The process of Selective Laser Melting (SLM) is an innovative technology for rapid prototyping that can be included among the SFF (Solid Freeform Fabrication) techniques, which are characterized by "free-form" manufacturing of solid parts. SLM is an additive technology that operates starting from the data encoded in the three-dimensional computer aided design (CAD) file of the component to be built. After the slicing operation made on the 3D model of the component, the consequent data file is sent to a computer-controlled laser device that fuses successive layers of metal powder to create the three-dimensional product. The SLM is a technological process which involves optical, thermal and solidification phenomena; thus the analysis of the process is rather complex. This work aims to study the molten/solidified zone in SLM samples through the experimental analysis of the shape and the size of laser tracks. The functional relationships between dimensional parameter of the molten/solidified track and the main parameters used to control the process was identified. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

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.

Friction Stir Welding (FSW) has demonstrated a significant potential for joining low melting point non-ferrous metals in several joint configurations. During FSW metals are joined in the solid state due to the heat generated by the friction and flow of metal by the stirring action of a pinned tool. This paper reports an experimental investigation on the effects of geometry and surface coating of the tool shoulder on the defectiveness, the microstructure and the microhardness of a 3 mm thick 5754H11 aluminium alloy butt weld. During the experiments the diameter and slope of the shoulder varied. Moreover a tungsten carbide coated was tested. The pin geometry and dimensions were kept constant. Four different tools for shoulder geometry and coating condition were tested. The weld was characterized in terms of the bead morphology and the grain size. The weld microhardness profile was measured for all the microstructural zones of the friction stir welding process. The obtained results provide a deeper knowledge of the effect of the tool shoulder geometry and surface condition on the aluminium alloy weldability

Laser milling (LM) can be classified as a layer manufacturing process in which the material is removed by a laser beam by means of the ablation mechanism. It is a laser machining process which uses a laser beam to produce 3D shapes into a wide variety ofmaterials. It is also known as laser ablation. It shows clear advantages versus the traditional milling such as the unlimited choice of materials, the direct use of computer-aided design structure data, the high geometric flexibility, and the touchless tool. LM requires the selection of optimal machining parameters for the job. Unlike the mechanical milling and themechanical incision, the depth of the single removed layer is chosen at the beginning as input parameter of the process. In LM, the ablated depth depends from the process parameters such as laser power, scan speed, pulse duration, and pulse frequency. This work aims to develop an algorithm that can predict the parameters necessary to execute the material removal with a preset ablation depth. Using the results of an experimental campaign, the laser milling process was modeled by means of a back-propagation artificial neural network. Then, an iterative algorithm, based on the previous trained neural network, permitted to calculate the scanning velocity and pulse frequency that approached for the best the preset ablation depth. The developed approach represents a mean for the rational selection of laser ablation process parameters. It can be performed in an intuitive manner since it uses simple artificial intelligence like the artificial neural network.

In this paper the effects of the strain rate on the inelastic behavior and the self-heating under load conditions are presented for polymeric materials, such as polymethyl methacrylate (PMMA), polycarbonate (PC), and polyamide (PA66). By a torsion test, it was established that the shear yield stress behavior of PMMA, PC, and PA66 is well-described by the Ree-Eyring theory in the range of the considered strain rates. During the investigation, the surface temperature was monitored using an infrared camera. The heat release appeared at the early stage of the deformation and increased with the strain and strain rate. This suggested that the external work of deformation was dissipated into heat so the torsion tests could not be considered isothermal. Eventually, the effect of the strain rate on the failure modes was analyzed by scanning electron microscopy.

In this paper a new generation of fiber laser assisted by a MIG source was used to weld AA5754-H111 aluminum alloy in 3. mm thick butt configuration. The effects of laser and arc powers on the weld geometry and properties were studied. Weld geometry and porosity were measured. The microstructure was investigated by optical microscope and Vickers micro-hardness was taken. The residual stress close to the heat affected zone was measured by the incremental hole-drilling method. Eventually, the tensile test was conducted in order to compare the mechanical properties of the weld with those of the parent metal.For the first time the sensitiveness of the hybrid welding of the 5754 aluminum alloy to the arc and laser powers was demonstrated. Higher laser power favored the stability of the process and provided good structural and geometrical properties of the weld. Further investigation can be performed in order to optimize the weld soundness and the energy efficiency of hybrid welding an aluminum alloy using a fiber laser.

The objective of this chapter is to give an essential presentation on the theoretical foundations of the finite-element modeling of weld phenomena. The presented fundamentals of thermal, microstructure, and mechanical analysis embrace models from computational solid mechanics. The modeling of the weld pool fluid calls for computational fluid dynamics. The modeling techniques are validated against a variety of reference solutions for both fusion and solid-state welding.

La saldatura del titanio è largamente diffusa nei vari settori dell’industria metalmeccanica e aerospaziale. Negli ultimi anni è aumentata la necessità di saldare il titanio ad altre leghe leggere ferrose e non come l’alluminio. Le maggiori difficoltà nella saldatura eterogenea del titanio sono dovute alla formazione di un ossido superficiale che si può opporre alla fusione o alla saldobrasatura con metalli dissimili. In questa memoria sono riportati i risultati relativi alla saldatura con laser a fibre del titanio Ti6Al4V con una lega d’alluminio 5754. I due metalli sono saldati mediante un irraggiamento laser della superficie del titanio in prossimità del giunto con l’alluminio. Quest’ultimo fonde a causa dell’onda di calore che si trasmette dalla zona fusa del titanio verso l’alluminio. La caratterizzazione metallurgica e meccanica del giunto dimostra la possibilità di arrivare così a un giunto di qualità accettabile senza particolari preparazioni delle superfici a contatto.