Abstract
The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 µm, 10.6 µm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650 °C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.
Highlights
Nowadays laser materials processing is well-established in industry for several applications such as welding, cutting, cladding, etc
Since existing methods for the determination of the absorptivity mostly have shortcomings when it comes to the estimation of the energy coupling at high temperatures, a new measuring technique was developed
Little is known about the effect of high temperatures as well as of a process-induced surface oxidation on the energy coupling of a laser beam in materials
Summary
Nowadays laser materials processing is well-established in industry for several applications such as welding, cutting, cladding, etc. These processes mostly involve temperatures above the melting point and can even reach the boiling point. The effect of higher temperatures on the energy coupling of laser radiation is still scarcely explored. Tabulated values of optical properties such as refractive index n and extinction coefficient k in standard textbooks [1,2,3] are reported for room temperature or for particular measuring conditions far below room temperature. Some studies tried to examine the effect of non-laboratory conditions on the energy coupling of laser radiation
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