Laser Metal Deposition enhancement by holistic simulation of powder mass flow and deposition into the melt pool

El contenido de los capítulos 3, 4 y 5 está sujeto a confidencialidad. 251 p.En el presente trabajo de investigación se ha desarrollado una metodología para la mejora del proceso de aporte por láser mediante la modelización del mismo. El problema se ha abordado en diferentes pasos. Primero de todo, se ha desarrollado un cabezal de aporte que cumple con todos los requerimientos del proceso mediante un software comercial de CFD. Posteriormente, se ha fabricado y validado el mismo. Además, con el objetivo de mejorar la eficiencia de la boquilla e incrementar la estabilidad del proceso, se ha desarrollado un sistema novedoso de regulación del caudal del polvo. El cabezal de aporte ha sido empleado satisfactoriamente para la reparación y fabricación de diversas piezas. En lo que respecta a la modelización, se ha desarrollado un modelo que considera los fenómenos fluido-dinámicos que se producen dentro del baño fundido generado por un haz láser. Una vez se ha validado el modelo, se ha empleado para evaluar la importancia de considerar u omitir el movimiento del material fundido. Los resultados obtenidos indican que la influencia del movimiento del material fundido es mínima en el proceso de aporte por láser y pueden ser omitidos sin que ello suponga una pérdida de precisión. Basándose en esta última afirmación, se ha desarrollado un modelo tridimensional que simula el proceso de aporte por láser al completo. Este modelo calcula la transferencia de calor por conducción dentro de la pieza y la geometría del material aportado. Además, en función de los ciclos de calentamiento y enfriamiento que sufre el material, es capaz de predecir las propiedades mecánicas resultantes, tales como dureza, microestructura o la formación de poros

Laser Metal Deposition enhancement by holistic simulation of powder mass flow and deposition into the melt pool

El contenido de los capítulos 3, 4 y 5 está sujeto a confidencialidad. 251 p.En el presente trabajo de investigación se ha desarrollado una metodología para la mejora del proceso de aporte por láser mediante la modelización del mismo. El problema se ha abordado en diferentes pasos. Primero de todo, se ha desarrollado un cabezal de aporte que cumple con todos los requerimientos del proceso mediante un software comercial de CFD. Posteriormente, se ha fabricado y validado el mismo. Además, con el objetivo de mejorar la eficiencia de la boquilla e incrementar la estabilidad del proceso, se ha desarrollado un sistema novedoso de regulación del caudal del polvo. El cabezal de aporte ha sido empleado satisfactoriamente para la reparación y fabricación de diversas piezas. En lo que respecta a la modelización, se ha desarrollado un modelo que considera los fenómenos fluido-dinámicos que se producen dentro del baño fundido generado por un haz láser. Una vez se ha validado el modelo, se ha empleado para evaluar la importancia de considerar u omitir el movimiento del material fundido. Los resultados obtenidos indican que la influencia del movimiento del material fundido es mínima en el proceso de aporte por láser y pueden ser omitidos sin que ello suponga una pérdida de precisión. Basándose en esta última afirmación, se ha desarrollado un modelo tridimensional que simula el proceso de aporte por láser al completo. Este modelo calcula la transferencia de calor por conducción dentro de la pieza y la geometría del material aportado. Además, en función de los ciclos de calentamiento y enfriamiento que sufre el material, es capaz de predecir las propiedades mecánicas resultantes, tales como dureza, microestructura o la formación de poros

Analysis of Photodiode Monitoring in Laser Cutting

The paper presents the results of an analysis based on the photodiode monitoring signals obtained during the laser cutting of aluminum and stainless steel plates. The mean level of the monitoring signal was measured and related to the process parameters and the quality achieved. The investigation was conducted in the visible and infrared spectra simultaneously for each experiment and a similar behavior at both spectra was observed, concluding the existence of a relationship between the monitoring signal, the quality of the performed cut, and the characteristics of the cutting scenario. Both visible and infrared monitoring signals were found not to vary as long as the parameter used values ensuring that the cut quality was good. Nevertheless, their mean values tended to increase as the cutting quality became worse. The measured intensity of the visible spectrum signal was associated with the vapor plume formation during the cutting process, whereas the infrared signal was related to the temperatures reached.This research was supported by the Basque Government in the Elkartek project “Digicut: Estudio fundamental de procesos de corte y definición de las bases para su digitalización” (KK-2019/00071)

Study of the Environmental Implications of Using Metal Powder in Additive Manufacturing and Its Handling

Additive Manufacturing, AM, is considered to be environmentally friendly when compared to conventional manufacturing processes. Most researchers focus on resource consumption when performing the corresponding Life Cycle Analysis, LCA, of AM. To that end, the sustainability of AM is compared to processes like milling. Nevertheless, factors such as resource use, pollution, and the effects of AM on human health and society should be also taken into account before determining its environmental impact. In addition, in powder-based AM, handling the powder becomes an issue to be addressed, considering both the operator´s health and the subsequent management of the powder used. In view of these requirements, the fundamentals of the different powder-based AM processes were studied and special attention paid to the health risks derived from the high concentrations of certain chemical compounds existing in the typically employed materials. A review of previous work related to the environmental impact of AM is presented, highlighting the gaps found and the areas where deeper research is required. Finally, the implications of the reuse of metallic powder and the procedures to be followed for the disposal of waste are studied.This research was funded by the European Union through the H2020-FoF13-2016 PARADDISE project under Grant 723440 and the Basque Government through the ADDISEND project under Grant Elkartek-KK00011

Analysis of the Influence of the Use of Cutting Fluid in Hybrid Processes of Machining and Laser Metal Deposition (LMD)

Hybrid manufacturing processes that combine additive and machining operations are gaining relevance in modern industry thanks to the capability of building complex parts with minimal material and, many times, with process time reduction. Besides, as the additive and subtractive operations are carried out in the same machine, without moving the part, dead times are reduced and higher accuracies are achieved. However, it is not clear whether the direct material deposition after the machining operation is possible or intermediate cleaning stages are required because of the possible presence of residual cutting fluids. Therefore, different Laser Metal Deposition (LMD) tests are performed on a part impregnated with cutting fluid, both directly and after the removal of the coolant by techniques such as laser vaporizing and air blasting. The present work studies the influence of the cutting fluid in the LMD process and the quality of the resulting part. Resulting porosity is evaluated and it is concluded that if the part surface is not properly clean after the machining operation, deficient clad quality can be obtained in the subsequent laser additive operation.This study was supported by the H2020 FoF13 PARADDISE Project (Grant Agreement No. 723440)

Study of the flexural behaviour and bonding strength of WC-Co metal matrix composite coatings produced by Laser Directed Energy Deposition

Surface coatings enable more durable and sustainable solutions to face the degradation of the functional surfaces of high-added-value components. Particularly, metal matrix composites (MMC) are known to mitigate friction efficiently. However, the bonding strength of MMCs severely limits their durability. Hence, it is not sufficient to focus on wear performance. In this work, the flexural strength and interfacial bonding of Stellite 6/WC MMCs produced by Laser Directed Energy Deposition were investigated. The manufactured coatings exhibited a strong bond to the substrate regardless of the WC content, as no delamination was observed. Additionally, all MMC coatings produced under different processing conditions and with the same composition showed similar elastoplastic behaviour, while specimens containing a higher WC% failed prematurely. This was ascribed to the local embrittlement of the reaction layer surrounding the WC particles, which were found to be crack initiation sites.Authors would like to acknowledge the Basque Government (Eusko Jaurlaritza) in call IT 1573-22 for the financial support of the research group

Analysis of the Process Parameter Influence in Laser Cladding of 316L Stainless Steel

Laser Cladding is one of the leading processes within Additive Manufacturing technologies, which has concentrated a considerable amount of effort on its development. In regard to the latter, the current study aims to summarize the influence of the most relevant process parameters in the laser cladding processing of single and compound volumes (solid forms) made from AISI 316L stainless steel powders and using a coaxial nozzle for their deposition. Process speed, applied laser power and powder flow are considered to be the main variables affecting the laser cladding in single clads, whereas overlap percentage and overlapping strategy also become relevant when dealing with multiple clads. By setting appropriate values for each process parameter, the main goal of this paper is to develop a processing window in which a good metallurgical bond between the delivered powder and the substrate is obtained, trying simultaneously to maintain processing times at their lowest value possible. Conventional metallography techniques were performed on the cross sections of the laser tracks to measure the effective dimensions of clads, height and width, as well as the resulting dilution value. Besides the influence of the overlap between contiguous clads and layers, physical defects such as porosity and cracks were also evaluated. Optimum process parameters to maximize productivity were defined as 13 mm/s, 2500 W, 30% of overlap and a 25 g/min powder feed rat

Functionally Graded AISI 316L and AISI H13 Manufactured by L-DED for Die and Mould Applications

Tooling in the die and mould industry is subjected to high-wear and high-temperature environments, which often leads to the premature failure of this high-added-value tooling. When severe damage occurs, an alternative to replacing the whole component consists of the repair by laser-directed energy deposition (L-DED). For that end, intermediate layers are commonly employed as buffer material, where introducing a functionally graded material (FGM) might be beneficial to avoid material incompatibilities and improve the overall performance of the tooling. In the present work, an FGM composed of gradient AISI 316L to AISI H13 has been manufactured, and its microstructure and hardness analysed. Firstly, cracking owing to the formation of brittle intermediate phases has been detected. Secondly, an increase of the hardness and a decrease of the corrosion resistance has been observed when transitioning from AISI 316L to AISI H13. Thirdly, despite the FGM composition evolving linearly, nonlinear material properties such as hardness and corrosion have been observed, which are conditioned by the microstructure formed during the L‑DED process and the nonlinear influence of the composition of steel on such properties. Consequently, nonlinear compositional gradients are recommended if linear mechanical properties are to be obtained in the case of steel FGMs.This research was funded by the Basque Government (Eusko Jaurlaritza) under the ELKARTEK Program, QUALYFAM project, grant number KK-2020/00042 and Spanish Ministry of Industry and Competitiveness under the PID2019-109220RB-I00 ALASURF project

Numerical Model for Predicting Bead Geometry and Microstructure in Laser Beam Welding of Inconel 718 Sheets

A numerical model was developed for predicting the bead geometry and microstructure in laser beam welding of 2 mm thickness Inconel 718 sheets. The experiments were carried out with a 1 kW maximum power fiber laser coupled with a galvanometric scanner. Wobble strategy was employed for sweeping 1 mm wide circular areas for creating the weld seams, and a specific tooling was manufactured for supplying protective argon gas during the welding process. The numerical model takes into account both the laser beam absorption and the melt-pool fluid movement along the bead section, resulting in a weld geometry that depends on the process input parameters, such as feed rate and laser power. The microstructure of the beads was also estimated based on the cooling rate of the material. Features such as bead upper and bottom final shapes, weld penetration, and dendritic arm spacing, were numerically and experimentally analyzed and discussed. The results given by the numerical analysis agree with the tests, making the model a robust predictive tool.Thanks are addressed to H2020-FoF13-2016 PARADDISE project (contract number 723440). Special thanks are addressed to the University of the Basque Country (UPV-EHU) for the funding support received from the contracting call for the training of research staff in UPV-EHU 2015

Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations

Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilledSpecial thanks are addressed to the Industry and Competitiveness Spanish Ministry for the support on the DPI2016-79889-R INTEGRADDI project and to the PARADDISE project H2020-IND-CE-2016-17/H2020-FOF-2016 of the European Union's Horizon 2020 research and innovation program