Mecanismos flexibles: desde el diseño conceptual hasta su manufactura

The compliant mechanisms (CMs) are monolithic structures where the displacement is given by the flexibility of their structural members. Thus, the CMs show certain advantages compared with their counterparts, the rigid bodies; since assembling or lubrication are not required. This paper presents a systematic methodology to produce a gripper-type CM, from the design to their manufacture. For designing the CM, the topology optimization method (TOM) is used, where optimal structures are automatically designed by distributing a given amount of material within a specified design domain seeking for maximizing the displacement at a point. Next, a series of operations are applied to the TOM design for reducing the geometry complexity and then manufacturing costs. With the proposed methodology, an optimal and functional CM with innovative geometry is obtained.Los mecanismos flexibles (MFs) son estructuras monolíticas donde su desplazamiento se da gracias a la flexibilidad de sus miembros estructurales. Esto hace que los MFs presenten ciertas ventajas en comparación con sus homólogos, los cuerpos rígidos, tales como no requerir de lubricación ni ensamble. Este trabajo muestra una metodología sistemática para la producción de un MF tipo pinza, desde el diseño conceptual hasta su manufactura. Para el diseño del MF se usa el método de optimización topológica (MOT), el cual permite diseñar estructuras óptimas de forma automática distribuyendo una cantidad de material dada dentro de un dominio de diseño especifico buscando maximizar el desplazamiento en un punto. Al diseño obtenido mediante el MOT se le aplican una serie de operaciones tendientes a disminuir la complejidad de la geometría obtenida con el fin de reducir los costos de manufactura. Con la metodología propuesta se obtiene un MF óptimo, funcional y con geometría innovadora.

Simulación de moldeo por inyección basado en el método de volúmenes finitos (FVM)

One of the main concerns in the mold injection industry is to ensure efficient material processing and procurement of products at reasonable costs that reflect solid economies of scales for large production series. Cooling time is an influential and decisive variable for the efficiency of these series, under a certain temperature condition, it increases along with the thickness of the piece. Therefore, for a certain thickness, a low mold temperature and a high piece extraction temperature have a considerable influence on the reduction of cooling time, which constitutes a large span of the process cycle time: between 80 % and 85%. In this work, the injection molding process is simulated to explore the temperature distribution and material filling process of a mold designed to make ‘ear tags’, which are used for the visual control of cattle. The main goal is to identify the essential variables in the process (time process, injection and packaging pressures, clamping forces and injection velocity), as well as their influence on compression times and temperature distribution. For the above, an experiment design methodology (DOE) is stablished based on the 2k factorial design, based on simulations based on the finite volume method (FVM). This DOE, adapted to the numerical results, reveals as a fundamental result of this work, the study variables that are inherent in the process, in addition to achieving its characterization. The results allowed studying the temperature behavior distribution in the mold, identifying as initial variables to consider in the experimentation: the initial mold temperature and the interactions between the cooling times-packaging and cooling times-initial mold temperature.Una de las principales preocupaciones en la industria de moldeo por inyección es garantizar un procesamiento eficiente de materiales y la adquisición de productos a costos razonables que reflejen sólidas economías de escalas para grandes series de producción. El tiempo de enfriamiento es una variable influyente y decisiva para la eficiencia de estas series, en ciertas condiciones de temperatura, aumenta junto con el espesor de la pieza. Por lo tanto, para cierto espesor, una baja temperatura del molde y una alta temperatura de extracción de la pieza tienen una influencia considerable en la reducción del tiempo de enfriamiento, lo que constituye un gran lapso del tiempo del ciclo de proceso: entre 80% y 85%. En este trabajo, el proceso de moldeo por inyección se simula para explorar la distribución de la temperatura y el proceso de llenado del material de un molde diseñado para hacer "etiquetas de oreja-chapetas", que se utilizan para el control visual del ganado. Como objetivo fundamental se busca identificar las variables esenciales en el proceso (tiempos de cierre y llenado del molde, presiones de inyección y empaquetamiento, fuerzas de sujeción y velocidad de inyección), así como su influencia en los tiempos de enfriamiento y la distribución de temperaturas finales del molde. Para lo anterior se establece una metodología de diseño de experimentos (DOE) basado en el diseño factorial 2k, partiendo de simulaciones basadas en el Método de Volúmenes Finitos (FVM). Este DOE, adaptado a los resultados numéricos, revela como resultado fundamental de este trabajo, las variables de estudio que son inherentes en el proceso, además de lograr su caracterización. Los resultados permitieron estudiar el comportamiento de la distribución de la temperatura en el molde, identificando como variables fundamentales a considerar en la experimentación: la temperatura inicial del molde y las interacciones comprendidas entre tiempo de enfriamiento - empaquetamiento y tiempo de enfriamiento - temperatura inicial del molde

Topology optimization of piezoelectric transducers considering functionally graded material: design, simulation, analysis and fabrication.

Materiais piezelétricos geram deslocamentos ao serem excitados com potencial elétrico, bem como potencial elétrico ao serem submetidos a força ou pressão. Eles são amplamente utilizados em aplicações relacionadas principalmente com a área de Mecânica de Precisão, Mecatrônica e aquisição de imagens por Ultra-Som. Por outro lado, os Materiais com Gradação Funcional (MGF) são materiais avançados compostos, os quais são projetados de forma que sua composição varie gradualmente numa direção espacial. Esses materiais combinam as vantagens de certas características de cada fase constitutiva; por exemplo, alta resistência à temperatura dos materiais cerâmicos com alta resistência mecânica dos metais. Vários trabalhos têm mostrado as vantagens de aplicar o conceito MGF ao projeto de transdutores piezelétricos. Entre essas vantagens podem-se mencionar: (i) atuadores flextensionais ou bilaminares sem interface entre materiais (ex: PZT e Alumínio); (ii) suavização da distribuição de tensões mecânicas; e (iii) aumento da largura de banda e redução das ondas refletidas em transdutores de ultra-som, principalmente. No entanto, na mesma literatura se observa uma carência de métodos computacionais para a sua modelagem e o seu projeto otimizado e sistemático. Baseado nessas idéias, esta tese propõe a formulação e desenvolvimento de modelos analíticos, algoritmos de elementos finitos, e algoritmos de otimização topológica para projetar Transdutores Piezelétricos com Gradação Funcional (TPGF) inovadores. Adicionalmente, amostras de TPGFs são fabricadas mediante Spark Plasma Sintering SPS, sendo estudado o seu comportamento dinâmico e as suas características micro-estruturais. Assim, através de modelagem, análise, simulação, projeto otimizado, fabricação e caracterização explora-se a potencialidade do conceito de MGF em TPGFs; em particular, evidenciam-se as melhoras que os TPGF podem trazer em aplicações de ensaios não-destrutivos e aquisição de imagens médicas por ultra-som, e no aumento da vida útil de transdutores piezelétricos flextensionais.Piezoelectric materials generate displacements when they are excited by electrical potential and electrical potential when they are excited by force or pressure. These materials are widely applied in Precision Mechanics, Mechatronics, and Ultrasonic imaging areas. On the other hand, Functionally Graded Materials (FGM) are advanced materials, whose properties change continuously in a specified direction. These materials combine desirable features of their constituent phases; for instance, high temperature resistance typical of ceramics with mechanical strength of metals. Several works have shown the advantages of applying FGM concept to piezoelectric transducer design. These advantages are; for example: (i) flextensional actuators without interfaces (e.g. PZT and Aluminum); (ii) smoothing mechanical stresses; and (iii) increasing bandwidth and reducing reflected waves in ultrasonic transducers. However, in the literature, a lack of computational methods for modeling and systematic designing of Functionally Graded Piezoelectric Transducers (FGPT) is observed. According to above ideas, this work proposes the formulation and development of analytical models, finite element algorithms, and topology optimization algorithms to design novel Functionally Graded Piezoelectric Transducers (FGPT). In addition, FGPT samples are manufactured by using Spark Plasma Sintering SPS, where it is studied their dynamic behavior and their microstructural characteristics. Hence, by performing analysis, optimal designing, manufacturing and characterization, the FGM concept potential is explored for FGPTs; particularly, FGPTs can bring advantages in ultrasonic non-destructive testing and ultrasonic medical imaging, and increasing life-time of flextensional piezoelectric transducers

Untitled in english

Sistemas microeletromecânicos ou \"MEMS\" em inglês são sistemas mecânicos projetados em escalas micrométricas. Um tipo comum de \"MEMS\" são os \"MEMS\" eletrotermomecânicos, os quais acoplam domínios elétrico, térmico e mecânico para gerar deslocamentos. Nesses \"MEMS\" uma corrente elétrica é convertida em calor pelo efeito de Joule e esse calor gera deformações térmicas, as quais por sua vez causam deformação estrutural. Os \"MEMS\" eletrotermomecânicos são projetados como mecanismos flexíveis; estes mecanismos conseguem sua mobilidade da flexibilidade da sua estrutura ao contrário das estruturas de corpo rígido que obtém sua mobilidade de dobradiças, rolamentos e guias deslizantes. O projeto de \"MEMS\" eletrotermomecânicos não é uma tarefa fácil de realizar usando métodos de tentativa e erro; portanto, neste trabalho o Método de Otimização Topológica (MOT) é aplicado, o qual combina algoritmos de otimização com o Método dos Elementos Finitos para projetar a melhor topologia estrutural, distribuindo o material no interior de um domínio de projeto fixo segundo um critério de custo. Em \"MEMS\" eletrotermomecânicos, este critério de custo consiste de maximizar o deslocamento de saída, com o menor peso, quando um potencial elétrico é aplicado à estrutura. O principal objetivo deste trabalho é projetar \"MEMS\" eletrotermomecânicos utilizando o Método de Otimização topológica. Um modelo de material baseado no tradicional modelo \"SIMP\" é adotado e o algoritmo de otimização é construído usando a Programação Linear Seqüencial (PLS). Uma técnica de filtragem é aplicada para controlar a dependência da malha e o problema das instabilidades de xadrez. Uma forma alternativa é aplicada para controlar o problema das instabilidades de xadrez: o MOT baseado no método da aproximação contínua de distribuição de material - \"CAMD\". Vários exemplos de \"MEMS\" eletrotermomecânicos bidimensionais otimizados são incluídos. ) Além disso, a influência de diversos valores dos parâmetros de otimização na topologia final é discutida.MEMS are MicroElectroMechanical Systems designed in micrometric scale. A very common type of MEMS are the electrothermomechanical MEMS, which couples electrical, thermal and mechanical field to generate displacements. In these MEMS an electrical current is converted to heat by Joule effect and the heat causes thermal strain, which in turn causes structural deformation. Electrothermomechanical MEMS are designed as compliant mechanisms; they attain their mobility from flexibility of their structure as opposed to rigid body structure that attains their mobility from hinges, bearings and sliders. Design of electrothermomechanical MEMS is not an easy task to be accomplished by using trial and error methods; therefore, in this work Topology Optimization Method (TOM) is applied, which combines optimization algorithms with Finite Element Method to design the best structure topology, distributing the material in the interior of a fixed domain according to cost criteria. In electrothermomechanical MEMS, this cost criteria consists of maximizing the output displacement, with the least weight, when an electric potential is applied to the structure. The main goal of this work is to design electrothermomechanical MEMS using the Topology Optimization Method. A material model based on the traditional SIMP model is adopted and the optimization algorithm is constructed based on sequential linear programming (SLP). A filtering technique is applied to control the meshdependency and the checkerboard problem. An alternative way is applied to control the checkerboard problem: TOM based on the method of continuous approximation of material distribution - CAMD. Several examples of optimized two-dimensional electrothermomechanical MEMS are included. In addition, the influence of different values of optimization parameters upon the final topology is discussed

Design of compliant mechanisms considering thermal effect compensation and topology optimization

Compliant mechanisms can achieve a specified motion as a mechanism without relying on the use of joints and pins. They have broad application in precision mechanical devices and Micro-Electro Mechanical Systems (MEMS) but may lose accuracy and produce undesirable displacements when subjected to temperature changes. These undesirable effects can be reduced by using sensors in combination with control techniques and/or by applying special design techniques to reduce such undesirable effects at the design stage, a process generally termed ""design for precision"". This paper describes a design for precision method based on a topology optimization method (TOM) for compliant mechanisms that includes thermal compensation features. The optimization problem emphasizes actuator accuracy and it is formulated to yield optimal compliant mechanism configurations that maximize the desired output displacement when a force is applied, while minimizing undesirable thermal effects. To demonstrate the effectiveness of the method, two-dimensional compliant mechanisms are designed considering thermal compensation, and their performance is compared with compliant mechanisms designs that do not consider thermal compensation. (C) 2010 Elsevier B.V. All rights reserved.FAPESP-Sao Paulo State Foundation Research AgencyFAPESP[2006/57805-7]CNPq-National Council for Scientific and Technological Development[303689/2009-9

Toward Optimal Design of Piezoelectric Transducers Based on Multifunctional and Smoothly Graded Hybrid Material Systems

This work explores the design of piezoelectric transducers based on functional material gradation, here named functionally graded piezoelectric transducer (FGPT). Depending on the applications, FGPTs must achieve several goals, which are essentially related to the transducer resonance frequency, vibration modes, and excitation strength at specific resonance frequencies. Several approaches can be used to achieve these goals; however, this work focuses on finding the optimal material gradation of FGPTs by means of topology optimization. Three objective functions are proposed: (i) to obtain the FGPT optimal material gradation for maximizing specified resonance frequencies; (ii) to design piezoelectric resonators, thus, the optimal material gradation is found for achieving desirable eigenvalues and eigenmodes; and (iii) to find the optimal material distribution of FGPTs, which maximizes specified excitation strength. To track the desirable vibration mode, a mode-tracking method utilizing the `modal assurance criterion` is applied. The continuous change of piezoelectric, dielectric, and elastic properties is achieved by using the graded finite element concept. The optimization algorithm is constructed based on sequential linear programming, and the concept of continuum approximation of material distribution. To illustrate the method, 2D FGPTs are designed for each objective function. In addition, the FGPT performance is compared with the non-FGPT one.FAPESP (Sao Paulo State Foundation Research Agency)[05/01762-5]FAPESP (Sao Paulo State Foundation Research Agency)[2006/57805-7]FAPESP (Sao Paulo State Foundation Research Agency)[2008/5070-0]CNPq - National Council for Research and Development, Brazil[304208/2006-0

Analysis, manufacture and characterization of Ni/Cu functionally graded structures

In this work, an experimental and numerical analysis and characterization of functionally graded structures (FGSs) is developed. Nickel (Ni) and copper (Cu) materials are used as basic materials in the numerical modeling and experimental characterization. For modeling, a MATLAB finite element code is developed, which allows simulation of harmonic and modal analysis considering the graded finite element formulation. For experimental characterization, Ni-Cu FGSs are manufactured by using spark plasma sintering technique. Hardness and Young's modulus are found by using microindentation and ultrasonic measurements, respectively. The effective gradation of Ni/Cu FGS is addressed by means of optical microscopy, energy dispersive spectrometry, scanning electron microscopy and hardness testing. For the purpose of comparing modeling and experimental results, the hardness curve, along the gradation direction, is used for identifying the gradation profile; accordingly, the experimental hardness curve is used for approximating the Young's modulus variation and the graded finite element modeling is used for verification. For the first two resonance frequency values, a difference smaller than 1% between simulated and experimental results is obtained. (C) 2012 Elsevier Ltd. All rights reserved.FAPESP (Sao Paulo State Foundation Research Agency) [05/01762-5]FAPESP (Sao Paulo State Foundation Research Agency)USA National Science Foundation (NSF)USA National Science Foundation (NSF)CNPq (National Council for Research and Development, Brazil)CNPq (National Council for Research and Development, Brazil) [303689/2009-9]FAPESPFAPESP [2011/02387-4

Analysis and Advances in Additive Manufacturing as a New Technology to Make Polymer Injection Molds for World-Class Production Systems

The currently growing demand for metallic and polymeric products has undoubtedly changed the rules of manufacturing, enabling customers to more functionally define their products based on their needs. Nowadays, a new technique for rapid tooling, Additive Manufacturing (AM), can create customized products with more complex geometries and short life cycles (flexibility) in order to keep up with the new variables imposed by the manufacturing environment. In the last two decades, the migration from subtractive manufacturing to AM has materialized such products with reduced costs and cycle times. AM has been recently promoted to develop polymer molds for product manufacturing. This paper reviews the main findings in the literature concerning polymer molds created by AM compared to conventional (metal) molds obtained by subtractive manufacturing. Information about specific topics is scarce or nonexistent, for example, about the characterization of the most commonly injected materials and molds used in this type of technology, their mechanical properties (part and mold), designs for all types of geometries, and costs. These aspects are addressed in this literature review, highlighting the advantages of this alternative manufacturing process, which is considered a desirable technology worldwide