Laser beam welding (LBW) is a highly demanded process for premium-quality joints in aeronautic, energy, or industrial sectors, where flexibility and low-heat-affected zones are required. One of the main applications of LBW in the near future is expected to be the welding of new turbine engine components, which are typically made of Nickel-based superalloys. However, parameter setup is time- and resource-consuming, where experiment-based methods are typically employed. Therefore, the process development is far from an efficient resource utilization. In the present work, an LBW numerical model is developed and experimentally validated through a machine-integrated monitoring system. The LBW model is based on solving the heat transfer problem produced by the laser and provides the resulting temperature field, as well as the weld bead dimensions. The model includes a variable heat source that automatically adapts to the welding regime, conduction, or keyhole. For the model validation, two Inconel 718 sheets of different thicknesses are butt-welded and an error of around 10% is obtained, which ensures the validity of the model.

The aim of the present research work is the characterization of the 15CDV6 powder material for Laser Directed Energy Deposition (L DED) processes. The novelty of the work lays on the fact that this aeronautical steel has never been employed before in powder L DED process. Therefore, the mentioned steel powder was atomized specifically for the present work and the chemical composition and shape of the particles was measured to ensure the quality of the material. Afterwards, the suitability of the 15CDV6 steel for the L-DED process was studied and the employed methodology consisted of 3 sequential steps: single bead tests, overlapping beads deposition and thin wall construction. The results of each sequence are used as the basis for the following ones. In addition to the determination of the main process parameters, the influence of the deposition strategy on the process efficiency is analyzed and a correlation between the microstructure resulting from the thermal process and the hardness HV0.3 values was obtained. To finish the characterization of the process, a demonstrator part was fabricated using the optimum parameters defined during the tests. Based on the obtained results, the viability of employing 15CDV6 steel in the L-DED process is ensured. Also, it is concluded that if a sufficient cooling rate is ensured, Acicular Ferrite microstructure is obtained, which provides good mechanical properties to the L-DED manufactured parts. Nevertheless, the thermal evolution of the process needs to be controlled in order to avoid heat accumulation and cooling stops are to be applied when required. Keywords: 15CDV6, powder, L-DED, characterization, atomization. El objetivo del presente trabajo de investigación es la caracterización del material en polvo 15CDV6 para procesos de aporte directo de energía mediante láser (L-DED). La novedad del trabajo radica en el hecho de que este acero aeronáutico no ha sido empleado previamente en procesos de L DED en formato de polvo. Por lo tanto, el polvo de acero mencionado ha sido atomizado específicamente para el presente trabajo y se han medido la composición química y la forma de las partículas para asegurar la calidad del material. Posteriormente, se ha estudiado la idoneidad del acero 15CDV6 para el proceso de L-DED, donde la metodología empleada ha consistido en 3 pasos secuenciales: pruebas de cordones individuales, aporte de cordones superpuestos y construcción de paredes delgadas. Los resultados de cada paso se utilizan como base para las siguientes. Además de la determinación de los principales parámetros del proceso, se ha analizado la influencia de la estrategia de deposición en la eficiencia del proceso y se ha obtenido una correlación entre la microestructura resultante del proceso térmico y los valores de dureza HV0.3. Para finalizar con la caracterización del proceso, se ha fabricado una pieza demostradora utilizando los parámetros óptimos definidos durante las pruebas. En base a los resultados obtenidos, se asegura la viabilidad de emplear el acero 15CDV6 en el proceso L-DED. Asimismo, se concluye que, si se asegura una velocidad de enfriamiento suficiente, se obtiene una microestructura de Ferrita Acicular que proporciona unas excelentes propiedades mecánicas a las piezas fabricadas mediante L DED. No obstante, es necesario controlar la evolución térmica del proceso para evitar la acumulación de calor y aplicar paradas de enfriamiento cuando sea necesario. Palabras clave: 15CDV6, polvo, DED por Láser, caracterización, atomización.

Etorkizunean, batez ere sektore aeronautikorako, Inconel 718 piezen fabrikazio-prozedura eraginkorragoa posible den aztertzeko lehen urratsak eman dira lan honetan. Forja-prozesuak propietate mekaniko oso onak eskaintzen ditu, baina geometria konplexutasuna mugatua dauka. Aldiz, fabrikazio gehigarriak diseinu askatasun handia ematen du, baina prozesu honekin fabrikaturiko piezen portaeraren inguruan ziurgabetasuna handiagoa da. Hortaz, lan honetan bi prozesu horien arteko hibridazioa aztertu da, prozesu bakoitzaren alderdi ahulei aurre egiteko asmoz. Zehazki, fabrikazio gehigarriaren barneko Laser bidezko Zuzeneko Energia Gehikuntza (L-ZEG) teknologia erabili da, materiala desira den gunean gehitzeko aukera eskaintzen duelako eta beraz, hibridaziorako prozesu egokia delako. Ikerlan honetan, lehendabizi Forjaturiko Inconel 718 oinarriaren gainean L-ZEG bidez xehetasunak gehitzeko parametro optimoak zehaztu dira. Loturaren kalitatea analisi metalografiko bidez baieztatu da. Bigarren pauso batean, trakzioko saiakuntza bidez, fabrikazio-prozesu bien arteko lotura mekanikoa egokia dela ikusi da eta, bi prozesuen hibridazioa bideragarria dela ondorioztatu da.

Laser welding is most of the times chosen because of its capability for providing low distortion in the part. However, thermal expansion and contraction cycles during the joining process must be taken into account, since they can cause deformations. For minimizing the distortions caused by the weld bead, the optimization of welding sequences is essential, although it is time- and resource-consuming. Therefore, deformation prediction by employing finite elements (FEM) is one of the solutions that have been employed in recent years. In this research it is proposed to develop a model capable of predicting the simulation of structures with thicknesses of approximately 5 mm by means of simplified methods. Simplified methos are employed because the conventional analysis of thermomechanical FEM models is difficult to use in large welds due to the excessive calculation time. In parallel, the optimization of the laser welding process is carried out by studying the input parameters and results. In addition, an in-situ monitoring system is included to measure the deformations during the welding process, feeding these measurements to the FEM model. Finally, the simulation of the calibrated model is carried out for a real structure of larger size. Key words: laser welding, FEM simulations, eigenstrains method, distortions.