Nicola Contuzzi

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.

Manufacturing and Characterization of Ti6Al4V Lattice Components Manufactured by Selective Laser Melting

The paper investigates the fabrication of Selective Laser Melting (SLM) titanium alloy Ti6Al4V micro-lattice structures for the production of lightweight components. Specifically, the pillar textile unit cell is used as base lattice structure and alternative lattice topologies including reinforcing vertical bars are also considered. Detailed characterizations of dimensional accuracy, surface roughness, and micro-hardness are performed. In addition, compression tests are carried out in order to evaluate the mechanical strength and the energy absorbed per unit mass of the lattice truss specimens made by SLM. The built structures have a relative density ranging between 0.2234 and 0.5822. An optimization procedure is implemented via the method of Taguchi to identify the optimal geometric configuration which maximizes peak strength and energy absorbed per unit mass.

Manufacturing of 18 Ni Marage 300 Steel Samples by Selective Laser Melting

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.

Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting

The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456–0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading.

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.

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.

Analysis of the Material Removal Rate of Nanosecond Laser Ablation of Aluminium Using a Parallel Hatching Mode

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.

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.

Analysis of Shape Geometry and Roughness of Ti6Al4V Parts Fabricated by Nanosecond Laser Ablation

Laser milling is a micro-machining process that uses a laser beam as a tool to remove material through the layer-by-layer ablation mechanism. Generally in laser ablation, the quality of parts is reduced by melt accretions and thermal damage; therefore, this problem is reduced with shorter pulse duration, although ablation efficiency decreases as well. Thus, laser ablation in the nanosecond range still offers a good compromise between process quality and efficiency. Therefore, laser milling with nanosecond laser ablation requires an accurate study to reduce geometric defects induced by the process. The aim of this paper was to study the shape geometry and roughness of Ti6Al4V parts fabricated by laser milling using a nanosecond Nd:YAG laser source. The impact of the laser processing parameters on machining outcomes was studied in order to determine the optimized processing conditions for reducing geometrical defects and improving surface quality. In particular, the influence of average laser power, frequency, and scanning speed was investigated. The geometry of micro-parts was revealed using a 3D digitizing system, the Optimet Mini Conoscan 4000, which combines a non-contact, single-point measuring sensor based on conoscopic holography technology. The use of this measurement technology yielded complete information of the shape geometry and dimensions of the built parts. In addition, the roughness of manufactured surfaces was assessed to complete the analysis.