Using the model of a cylinder-type heat source, the power loss owing to heat conduction in laser cutting and welding of metals is calculated analytically. The case of laser cutting is described by taking into account the influence of the generated cutting kerf using numerical calculations. Both the analytical and the numerical solution for the power loss deposited into the material are well described by approximative formulae. The theoretically predicted power loss into the cut workpiece is confirmed by measurements of the temperature rise within the metal sheet in laser cutting experiments.

The laser-induced vaporization process of a metallic surface is incorporated into a simple model which describes the phase transformation and the expansion of the metal vapour against the ambient air as a function of the laser intensity and material properties. It is shown that there exists a material-dependent minimal laser intensity, where the vapour properties at the vaporization front become independent from further expansion against the ambient gas. This laser intensity is called critical intensity and also depends on the beam waist at the vaporization front. To check the model, a comparison with an experimental situation is performed, where a metal surface is irradiated by a Nd:YAG laser beam. The position of a shock front coming from the vaporizing metal surface were detected and compared with the calculated position.

The process of vaporisation of a light-absorbing metal under laser irradiation is investigated from a theoretical point of view. The tools are the Euler equations, the stationary heat-flow equation and the kinetic equations to calculate the gas dynamical properties of the edge of the Knudsen layer. Using the one-dimensional deflagration theory, it is shown that the local sound velocity is an upper bound for the metal vapour velocity at the phase boundary. Furthermore, it is shown that for an absorbed intensity Ia, which is greater than a certain threshold intensity Ic, the vaporisation process is independent of the ambient gas. This intensity Ic is calculated for aluminium and iron. On the assumption that a stationary limit of the vaporisation process is reached, the solution of the Euler equations is equivalent to the solution of a Riemann problem.

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