Design surfaces by laser remelting

Abstract

Molds and dies are used today in the manufacturing of a wide range of industrial products. They have a broad field of applications from the air and space technology, the automotive sector, to electrical engineering, to household products and consumer goods. The surface of a part or product strongly influences its properties and functions e.g. it's visual appearance. The gloss thereby reflects one of the most important properties of a surface when it comes to evaluate the visual appearance. Therefore, among others, in this paper the influence of laser polishing on the generated specular gloss is investigated for the hot work steel 1.2343 (AISI: H11). On the one hand laser polished surfaces are measured by WLI and investigated by a spectral analysis of surfaces roughness. A spectral analysis is achieved by a discrete convolution of the surface profile with a Gaussian loaded function similar to ISO 11562. On the other hand specular gloss measurements were carried out at 20°, 60° and 85°. For the experiments a fiber‐coupled solid state disc laser (Yb : YAG; Q‐switched) is used (PL,max = 550 W; repetition frequency: fP = 5–20 kHz, pulse duration: tP = 0,7–3,5 µs, pulsed and cw‐operation). In general, scanning velocity and average laser power are two crucial procedural parameters for laser polishing with significant influence on the resulting surface roughness. These procedural parameters are investigated systematically, while other procedural parameters, such as laser beam diameter dL = 250 µm and track offset dy = 25 µm were kept constant. By this a significant reduction of roughness was achieved, especially for the wavelength interval λ < 320 µm. A correlation between specular gloss of surfaces and the measured micro‐roughness is carried out. In order to make a systematic classification laser polished fields are compared to surfaces which were prepared by conventional mechanical manufacturing processes, such as turning, milling, grinding, high end manual polishing etc. Specular gloss shows a good exponential correlation with micro‐ and meso‐roughness were as macro roughness shows no significant influence on the specular gloss. Additionally, a complete process chain for selectively laser polishing of metallic surfaces was developed in order to apply different levels of gloss onto free formed work pieces. Selective laser polishing and the process chain are demonstrated for a free formed tool insert with leather textured surface, where only the indentations of the leather texture were laser polished selectively

Laser surface melting of stainless steel anodes for reduced hydrogen outgassing

“…2a is an SEM image of the raster scanned surface of the SS sample, tilted at 45 degrees to the electron beam column; the LSM-treated and untreated areas are visible. The individual laser tracks can be seen as can the ripples within each track that are ori-ented in the direction of the laser beam scan; a phenomenon in CW laser melting commonly observed at high laser ED values [20]. Processing with lower ED tends to avoid ripple formation in the irradiated area but also reduces grain growth in the lattice of the sample.…”

Selective polishing method to increase precision in large format lightweight machine tools working with petrous material

“…Wang [22] developed a prediction model material removal with grinding stones; the relationship between pressure and depth removal is analyzed creating a distinctive profile material removal using Hertzian distribution. Temmler [23] developed an algorithm called selective laser polishing to enhance the surface appearance, through reallocation of material instead of ablation with laser remelting in metallic surfaces. This algorithm is not achieving the flatness and the material is not removed.…”

Suppression effect of a steady magnetic field on molten pool during laser remelting

“…Many surface engineering techniques have been applied to improve the surface properties of metal alloys, laser surface remelting technique is one of them [1]. This technique allows selective heating and melting of a surface, and modifies the surface properties by rapid melting and solidification [2][3][4].…”