The Experimental Research Of Laser-cutting Stainless Steel Underwater

Some new methods and equipments for cutting underwater have been developed successively in order to adapt the development of project construction and disintegration underwater and the requirement of the special construction and the special environment. They have been applied to the actual production. Thus, it increases cutting capability, speed and quality underwater.When laser cutting, the laser-beam which is focused to the high power density exposes to the surface of the work-piece. The material which is exposed melts, vaporizes, ablates or reaches ignition point. At the same time, high speed air-stream which is coaxial with the laser-beam blows the fusing mass. Thus, the work-piece will be cut off. Using the technique of laser cutting people can cut many hard material ,such as metal, non-metal board ,composite material, as well as tungsten carbide and titanium carbide. It is applied extensively in the fields of defense construction, aerospace and mechanical project.In this subject,304 stainless steel is used for experimental material .We cut the 304 stainless steel plates underwater with laser-beam. The plates are placed underwater, and the gas is not allowed to use. The cutting type is melting cutting. The laser parameters such as output power, cutting velocity, focal position and pressure of subsidiary gas are not regarded. We research chiefly the cutting quality with the influence which is taken by the parameters such as distance underwater, laser wavelength, velocity of water and the circumstance around.The research indicates that the absorptivity of water to the laser with different wavelength is different. The absorptivity to the laser which wavelength is near ultraviolet light is worst. It is to say that the penetration of the laser in this area is most intensive. When the distance underwater is increased, the kerf width is reduced, and the surface roughness is increased. As the velocity of water is increased, the kerf width is reduced firstly, and then increased; the surface roughness is reduced firstly, and then increased, too. This is related to the state of the flow(lamellar flow or turbulent flow).When the turbidity of the flow is increased, the absorptivity of particle to the laser is intensified. The laser energy that reaches to the surface of the work-piece is reduced greatly. It influences cutting quality seriously.The amount of the laser energy that reaches to the surface of the work-piece results in the area of heat-affected zone. And it influences the cutting quality directly. Using the method of numerical analysis, we can simulate the formation of heat-affected zone, and predict the thermal distribution of cutting underwater. Thus, we can certify the reliability of theoretical analysis, and instruct the actual operation.In all, the complexity of the underwater environment determines the hardness of cutting underwater. When cutting underwater, we should take these factors account to get the best cutting quality.