Integrated laser remelting repair method for rail surface fatigue cracks and rail white layer

Abstract

The present invention belongs to the field of laser processing technology, and specifically discloses an integrated laser remelting repair method for fatigue cracks on the surface of rails and white layers of rails, comprising the following steps: performing flaw detection on damaged rails, determining the damage type and damage area on the surface of the service rails, and determining the first laser remelting process parameters according to the weight coefficients corresponding to different damage types; installing an integrated laser remelting repair device; determining the integrated laser remelting repair process according to different damage types; starting the integrated laser remelting repair device, and performing multiple gradient laser remelting treatments on the damaged area of ​​the rails; and judging and evaluating the repair effect in real time. The present invention uses an integrated laser remelting technology to repair fatigue cracks on the surface of rails and white layers of rails, so that pre-repair treatment, laser remelting repair and evaluation of repair effects are carried out simultaneously. Under the premise of ensuring the quality of the repair area, fatigue cracks on the surface of rails and white layers of rails are eliminated, and the process is simple, the cost is low and the repair efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of laser processing, and in particular to an integrated laser remelting and repairing method for a rail surface fatigue crack and a rail white layer. Background Art

[0002] As rail transit vehicles develop towards high speed and heavy load, the wear and damage of rails are becoming increasingly prominent. The initiation and expansion of fatigue cracks on the rail surface will cause the rail surface to peel off, seriously threatening the safety of train operation. Therefore, in the early stage of rail damage, timely use of a fast and effective method to repair the damaged area can greatly reduce the manpower and material costs caused by rail replacement and improve the safety of train operation.

[0003] Traditional repair methods include repair welding, arc surfacing, and thermite welding. However, the traditional welding process has a large heat input, and the depth of the heat-affected zone on the repaired surface is large, which increases the brittleness of the rail and easily causes rail breakage accidents during the service of the rail. At the same time, new impurities are easily introduced during the welding process, resulting in damage inside the rail and reducing the mechanical properties of the rail. In recent years, with the continuous development of laser technology, some scholars have applied laser technology to rail repair. Laser remelting technology, as a kind of rail surface modification technology, uses a high-energy laser heat source to irradiate the surface of the material, so that the material melts and solidifies rapidly, and the solidified surface has a high degree of finish. However, due to the characteristics of rapid heating and cooling of lasers, the solidification rate of the material in the laser irradiation area is relatively fast, and it is difficult to ensure that the cracks are completely healed during the repair process. At the same time, during the service of the rail, due to the effect of thermal-mechanical coupling, a layer of martensitic white layer will form on the surface of the rail. Rail white layer (WEL) refers to a structure that appears white under an optical microscope after the rail material is etched by a nitric acid-alcohol solution. A large number of studies have shown that the white layer of rails is brittle and prone to cracking during service, which reduces the mechanical properties of the rails. In addition, due to the material properties of the rails, the high-energy laser beam will promote the formation of the white layer of the rails. Therefore, it is difficult to meet the repair requirements using existing laser repair methods. In addition, the current repair process for damaged rails is mainly carried out in the order of grinding, repair, grinding, and finally testing. Each step is carried out in sequence, which will incur a lot of time costs.

[0004] In summary, the current repair methods for surface cracks and white layer of rails in service still have many shortcomings. Therefore, considering the aspects of controllable precision, on-site use, high efficiency and low cost, and ensuring the mechanical properties of the repaired rails, it is of great engineering significance to develop an integrated repair method for surface fatigue cracks and white layer of rails in service. Rail brown layer (BEL) refers to a structure that appears brown under an optical microscope after the rail material is etched with nitric acid-alcohol solution. The rail brown layer is a product of martensite decomposition, and its main component is near-bainite structure. Related studies have shown that the rail brown layer has better plasticity and toughness, and can improve the mechanical properties of the repaired rail.

[0005] Therefore, there is an urgent need for a method for repairing surface fatigue cracks and white layer of service rails that can reduce time costs and completely eliminate fatigue cracks and white layer of rails. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides an integrated laser remelting repair method for rail surface fatigue cracks and rail white layer, which realizes the transformation of rail white layer into rail brown layer by multiple laser remelting methods, so as to achieve the purpose of eliminating the rail white layer; at the same time, during the laser remelting process, an integrated laser remelting repair device is installed, which can make pretreatment, laser repair and post-repair detection be carried out simultaneously, greatly reducing the time cost, and can completely eliminate rail fatigue cracks and rail white layer, and can evaluate the repair effect of rail in real time, thereby solving the problems mentioned in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: an integrated laser remelting repair method for rail surface fatigue cracks and rail white layer, comprising the following steps:

[0008] S1. Detect the damaged rails, determine the damage type and damage area on the surface of the service rails, and determine the first laser remelting process parameters according to the weight coefficients corresponding to different damage types;

[0009] S2. Install integrated laser remelting repair device;

[0010] S3. Determine the integrated laser remelting repair process according to different damage types;

[0011] S4. According to the determined integrated laser remelting repair process, the integrated laser remelting repair device is turned on to perform multi-pass and multi-gradient laser remelting treatment on the damaged area of ​​the rail;

[0012] S5. Based on the synchronous detection results, the repair effect and evaluation are judged in real time to complete the on-site repair of the service rails.

[0013] Preferably, in step S1, the flaw detection of the damaged rail specifically refers to: using a crack detection module and a white layer detection module in the integrated laser remelting repair device to scan the surface damage of the service rail;

[0014] The damage types are divided into four categories. The first type of damage is single fatigue crack damage, and the fatigue crack depth is less than 0.5mm; the second type of damage is a single white layer of the rail; the third type of damage is the coexistence of fatigue cracks and the white layer of the rail, and the fatigue crack depth is less than 0.5mm; the fourth type of damage is fatigue cracks and the white layer of the rail, and the fatigue crack depth is greater than 0.5mm.

[0015] Preferably, in step S1, determining the first laser remelting process parameters according to the weight coefficients corresponding to different damage types specifically includes:

[0016] The relationship between crack depth and laser power weight coefficient satisfies:

[0017]

[0018] Where η P is the weight coefficient of crack depth to laser power, d c is the crack depth, i is the sample number, n is the total number of crack samples, d ci is the crack depth of the i-th crack sample, d cmax is the maximum crack depth in the cracked sample, d cmin is the minimum crack depth in the cracked sample;

[0019] The relationship between crack depth and scanning speed weight coefficient satisfies:

[0020]

[0021] Where η v is the weight coefficient of crack depth to scanning speed;

[0022] The relationship between the white layer thickness and the laser power weight coefficient satisfies:

[0023]

[0024] In the formula, λ P is the weight coefficient of white layer thickness to laser power, d w is the thickness of the white layer, is the average white layer thickness, d wmax is the maximum white layer thickness in the white layer sample, d wmin is the minimum white layer thickness in the white layer sample;

[0025] The relationship between the white layer thickness and the scanning speed weight coefficient satisfies:

[0026]

[0027] In the formula, λ v is the weight coefficient of white layer thickness to laser power;

[0028] The relationship between the first laser remelting power and the weight coefficient satisfies:

[0029] P = 1000·(η P +λ P )

[0030] Where P is the laser power;

[0031] The relationship between the first laser remelting scanning speed and the weight coefficient satisfies:

[0032] v = 45-20 (η v +λ v )

[0033] Where v is the scanning speed.

[0034] Preferably, in step S2, the integrated laser remelting repair device consists of an integrated bracket, a synchronous grinding device, a synchronous preheating device, a synchronous molten pool monitoring module, a laser head, a synchronous infrared module, a synchronous ultrasonic vibration module, a synchronous crack detection module and a synchronous white layer detection module.

[0035] Preferably, the synchronous grinding device, synchronous preheating device, laser head, synchronous infrared module, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module are all connected to the integrated bracket by bolts;

[0036] The integrated bracket is a cross-shaped structure, the bracket arm I of the integrated bracket is consistent with the direction of the laser scanning speed, and the bracket arm II is perpendicular to the direction of the laser scanning speed.

[0037] Preferably, the synchronous grinding device is installed at the front end of the support arm I, and the synchronous preheating device is installed between the synchronous grinding device and the laser head; the synchronous crack detection module is adjacent to the laser head, the synchronous white layer detection module is installed at the tail of the support arm I, the synchronous infrared module and the synchronous ultrasonic vibration module are both installed on the support arm II and located on both sides of the laser head, and the synchronous molten pool monitoring module is fixed to the upper part of the laser head by bolts;

[0038] The synchronous grinding device is composed of a hydraulic cylinder, a lifting module, a grinding motor and a grinding wheel; the grinding wheel is installed on the grinding motor, and the grinding motor is installed on the lifting module; the lifting module is connected to the hydraulic cylinder, and the hydraulic cylinder drives the lifting module to move up and down to adjust the grinding pressure;

[0039] The synchronous preheating device is composed of a heater and a heating coil; the heating coil is similar to the surface profile of the rail so as to preheat the rail.

[0040] Preferably, in step S3, the integrated laser remelting repair process determined according to different damage types specifically refers to: according to different damage types, for the first, second and third types of damage, there is no need to start the synchronous grinding device, only the laser head, synchronous preheating device, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module need to be turned on to perform integrated laser remelting repair; for the fourth type of damage, it is necessary to simultaneously turn on the synchronous grinding device, laser head, synchronous preheating device, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module to perform integrated laser remelting repair.

[0041] Preferably, the grinding wheel speed of the synchronous grinding device is 500-750r / min, and the synchronous grinding pressure is 400-600N; the preheating temperature of the synchronous preheating device is 200-300°C; the vibration frequency of the synchronous ultrasonic vibration module is 20-22kHz, and the vibration current of the synchronous ultrasonic vibration module is 0.2-0.6A.

[0042] Preferably, in step S4, the following steps are included:

[0043] S41, combining the relationship between temperature and laser remelting process parameters and using a synchronous infrared module and a synchronous molten pool monitoring module to monitor the temperature change during the repair process;

[0044] The relationship between temperature and laser remelting process parameters satisfies:

[0045]

[0046] Where A is the absorption coefficient, P is the laser power, k is the thermal conductivity, α is the thermal diffusivity, r is the distance from the moving coordinate origin to the calculation point, x is the distance from the laser irradiation point to the coordinate origin, and v is the scanning speed;

[0047] Then, the temperature curve during the repair process is monitored by the synchronous infrared module and the synchronous molten pool monitoring module, and the average temperature curve slope k during the laser remelting process is calculated. a ,If the slope is less than 0.15, it indicates that the heat accumulation is small during the laser remelting process and the process selection is appropriate;

[0048] The temperature curve slope calculation formula is:

[0049]

[0050] In the formula, k a is the slope, ΔT is the temperature change, and Δt is the remelting time;

[0051] S42, using multi-pass multi-gradient laser remelting treatment to complete integrated laser remelting repair;

[0052] The multi-pass and multi-pass gradient laser remelting process is a laser remelting method in which the laser power and the scanning speed change in a gradient, that is, after each laser remelting is completed, the initial power and the scanning speed of the next laser remelting are in a gradient decreasing trend compared with the initial power and the scanning speed of the previous laser remelting;

[0053] For the first type of damage, the initial power of laser remelting is 1200~1600W, and the scanning speed is 20~25mm / s; for the second type of damage, the initial power of laser remelting is 1100~1400W, and the scanning speed is 18~24mm / s; for the third type of damage, the initial power of laser remelting is 1500~2500W, and the scanning speed is 16~20mm / s; for the fourth type of damage, the initial power of laser remelting is 2000~3000W, and the scanning speed is 15~18mm / s; for the above four types of damage, the initial power of the second laser remelting is 600~1100W, and the scanning speed is 10~15mm / s, and the initial power of the third and above laser remelting is 400~600W, and the scanning speed is 6~10mm / s.

[0054] Preferably, in step S5, the following is specifically included:

[0055] First, the unserviced rails are inspected by using the synchronous crack detection module and the synchronous white layer detection module to establish an evaluation standard database;

[0056] Perform integrated laser remelting repair on-site for the serving rails, compare the output voltage of the repaired rails detected by the synchronous crack detection module and the synchronous white layer detection module with the data in the standard database for the evaluation of the test results of unserved rails, and evaluate the repair quality;

[0057] The relationship between the output voltage and the number of rail fatigue cracks is shown in the following formula:

[0058] y1=1.37x1+1.198

[0059] Where y1 is the output voltage of the synchronous crack detection module, and x1 is the crack depth;

[0060] The relationship between the output voltage and the thickness of the white layer on the inner surface of the rail is shown in the following formula:

[0061] y2=0.08x2+1.092

[0062] Where y2 is the output voltage of the synchronous white layer detection module, and x2 is the thickness of the white layer;

[0063] For the nondestructive testing results of cracks, when the output voltage y1>0.15V, it indicates that there are fatigue cracks on the rail surface;

[0064] Regarding the detection results of the white layer of the rail, when 1.2V<output voltage y2<0.3V, it indicates that there is a martensitic white layer on the inner surface of the rail; when the output voltage y2>0.3V, it is considered that there is no white layer on the rail.

[0065] The beneficial effects of the present invention are:

[0066] 1) The present invention first determines the damaged area and damage type of the rail surface through non-destructive testing technology, and adopts integrated laser remelting technology to repair the fatigue cracks and white layer of the rail surface, so that the pre-repair treatment, laser remelting repair and repair effect evaluation are carried out simultaneously. Under the premise of ensuring the quality of the repair area, the fatigue cracks and the white layer of the rail surface are eliminated, and a repaired surface with higher smoothness can be obtained. The process is simple, the repair effect is excellent, the cost is low, the repair efficiency is high, the effect is reliable, the maintenance cost of the rail is reduced, and the application range is wide.

[0067] 2) The method of the present invention simultaneously applies high-frequency ultrasonic vibration during laser remelting, which promotes the flow of the molten pool in the laser irradiation area, can promote the self-healing of fatigue cracks on the rail surface during laser remelting, further ensures that the fatigue cracks on the rail surface can be completely healed, and improves the repair efficiency.

[0068] 3) The method of the present invention can design and adjust the laser remelting repair process method according to the different service conditions and different damage states of the on-site rails, and according to the actual conditions such as the area of ​​the fatigue crack area and the degree of damage, so that the repair area has the microstructure and mechanical properties that meet the repair requirements, and can cope with damage of various sizes and types. The process is convenient, the repair efficiency is high, and the applicability is wide.

[0069] 4) In order to further reduce the impact of the repair process on the parent material, the present invention combines temperature monitoring and molten pool monitoring means to adjust the laser power of each remelting process to ensure that the width of each molten pool is the same and reduce heat input. At the same time, considering the characteristics of the rail material, a multi-pass multiple gradient laser remelting method is adopted, which can play a role in tempering the repair area, so that the martensitic white layer in the repair area is decomposed and forms a rail brown layer, which plays a role in eliminating the martensitic white layer, thereby ensuring the mechanical properties of the repaired rail. By adopting the repair method described in the present invention, no fatigue cracks are detected on the surface of the rail after repair, and the white layer of the rail on the inner surface of the rail is completely converted into a rail brown layer, completely eliminating the fatigue cracks and white layer of the rail generated during the service of the rail, and reducing the impact on the parent material by 40%. The multi-pass multiple gradient laser remelting repair method can repair the white layer of the rail that cannot be achieved by traditional methods, and has little impact on the parent material. It can quickly and accurately eliminate the fatigue cracks and white layer of the rail surface, reducing the maintenance cost of the rail during service. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the steps of the method of the present invention;

[0071] Figure 2 This is a schematic structural diagram of an integrated laser remelting repair device in Example 1 of the present invention;

[0072] Figure 3 This is a schematic diagram of the integrated bracket structure in Example 1 of the present invention;

[0073] Figure 4 This is a schematic structural diagram of a synchronous grinding device in Example 1 of the present invention;

[0074] Figure 5 This is a schematic diagram of the structure of the synchronous preheating device in Example 1 of the present invention;

[0075] Figure 6 Schematic diagram of the effect of ultrasonic vibration on the molten pool in Example 1 of the present invention, wherein (a) is a schematic diagram of the molten pool without ultrasonic auxiliary vibration, and (b) is a schematic diagram of the effect of ultrasonic vibration on the molten pool;

[0076] Figure 7 This is a schematic diagram of the nondestructive testing results of cracks and white layers of unserved rails in Example 2 of the present invention;

[0077] Figure 8 This is a schematic diagram of the nondestructive testing results of the damage form of the damaged rail before repair in Example 2 of the present invention;

[0078] Fig. 9 This is a schematic diagram of the nondestructive testing results of cracks and white layers of the damaged rail after repair in Example 2 of the present invention;

[0079] Fig.10 1 is a temperature curve of the repaired area under different laser remelting methods in Example 2 of the present invention, wherein (a) is when the laser power is not adjusted, and (b) is when the laser power is adjusted;

[0080] Fig.11 Schematic diagram of the distribution of fatigue cracks on the surface of a service rail before and after laser remelting in Example 2 of the present invention, wherein (a) is before laser remelting, and (b) is after laser remelting;

[0081] Fig.12 Schematic diagram of the microstructure morphology of the repair area under different laser remelting methods in Example 2 of the present invention, wherein (a) is a single laser remelting at a constant power, (b) is multiple laser remelting at a constant power, and (c) is multiple laser remelting at a variable power;

[0082] In the figure, 1-integrated bracket; 2-synchronous grinding device; 3-synchronous preheating device; 4-synchronous molten pool monitoring module; 5-laser head; 6-synchronous infrared module; 7-synchronous ultrasonic vibration module; 8-synchronous crack detection module; 9-synchronous white layer detection module; 10-bracket arm I; 11-bracket arm II; 12-hydraulic cylinder; 13-lifting module; 14-grinding motor; 15-grinding wheel; 16-heater; 17-heating coil. DETAILED DESCRIPTION

[0083] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0084] Example 1

[0085] An integrated laser remelting repair method for rail surface fatigue cracks and rail white layer comprises: pre-repair detection of service rail surface fatigue cracks and rail white layer, and integrated laser remelting treatment of pre-treatment, repair and detection of service rail surface fatigue cracks and rail white layer simultaneously, so as to achieve the repair of service rail surface fatigue cracks and rail white layer.

[0086] This embodiment uses U71Mn rail material, and the chemical composition of the rail is as follows: C0.65-0.75, Si0.15-0.35, Mn 1.10-1.40, P≤0.030, S≤0.030. Figure 1 As shown, the specific steps of the above method are as follows:

[0087] S1. Detect the damaged rails, determine the damage type and damage area on the surface of the service rails, and determine the first laser remelting process parameters according to the weight coefficients corresponding to different damage types;

[0088] S2. Install integrated laser remelting repair device;

[0089] S3. Determine the integrated laser remelting repair process according to different damage types;

[0090] S4. According to the determined integrated laser remelting repair process, the integrated laser remelting repair device is turned on to perform multi-pass and multi-gradient laser remelting treatment on the damaged area of ​​the rail;

[0091] S5. Based on the synchronous detection results, the repair effect and evaluation are judged in real time to complete the on-site repair of the service rails.

[0092] Furthermore, in step S1, the rail material is determined, the oxide layer on the rail surface is removed by sandpaper, and the rail surface is cleaned with anhydrous ethanol to remove dirt on the rail surface. The flaw detection of the damaged rail specifically refers to: using the crack detection module and the white layer detection module in the integrated laser remelting repair device to scan the surface damage of the service rail;

[0093] The damage types are divided into four categories. The first type of damage is a single fatigue crack damage (Type I mild damage), and the fatigue crack depth is less than 0.5mm; the second type of damage (Type II mild damage) is a single rail white layer; the third type of damage (Type I moderate damage) is the coexistence of fatigue cracks and rail white layer, and the fatigue crack depth is less than 0.5mm; the fourth type of damage (Type I severe damage) is fatigue cracks and rail white layer, and the fatigue crack depth is greater than 0.5mm.

[0094] Determining the first laser remelting process parameters according to the weight coefficients corresponding to different damage types specifically includes:

[0095] The relationship between crack depth and laser power weight coefficient satisfies:

[0096]

[0097] Where η P is the weight coefficient of crack depth to laser power, d c is the crack depth, i is the sample number, n is the total number of crack samples, d ci is the crack depth of the i-th crack sample, d cmax is the maximum crack depth in the cracked sample, d cmin is the minimum crack depth in the cracked sample;

[0098] The relationship between crack depth and scanning speed weight coefficient satisfies:

[0099]

[0100] Where η v is the weight coefficient of crack depth to scanning speed;

[0101] The relationship between the white layer thickness and the laser power weight coefficient satisfies:

[0102]

[0103] In the formula, λ P is the weight coefficient of white layer thickness to laser power, d w is the thickness of the white layer, is the average white layer thickness, d wmax is the maximum white layer thickness in the white layer sample, d wminis the minimum white layer thickness in the white layer sample;

[0104] The relationship between the white layer thickness and the scanning speed weight coefficient satisfies:

[0105]

[0106] In the formula, λ v is the weight coefficient of white layer thickness to laser power;

[0107] The relationship between the first laser remelting power and the weight coefficient satisfies:

[0108] P = 1000·(η P +λ P )

[0109] Where P is the laser power;

[0110] The relationship between the first laser remelting scanning speed and the weight coefficient satisfies:

[0111] v = 45-20 (η v +λ v )

[0112] Where v is the scanning speed.

[0113] Further, in step S2, the integrated laser remelting repair device is composed of an integrated bracket 1, a synchronous grinding device 2, a synchronous preheating device 3, a synchronous molten pool monitoring module 4, a laser head 5, a synchronous infrared module 6, a synchronous ultrasonic vibration module 7, a synchronous crack detection module 8 and a synchronous white layer detection module 9. Figure 2 shown.

[0114] The crack detection module adopts an alternating current magnetic field detection module (ACFM), and the white layer detection module adopts a magnetic Barkhausen noise detection module (MBN). The crack detection module and the white layer detection module are highly adjustable, which can improve the detection accuracy and adapt to different working conditions. The synchronous infrared module and the synchronous ultrasonic vibration module are angle-adjustable, which can adjust the shooting angle and the ultrasonic application angle, and improve the accuracy and versatility of the equipment.

[0115] The synchronous grinding device 2, the synchronous preheating device 3, the laser head 5, the synchronous infrared module 6, the synchronous ultrasonic vibration module 7, the synchronous crack detection module 8 and the synchronous white layer detection module 9 are all connected to the integrated bracket 1 by bolts. Figure 3 shown.

[0116] The integrated bracket 1 is a cross-shaped structure, the bracket arm Ⅰ10 of the integrated bracket 1 is consistent with the direction of the laser scanning speed, and the bracket arm Ⅱ11 is perpendicular to the direction of the laser scanning speed.

[0117] Furthermore, the synchronous grinding device 2 is installed at the front end of the support arm Ⅰ10, and the synchronous preheating device 3 is installed between the synchronous grinding device 2 and the laser head 5; the synchronous crack detection module 8 is adjacent to the laser head 5, and the synchronous white layer detection module 9 is installed at the rear of the support arm Ⅰ10. The synchronous infrared module 6 and the synchronous ultrasonic vibration module 7 are both installed on the support arm Ⅱ11 and located on both sides of the laser head 5. The synchronous molten pool monitoring module 4 is fixed to the upper part of the laser head 5 by bolts;

[0118] The synchronous grinding device 2 is composed of a hydraulic cylinder 12, a lifting module 13, a grinding motor 14 and a grinding wheel 15. Figure 4 As shown; the grinding wheel 15 is mounted on the grinding motor 14, and the grinding motor 14 is mounted on the lifting module 13; the lifting module 13 is connected to the hydraulic cylinder 12, and the hydraulic cylinder 12 drives the lifting module 13 to move up and down to adjust the grinding pressure.

[0119] The synchronous preheating device 3 is composed of a heater 16 and a heating coil 17. Figure 5 As shown; the heating coil 17 is similar to the surface profile of the rail in order to preheat the rail.

[0120] Further, in step S3, the integrated laser remelting repair process determined according to different damage types specifically refers to: according to different damage types, for the first, second and third types of damage, there is no need to start the synchronous grinding device, only the laser head, synchronous preheating device, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module need to be turned on for integrated laser remelting repair; for the fourth type of damage, it is necessary to simultaneously turn on the synchronous grinding device, laser head, synchronous preheating device, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module for integrated laser remelting repair.

[0121] The grinding wheel speed of the synchronous grinding device is 500-750r / min, and the synchronous grinding pressure is 400-600N; the preheating temperature of the synchronous preheating device is 200-300°C. The vibration frequency of the synchronous ultrasonic vibration module is 20-22kHz, and the vibration current of the synchronous ultrasonic vibration module is 0.2-0.6A. Figure 6 As shown, (a) is a schematic diagram of the molten pool without ultrasonic assisted vibration, and (b) is a schematic diagram of the influence of ultrasonic vibration on the molten pool. The stirring effect of ultrasonic vibration on the molten pool can promote the molten pool to flow more fully, which is beneficial to the self-healing of fatigue cracks.

[0122] Furthermore, in step S4, the following steps are included:

[0123] S41. Combine the relationship between temperature and laser remelting process parameters and use the synchronous infrared module (infrared thermal imager) and the synchronous molten pool monitoring module to monitor the temperature change during the repair process; use the infrared thermal imager as an auxiliary means of laser remelting process optimization. Based on the relationship between laser remelting process parameters and temperature, estimate the power of each subsequent laser remelting pass based on the power of the first laser remelting pass.

[0124] The relationship between temperature and laser remelting process parameters satisfies:

[0125]

[0126] Where A is the absorption coefficient, P is the laser power, k is the thermal conductivity, α is the thermal diffusivity, r is the distance from the moving coordinate origin to the calculation point, x is the distance from the laser irradiation point to the coordinate origin, and v is the scanning speed;

[0127] Then, the temperature curve during the repair process is monitored by the synchronous infrared module and the synchronous molten pool monitoring module, and the average temperature curve slope k during the laser remelting process is calculated. a ,If the slope is less than 0.15, it indicates that the heat accumulation is small during the laser remelting process and the process selection is appropriate;

[0128] The temperature curve slope calculation formula is:

[0129]

[0130] In the formula, k a is the slope, ΔT is the temperature change, and Δt is the remelting time;

[0131] S42, adjusting the laser power in real time according to the monitoring results, and completing the integrated laser remelting repair by using multi-pass multi-gradient laser remelting treatment;

[0132] The multi-pass and multi-pass gradient laser remelting process is a laser remelting method in which the laser power and the scanning speed change in a gradient, that is, after each laser remelting is completed, the initial power and the scanning speed of the next laser remelting are in a gradient decreasing trend compared with the initial power and the scanning speed of the previous laser remelting;

[0133] For the first type of damage, the initial power of laser remelting is 1200-1600W, and the scanning speed is 20-25mm / s; for the second type of damage, the initial power of laser remelting is 1100-1400W, and the scanning speed is 18-24mm / s; for the third type of damage, the initial power of laser remelting is 1500-2500W, and the scanning speed is 16-20mm / s; for the fourth type of damage, the initial power of laser remelting is 2000-3000W, and the scanning speed is 15-18mm / s; for the above four types of damage, the initial power of the second laser remelting is 600-1100W, and the scanning speed is 10-15mm / s, and the initial power of the third and above laser remelting is 400-600W, and the scanning speed is 6-10mm / s. After the initial power of each laser remelting is determined, the subsequent laser power is reduced step by step according to the feedback results of the molten pool monitoring.

[0134] Furthermore, in step S5, the following is specifically included:

[0135] First, the unserviced rails are inspected by using the synchronous crack detection module and the synchronous white layer detection module to establish an evaluation standard database;

[0136] The service rails are repaired by integrated laser remelting on site. The output voltage of the repaired rails detected by the synchronous crack detection module and the synchronous white layer detection module are compared with the data in the standard database of the unservice rail inspection results to evaluate the repair quality. If the results are similar, it means the repair is successful, otherwise it means the repair has failed.

[0137] The relationship between the output voltage and the number of rail fatigue cracks is shown in the following formula:

[0138] y1=1.37x1+1.198

[0139] Where y1 is the output voltage of the synchronous crack detection module, and x1 is the crack depth;

[0140] The relationship between the output voltage and the thickness of the white layer on the inner surface of the rail is shown in the following formula:

[0141] y2=0.08x2+1.092

[0142] Where y2 is the output voltage of the synchronous white layer detection module, and x2 is the thickness of the white layer;

[0143] For the nondestructive testing results of cracks, when the output voltage y1>0.15V, it indicates that there are fatigue cracks on the rail surface;

[0144] Regarding the detection results of the white layer of the rail, when 1.2V<output voltage y2<0.3V, it indicates that there is a martensitic white layer on the inner surface of the rail; when the output voltage y2>0.3V, it is considered that there is no white layer on the rail.

[0145] The nondestructive testing results were verified by color flaw detection and microscopic analysis of the rail profile: a sample block with a side length of 3 to 5 mm was cut using an electric spark wire cutting machine, and the sample was mounted using the cold mounting method and then polished. The sample surface was then corroded using a 4% nitric acid alcohol solution for 2 to 5 seconds, and the microstructure of the rail profile was analyzed using an ultra-depth of field optical microscope.

[0146] Example 2

[0147] This embodiment adopts the above-mentioned integrated laser remelting repair method for rail surface fatigue cracks and rail white layer, and the steps are as follows:

[0148] Step 1: Determine that the rail to be repaired is a U71Mn rail, test the unserviced U71Mn rail using non-destructive testing technology, and establish an evaluation standard database, such as Figure 7 As shown;

[0149] Step 2: Use nondestructive testing technology to determine the damage type and damage area of ​​the service rails. It is determined that the damage form of the rails is the coexistence of fatigue cracks and the white layer of the rails, and the crack depth is about 0.6mm. The damage type is the fourth type of damage, such as Figure 8 As shown;

[0150] Step 3: Install the integrated laser remelting device;

[0151] Step 4: According to the type of rail damage, determine that the integrated laser remelting repair process requires turning on the synchronous grinding device, laser head, synchronous preheating head, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module.

[0152] Step 5: Perform integrated laser remelting repair on the damaged area according to the process flow. The specific parameters of laser remelting are: the initial power of the first laser remelting is 2100W, and the scanning speed is 15mm / s; the initial power of the second laser remelting is 750W, and the scanning speed is 11mm / s; the initial power of the third laser remelting is 450W, and the scanning speed is 8mm / s. The results of synchronous non-destructive testing after repair are as follows Fig. 9 Compared with the traditional repair method, the laser remelting repair method of the present invention has less heat accumulation and the average temperature change during the repair process is not obvious. Fig.10 As shown, (a) is the unregulated laser power and (b) is the regulated laser power.

[0153] Step 6: Evaluate the repair effect of the damaged rail integrated laser remelting based on the detection results of the synchronous crack detection module and the synchronous white layer detection module;

[0154] Step 7: After the rails have cooled, use the color flaw detection technology to verify the nondestructive testing results of the rail cracks. The distribution of fatigue cracks on the surface of the repaired rails is as follows: Fig.11 As shown in the figure, (a) is before laser remelting, and (b) is after laser remelting. A sample with a side length of 3 mm was cut using an EDM wire cutting machine, polished and etched for 3 seconds, and the non-destructive testing results of the white layer of the repaired part were verified, as shown in the figure. Fig.12 As shown, (a) is a single laser remelting at a constant power, (b) is a multiple laser remelting at a constant power, and (c) is a multiple laser remelting at a variable power. It can be seen that compared with the traditional repair method, the method of the present invention completely eliminates the fatigue cracks and white layer of the rail generated during the service of the rail, and reduces the impact on the parent material by 40%.

[0155] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An integrated laser remelting repair method for rail surface fatigue cracks and rail white layer, characterized in that: The steps include: S1. Detect the damaged rails, determine the damage type and damage area on the surface of the service rails, and determine the first laser remelting process parameters according to the weight coefficients corresponding to different damage types; S2. Install integrated laser remelting repair device; S3. Determine the integrated laser remelting repair process according to different damage types; S4. According to the determined integrated laser remelting repair process, the integrated laser remelting repair device is turned on to perform multi-pass and multi-gradient laser remelting treatment on the damaged area of ​​the rail; S5. Based on the synchronous detection results, the repair effect and evaluation are judged in real time to complete the on-site repair of the service rails; In step S1, the flaw detection of the damaged rail specifically refers to: using the crack detection module and the white layer detection module in the integrated laser remelting repair device to scan the surface damage of the service rail; The damage types are divided into four categories. The first type of damage is a single fatigue crack damage with a fatigue crack depth of less than 0.5 mm. The second type of damage is a single rail white layer. The third type of damage is the coexistence of fatigue cracks and rail white layers with a fatigue crack depth of less than 0.5 mm. The fourth type of damage is fatigue cracks and rail white layers with a fatigue crack depth greater than 0.5 mm. In step S1, the first laser remelting process parameters are determined according to the weight coefficients corresponding to different damage types, specifically including: The relationship between crack depth and laser power weight coefficient satisfies: Where η P is the weight coefficient of crack depth to laser power, d c is the crack depth, i is the sample number, n is the total number of crack samples, d ci is the crack depth of the i-th sample, d cmax is the maximum crack depth in the cracked sample, d cmin is the minimum crack depth in the cracked sample; The relationship between crack depth and scanning speed weight coefficient satisfies: Where η v is the weight coefficient of crack depth to scanning speed; The relationship between the white layer thickness and the laser power weight coefficient satisfies: In the formula, λ P is the weight coefficient of white layer thickness to laser power, d w is the thickness of the white layer, is the average white layer thickness, d wmax is the maximum white layer thickness in the white layer sample, d wmin is the minimum white layer thickness in the white layer sample; The relationship between the white layer thickness and the scanning speed weight coefficient satisfies: In the formula, λ v is the weight coefficient of white layer thickness to laser power; The relationship between the first laser remelting power and the weight coefficient satisfies: P=1000·(η P +λ P ) Where P is the laser power; The relationship between the first laser remelting scanning speed and the weight coefficient satisfies: v=45-20(h v +λ v ) Where, v is the scanning speed; In step S4, the following steps are included: S41, combining the relationship between temperature and laser remelting process parameters and using a synchronous infrared module and a synchronous molten pool monitoring module to monitor the temperature change during the repair process; The relationship between temperature and laser remelting process parameters satisfies: Where A is the absorption coefficient, P is the laser power, k is the thermal conductivity, α is the thermal diffusivity, r is the distance from the moving coordinate origin to the calculation point, x is the distance from the laser irradiation point to the coordinate origin, and v is the scanning speed; Then, the temperature curve during the repair process is monitored by the synchronous infrared module and the synchronous molten pool monitoring module, and the average temperature curve slope k during the laser remelting process is calculated. a ,If the slope is less than 0.15, it indicates that the heat accumulation is small during the laser remelting process and the process selection is appropriate; The temperature curve slope calculation formula is: In the formula, k a is the slope, ΔT is the temperature change, and Δt is the remelting time; S42, using multi-pass multi-gradient laser remelting treatment to complete integrated laser remelting repair; The multi-pass and multi-pass gradient laser remelting process is a laser remelting method in which the laser power and the scanning speed change in a gradient, that is, after each laser remelting is completed, the initial power and the scanning speed of the next laser remelting are in a gradient decreasing trend compared with the initial power and the scanning speed of the previous laser remelting; For the first type of damage, the initial power of laser remelting is 1200-1600W, and the scanning speed is 20-25mm / s; for the second type of damage, the initial power of laser remelting is 1100-1400W, and the scanning speed is 18-24mm / s; for the third type of damage, the initial power of laser remelting is 1500-2500W, and the scanning speed is 16-20mm / s; for the fourth type of damage, the initial power of laser remelting is 2000-3000W, and the scanning speed is 15-18mm / s; for the above four types of damage, the initial power of the second laser remelting is 600-1100W, the scanning speed is 10-15mm / s, and the initial power of the third and above laser remelting is 400-600W, and the scanning speed is 6-10mm / s; In step S5, the specific steps include: First, the unserviced rails are inspected by using the synchronous crack detection module and the synchronous white layer detection module to establish an evaluation standard database; Perform integrated laser remelting repair on-site for the serving rails, compare the output voltage of the repaired rails detected by the synchronous crack detection module and the synchronous white layer detection module with the data in the standard database for the evaluation of the test results of unserved rails, and evaluate the repair quality; The relationship between the output voltage and the number of rail fatigue cracks is shown in the following formula: y1=1.37x1+1.198 Where y1 is the output voltage of the synchronous crack detection module, and x1 is the crack depth; The relationship between the output voltage and the thickness of the white layer on the inner surface of the rail is shown in the following formula: y2=0.08x2+1.092 Where y2 is the output voltage of the synchronous white layer detection module, and x2 is the thickness of the white layer; For the nondestructive testing results of cracks, when the output voltage y1>0.15V, it indicates that there are fatigue cracks on the rail surface; Regarding the detection results of the white layer of the rail, when 1.2V<output voltage y2<0.3V, it indicates that there is a martensitic white layer on the inner surface of the rail; when the output voltage y2>0.3V, it is considered that there is no white layer on the rail.

2. The integrated laser remelting repair method for rail surface fatigue cracks and rail white layer according to claim 1 is characterized in that: In step S2, the integrated laser remelting repair device is composed of an integrated bracket (1), a synchronous grinding device (2), a synchronous preheating device (3), a synchronous molten pool monitoring module (4), a laser head (5), a synchronous infrared module (6), a synchronous ultrasonic vibration module (7), a synchronous crack detection module (8) and a synchronous white layer detection module (9).

3. The integrated laser remelting repair method for rail surface fatigue cracks and rail white layer according to claim 2 is characterized in that: The synchronous grinding device (2), the synchronous preheating device (3), the laser head (5), the synchronous infrared module (6), the synchronous ultrasonic vibration module (7), the synchronous crack detection module (8) and the synchronous white layer detection module (9) are all connected to the integrated bracket (1) by bolts; The integrated bracket (1) is a cross-shaped structure; the bracket arm I (10) of the integrated bracket (1) is consistent with the direction of the laser scanning speed, and the bracket arm II (11) is perpendicular to the direction of the laser scanning speed.

4. The integrated laser remelting repair method for rail surface fatigue cracks and rail white layer according to claim 2 or 3, characterized in that: The synchronous grinding device (2) is installed at the front end of the support arm I (10), and the synchronous preheating device (3) is installed between the synchronous grinding device (2) and the laser head (5); the synchronous crack detection module (8) is adjacent to the laser head (5), the synchronous white layer detection module (9) is installed at the rear of the support arm I (10), the synchronous infrared module (6) and the synchronous ultrasonic vibration module (7) are both installed on the support arm II (11) and located on both sides of the laser head (5), and the synchronous molten pool monitoring module (4) is fixed to the upper part of the laser head (5) by bolts; The synchronous grinding device (2) is composed of a hydraulic cylinder (12), a lifting module (13), a grinding motor (14) and a grinding wheel (15); the grinding wheel (15) is mounted on the grinding motor (14), and the grinding motor (14) is mounted on the lifting module (13); the lifting module (13) is connected to the hydraulic cylinder (12), and the hydraulic cylinder (12) drives the lifting module (13) to move up and down to adjust the grinding pressure; The synchronous preheating device (3) is composed of a heater (16) and a heating coil (17); the heating coil (17) is similar in shape to the surface profile of the rail so as to preheat the rail.

5. The integrated laser remelting repair method for rail surface fatigue cracks and rail white layer according to claim 1 is characterized in that: In step S3, the integrated laser remelting repair process determined according to different damage types specifically refers to: according to different damage types, for the first, second and third types of damage, there is no need to start the synchronous grinding device, only the laser head, synchronous preheating device, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module need to be turned on for integrated laser remelting repair; for the fourth type of damage, it is necessary to simultaneously turn on the synchronous grinding device, laser head, synchronous preheating device, synchronous ultrasonic vibration module, synchronous crack detection module and synchronous white layer detection module for integrated laser remelting repair.

6. The integrated laser remelting repair method for rail surface fatigue cracks and rail white layer according to claim 5 is characterized in that: The grinding wheel speed of the synchronous grinding device is 500-750r / min, and the synchronous grinding pressure is 400-600N; the preheating temperature of the synchronous preheating device is 200-300°C; the vibration frequency of the synchronous ultrasonic vibration module is 20-22kHz, and the vibration current of the synchronous ultrasonic vibration module is 0.2-0.6A.

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