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%

Obtención de gráficos tangibles mediante técnicas de Prototipado Rápido: el volumen como elemento compositivo de diseño

Se presentan los sistemas de producción de Prototipado Rápido, y se exponen algunas de sus aplicaciones prácticas en el ámbito de la realización de gráficos tangibles para su utilización por personas con discapacidad visual. Se refieren sintéticamente los procesos de fabricación más empleados en la actualidad para realizar este tipo de gráficos en relieve, y se analizan las distintas técnicas desarrolladas para la impresión de objetos físicos en volumen y su modo de realización con técnicas de diseño asistido por ordenador. Se describen los antecedentes y experiencias más significativos en este ámbito, y se plantean algunos aspectos de la teoría compositiva del diseño, que posibilitan un mejor aprovechamiento de estas técnicas.Rapid prototyping systems are described, along with practical applications in the production of tangible graphics for people with visual disability. The article summarises the most popular and recent manufacturing methods for this type of relief graphics and analyses the techniques developed to print physical objects in three dimensions, drawing from computer-assisted design software. A description of the most significant precedents and experiences in the field is followed by a discussion of the particulars of the «compositional theory of design» that facilitate more effective use of these techniques

Manufacturing variation models in multi-station machining systems

In product design and quality improvement fields, the development of reliable 3D machining variation models for multi-station machining processes is a key issue to estimate the resulting geometrical and dimensional quality of manufactured parts, generate robust process plans, eliminate downstream manufacturing problems, and reduce ramp-up times. In the literature, two main 3D machining variation models have been studied: the stream of variation model, oriented to product quality improvement (fault diagnosis, process planning evaluation and selection, etc.), and the model of the manufactured part, oriented to product and manufacturing design activities (manufacturing and product tolerance analysis and synthesis). This paper reviews the fundamentals of each model and describes step by step how to derive them using a simple case study. The paper analyzes both models and compares their main characteristics and applications. A discussion about the drawbacks and limitations of each model and some potential research lines in this field are also presented

Design and implementation of a function block-based holonic control architecture for a new generation flexible manufacturing system

In this research work a control architecture which gives response to the requirements of new generation of flexible manufacturing systems in terms of flexibility, reconfigurability, robustness and autonomy is designed and implemented. To do so the main principles of the Holonic Manufacturing paradigm are applied using the IEC61499 function block (FB) technology. Unlike other similar research proposals, in this work FBs are not relegated to low-level control but are used to model manufacturing execution and control high-level control tasks. This is done with the objective of evaluating the viability of using FBs to develop holonic architectures in comparison to more established technologies like multi-agent systems. Moreover, the proposed control architecture also focuses on better integrating and exploiting the products’ information to enhance its flexibility and adaptability. For this STEP-NC (ISO14649) is used to model richer process plans which include manufacturing alternatives and could be easily integrated in the control itself

Influencia de los defectos geométricos en la superficie de contacto de un disipador de calor, orientado a la asignación de sus tolerancias de fabricación

Comunicación presentada en el XXI Congreso Nacional de Ingeniería Mecánica, celebrado en Elche en Noviembre de 2016.Las desviaciones de la geometría real en los componentes fabricados respecto de la geometría ideal tratada durante el diseño provocan la aparición de anomalías durante el funcionamiento de componentes ensamblados, siendo necesario limitar estas desviaciones mediante una apropiada síntesis de tolerancias (su especificación y la asignación de sus valores) de modo que se garantice la funcionalidad. Esta síntesis de tolerancias se deberá llevar a cabo efectuando un estudio detallado de cómo las desviaciones de fabricación afectan a la función, y asignando valores de las tolerancias atendiendo a criterios de capacidad y de costes de fabricación. Sin embargo, las relaciones entre el valor de las tolerancias y la calidad de funcionamiento no están siempre claras, por lo que las tolerancias se especifican asignando valores "habituales" o recomendados. Este proceder es frecuente y lleva a que se establezcan, con gran frecuencia, esquemas inconsistentes de tolerancias, que conducen a asignar valores para las tolerancias excesivamente estrechos. Como consecuencia de todo ello las piezas resultan caras y el propio funcionamiento del conjunto puede incluso no quedar garantizado. En este trabajo se analiza un sistema compuesto por un circuito integrado (CI) y un disipador de calor sobre él montado, estudiando cómo influyen los errores de fabricación presentes en la superficie del disipador en la capacidad de transmisión de calor en la zona de contacto entre CI y disipador, siendo el requisito funcional la transmisión de una cantidad de calor Q definida bajo unas condiciones de contorno ambientales. Como resultado se obtendrán las ecuaciones funcionales que ligan el RF con la tipología y magnitud de los errores, particularizado para el caso concreto de los defectos de rugosidad superficial en la superficie del CI

Analysis of the hardness ratio effect on the tribological performance of NiCrBSi coating/debris particles using the Stribeck Curve

This work aims to propose an approach to estimate the final surface roughness as a function of the hardness ratio between coating and debris (Hpin/Hdebris = Hp/Hd) under lubricated conditions employing pin-on-disc configuration. Using this approach provides a better understanding and prediction of the lubrication regime (Stribeck Curve) compared with the traditional approach that uses the initial surface roughness. Our results demonstrate that a lower hardness ratio induces a higher friction coefficient and contributes to a marked increase in wear rate in lubricated conditions. To find an effective method for simulating the debris effect, four types of NiCrBSi powders were used as a source of debris: two metallic powders with a completely spherical morphology but different Cr concentrations and two other NiCrBSi (15.25%Cr) powders mixed with different concentrations 40 and 60% of ceramic, Zr + 7% Y2O3 (ZSP), composed of spherical particles morphology. Therefore, a set of four sources of debris material specimens were simulated by different types of particles with a similar size distribution but different average hardness. Each of these particles was dispersed in an oil lubricant. Observation of the worn surfaces using a rugosimeter and scanning electron microscope suggested that, together with the shape, size and number of debris, the hardness ratio must be considered when studying the tribological behavior of machine components. The proposed methodology may help to predict the variation in lubrication regime parameters (Stribeck curve) by controlling the hardness ratio.Funding for open access charge: CRUE-Universitat Jaume

Study of additive manufacturing techniques to obtain tactile graphics

Ponència presentada a la 9th Manufacturing Engineering Society International Conference (MESIC 2021) 23rd-25th June 2021, Gijόn, SpainTactile graphics (TG) are intended to facilitate communication for people with total or partial visual impairment. For this purpose, TG include elements in relief that can be perceived through the sense of touch. TG can be fixed or portable. Fixed TG are expensive, as they are typically produced in very short runs, mostly single part production. Portable TG can be made by thermoforming polymer sheets, but a mould is still required, even though production runs are short (some tens). For this reason, the use of Rapid Manufacturing (RM) and Rapid Tooling (RT) strategies to manufacture TG can be of great interest. In this work, a literature review to study the application of Additive Manufacturing (AM) to obtain TG, both as RM and RT, is carried out. The review reveals the suitability of AM techniques to manufacture TG. In addition, some AM techniques are analysed to be used for a new type of TG, which is based on the deposition of glaze on ceramic tiles

Prensado, con métodos de la cerámica plana, de piezas cerámicas curvas con especificaciones geométricas de elevada precisión

In order to obtain high-precision three-dimensional pieces by dry pressing, two approaches were studied: modelling the material flow and strain during pressing; and evaluating the bulk density (Da) distribution in a pressed piece and using shrinkage models that allow the post-firing geometry to be predicted. It would thus become possible to act in the design phase (functional geometry and rear) and in the process. This paper describes the studies carried out to predict the final geometry of three-dimensional pieces of the sheet type obtained by conventional pressing techniques, from the Da distribution in each point of the piece. For this purpose, pieces were modelled using finite element method (FEM), applying simulation processes to obtain the strain at each point of the piece as a function of its Da. The experimental validation was performed using the X-ray absorption method for Da and a CMM (coordinate measuring machine) for the geometr

Análisis del aprovechamiento de material digital web para el aprendizaje de las Tecnologías de Fabricación

La docencia universitaria en torno a los procesos de fabricación tiende a ser descriptiva y de difícil aprendizaje a pesar de la introducción en los últimos años de material audiovisual de apoyo en las sesiones teóricas. Actualmente, el uso extendido de smartphones, tablets y similares generan la oportunidad de crear contenidos digitales reducidos que podrían fácilmente completar las explicaciones realizadas en el aula, resumir contenidos, remarcar errores habituales de concepto que se repiten curso tras curso, etc. En este trabajo se analiza la utilidad del uso de una serie de contenidos digitales orientados a la consulta rápida on-line que permita asentar los conceptos explicados en clase y a su vez facilite la interacción con el profesorado como si de una tutoría virtual se tratara. Los contenidos elaborados están organizados en un sitio web de Google y son de tres tipos: videos de los procesos de fabricación; resolución de problemas recalcando las FAQ del mismo; y video clases de 10-15 min con el contenido más relevante de cada tema de la asignatura. Para analizar la posible mejora educativa, se analiza el uso de estos contenidos digitales y la posible mejora del rendimiento académico del alumno