Directed Energy Deposition of stainless steel wire with laser beam: evaluation of geometry and affection depth

Abstract This paper is aimed at investigating the process of Directed Energy Deposition of steel wire to the purpose of maintenance and repair: this technology is receiving increasing interest in the frame of Additive Manufacturing and has been investigated for different metals and different substrates. An experimental plan has been designed here to investigate the dependence of the geometry on the governing factors in single-track deposition and quantify the depth of the affection in the substrate in terms of geometrical dilution and variation of the micro-hardness

Optimization of laser beam welding of steel parts made by additive manufacturing

AbstractTo pursue all the benefits of additive manufacturing of metals, recent studies have been aimed at assessing a proper welding technology to obtain large products by means of joining smaller parts. Indeed, at present, two or more parts must be manufactured individually and then assembled to produce the final component, when the size is incompatible with the building chamber or severe deformations arise during building. In this paper, laser beam welding is explored to join stainless steel components made by the process of laser powder bed fusion, in order to benefit from all the known advantages of this joining technique, aiming at producing a welding bead with homogeneous mechanical features with respect to the unwelded counterpart: a factorial plan is built, and the response surfaces are presented; then, the consolidated method of the desirability function is used to find the optimum condition of welding with reference to the current international standards, taking into account the geometry, the welding imperfections, and the extent of the heat-affected zone. The suggested optimum is eventually assessed via tensile testing and compared to the unwelded sample

Disk laser welding of metal alloys for aerospace

2011 - 2012Laser welding is the logical processing solution to accomplish different needs. Improvements at the design stage are actually aimed to remove any mechanical fastening, thus moving towards a technology which would not increase the joint thickness; moreover, a number of benefits in comparison with conventional welding methods are provided when considering laser beams, since deep penetration is achieved and the energy is effectively used where needed, thus melting the interface to be joined rather than excessively heating up the base metal, which would suffer from thermal distortion and degradation of metallurgical properties otherwise. Further advantages are achieved in laser welding with thin disk sources, since high output power, high efficiency and good beam quality are simultaneously delivered, unlike traditional laser systems; costs are significantly reduced in comparison with lamp-pumped laser systems. As a consequence, specific interest is shown in aerospace where strict specifications apply. Nevertheless, a number of issues must be addressed, depending on the material to be welded, as many variables and sub processes concerning fusion and vaporization are involved in laser welding and a delicate balance between heating and cooling is in place within a spatially localized volume. Therefore, extensive studies are required to manage both the stability and the reproducibility of the overall process, before introducing any change in industrial environments. Methods, experimental results and discussions concerning laser welding of common metal alloys for aerospace are provided in this Ph.D. thesis. A general view of applications and basic advantages of laser welding is first given, with mention to diagnostics and safety. Hence, the principles of laser emission are examined, with respect to the architecture of the sources, beam geometry, quality and efficiency, in order to better portray the benefits of a thin disk laser concept. Processing dynamics of laser welding are explained afterward, referring to conduction and key-hole mode, instability, gas supply and leading governing parameters such as laser power, welding speed, defocusing and beam angle to be considered in the experimental work. Procedures are provided for proper bead characterization, from preliminary examinations including non destructive tests such as fluorescent penetrant inspections and radiographic tests, to sample preparation and eventual mechanical assessment in terms of tensile strength and Vickers micro hardness in the fused zone. A straightforward description of the design of experiment approach and the response surface methodology is given, so to introduce the testing method to be taken, as well as the steps for data elaboration via statistical tools. Hence, four case studies about metal aerospace alloys are presented and discussed in their common seam configuration: autogenous butt and overlapping welding of aluminum alloy 2024; autogenous butt welding of titanium alloy Ti-6Al-4V; dissimilar butt welding of Haynes 188 and Inconel 718; dissimilar overlapping welding of Hastelloy X and René 80. All of the welding tests were conducted at the Department of Industrial Engineering at the University of Salerno; a Trumpf Tru-Disk 2002 Yb:YAG disk-laser source with a BEO D70 focusing optics, moved by an ABB IRB 2004/16 robot was employed. When needed, additional tests for the purpose of specific bead characterization were conducted by Avio and Europea Microfusioni Aerospaziali. As general procedure for each topic, the operating ranges to be examined are found via preliminary trials in combination with the existing literature on the subject. Then, special consideration is given to the processing set-up, the resulting bead profile, possible imperfections, defects and overall features; consistent constraint criteria for optimization of the responses are chosen on a case-by-case basis depending on materials and seam geometry and referring to international standards as well as customer specifications for quality compliance. Optimal combinations of the input welding parameters for actual industrial applications are eventually suggested, based on statistical tools of analysis. Convincing reasons are provided to give grounds to improvements in real applications. Moreover, based on the results, a proper device for bead shielding, to be conveniently adjusted depending on both geometry and materials to be welded has been designed, produced and patented (SA2012A000016). As concerning aluminum welding, a comprehensive description is given for laserrelated issues: reflectivity and thermal conductivity influence on the material response is illustrated; the porosity evolution is discussed with respect to thermal input and defocusing; a theory for softening in the fused zone is provided through energy dispersive spectrometry and estimations of magnesium content in the crosssection. Optimization is performed for butt configuration of 1.25 mm thick sheets; the discussion about the interactions among the governing factors is deepen with reference to overlapping welding. With respect to titanium welding, optimization is performed for 3 mm thick butt welding; the resulting micro structure in the weld is discussed since it is thought to be closely related to the mechanical properties. In particular, special care is taken of the grain size as a function of the governing factors. Dissimilar welding of super alloys is considered for gas turbine components; for this specific purpose, laser welding is expected to offer a valid alternative to arc and electron beam welding, whose weaknesses are pointed out. Given their actual application in the engine, Haynes 188 and Inconel 718 are examined in butt welding configuration, whilst an overlapping geometry is preferred for Hastelloy X and René 80. Considerable tolerances are matched, thus promoting the suggested range of the operating variables. [edited by author]XI n.s

Additive manufacturing of biomorphic scaffolds for bone tissue engineering

AbstractBone tissue engineering has evolved owing to new opportunities of deep customisation offered by additive manufacturing technologies. Gyroid structures, which have been widely used for energy absorption or chemical catalysis, are now being employed as biomorphic structures as well to provide customer-oriented scaffolds for missing or injured bones. Unfortunately, limited data in terms of manufacturability and mechanical properties are available in the literature to support a wide application scope, because the bone to match is strongly dependent on the individual. Therefore, the study aimed at addressing this lack of knowledge, assessing the manufacturability of metal gyroids and further developing the correlation of the structural response with the designed geometry, so to allow the designer to provide the proper biomorphic structure on a case-by-case basis. Biocompatible steel was used to manufacture samples via laser powder-bed fusion; their elastic moduli and yield strengths were evaluated as a function of the orientation of the elementary cells, the symmetry and the wall thickness based on compression testing. Grounds have been given to support potential applications for tibias and vertebras

Laser powder-bed fusion of Inconel 718 to manufacture turbine blades

In the frame of additive manufacturing of metals, laser powder-bed fusion is investigated in this paper as an advanced industrial prototyping tool to manufacture Inconel 718 turbine blades at a predesign stage before flow production. Expediting of the evaluation of any upgrade to the part is aimed. To this purpose, possible anisotropy of manufacturing is preliminarily investigated via tensile testing at room and elevated temperature as a function of the sloping angle with the building plate; the normalized strength is given and compared with similar studies in the literature. Positioning and proper supporting in manufacturing are discussed; the parts are further investigated to assess their compliance with the intended nominal geometry

Porosity evolution in aluminum alloy 2024 bop and butt defocused welding by Yb-YAG disk laser

In many industrial applications, in order to obtain good results in laser welding processes, it may not be sufficient to use a focused beam on the upper surface, so a defocused beam is required instead. This study aims to investigate which advantages a defocused beam may offer in welding aluminum alloy 2024 using Yb:YAG disk laser. A characterization of laser beam geometry is preliminary necessary, in order to correlate bead features and effective specific energy provided. Porosity content decrease and enhanced penetration depth have been obtained with defocused beam; welding behavior has been related to magnesium loss via EDS analysis. Considering the shape of the cross sections of the bead in butt welding, the relation between key-hole instability and porosity formation has also been discussed. For the alloy in exam, the welding range to perform structurally sound and defect-free welds is found to be tight

Felipe segundo, Rey de España : tragedia en cinco actos

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 201

Tragedia en cinco actos, titulada Polinice o Los hijos de Edipo / traducida por Don A. S.

Precede al tít.: "Núm. 173.". - Nom de l'autor i del traductor presos del Catálogo de la BN de EspañaAutor y traductor tomado de la BNEDatos de publicación tomados del colofó

Technical Feasibility of Laser Dissimilar Welding of Superalloys on Casted Nozzle Guide Vanes

Abstract An increasing degree of automation is required both in the automotive and aircraft industry in order to allow scrap reduction and flexibility. In this frame, the shift from arc welding to laser beam welding is being investigated for a number of applications on metals in aerospace engineering, where strict standards apply. In comparison with conventional welding methods, a number of advantages are benefited; nevertheless, when moving to a new technology, some issues must be addressed. Hence this study is aimed to investigate laser dissimilar welding of real metal components, in order to assess the technical feasibility as well as to discuss set-up and operating issues in view of the implementation of the process for actual industrial application. A second-stage stator of low-pressure turbine is considered: lightening of the airfoils of the nozzle guide vane is achieved thanks to inner hollows which are drained from wax upon casting; afterward, the core exits on the outer side of the nozzle must be conveniently closed off by means of metal plates. Joining of the plates to the nozzle is performed by fusion welding along the edge of each plate and a condition of dissimilar welding is in place, being the nozzle and the plates made of C1023 and Nimonic 75, respectively. A mixed factorial plan has been arranged, laser power, welding speed and focus position being the leading processing parameters; a convenient welding set-up is proposed. Reasons are given for the implementation of laser beam welding as an alternative to conventional arc welding