Development of a novel differential velocity sideways extrusion process for forming curved profiles with fine grains and high strength

The aim of this study is to develop a novel process, differential velocity sideways extrusion (DVSE), for forming curved profiles with fine grains and high strength. In this new forming-bending-refining process, billets are used as the work-piece material to directly form curved profiles with certain cross-sections in order to increase the manufacturing efficiency and decrease the bending defects in conventional bending process. The DVSE process has been studied in this thesis by using forming experiments, microstructure characterisation experiments, finite element (FE) modelling and theoretical modelling. A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was designed and manufactured. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Feasibility studies for the DVSE process were carried out through a series of designed experimental programmes on plasticine, in which punch/extrusion velocity ratio, extrusion ratio and die land length were process parameters. Ultimately, trial tests using AA1050 at room temperature and AZ31 at elevated temperatures were conducted. Effects of extrusion velocity ratio, extrusion ratio, die land length, forming temperature and strain rate on profile curvature were studied. The microstructure evolution of the formed curved AA1050 bar by DVSE at room temperature was studied through EBSD. The evolution of grain structure and texture of formed curved AZ31 bars at different DVSE process conditions (temperature and strain rate) was investigated through optical microscopy and EBSD, and the optimum temperature and strain rate condition for obtaining fine equiaxed and homogeneous microstructure was identified. The different grain refinement mechanisms of AA1050 and AZ31 during the DVSE process were revealed. Micro-hardness of formed curved AA1050 and AZ31 bars was examined. Process mechanics of DVSE were modelled using FE modelling and upper bound theorem. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, was identified. A dead zone of roughly triangular shape, which exists on the chamber wall opposite the die exit orifice, was determined. The effective strain of the formed curved profiles was studied to confirm the rise of severe plastic deformation (SPD). The effective strain rate in the intersection regions of the channels was investigated to identify the source of severe plastic deformation. An analytical upper-bound-based model has been developed with the consideration of the determined dead zone. The extrusion force and curvature predicted by the analytical method agreed reasonably well with results from experiments and FE modelling. Discussions were made about the correlations between experimental and modelling approaches and results. The relationships between mechanical properties (yield strength, ultimate tensile strength, and elongation to failure) and microstructures (grain size, micro-texture) of formed curved profiles were correlated. From the experimental and modelling work, it has been demonstrated that the DVSE process proposed in this thesis is an effective way to efficiently form curved aluminium and magnesium profiles with controlled curvature and improved properties.Open Acces

Controlo e execução de estampagem incremental com cinemática paralela

Mestrado em Engenharia MecânicaO projeto SPIF-A é um verdadeiro desa o de engenharia: desenvolver uma má- quina totalmente nova e inovadora para conformação plástica de chapa. Trata-se principalmente de um trabalho de equipa, que abrange varias áreas da engenharia mecânica, desde análise estrutural até automação e controlo, passando pela termodin âmica e cinemática, entre outras. Esta dissertação sendo mais uma peça no puzzle, vai-se focar no seu desenvolvimento, principalmente no estudo da cinemática inversa e directa da plataforma de Stewart, assim como no desenvolvimento do primeiro sistema de controlo de posição. O referido sistema é um controlador de lógica difusa e será implementado através de software num computador de processamento em tempo real. Durante o desenvolvimento destes componentes também foram optimizados e/ou actualizados os sistemas hidráulicos, eléctricos e mecânicos da máquina assim como se implementou e calibrou um sistema de medição de forças de trabalho recorrendo ao uso de células de carga.The SPIF-A project is a true engineering challenge: to develop an entirely new and innovative machine for sheet metal forming. It is mostly a team e ort, covering various engineering subjects from structural analysis to automation and control but also thermodynamics, kinematics, among others. This dissertation being another piece of that puzzle, will focus on machine development, namely on de ning the machine's Stewart platform inverse kinematics, proposing a solution for the forward kinematics and devising its rst position control system. The referred system will be a fuzzy logic controller and will be implemented via software on a real time targeting machine. During this work several components like from its hydraulic, electrical and mechanical systems were updated and a force measuring system, using load cells was installed and calibrated

Improving Strength and Stability in Continuum Robots

Continuum robots, which are bio-inspired ’trunk-like’ robots, are characterized for their inherent compliance and range of motion. One of the key challenges in continuum robotics research is developing robots with sufficient strength and stability without adding additional weight or complexity to the design. The research conducted in this dissertation encompasses design and modeling strategies that address these challenges in strength and stability. This work improves three continuum robot actuation paradigms: (1) tendon-driven continuum robots (TDCR), (2) concentric tube robots (CTR), and (3) concentric push-pull robots (CPPR). The first chapter of contribution covers strategies for improving strength in TDCRs. The payload capacity and torsional stiffness of the robot can be improved by leveraging the geometry of the backbone design and tendon routing, with design choices experimentally validated on a robot prototype. The second chapter covers a new bending actuator, concentric precurved bellows (CPB), that are based upon CTR actuation. The high torsional stiffness of bellows geometry virtually eliminates the torsional compliance instability found in CTRs. Two bellows designs are developed for 3D printing and the mechanical properties of these designs are characterized through experiments on prototypes and in static finite element analysis. A torsionally rigid kinematic model is derived and validated on 3D printed prototypes. The third chapter of contribution covers the development and validation of a mechanics-based CPPR kinematics model. CPPRs are constructed from concentrically nested, asymmetrically patterned tubes that are fixed together at their distal tips. Relative translations between the tubes induces bending shapes from the robot. The model expands the possible design space of CPPRs by enabling the modeling of external loads, non-planar bending shapes, and CPPRs with more than two tubes. The model is validated on prototypes in loaded and unloaded experiments

Soft Robotics for Chemists

Soft robots: A methodology based on embedded pneumatic networks (PneuNets) is described that enables large-amplitude actuations in soft elastomers by pressurizing embedded channels. Examples include a structure that can change its curvature from convex to concave, and devices that act as compliant grippers for handling fragile objects (e.g., a chicken egg).Chemistry and Chemical Biolog

Mastering Uncertainty in Mechanical Engineering

This open access book reports on innovative methods, technologies and strategies for mastering uncertainty in technical systems. Despite the fact that current research on uncertainty is mainly focusing on uncertainty quantification and analysis, this book gives emphasis to innovative ways to master uncertainty in engineering design, production and product usage alike. It gathers authoritative contributions by more than 30 scientists reporting on years of research in the areas of engineering, applied mathematics and law, thus offering a timely, comprehensive and multidisciplinary account of theories and methods for quantifying data, model and structural uncertainty, and of fundamental strategies for mastering uncertainty. It covers key concepts such as robustness, flexibility and resilience in detail. All the described methods, technologies and strategies have been validated with the help of three technical systems, i.e. the Modular Active Spring-Damper System, the Active Air Spring and the 3D Servo Press, which have been in turn developed and tested during more than ten years of cooperative research. Overall, this book offers a timely, practice-oriented reference guide to graduate students, researchers and professionals dealing with uncertainty in the broad field of mechanical engineering

Projecto e construção de uma máquina para estampagem incremental

Mestrado em Engenharia MecânicaSingle Point Incremental Forming is a recent technology that is currently under development. Its applicability is diverse because it allows the attainment of functional parts in sheet metal without great costs. Due to this characteristic, areas such as biomechanics, rapid prototyping and products of customizable features make this process a target of interest. Unfortunately, the means of obtaining parts using single point incremental forming are limited. Usually, CNC machining centers are utilized but due to their cutting-type characteristics, the implementation of the Single Point Incremental Forming is limited and inefficient. Also, the market supply of dedicated machinery requires high investments, thus becoming an unattractive solution. A major obstacle to the application of this technique focuses on the superior time of forming especially when compared to conventional forming techniques. Another disadvantage of this process is the low dimensional accuracy, however, with the development of numerical studies and correction algorithms this problem tends to be minimized. This work aims to complete the project of a single point incremental forming machine that began in previous years. This project has the objective of overcoming the limitations of the current incremental forming machines, but not ignoring the economic factor. Also, this project aims to enlarge the horizons for future research and development of the process, not only improving the machine but also developing and understanding the forming mechanism and the consequent effects of improved material formability.A estampagem incremental é um processo recente que está em desenvolvimento. A sua aplicabilidade é variada pois permite a obtenção de peças funcionais em chapa metálica sem grandes custos associados. Devido a esta característica, áreas como a biomecânica, prototipagem rápida e produtos de características personalizáveis fazem deste processo um alvo de interesse. Infelizmente, os meios de obtenção de peças usando estampagem incremental por ponto único são limitados. Normalmente faz-se uso de centros de maquinagem CNC adaptados, que devido às suas características próprias de corte por arranque de apara, tornam a aplicação da estampagem incremental limitada e ineficiente. Além disso, a oferta de mercado em maquinaria com características dedicadas ao uso de estampagem incremental requerem elevados investimentos, tornando-se assim uma solução pouco atractiva. Um dos principais obstáculos à aplicação desta técnica centra-se no tempo de conformação elevado, principalmente quando comparado com técnicas de estampagem convencionais. Outra desvantagem deste processo é a baixa precisão dimensional, que todavia com o avanço dos estudos numéricos e com o desenvolvimento de algoritmos de correcção tende a ser minimizado. Neste trabalho pretende-se concluir o projecto de uma máquina para realização de estampagem incremental por ponto único que teve início em anos anteriores. Este projecto tem por objectivo a obtenção de uma máquina que ultrapasse as limitações das máquinas actuais, mas não desconsiderando o factor económico. Além disso este projecto visa ampliar os horizontes para futuras pesquisas e desenvolvimento do processo, tanto na melhoria da máquina, mas também no desenvolvimento e na compreensão do mecanismo de deformação existente e aumento associado da formabilidade material

4th DORP 2011 - Dortmunder Kolloquium zum Rohr- und Profilbiegen

1st International Tube and Profile Bending Conference, 4th DORP 2011, Dortmunder Kolloquium zum Rohr- und Profilbiegen, Dortmund, Germany 24th–25th November 201

DESIGN AND DEVELOPMENT OF IN VITRO TOOLS TO ASSESS FIXATION AND MOTION IN THE SPINE

In vitro biomechanical testing of the spine is an important method for evaluating new surgical methods and components, prior to in vivo implementation. This relies upon special laboratory tools and techniques to create spinal motion and loading similar to those experienced in the body. In this thesis, two different studies were performed to evaluate the effects of spinal fixation and motion. The first study compared the fixation of a novel hollow screw and a conventional solid screw in an in vitro sacral model. Screws were tested in seven cadaveric sacra and subjected to stair-cased cyclic flexion- extension loading to simulate the clinical loading scenario. The hollow screw was less resistant to loosening compared to the solid screw in this model. In the second part of this thesis, a spinal loading simulator was developed as a modification to an existing Instron® materials testing machine to produce motion in a multi-segment spine using applied pure bending moments (i.e. flexibility protocol). A custom-designed 2D optical tracking system was used to record the planar motion achieved. An experimental validation study was performed using the developed apparatus, and showed the device was capable of independently producing repeatable and reproducible spine motions (i.e. flexion-extension, lateral bending, and axial rotation) in a single cadaveric specimen. Future work will focus on the continued development of the simulator for use in the assessment of spinal orthopaedic interventions

Impulse-Based Manufacturing Technologies

In impulse-based manufacturing technologies, the energy required to form, join or cut components acts on the workpiece in a very short time and suddenly accelerates workpiece areas to very high velocities. The correspondingly high strain rates, together with inertia effects, affect the behavior of many materials, resulting in technological benefits such as improved formability, reduced localizing and springback, extended possibilities to produce high-quality multi material joints and burr-free cutting. This Special Issue of JMMP presents the current research findings, which focus on exploiting the full potential of these processes by providing a deeper understanding of the technology and the material behavior and detailed knowledge about the sophisticated process and equipment design. The range of processes that are considered covers electromagnetic forming, electrohydraulic forming, adiabatic cutting, forming by vaporizing foil actuators and other impulse-based manufacturing technologies. Papers show significant improvements in the aforementioned processes with regard to: Processes analysis; Measurement technique; Technology development; Materials and modelling; Tools and equipment; Industrial implementation

Design of a Test Rig and its Testing Methods for Rotation and Expansion Performing Assemblies in Parabolic Trough Collector Power Plants

The present master’s thesis deals with the design of a new test rig for the investigation of durability and failure mechanisms of flexible pipe connections – so called Rotation and Expansion Performing Assemblies (REPAs) –, which are utilized in Parabolic Trough Collector power plants. Said assemblies compensate for the motion of the absorber tubes relative to the fixed piping of the header connection. The work focusses on the test rig’s design in view of a realistic simulation of all loads a REPA is exposed to in commercial applications. To achieve this, all possible requirements of the components, which are supposed to endure a lifetime of up to 30 years in power plants, are depicted. A literature research is carried out in order to investigate and evaluate existing test rigs for REPAs or their single components. By means of the findings, a specification sheet is derived. The test rig is composed of two main assemblies. On the one hand, a Kinematics Unit is used to reproduce the cyclic rotational and translational motions of a Parabolic Trough Collector. On the other hand, an HTF cycle (Heat Transfer Fluid cycle) conduces to set up pressure, temperature and flow rate circulating through the test specimens. The main part of the thesis contributes to the integration of the externally designed Kinematics Unit into the HTF cycle – taking into consideration realistic operation conditions and a complete and precise measurement of all parameters. Special emphasis is put on an accurate acquisition of the mechanical loads the test objects have to cope with. As a result of this work, a test rig is erected enabling realistic endurance tests of two serially connected REPAs in less than three months. The hydraulic properties are adjustable in terms of mass flow (6−60 m3/h), pressure (up to 40 bars) and temperature (up to 450 °C). The investigations can be tailored to customized applications of the REPA concept (Ball Joint Assemblies or Rotary Flex Hose Assemblies) and the collector geometry (e.g. focal length)