Laser-CMT hybrid welding is a new laser arc hybrid welding technology combining high-energy beam laser and cold metal transition (CMT) technique. Compared with traditional laser MIG hybrid welding, CMT process has extremely low heat input, more stable welding process, which can realize high-efficiency spatter free welding process and is easy to obtain high-quality welded joints. This technology has attracted more and more attention from scholars at home and abroad. It has been continuously explored and recognized in terms of refractory and weldable connection, and has a wide range of industrial application scenarios. Based on the analysis of relevant literature, this paper first summarizes the composition and connotation of laser-CMT hybrid welding system, then reviews the development status of weld formation, droplet transfer, weld pool morphology and welded joints in laser-CMT hybrid welding, as well as some existing problems. Secondly, the necessity and research method of simulation of laser-CMT hybrid welding process are put forward. Finally, the future development direction and research focus of laser-CMT hybrid welding technology are prospected.

Laser ablation-assisted laser welding can regulate the porosity and further improve the tensile strength. In this paper, the effect of laser ablation density on the surface oxygen content and surface morphology was studied after the welding parameters were optimally selected. With 0 J/cm2, the surface oxygen content was 8.91% and the surface was flat. After laser ablation, the oxygen content first decreased and then increased. With 8.75 J/cm2, the oxygen content was 2.75%, which was only 30.86% of 0 J/cm2. A uniform crater morphology was formed. The excessive energy caused thermal oxidation and irregular ablation morphology. Quantitative analysis was performed using σa and σb as the standard deviations of the ejected plasma and molten pool fluctuations, respectively. σa and σb were 0.173 and 0.045 with 0 J/cm2. With 8.75 J/cm2, σa and σb were 0.176 and 0.049, respectively, which were closest to 0 J/cm2. With 35 J/cm2, it was the opposite. With 0 J/cm2, a large number of pores were found and the porosity was 1.85%. Three locations of pore formation under the influence of keyhole and molten pool behavior were analyzed. With 8.75 J/cm2, only a very small amount of porosity was observed, with porosity of 0.28%. The room temperature tensile strengths with 0 J/cm2 and 8.75 J/cm2 were 962.94 MPa and 1 130.47 MPa, respectively. The fracture morphology exhibited ductile fracture.

Laser cladding technology with environmental protection and high cost performance has been widely used in the field of workpiece remanufacturing. However, it is difficult to control the quality of cladding layer in remanufacturing process due to the complex nonlinear relationship between laser cladding process parameters and cladding layer quality. To solve the above problem, a multi-objective optimization strategy of laser cladding process parameters for remanufacturing is proposed in this paper, taking microhardness, heat affected zone depth, and porosity as the optimization objectives. This method provides the nonlinear mapping relationship between laser cladding process parameters and optimization objectives based on the support vector mechanism for regression. The process parameters of laser cladding are optimized though multi-objective particle swarm optimization algorithm. On the basis of Pareto solution set, the decision analysis module is constructed by TOPSIS that gets a weight input by analytic hierarchy process, and the optimal parameter selection scheme is found out from Pareto solution set. Finally, the remanufacturing case of steam turbine valve seat parts proves that this method can improve the overall quality of remanufactured products.

Cu-10Pb-10Sn cladding layer was prepared on Q235 carbon steel substrate by laser cladding technology. The effect of laser power on porosity, microstructure, and microhardness of the cladding layer was studied. The results show that the change of laser power has a great influence on the macroscopic morphology of lead bronze alloy, and the porosity of the cladding layer decreases first and then increases with the increase of laser power. The holes in the cladding layer are formed because the low melting point substances Pb and Sn in the cladding material do not escape in time after evaporating into metal vapor. In cladding α-Cu (Sn) solid solution and γ-"Liquid phase separation" occurs in Fe phase, and Pb phase is distributed as dot dispersion. The microhardness of the cladding layer is greatly affected by the laser power. The minimum hardness is 104.5 HV, and the maximum hardness is 134.4 HV.

In order to solve the problem of serious surface wear and difficulty in repairing during the maintenance process aiming the wear failure of the reducer shaft surface, laser cladding technology was used to remanufacture the worn reducer shaft surface. The effect of laser cladding on the metallographic microstructure, hardness, wear resistance and corrosion resistance of the reducer shaft surface was studied. The research results show that after the reducer shaft is remanufactured by laser cladding, the surface cladding layer has a fine and dense structure, and the properties of the cladding layer are significantly improved. The wear resistance and corrosion resistance are about 2.5 times and 2 times that of the reducer shaft base material, respectively. The laser cladding technology has broad application prospects in the remanufacturing of the reducer shaft.

The deposited state and microstructure characteristics of GH3536 alloy formed by selective laser melting were investigated, and the effects of different cooling methods on microstructure and high temperature tensile properties were compared. Through continuous optimization of GH3536 printing parameters, it can be seen that high laser power will cause serious sputtering problems, and low laser power will produce pores. It is confirmed that the optimal power range is 50~70 J/mm3. The optimal printing parameters are: laser power is 170 W, scanning rate is 1 060 mm/s, scanning spacing is 0.08 mm, layer thickness is 30 μm, the scanning angle between layers is 67°, and the density of the alloy can reach 99.97%. After holding at 1 175 ℃ for 30 minutes, recrystallization occurs in the alloy after three cooling modes: water cooling, air cooling, and furnace cooling. Under the condition of furnace cooling, a certain amount of carbide precipitates at the grain boundary; Under the condition of water cooling, annealing twins are formed in the crystal. Through the high temperature tensile test at 855 ℃, the fracture tensile rates are obtained under the three cooling methods are more than 25%. Under the condition of furnace cooling, because the carbide precipitated at the grain boundary strengthens the grain boundary and improves the high-temperature plasticity of GH3536, the tensile rate is the best, up to 29%. The heat treatment system effectively improves the poor high-temperature plasticity of deposited GH3536, and provides a reliable scheme for the application of aerospace combustor parts.

Under the conditions of the laser power is 70 W, the powder spreading thickness is 0.03 mm, and the laser scanning speed is 400 mm/s, the stainless steel specimens were formed. The effects of different heat treatment temperatures on tensile properties, hardness, and wear resistance of specimens were studied. The experimental results show that with the increase of heat treatment temperature, the residual metal powder in the specimen further melts and fills the holes, cracks, and other forming defects, which makes the internal microstructure of stainless steel uniform refinement and improves the tensile properties of the specimen. With the increase of temperature, the content of high hardness alloy also has a certain improvement, so that both the hardness of stainless steel specimens and the wear resistance are improved.

In order to improve the machining accuracy of lubricating pad used in joint bearings, this paper put forward the application of laser vaporization cutting technology in the production process, and systematically studied the process steps of lines. The main contents included: the graphical layout and location of liners, the laser cutting parameters of three typical self-lubricating liners, and the detection requirements. The cutting gap changes and depth changes were analyzed with the help of stereomicroscope. Finally, the self-lubrication liners were used on spherical plain bearings to verify the reliability. The results showed that the layout of laser cutting routes by using computer is compact, the visualization is more convenient and flexible, and even could be used repeatedly. Laser cutting positioning is simple and convenient. The cutting effect is negatively correlated with the laser frequency and laser traverse speed, and positively correlated with the duty cycle. The best parameters for liner cutting were obtained: the laser frequency is 20~30 kHz, the laser traverse speed range is between 150 mm/s and 200 mm/s, the duty cycle is 50%, and cutting times is the number of the liner which are just falling off.

In this paper, a continuous fiber laser was used to study the surface nitriding effect on CNC machine drive shaft by 12 groups (Group A~L) of different laser parameters. Three groups of optimum parameters were selected to study the microstructure and properties after laser nitriding, in order to lay a foundation for revealing the evolution law of microstructure, composition, and physical mechanical behavior. The results show that when the laser power and scanning speed is 1.2 kW and 3 mm·s-1 respectively, the surface roughness of the nitrided layer is Ra=1.6 μm, which is the lowest compared with other parameters. The microstructure is not only refined, but also changed from tempered sorbite to a mixture of martensite, carbide, nitride, and matrix. In addition, the microhardness, wear resistance, and tensile strength of nitriding layer are improved accordingly.参考文献原文> YANG Z J, CHEN C H, CHEN F, et al. Progress in the research of reliability technology of machine tools［J］. Journal of Mechanical Engineering, 2013, 49(20): 130-139.杨兆军, 陈传海, 陈菲, 等. 数控机床可靠性技术的研究进展［J］. 机械工程学报, 2013, 49(20): 130-139.

Based on the maxwell's equations, plasma excitation conditions were derived. Metal dielectric metal (MIM) periodic hole array films were prepared based on the principle of surface plasmon enhanced light transmission in subwavelength hole periodic arrays. This film structure can supplement the momentum imbalance between the incident light and plasma elements, and then successfully realize the excitation of surface plasma on the metal surface. Finally, the MIM periodic hole array structure was used to conduct laser micro-nano machining experiments and its role in laser micro-nano machining was explored. Monocrystalline silicon was selected as the object of laser micro-nano processing. The experimental results show that this kind of thin film structure can remove materials by inductively excited plasma, and a wide range of microporous structures can be prepared on the surface of silicon wafers.

The hydrophilic surface structure is beneficial to the deposition of hydroxyapatite, the ingrowth of bone tissue, and the biological activity of the implant surface. Therefore, the preparation of hydrophilic surface structure is beneficial to the implant to work better in the body and improve the success rate of implant implantation. In this paper, using fiber laser, when the processing speed is 25 mm·s-1, the number of scans is 10, laser power is 14 W, and laser frequency is 10 kHz, the laser produced a high-energy laser beam on the material surface,the processed groove width was about 24 μm, and the contact angle was measured as 93.7°. Using anodizing method, the diameter of the nanotube prepared by electrolysis at 30 V for 2 h is about 65 nm. The nanotube helps to enhance the capillary force. The contact angle is measured as 43.8°; the contact angle of the sample prepared by laser processing and anodization is the smallest, with a value of 26.5°. The micro-nano composite structure increases the contact area and gives full play to the capillary effect of the nanotubes. The preparation of the micro-nano structure improves the hydrophilicity of the implant surface, and the fiber laser and anodization obtain a micro-nano composite structure, which provides a simple, easy,and effective method for the surface modification of the implant.

In order to improve the surface properties of 304 stainless steel, laser alloying technology is used to prepare Ta-based alloyed layers with different process parameters on the surface of 304 stainless steel. X-ray diffractometer and scanning electron microscope are used to analyze and observe the composition and morphology of the alloyed layers. The hardness tester is used to test the hardness of the alloyed layer. The friction and wear tester is used to test the wear resistance of the alloyed layer. The electrochemical workstation is used to study the corrosion resistance of the sample in 3.5% NaCl solution. The results show that when the laser power is 900 W and the laser scanning rate is 1.5 mm/s, the prepared alloyed layer is more uniform and dense, and the main component of the alloyed layer is TaC. the average hardness of the 3# sample reaches 1 113.52 HV, which is 3.27 times that of base 0# sample. 2# sample has a friction factor of 0.45, which is 25% less than stainless steel; 3# sample has better corrosion resistance, the corrosion potential of base sample 0# Ecorr=-0.98 V, and the corrosion current density Jcorr=4.57×10-5 A·cm-2. Compared with the matrix sample 0#, the corrosion potential (-0.36 V) of the 3# sample is significantly increased, and the corrosion current density (2.81×10-7 A·cm-2) is significantly reduced. The alloyed layer prepared on the surface of 304 stainless steel can fully improve its hardness, wear resistance, corrosion resistance, and other properties, which broadens the application field of 304 stainless steel.

Obstacle detection is one of the key points of unmanned vehicle research, which needs to obtain obstacle data from multiple angles. A method on driving obstacle detection of new energy vehicle unmanned vehicle based on infrared technology and lidar is proposed. Using Trimble MX2 3D lidar equipment and infrared sensor, the obstacle data during driving is obtained, and the data acquisition error is reduced through preprocessing. The processed obstacle data points are connected into an obstacle contour, and the obstacle detection is completed according to the obstacle classification information. Based on the building of a detection performance test environment,, experimental results show that the combination of infrared technology and lidar can accurately detect all obstacles, accurately divide the types of obstacles, keep the misclassification rate of driving obstacle classification between 0%~10%, and keep the detection time within 2 s. The detection and recognition effect is good, which can improve the safety factor of unmanned vehicle driving at night.

In order to reduce the access time of wireless laser communication users and enhance the utilization rate of channels, a parallel channel equalization method at the receiving end of wireless laser communication under multipath interference is proposed. Firstly, the preprocessing of wireless laser communication signal filtering is performed, and the signal is denoised by the filter to ensure the quality of the signal, and at the same time, it is normalized to facilitate the equalization of the channel. Secondly, the communication channel under multipath interference is estimated, and the parallel concept is added on the basis of the channel estimation result to obtain the channel equalization processing result, and realize the parallel equalization of the wireless laser communication receiving end channel. The experimental results show that the proposed method has strong anti-interference performance, better channel equalization performance, and faster channel estimation speed, with an average channel estimation speed of 1.96 m/s.

In the process of using an X-ray imager to detect contraband, the conversion, and transmission of detection signal are easy to lead to the problems of low contrast and blurred edges of contraband images. In this paper, a double mask image enhancement algorithm based on image preprocessing and resharpening is proposed to improve the quality of X-ray contraband images. Image preprocessing is mainly used to remove the noise and corner shadow in the process of image imaging. The experimental results show that the image preprocessing algorithm proposed in this paper has an obvious effect on the removal of the corner and corner problems and image noise. In this paper, a counter-sharpening double mask image enhancement method is proposed to enhance the image details of different scales. Experimental results show that the anti-sharpening double mask image enhancement algorithm has an obvious enhancement effect on image contrast and edge details of contraband, and can effectively improve the accuracy and efficiency of contraband detection. By changing the tube voltage to change the brightness of the image, the image preprocessing and image enhancement methods are proven to have good robustness.

The forward scattering of nonspherical aerosols leads to errors in the extinction coefficient measured by the solar radiometer, the error needs to be corrected theoretically. The forward scattering characteristics of ellipsoidal, cylindrical and Chebyshev particles and their effects on the forward scattering correction factor are studied by T-matrix method. The results show that the forward scattering intensity of ellipsoidal particles increases with the increase of equivalent radius and axial ratio. In dust aerosol particles, the correction factor will oscillate and decrease with the increase of particle size parameters. When the size parameters exceed 10, the forward scattering correction factor will be lower than 0.98. With the increase of the parameters, the correction factor will reach about 0.96. Ellipsoidal particles with different axial ratios and cylindrical particles with different length diameter ratios have great influence on the correction factor, while the deformation parameters and ripple parameters of Chebyshev particles have no obvious influence on the correction factor. These results provide theoretical guidance for studying forward scattering of atmospheric aerosol particles and the application of solar radiometer.

As an auxiliary means of periodontal basic treatment and periodontal surgical treatment, Nd:YAG laser (neodymium-dopedyttrium-aluminium-garnetlaser) has many functions, such as tissue ablation, sterilization, hemostasis, biological stimulation and so on. It has a broad application prospect in the field of periodontal disease treatment. In this paper, the application and research progress of Nd:YAG laser in the treatment of periodontal disease are reviewed, and the working principle of Nd:YAG laser and its application in periodontal soft and hard tissues are introduced systematically, so as to better guide the application of Nd:YAG laser in clinical periodontal therapy.