Several typical blue laser pointer processing, laser cladding and heat treatment, small splash, long focal length lens less pollution; laser cutting nozzle outlet is small, big pressure, can effectively prevent the laser welding spatter; focal length is short, sharp, molten pool reaction big splash, but the protection of gas flow is limited, so easily the pollution caused by the lens, become a very difficult problem in the industrialization of laser welding. Lens contamination causes laser beam to produce scattering, focusing on the poor, long time work will be the focus of drift, transmission to the work of the laser power loss, so that the laser welding performance is poor. The frequent cleaning and replacement of lenses seriously affect the efficiency of the work, a large number of splash to make crystal lenses due to thermal theory research.
Distortion and rupture. Non ferrous metals (such as Al, Cu) and powder metallurgy materials (such as diamond saw blades), such as laser welding, the splash is particularly serious, very easy to cause damage to the lens. The traditional burning laser pointer welding nozzle is conical, two gas: a coaxial gas for the protection of the weld, generally using inert gas Ar gas and He gas; another way for the side assist gas, used to control the plasma shielding to reduce plasma laser, increase penetration. The traditional coaxial nozzle gas flow are strictly limited, the nozzle diameter is 2 5mm, the gas flow rate is 7~9L/min, the gas flow is too large, the molten pool turned bad, uneven weld, hole.
The pneumatic window has been applied in the 10kWC2 laser of this unit. The purpose is to isolate the working gas from the outside air. We study the pneumatic nozzle is in the vertical direction of laser beam with high speed airflow, forming a gas barrier layer at the bottom of the optical components, on barrier metal spatter. The successful development and application of this kind of nozzle has important theoretical significance and practical value to solve the high power brightest laser pointer welding of easy to splash metal (such as powder metallurgy material).
Theoretical analysis and structural design of 1.1 gas dynamic analysis for pneumatic nozzle pneumatic transverse motion equation of the window size and the required gas flow M2: mechanical processing, local damage can be replaced. As shown, 4 parts respectively cross flow inlet channel, flow outlet channel, cylindrical and conical tip substrate. The inlet channel is provided with a square wire mesh, in order to reduce dead straight, uniform gas, by adjusting the different screen to determine the optimum air flow area and flow rate. Test conditions and methods using the American 1.25kW Coherent axial flow CO2 100mw laser pointer, quasi base mode output. Respectively, by using ZnSe transmission type focusing mirror and metal reflective focusing mirror, the 45 degree mirror is Cu mirror M.; the reflection type parabolic focusing mirror is Mo, the lens is easy to clean. The welding test material is 45 steel, surface polishing, plasma thermal spraying a layer of square specimen in inches NC workbench, after welding along the weld cross section cut, with the United States M400-H, optical microscope to observe and measure the morphology of weld. The main welding process parameters are: laser power P=1.2kW, welding speed 1.5mm - V, welding seam protection gas flow 7L/min, Ar gas protection.
The laser power of the laser is irradiated to the work piece by a hand held heat power meter, which is used for the protection of different nozzles. For the test of different lenses, after welding, the lens is removed, with a clean tape to splash particles deposited on the lens stick down, in the low magnification microscope observation and measurement of their size distribution, number of particles within a specific area of the record. The test results and analysis of 3.1 lens destructive test firstly using ZnSe lens, a common nozzle coaxial protection, 2800mm welding, lens rupture, it was observed that the fracture surface of the lens attached with a layer of fine granular spatter, transmission layer barrier of the 200mw laser pointer beam, the laser power measurement, the splash pollution caused by the transmission of laser energy the loss of up to 25%, the high heat causes the lens thermal distortion and damage; another piece of ZnSe lens using pneumatic nozzle, lateral gas flow 200L/min, 7000mm welding, intact lens. At the same time to study the relationship of transverse current to the nozzle tip coaxial flow, the results also show that the transverse current switch, transient and normal operation, the coaxial nozzle tip almost undetectable effect of transverse flow added, namely protective effect on the weld without any adverse effect.
The laser transmission efficiency by comparing the measured focusing system of laser power and laser power before the ratio of transmission efficiency, the ratio decreased with the increase of welding length, as shown in the welding of equal length 2800mm, ordinary nozzle transmission efficiency is only 71%, while the pneumatic nozzle improves 25%. presumably is 96%, when transmission the efficiency to 71%, the pneumatic nozzle can be welded 18000mm, is 6 times more than the ordinary nozzle. The particle distribution of the splash particles is shown to be almost 80% of the smaller particles (less than 0.2mm2 71994-2015ChinaAcademicournal) and all particles larger than 0.2mm2, compared with the common nozzle. The weld quality analysis comparative analysis also shows that the difference between the two nozzle welding characteristics, heat transfer welding lens into ordinary nozzle began to finite depth deep penetration appeared after a certain length, the ratio of weld penetration weld and heat transfer of the length of 1 according to the experimental phenomena can be seen, the weld changes are due to lens pollution so that the light beam is not stable 300mw laser pointer, power down. Pneumatic nozzle weld seam inspection results showed that 95% of the total length for deep penetration welding.
The pore distribution area of the weld cross section as shown, according to the observation, the pneumatic nozzle cross section has a few small pores (4X103 10m2) the average porosity of weld is about 2%, the ordinary single hole nozzle of atmospheric a0Ym2) the average porosity of up to 17%, according to the analysis, gas hole rate of different reasons is due to the use of pneumatic nozzle protective lenses, weld shield gas flow can be reduced, thereby reducing the disturbance of the weld pool, the low porosity, and ordinary nozzle to protect the lens, must use more air flow, make the weld porosity increase 4 Q. conclusion in the welding nozzle structure, the horizontal pneumatic nozzle is very effective in the the protection of reflective and transmissive optical elements, ZnSe lenses in the horizontal airflow under the protection of 7000mm after welding is still intact, and the ordinary nozzle welding after 2800mm damage, the same welding length, Compared with the conventional nozzle, the pneumatic nozzle can remove almost 80% of the particles. The results show that the advantages of pneumatic nozzle are as follows: (1) 400mw laser pointer beam focusing lens to protect the real power loss on the workpiece can be reduced by 25% with the gas; (2) stable deep welding welding up to the total length of the above 90%; (3) poly welding length between the lens cleaning two times 6 times of ordinary nozzle; (4) the weld porosity is lower than that of 2%. (5) of the nozzle tip without transverse flow.
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