Variation propagation of bench vises in multi-stage machining processes

Comunicación presentada a MESIC 2019 8th Manufacturing Engineering Society International Conference (Madrid, 19-21 de Junio de 2019)Variation propagation has been successfully modeled by the Stream of Variation (SoV) approach in multistage machining processes. However, the SoV model basically supports 3-2-1 fixtures based on punctual locators and other workholding systems such as conventional vises are not considered yet. In this paper, the SoV model is expanded to include the fixture- and datum-induced variations on workholding devices such as bench vises. The model derivation is validated through assembly and machining simulations on Computer Aided Design software. The case study analyzed shows an average error of part quality prediction between the SoV model and the CAD simulations of 0.26%

Incorporation of form deviations into the matrix transformation method for tolerance analysis in assemblies

Comunicación presentada a MESIC 2019 8th Manufacturing Engineering Society International Conference (Madrid, 19-21 de Junio de 2019)Mathematical models for tolerance representation are used to assess how the geometrical variation of a specific component feature propagates along the assembly, so that tolerance analysis in assemblies can be carried out using a specific tolerance propagation method. Several methods for tolerance analysis have been proposed in the literature, being some of them implemented in CAD systems. All these methods require modelling the geometrical variations of the component surfaces: parametric models, variational models, DoF models, etc. One of the most commonly used models is the DoF model, which is employed in a number of tolerance analysis methods: Small Displacement Torsor (SDT), Technologically and Topologically Related Surfaces (TTRS), Matrix Transformation, Unified Jacobian–Torsor model. However, none of the DoF-based tolerance analysis methods incorporates the effect of form deviations. Among the non DoF-based methods, there are two that include form tolerances: the Vector Loop or Kinematic method and the Tolerance Map (T-Map) model, although the latter is still under development. In this work, a proposal to incorporate form deviations into the matrix transformation method for tolerance analysis in assemblies is developed using a geometrical variation model based on the DoF model. The proposal is evaluated applying it to a 2D case study with components that only have flat surfaces, but the proposal can be extrapolated to 3D cases

Dark Halo and Disk Galaxy Scaling Laws in Hierarchical Universes

We use cosmological N-body/gasdynamical simulations that include star formation and feedback to examine the proposal that scaling laws between the total luminosity, rotation speed, and angular momentum of disk galaxies reflect analogous correlations between the structural parameters of their surrounding dark matter halos. The numerical experiments follow the formation of galaxy-sized halos in two Cold Dark Matter dominated universes: the standard Omega=1 CDM scenario and the currently popular LCDM model. We find that the slope and scatter of the I-band Tully-Fisher relation are well reproduced in the simulations, although not, as proposed in recent work, as a result of the cosmological equivalence between halo mass and circular velocity: large systematic variations in the fraction of baryons that collapse to form galaxies and in the ratio between halo and disk circular velocities are observed in our numerical experiments. The Tully-Fisher slope and scatter are recovered in this model as a direct result of the dynamical response of the halo to the assembly of the luminous component of the galaxy. We conclude that models that neglect the self-gravity of the disk and its influence on the detailed structure of the halo cannot be used to derive meaningful estimates of the scatter or slope of the Tully-Fisher relation. Our models fail, however, to match the zero-point of the Tully-Fisher relation, as well as that of the relation linking disk rotation speed and angular momentum. These failures can be traced, respectively, to the excessive central concentration of dark halos formed in the Cold Dark Matter cosmogonies we explore and to the formation of galaxy disks as the final outcome of a sequence of merger events. (abridged)Comment: submitted to The Astrophysical Journa

Design of a machine to rectify ceramic tiles for laboratory tests

Ponència presentada a 9th Manufacturing Engineering Society International Conference (MESIC 2021) 23rd-25th June 2021, Gijόn, SpainThe tile rectification process, also called squaring, consists of machining the edges of the tile to make them straight, parallel two by two and perpendicular to the other two in addition to controlling the size of the tile (calibrating). The current industrial lines are based on multiple heads (abrasive wheels) where the characterization of the process in terms of product quality and power consumption is hard to be conducted. In this work we present a laboratory machine equipped with a single grinding wheel to be used for testing and simulating the working conditions of a conventional rectification tile. The specifications of the machine that are required and the analysis of the different functional systems designed (clamping and motion, cutting, cooling, structure/enclosure, and electrical/control system) is reported. This machine may lead researchers to characterize the rectification process and propose actions for improving the efficiency and the sustainability of the industrial process

Influence of polydispersity on the critical parameters of an effective potential model for asymmetric hard sphere mixtures

We report a Monte Carlo simulation study of the properties of highly asymmetric binary hard sphere mixtures. This system is treated within an effective fluid approximation in which the large particles interact through a depletion potential (R. Roth {\em et al}, Phys. Rev. E{\bf 62} 5360 (2000)) designed to capture the effects of a virtual sea of small particles. We generalize this depletion potential to include the effects of explicit size dispersity in the large particles and consider the case in which the particle diameters are distributed according to a Schulz form having degree of polydispersity 14%. The resulting alteration (with respect to the monodisperse limit) of the metastable fluid-fluid critical point parameters is determined for two values of the ratio of the diameters of the small and large particles: $q\equiv\sigma_s/\bar\sigma_b=0.1$ and $q=0.05$. We find that inclusion of polydispersity moves the critical point to lower reservoir volume fractions of the small particles and high volume fractions of the large ones. The estimated critical point parameters are found to be in good agreement with those predicted by a generalized corresponding states argument which provides a link to the known critical adhesion parameter of the adhesive hard sphere model. Finite-size scaling estimates of the cluster percolation line in the one phase fluid region indicate that inclusion of polydispersity moves the critical point deeper into the percolating regime. This suggests that phase separation is more likely to be preempted by dynamical arrest in polydisperse systems.Comment: 11 pages, 10 figure

Normalizing Rejection

Getting turned down for grant funding or having a manuscript rejected is an uncomfortable but not unusual occurrence during the course of a nurse researcher’s professional life. Rejection can evoke an emotional response akin to the grieving process that can slow or even undermine productivity. Only by “normalizing” rejection, that is, by accepting it as an integral part of the scientific process, can researchers more quickly overcome negative emotions and instead use rejection to refine and advance their scientific programs. This article provides practical advice for coming to emotional terms with rejection and delineates methods for working constructively to address reviewer comments

Sampling protocol for skeletal structures of North Atlantic albacore tuna (Thunnus alalunga) and ageing interpretation

This paper presents a standardized protocol for sampling skeletal hard parts (dorsal fin ray and otoliths), preparation and age interpretation of albacore first dorsal fin ray. Ageing of albacore is focused in interpretation and reading of annual temporal marks (translucent bands) in first ray of dorsal fin. Preparation of fin ray sections (spines) is presented in detail using two different methods. The spines are usually cut individually using a low speed cutter. Depending of the size of spines, a new procedure has been developed for small spines based on encasing spines in a matrix of plastic resin allowing multiple spines cutting. Interpretation of growth marks on spine sections is explained and examples are presented for a range of size of albacore aged using this method.Ce document présente un protocole standardisé pour l’échantillonnage des pièces dures du squelette (rayon de la nageoire dorsale et otolithes), la préparation et l’interprétation de l’âge du rayon du premier rayon de la nageoire dorsale du germon. La détermination de l’âge du germon se centre sur l’interprétation et la lecture des marques temporelles annuelles (bandes translucides) du premier rayon de la nageoire dorsale. La préparation des sections du rayon de la nageoire (épines) est présentée en détail à l’aide de deux méthodes différentes. Les épines sont généralement sectionnées individuellement en utilisant un couteau basse vitesse. Selon la taille des épines, une nouvelle procédure a été élaborée pour les petites épines, consistant à enfermer les épines dans une matrice en résine plastique qui permet le découpage de plusieurs épines. L’interprétation des marques de croissance sur les sections des épines est expliquée et des exemples sont donnés pour une gamme de tailles de germon dont l’âge a été déterminé à l’aide de cette méthode.En este documento se presenta un protocolo estandarizado para el muestreo de partes duras del esqueleto (otolitos y rayo de la aleta dorsal) y para la preparación e interpretación de la edad del primer rayo de la aleta dorsal del atún blanco. La determinación de la edad del atún blanco se centra en la interpretación y lectura de las marcas temporales anuales (bandas traslucidas) en el primer rayo de la aleta dorsal. Se presenta en detalle la preparación de las secciones del rayo de la aleta (espinas) utilizando dos métodos diferentes. Las espinas suelen cortarse generalmente de forma individual utilizando un cortador de baja velocidad. Dependiendo del tamaño de las espinas, se ha desarrollado un nuevo procedimiento para las espinas pequeñas, que consiste en introducir las espinas en una matriz de resina plástica que permite cortar espinas múltiples. Se explica la interpretación de las marcas de crecimiento en las secciones de espinas y se presentan ejemplos para una gama de tallas de atún blanco cuya edad se determinó utilizando este método