The NiCrBSi/40% ( mass fraction ) TiC composite coating was fabricated by the laser cladding with coaxial powder feeding method, and the microstructure, residual stress, microhardness, and wear resistance of the composite coating were analyzed. The results showed that the TiC particles and Ni-based structure of the composite coating can be refined by the laser remelting power with 800 W. The composite coatings were residual tensile stress with various laser remelting powers, and the residual tensile stress decreased with the increase of laser remelting power, the minimum residual tensile stress was 463 MPa, it can be obtained by the laser remelting power with 1 000 W. The microhardness and wear resistance of the composite coating first increased and then decreased with the increase of the laser remelting power. The best microhardness and wear mass loss was 65.8 HRC, 5.4 mg, respectively. Hence, the composite coating had perfect microhardness, and wear resistance when the coating was proceed by 800 W. The composite coating had obvious abrasive and adhesive wear coexisting in various laser remelting powers.

With the background of marine engineering emergency repair, the laser wire filling cladding experiment on Q345B low carbon steel plate was carried out by using hyperbaric welding test chamber to simulate water depth pressure under environmental pressures of 0.1 MPa, 0.2 MPa, and 0.3 MPa respectively. The laser cladding was compared and analyzed for exploring the feasibility of hyperbaric laser repair in 30 m water depth. The microstructure, chemical composition, and phase composition of the cladding layer were analyzed by optical microscope, XRD, and EDS. The hardness was tested by microhardness tester. The corrosion resistance of the cladding layer was studied by potentiodynamic polarization curve. The results show that the cladding layer is well formed under the pressure of 0.1 MPa, 0.2 MPa, and 0.3 MPa, and no obvious defects are found. The cladding layer is mainly composed of cladding zone, overlapping zone, phase transformation affected zone, fusion zone, and heat affected zone. The microstructure is mainly composed of ferrite, pearlite, and part of Widmanstatten structure. With the increase of environmental pressure, the size of ferrite and the number of Widmanstatten structure increases. With the influence of microstructure, the hardness variation trends are the same under the three environmental pressures, and the hardness of the cladding layer is better than that of the base metal. In 3.5% NaCl solution, the cladding layer exhibits obvious passivation behavior, and its corrosion resistance is better than that of the base metal. With the increase of environmental pressure, the corrosion resistance decreases. The experimental results show that laser wire filling cladding technology has good adaptability and feasibility for hyperbaric underwater repairment.

Laser cladding technology was used to cladding cobalt WC composite cladding layer on 304 stainless steel substrate. Micro-Vickers hardness tester and friction and wear tester were used to test and analyze the hardness and friction and wear properties of the cladding layer. WC content, laser power and scanning speed were selected as process parameters. Friction and wear, friction coefficient, and surface hardness were optimized. Then L12 (34) orthogonal experiment was designed, the experimental results were analyzed by range anlysis, then the optimal process parameters were obtained. The optimal process parameters are as follows: WC content is 30%, laser power is 4 500 W, scanning speed is 8 mm/s.

The effects of different focal spot diameters and powder particle sizes on the surface morphology, surface roughness, density, hardness, tensile strength, elongation, and microstructure of 316L stainless steel selective laser melting (SLM) forming parts were investigated to obtain higher quality 316L stainless steel SLM forming parts. The findings reveal that the particle size of the powder has a considerable impact on the SLM forming quality. Using 0-25 μm particles yielded superior surface roughness and elongation, which were 3.27 μm and 50.71%, respectively. The powders with 15-53 μm particle size had 238.82 HV and 748.16 MPa hardness and tensile strength, respectively. The combination of focal spot diameter and powder particle size has an impact on SLM forming quality. Surface roughness, hardness, tensile strength, and elongation of SLM with different powder particle sizes differed more from those of SLM with a focal spot diameter of 25 μm when compared to those of SLM with a focal spot diameter of 50 μm.

In order to realize the development and optimization of thick plate welding process for offshore wind power towers, the applicability of high-power laser welding technology in thick plate welding was explored based on laser blunt edge bottoming welding and narrow gap laser wire filling welding. The high-efficiency welding of the Q355ND low-alloy high-strength steel plate was completed, and the excellent welded joint of the 25 mm thick plate was obtained. The welding seam was mainly completed by 10 mm laser primer welding and 2 laser wire filling welding. The stacking height of each layer of filler wire welding were 7.2 mm and 7.8 mm respectively, and the width of the welding seam was about 3.8 mm. Optical microscope, microhardness tester and electrochemical workstation were used to analyze the microstructure, microhardness and corrosion resistance of the weld center, heat affected zone and base metal of laser backing welding, and narrow gap laser wire filler welding. The results show that the columnar grain structure is ferrite and a small amount of martensite in the center of the laser backing welding weld, and the microstructure of the heat affected zone is granular bainite and martensite. The microstructure is composed of acicular and massive ferrite, with a small amount of bainite and massive ferrite interphase distribution. The structure of the heat affected zone is lath martensite and bainite. The average hardness of the center of the backing weld is 360.5 HV, and the average hardness of the heat-affected zone of the wire filler weld is 349.1 HV. The corrosion resistance and pitting corrosion resistance of the weld area of the welded joint are excellent and higher than that of the base metal.

Fiber laser welding process of Nb521 (Nb-5W-2Mo-1Zr) niobium alloy was studied. The effect of different process parameters on the weld forming and macroscopic morphology was studied. The microstructure and mechanical properties of the welded joint were analyzed. The welding powerwas kept constant at 6 kW, and the welding speed and defocuing were changed respectively. The results show that with the increase of the welding speed, the collapse of the weld is improved, but the continuity of the weld is gradually worse. When the welding speed reaches a certain value, many discontinuous humps appear on the back of the weld. When defocusing is positive, the weld formation quality is poor. When defocusing is negative, the edge biting phenomenon of weld is improved. When the laser power is 6 kW, the welding speed is 45 mm/s and the defocusing is -1 mm, showing that the weld is well formed. Under the optimized process parameters, the weld is a coarse columnar grain structure perpendicular to the fusion line, and the base metal is a fine equiaxed grain structure. The average tensile strength of the welded joints is 481 MPa at room temperature, which is equivalent to that of the base metal. The welded joints fracture in the heat-affected zone and the base metal respectively, and all of them are ductile fractures. The microhardness of weld is higher than that of base metal and heat-affected zone. In the top and bottom part of the welded joint, the microhardness of the heat affected zone softened and is lower than that of the base metal. The microhardness of the middle heat affected zone of the welded joint is similar to that of the base metal.

The purpose of this work is to evaluate the sensing capabilities of a device based on a single mode fiber-thin core fiber-single mode fiber Mach-Zehnder interferometer for high temperature, curvature, and refractive index measurements. A femtosecond laser is used to produce a straight line on the entire thin core, and the fiber core is destroyed to increase the sensor′s sensitivity to the changes in external parameters. With a temperature sensitivity of 15.5 pm/℃ and a linear fitting of 0.988 in the range of temperature to 330 ℃, experimental results show that this sensor is well-suited for high-temperature measurement. Temperature sensitivity increases to 40.9 pm/℃ with a linear fitting of 0.996 in the temperature range of 330 ℃ to 580 ℃. The sensor also has a curvature sensitivity of 2.35 7 dB/m-1 with a linear fitting of 0.971 7 in the curvature range of 0.362 2 m-1 to 1.145 4 m-1, as well as a refractive index sensitivity of -24.327 nm/RIU with a linear fitting of 0.989 9 in the refractive index range of 1.333 0~1.365 2. This sensor is easy to make, extremely sturdy, compact, and capable of monitoring high temperatures, curvature, and refractive index.

AlCoCrFeNi high entropy alloy coating was prepared by laser cladding technology with H13 steel as the substrate under different laser energy density. The microstructure and microhardness of high entropy alloy coating were identified by optical microscope and microhardness tester, respectively. Moreover, the Weibull distribution characteristics of microhardness were further studied. Results show that the high entropy alloy coating prepared under the condition of low or high laser energy density is easy to produce metallurgical defects such as pores, cracks and coarsened microstructure. When the laser energy density is 7.23 kJ/cm2, the high entropy alloy coating with relatively smooth surface, few metallurgical defects and obvious refinement as well as homogenization of microstructure can be obtained. The microhardness of the high entropy alloy coating is significantly higher than that of the substrate. The microhardness value of the coating (540.7 HV) is the highest when the laser energy density is 7.23 kJ/cm2, which is about 140.3% higher than that of the substrate (225 HV). The microhardness Weibull modulus of the high entropy alloy coating prepared under the action of this laser energy density is two times than that of the high entropy alloy coating prepared under other laser energy densities, exhibiting the most concentrated microhardness and more evenly distributed microstructure.

The aluminum alloy body of the high-speed train needs to be textured before painting to improve the painting performance. The QCW 1 500 W fiber laser is used to carry out systematic experiments of laser roughen process on the 6061 aluminum alloy die steel surface. The influence of pulse width, laser power, and scanning speed were analyzed by single factor method. The roughness, corrosion resistance, and coating adhesion before and after texturing were measured. The results show that the laser parameters have significant impact on the textured shape and size. The corrosion rate of the surface after texturing can be reduced to 1/3 of that before texturing. The textured morphology with one side pit and one side convexity significantly improves the coating adhesion on the surface, which can reach more than 2 times that before texturing.

Aiming at the problems of heavy workload, low efficiency, and difficulty of complex ground object volume calculation in the process of traditional engineering operation, a volume calculation method based on lidar scanning technology is proposed in this paper. The point cloud data of space volume was obtained by UAV lidar scanning system, and the regular grid method was used to resample the point cloud and obtained the volume of space volume. Taking the vehicle as an example, collected the twice point cloud data of the ground and the vehicle, calculated the trajectory and coordinates, and the original data were pre-processed by using cloth simulation filter and resampled. The volume of surface vehicle was calculated by dividing regular grid and compared with the actual volume. The results showed that the volume errors were 6.989%, 1.937%, 0.190%, and 0.541% at the resampling spacing of 1 m, 0.5 m, 0.25 m, and 0.1 m, respectively. The calculation accuracy was the highest at 0.25 m resampling interval. The method has high efficiency and accuracy in calculating the volume of ground objects, and can realize the volume calculation of irregular ground objects, which provides a reference for related engineering applications.

3D LiDAR is an important part of the environment perception in the fields of unmanned driving and robots. There is a large number of noise data such as outliers in the point cloud data obtained by scanning the surrounding environment. Aiming at the problem of inaccurate filtering of noise points, this paper innovatively proposes an improved density clustering (DBSCAN) algorithm, which uses a grid network to find the grid with the highest density of point clouds, selects the initial points in it, and adjusts the clustering radius and parameters adaptively, and finally complete the clustering filtering. The experimental results show that the algorithm can effectively filter out outliers while retaining the original point cloud features, and the effect is better than other traditional filtering algorithms when the filtering time is basically unchanged.

In order to improve the accuracy of the traditional laser tracking interferometric measurement method and make the datum traceability more reliable, an optimization method of datum measurement in multiple attitudes is proposed in this paper. The method firstly constructs a multi-attitude datum layout on the basis of the traditional laser tracking interferometry, and collects measurement information in different datum directions by laser tracker, and then uses a weight-based measurement result optimization strategy to optimize the combination of measurement data, and then outputs the measurement results and performs error source analysis and uncertainty evaluation. The experimental analysis of the reference ruler based on this optimization scheme and the comparison with the higher accuracy CMM method, the En value is 0.1, which verifies the reasonableness of the uncertainty assessment, and the experimental comparison shows that the reference length output by the multi-attitude measurement optimization scheme is more reliable than the single attitude. The optimized method provides a new calibration scheme for realizing the measurement traceability of high-precision large-size datum rulers, which has a good practicality and certain guiding significance.

This paper mainly discusses the application of three-dimensional laser tracking technology in the installation of pressure vessels in nuclear power plants. In order to meet the high-precision requirements of the installation of the main system equipment in nuclear power plants, control the manufacturing error of the equipment body, reduce the impact of the equipment body deviation on the later installation, obtain the measurement data required for processing in advance, and shorten the on-site construction time, it is necessary to measure the body size of the pressure vessels before leaving the factory. This method is mainly based on the advantages of high accuracy and efficiency of 3D laser tracking technology in the measurement of large size workpieces. Through the analysis and research of key construction technologies such as instrument station, common point layout of transfer station, measurement feature point selection, data acquisition method, data processing method, etc., the size data of pressure vessel body is finally obtained. Comparing it with the relevant design data, the size data required for on-site installation is calculated, so as to achieve accurate measurement and efficient processing of the size data of the pressure vessel body, providing reliable technical support for subsequent on-site construction.

The traditional robot grinding of large heterogeneous workpieces is processed according to the unified teaching path of a single workpiece model. Due to the dimensional deviation between the actual workpiece and the theoretical model, there are problems such as grinding empty stroke or excessive removal. In this paper, the method of laser scanning the workpiece with moving line by robot is proposed to obtain the point cloud daa from different perspectives. The combination of SAC-IA rough registration based on FPFH and ICP fine registration is used for point cloud stitching. The KD-tree corresponding point distance algorithm is used to delete the redundant points in the overlapping area, and then the 3D model reconstruction is completed by the greedy projection algorithm based on Delaunay triangle growth principle, which can be provided to the robot for adaptive grinding. The blade with length of 600 mm and width of 200 mm is used for the experiment. Compared with ICP and NDT + ICP, the registration accuracy of this method is improved by 71.90% and 31.53% respectively. The size deviation between the reconstructed model and the actual workpiece is less than 0.15 mm.

As a relatively advanced detection method, lidar is widely used in the fields of unmanned driving, AGV, unmanned aerial vehicle, floor sweeping robot and so on. The mechanical scanning lidar is the core sensor of AGV and sweeper. In this paper, a lidar for robot is designed, which can scan the target 360 °. In order to reduce the overall size of the radar, the first coaxial structure is adopted. At the same time, the spherical cylindrical lens is used to compress the fast axis of the laser, and then the beam is collimated with the aspherical lens, so that the reflected light can obtain a small divergence angle. For the target with diffuse reflectance of 90%, the measurement distance is 60 m, and the half angle of laser emission of the emission system is ≤0.1 °.

Automotive paint is one of the common physical evidence at the scene of traffic accidents. Rapid inspection of automotive paint can provide clues and evidence for case investigation. Optical coherence tomography (OCT), which has the advantages of strong tomography, has significant advantages in vehicle paint inspection, but noise interference will weaken the signal. In order to improve the recognition ability, this paper collected A-scan signals of 102 vehicle paint samples from 6 different brands, and three kinds of fast Fourier transform filters and Hilbert transform filters were used to denoise the original data of vehicle paint samples. Two classification models, support vector machine and Fisher discriminant analysis, were constructed to identify different brands of paint samples. The filter with the best noise reduction effect and the optimal classification model were selected according to the recognition accuracy and overall classification accuracy of different brands of paint samples. Results show that the overall classification accuracy of sample data processed by Hilbert transform filter and fast Fourier transform low-pass filter is significantly improved, and Hilbert transform filter is better than fast Fourier transform filter. Moreover, the overall classification accuracy of Fisher discriminant analysis model is higher than that of support vector machine model. The Fisher discriminant functions based on Hilbert transform filter realize the accurate recognition of six brand car paint samples, and the overall classification accuracy reaches 100%. The preprocessing method based on filter can effectively suppress the noise interference in the sample data, and greatly improve the efficiency and ability of optical coherence tomography in examining vehicle paint evidence.

As a new generation of hydrodynamic laser system, Er, Cr: YSGG laser has the advantages of accurate cutting, efficient sterilization, anti-inflammatory, and promoting wound healing. Its wavelength is similar to the absorption peaks of water and hydroxyl in hydroxyapatite, which can be absorbed by the oral tissues well. This paper summarizes the operational principle, its application, and research progress of Er, Cr: YSGG laser in orthodontic therapy.