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In laser material processing, understanding the laser interaction and the effect of processing parameters on this interaction is fundamental to any process if the system is to be optimized. Expanding this to different materials or other laser systems with different beam characteristics makes this interaction more complex and difficult to resolve. This work presents a relatively simple physical model to understand these interactions in terms of mean surface enthalpy values derived from both material parameters and laser parameters. From these fundamental properties the melt depth and width for any material can be predicted using a simple theory. By considering the mean enthalpy of the surface, the transition from conduction limited melting to keyholing can also be accurately predicted. The theory is compared to experimental results and the predicted and observed data are shown to correspond well for these experimental results as well as for published results for stainless steel and for a range of metals. The results suggest that it is important to keep the Fourier number of the weld much smaller than one to make it efficient. It is also discussed that the surface enthalpy could be used to prodict other effects in the weld such as porosity and material expulsion.

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