The non-contact bonding structure can be realized by laser micro-welding, which is suitable for packaging between alloy. In order to improve the comprehensive performance of TA2/316L composite plate with mechanical dynamic connection structure, the high repetition frequency laser welding was used to fabricate it. The joint strength of TA2/316L composite plate was analyzed, and the optimal process parameters of high repetition frequency laser parameters were determined as follows: pulse power 14 μJ, defocus 0 μm, repetition rate 500 kHz, welding speed 0.6 mm/s, and the joint strength could be increased to 8.8 MPa, which promoted the obvious improvement of welding efficiency. The performance of transverse truncation surface in welding zone was analyzed by experimental test. Results show that the molten TA2 penetrates into 316L to produce many pits, and 316L is mixed with TA2. After 316L high repetition laser ablation, high temperature plasma is formed and the surface of TA2 melts, filling 316L ablated micropores. A large number of irregular distribution holes are formed on the side of TA2, and obvious raised packets are generated on the side of 316L. A large number of TA2 covers exist on the surface of 316L, which can closely connect TA2/316L composite plate.

In order to improve the structure and overall quality of the traditional laser cladding coating, the coating was prepared in vacuum environment. 304L + La2O3 coating was prepared on the surface of 45 steel. The macroscopic appearance, microstructure, phase composition, microhardness and friction and wear properties of the cladding layer were analyzed and studied. Results show that the vacuum environment can insulate oxygen and prevent oxidation in macroscopic appearance. The fluidity of the molten pool can be increased and the density of the microstructure can be improved. The hardness of cladding layer in vacuum is 797.9 HV, which is 13.4% higher than that in vacuum free environment. The friction coefficient and wear amount decreased 8.6% and 16.9%, respectively, and the wear resistance increased.

In the process of ultra-high speed laser cladding, the attenuation of laser energy by powder is one of the key problems to study the temperature field of laser cladding powder flow, and it is also the basis to realize the reasonable distribution of laser energy in ultra-high speed laser cladding. In this paper, the coaxial four way powder feeding tube laser cladding head and ultra-high speed laser cladding ring cladding head are taken as the research objects. Using the unsteady particle tracking mode, an algorithm is designed to calculate the energy attenuation of the powder to the laser. According to the calculation results of the algorithm, the energy attenuation of the two cladding heads under different process parameters is analyzed. The phenomenon of laser energy attenuation in the process of laser powder interaction is verified by experiments. Results of simulation and experiment show that the laser energy attenuation mainly occurs in the high powder concentration region under the cladding head, and the attenuation curve has the character of Gauss function. The reliability of the simulation model is verified by the light attenuation experiment of the cladding head of coaxial four-way powder feeding tube. It is also verified that the attenuation curve of laser through powder has the character of Gauss function, and there is an optimal powder feeding quantity.

Aiming to explore the forming quality of Laser Cladding Ni45A, the response surface center composite design method was adopted to establish a mathematical model between the process parameters and the geometric characteristics of the cladding layer. The influence of laser power, scanning speed, and gas flow on the geometric characteristics was analyzed. Through the sensitivity analysis method, the sensitivity of the cladding layer′s geometric characteristics to the process parameters was obtained. Results show that increasing the laser power and reducing the scanning speed are beneficial to increase the height, width and the area of the cladding layer. Input energy in the molten pool is the main factor affecting the morphology of the cladding layer. In addition, sensitivity analysis shows that the geometric characteristics of the cladding layer are the most sensitive to the laser power. These research results provide a sensitive characteristic diagram for the geometric characteristics of laser cladding Ni45A, which provides a theoretical basis for further effective control of the forming quality of the cladding layer.

This paper presents the simulation of temperature in single-track selective laser melting (SLM). The properties of solid metal materials changing with temperature and the phase transition process, as well as the effect of porosity of the metal powder on material properties are considered. The enthalpy-porosity method is adopted to simulate the momentum dissipation during solidification of the melt pool, and the solid-liquid interface is determined. According to the Law of Conservation of Energy, a Parabolic Optical Penetration Depth (POPD) volumetric heat source method is proposed based on the existing cylinder heat source method. The prediction results of the temperature distribution and the melt pool size are compared between the traditional Gaussian surface heat source model and the POPD volumetric heat source model. The results show that the average prediction errors of the molten pool width are 12.18% for the POPD volumetric heat source model, and 7.07% for the traditional Gaussian surface heat source model within the explored laser energy density range. With respect to the width of the molten pool, the prediction accuracy of Gaussian surface heat source is better than that of POPD volumetric heat source mode. When the laser energy density is between 40~100 J/mm3, the average prediction errors of the melt pool depth are 17.00% for the POPD volumetric heat source model, and 38.20% for the traditional Gaussian surface heat source model. With respect to the depth of the molten pool, the prediction accuracy of the POPD volumetric heat source is superior to the Gaussian surface heat source mode. In addition, it is found that the melt pool temperature distribution is much more uniform when considering the melt pool flow effect.

Bridge structure was prepared with TC4 titanium by selective laser melting. The effects of process parameters and span lengths on surface roughness of under bridge surface, density and forming angle of under bridge surface before and after sandblasting were studied. The results show that with the increase of span lengths, the density and the forming angle of under bridge surface decrease. When the span lengths is 6 mm, the edge of the forming angle of under bridge surface disconnects with the vertical overhang surface. By optimized the process parameters, when the span lengths is 4 mm, the laser power is 285 W and the point spacing is 50 μm, the comprehensive performance is best on surface roughness of under bridge, density and forming angle of under bridge surface. After sandblasting treatment, the density is increased by 4%-15% and remains stable, and the maximum density is 98.73%. The forming angle of under bridge surface become smaller, and the minimum forming angle is 21.7°. The changing trends of forming angle of under bridge surface by different process parameters are similar with before sandblasting. Through the observation of the microstructure of TC4 sample, the microstructure of TC4 sample is occupied by acicular martensite α′ phase.

The intelligent additive manufacturing platform is mainly composed of laser selective melting equipment, intelligent on-line monitoring and feedback regulation system, AM cloud platform software, process data processing software, and intelligent process parameter library and equipment health and safety management software, in order to realize the functions of remote process optimization, on-line quality diagnosis, equipment fault early warning and remote maintenance. The development of the platform provides an important method to solve the quality control and traceability in the additive manufacturing process of complex metal components in aerospace, aviation, and other fields, which is of great significance to comprehensively improve the intelligent level of additive manufacturing in China.

When complex structure parts are formed on machined matrix parts by selective laser melting (SLM) technology, large residual stress is easily generated at the interface. The single-layer multi-channel three-dimensional transient numerical model of composite forming 316L stainless steel based on SLM process was established by using ANSYS (APDL) and compared with the experimental results. Based on the finite element model of composite forming 316L stainless steel, the distribution and evolution of temperature field and stress field during composite forming were studied, and the effects of preheating temperature on the thermal behavior, stress evolution, and residual stress distribution of molten pool were analyzed. The results show that the maximum cooling rate, the boundary temperature gradient and the residual stress decrease with the increase of preheating temperature.

As deposited 18Ni300 was prepared by selective laser melting, the “ball-on-disk” sliding wear test were performed to study its wear characteristics with different sliding speed and load. Friction factor were recorded during the test, and the wear tracks were analyzed by Contour GT-K 3D profilometer to calculate the volume wear rate. The microstructure and wear area were analyzed by HITACHI SU3500 SEM, and the chemical composition of partial wear area were analyzed by EDS. The results show that: friction factor increased with the increase of sliding, and decreased with the increase of testing load. The volume wear rate increased with the increase of sliding speed and testing load. When the sliding speed was 0.4 m/s, the wear mechanism were oxidation wear and abrasive wear under the testing load of 15 N and 20 N, the wear mechanism turned to adhesive wear and abrasive wear with the increasing of the sliding speed. The wear mechanism was abrasive wear and oxidation wear under the 1.2 m/s sliding speed and 20 N testing load.

CrFeNiAlSiB0.1Tix (x=0.1,0.3,0.5) high entropy alloys were prepared by laser sintering. XRD、 OM、SEM and EDS, Vickers microhardness tester and electrochemical workstation were used to characterize the phase structure, microstructure, hardness and corrosion resistance of the analytes. The results showed that CrFeNiAlSiB0.1Tix high entropy alloys contain ordered BCC phase and Cr3Si phase, and Ti5Si4 phase appears after doping Ti element. The alloys are composed of dendrites and interdendrite structures, most of which are dendritic and petal-like. Cr and Si elements are enriched in the dendrite arm of CrFeNiAlSiB0.1 alloy, which is Cr3Si phase, and Al and Ni elements are enriched in the interdendrite of BCC phase. The Cr3Si phase and Ti5Si4 phase in CrFeNiAlSiB0.1Ti0.5 alloy are distributed in dendrite arm. The microhardness of CrFeNiAlSiB0.1Ti0.5 alloy reaches the maximum of 1 067 HV, and the wear resistance of CrFeNiAlSiB0.1Ti0.5 alloy is the best, which is 46.56 mg·cm-2. In 1 mol/L H2SO4 solution and 1 mol/L NaOH solution, CrFeNiAlSiB0.1Ti0.5 alloy has relatively low self-corrosion current densities, which are 104.32 μA·cm-2 and 86.41 μA·cm-2, respectively.

Under the policy background of carbon peaking and carbon neutralization in China, it is of great social significance and market value to carry out high-precision and long-time on-line monitoring of COS and CO2 in the process of vegetation carbon absorption. According to the needs of TDLAS detection of vegetation carbon absorption gas, a pressure control system for TDLAS detection of vegetation carbon absorption gas is designed based on TDLAS long-range absorption tank. The system uses STM32 as the main control, uses the air pressure sensor to collect the actual air pressure in the long-range absorption tank, and uses the gas proportional valve and vacuum air pump as the actuator to realize the gas replacement in the long-range absorption tank and ensure the stability of low pressure at the same time. After the gas gradient control test and field long-term stability test, the system works stably, has high control accuracy, can adapt to the field environment, can meet the needs of TDLAS detection of vegetation carbon absorption gas. The system is also suitable for other detection systems based on long-range absorption tank.

In order to improve the poor quality and low contrast of underwater polarization image, an underwater polarization image fusion algorithm based on Retniex and wavelet transform is proposed. Firstly, the intensity image was preprocessed by Retniex enhancement. Then the intensity image and polarization image were decomposed by wavelet transform (DWT). The low frequency component was fused by a fusion rule based on significance graph, and the high frequency component was fused by increasing the absolute value of pixel. Finally, the inverse wavelet transform was used to obtain the fused enhanced image. The experimental results show that the visual effect of images achieved by this algorithm is better, with more obvious details and higher clarity. Objectively, the information entropy, contrast and average gradient of fused images are improved by 6.6%, 98.5% and 39.2% respectively, and the quality of underwater images is significantly improved.

The refractive index of sea water is one of the important parameters of ocean optical characteristics, which is of great significance for seabed imaging and underwater detection. In order to facilitate the simulation of 1 km underwater laser transmission in geomagnetic environment, we designed a seawater experiment device with a length of 1 m in the laboratory, and the longitudinal magnetic field intensity in seawater test unit is from 0T to 0.05T generated by energized finite length solenoid. CCD method was used to measure the refractive index of salt solution under the applied longitudinal magnetic field. It is found that the refractive index of different salt solutions varies with the intensity of applied longitudinal magnetic field. In combination with the experiment, it is proposed that the electron cloud polarization is caused by lorentz force when the magnetic field intensity increases, and then the refractive index changes. It is preliminarily concluded that the refractive index of salt solution increases with the increase of longitudinal magnetic field strength. Origin software is used to analyze and fit the test data. The relationship formula is obtained, which provides a theoretical basis for the influence mechanism of geomagnetic environment on the optical properties of seawater.

In order to realize the high-precision calibration of the line-structured light vision measurement system, in view of the shortcomings of the traditional calibration method that the number of feature points is small and the calibration accuracy is affected by the grayscale extraction accuracy of the structured light to a certain extent, a two-dimensional plane-based method is designed. Target Improved Line Structured Light Algorithm. On the basis of the cross-ratio invariance theorem, the algorithm obtains a large number of characteristic data points through a simple checkerboard target, and then obtains the initial light plane equation through the least squares method. According to the characteristic that the center point of the structured light is on the light plane and on the plane of the checkerboard calibration board, the abnormal data points with large errors are screened out, and finally the light plane equation is optimized and fitted by the screened data points. In the general experimental environment, the results of the optical plane calibration comparison test show that the improved calibration method has a very significant improvement in measurement accuracy.

Semiconductor lasers are widely used in many fields, such as industry, medical treatment, scientific research, information, and military. Because the output wavelength and power of semiconductor laser will change significantly when the working temperature of semiconductor laser changes slightly, a high stability constant temperature and constant current driving power supply for semiconductor laser is developed in this paper. A constant current source consist of a field effect transistor and an operational amplifier is used for providing a high-precision and high-stability input current for that laser; a slow starting circuit is designed to protect the semiconductor laser and avoid the damage to the semiconductor laser caused by the peak and overshoot of the output current waveform of the power supply during starting. The MAX1978 chip is used to perform PID operation on the deviation between the real-time working temperature collected by the thermistor and the preset temperature, and the TEC is controlled to refrigerate or heat so as to realize the long-term stability of the working temperature of the semiconductor laser. The test results show that the output current of the power supply is continuously adjustable from 0 to 100 mA, the current accuracy is 0.01 mA, the control temperature accuracy is 0.01 ℃, and the power is stable for a long time. The power supply has the characteristics of good real-time adjustment performance, low cost, and easy implementation.

In view of the installation error of double through holes in large components when measuring cross sections of multiple holes, a coaxial measuring device based on position sensitive detector (PSD)positioning principle is proposed, which uses pneumatic mandrel and sliding table motion device of lead screw and nut. The lead screw and nut slide table is used as the motion measurement part to collect the parameter information of the measured spot. The detailed structure design of the fixture mechanism and the parts of the PSD installation and motion device is carried out to realize the PSD translation and rotation in the hole section. At the same time, the upper computer software is constructed to realize the system login, and automatic data processing and storage. The automatic operation of the whole device requires only simple loading and unloading. The final measurement results can be visualized by LabVIEW host computer software, and the deviation between the center line of the measured hole in each location and the standard center point can be displayed in real terms, and the coaxiality can be quantified and evaluated.