In order to improve the quality of laser welding process of 304 stainless steel, a laser welding system with ultrasonic was designed to study the effect of ultrasonic frequency on weld properties. The ultrasonic sound field model was established, and the ultrasonic characteristic frequency and sound pressure distribution were simulated based on COMSOL. Through the real-time monitoring system, the effect of ultrasonic on molten pool area, molten pool flow rate and metal vapor pressure was obtained. Under the condition of different ultrasonic excitation frequencies, the changes of weld microstructure, wear morphology, microhardness and oxidation were studied. The results show that ultrasonic vibration can significantly improve the wear resistance, hardness and corrosion resistance of 304 stainless steel weld. The ultrasonic energy efficiency under the second-order characteristic frequency is higher, the flow rate of molten pool is low and the joint quality is better.

The effects of welding wire with and without Er on the forming, microstructure and tensile properties of the 2524 aluminum alloy in the state of de-oxide-film and de-coated-aluminum-layer were investigated by laser butt welding. The results showed that, there is an aluminum clad layer with a thickness of about 30 μm on the surface of the 2524 aluminum alloy, and there is an oxide film with a thickness of about 4 μm on the surface of aluminum clad layer; under the same surface state, the weld width of the welding wire with Er is larger than that of the welding wire without Er, the forming coefficient is less than that of the welding wire without Er, the average spacing (Ed) of equiaxed dendrites and the average spacing (Cd) of columnar dendrites in the weld center and near the fusion line of the welding wire with Er are less than that of the welding wire without Er, and the width of the maximum solute poor zone near the grain boundary of the fusion zone is less than that of the welding wire without Er; In the state of de-oxide-film and de-coated-aluminum-layer, the fractures of the samples with and without Er are located in the fusion zone of the welded joint, the tensile strength and elongation of the samples with Er are higher than those without Er, and the strength and plasticity of the samples with de-coated-aluminum-layer state are better under the same welding wire conditions. This is mainly related to the existence of micron primary Al3Er phase which can refine grains, and nano Al3Er phase which can strengthen in welding wire with Er.

The effects of laser power, welding current and optical wire distance on the relative melting rate and the relationship between the joint penetration depth and the melting rate under different conditions were studied by using laser-MIG composite welding method. The experimental results show that the optical distance has the greatest influence on the relative melting rate. When no parameter is considered, the relationship between the joint penetration depth and the relative melting rate is disordered. Under the same laser power condition, greater welding penetration means greater relative melting rate can be obtained.

The absorption rate of red copper to fiber laser with wavelength was low, only was 4%, required of high power laser to weld, high power was easy to produce defects such as pores. In this paper, the blue light diode and fiber laser were used to weld the red copper with a thickness of 3 mm, and the welding process parameters were optimized. The cross section and micro-structure of fiber laser welding, blue light diode laser welding, blue light diode laser and fiber laser composite welding were compared and analyzed, and the micro hardness of the welds was tested. When the diode laser was 1 000 W, the fiber laser was 2 000 W, and the welding speed was 10 mm/s, the 3 mm copper can be welded, and the tensile strength of the weld reached to 182 MPa, which was 60% of the tensile strength of the base metal, and there was no porosity in the welds. The composite optical fiber laser welding and blue diode laser welding, used the high absorption rate of copper in wavelength of 450 nm, the total input power was low, which can maintain the stability of the molten pool, and can improve the fluidity of molten pool. No pores would be generated, and the 3 mm thick was penetration welding.

In order to study the influence of different heat treatment processes on the microstructure and mechanical properties of 18Ni300 stainless steel manufactured by laser selective melting, Aging, solid solution + aging treatments were performed on the samples respectively. The phases, microstructure and mechanical properties of different heat-treated samples were tested by X-ray diffractometer, metallographic microscope, scanning electron microscope, tensile testing machine and hardness tester, etc.. The results show that the content of retained austenite in printed and aged samples is slightly higher than solid solution + aged state. Comparing with printed state, the laser melting pool boundary of aged sample becomes shallower, and the microstructure is mainly small lath-like horses. The boundary of the laser melting pool of the aged sample becomes shallower, and the structure is mainly fine lath martensite, and there are more fine Ni3Ti and other precipitates dispersed in the martensite boundary. The laser melting pool boundary of solid solution + aging state sample can no longer be distinguished, the microstructure is uniform and fine lath martensite, and the precipitated phases are distributed at grain boundary, martensite lath boundary, and dislocation interlacing; Aging and solid solution + aging treatment significantly improve the strength and hardness of samples, but reduce the toughness and plasticity. The printed tensile fracture has obvious necking, there are a large number of large dimples and a certain amount of holes in the fracture fiber area. There are obvious signs of tearing at the edge of dimples. The fracture form is ductile fracture. After aging, solution + aging treatment, it is mainly shallow dimples, and the small isometric dimples of shear lip are significantly smaller than printed state.

In this paper, diamond turning of monocrystalline silicon under laser-assisted conditions is taken as the object, the temperature field model of laser-assisted heating is established, and the temperature field distribution of monocrystalline silicon surface and sub-surface is simulated by COMSOL software. The experimental results of temperature measurement and temperature field simulation of monocrystalline silicon with laser assisted heating were compared and verified. Finally, the experiments of laser-assisted diamond turning with monocrystal silicon were carried out to study the effects of laser power and spindle speed on cutting force, surface roughness, chip morphology and tool wear under the conditions of constant feed and backdraft. The results show that the surface temperature reaches the brittle-plastic transition temperature when the spindle speed is 2 000 r/min, the laser power is 32-40 W, and the sub-surface heat transfer depth exceeds 6.8 μm above 500 ℃. The effect of laser softening materials is affected by both power and spindle speed. With the increase of laser power and the decrease of spindle speed, the machining performance and surface quality of monocrystalline silicon are improved and tool wear is reduced. However, the surface roughness of monocrystalline silicon increases greatly due to the thermal damage caused by laser power up to 48 W. The minimum surface roughness of monocrystal silicon can reach 3 nm under the conditions of 40 W laser power and 2 000 r/min spindle speed.

This paper studied the effect of initial plane of focal spot in femtosecond laser drilling of inclined holes on SiC/SiC composite. A set of drilling experiments has been conducted on SiC/SiC specimen with 4 mm thickness and approximate 1.5 mm using beam concentric scanning mode. The effect of initial focal plane on entry size and hole taper have been analyzed. The results show that the entry size will be increased and hole taper will be decreased in case of initial focal plane is put at leading edge. This is because machining time was longer and greater volume material was removed, compared with a lower position of focal plane. For the drilling of inclined holes, the deposition of slag can be found at the lower edge of the entry because these slag is tend to be carried away from that area. In case of 45° inclined hole drilling, relatively large cracks can be found at the lower edge of the entry, this is because the exhaust intensity of the heat and slag is relatively high for large inclined hole machining. In addition, the taper angle of the two sides of the inclined hole is different with drilling angle. This study provides useful results for the future research of fs laser drilling of SiC/SiC.

In order to optimize the optimal combination screening method of laser processing parameters in the early stage of laser processing surface bionic texture of reciprocating pump plunger, a laser engraving texture experiment on the surface of the plunger was carried out. Based on the experimental data, a BP artificial neural network prediction model between laser parameters and texture volume was established and successfully trained. The results show that the effects of laser power, travel speed, and scanning pass on the texture volume are mutually independent and equivalently related. Also, the average prediction accuracy of the three-layer BP neural network model with 4 neurons in the hidden layer is about 92%. Based on the forward prediction of laser parameters to texture volume, this research is of great significance for the industrial batch application of bionic texture technology on the surface of fracturing pump plunger.

Nanosecond laser drilling micro-holes are widely used in industry. However, the existence of recasting layer reduces the service performance and life of micropores. How to reduce recasting layer thickness and improve hole wall finish remains to be further studied. In this paper, the Ni-base superalloy is taken as the research object. By comparing with the ultrasonic assisted nanosecond laser drilling, the influence of ultrasonic assisted water on the micropore geometry, the roughness of the hole wall and the recasting layer is analyzed. The results show that for the through holes made by nanosecond laser, the ultrasonic assisted method can reduce the roundness error of the outlet hole, increase the taper, reduce the roughness of the hole wall, reduce the recasting layer of the hole wall, and improve the quality of the micro-hole. However, under experimental conditions, water-based ultrasonic assistance has little influence on the geometrical size and hole wall morphology of the blind hole. It can be seen that the quality of nanosecond laser hole making can be improved to a certain extent with the help of ultrasound.

In order to improve the surface properties of E690 steel used for automobile plate, the surface was strengthened by nanosecond laser shock. The effects of nanosecond laser shock times on its hardness and fatigue properties were analyzed. The action mechanism of E690 steel subjected to high energy pulse laser was studied, which provided a reference value for improving the anti-fatigue performance of E690 steel aeronautical components. The results show that the surface hardness of E690 steel can be increased and the residual compressive stress can be formed by increasing the nanosecond laser shock times. After 3 times of nanosecond laser shock, the saturated plastic deformation is reached. With the increase of the stress intensity factor (SIF) amplitude, the crack growth rate of the specimens subjected to multiple shocks decreased significantly. With the increase of nanosecond laser shock times, the crack length decreases and the fatigue life is enhanced. During the impact process, the fatigue band width decreases with the increase of nanosecond laser shock times. nanosecond laser shock causes the residual compaction on the surface of the alloy and closes the crack.

316L stainless steel HVAC pipe was used as the base material. Laser surface treatment and powder embedding and aluminizing were used to enhance the surface treatment of 316L. The influence of power density on laser impingement aluminizing structure and thermal tensile properties of the 316L surface were studied through experimental testing methods. The results show that there are more pits in the aluminized layer after laser shock. With the increase of power density, the roughness increases. With the increasing of power density, the diffraction peak becomes stronger. As the depth increased, the hardness continued to decrease. With the increasing of laser power density, the hardness increases. The mechanical properties of samples treated by laser shock intensification are better. With the increasing of laser power density, the mechanical properties are improved more obviously. Higher mechanical properties were obtained when the power density was 6 GW/cm2, and the tensile strength and yield strength are 531 MPa and 443 MPa, respectively. After laser impact, many equiaxial dimples with different sizes were observed at the fracture site, and tear edges were generated, generating a large number of dimples. After increasing the laser power density, the size difference of each dimple becomes more obvious, and the hole size also increases.

In view of the problem of removing local damaged paint layer on workpiece surface, it is an effective method to improve the cleaning quality and efficiency to implement the laser partition cleaning in high efficiency, and accurate identification of local damaged paint layer area contour is the premise of partition cleaning, therefore, a method of contour identification for laser partition cleaning based on machine vision is proposed. Aiming at the problem of difficulty to identify paint layer area contour caused by low camera exposure, an image enhancement method based on camera response model is adopted. Aiming at the problem of complex contour precise identification of paint layer area, a method of contour identification based on chroma coordinate value is proposed. In order to realize laser partition cleaning in high efficiency, a method of complex contour regularization of paint layer area based on minimum envelope rectangle is adopted, and a method of generation scanning path in variable distance is used. The experimental results show that this method achieves accurate identification of complex contour of paint layer area with low illumination, and improves the identification accuracy compared with the traditional iterative method.

The propagation characteristics of Ince-Gaussian (IG) beams in turbulent ocean environment are calculated and simulated by using step-by-step phase screen method. The effects of propagation distance, mode order and ellipticity parameter of IG beam on propagation performance are studied. The changes of beam intensity distribution, beam width, spot centroid wander and scintillation index parameters during transmission are analyzed. It is found that in the oceanic turbulence propagation, with the increase of propagation distance, the spot of IG beam will diffuse. At the propagation distance of 100 m, the IG beam with ellipticity parameter less than 2 will be transformed into a hollow beam. Secondly, the oceanic turbulence has a broadening effect on IG beam during propagation, and the standard deviation of spot centroid wander gradually increases with the increase of mode ellipticity parameter. In addition, the scintillation index increases with the increase of the order of IG mode. With the increase of ellipticity parameter of IG mode, the scintillation index first decreases and then tends to be flat. The research results have guiding significance for the marine application of IG beam.

In order to get better 3D photoacoustic tomography, focused ultrasound transducer is used to detect the photoacoustic signal of ring source excitation, then the filtered back projection algorithm, finally the 3D photoacoustic tomography of simulated blood vessel and carbon was formed by Volview software. The simulation and experimental results show that the image comes in true with high resolution and good contrast using the method, and the reconstructed images are in good agreement with the real objects in the 3D image. The YAG laser source has a wavelength of 780 nm, repetition frequency of 10 Hz, pulse width of 16 ns, the PA signal detector is a cylindrical focused ultrasonic transducer, with a receiving diameter of 3 cm.

As the transmission line point cloud in complex environment is different due to the structure and point cloud density and structure of each power element, the noise point distribution around the power element is irregular and uneven, so the traditional denoising method is difficult to denoise uniformly. To address this problem, this paper proposes a coarse classification-based denoising algorithm for transmission line 3D point cloud data. Firstly, a location-based point cloud extraction method is introduced to coarsely classify the tower point clouds, and the coarsely classified power line point clouds and feature point clouds are obtained based on the Euclidean clustering segmentation algorithm (euclidean cluster extraction). The coarse-classified tower point clouds and feature point clouds are denoised using the density-based spatial clustering algorithm (DBSCAN) and statistical filtering algorithm with adaptive thresholding, respectively. For power line point clouds, this paper proposes a coordinate transformation algorithm based on the principal component analysis (PLE-PCA) algorithm of power line direction estimation, which can realize the point cloud denoising under the sparse and uneven distribution of power line point clouds by effectively amplifying the distance between noise points and power line point clouds. The study uses UAV dense matching point cloud data and UAV laser point cloud for denoising experiments. The comparison experimental results with radius filtering algorithm and statistical filtering algorithm show that the method has good robustness in the complex environment of transmission line laser point cloud and dense matching point cloud with dense noise, mixed power elements and noise points, low density and uneven distribution of power line point cloud.

As a new type of space fuel, ADN (ammonium dinitramide) has attracted people′s attention for its green, environmental protection and high energy characteristics. As a new micro propulsion method, laser propulsion has the advantages of small thrust and adjustable in a certain range. In this paper, ADN is used as working medium to study the relationship between ADN absorption rate and propulsion performance in laser propulsion. Infrared dye was used as light absorbing material, and the absorption rate of working medium was controlled by changing its ratio. Laser ablation was carried out in a microablative chamber (about 5.33nL) to study the change of its propulsion performance and observe the evolution process of plume. The results show that there is no impulse between pure ADN solution and 0%ADN solution, 20%ADN has better propulsion performance, and the maximum impulse is 6.02 μN/s, and the atomization degree of droplets produced by 20%ADN solution is higher. Therefore, it is concluded that with the increase of ADN absorption rate, its propulsive performance also presents an upward trend.

In this paper, laser-assisted heating technology is introduced. On the basis of heat transfer theory model, the temperature field distribution of 2024 aluminum alloy material under laser heating condition is obtained by using the finite element analysis software COMSOL Multiphysics, and the influence of laser parameters on the surface and depth direction temperature field is studied. The simulation results show that the surface temperature of aluminum alloy can be improved obviously by laser heating assisted machining. The maximum temperature at laser center on aluminum alloy surface increases with the increase of laser power. It decreases with the increase of spot size. At the same time, in the depth direction, with the accumulation of heating time, the laser heating assistant has a certain warming effect, and the heat accumulation effect of laser heating is significant. In terms of the uniformity of the surface temperature field distribution, the uniformity is best in the high temperature region, namely 300 ℃ to 390 ℃, the power is 20 W, the laser radius is 0.10 mm; The temperature uniformity is best when the power is 20 W and the radius is 0.15 mm in the medium temperature region, 200 ℃ to 300 ℃. Temperature uniformity is best in the low-temperature region, 60 ℃ to 180 ℃, with a power of 10 W and a radius of 0.10 mm.

To separate the common kinds of plastics (HDPE, LDPE, PET, PP, PC, PPS, PE, PVC, ETC) by using Raman spectrum and laser-induced fluorescence spectrum (LIFS), the paper propose a method of combinating 1 064 nm laser Raman spectrum and 405 nm laser fluorescence spectrum at the same time to identify the plastic. The results showed that the dual-spectrum combination method classify plastics very well by comparing the correlation with the data in the spectrum library. The recognition accuracy is nearly 100%, which provides a novel way to identify the plastic for the effective recycling of plastic waste.