To improve the performance of W18Cr4V tool steel, Ni60A layer was obtained by laser cladding on its surface. The precipitates of Ni-based coating prepared at different pulse laser frequencies and their effects on wear resistance and impact were compared. Results show that coarser primary dendrites are formed and the eutectic zone is decreasing with increase of pulse frequency. When the pulse frequency is 80 Hz, the equiaxed crystal obtained basically shows the same size, and the number of particles in eutectic zone decreases obviously. When the pulse frequency is increased, the hardness of the coating continues to decrease, which results in higher wear rate. Moreover, furrows become fewer while the wear width continues to increase, and spalling and adhesion wear occur greatly. The impact toughness firstly increases and then decreases with rise of pulse frequency. The coating achieves the optimal impact resistance when the pulse frequency reaches 80 Hz. Under the action of pulsed laser, it is found that the small section size is similar to the grain size. It is inferred that the intergranular fracture appears with fewer stress concentration points.

In order to improve the wear resistance of 34CrNiMo6 steel used for cutting tools, the WC/Ti-Al coating was prepared on the surface of 34CrNiMo6 steel by laser cladding. The effects of Al content on its microstructure and tribological properties were analyzed by experimental testing methods. Results show that the cladding layer with better structure is obtained by gradually increasing Al content, while the surface quality of cladding layer decreases when Al content is too high. The bonding phase composed of Al phase and Ti-Al phase is formed by adding Al cladding layer, and the composite cladding layer composed of WC, TiC and Al2O3 is obtained by in-situ growth. After adding 20%Al, the cladding layer with dense structure is prepared, and the uniform grain size is obtained, which formed a good metallurgical bonding with the matrix. The hardness of Al-free cladding layer is lower than that of HSS substrate. When the Al content reaches 20%, the hardness of cladding layer is the maximum, and the hardness of each position is similar. Lower friction coefficient is obtained by adding Al into the cladding layer. With the increasing of Al content, the wear of the cladding layer decreases and then increases, and the microstructure of the cladding layer becomes denser, and a certain degree of plastic flow occurs and chip chips are generated.

To solve the problem of repairing and remanufacturing for the mechanical parts, the new process method “laser-resistance composite wire cladding” is used for process research in this study. The laser-resistance composite cladding experiments of multi-channel 630 stainless steel wire under different laser powers were carried out on the surface of No.45 steel. The macro morphology, microstructure, microhardness, and wear resistance of the multi-channel repair layer under different laser powers were compared and analyzed. Results show that with the increase of laser power, the surface smoothness of the repaired layer is higher, and the bonding layer with the substrate gradually becomes smooth. Meanwhile, there is an obvious boundary between the repaired layer and the bonding layer. The grain size of the repaired layer gradually refined is increased with the increasing of laser power. Furthermore, the microhardness of the repaired layer gradually is increased while increasing the laser power. When the laser power is 3 000 W, the average microhardness is 1.16 times higher than that when the laser power is 1 800 W. Moreover, the wear resistance of the repaired layer is the highest when the laser power is 3 000 W, where the primary wear forms are abrasive wear and slight adhesive wear.

In response to the repair requirements of U75V rails, a laser wire-filled cladding process test was carried out, and the cladding layer formed under the optimized process parameters was tempered and heat treated. By comparing the properties of the base material and the rail welding repair requirements, the effect of tempering on the microstructure and properties of the cladding layer was investigated. Results show that after tempering at 300 ℃, the heat-affected zone is mainly tempered martensite, the hardness does not change significantly, and the hardness gradually increases near the fusion line in the cladding zone. After tempering at 600 ℃, the overall wear resistance of the cladding layer is weaker than that of the steel rail, and the difference between the average hardness of the cladding zone and the heat-affected zone and the base metal is less than 15%. The heat-affected zone is mainly tempered sorbite, and its wear amount and friction coefficient in the wear resistance test are smaller than the rest of the cladding layer. The tensile strength and elongation of the cladding area after tempering at 600 ℃ are basically the same as those of the base material, which meets the corresponding performance requirements for rail repair.

The outer cylinder of aircraft landing gear is often subject to complex alternating pressure and prone to different degrees of failure, so it is of great significance to explore the rapid repair process on site. In this paper, 15-5PH alloy powder was used to repair the inner surface, outer surface and hole structure of aircraft landing gear outer cylinder by laser cladding, and the mechanical properties of the repaired cladding layer were tested. Results show that when the laser power P=1 400 W, scanning speed Vs=0.36 m/min, powder feeding speed Vf=1.4 rad / min and overlap coefficient f=40%, the ideal cladding layer can be obtained. The microstructure of cladding layer is dense, the composition is uniform, and there is no obvious macro-segregation. Good metallurgical bonding can be obtained between the layer and the matrix interface. The imaging agent is used to detect the repair area of the outer cylinder, and there is no obvious defect in the repair area. The tensile strength, yield strength, elongation and impact toughness of the cladding layer all exceed 90% of the performance of the matrix, which meets the requirements of repairing applications.

In order to improve the accuracy of numerical simulation of laser cladding repairing aero-engine variable-curvature failure blades and to identify errors in a timely and accurate manner, a method of loading area in the repair process based on dynamic boundary conditions is proposed. Firstly, a blade finite element model with a higher degree of restoration was established based on the variable-curvature failed blade to ensure that the model can reflect the true state of the variable-curvature failed blade during repair. Secondly, the proposed method was used to repair the variable-curvature failure by laser cladding. The thermal-stress field simulation calculation of the blade is used to extract real-time working condition data to realize the quantitative study of the influence of process parameters on the results. Finally, the influence of laser parameters and process parameters on the temperature field and stress field of the variable curvature blade is analyzed separately. Results show that when the values before and after the laser scanning speed increase proportionally, the difference between the melt pool temperature before and after the variable curvature blade is around 500 ℃. The appropriate cooling time between passes can greatly reduce the melt pool temperature of the variable curvature blade, but it has small impact on the stress field.

The effects of different laser power and scanning speed on the surface morphology and roughness of single track CuSn10 thin-walled side surface fabricated by SLM were studied in this paper. Moreover, the optimized manufacturing process was obtained. Double track CuSn10 thin-walled parts were fabricated by the above process, and the effects of different scanning space on the surface roughness of the two forming sides were studied. Taking the above scanning space as the contour offset, 0.5 mm thin-walled parts were fabricated with two scanning strategies of long linear scanning filling and short linear scanning filling. Results show that when the laser power is 195 W and the scanning speed is 550 mm/s, the minimum average roughness of single track thin-walled parts is 2.3 μm±0.2 μm. With the increase of scanning space, the roughness of the second forming surface decreases. When the scanning space is 120 μm, 140 μm, 160 μm, the interaction between the two parallel melting is low, and the effect on the roughness is small. The short linear scanning filling has a lower surface roughness value than the long linear scanning filling. When the offset is 160 μm, the minimum average roughness value of the side surface of the thin-walled part manufactured by short linear scanning filling is 2.27 μm±0.4 μm.

AlSi7Cu2Mg was selected as the test substrate, nano TiN particles and sub-micron SiC were used as reinforcement, and the TiN/SiC aluminum composite was prepared by SLM treatment. The microstructure and mechanical properties of the material matrix were analyzed. Results show that a large number of micropores are formed on the surface of AlSi7Cu2Mg sample and the spheroidization of tissue took place. However, 3.5%SiC/AlSi7Cu2Mg and 1.5%TiN/3.5%SiC/AlSi7Cu2Mg form smooth surface structure. It is found that there are four phases of Si, Al, Mg2Si and SiC, and only a small amount of Al4C3 is formed. Fine grains are formed in 1.5%TiN/3.5%SiC/AlSi7Cu2Mg, and obviously different grain orientation and configuration are formed. There are a large number of small equiaxed grains with average size of 4.15 μm and maximum size of 13 μm. The tensile strength and elongation of 1.5%TiN/3.5%SiC/AlSi7Cu2Mg samples are 486 MPa and 9.8%, respectively. Compared with the AlSi7Cu2Mg samples prepared by SLM process, the tensile strength and elongation of 1.5%TiN/3.5%SiC/AlSi7Cu2Mg samples are nearly 20% higher than those prepared by SLM process, and obvious river grain is formed at the fracture site.

The TiN-reinforced TiN/FGH4097 alloy was prepared by selective laser melting (SLM) method. The microstructure and mechanical properties of the alloy were tested by heat treatment with different aging processes. Results show that a large number of fish scales are formed on the surface of formed FGH4097 alloy. The dispersed TiN particles were formed in the formed TiN/FGH4097 alloy, which achieved good bonding property with the matrix and formed shorter dendrites. After solid-solution aging (SA) treatment, Laves phase solution occurred in the matrix, and a large number of fine needle tissue and δ phase were precipitated. After TiN/FGH4097 homogenization solid-solution aging (HSA) treatment, a large number of needle-shaped δ phases were generated in the matrix, and a significant Characteristic peak of Ti2N was formed. The hardness of TiN/FGH4097 sample increases by 38 HV. Double aging (DA) heat treatment results in a significant increase in hardness. The tensile strength of TiN/FGH4097 specimen increases by 75 MPa, while the elongation decreases. The shape alloy formed dimples with larger size and depth, and the HSA heat treatment formed smaller dimples. This study has great theoretical reference significance for further optimization of SLM additive manufacturing of nickel-based superalloy.

Three kinds of micro textures were processed on the rake face of cemented carbide tools on NC lathe by 532 nm femtosecond laser. Based on the interaction mechanism between laser and material, the formation mechanism of micro texture of cemented carbide processed by green laser is clarified, and its friction, wear and cutting properties under lubrication are tested. Results show that for all laser textured samples, all of the texture depth is about 18 μm±1.8 μm. The friction coefficient of cemented carbide on the original surface firstly increases and then decreases, with an average of 0.68, while the average friction coefficients of cemented carbide with groove, wide mesh and narrow mesh are 0.55, 0.45, 0.36, respectively. The cemented carbide with narrow mesh texture has the strongest wear resistance under lubrication. At the same time, the narrow mesh texture morphology of the rake face after cutting is the most complete, and the cutting depth is the largest, which is about 18.5 μm±0.9 μm.

Four different micro textures were processed by 523 nm femtosecond laser on the diamond tool of NC lathe. Based on the transient double temperature model, the thermal erosion mechanism of femtosecond laser processing diamond rake face (100)was clarified. Results show that the residual stress of laser processed mesh texture is compressive stress, and the wide mesh texture and narrow mesh texture are -28 MPa±8 MPa and -43 MPa±9 MPa, respectively. Under dry friction conditions, the friction coefficients of all micro textured surfaces increase, and the worn surface has serious adhesive wear and poor wear morphology. However, the friction coefficient decreases significantly under lubrication condition, and the friction forms are mainly abrasive wear and sliding wear. The ability of grid texture to store lubricating oil is stronger than groove texture, and its anti-wear ability is the strongest.

When the current method is used to identify lidar hardware failure data, the characteristics of Lidar echo data under different weather conditions are not analyzed and compared, which leads to the problems of high false positive rate, low recall rate and harmonic index. A method for identifying lidar hardware fault data based on data mining technology is proposed. Firstly, the combined method of EMD and wavelet threshold is used to remove clutter in the lidar echo data, and then the denoised data is clustered by fuzzy C-means clustering. Moreover, its data characteristics are mined, and finally the characteristic probability distribution model of normal echo signal data and fault echo signal data under different weather influences is developed to complete the identification of fault data. Experimental results show that the proposed method can effectively reduce the misjudgment rate and improve the recall rate and the coordination index.

In view of the influence of aerosol on off-axis laser beam guidance, based on Mie scattering theory, the scattering characteristics of atmospheric molecules and aerosol particles are analyzed, and an off-axis laser detection model is established. By studying the transmission characteristics of 1.064 μm laser in low-altitude atmosphere, the correlation between three aerosol types and phase function, direct radiation and scattered radiation is simulated and analyzed. Results show that aerosol type is an important factor affecting the off-axis laser detection results. Under the influence of aerosol, the maximum attenuation of direct radiation energy is 60%. Under the condition of constant aerosol type, relative humidity and detector, the irradiance intensity in short distance (1 km, 3 km) decreases rapidly, while in long distance (8 km), it can be received by the detector at a further off-axis distance, and the final intensity approaches 1 W/m2. When the off-axis detection angle is different, the smaller scattering angle will propagate to farther off-axis distance, and the larger scattering angle will receive more irradiance energy.

In order to detect and locate crack defects in aluminum plate, in this paper, COMSOL is used to establish the internal crack defect model of aluminum plate and analyze the action mechanism between laser ultrasonic and defects with different buried depths. Compared with transverse waves (S waves) and longitudinal waves (L waves), surface waves (R waves) have obvious interaction with near-surface defects with a buried depth of less than 1 mm. Therefore, R wave is also more suitable for detection in the buried depth range, whereas S wave and L wave are more suitable for detecting internal defects with buried depth greater than 1 mm. This paper proposes methods for optimizing positioning and quantitative length measurement. The amplitude and peak position of transmitted surface wave (TR) can be used to quantify the buried depth and length of near-surface defects. The accuracy of crack length quantification can be improved by using reflected surface waves (RR) to assist the quantitative calculation of crack length. In addition, according to the analysis of the acoustic wave path, this paper proposes that the arrival time of the reflected wave (2S) and the creeping wave along the crack (SCS) at the crack can be used to quantitatively estimate the buried depth of cracks with greater than 1mm, and the feasibility was verified by simulation. The method proposed in this paper lays a theoretical foundation for real-time detection of defects in additive workpieces.

Based on the theory of heat conduction, a two-dimensional axisymmetric thermal model was established for the temperature field characteristics of aluminum alloy irradiated by a combination of millisecond pulse and continuous laser. The process of laser irradiating aluminum alloy was numerically simulated by finite element method, and the temperature field distribution and variation rule of laser irradiating aluminum alloy surface under different loading time interval and different spot radius were obtained. The results show that the temperature of target center increases with the increase of laser loading time interval. At the end of the pulse laser irradiation period, the temperature of the target radiated by the continuous laser will increase significantly. The temperature field of aluminum alloy irradiated by combined laser is mainly determined by continuous laser, but the temperature of the center point of the target can be increased appropriately if appropriate pulse laser parameters are selected, especially when the power density of pulse laser is greater than 8.8×104 W/cm2.

The existing intrusion attack source location methods have low location accuracy and laser communication network attack detection accuracy because the database is not perfect. Therefore, a laser communication network intrusion attack source location method based on knowledge map is proposed. The knowledge map of laser communication network is constructed, and the characteristics of laser communication network are analyzed. The attack detection of network samples is carried out by using hierarchical clustering algorithm, including hierarchical clustering algorithm, iterative clustering algorithm, optimal scheme selection, and network attack detection. The abnormal data in laser communication network is obtained. According to the abnormal data detection results, the abnormal data location is preliminarily located by trilateral positioning method. Finally, the intrusion source location of laser communication network is realized by improving particle swarm optimization algorithm. Experimental results show that the proposed method can accurately locate the coordinate position of the attack source, and the laser communication network attack detection accuracy is high.

In the current application of 3D laser projection technology, the standard processing of projection coordinates is ignored and the full-angle laser scanning on the surface cannot be realized, resulting in poor fusion of laser point cloud data and large scene reconstruction error. Therefore, a 3D reconstruction model of interior scene based on 3D laser projection application optimization is constructed. A voxelized raster sampling algorithm is constructed based on point cloud surface eigenvalues and split cells to denoise laser point cloud data. Using the world coordinate system to normalize the 3D laser projection coordinates, the 3D laser projection model is established and the optimal projection rotation angle is obtained. The 3D model of indoor scene is reconstructed by using calibration plate and rotation angle stitching fusion point cloud data. The experimental results show that the proposed method has a good indoor scene reconstruction effect under the application of 3D laser projection, the error of laser point cloud data is small, the peak signal-to-noise ratio is high, and the performance of point cloud can be better fused.

Samples to be scanned are gradually showing diversified development trends. In order to further improve the accuracy of fluorescence signal acquisition, an infrared fluorescence scanning system is designed with embedded technology as the basic environment. Using power supply circuit, LED lamp control circuit, motor control circuit, AD conversion circuit, network module, USB module, serial port module and other peripheral module circuits, the circuit architecture of the backplane is built. S3C2440 ARM processor is selected as the system processor. Through a series of processes such as three-axis stepping motor drive, current-voltage signal conversion, signal amplification and signal noise removal, the signal acquisition circuit module is improved. Based on the infrared fluorescence scanning requirements, the scanning system software functions are composed of system self-checking, paper strip detection, record search, system setting and other modules. Ring buffer queues are constructed at the upper and lower computers of the scanning system to realize the parallel operation of each module. After setting the scanning system parameters, the performance of AD conversion circuit, signal amplification circuit and double ring buffer queue of the system are evaluated. According to the experimental results, it can be seen that the system has certain validity and feasibility, and the system accuracy and transmission rate are relatively ideal.

The off-axis negative-branch unstable resonator has been adopted in high power diffusion-cooled RF-excited slab CO2 laser, the output beam of this resonator is a simple astigmatic beam. The beam shaping system must be applied before it could be used for laser processing. When the mirrors radius of curvature increased within a certain range, the power extraction efficiency and the anti-misalignment of the non-confocal unstable resonator with parabolic mirrors is increased compared with the confocal one. The beam shaping system must be redesigned as a result of the propagation characteristics of the output beam for the non-confocal unstable resonator with parabolic mirrors are different from the confocal one. In this paper, the beam shaping system of non-confocal unstable resonator with parabolic mirrors is investigated when the radius of curvature of the cavity mirrors increased by 2 mm. The location of the spatial filter is determined, and the radius of curvature of the cylindrical mirror is adjusted. Finally, the mode similar to fundamental Gaussian beam is obtained whose beam propagation factors are M2=1.09 in the unstable direction and M2=1.08 in the waveguide direction.

Donut mode with annular shaped light distribution has the ability to carry the orbital angular momentum corresponding to the optical axis, which has attracted wide attention in scientific research, laser processing and other fields. In this paper, a diffractive optical element and a spiral phase plate have been used respectively to convert the mode similar to fundamental Gaussian beam into the Donut mode beam, while the propagation characteristics, beam quality, and efficiency of beam shaping for the shaped beam are analyzed. The results show that near-field propagation characteristics of the shaped beam are unacceptable when use the diffractive optical element which similar to the ring-shaped concave mirror structure designed by the G-S algorithm. However, better near-field propagation characteristics of the Donut mode beam is finally obtained through the spiral phase plate, and the far-field characteristics of Donut mode beam are relatively ideal. The efficiency of beam shaping is 97.1%, and the beam quality M2 factor is 2.29.