Showing papers by "Giuseppe Casalino published in 2017"
TL;DR: In this article, the feasibility of using a fiber laser to perform a dissimilar metal joining was explored, and the laser offset welding (LOW) method was demonstrated to be a promising technique to join dissimilar metals welds, being capable to produce an effective bonding with good tensile strength.
70 citations
TL;DR: In this article, the authors present a study which integrated the numerical and experimental approaches, for the evaluation of the properties of 18 Ni (300) laser deposited marage powder, which was deposited onto AISI 304 substrate by a CO2 laser.
Abstract: Direct laser powder deposition (DLPD) is a laser process that can produce fully dense components from powders for production and repairing purposes. Marages are high-strength steels that are hardened through ageing treatment. This work presents a study which integrated the numerical and experimental approaches, for the evaluation of the properties of 18 Ni (300) laser deposited marage powder. The powder was deposited onto AISI 304 substrate by a CO2 laser. During the experiments, laser power, scanning speed, powder flow rate and degree of overlapping varied according to a Taguchi plan. In particular, the degree of overlapping between adjacent layers and between successive tracks was calculated using an analytical model. Density, porosity, dilution, microstructure, adhesion to the substrate and microhardness of multilayer samples were evaluated using statistical algorithms. Both clad-substrate and clad-clad interfaces were characterised by metallographic and SEM analysis. High-density samples, with a satisfactory level of porosity, for successful additive and part repair applications, were fabricated through the method proposed and characterised in this paper.
46 citations
10 Aug 2017
TL;DR: In this paper, both two-dimensional and three-dimensional Gaussian heat sources were studied for the thermal analysis of the fiber laser welding of titanium and aluminum dissimilar butt joint, and the models were calibrated comparing the fusion zone of the experiment with that of the numerical model.
Abstract: For a dissimilar laser weld, the model of the heat source is a paramount boundary condition for the prediction of the thermal phenomena, which occur during the welding cycle. In this paper, both two-dimensional (2D) and three-dimensional (3D) Gaussian heat sources were studied for the thermal analysis of the fiber laser welding of titanium and aluminum dissimilar butt joint. The models were calibrated comparing the fusion zone of the experiment with that of the numerical model. The actual temperature during the welding cycle was registered by a thermocouple and used for validation of the numerical model. When it came to calculate the fusion zone dimensions in the transversal section, the 2D heat source showed more accurate results. The 3D heat source provided better results for the simulated weld pool and cooling rate.
38 citations
25 Jul 2017
TL;DR: In this paper, the weld microstructure and those compounds over two different technologies: the laser offset welding and the hybrid laser-MIG (Metal inert gas) welding were explored.
Abstract: Welding between Fe and Al alloys is difficult because of a significant difference in thermal properties and poor mutual solid-state solubility. This affects the weld microstructure and causes the formation of brittle intermetallic compounds (IMCs). The present study aims to explore the weld microstructure and those compounds over two different technologies: the laser offset welding and the hybrid laser-MIG (Metal inert gas) welding. The former consists of focusing the laser beam on the top surface of one of the two plates at a certain distance (offset) from the interfaces. Such a method minimizes the interaction between elevated temperature liquid phases. The latter combines the laser with a MIG/MAG arc, which helps in bridging the gap and stabilizing the weld pool. AISI 316 stainless steel and AA5754 aluminum alloy were welded together in butt configuration. The microstructure was characterized and the microhardness was measured. The energy dispersive spectroscopy/X-ray Diffraction (EDS/XRD) analysis revealed the composition of the intermetallic compounds. Laser offset welding significantly reduced the content of cracks and promoted a narrower intermetallic layer.
30 citations
TL;DR: In this paper, dissimilar 2-mm thickness AA6000 and Ti6Al4V butt joints were produced by shifting an Yb fiber laser beam on the upper surface of the Ti sheet.
25 citations
TL;DR: In this article, the quality of micro-holes, which were drilled by Yb:KGW laser end-pumped by high-power diode bars, was evaluated by the ANOVA analysis.
23 citations
05 Sep 2017
TL;DR: In this article, the influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging between 30 and 100 mm/min.
Abstract: The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging between 30 and 100 mm/min. The effect of the tool dwelling was also analysed. The force vs. processing time curve has shown a very complex behaviour during the lowering motion of the pin tool related to the occurrence of both primary and secondary plunging. The tool dwelling produces a quick decrease in the vertical force with growing processing time until reaching a constant value. It was also seen that the tool dwelling does not influence the vertical force in the subsequent stage. As the tool began its welding motion, the vertical force immediately gets to a constant value until tool pulling out takes place. Furthermore, it was shown that the growth in the welding speed and the decrease in the rotational speed lead to an increase in the vertical force. The mechanical properties of the joints were evaluated versus the process parameters and the relationships among the ultimate tensile strength and ultimate elongation and the vertical force were defined. Finally, the microstructure developed during the friction stir welding was investigated and related to the mechanical properties of the joints.
22 citations
TL;DR: In this article, the effects of two important process parameters, i.e., hatch spacing and step height, on the properties of the built parts were analyzed. And the statistical significance of the studied process parameters was assessed by the analysis of the variance.
Abstract: This paper presents a study on process parameters and building strategy for the deposition of Colmonoy 227-F powder by CO 2 laser with a focal spot diameter of 0.3 mm. Colmonoy 227-F is a nickel alloy especially designed for mold manufacturing. The substrate material is a 10 mm thick plate of AISI 304 steel. A commercial CO 2 laser welding machine was equipped with a low-cost powder feeding system. In this work, following another one in which laser power, scanning speed and powder flow rate had been studied, the effects of two important process parameters, i.e. hatch spacing and step height, on the properties of the built parts were analysed. The explored ranges of hatch spacing and step height were respectively 150–300 μm and 100–200 μm, whose dimensions were comparable with that of the laser spot. The roughness, adhesion, microstructure, microhardness and density of the manufactured specimens were studied for multi-layer samples, which were made of 30 layers. The statistical significance of the studied process parameters was assessed by the analysis of the variance. The process parameters used allowed to obtain both first layer-to-substrate and layer-to-layer good adhesions. The microstructure was fine and almost defect-free. The microhardness of the deposited material was about 100 HV higher than that of the starting powder. The density as high as 98% of that of the same bulk alloy was more than satisfactory. Finally, simultaneous optimization of density and roughness was performed using the contour plots.
22 citations
TL;DR: In this article, the authors used ElectroSpark Deposition (ESD) to fabricate a 2024 aluminum alloy deposit on a similar substrate, which was characterized by the overlapping of layers with a mixed microstructure.
Abstract: ElectroSpark Deposition (ESD) is a pulsed micro-welding process that is capable of depositing wear and corrosion resistance deposit to repair, improve, and to extend the service life of the components and tools. Major new applications have taken place in gas turbine blades and steam turbine blade protection and repair, and in military, medical, metal-working, and recreational equipment applications. In this study, the ESD technique was exploited to fabricate 2024 aluminum alloy deposit on a similar substrate. The deposits were deposited using different process parameters. Heat input was varied on three levels. The outcoming microstructure was analyzed by optical and scanning electron microscopies. The deposit was characterized by the overlapping of layers with a mixed microstructure. The average hardness was independent from the process parameters. Both porosity inside the deposits and cracks at the deposit/substrate interface were detected. The porosity lowered with the heat input and increased the average length of cracks.
19 citations
25 Jan 2017
TL;DR: In this paper, strong, light-weight, multi-functional, high performing products are key for achieving success in the worldwide markets, meeting those requirements calls for enabling technologies that lead to innovative and sustainable manufacturing.
Abstract: Nowadays, strong, light-weight, multi-functional, high performing products are key for achieving success in the worldwide markets. Meeting those requirements calls for enabling technologies that lead to innovative and sustainable manufacturing [1].[...]
14 citations
19 Jun 2017
TL;DR: The control framework of the DexROV Horizon 2020 project is presented, based on the task priority concept, extended by the authors to allow the activation and deactivation of tasks.
Abstract: In this work, the control framework of the DexROV Horizon 2020 project is presented. The framework is based on the task priority concept, extended by the authors to allow the activation and deactivation of tasks. The general concepts of control objectives, task and actions are given. The execution of a pipeline's weld inspection is used as study case to test the proposed framework in a simulation setting.
01 Jun 2017
TL;DR: The paper presents the first simulative results and algorithmic developments of the task-priority based control applied to a distributed sampling network in an area coverage or adaptive sampling mission scenario.
Abstract: The paper presents the first simulative results and algorithmic developments of the task-priority based control applied to a distributed sampling network in an area coverage or adaptive sampling mission scenario. The proposed approach allowing the fulfilment of a chain of tasks with decreasing priority each of which directly related to both operability and safety aspects of the entire mission. The task-priority control is presented both in the centralized and decentralized implementations showing a comparison of performance. Finally simulations of the area coverage mission scenario are provided showing the effectiveness of the proposed approach.