Study of the lateral pass width for conventional and ultrasonic vibrations-assisted ball burnishing on Ti-6Al-4V specimens

Ball burnishing is a technological finishing process based on plastic deformation of the objective surface by means of a hard ball gliding over it. Along with its easiness of application, possible on the same machine where machining was performed [1], burnishing is a comprehensive process able to achieve surface roughness improvements, and compressive residual stresses up to deep layers of the material [2]. Burnishing results have proved to be depending of a proper selection of parameters, which must be correctly controlled during the process. That is the case of burnishing force or the number of passes [3]. Among these parameters, the lateral pass width has proved to be influential on the surface roughness results, due to the behavior that most materials show when being plastically deformed. In effect, the applied force makes the material to flow to the borders of the burnishing imprint, giving way to a pile-up effect. This paper deals with indentation experiments on Ti-6Al-4V to deepen in the burnishing process of this material. Single burnishing imprints are geometrically characterized combining different levels of force, number of passes, and comparing the conventional process with that assisted with vibrations. An optimal lateral pass width is thus determined, and technological recommendations are made for future applications of the process.Peer ReviewedPostprint (author's final draft

Comparison of thermal performance of 3D printer liquefiers through finite element models

Open source 3D printers have experienced an intense expansion during the last years, mainly because of their accessibility and the vast availability of information thanks to user communities. This fact presents researchers with a perfect context for hardware innovation, by improving the overall printing process, also in terms of durability of the printing machine. A 3D printer liquefier must transmit heat to the thermoplastic material in order to extrude it, reaching temperatures above 200 degrees for some materials like ABS on the tip of the nozzle. The design of the heating process must comply with keeping the balance between proper heating of the material and controlling the temperature along the extruding body, so that the printer itself is not harmed for overtemperature. On the other hand, the design must guarantee that the melting front is located in an intermediate point between the nozzle tip and the entrance of the raw material, to minimize pressure drops in the system, and so decreasing the demanding energy to the feeding motors. An alternative design of the heating system, Twist3D, is proposed in this paper.Peer ReviewedPostprint (published version

But Still Enthusiastic: The Unchanged Europeanness of the Spanish Parliamentary Elite During the Eurozone Crisis

Since the adhesion of Spain to the EEC in 1986, the Spanish electorate has shown a high level of support for the European integration process. Even more enthusiastic than their fellow citizens, Spanish political elites also expressed a strong commitment to the European integration project, based in a pro-EU consensus beyond party and ideological divides. However, Spain has also been one of the countries most affected by the economic and financial crisis that has hit the EU (particularly the Eurozone) since 2010. The main questions we aim to answer in this paper is whether this crisis and its management by EU institutions has eroded the traditional support for the EU shown by Spanish domestic political elites and, if so, to what extent. To this end, we draw on survey data provided by the InTune and ENEC-2014 projects on the attitudes of Spanish MPs towards the EU in the years 2007, 2009, and 2014. Results show that the traditional pro-EU stance of Spanish MPs has remained mostly stable during the crisis, yet such stability has increased the representation gap with citizens in this area

Experimental analysis of manufacturing parameters’ effect on the flexural properties of wood-PLA composite parts built through FFF

This paper aims to determine the flexural stiffness and strength of a composite made of a polylactic acid reinforced with wood particles, named commercially as Timberfill, manufactured through fused filament fabrication (FFF). The influence of four factors (layer height, nozzle diameter, fill density, and printing velocity) is studied through an L27Taguchi orthogonal array. The response variables used as output results for an analysis of variance are obtained from a set of four-point bending tests. Results show that the layer height is the most influential parameter on flexural strength, followed by nozzle diameter and infill density, whereas the printing velocity has no significant influence. Ultimately, an optimal parameter set that maximizes the material’s flexural strength is found by combining a 0.2-mm layer height, 0.7-mm nozzle diameter, 75% fill density, and 35-mm/s velocity. The highest flexural resistance achieved experimentally is 47.26 MPa. The statistical results are supported with microscopic photographs of fracture sections, and validated by comparing them with previous studies performed on non-reinforced PLA material, proving that the introduction of wood fibers in PLA matrix reduces the resistance of raw PLA by hindering the cohesion between filaments and generating voids inside it. Lastly, five solid Timberfill specimens manufactured by injection molding were also tested to compare their strength with the additive manufactured samples. Results prove that treating the wood-PLA through additive manufacturing results in an improvement of its resistance and elastic properties, being the Young’s module almost 25% lower than the injected material.Preprin

Los hábitats artificiales marinos favorecen a largo plazo a una única especie: la dominancia de Boops boops en las jaulas de acuicultura en mar abierto

Off-shore fish cages are new artificial habitats that can affect pelagic fish assemblages and constitute an important food source for wild fish assemblages. This aggregation has noticeable ecological consequences in cage areas in impoverished ecosystems such as those in the Canary archipelago (NE Atlantic Ocean). However, this new habitat could be dominated by a single species, reducing its positive ecological effects. Wild fish assemblages associated with an off-shore fish lease on the northeastern coast of Tenerife (Canary Islands) were sampled for six years. Fish assemblage structure beneath fish cages and at controls ( > 500 m from cages) differed significantly between locations, with 13 times greater abundance at cage locations. These differences were mainly explained by the dominance of bogue (Boops boops) around fish cages. This trend was consistent in the long-term throughout the study period (2004-2009), affecting local fisheries. The presence of fish cages significantly altered wild fish assemblages in the study area, enhancing mainly biomass and abundance of one species, bogue, and causing shifts in species composition.Las jaulas de acuicultura en mar abierto constituyen un hábitat artificial nuevo que puede afectar a las poblaciones de peces pelágicos porque constituyen una fuente importante de alimentación para las comunidades de peces salvajes. Esta congregación tiene consecuencias ecológicas notables en áreas caracterizadas por ecosistemas empobrecidos como ocurre en el archipiélago canario (Atlántico Noreste). Sin embargo, este nuevo hábitat puede encontrarse dominado por una única especie, limitando sus efectos ecológicos positivos. Las comunidades salvajes de peces asociadas a jaulas en mar abierto localizadas en la costa noreste de la isla de Tenerife (Islas Canarias) fueron muestreadas a lo largo de 6 años. La estructura de la comunidad íctica varió significativamente entre las localidades de las jaulas y los controles ( > 500 m de distancia de las jaulas), con abundancias que fueron 13 veces superiores en las jaulas. Estas diferencias fueron debidas principalmente a la dominancia de la boga (Boops boops) alrededor de las jaulas de acuicultura. Esta tendencia fue consistente a lo largo del período de estudio (2004-2009), afectando a las capturas de los pescadores locales. La presencia de las jaulas de acuicultura afectó de forma significativa las poblaciones de peces en el área de estudio, con un incremento de la biomasa y abundancia de una especie, la boga, que determinó cambios en la composición de las especies

Surface roughness assessment after different strategy patterns of ultrasonic ball burnishing

Ball burnishing is a comprehensive finishing process consisting on deforming plastically a certain surface by the action of a rolling sphere-shaped indenter. In this work, an AISI 1038 workpiece is burnished in two phases. The first phase covers the burnishing of a 10x10 mm patch, performed along the direction of the previous milling. The second pass is applied on the previous patch, following three different strategies, namely, parallel, perpendicular and at a 45-degrees angle with regards to that first burnishing direction. The comparison between the non-vibration assisted ball burnishing (NVABB) and vibration-assisted ball burnishing (VABB) effects is included in the study. To assess the influence of these strategies on the final roughness profile, an L9 Taguchi orthogonal array is designed, including as factors the vibrations amplitude, the burnishing force, and the lateral pass width. Surface roughness is measured and compared to determine the optimal burnishing orientation. The VABB process proves to be more effective in surface roughness improvement. Technical recommendations are given to select the best process parameters inside the tested levels for each factor. All burnishing strategy prove to have different effects on the surface, and should be selected according to the preferential burnishing direction and in service application of the part.Postprint (published version

Impresión 3D: Del laboratorio a casa. Programa de divulgación científico-tecnológica sobre la tecnología de impresión 3D

La impresión 3D comienza a ser un fenómeno tecnológico en España, dada la gran variedad de modelos a la venta para aquellas personas emprendedoras que deseen disponer de esta tecnología en su entorno doméstico. Sin embargo, existe un gran desconocimiento sobre de qué consiste la tecnología en que se basa, y cuales son sus potencialidades. Los investigadores implicados en este proyecto han emprendido una serie de acciones financiadas por la FECYT que se realizarán durante el 2015, con la intención de divulgar los avances científicos ligados a las impresoras 3D, y, en particular, a la tecnología en que se basa la fabricación de piezas con estos dispositivos: la FDM (fused deposition modeling). Estas acciones pasan por el lanzamiento de una web donde se publicarán programas y documentales de producción propia sobre impresión 3D, una aplicación móvil que facilite la conexión entre dispositivos móviles e impresoras, y la celebración de cursos de formación destinados a público no universitario que les permitan entrar en contacto con estos dispositivos. Se espera que cientos de personas no universitarias se sientan interesadas en incorporar a su ámbito doméstico una impresora 3D como una nueva herramienta de futur

Mechanical properties of 3D-printing polylactic acid parts subjected to bending stress and fatigue testing

This paper aims to analyse the mechanical properties response of polylactic acid (PLA) parts manufactured through fused filament fabrication. The influence of six manufacturing factors (layer height, filament width, fill density, layer orientation, printing velocity, and infill pattern) on the flexural resistance of PLA specimens is studied through an L27 Taguchi experimental array. Different geometries were tested on a four-point bending machine and on a rotating bending machine. From the first experimental phase, an optimal set of parameters deriving in the highest flexural resistance was determined. The results show that layer orientation is the most influential parameter, followed by layer height, filament width, and printing velocity, whereas the fill density and infill pattern show no significant influence. Finally, the fatigue fracture behaviour is evaluated and compared with that of previous studies’ results, in order to present a comprehensive study of the mechanical properties of the material under different kind of solicitations.Peer ReviewedPostprint (published version

Housing prices and credit constraints in competitive search

We embed a competitive search model of the real estate market into a heterogeneous agentsetting where hoeholds face credit constraints and idiosyncratic turnover shocks. Householdscan accumulate a risk-free asset to build a down payment and to smooth non-housing consumption.There is an inelastic supply of identical homes. The model is "block recursive". Inequilibrium wealthier home buyers sort into submarkets with higher prices and shorter buyingtimes. We identify a novel amplification mechanism, arising from sorting, by which demandshocks can substantially affect housing prices. In particular, lowering down payment requirementsinduces entry of new buyers in the market and higher asset accumulation by currentsearchers, as these agents target more expensive (less congested) submarkets. This affects thedistribution of prices and trading probabilities, and thereby the wealth distribution. Our quantitativeresults suggest that the effects on the long-run level and dispersion of housing pricescan be significant.Support from the Spanish Ministerio Economía y Competitividad, grants ECO2016-76818-C3-1-P and ECO2017-86261-P, MDM 2014-0431, and Comunidad de Madrid, MadEco-CM (S2015/HUM-3444), is gratefully acknowledged

A comparative study of the thermal behavior of three different 3D printer liquefiers

The expansion of 3D printing systems as mechatronic devices able to localize manufacturing activities has attracted the attention in academic and professional labs worldwide. However, little is known from a formal point of view about the actual possibilities of optimization in terms of hardware and software. This paper proposes alternative geometrical designs of RepRap 3D printer liquefiers, and offers an evaluation of their thermal performance by analyzing the temperature profiles derived from their functioning in a steady state regime. For that purpose, finite element calculation and experimental techniques are combined and compared. A detachable model of liquefier, used in numerous RepRap 3D printers, has been taken as a reference to design and manufacture two new variations. As the objective of the liquefier is to heat the plastic material while limiting the temperature at its top, heat conduction must be prevented by means of a refrigerating fan faced at the liquefier body. The effect of that fan has been introduced in the system of study, by evaluating the influence of five different fan velocities on the final temperature profile. All combinations of fan speed and liquefier geometry have been calculated through a finite elements model. Then, they have been reproduced experimentally, measuring discrete temperatures at different heights of the liquefier by a group of thermocouples installed on the surface of the fins composing the liquefier heat sink. Results showed that the defined FEM model reproduces acceptably the final temperature profiles obtained by experimental measures. Furthermore, the new proposed design provided with thick fins shows its good performance when the 3D printing process is performed with a fan speed higher than 10% (defined according to a PWM function programmed at the 3D printer's firmware), while its design presents a much lower manufacturing time with regards to the present available design. It is also concluded that refrigerating the liquefier during a standard 3D printing process with an airflow higher than PWM¿=¿20% is not recommended, due to a fall in efficiency and not remarkable refrigerating effect obtained through it.Postprint (author's final draft