José Luis Valencia

Inserts Selection for Intermittent Turning of Magnesium Pieces

The present work shows an experimental study for selecting the best tools to use in the intermittent turning of pieces of UNS M11917 magnesium alloy under low performance conditions based on the surface roughness. Namely, two types of tools are considered: one, specific for non-ferrous materials, and the other, for materials usually combined with the magnesium to form hybrid parts such as titanium or steel. In order to carry out this study, a combined design of experiments (DOE) L4x32 is established. Concretely, the factors that are taken into account in the design, in addition to the type of tool, are considered the next ones: depth of cut, feed rate, spindle speed, quantity of lubrication, type of interruption, and measurement zones of the surface roughness in terms of the measurement length and of the measurement generatrix. Obtained data are analysed by means of the analysis of variance (ANOVA) method. In this case, feed rate is the most influential factor on the variability of surface roughness followed, although at a large distance, by: type of interruption, interaction feed rate-quantity of lubrication, type of tool, quantity of lubrication, interaction type of tool-type of interruption and spindle speed. As conclusion, it is possible to affirm that, in general, the surface roughness is slightly lower when using non-ferrous tools than when using the other types tried.

Tool selection based on surface roughness in dry facing repair operations of magnesium pieces

This paper presents an experimental study on the dry facing of pieces of UNS M11917 magnesium. The work was focused on repair operations that are typically carried out with low-performance cutting conditions. The main goal of this study was to determine the tool that best suits the requirements of surface roughness for these operations. The tools considered had the same geometry but different coatings and were selected from among the most commonly used tools for magnesium and the hybrid structures formed by magnesium and other materials. The effects of spindle speed and feed rate were also considered to determine which factors and their possible interactions are more crucial. The tests were conducted following the Taguchi orthogonal design of experiments (DOE), and the results were analysed by the analysis of variance (ANOVA) method. A model for estimating the expected surface roughness in terms of the average roughness, Ra, was also developed.

Evaluation of extreme temperature events in northern Spain based on process control charts

Extreme climate events have recently attracted the attention of a growing number of researchers because these events impose a large cost on agriculture and associated insurance planning. This study focuses on extreme temperature events and proposes a new method for their evaluation based on statistical process control tools, which are unusual in climate studies. A series of minimum and maximum daily temperatures for 12 geographical areas of a Spanish region between 1931 and 2009 were evaluated by applying statistical process control charts to statistically test whether evidence existed for an increase or a decrease of extreme temperature events. Specification limits were determined for each geographical area and used to define four types of extreme anomalies: lower and upper extremes for the minimum and maximum anomalies. A new binomial Markov extended process that considers the autocorrelation between extreme temperature events was generated for each geographical area and extreme anomaly type to establish the attribute control charts for the annual fraction of extreme days and to monitor the occurrence of annual extreme days. This method was used to assess the significance of changes and trends of extreme temperature events in the analysed region. The results demonstrate the effectiveness of an attribute control chart for evaluating extreme temperature events. For example, the evaluation of extreme maximum temperature events using the proposed statistical process control charts was consistent with the evidence of an increase in maximum temperatures during the last decades of the last century.

Cutting Parameter Selection for Efficient and Sustainable Repair of Holes Made in Hybrid Mg–Ti–Mg Component Stacks by Dry Drilling Operations

Drilling is one of the most common machining operations in the aeronautic and aerospace industries. For assembling parts, a large number of holes are usually drilled into the parts so that they can be joined later by rivets. As these holes are subjected to fatigue cycles, they have to be checked regularly for maintenance or repair, since small cracks or damage in its contour can quickly cause breakage of the part, which can have dangerous consequences. This paper focuses on finding the best combinations of cutting parameters to perform repair and maintenance operations of holes in stacked hybrid magnesium–titanium–magnesium components in an efficient, timely, and sustainable (without lubricants or coolants) manner, under dry drilling conditions. For the machining trials, experiments were designed and completed. A product of a full factorial 23 and a block of two factors (3 × 2) was used with surface roughness as the response variable measured as the mean roughness average. Analysis of variance (ANOVA) was used to examine the results. A set of optimized tool and cutting conditions is presented for performing dry drilling repair operations.

Técnica estadística para el control de calidad en prospección arqueológica.

espanolMetodo estadistico de aplicacion general para el control de calidad de las prospecciones arqueologicas dirigido a conocer la fiabilidad de los resultados. Consiste en efectuar una Prospeccion de Control sobre una muestra obtenida de forma aleatoria, que supone solo entre un 0,2 y un 8% del total, dependiendo del tamano de la superficie a controlar (Tabla 1). Una sencilla operacion y la utilizacion de unas tablas normalizadas (Tabla 2) permiten determinar con seguridad si la calidad de la prospeccion controlada es aceptable o no. EnglishStatistical method for quality control in archaeological surveys, in order to know the reliability of their results. A control survey has to be made on a random sample, which only supposes between 0,2 and 8% of the total area, depending on the size of the surface to be controlled (Table 1). A simple statistical operation and the use of standard tables (Table 2) allow us to determine wether the controlled prospection has an acceptable quality.