5 research outputs found

    Aplicación de nuevas tecnologías en la realización de herramientas para moldes de inyección de termoplásticos

    Full text link
    Resumen En la actualidad, y desde sus inicios, el sector de la industria dedicada a la fabricación de piezas de plástico de consumo está sufriendo cambios en las directrices de su mercado. Tras los inicios, en los que las piezas de plástico raramente se encontraban en alguna maquinaria, equipo o aparato, hasta el día de hoy, donde es impensable que esos mismos tipos de máquinas, equipos o aparatos, no incorporen algún componente fabricado en plástico, las tendencias han pasado por diferentes etapas. Los orígenes se centraban en desarrollar nuevos materiales, técnicas y maquinas de transformación. Después se pasó a perfeccionar todos estos aspectos para lograr condiciones óptimas de producción y piezas con las mejores cualidades posibles, cosa que aún hoy en día continúa. Esto, junto con la incorporación de nuevos planteamientos a la hora de diseñar los productos, derivó en lograr el uso de piezas de plástico de forma masiva e incluso, en ocasiones, en aplicaciones a veces impensables hace pocos años, con unos resultados realmente sorprendentes. Así mismo la demanda de este tipo de piezas también ha evolucionado. Inicialmente hubo una gran reticencia en el uso de los plásticos. Algo lógico si se tienen en cuenta las cualidades de las piezas inicialmente producidas en estos materiales. Después se tendió a incorporar paulatina pero constantemente más partes de plástico como componentes de casi cualquier producto, lográndose introducir este tipo de piezas en las tendencias de la demanda. En los últimos tiempos y sobre todo por motivos económicos, la producción y en paralelo la demanda de productos con piezas de plástico se ha generalizado. Sin embargo en las últimas décadas las tendencias de este mercado están derivando en producir piezas de plástico, pero no sólo de una forma masiva (cosa que también sigue ocurriendo), sino adaptándose a la demanda real de cada momento, situación, lugar y aplicación. Este ajuste se intenta hacer en todos los aspectos: materiales, calidades, plazos, costes, formas, geometrías, dimensiones, funcionalidades, gustos estéticos,… De tal manera que se pretende satisfacer, de forma casi individualizada, las necesidades planteadas en cada caso. Todo esto ha llevado a desarrollar, desde hace pocos años, nuevas técnicas y tecnologías en el desarrollo de nuevos productos, que complementen a las tradicionales. Entre ellas se encuentran las tecnologías CAD-CAM-CAE, que junto con herramientas software de diseño, gestión, control, optimización y aseguramiento de la calidad en la producción, han revolucionado dicho desarrollo. Pero estas tecnologías por si solas no son capaces de materializar las piezas de los productos, teniéndose que “comunicar” con los sistemas de producción. Esto se ha logrado con más o menos problemas y éxitos con los sistemas de producción tradicionales, en los cuales la automatización de los procesos también se ha extendido. Sin embargo en paralelo se han ido desarrollando nuevas tecnologías de fabricación que, por sus propias características, están mucho mejor adaptadas a cubrir esa demanda casi individualizada. Estas nuevas técnicas y tecnologías se denominan de prototipado y fabricación rápidos (“Rapid Prototyping and Manufacturing”). De forma general, basan sus principios de fabricación en la adición de material o en el copiado rápido de formas, en vez de en la eliminación (mecanizado) de material como sucede con las tradicionales. Este nuevo tipo de tecnologías se encuentra, pese a su relativamente rápida incorporación en las metodologías de desarrollo de productos, en etapas iniciales de desarrollo. Con la gran parte de estas nuevas tecnologías hasta ahora se obtienen prototipos o Resumen pequeñas y medianas series de una pieza. Esto, en la mayoría de los casos, se hace en materiales no finales, teniéndose que recurrir casi siempre a técnicas tradicionales si se quieren piezas finales, sea cual sea la cantidad necesitada de éstas. La progresión, que estas nuevas técnicas están teniendo en los últimos años, va encaminada a la obtención de esas piezas finales de la forma más rápida y precisa posible. Para ello, una vía seguida es la innovación en materiales que permitan mediante estas nuevas técnicas dicho objetivo. Otra vía, que va unida a la anterior, es el desarrollo de nuevas técnicas y tecnologías que no existían hasta ahora. La tercera vía es buscar nuevas combinaciones entre las técnicas y tecnologías ya existentes, tanto tradicionales como de prototipado y fabricación rápidos, para lograr aprovechar las ventajas que aportan cada una de ellas. Esta tesis aborda esta tercera vía. En las investigaciones que se han realizado se hace uso de la experiencia que se tiene, por separado y por parte de distintos agentes, en la utilización tanto de técnicas tradicionales, como de las de prototipado y fabricación rápidos, para buscar nuevas combinaciones con todas ellas que permitan avanzar en la obtención de piezas finales casi individualizadas. Las nuevas técnicas se pueden dividir en dos grandes grupos las de “Rapid Prototyping” y las de “Rapid Tooling”. Las primeras se centran en obtener la pieza final directamente por esas nuevas técnicas. Las segundas buscan fabricar las herramientas (moldes, matrices,…) con esas nuevas técnicas, para después usar dichas herramientas con técnicas tradicionales de producción y obtener las piezas. Los trabajos de investigación recogidos en esta tesis se centran en las del segundo grupo. Sin embargo en ello se han empleado tanto técnicas y tecnologías tradicionales como nuevas. Y dentro de estas últimas se ha hecho uso de técnicas que en su concepción inicial fueron consideradas de “Rapid Prototyping” y de otras que lo fueron de “Rapid Tooling”. Tras un estudio inicial de la situación actual y en base a experiencias previas, se han planteado unas alternativas en la forma de combinar las tecnologías disponibles para intentar cubrir unas carencias que se han detectado. El Objetivo General de esta tesis es profundizar en el campo del Rapid Tooling y aportar alternativas nuevas en la fabricación de moldes de inyección, para cubrir las necesidades de realización de series finales muy cortas y de obtención de prototipos individuales de piezas producidas por inyección de termoplásticos. Como Objetivos Particulares se plantea principalmente estudiar la viabilidad técnica y la viabilidad económica de las diferentes alternativas. Con ello se podrá extraer, de los trabajos realizados, unos resultados más tangibles y evaluables y, sobre todo, aprovechables industrialmente. Para ello, durante las investigaciones se han definido metodologías de trabajo y se han desarrollado los procedimientos a seguir. Abstract Abstract At present and from its beginnings the sector of the industry dedicated to the manufacture of consumption plastic pieces is undergoing changes in the directives of its market. After the beginnings in which the plastic pieces rarely were in any machinery, equipment or apparatus, until today where it is unthinkable that those same types of machines, equipment or apparatuses do not incorporate some component made in plastic, the tendencies have happened through different stages. The origins concentrated efforts in developing new materials, techniques and machines of transformation. Later it went to perfect all these aspects to obtain optimal conditions of production and pieces with the best possible qualities, something that still nowadays continue. This, along with incorporating new expositions at the time of designing products, derived in obtaining the use of plastic pieces of massive form and even in sometimes unthinkable applications few years ago, with really surprising results. Also the demand of this type of pieces also has evolved. Initially there was a great reluctance in the use of plastics. Something logical if are considered qualities of the pieces initially produced in these materials. Later it derived to incorporate gradual but constantly more parts of plastic as components of almost any product, being obtained to introduce this type of pieces in the tendencies of the demand. Lately and mainly by economic reasons, the production and in parallel the demand of products with plastic pieces has become general. Nevertheless in the last decades the tendencies of this market are deriving in producing plastic pieces, but not only of a massive form (something that also continues happening), but adapting to the real demand of every moment, situation, place and application. This adjustment is tried to do in all the aspects: materials, qualities, terms, costs, forms, geometries, dimensions, functionalities, aesthetics,… In such a way that it is tried to satisfy, of almost individualized form, the needs raised in each case. All of this has taken to develop, since few years ago, techniques and technologies in the development of new products, which complement to the traditional ones. Among them are CAD-CAM-CAE technologies, which along with software tools of design, management, control, optimization and securing of the quality in production, has revolutionized this development. But these technologies by themselves are not able to materialize parts of products, because they have “to communicate” with the production systems. This has been achieved with more or less problems and successes with traditional production systems, in which process automation also has extended. Nevertheless in parallel it has been developed new technologies of manufacture that, by their own characteristics, are far better adapted to cover that almost individualized demand. These new techniques and technologies are denominated “Rapid Prototyping and Manufacturing” technologies. In general, they base his manufacture principles in the addition of material or in the rapid copy of forms, instead of in the elimination (mechanized) of material as it do the traditional ones. This new type of technologies is, in spite of his relatively fast incorporation in product development methodologies, in initial stages of development. With the great part of these new technologies until now it is possible to obtain prototypes or small and medians series of a piece. This, in Abstract the majority of the cases, becomes in no-final materials, and it has to resort almost always to traditional techniques if final pieces are wanted, whatever amount needed of these. The progression, that these new techniques are being in the last years, goes directed to obtain those final pieces in the fastest and accurate possible way. For it, a followed route is materials innovation that allows with these new techniques this objective. Another route, that goes united to the previous one, is the development of new techniques and technologies that did not exist until now. The third route is to look for new combinations between the ones already exist, both traditional ones and rapid prototyping and manufacturing ones, to manage to take advantage of advantages that each of them contribute. This thesis approaches this third option. In the investigations that have been realised it makes use of the experience that it is had, separately and by different agents, in the use of both traditional techniques and those of rapid prototyping and manufacturing, to look for new combinations with all of them that allow to advance in obtaining of almost individualized final pieces. The new techniques can be divided in two great groups those of “Rapid Prototyping” and those of “Rapid Tooling”. First ones concentrate in directly obtaining final piece by those new techniques. Second ones look for to make tools (moulds) with those new techniques, to use these tools with traditional production techniques and to obtain the pieces. The investigation works contained in this thesis are concentrated in those of the second group. Nevertheless in that objective it have been used both traditional and new techniques and technologies. And within these last ones it has used techniques that in their initial conception were considered as “Rapid Prototyping” and other ones that were judged as “Rapid Tooling”. After an initial study of the present situation and on the basis of previous experiences, is has been considered alternatives in the form to combine available technologies trying to cover deficiencies that have been detected. The General Objetive of this thesis is to deepen in the field of the Rapid Tooling and to contribute new alternatives in injection moulds manufacturing, to cover the needs of achieving very short final series and of obtaining individual prototypes of pieces produced by thermoplastic injection. As Particular Objectives it is mainly considered studying technical and economic viability of the different alternatives. In this way it will be possible to extract, from the works carried out, more tangible and appraisable results and, mostly, usable in industry. For it, during investigations, work methodologies have been defined and procedures to follow have been developed

    Physical ageing of a PU based shape memory polymer: influence on their applicability to the development of medical devices.

    Get PDF
    The variation in the properties of polymeric materials through ageing has considerable implications, since it affects the performance of any associated devices. Specially in the case of implantable devices with shape memory, any change in the switching temperature can give rise to problems in the thermal activation of the geometrical changes necessary to treat certain pathologies.This paper presents a study about the physical ageing of a polyurethane based shape memory polymer, SMP, at different temperatures using differential scanning calorimetry, DSC, and microhardness, MH, tests. The benefits of the combinated application of both testing techniques is shown, since DSC tests give information on the evolution of the glass transition temperature and the MH tests provide details of changes regarding mechanical properties

    Models for predicting friction coefficient and parameters with influence in elastohydrodynamic lubrication

    Get PDF
    This article shows different friction prediction models applicable to lubricants in point contacts under an elastohydrodynamic regime. The types of models used are two variations of the Newtonian theory, the Limiting Shear Stress model and the one based on Carreau's equation. The article sets out the theoretical calculation procedures and the ensuing equations for calculating the friction coefficient. The aims of the article are to study the effect of the parameters with influence on friction and to compare the model's results with those given by an experimental stage performed on a mini traction machine. This test system allows the measurement of friction coefficient in point contacts (ball–disc) under a wide range of variation of parameters such as temperature, slide-roll ratio, lubricant, material, load, or velocity

    Instrumented splint for the diagnosis of bruxism

    Get PDF
    Bruxism is a health problem consisting in grinding or tightly clenching the upper and lower teeth. Both the grinding and sliding lead to wear of the teeth and produce a noise during the night that is sufficiently loud to disturb the sleep of anyone sharing the bedroom. The tension produced causes problems in the muscles, tissues and other structures surrounding the jaw, ear pain, headaches, lesions to the teeth and disorders in the jaw joints. For an early, rapid, effective and economical diagnosis of bruxism, we propose the use of instrumented splints to detect and record the intensity and duration of inter dental pressure episodes. This paper sets out the design, manufacture and testing of an instrumented splint for diagnosing the signs of bruxism. The system stands out for its use of piezoelectric polymeric sensors which, because of their reduced thickness, do not cause any alteration to the patient’s bite. It lets a quantitative assessment of intraoral pressure be made and bruxism behavior be diagnosed at an early stage, so as to being able to programme corrective actions before irreversible dental wear appears. The first “in vitro” simulations and “in vivo “trials performed served to demonstrate the feasibility of the system in accordance with the initial objectives

    The Evolution and Development of Mechanical Engineering through large cultural areas

    Get PDF
    Mechanical Engineering is probably the forerunner of many branches of Engineering and has persistently been their companion up to the present. For this reason, the History of Machines embraces a very broad period of the History of Mankind, and can be studied from many perspectives. This paper attempts to link progress in Mechanical Engineering to the great cultures that have arisen throughout the History of Mankind. This paper begins with the anonymous mechanical developments that appeared in Prehistory and opened up the way to the first civilisations, marked to a large extent, maybe, by Greco-Roman culture in Europe and by China in Asia. After them came the Islamic world, which, in the Middle Ages stimulated society to find new mechanical devices and set the foundations that would lead to the Renaissance. Outstanding in this period was the expansion of Italian, French and German creative and innovative thinking with its “Treatises on Machines”, which, for a short time, coincided with the advance of the Iberian Empire and the development of machinery for the New World. Finally, the Industrial Revolution became the climax of all previous developments and a period of rapid mechanical evolution began that was to be highly interesting from a historical and technological point of view. This was accompanied by a parallel interest in reflecting on and analysing machines, which has led to the appearance of countless “Treatises on Machines”
    corecore