In this paper the image by high-speed photography of plasma in CO2 laser welding is studied including the area of these images, the change rate of these images, the isogray line of the image and the maximal variation of the image gray. The used laser is RS850 made in German and the high-speed photography is NAC-10 made in Japan. The weld material is low carbon steel. The welding parameters include laser power 4KW, welding speed 1.2m/min, shielding gas Helium, Helium flow rate 11L/min. The parameters for high-speed photography are as exposure time 1/5000 of second, shoot frequency 1000 frame/s. According to the analyses the main conclusion as follows: In the experiment, the values of gray of these images cover from 40 to 255. The area of the plasma is oscillation and the average frequency of the oscillation is about 300Hz. The laser welding plasma can be divided to three parts: periphery, smoothness and core from the external to inner. The isogray line of the periphery is very irregular because of shocking of the shielding gas and the metal spatter. In the core region, the thermal motion of the electrons is violent, so there is lots of little division with complex shape. The gap of isogrey line in the periphery region and core region are larger than it in the smoothing region. The isogrey lines of the image in the melting pool link with the isogray line of the image of the laser welding plasma, so it can be used to checking the temperature field each other. There exits an isothermal kernel in the core region.
In this study, the method of three-dimension reconstruction of laser welding plasma on the basis of three-dimension synchrony high-speed photo is proposed. The method of anti-RADON transformation is used to finish three-dimension reconstruction. The anti-RADON transformation utilizes the projected data to reconstruct the initial image, which bases on the projection of the parallel beam. It is found that there are the cavitations on most section images and the area of cavitations is ever-changing. The space shape of plasma represents irregularity on the different surface.
During CO2 laser deep penetration welding, the laser-induced plasma significantly effects the process stability and efficient. In this study, the method of three-dimension synchrony high-speed photography is adopted to record the charge of plasma during laser deep penetration welding. The primary version image is in the image plane directly, the vertical view and the side view image also are in the same image plane by two optical fibers and finally three images distribute at the different area of a film. It is clear that the direction variation of laser welding plasma is acute. The reason is that the change of keyhole shape leads to the impact direction variation of the metal vapor to the plasma and it finally affects the motion direction of the laser-induced plasma. The plasma is in the state of irregular rotation and wobbling in space during the laser welding process. The area change curve on continuous 80 frames image are given out. The change extent of relative area on the three images are calculated and the curves of the relative area are showed. It is found that the shape of plasma change quickly and the maximum relative area ratio of the side view image is up to 40 during laser welding.
In this paper the effect of activating flux on plasma during laser welding is studied and the Activating Flux-Laser Beam Welding (A-LBW) is proposed. The stainless steel (1Cr18Ni9Ti) is respectively welded by using activating flux and by not using activating flux. And the shape variation of plasma during laser welding is recorded directly by using three-dimension synchrony high-speed photography separately. It is found that the penetration of using activating flux is larger than the penetration not using it. When not using activating flux, there are so many negative effects such as reflection, scatter, absorption and refraction etc, which resulted in power density of acting on the work piece surface decreases and the penetration is lower. But when using activating flux, its molecules evaporated could trap electrons in the plasma to form negative corpuscles. Although the total number of the electron in the laser welding plasma aren’t decreased, but the mass of negative corpuscle is larger and then these corpuscles also became the background of the motion of electrons. Eventually the effective electron density is decreased and then the penetration is increased.
In this paper, the electron rotating radius and the corresponding length above surface of the workpiece where the electron density is notably reduced are calculated on the condition of adding magnetic field in laser welding according to the temperature of plasma and the average velocity of electron motion. The experiments results indicate that on the set condition, the weld area is increased by 18% with the weld penetration and the melting efficiency being increased by 22% and 13% respectively when the magnetic flux density added is set at 96 mT.
This research project aims at establishing a computer platform especially for the analysis of process of laser welding. After the laser induced plasma photographs, metallographic photographs of the weld are scanned into computer and the welding parameters are input, the results of the analysis can be obtained by means of selecting different function-keys. The main results of analysis include: the solid angle of spatter distribution, the velocity of the unit volume spatter, the area of the weld, the penetration-to-width ratio of the weld, the included angle of side boundary line of the weld, the RGB chart and the grey isothermal chart of plasma and the area of laser welding plasma in the different temperature district and so on.
In this paper, according to the relation of light source, RGB tricolor and color temperature, considering the rule of constant brightness, firstly, the color pictures of laser welding plasma were input into computer in the term of COLOR RGB through AGFA SCANNER, then grading grey scale properly to each picture element's three primary color, so the constant value lines of three primary color and the constant value line of the color picture brightness can be determined. Apparently, each constant value line of brightness corresponds a isothermal line and the denser the constant value lines are, the larger the gradient of temperature change is.
In this research, the method of computer processing organic- glass burning-mark is used to measure the high power CO2 laser mode and space parameters (beam diameter, beam waist diameter, beam quality factor and divergence angle). The graphs of intensity distribution in cross-section of beam and its magnitude contours are given out. The results indicate that the output mode of some a import 5 kW transverse CO2 laser is non-symmetric Laguerre-Gauss beam which is mainly consisted of TEM02, TEM20 and TEM03, whose center region intensity is less than adjacency intensity, the size of the center bright spot is bigger, the distribution of power density is relatively uniform.
KEYWORDS: Transmission electron microscopy, High power lasers, Carbon dioxide lasers, 3D displays, Combustion, Laser processing, 3D image processing, Scanners, Laser energy, Resonators
The CPOB (computer processing organic-glass burning-mark) method is used to measure TEM of High Power CO2 laser, the three-dimensional display of the TEM profile. So the center of light spot, the diameter of light spot, the distribution of power density along the line and the distribution of average power density on a circles area of different radius can be determined. This method is of great importance in the material laser machining field.
Design and fabrication of a weld protection drag-cover has been discussed in the paper as using high-power CO2 laser to weld Ti6A14V in various thickness. Argon was used to protect the weld and its nearby region from contamination from hydrogen, oxygen and nitrogen as their temperature were higher than 300 degrees Celsius. The protection effect has been proven to be good, since the weld surface was smooth, the obverse side appeared silvery white, and the reverse side appeared light-yellow.
According to the quasi-neutrality equation, the law of partial pressure, pressure equation, Saha equation and the principle of superposition on plasma refractive index, the Ar, He plasma's electron density, atom density, ion density and the variation of refractive index with changing of temperature are calculated when the pressure is 1,3,5,7 atm. respectively. Moreover it is analyzed that Ar, He plasma act on CO2 laser beam welding from the point of view that plasma and laser affect each other.
According to the power transmission on the high power CO2 laser welding, a new 2-point-1-line heat transfer model about laser beam welding is put forward. In this paper, an empiric formula is also brought forward which is proved to be consistent to the result of the actual welding.
This paper describes Ti-6Al-4V plae 1.3 mm thick welded by CO2 laser beam. The orthogonal test of 3-level and 3- factor is adopted and technological parameters are optimized. The shielding case full of Helium is put behind the pool This experiment indicates that the tensile strength of the weld can reach up to that of parent metal, when the weld joint is regular. Moreover the joint structure is analyzed also.
In the process of high-powered CO2 laser beam welding, the plasma produced above the welding pool shields the workpiece from the laser beam. In this paper the study about the effect of an added magnetic field on the penetration is made, it is proved that a suitable added magnetic filed can reduce the shielding effect of the plasma to the laser beam. The energy absorption ratio of the workpiece to the energy of laser beam is calculated. And the principle governing the penetration of sudden changes has been analyzed.
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