Experimental and numerical analysis of the influence of drill point angle when drilling biocomposites

Biocomposites are promising materials for traditional composites replacement in specific applications due to their interesting properties and sustainability. Although the composite components are manufactured near net shape, some machining operations, commonly drilling, are commonly required prior to mechanical joining of the components. Tool geometry, mainly the point angle of the drill, strongly affects the performance of the drilling process of composites in terms of machining induced damage. The aim of this work is analyzing the influence of the point angle of the drill on the damage generated during drilling of 100% biodegradable composite, using both numerical and experimental approaches. The novelty of the work relies on the lack of studies of drilling 100% biodegradable composites. The influence of the point angle on the thrust forces and hence in the machining induced damage was demonstrated.The authors acknowledge the financial support to the Ministry of Economy and Competitiveness of Spain and FEDER program through the projects DPI2017-89197-C2-1-R and DPI2017-89197-C2-2-R

Analysis of orthogonal cutting of biocomposites

The use of 100% biodegradable composites in the industry is increasing significantly over the years, mainly due to their excellent properties as well as to the growing ecologic concern. However, after their manufacture, the composite pieces do not always have the final shape, requiring subsequent processing operations, usually drilling and trimming. The performance of cutting processes on fully biodegradable composites are often limited by induced damage as fraying and delamination. This type of phenomena is related, among others, with the cutting parameters and geometries of the tool. Orthogonal cutting is a simplified process that could help in the understanding of damage mechanisms, it is a well-known technique in traditional composites but its use in biocomposites is an almost unexplored field. This work focuses on flax/PLA 100% biodegradable woven composites. The specimens have been manufactured with different angles of orientation, ranging from 0° to 60°, being subjected to orthogonal cutting in a special machine developed for that purpose that allows to develop cutting tests with linear displacement at high speeds. Damage extension, failure modes, and cutting forces are analyzed allowing the extraction of important experimental information.Authors gratefully acknowledges the financial support to the Ministry of Economy and Competitiveness of Spain and FEDER program through the project DPI2017-89197-C2-1-R

Sustainable high-speed finishing turning of haynes 282 using carbide tools in dry conditions

Nickel-based superalloys exhibit an exceptional combination of corrosion resistance, enhanced mechanical properties at high temperatures, and thermal stability. The mechanical behavior of nickel-based superalloys depends on the grain size and the precipitation state after aging. Haynes 282 was developed in order to improve the creep behavior, formability, and strain-age cracking of the other commonly used nickel-based superalloys. Nevertheless, taking into account the interest of the industry in the machinability of Haynes 282 because of its great mechanical properties, which is not found in other superalloys like Inconel 718 or Waspaloy, more research on this alloy is necessary. Cutting tools suffer extreme thermomechanical loading because of the high pressure and temperature localized in the cutting zone. The consequence is material adhesion during machining and strong abrasion due to the hard carbides included in the material. The main recommendations for finishing turning in Haynes 282 include the use of carbide tools, low cutting speeds, low depth of pass, and the use of cutting fluids. However, because of the growing interest in sustainable processes and cost reduction, dry machining is considered to be one of the best techniques for material removal. During the machining of Haynes 282, at both the finishing and roughing turning, cemented carbide inserts are most commonly used and are recommended all over the industry. This paper deals with the machining of Haynes 282 by means of coated carbide tools cutting fluids (dry condition). Different cutting speeds and feeds were tested to quantify the cutting forces, quality of surface, wear progression, and end of tool life. Tool life values similar to those obtained with a lubricant under similar conditions in other studies have been obtained for the most favorable conditions in dry environments.This research was funded by the Ministry of Economy, Industry, and Competitiveness, and the FEDER program, grant number DPI2017-89197-C2-1-R

A Joint Optimization Criterion for Blind DS-CDMA Detection

This paper addresses the problem of the blind detection of a desired user in an asynchronous DS-CDMA communications system with multipath propagation channels. Starting from the inverse filter criterion introduced by Tugnait and Li in 2001, we propose to tackle the problem in the context of the blind signal extraction methods for ICA. In order to improve the performance of the detector, we present a criterion based on the joint optimization of several higher-order statistics of the outputs. An algorithm that optimizes the proposed criterion is described, and its improved performance and robustness with respect to the near-far problem are corroborated through simulations. Additionally, a simulation using measurements on a real software-radio platform at 5 GHz has also been performed.Ministerio de Ciencia y tecnología TEC2004-06451-C05-0

Finishing Turning of Ni Superalloy Haynes 282

Nickel-based superalloys are widely used in the aeronautical industry, especially in components requiring excellent corrosion resistance, enhanced thermal fatigue properties, and thermal stability. Haynes 282 is a nickel-based superalloy that was developed to improve the low weldability, formability, and creep strength of other gamma'-strengthened Ni superalloys. Despite the industrial interest in Haynes 282, there is a lack of research that is focused on this alloy. Moreover, it is difficult to find studies dealing with the machinability of Haynes 282. Although Haynes 282 is considered an alloy with improved formability when compared with other nickel alloys, its machining performance should be analyzed. High pressure and temperature localized in the cutting zone, the abrasion generated by the hard carbides included in the material, and the tendency toward adhesion during machining are phenomena that generate extreme thermomechanical loading on the tool during the cutting process. Excessive wear results in reduced tool life, leading to frequent tool change, low productivity, and a high consumption of energy; consequentially, there are increased costs. With regard to tool materials, cemented carbide tools are widely used in different applications, and carbide is a recommended cutting material for turning Haynes 282, for both finishing and roughing operations. This work focuses on the finishing turning of Haynes 282 using coated carbide tools with conventional coolant. Machining forces, surface roughness, tool wear, and tool life were quantified for different cutting speeds and feeds.This research was funded by the Ministry of Economy, Industry and Competitiveness and the FEDER program, grant number DPI2014-56137-C2-2-R

High-pressure cooling in finishing turning of haynes 282 using carbide tools: Haynes 282 and inconel 718 comparison

Despite the interest of industry in nickel-based superalloys and its main features (high temperatures resistance, hardness, low thermal conductivity, among others), even today they are still materials that are difficult to cut. Cutting tools withstand both high pressures and temperatures highly localized at the cutting area because of the elevated work hardening of the alloy and the problems for the cutting fluid to access the region, with the consequent strong tool wear. The use of cutting fluids at high pressures improves coolant access and heat removal. This paper analyzed the machining of Haynes 282 alloy by means of coated carbide tools under high-pressure cutting fluids at finishing conditions. Tests were developed at different cutting speeds and feeds quantifying the machining forces, surface roughness, tool wear, and tool life. Values of 45.9 min and Ra between 2 µm and 1 µm were obtained in this study for tool life and roughness, respectively, for the combination of cutting speed 50 m/min and feed 0.1 mm/rev. Likewise, a comparative analysis is included with the results obtained in previous works developed by the authors relating to the finishing turning of Haynes 282 and Inconel 718 under conventional pressure cooling. The comparative analysis with Inconel 718 is included in the study due to its importance within the nickel base superalloys being widely used in industry and widely analyzed in scientific literature.The authors gratefully acknowledge the funding support received from the Spanish Ministry of Science and Innovation and the FEDER program for funding the projects PID2020-112628RA-I00, PID2020-118480RB-C22 and PDC2021-121368-C21

Pleito de Villarejo : informe

Autor tomado del textoTít. tomado de la cub.Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

Análisis experimental y numérico del taladrado de materiales compuestos

Los procesos de mecanizado por arranque de viruta están muy extendidos en la industria. En estos procesos, el tamaño de la pieza original circunscribe la geometría final, y el material sobrante es arrancado en forma de virutas. El taladrado es especialmente importante dentro de este conjunto de procesos, ya que se utiliza frecuentemente al final del proceso de fabricación, por lo que un fallo puede representar cuantiosas pérdidas. Los materiales compuestos se emplean ampliamente en diferentes sectores industriales debido principalmente a propiedades como su elevada resistencia, su baja densidad y buena resistencia a la corrosión. Dentro de éstos, los más empleados son los materiales compuestos con refuerzos de fibras largas. El daño mecánico del material que se produce en los procesos de mecanizado de los materiales compuestos es muy relevante debido principalmente a su disposición en forma de apilado y a la separación de las mismas durante el procesado de éste, originando su consecuente merma de propiedades. El objetivo principal de esta Tesis es el análisis del proceso de taladrado en seco de distintos materiales compuestos, pertenecientes a las familias de: fibra de carbono, fibras de aramida y naturales. Los defectos en la superficie alrededor del taladro, así como la posible separación de las láminas son especialmente significativos en este tipo de procesos, lo que justifica el interés del objetivo planteado. Se ha llevado a cabo un estudio experimental, realizando ensayos de taladrado con herramientas de distintas geometrías, y diferentes parámetros de corte. Durante el proceso se determinó la evolución de la fuerza de avance, el par torsor, así como los posibles defectos presentes en los materiales durante el mismo. De igual forma, se desarrolló y validó, un modelo numérico tridimensional basado en Elementos Finitos, reproduciendo las condiciones de corte consideradas. A continuación, se indican las principales aportaciones del trabajo realizado en el marco de esta Tesis. - Se ha desarrollado una metodología de ensayos de taladrado que permite obtener experimentalmente la fuerza axial y el par torsor. - Se han diseñado y fabricado los utillajes específicos requeridos para el posicionamiento y fijación del material, herramientas e instrumentación. También se ha realizado la puesta a punto y verificación del sistema. - Se han realizado ensayos de taladrado en seco sobre materiales compuestos de fibra de carbono, fibras de aramida y fibras naturales, empleando diferentes condiciones de corte, y brocas con distintas geometrías por cada material. Los resultados experimentales obtenidos presentan una gran repetibilidad y se corresponden con un amplio rango de condiciones de mecanizado. - El análisis de los resultados experimentales obtenidos ha permitido establecer los parámetros de corte y geometrías de broca óptimos para cada material estudiado, minimizando el daño generado durante el proceso de taladrado. - Se ha desarrollado un modelo numérico tridimensional de procesos de taladrado en seco de los distintos materiales compuestos para cada geometría de broca. El modelo ha sido validado experimentalmente obteniéndose una buena correlación en relación con las fuerzas de mecanizado.Machining processes are widely used in industry. In these processes, the size of the original piece circumscribes the final geometry, and the excess of material is removal. Drilling is especially important within this set, since it is widely used and it is often performed at the end of the manufacturing route, so a failure can represent large losses. Composites are widely used in different industrial sectors mainly due to properties such as high strength, low density and very good resistance to corrosion. Among these, the most used are composite materials with long fiber reinforcements. The mechanical damage of the material that is produced in the machining processes of the composite materials is very relevant due to its layering and the separation of the same during the processing of this one, causing its consequent property loss. Main objective of this thesis is the analysis of dry drilling process of different composite materials: carbon fiber, aramid and natural fibers. The defects in the Surface around the drill, as well as the possible separation of the layers are especially significant in this type of processes, which justifies the interest of the proposed objective. For this purpose, drilling tests were carried out with different tool geometries, and considering different cutting parameters. During the process the evolution of the feed force, torque and possible defects in materials during the process were determined. In the same way, a three - dimensional numerical model based on Finite Elements was developed, and validated reproducing the considered cutting conditions. Main contributions of the work carried out in the framework of this thesis are indicated below. - A drilling test methodology has been developed and applied, allowing experimental determination of axial force and torque. - The specific tooling required for positioning and fixing the material, tool and instrumentation have been designed and manufactured. The system has also been set up and verified. - Dry drilling tests were carried out on carbon fiber, aramid fibers and natural fibers, using different cutting conditions and drills with different cutting geometries for each material. The experimental results obtained are highly reliable and correspond to a wide range of machining conditions. - The analysis of the experimental results obtained allowed establishing the optimum cutting parameters and drill geometries for each material studied, trying to minimize the damage generated during the drilling process. For this reason, they represent a novel contribution of interest for the knowledge of the processes of dry drilling on composite material. - A three-dimensional numerical model of dry drilling processes of the different composite materials for each drill geometry has been developed. The model has been validated experimentally obtaining a good correlation in relation to the machining forces.Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: José Luis San Román García.- Secretario: María Rosario Domingo Navas.- Vocal: Eugenio Giner Maravill

Experimental analysis of the influence of drill point angle and wear on the drilling of woven CFRPs

This paper focuses on the effect of the drill geometry on the drilling of woven Carbon Fiber Reinforced Polymer composite (CFRPs). Although different geometrical effects can be considered in drilling CFRPs, the present work focuses on the influence of point angle and wear because they are the important factors influencing hole quality and machining forces. Surface quality was evaluated in terms of delamination and superficial defects. Three different point angles were tested representative of the geometries commonly used in the industry. Two wear modes were considered, being representative of the wear patterns commonly observed when drilling CFRPs: flank wear and honed cutting edge. It was found that the crossed influence of the point angle and wear were significant to the thrust force. Delamination at the hole entry and exit showed opposite trends with the change of geometry. Also, cutting parameters were checked showing the feed's dominant influence on surface damage.This work was supported by the Ministry of Economy and Competitiveness of Spain under the project DPI2011-25999Publicad

Centroid-Based Clustering with ab-Divergences

Centroid-based clustering is a widely used technique within unsupervised learning algorithms in many research fields. The success of any centroid-based clustering relies on the choice of the similarity measure under use. In recent years, most studies focused on including several divergence measures in the traditional hard k-means algorithm. In this article, we consider the problem of centroid-based clustering using the family of ab-divergences, which is governed by two parameters, a and b. We propose a new iterative algorithm, ab-k-means, giving closed-form solutions for the computation of the sided centroids. The algorithm can be fine-tuned by means of this pair of values, yielding a wide range of the most frequently used divergences. Moreover, it is guaranteed to converge to local minima for a wide range of values of the pair (a, b). Our theoretical contribution has been validated by several experiments performed with synthetic and real data and exploring the (a, b) plane. The numerical results obtained confirm the quality of the algorithm and its suitability to be used in several practical applications.MINECO TEC2017-82807-