Abstract
Within the scope of this study, basic experimental research was carried out on macro-laser polishing of tool steel 1.2379 (D2) using a square intensity distribution and continuous wave laser radiation. The influence of the individual process parameters on surface topography was analyzed by a systematic investigation of a wide range of process parameters for two different, square laser beam diameters. Contrary to a typical laser polishing approach, it was shown that short interaction times (high scanning velocity and small laser beam dimensions) are required to reduce both micro-roughness and meso-roughness. A significant reduction of surface roughness of approx. 46% was achieved from Raini = 0.33 ± 0.026 µm to Ramin = 0.163 ± 0.018 µm using a focused square laser beam with an edge length of dL,E = 100 µm at a scanning velocity of vscan = 200 mm/s, a laser power PL = 60 W and n = 2 passes. However, characteristic surface features occur during laser polishing and are a direct consequence of the laser polishing process. Martensite needles in the micro-roughness region, undercuts in the meso-roughness region, and surface waviness in the macro-roughness region can dominate different regions of the resulting surface roughness spectrum. In terms of mechanical properties, average surface hardness was determined by hundreds of nano-indentation measurements and was approx. 390 ± 21 HV0.1 and particularly homogeneous over the whole laser polished surface.
Highlights
Laser polishing of metallic surfaces is an emerging manufacturing process that aims to replace time consuming and cost intensive manual polishing operations
The most recent scientific publications focusing on laser polishing of steels, on modelling of continuous wave laser remelting/laser polishing process, on special approaches of laser polishing, and on an analysis of the microstructural properties of laser polished surface layers of steels were described by Temmler et al [9]
In this work we investigated cw laser polishing of tool steel 1.2379 (AISI D2) for two different laser beam sizes, three different scanning velocities and up to four remelting/polishing steps
Summary
Laser polishing of metallic surfaces is an emerging manufacturing process that aims to replace time consuming and cost intensive manual polishing operations. This is underlined by the fact that currently no coherent theoretical or numerical model exists that can predict the surface roughness after laser polishing with high reliability Such approaches exist, e.g., for LμP (Vadali et al [22], Ma et al [23], Chow et al [24]) or laser polishing/remelting using continuous laser radiation (Ukar et al [25], Richter et al [26], Temmler and Pirch [27]), none of these models takes into account material-specific structure formation processes during or after laser remelting or laser polishing, as described for example by Nüsser et al [21].
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