Laser scanning welding experiment and simulation study were carried out for 7075-T6 aluminum alloy 10 mm medium thickness plate. The inhibition law of laser scanning welding on weld porosity was investigated by X-ray nondestructive testing and molten pool flow simulation. Experimental results show that the porosity decreases with the increase of scanning frequency and amplitude. By analyzing the simulation results at different scanning frequencies, it is found that the "large keyhole" structure is more stable and less likely to collapse and form bubbles due to the superposition of keyholes at high frequency scanning, compared with the slender keyhole at low frequency scanning. At the same time, the beam scanning increases the width of molten pool and the probability of bubbles escaping. By analyzing the simulation results under different scanning amplitudes, it is found that the large amplitude significantly reduces the depth of the keyhole, which reduces the aspect ratio of the keyhole and enhances the stability of the keyhole. At the same time, the increase of amplitude further expands the width of the molten pool, which increases the probability of bubble escape and then reduces the porosity in the weld.

In order to optimize the weld formation and process parameters of DP800 vehicle high strength steel composite welding, based on the response surface method, the mathematical model between the main process parameters and weld characteristic parameters of laser-arc hybrid welding is established, and the analysis of variance is carried out. Aiming at specific penetration depth and minimum penetration width, the laser power, welding current and welding speed are optimized to obtain the optimal process parameters, which are verified by experiments. Results show that laser power and welding current are positively correlated with weld penetration, and welding speed is negatively correlated with weld penetration. With the increase of welding current or the decrease of welding speed, the weld width increases gradually, and the laser power has little effect on the weld width. The accuracy of the model is verified by experiments under the optimal process parameters, and the error rates of penetration depth and width are less than 5%.

Aiming at the welding technology of TC4 titanium alloy formed by diffusion bonding with a thickness of (2.0+1.5) mm, the laser welding and TIG filler wire welding process research were carried out. The joints of the two welding methods were subjected to post-weld heat treatment at 650 ℃ to relieve stress. The microstructure of the joints of each method is analyzed, and the mechanical properties of the joints are tested. Results show that the two welding methods can obtain well-formed joints with appropriate processes. Compared with argon arc welding, the crystal grains of laser welding joints are smaller, and α′ phase is more. Laser welding shear strength and tensile properties parallel to the weld are higher than argon arc welding, but the bending strength and tensile properties perpendicular to the weld are lower than argon arc welding.

A 10 000 W fiber laser was used to carry out the process experiment of magnetic field assisted laser swing welding of 10 mm thick 6061-T6 aluminum alloy. Ultra-depth-of-field microscopy and scanning electron microscopy (SEM) were used to analyze the macro-morphology and micro-structure of the weld section. Under the action of magnetic field assisted laser swing welding, the defects such as sagging, spattering and pitting of welded joints are obviously restrained. Then , the behavior characteristics of the molten pool and the small holes during the welding process were directly observed by high-speed camera, and it was observed that the magnetic field has the effect of stabilizing the flow of the magnetic field. Then X-ray flaw detection was carried out to test the porosity of the weld. The porosity of the 200mT magnetic field-assisted laser swung welding was the smallest, which could reach 0.856%. Finally, the tensile property test was carried out , and the tensile strength of magnetic field-assisted laser swing welding can reach 318.85 MPa at the highest.

In order to investigate the thermal accumulation effect on the properties of two build directions of 0° and 90° during the selective laser melting. Based on the ANSYS simulation of molten pool size and thermal accumulation effect, the mechanical properties of the two build-formed parts were explored experimentally, and the differences in melt pool size, density, XRD, microstructure and mechanical properties between 0° and 90° build directions were analyzed. Results show that the thermal accumulation of the vertical build-formed parts is higher than that of the horizontal build-formed parts under the same bulk energy density, which results in higher melt pool size and γ-phase content than that of the horizontal build-formed parts, and thus the difference in the densities and mechanical properties between the two build-formed parts. Due to the effect of heat accumulation, the γ-phase content of different forming parts of the vertical build forming parts changes.

The microstructure and mechanical properties of Ti-6Al-4V repaired by laser additive manufacturing were studied, and the effect of the build orientation on additive zone microstructure, microhardness, tensile properties and fracture morphologies of Ti-6Al-4V were investigated. Results show that a typical basketweave microstructure is featured in the additive zone, of which the fine basketweave microstructure is obtained in the additive height direction, and the basketweave microstructure including the equiaxed α phase is obtained in the tile direction. There are plenty of elongated α lath and a few acicular α′ in the scanning direction, due to the less heat accumulation, rapid heat dissipation, and its proximity to the junction zone. The microhardness is approximately 345 HV in the scanning direction, which is increased by 4.1% compared to that in the height and tilt direction for the additive zone. For the junction zone, the microhardness is the highest in the scanning direction, which can reach 362 HV. The room-temperature tensile properties show obvious anisotropy for different orientations. The highest tensile strength is exhibited in the scanning direction, while the plasticity is slightly reduced. On the contrary, the property with lower tensile strength and higher plasticity is exhibited in the height and tilt direction, and the fracture morphology is characterized by ductile fracture for different orientations.

The Ti2AlNb forging sample used for internal combustion engine was selected as the test material. The powder feeding laser additive treatment was applied to the sample. The microstructure characteristics of cladding under different laser energy densities were tested, and the mechanical properties of the bonding zone of samples were analyzed. Results show that when the linear energy density is 100 J/mm, the microstructure of lower substrate is the same as that of the forged substrate. There are β columnar crystals in the apical region that penetrate into the sedimentary layer. There are two α phases in the lower region, i.e., equiaxed and lamellar. There are equiaxed and lamellar α phases in the middle part, and secondary α phases in the β phase. The number of α phases increases with the increasing of linear energy density. There are α lamellar structures in the β grains. When the linear energy density is increased, the tensile strength and yield strength decrease, while the elongation increases. When the linear energy density is 100 J/mm, the microstructure of the bond zone with the best mechanical properties is formed, and the maximum tensile and yield strength is obtained. There are shear lip and dimple morphology in the tensile fracture of the specimen, and the ductile fracture occurs.

In order to improve the comprehensive properties of Al-12Si alloy formed by selective laser melting (SLM), Al-12Si-(Er-Zr) alloy was prepared by SLM after the addition of Er and Zr elements by aerosol treatment. The microstructure, physical and mechanical properties of Al-12Si-(ER-Zr) alloy were studied by means of experimental tests, and the strengthening mechanism of Er and Zr elements during the SLM processing was analyzed in depth. Results show that the highest relative density of 99.2% can be obtained when the energy density reaches 57.5/mm3. There are gray Al and white eutectic Si structures in Al-12Si-(Er-Zr) alloy prepared by SLM, and the morphology characteristics of network distribution show that Er and Zr elements can significantly refine the grain size of Al-12Si-(Er-Zr) alloy. Compared with Al-12Si alloy, the hardness of Al-12Si-(ER-Zr) alloy prepared by SLM increases by 26.1%, tensile strength increases by 20%, yield strength increases by 27%, and elongation does not change significantly. The grain size of Al-12Si-(Er-Zr) alloy prepared by SLM reaches larger Schmid factor, contains more high Taylor factor, higher proportion of Brass cold rolled texture and Copper tensile texture, resulting in higher mechanical strength of Al-12Si-(Er-Zr) alloy.

In order to improve the effect of lidar point cloud denoising, different scale algorithms are proposed. Firstly, the mean value method is used to delete duplicate points from Lidar point cloud data. Secondly, the noise points are estimated. Thirdly, the distance threshold is dynamically set for large-scale noise far away from the main point cloud, small distance is deleted the noise points in a large range, and distance value is delete the noise points in a small range. Finally, small scale noise points mixed with the main point cloud is processed with improving the bilateral filtering algorithm, the data points are gathered in the normal direction, and the position and coordinate of the sampling points are adjusted to the corrected position, which leads to that lidar point cloud denoising was smooth. Experiments show that different scale algorithm can maintain the overall and local characteristics of the scanning target, the signal-to-noise ratio index mean value is 17.56 dB, the root mean square error index mean value is 0.34, and the smoothness index mean value is 0.21, which is better than other algorithms.

To address the problem that the existing trunk extraction methods are affected by sagging branches and leaves as well as noise, this paper proposes a hierarchical trunk segmentation method based on the normal statistical features of point clouds. The trunk is firstly nested to preserve the complete trunk while removing the sagging branches and leaves. Furthermore, the trunk is layered, and the point cloud is statistically filtered for each layer. Finally, the normal vector of each layer is calculated to calculate the correct segmentation height based on its statistical features. Experiments were conducted with two trees, Ginkgo biloba, Metasequoia and willow, and the coefficient of determination were 0.974, 0.934 and 0.922, respectively, and the root mean square errors were 0.070 m, 0.075 m and 0.132 m, respectively, which indicates that the method has high segmentation accuracy and can provide technical support for the accurate extraction of tree structural parameters.

Loop detection is an important and challenging problem in simultaneous localization and mapping (SLAM). At present, most researches have been focused on the visual position recognition, which is to identify overlapping positions through appearances. Therefore, a loop detection laser SLAM algorithm with global descriptor is proposed, which is used to improve the efficiency of loop detection, calculate the distance between two scanning contexts by the similarity score and detect loops effectively with a two-stage search algorithm. The algorithm is evaluated by testing on the public dataset KITTI, and the result shows that compared with the existing LeGO-LOAM algorithm, this kind of algorithm works better.

When the current method is used for pulsed laser ranging, the cumulative time error generated by the sine function cannot be eliminated, and there are problems of low reconstruction accuracy and large ranging error. A high-precision pulsed laser ranging research method supported by ARM embedded is proposed. This method introduces the ARM embedded high-speed core processor in the pulsed laser ranging to perform multi-frame correlation detection, adaptive threshold detection, and filter noise reduction. The point averaging method eliminates the accumulated time error in the pulse laser ranging process, and on this basis, the pulse laser ranging accuracy is improved by the difference frequency phase measurement method. Experimental results show that the proposed method has high reconstruction accuracy and small ranging error.

In this paper, the vehicle mounted laser pavement flatness detection system based on the highway comprehensive detection vehicle is adopted. Through experimental research, it is found that there are abnormal fluctuations in the vertical section elevation and the corresponding international roughness index IRI test results under continuous longitudinal slope and small radius circular curve sections. The main reason is that the vehicle posture is tilted back in the continuous uphill stage, and the vehicle posture is dive in the continuous downhill stage. When turning left, the vehicle posture is tilted right, and when turning right, the vehicle posture is tilted left. The pitch and roll of the vehicle posture will offset together with the laser ranging sensor. As a result, the output of section elevation data is abnormal, and the international flatness index IRI test results are distorted. Testing results show that the vehicle mounted laser pavement flatness detection system based on laser ranging and uniaxial acceleration inertia correction technology is not applicable to the complex linear sections of low-grade highway, and the corresponding laser ranging correction technology needs to be further studied.

In additive manufacturing rapid development and increasing green under the joint action of sustainable development, additive repair technology is developing rapidly in various fields of Chinese industry. At the same time, our country issued relevant policies to strongly support the development of additive manufacturing technology, and additive repair technology has become mature and developed rapidly with a large number of scholars, which has a wide application prospect. This paper introduces the material to repair the main application of key technologies, as well as the increase of material repair technology in the field of aerospace navigation, military areas, as well as the present situation of the application of engineering machinery area, etc. Moreover, the current problems faced by additive repair application technology are put forward, and finally the future development direction of additive repair technology is prospected and suggested.

Laser hole machining of carbon fiber reinforced polymer (CFRP) has received a lot of research in recent years. However, most of them are hole cutting machining, and there are few reports on high-quality blind hole machining. In this paper, a femtosecond laser helical drilling device is proposed. It can realize beam deflection and translation through scanning device and a group of lenses respectively, and finally obtain the effect of beam oblique focusing. With beam scanning, the machining taper caused by the focusing characteristics of Gaussian beam can be avoided. Using this device, we studied the 0.3 mm blind hole processing of CFRP, the influence of processing parameters on the machining results and optimization parameters were obtained, and finally a better processing effect of 0.15 mm deep flat bottom straight blind hole was achieved. On this basis, the processing of special-shaped bottom blind hole was further explored. Through layer-by-layer processing, the processing effect of hemispherical blind hole with a section diameter of 0.3 mm is finally obtained. The overall machining quality of the hole is good, and the heat affected zone is less than 5 μm.

The wired communication mode of industrial bridge crane will increase the labor cost, and the later maintenance is relatively difficult. Therefore, a design scheme of laser wireless communication system based on PLC is proposed. The hardware part of the system is composed of laser sensor information acquisition layer, information transmission layer and information fusion output layer. The laser sensor obtains data information, completes transmission through ZigBee communication technology, and realizes data fusion in the information fusion module. The system software consists of PLC module, laser sensor routing node module and information fusion module. PLC module receives external signals and determines signal status information. The routing node module records the address information of the sensor data. By using BP neural network algorithm to remove redundant data and compress the amount of data, the sensor information can get ideal fusion results. Through the system performance test, the results show that the proposed system has low communication error rate, low communication delay and communication overhead, which can realize efficient and fast laser communication transmission.