Laser polishing of tool steel with CO₂ laser and high-power diode laser

This paper presents the effect of the laser-polishing process applied to a milled and EDMed surface of DIN 1.2379 tool steel commonly used in the die and mold industry. The martensitic structure of this type of steel (showing hardness values up to 62 HRC) makes the polishing operation extremely difficult. At present polishing must be carried out manually by skilled workers, and this entails an expensive and prolonged process. An alternative to automation of the polishing process is a laser-polishing process, based on tightly controlled melting of a micro-layer of surface material which flows into and fills topographic valleys for a smoothed surface topography. Thus the main process parameters have been identified and optimized using two different types of industrial laser: a CO₂ laser and a high-power diode laser (HPDL), obtaining up to 90% roughness reduction with mean roughness values (Ra) below 0.5 μm. Moreover, in order to secure a complete study of the process in accordance with the energy radiated, three-dimensional topographic surfaces were measured and a metallurgical study performed to determine the effect of laser radiation on the structure of the material.