Andrea Angelastro

Capabilities and Performances of the Selective Laser Melting Process

The current market is in a phase of accelerated process of change, that leads companies to innovate in new techniques or technologies to respond as quickly as possible to the everchanging aspects of the global environment. The economy of a country is heavily dependent on new and innovative products with very short development time. Companies, currently, have considerable success, only if they develop the ability to respond quickly to changing of customer needs and to use new innovative technologies. In this context, the companies that can offer a greater variety of new products with higher performance resulting in advantage over the other. At the heart of this environment there is a new generation of customers, who forced organizations to research new technologies and techniques to improve business processes and accelerate product development cycle. As a direct result, factories are forced to apply a new philosophy of engineering as the Rapid Response to Manufacturing (RRM). The concept of the RRM uses products previously designed to support the development of new products. The RRM environment was developed by integrating the various technologies, such as CAD-based modelling, the knowledge-based engineering for integrated product and process management and the direct production concepts. Direct production uses prototyping, tooling and rapid manufacturing technologies to quickly test the design and build the part (Cherng et al., 1998). Among RRM technologies, Rapid (RP) and Virtual (VP) Prototyping are revolutionizing the way in which artefacts are designed. Rapid Prototyping (RP) technologies embraces a wide range of processes for producing parts directly from CAD models, with little need for human intervention; so, designers can produce real prototypes, even very complex, in a simple and efficient way, allowing them to check the assembly and functionality of the design, minimizing errors, product development costs and lead times (Waterman & Dickens, 1994). The SLS technology was developed, like other RP technologies, to provide a prototyping technique to decrease the time and cost of the product cycle design. It consists of building a three dimensional object layer by layer selectively sintering or partial melting a powder bed by laser radiation.

Optimization of Ni-Based WC/Co/Cr Composite Coatings Produced by Multilayer Laser Cladding

As a surface coating technique, laser cladding (LC) has been developed for improving wear, corrosion, and fatigue properties of mechanical components. The main advantage of this process is the capability of introducing hard particles such as SiC, TiC, and WC as reinforcements in the metallic matrix such as Ni-based alloy, Co-based alloy, and Fe-based alloy to form ceramic-metal composite coatings, which have very high hardness and good wear resistance. In this paper, Ni-based alloy (Colmonoy 227-F) and Tungsten Carbides/Cobalt/Chromium (WC/Co/Cr) composite coatings were fabricated by the multilayer laser cladding technique (MLC). An optimization procedure was implemented to obtain the combination of process parameters that minimizes the porosity and produces good adhesion to a stainless steel substrate. The optimization procedure was worked out with a mathematical model that was supported by an experimental analysis, which studied the shape of the clad track generated by melting coaxially fed powders with a laser. Microstructural and microhardness analysis completed the set of test performed on the coatings.

Characterization of Colmonoy 227-F Samples Obtained by Direct Laser Metal Deposition

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.

Study of a fiber laser assisted friction stir welding process

Friction stir welding is a relatively new joining technique. This technique, which is considered a derivative of the more common friction welding method, was developed mainly for aluminum and its alloys. In recent years, this method has been used to join various other alloys. FSW has many advantages, including the following: the welding procedure is relatively simple with no consumables or filler metal; joint edge preparation is not needed; oxide removal prior to welding is unnecessary; high joint strength has been achieved in aluminum and magnesium alloys; FSW can be used with alloys that cannot be fusion welded due to crack sensitivity. The drawbacks of FSW include the need for powerful fixtures to clamp the workpiece to the welding table, the high force needed to move the welding tool forward, the relatively high wear rate of the welding tool, and weld speeds in FSW are slower, which can lead to longer process times. To overcome these drawbacks, a fiber laser-assisted friction stir welding system was designed (FLAFSW). The system combined a conventional commercial friction machine and a fiber pumped laser system. The scope is to investigate the influence of the laser assistance on the weld quality. A number of different aluminum plates, which are still mentioned to be difficult to be joint as intermetallic phases appear during melting welding techniques, were used. The evaluation of quality was performed through analysis of appearance, mechanical and microstructure characterization of the weld.

A Methodology for Optimization of the Direct Laser Metal Deposition Process

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.

Laser-assisted friction stir welding of aluminum alloy lap joints: microstructural and microhardness characterizations

Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. The laser Assisted Friction Stir Welding (LAFSW) combines a Friction Stir Welding machine and a laser system. Laser power is used to preheat and to plasticize the volume of the workpiece ahead of the rotating tool; the workpiece is then joined in the same way as in the conventional FSW process. In this work an Ytterbium fiber laser with maximum power of 4 kW and a commercial FSW machine were coupled. Both FSW and LAFSW tests were conducted on 3 mm thick 5754H111 aluminum alloy plates in lap joint configuration with a constant tool rotation rate and with different feed rates. The two processes were compared and evaluated in terms of differences in the microstructure and in the micro-hardness profile.

Experimental Analysis of the Direct Laser Metal Deposition Process

In the current economic situation, with a liberalized and worldwide trade, the weight of time and costs reduction for developing new products increases. In particular, the tooling processes, which are already expensive and time consuming, recently became a critical trouble. The geometric complexity, the number of variants and the amount of requirements that characterize the products that are required by market increase this trouble. Reducing time to market and the international competitiveness are two of the biggest challenges for manufacturing companies of the twenty-first century. They not only have to produce component with high quality, low cost and better functionality than before, but also have to respond to customer requests in a more reactive way as possible. To do this they have to accelerate, of course, the tooling stage and to reduce processing times. Indeed, it is known that a delay of some weeks during the development and the commercialization of a new product may result in a loss of profits of 30%. These factors thrust the manufacturing companies to find solutions both in technology and in organization. The Material Accretion Manufacturing (MAM), consisting of additive technologies, and the modern operational structures, such as those provided by the Concurrent Engineering, are effective tools that help to reduce time and costs. Probably, they are the best weapons that western industry can take to survive the fierce competition with those countries, mainly asiatic and eastern europe countries, where labor has a very low cost, but is nowadays able to achieve good quality products. Among the various technologies MAM, thanks to which it is possible to apply the basic concepts of Rapid Prototyping to realize finished products, stands out, with its huge capacity, the Direct Laser Metal Deposition (DLMD) process of metal powders. But what are the key features of this process? What are the properties of the products it is able to accomplish? For what types of applications have already been used or are expected to do it? This chapter will give a comprehensive answer to these questions. The DLMD pertain the group of technologies called Material Accretion Manufacturing (MAM), and, in particular, is based on the principles of rapid prototyping (RP) and laser cladding (Peng et al., 2005). The MAM technologies start by the 3D design to get the object in a single pass through an additive processing, that is overlapping each other layers with a small thickness. Other words, there is a conversion of the three-dimensional piece into N two-dimensional overlapping pieces, that constitute the layers.

Preliminary investigation on hybrid welding of selective laser molten parts

In this paper the innovative arc-fiber laser welding process (hybrid welding) was investigated on steel parts built by the Selective Laser Melting (SLM) process.SLM is probably the most rapidly growing technique in Additive Manufacturing (AM) technologies. This success results mainly from the possibility to create metal parts with complex shape, intrinsic engineered features and mechanical properties comparable with those of components produced with traditional processes.A preliminary study was performed on the possibility of welding SLM parts. The choice of the hybrid arc-fiber laser welding was justified by the possibility of this process to avoid air inclusions and fill gaps along the seam due to the relevant roughness of SLM parts. The hybrid joints were characterized in terms of micro-hardness, microstructure and shape of the transverse cross section. Comparisons between wrought, sintered and dissimilar welds were performed.In this paper the innovative arc-fiber laser welding process (hybrid welding) was investigated on steel parts built by the Selective Laser Melting (SLM) process.SLM is probably the most rapidly growing technique in Additive Manufacturing (AM) technologies. This success results mainly from the possibility to create metal parts with complex shape, intrinsic engineered features and mechanical properties comparable with those of components produced with traditional processes.A preliminary study was performed on the possibility of welding SLM parts. The choice of the hybrid arc-fiber laser welding was justified by the possibility of this process to avoid air inclusions and fill gaps along the seam due to the relevant roughness of SLM parts. The hybrid joints were characterized in terms of micro-hardness, microstructure and shape of the transverse cross section. Comparisons between wrought, sintered and dissimilar welds were performed.

Dimensional and metallurgical characterization of free-formed colmonoy 227-F samples obtained by laser radiation

Direct Laser Metal Deposition (DLMD) and Selective Laser Sintering (SLS) are actually the most growing techniques 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.In this work a comparison between the two above processes was performed. Experimental tests were conducted to study the effect of the main parameters involved in the two processes (laser power, scanning speed, density of energy) on the final quality of the manufactured parts in terms of adhesion, porosity, surface roughness and cracks.A fitted equipment was built and used for the experiments together with a CO2 laser machine with a maximum power of 3 kW. The material used was the Colmonoy 227-F on a substrate of AISI 304.Direct Laser Metal Deposition (DLMD) and Selective Laser Sintering (SLS) are actually the most growing techniques 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.In this work a comparison between the two above processes was performed. Experimental tests were conducted to study the effect of the main parameters involved in the two processes (laser power, scanning speed, density of energy) on the final quality of the manufactured parts in terms of adhesion, porosity, surface roughness and cracks.A fitted equipment was built and used for the experiments together with a CO2 laser machine with a maximum power of 3 kW. The material used was the Colmonoy 227-F on a substrate of AISI 304.

Thermal field monitoring and analysis of its influence on Direct Laser Deposition of single tracks of a nickel superalloy

Direct Laser Metal Deposition (DLMD) has been successfully applied for the coating or the repair of several kind of components, such as molds and dies. Recently, the aeronautical sector is also showing a high interest in this process for the repair of turbines and transmissions. However, technical requirements to be met for the repair of aeronautical components are much more stringent than standards of other industrial fields. Some of the deposited material defects that need to be carefully controlled are cracks and porosity, which largely depend on the temperature peaks and the cooling rates generated during the process. The aim of this work is to monitor the temperature field that was generated during the DLMD process, analyze its variation with some process parameters and study its effects on clad geometry and on dilution with the substrate. In this research, a number of experimental tests were designed for the deposition of single clads of a Nickel superalloy powder on an AISI 304 stainless steel substrate, using an Ytterbium fiber laser source. Temperature fields monitoring was carried out using a thermal camera capable of detecting temperatures up to 2500 °C.