Papers by Author: Sabina L. Campanelli

Abstract: Laser ablation is a new, very flexible process for micro-fabrication of micro-moulds and other micro-system devices. This process is suitable for machining difficult-to-machine materials, like ceramics, dielectrics, carbide and hardened steel with excellent productivity and surface. The paper presents the investigation on the material removal rate of aluminium 5754 using a nanosecond Nd:YAG laser with a wavelength of 1064 nm.

Abstract: Direct Laser Metal Deposition (DLMD) is actually one of the most attractive techniques in the group of Material Accretion Manufacturing (MAM) processes. In fact, the DLMD technology is able to realize, to repair and restore, objects, moulds and tools, directly from the 3D CAD model in a rapid and economic way. A great variety of metals, including those very difficult to work with the conventional techniques, can be shaped in a large number of complex geometries. This technique is also well suited to produce very hard coatings. The metallic parts, which are obtained through melting coaxially fed powders with a laser, present very good mechanical properties, with minimum porosity and good adhesion to the substrate. The objective of this work was to optimise the scanning velocity of the laser beam in order to maximize the density of DLMD parts. The optimization procedure was worked out with a mathematical model together with an experimental analysis to study the shape of the track clad generated melting coaxially fed powders with a laser. The material tested was Colmonoy 227-F, a nickel alloy specially designed for manufacturing moulds. The presented methodology has permitted to select the better combination of parameters that produce almost full density parts, free of cracks and well bonded to the substrate sintered parts.

Abstract: Selective Laser Sintering (SLS), has become one of the most popular technique in the layer manufacturing processes because of the ability to build complex geometries models with a wide range of materials. Recently, the interest in SLS is mainly focused into metals because of the possibility of producing models not only for the prototyping step but also as functional parts. Driven by the need to process nearly full dense objects, with mechanical properties comparable to those of bulk materials and by the desire to avoid long post processing cycles, Selective Laser Melting (SLM) has been developed. SLM represents an evolution of the SLS process: in the first one the complete melting of powder occurs rather than sintering or partial melting of the second one. SLM, is mainly suitable to produce tools and inserts with internal undercuts and channels for conformal cooling for injection molding. A careful control of the parameters which influence the melting and the amount of energy density involved in the process is necessary to get parts with optimized quality. The aim of this paper was to study the effect of the main process parameters (laser power, scan speed, scan spacing, hatch spacing, scanning strategy) and of thermal treatments on the quality of built parts in terms of hardness, density, microstructure, and mechanical properties. The 18 Ni Marage 300 steel, one of the most used materials in the die industry was investigated, using a Nd:YAG laser with a maximum power of 100W.

Abstract: Direct Laser Metal Deposition (DLMD) is an emerging technique in the group of Material Accretion Manufacturing (MAM) processes because of the possibility to fabricate and to repair a wide range of metal components with a complex geometry, starting from metal powders. DLMD is a technology which combines computer aided design, laser cladding and rapid prototyping. Fully dense metallic parts can be directly obtained through melting coaxially fed powders with a laser. The success of this technology in the die and tool industry depends on the parts quality to be achieved. An accurate control of the parameters such as laser power, spot diameter, scanning speed and powder mass flow rate is fundamental to obtain the required geometric dimensions and material properties. In this work, the performance of the DLMD process was examined in terms of hardness, porosity, microstructure, and composition. A fitting equipment was built and used for the experiments together with a CO2 laser machine with a maximum power of 3 kW. The material used for experimental tests was Colmonoy 227-F, a Nickel alloy specially designed for glass container mould protection and restoration.