Suchergebnisse

Simulation is a very useful tool in the design of the part and process conditions of high pressure die casting (HPDC), due to the intrinsic complexity of this manufacturing process. Usually, physics-based models solved by finite element or finite volume methods are used, but their main drawback is the long calculation time. In order to apply optimization strategies in the design process or to implement online predictive systems, faster models are required. One solution is the use of surrogate models, also called metamodels or grey-box models. The novelty of the work presented here lies in the development of several metamodels for the HPDC process. These metamodels are based on a gradient boosting regressor technique and derived from a physics-based finite element model. The results show that the developed metamodels are able to predict with high accuracy the secondary dendrite arm spacing (SDAS) of the cast parts and, with good accuracy, the misrun risk and the shrinkage level. Results obtained in the predictions of microporosity and macroporosity, eutectic percentage, and grain density were less accurate. The metamodels were very fast (less than 1 s); therefore, they can be used for optimization activities or be integrated into online prediction systems for the HPDC industry. The case study corresponds to several parts of aluminum cast alloys, used in the automotive industry, manufactured by high-pressure die casting in a multicavity mold. ; This work was supported by projects OASIS and SMAPRO. The OASIS project has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement No 814581. The SMAPRO project has received funding from the Basque Government under the ELKARTEK Program (KK-2017/00021).

The use of optimization algorithms to adjust the numerical models with experimental values has been applied in other fields, but the efforts done in metal casting sector are much more limited. The advances in this area may contribute to get metal casting adjusted models in less time improving the confidence in their predictions and contributing to reduce tests at laboratory scale. This work compares the performance of four algorithms (compass search, NEWUOA, genetic algorithm (GA) and particle swarm optimization (PSO)) in the adjustment of the metal casting simulation models. The case study used in the comparison is the multiscale simulation of the hypereutectic ductile iron (SGI) casting solidification. The model fitting criteria is the value of the tensile strength. Four different situations have been studied: model fitting based in 2, 3, 6 and 10 variables. Compass search and PSO have succeeded in reaching the error target in the four cases studied, while NEWUOA and GA have failed in some cases. In the case of the deterministic algorithms, compass search and NEWUOA, the use of a multiple random initial guess has been clearly beneficious. ; This research was funded by the Basque Government under the ELKARTEK Program (ARGIA Project, ELKARTEK KK-2019/00068) and by the HAZITEK Program (CASTMART Project, HAZITEK ZL-2019/00562).

Diamond like carbon (DLC) coatings typically present good self-lubricating tribological properties that could be of interest in sliding dielectric contacts in multiple electrical applications. In this work electro-tribological studies have been performed on several DLC coatings against aluminum in different humidity conditions, in which the coefficients of friction (CoFs) and electrical contact resistance (ECR) were continuously monitored. Results show that CoF and ECR data can be linked to the properties of the coatings (thickness, finishing, microstructure, residual stresses, and wettability) and the degradation modes of their tribological and electrical properties. Therefore, electro-tribological data can provide valuable information about the performance of dielectric coatings, the reasons behind it, and assist in the development of the coatings. ECR also shows potential for on-line monitoring of coated parts in operation. ; This work was financially supported by FUTURE GRIDS‐2020, Frontiers, and nG‐17 projects (Elkartek, Economic Development Department at the Basque Government).

El alcaudón dorsirrojo presenta un progresivo declive en la península Ibérica por lo que es interesante conocer las causas de este proceso. Analizamos en este estudio los factores determinantes de su distribución, abundancia y éxito reproductor en Bizkaia (Comunidad Autónoma del País Vasco). Para ello, muestreamos entre 1 y 4 veces 675 cuadrículas de 1x1 km en la primavera de 2021. Además, cuantificamos la presencia de ganado en las cuadrículas muestreadas, la densidad local de ganado y de explotaciones ganaderas, la cobertura de campiña (prados y setos), la huella humana y la altitud, que utilizamos como un subrogado del clima. Los análisis preliminares (modelos lineales generalizados, GLM) sugirieron que la presencia de ganado, la densidad de explotaciones y la cobertura de campiña se asociaban positivamente con la aparición de los alcaudones. Se observó también un fuerte efecto del número de visitas por lo que se estudió la probabilidad de detección de la especie mediante una modelización jerárquica de la ocupación. Este nuevo análisis desveló una probabilidad de detección de 0,68 por visita (error estándar= 0,134), además del fuerte efecto de la cobertura de campiña, presencia de ganado y densidad de explotaciones en la probabilidad de ocupación del alcaudón dorsirrojo. Estos resultados nos permitieron calcular la presencia real de la especie en 236 cuadrículas (rango=169-311) de las 675 muestreadas. Considerando que se prospectó el 46,4% del hábitat potencialmente adecuado para la especie en el área de estudio, se estimó que la población del alcaudón dorsirrojo en Bizkaia rondaba las 517 parejas reproductoras (rango=373-679), una población mucho menor que la predicha por otras aproximaciones previas. El número de pollos volantones observados en 128 parejas reproductoras osciló entre 0 y 4 (media 1,6 pollos por pareja), con un 73 % de las parejas con uno o más pollos (un porcentaje similar al éxito reproductivo de otras poblaciones ibéricas). En este caso, el número de pollos solo se asoció significativamente a la cobertura de campiña. Los resultados de este estudio sugieren que la distribución de la especie parece estar fuertemente constreñida por la disponibilidad de campiña y la actividad del ganado, responsable de la creación de pastizales y prados heterogéneos en los que puede encontrar sustratos de caza.