving heat treatment at 300-400℃ after printing; and finally, performing post-machining processing. The repaired area exhibits a deformation of only 0.2-0.3mm, a tensile strength of ≥1342MPa, and an elongation of ≥12%, making it suitable for high-precision, low-deformation remanufacturing repair of high-speed rail brake discs.

Description

Technical Field

[0001] This invention belongs to the field of brake disc repair, and particularly relates to a laser selective melting precision repair method for worn brake discs. Background Technology

[0002] High-speed rail brake discs are a key component of the high-speed train braking system. They primarily convert the kinetic energy of the train during operation into heat energy through friction between the brake disc and brake pads, thereby achieving train deceleration and safe stopping. During high-speed operation and frequent braking, brake discs are subjected to complex service conditions such as mechanical friction, drastic temperature changes, and alternating loads, making them prone to damage such as wear, scratches, hot spots, warping deformation, and thermal fatigue cracks. Currently, high-speed rail brake discs are mostly made of 24CrNiMo alloy steel. Although this material has high mechanical properties and resistance to high-cycle fatigue, surface damage and structural degradation are still inevitable under long-term thermal cycling and high-load conditions. Due to the high manufacturing cost, high processing precision requirements, and complex service environment of high-speed rail brake discs, high-quality remanufacturing repair of damaged brake discs has significant engineering and economic value. Existing repair methods mainly include welding repair, thermal spraying repair, and laser cladding repair. Laser additive remanufacturing technology, due to its advantages such as high metallurgical bonding strength and controllable dilution rate and heat-affected zone, has become an important technical direction for high-quality repair of metal components.

[0003] However, traditional welding repair involves high heat input, easily leading to coarse microstructure and thermal cracks; the bonding strength between the thermal spray coating and the substrate is limited, making it difficult to meet long-term service requirements. While laser cladding repair can achieve localized additive manufacturing and metallurgical bonding, its large molten pool size and high heat input can easily cause heat accumulation, uneven microstructure, and warping deformation during the repair process—the maximum deformation of the brake disc after traditional laser cladding repair can reach 5mm, failing to meet the high-precision, low-deformation repair requirements of high-speed rail brake discs. Furthermore, existing repair technologies generally suffer from high residual stress in the repair area and unstable interlayer bonding quality, often resulting in mechanical properties after repair that fail to meet the standard requirements of the original cast steel parts. Therefore, how to achieve precision remanufacturing repair of damaged areas of high-speed rail brake discs with low heat input, low residual stress, high dimensional accuracy, and high microstructure uniformity has become a crucial technical problem urgently needing to be solved in the field of additive remanufacturing for rail transit. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a laser selective melting precision repair method for brake disc wear, comprising: The area of ​​the brake disc to be repaired is machined and ground to form a flat base surface. The brake disc, after being machined and ground, is clamped and positioned in the selective laser melting equipment; The brake disc is preheated to a preset temperature and maintained at the preset temperature throughout the entire laser selective melting repair process; Alloy powder is laid on the surface of the area to be repaired of the preheated brake disc, and laser selective melting technology is used to print and repair the area layer by layer. During the layer-by-layer printing and repair process, a checkerboard scanning path is used to scan the area to be repaired. The alloy powder is an alloy powder that is the same as or compatible with the material of the brake disc. After the printing repair is completed, the brake disc is subjected to stress-relieving heat treatment; The repaired area of ​​the brake disc, after stress-relief heat treatment, is subjected to post-machining processing.

[0005] Optionally, the brake disc, after being machined and ground, is clamped and positioned in a selective laser melting device, including: Using the existing mounting holes on the brake disc as positioning references, the brake disc is clamped and positioned on the special tooling of the selective laser melting equipment, so that the area to be repaired is aligned with the printing coordinate system of the selective laser melting equipment.

[0006] Optionally, preheating the brake disc to a preset temperature includes: The brake disc is preheated to 200°C and maintained at a constant temperature of 200°C ± 10°C throughout the laser selective melting repair process.

[0007] Optionally, the alloy powder is 24CrNiMo alloy powder, which, by weight percentage, comprises: Si 0.410%, C 0.240%, Cr 1.120%, Mn 1.100%, Ni 0.920%, Mo 0.600%, P 0.014%, S 0.014%, with the balance being Fe.

[0008] Optionally, the particle size of the alloy powder ranges from 15 μm to 45 μm.

[0009] Optionally, during the process of using laser selective melting technology to print and repair the area to be repaired layer by layer, the laser power is 120W to 140W, the scanning speed is 900mm / s to 1000mm / s, the powder thickness is 0.02mm, and the scanning interval is 0.08mm to 0.1mm.

[0010] Optionally, the area to be repaired is scanned using a checkerboard-style scanning path, including: The area to be repaired is divided into multiple independent checkerboard micro-area units. Short-path scanning is used for each checkerboard micro-area unit, and an alternating scanning method is used between adjacent checkerboard micro-area units. The size of a single checkerboard micro-area unit is 2mm×2mm to 10mm×10mm, the scanning direction angle between adjacent checkerboard micro-area units is 45° to 90°, the scanning direction between adjacent printing layers is rotated, and the scanning sequence of each checkerboard micro-area unit is a skip scan.

[0011] Optionally, the repaired area of ​​the brake disc after stress-relieving heat treatment undergoes post-machining processing, including: The repaired area is subjected to CNC machining, precision grinding, and surface polishing in sequence to restore the dimensional accuracy and surface flatness of the brake disc, reduce surface roughness, and improve the surface quality of the repaired area.

[0012] On the other hand, the present invention also provides an electronic device including a memory, a processor, and a computing program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computing program.

[0013] On the other hand, the present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method.

[0014] Compared with the prior art, the present invention has the following advantages and technical effects: This invention employs selective laser melting (SLM) technology to replace traditional laser cladding repair, significantly reducing heat input and heat accumulation during the repair process. The maximum deformation of the brake disc after repair is only 0.2–0.3 mm, far superior to the 3–5 mm deformation of traditional laser cladding repair, meeting the high-precision repair requirements of high-speed rail brake discs. Preheating the substrate to 200℃ and maintaining a constant temperature effectively reduces the crack sensitivity of the repair layer and improves the interlayer bonding quality. The checkerboard scanning path combined with rotating interlayer scanning directions and a skip-scanning sequence effectively avoids localized thermal stress concentration, further controlling residual deformation. The repaired layer achieves a tensile strength of 1342–1352 MPa and an elongation after fracture of 12%–12.5%, significantly exceeding the standards for traditional cast steel parts (tensile strength not less than 1050 MPa and elongation after fracture not less than 8%). The repaired area exhibits fine grains, free of cracks and porosity defects, achieving high-quality precision remanufacturing of the brake disc wear area. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the brake disc repair surface and positioning hole according to an embodiment of the present invention. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0017] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0018] Example 1 This embodiment provides a laser selective melting precision repair method for brake disc wear, including: (1) The worn area is machined and ground. In this embodiment, CNC turning, surface grinding or precision grinding is used to remove the surface oxide layer, fatigue damage layer and crack area, so that the area to be repaired forms a flat base surface, and the flatness of the repair surface is controlled to be ≤0.02mm.

[0019] (2) The machined high-speed rail brake disc is placed on a special fixture of the selective laser melting equipment. In this embodiment, the original 12 mounting holes of the brake disc are used as positioning references for clamping and positioning (e.g., Figure 1 (as shown), to ensure consistency between the repair area and the printing coordinate system.

[0020] (3) Before printing begins and throughout the printing process, the brake disc substrate temperature is preheated to 200°C, and this constant temperature is maintained throughout the entire selected area laser melting repair process. In this embodiment, the temperature fluctuation during preheating is controlled within ±10°C.

[0021] (4) 24CrNiMo alloy powder is laid on the surface of the area to be repaired on the brake disc. Its chemical composition is listed in Table 1.

[0022] Table 1 In this embodiment, the selected alloy powder has a particle size range of 15–45 μm. Subsequently, selective laser melting technology is used to perform layer-by-layer local printing repair on the area to be repaired. During the forming process, high-purity argon gas with a purity ≥99.999% is used as the protective atmosphere, and the oxygen content in the forming chamber is controlled below 1000 ppm. The key process parameters are as follows: laser power 120–140 W; scanning speed 900–1000 mm / s; powder thickness 0.02 mm; scanning spacing 0.08–0.1 mm.

[0023] (5) During the selected area laser melting process, a checkerboard scanning path is used to reduce heat accumulation and residual stress. Specifically, the area to be repaired is divided into multiple independent micro-units, each micro-unit is scanned using a short path, and adjacent micro-units are scanned alternately. In this embodiment, the size of a single checkerboard grid is 2mm×2mm~10mm×10mm; the scanning direction angle between adjacent micro-units is 45°~90°; the scanning direction between adjacent printing layers is rotated; and the scanning sequence of each micro-unit adopts a skip scanning method.

[0024] (6) After the printing repair is completed, the brake disc is subjected to stress-relieving heat treatment at a temperature of 300-400℃. After heat treatment, the repaired area is post-processed by CNC machining, precision grinding and surface polishing: CNC machining restores the dimensional accuracy and surface flatness of the brake disc; precision grinding reduces the surface roughness of the repaired area; and surface polishing improves the surface quality and service stability of the repaired area.

[0025] In this embodiment, by using selective laser melting (SLM) technology to replace traditional laser cladding repair technology, the maximum deformation of the repaired area is only 0.3 mm, while the maximum deformation of traditional laser cladding repair can reach 5 mm, significantly reducing the deformation. Simultaneously, utilizing the original mounting hole structure of the brake disc for positioning improves printing positioning accuracy and repeatability. Using an ultra-thin powder layer of 20 μm for printing results in a smaller melt pool size and lower heat input, effectively reducing heat accumulation and residual deformation. The repaired area exhibits a fine microstructure, with mechanical properties exceeding the standards of traditional cast steel parts (tensile strength ≥1050 MPa, elongation after fracture ≥8%). Furthermore, the checkerboard scanning path effectively reduces localized thermal stress concentration, and the substrate preheating treatment reduces the crack sensitivity of the repair layer and improves interlayer bonding quality.

[0026] On the other hand, this embodiment also provides an electronic device, including a memory, a processor, and a computing program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computing program.

[0027] On the other hand, this embodiment also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method.

[0028] Example 2 This embodiment provides a laser selective melting precision repair method for brake disc wear, including: A certain type of high-speed rail brake disc, made of 24CrNiMo alloy casting, showed significant wear on its surface after one service cycle, with a wear thickness reaching 1mm. The wear-affected brake disc was repaired using the repair process provided in the above-described embodiment of the present invention.

[0029] In this embodiment, the worn area is first subjected to surface grinding. Precision grinding is used to remove the surface oxide layer, fatigue damage layer, and cracked areas, so that the area to be repaired forms a flat base surface with a flatness of ≤0.02mm.

[0030] The machined high-speed rail brake disc is placed on a special fixture of the selective laser melting equipment, using the original 12 mounting holes of the brake disc as positioning references for clamping and positioning (e.g., Figure 1 (as shown), to ensure consistency between the repair area and the printing coordinate system.

[0031] In this embodiment, the process parameters for selective laser melting printing repair are as follows: the repair powder is 24CrNiMo alloy powder with a particle size of 15-45μm; the laser power is 120W; the scanning speed is 900mm / s; the scanning spacing is 0.08mm; the powder thickness is 0.02mm; a checkerboard scanning path is used with a checkerboard size of 10mm×10mm, the scanning direction angle between adjacent areas is 45°-90°, the scanning direction between adjacent layers is rotated, and the scanning sequence adopts a skip scanning method; the substrate preheating temperature is 200℃.

[0032] After the printing repair is completed, the brake disc is subjected to stress-relieving heat treatment to release residual stress at a temperature of 300℃.

[0033] Metallographic analysis of the repaired area showed fine grains and no obvious cracks or porosity defects. The repair layer achieved a hardness of HV0.2 = 430, a tensile strength of 1342.64 MPa, and an elongation at fracture of 12%. The fracture surface consisted of large and dense dimples. The mechanical properties exceeded the standards for traditional cast steel parts (tensile strength not less than 1050 MPa, elongation at fracture not less than 8%). Furthermore, the deformation after repair was only 0.2 mm, meeting the requirements for use after subsequent machining. In contrast, traditional laser cladding repair of a 1 mm thick wear layer resulted in a deformation of 3 mm, failing to meet the requirements.

[0034] Example 3 This embodiment provides a laser selective melting precision repair method for brake disc wear, including: After two cycles of service, a certain type of high-speed rail brake disc showed significant wear on its surface, with a wear thickness reaching 1 mm. The wear-affected brake disc was repaired using the repair process provided in the above-described embodiment of the present invention.

[0035] In this embodiment, the worn area is first subjected to surface grinding. Precision grinding is used to remove the surface oxide layer, fatigue damage layer, and cracked areas, so that the area to be repaired forms a flat base surface with a flatness of ≤0.02mm.

[0036] The machined high-speed rail brake disc is placed on a special fixture of the selective laser melting equipment, using the original 12 mounting holes of the brake disc as positioning references for clamping and positioning (e.g., Figure 1 (as shown), to ensure consistency between the repair area and the printing coordinate system.

[0037] In this embodiment, the process parameters for selective laser melting printing repair are as follows: the repair powder is 24CrNiMo alloy powder with a particle size of 15-45μm; the laser power is 140W; the scanning speed is 1000mm / s; the scanning spacing is 0.1mm; the powder thickness is 0.02mm; a checkerboard scanning path is used with a checkerboard size of 2mm×2mm, the scanning direction angle between adjacent areas is 45°-90°, the scanning direction between adjacent layers is rotated, and the scanning sequence adopts a skip scanning method; the substrate preheating temperature is 200℃.

[0038] After the printing repair is completed, the brake disc is subjected to stress-relieving heat treatment to release residual stress at a temperature of 400℃.

[0039] Metallographic analysis of the repaired area showed fine grains and no obvious cracks or porosity defects. The repair layer achieved a hardness of HV0.2 = 435, a tensile strength of 1352.4 MPa, and an elongation after fracture of 12.5%. The fracture surface consisted of large and dense dimples, exceeding the mechanical properties of traditional cast steel parts (tensile strength not less than 1050 MPa, elongation after fracture not less than 8%). Furthermore, the deformation after repair was only 0.3 mm, meeting the requirements for use after subsequent machining. In contrast, traditional laser cladding repair of a 1 mm thick wear layer resulted in a deformation of 5 mm, failing to meet the requirements.

[0040] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for precision repair of worn brake discs using laser selective melting, characterized in that, include: The area of ​​the brake disc to be repaired is machined and ground to form a flat base surface. The brake disc, after being machined and ground, is clamped and positioned in the selective laser melting equipment; The brake disc is preheated to a preset temperature and maintained at the preset temperature throughout the entire laser selective melting repair process; Alloy powder is laid on the surface of the area to be repaired of the preheated brake disc, and laser selective melting technology is used to print and repair the area layer by layer. During the layer-by-layer printing and repair process, a checkerboard scanning path is used to scan the area to be repaired. The alloy powder is an alloy powder that is the same as or compatible with the material of the brake disc. After the printing repair is completed, the brake disc is subjected to stress-relieving heat treatment; The repaired area of ​​the brake disc, after stress-relief heat treatment, is subjected to post-machining processing.

2. The method according to claim 1, characterized in that, The brake disc, after being machined and ground, is clamped and positioned in the selective laser melting equipment, including: Using the existing mounting holes on the brake disc as positioning references, the brake disc is clamped and positioned on the special tooling of the selective laser melting equipment, so that the area to be repaired is aligned with the printing coordinate system of the selective laser melting equipment.

3. The method according to claim 1, characterized in that, Preheating the brake disc to a preset temperature includes: The brake disc is preheated to 200°C and maintained at a constant temperature of 200°C ± 10°C throughout the laser selective melting repair process.

4. The method according to claim 1, characterized in that, The alloy powder is 24CrNiMo alloy powder, which, by weight percentage, contains: Si 0.410%, C 0.240%, Cr 1.120%, Mn 1.100%, Ni 0.920%, Mo 0.600%, P 0.014%, S 0.014%, with the balance being Fe.

5. The method according to claim 1, characterized in that, The particle size range of the alloy powder is 15μm to 45μm.

6. The method according to claim 1, characterized in that, During the process of using laser selective melting technology to print and repair the area to be repaired layer by layer, the laser power is 120W to 140W, the scanning speed is 900mm / s to 1000mm / s, the powder thickness is 0.02mm, and the scanning interval is 0.08mm to 0.1mm.

7. The method according to claim 1, characterized in that, The area to be repaired is scanned using a checkerboard-style scanning path, including: The area to be repaired is divided into multiple independent checkerboard micro-area units. Short-path scanning is used for each checkerboard micro-area unit, and an alternating scanning method is used between adjacent checkerboard micro-area units. The size of a single checkerboard micro-area unit is 2mm×2mm to 10mm×10mm, the scanning direction angle between adjacent checkerboard micro-area units is 45° to 90°, the scanning direction between adjacent printing layers is rotated, and the scanning sequence of each checkerboard micro-area unit is a skip scan.

8. The method according to claim 1, characterized in that, The repaired area of ​​the brake disc after stress-relief heat treatment undergoes post-machining processing, including: The repaired area is subjected to CNC machining, precision grinding, and surface polishing in sequence to restore the dimensional accuracy and surface flatness of the brake disc, reduce surface roughness, and improve the surface quality of the repaired area.

9. An electronic device comprising a memory, a processor, and a computing program stored in the memory and executable on the processor, characterized in that, When the processor executes the computing program, it implements the method of any one of claims 1-8.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1-8.

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