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Abstract

In this publication laser micro polishing with an additional laser beam for pre-heating of the surface is investigated.The influence of the following process parameters on the surface roughness is examined: Pre-heating laser power, scanning velocity, beam offset of the two laser beams, and intensity distribution of the pre-heating laser beam. The two materials which were used for the experiments (martensitic tool steel and TiAl6V4) showed a different behavior: For martensitic tool steel the micro roughness was increased in comparison to conventional laser polishing with only one laser beam (single-beam technology) due to increasing formation of martensite. For TiAl6V4 the meso roughness of the surfaces was decreased in comparison to conventional laser micro polishing due to longer melt duration, so smoother surfaces wereobtained (up to 36% lower surface roughness for one spatial wavelength regime).

In this publication laser micro polishing with an additional laser beam for pre-heating of the surface is investigated.The influence of the following process parameters on the surface roughness is examined: Pre-heating laser power, scanning velocity, beam offset of the two laser beams, and intensity distribution of the pre-heating laser beam. The two materials which were used for the experiments (martensitic tool steel and TiAl6V4) showed a different behavior: For martensitic tool steel the micro roughness was increased in comparison to conventional laser polishing with only one laser beam (single-beam technology) due to increasing formation of martensite.

For the investigations an experimental setup is used that allows the independent alignment and
superposition of two laser beams, fig.1. The laser radiation is guided to the setup by optical fibers. The
diameters of the cw (green) and pulsed (red) laser beam can be aligned with motorized beam expanders. The
optical setup allows the independent alignment of the p- and s-polarized parts of the cw laser beam, but this
feature is not used in this investigation, the diameter of both parts is the same in all experiments. The position
of the pulsed laser beam to the cw laser beam can be shifted relatively with two piezo elements. The
positioning of the beam is fast enough to realize a meanderly scanning of the surface, fig. 2. The two laser
beams are finally superpositioned by a wavelength multiplexer and guided into a scan head. A more detailed
description of the setup can be found in Temmler et al., 2013.