BEAM FOCUSING CHARACTERISTICS EFFECT ON ENERGY REFLECTION AND ABSORPTION IN DRILLING OR WELDING CAVITY OF PARABOLOID OF REVOLUTION

Energy flux absorbed by the cavity of a paraboloid of revolution subje ct to a focused high-intensity beam, is systematically and quantitativ ely investigated. The intensity of incident aux is a;Gaussian distribu tion, which is specified by the convergence angle, energy distribution parameter at the focal spot, and focal spot location relative to the workpiece surface. Absorption and scattering within the plasma in the cavity is assumed to be negligible. Using both analytical and Monte Ca rlo methods, and accounting for specular and diffuse reflections, the results find that energies absorbed by the cavity exhibit distinct reg ions for the focal spot lying above the cavity base. On the other hand , if the focal spot is below the base, absorbed energy flux is similar to a Gaussian distribution, and the maximum absorption is achieved. T he effects of the beam focusing characteristics on the distribution of absorbed flux are provided. Formations of weld defects such as spikin g and abnormally expanded fusion zone are proposed. (C) 1998 Elsevier Science Ltd. All rights reserved.