O presente trabalho tem como objetivo conhecer o comportamento do aço inoxidável austenítico AISI 304L para o processo de Estampagem Incremental de Chapas (ISF - Incremental Sheet Forming), baseado nos parâmetros: raio da ferramenta RT, ângulo de parede a e passo vertical dz. Os experimentos baseiam-se na variante da Estampagem Incremental denominada Estampagem Incremental com Ponto Simples (SPIF - Single Point Incremental Forming). Foram realizados 29 ensaios, em três ferramentas com raios de 5, 8 e 10 mm. Basicamente, a estrutura empregada foi um dispositivo para fixação da chapa, um centro de usinagem vertical e um software de CAD/CAM. O melhor acabamento da superfície conformada medido através da média da rugosidade Rz foi alcançado com ferramentas de raio de 10 mm. Após a conformação, os corpos de prova apresentaram um significativo encruamento de seus grãos, o que conduziu parte da microestrutura originalmente austenítica a uma transformação martensítica induzida por deformação (efeito TRIP). Pode-se constatar também, que existe uma tendência do aumento do ângulo de parede aumentar a microdureza da região encruada. Os ensaios de Estampagem Incremental nesta pesquisa mostram que os gráficos das deformações exibem a tendência de que o modo como ocorrem as deformações, aproximam-se muito da deformação plana (Q2 0). / The objective of this work is to study the behavior of austenitic stainless steel AISI 304L during the ISF process (Incremental Sheet Forming). The study was based on the following parameters: tool radius RT, wall angle and vertical depth dz. The tests were based on a variation of the ISF process, called SPIF (Single Point Incremental Forming). A total of 29 tests were performed with 5, 8 and 10 mm of tool radius. Basically, the structure used was a rig for attachment of the sheet, a Vertical Machining Center and a CAD/CAM software. The best surface finish formed, measured by parameter RZ, was obtained with 10 mm of tool radius. After the forming, the specimens presented a significant mechanical hardening of the grains, which induced part of the microstructure originally austenitic to a martensitic transformation induced by deformation (TRIP effect). It can also be verified that there is a tendency that the increase of the wall angle increases the micro hardness of the mechanical hardened area. The graphs of strains show a trend: the deformation mode is very close to plane strain conditions (Q2 0).

Este trabalho busca alternativas para fabricação de coletores solares planos aplicando técnicas inovadoras em conformação de chapas metálicas. O objetivo é desenvolver um processo de fabricação flexível para placa absorvedora, empregando a técnica da Estampagem Incremental. Esta técnica utiliza uma matriz de suporte de PU, um prensa-chapas e um pequeno punção em conjunto com um centro de usinagem CNC. A Ferramenta utilizada consiste um punção de ponta esférica de fácil fabricação que "desenha" o canal de passagem da água diretamente na chapa, promovendo uma deformação pontual e progressiva. Para compor o canal utilizou-se a técnica de solda por atrito (Friction Stir Welding) com uma ferramenta simples que aproveita o mesmo ferramental da estampagem incremental em um “set-up” rápido da CNC. Foram utilizadas chapas de alumínio de 1mm de espessura. O novo coletor apresenta uma eficiência aprimorada em comparação aos fabricados pelo método tradicional, com uma geometria que favoreça a área de contato com a água. Este processo permite uma formidável flexibilização, viabilizando a produção de pequenos lotes e tornando possível produzir uma enorme variedade de produtos e componentes de geometrias complexas a partir de um ferramental simples e tempos de “set-up” reduzidos. / This work searches alternatives for solar energy collectors manufacture, applying new technologies of sheet metal forming. The objective is to develop a flexible fabrication process for the absorber sheet, using Incremental Sheet Forming. It consists in a PU support die, a blank holder and a small tool, applied in a CNC machine Center. The tool consists in a spherical edge punch of easy fabrication that “draws” the water channel directly into the sheet, promoting a punctual and progressive deformation. To compose the channel, it was used a second sheet jointed by Friction Stir Welding technique, with a simple tool that uses the same tooling of the Incremental Forming in a quick setup of the CNC. Aluminum sheets of 1mm tick were used. It is expected that this new collector panel should improve the thermal efficiency when compared to the traditionally fabricated, and with a geometry that benefits the contact area with the water. This process allows a formidable flexibilization, making the low volume production feasible, allowing the production of a great variety of products and components with complex geometries from simple tooling and reduced setup times.

V současné době se zvyšuje potřeba rozvoje agilních výrobních postupů, které lze snadno přizpůsobit neustálému zavádění nových produktů na trh. Jednobodové inkrementální tváření je nový, inovativní a proveditelný tvářecí proces s jednoduchým uspořádáním. Proces se provádí při pokojové teplotě (tváření za studena) a vyžaduje CNC stroj, nástroj s kulovou hlavou a jednoduché příslušenství pro uchycení obrobku plechu. V samotném procesu jde o přírůstkové formování, řízené CNC programem. Plastická deformace je lokalizována pod formovacím nástrojem takže plech je tvářen souhrnem pohybů lokální plastické zóny. Tento proces je zdlouhavý a proto se hodí pouze pro prototypovou výrobu nebo pro malé výrobní dávky. Na druhé straně umožňuje vyšší tvářitelnost ve srovnání s konvenčními procesy tváření, umožňuje použití levných nástrojů a také je charakterizován krátkou dobou od návrhu po výrobu produktu. Tato práce je výsledkem mezinárodní spolupráce Danmarks Tekniske Universitet v Lyngby a Instituto Superior Técnico v Lisabonu. Práce začíná krátkým hodnocením dílčích tvářecích procesů, pokračuje představováním jednobodového inkrementálního tváření a identifikací jeho praktických aplikací. Teoretická část obsahuje přehled nového rámce pro jednobodové inkrementální tváření, který je vytvořen na základě analýzy styku třecích sil. Praktická část projektu poskytuje úplný popis experimentálních technik použitých pro charakterizaci materiálů a stanovení limitů tvářitelnosti, dále se analyzuje vliv různých vstupních parametrů procesu (poloměru nástroje, tepelné zpracování materiálu obrobku, druh maziva,...). Tato část také obsahuje přehled experimentálního uspořádaní procesu jednobodového inkrementálního tváření i krátký popis CAD / CAM vývoje tří testovacích modelů. Poté jsou popsány v samostatné kapitole výsledky pozorování a analýzy hlavních parametrů procesů, které ovlivňují tvařitelnostní limity v jednobodovém inkrementálním tváření v souvislosti s aplikovaným teoretickým rámcem. Výsledky experimentů z časti objasňují probíhající mezinárodní diskusi kolem tvářitelnosti mechanismu jednobodového inkrementálního tváření vzhledem k tradičním metodám tváření. Jako logické pokračování prováděných experimentů, byla práce rozšířena na více-stupňové jednobodové inkrementální tváření, které umožňuje tváření součástek (kalíšku) se svislými stěnami ve více krocích. Za účelem objasnění procesů spojených s tímhle procesem byly navrženy a ve čtyřech krocích vyrobeny dva experimentální modely. Hlavním přínosem této práce k více-stupňovému jednobodovému inkrementálnímu tváření byla úspěšná výroba součásti s nekruhovým průřezem a kolmými stěnami. S cílem aplikovat celkové znalosti získáných v předchozích částí práce byla vyrobena prototypová součást. Popis designu a vývoje prototypu je součástí práce. V neposlední řadě jsou celkové závěry uvedené v poslední kapitole. Předpokládá se, že tato práce přizpívá k lepšímu pochopení mechanismu jednobodového inkrementálního tváření.

Incremental sheet forming (ISF) is a novel metal shaping technology that is economically viable for low-volume manufacturing, customisation and rapid-prototyping. It uses a small tool that is controlled by a computer-numerically controlled sequence and the path taken by this tool over the sheet defines the product geometry. Little is currently known about how to design the tool-path to minimise geometric errors in the formed part. The work here addresses this problem by developing a model based tool-path optimisation scheme for ISF. The key issue is how to generate an efficient model for ISF to use within a path optimisation routine, since current simulation methods are too slow. A proportion of this thesis is dedicated to evaluating the applicability of the rigid plastic assumption for this purpose. Three numerical models have been produced: one based on small strain deformation, one based on limit analysis theory and another that approximates the sheet to a network of rods. All three models are formulated and solved as second-order cone programs (SOCP) and the limit analysis based model is the first demonstration of an upper-bound shell finite element (FE) problem solved as an SOCP. The models are significantly faster than commercially available FE software and simulations are compared with experimental and numerical data, from which it is shown the rigid plastic assumption is suitable for modelling deformation in ISF. The numerical models are still too slow for the path optimisation scheme, so a novel linearised model based on the concept of spatial impulse responses is also formulated and used in an optimal control based tool-path optimisation scheme for producing axisymmetric products with ISF. Off-line and on-line versions of the scheme are implemented on an ISF machine and it is shown that geometric errors are significantly reduced when using the proposed method. This work provides a new structured framework for tool-path design in ISF and it is also a novel use of feedback to compensate for geometrical errors in ISF.

O presente trabalho investiga o comportamento da chapa de latão C268, com 0,50 mm de espessura, quando exposto ao processo de Estampagem Incremental de Chapas de Metal (Incremental Sheet Metal Forming -ISMF). Especificamente para a pesquisa, foram utilizadas as modalidades de Estampagem Incremental com Ponto Simples (Single Point Incremental Forming- SPIF) e Estampagem Incremental de Múltiplos Passes (Multi Pass Single Point Incremental Forming- MSPIF). Os experimentos foram baseados em uma geometria de tronco de pirâmide de base quadrada com 100 mm de lado e 45 mm de profundidade. Para as estratégias de estampagem foi atribuído, a estampagem helicoidal. Como resultado principal, foi verificado o ângulo de parede máximo atingido por cada processo de estampagem incremental. Adicionalmente, ensaios de tração, análise de deformações e de rugosidade da chapa de latão foram realizados. Todos os seus resultados estão detalhados na investigação. Para os parâmetros adotados nestes experimentos, o ângulo de parede obtido por SPIF foi maior do que pelo estudo proposto por MSPIF. / The present study investigates the performance of the brass plate C-268 with 0.50 mm thickness, when exposed to Incremental Sheet Metal Forming (ISMF). Specifically for research, it was used the modalities Single Point Incremental Forming (SPIF) and Multi Pass Single Point Incremental Forming (MSPIF). The experiments were based on a truncated pyramid geometry with square base 100 mm side and 45 mm depth. For forming strategies has been assigned, the helical forming. As the main outcome, it was found the maximum wall angle achieved by each process of incremental printing. In addition, tensile tests, analysis of deformation and roughness of the brass sheet were performed. All results are detailed in the investigation. For the parameters used in these experiments, the wall angle obtained by SPIF is greater than the study proposed by MSPIF.

O presente trabalho investiga o comportamento da chapa de latão C268, com 0,50 mm de espessura, quando exposto ao processo de Estampagem Incremental de Chapas de Metal (Incremental Sheet Metal Forming -ISMF). Especificamente para a pesquisa, foram utilizadas as modalidades de Estampagem Incremental com Ponto Simples (Single Point Incremental Forming- SPIF) e Estampagem Incremental de Múltiplos Passes (Multi Pass Single Point Incremental Forming- MSPIF). Os experimentos foram baseados em uma geometria de tronco de pirâmide de base quadrada com 100 mm de lado e 45 mm de profundidade. Para as estratégias de estampagem foi atribuído, a estampagem helicoidal. Como resultado principal, foi verificado o ângulo de parede máximo atingido por cada processo de estampagem incremental. Adicionalmente, ensaios de tração, análise de deformações e de rugosidade da chapa de latão foram realizados. Todos os seus resultados estão detalhados na investigação. Para os parâmetros adotados nestes experimentos, o ângulo de parede obtido por SPIF foi maior do que pelo estudo proposto por MSPIF. / The present study investigates the performance of the brass plate C-268 with 0.50 mm thickness, when exposed to Incremental Sheet Metal Forming (ISMF). Specifically for research, it was used the modalities Single Point Incremental Forming (SPIF) and Multi Pass Single Point Incremental Forming (MSPIF). The experiments were based on a truncated pyramid geometry with square base 100 mm side and 45 mm depth. For forming strategies has been assigned, the helical forming. As the main outcome, it was found the maximum wall angle achieved by each process of incremental printing. In addition, tensile tests, analysis of deformation and roughness of the brass sheet were performed. All results are detailed in the investigation. For the parameters used in these experiments, the wall angle obtained by SPIF is greater than the study proposed by MSPIF.

O presente trabalho investiga o comportamento da chapa de latão C268, com 0,50 mm de espessura, quando exposto ao processo de Estampagem Incremental de Chapas de Metal (Incremental Sheet Metal Forming -ISMF). Especificamente para a pesquisa, foram utilizadas as modalidades de Estampagem Incremental com Ponto Simples (Single Point Incremental Forming- SPIF) e Estampagem Incremental de Múltiplos Passes (Multi Pass Single Point Incremental Forming- MSPIF). Os experimentos foram baseados em uma geometria de tronco de pirâmide de base quadrada com 100 mm de lado e 45 mm de profundidade. Para as estratégias de estampagem foi atribuído, a estampagem helicoidal. Como resultado principal, foi verificado o ângulo de parede máximo atingido por cada processo de estampagem incremental. Adicionalmente, ensaios de tração, análise de deformações e de rugosidade da chapa de latão foram realizados. Todos os seus resultados estão detalhados na investigação. Para os parâmetros adotados nestes experimentos, o ângulo de parede obtido por SPIF foi maior do que pelo estudo proposto por MSPIF. / The present study investigates the performance of the brass plate C-268 with 0.50 mm thickness, when exposed to Incremental Sheet Metal Forming (ISMF). Specifically for research, it was used the modalities Single Point Incremental Forming (SPIF) and Multi Pass Single Point Incremental Forming (MSPIF). The experiments were based on a truncated pyramid geometry with square base 100 mm side and 45 mm depth. For forming strategies has been assigned, the helical forming. As the main outcome, it was found the maximum wall angle achieved by each process of incremental printing. In addition, tensile tests, analysis of deformation and roughness of the brass sheet were performed. All results are detailed in the investigation. For the parameters used in these experiments, the wall angle obtained by SPIF is greater than the study proposed by MSPIF.

Um die wirtschaftliche Relevanz und die Flexibilität des Formdrückens zu erweitern, ist ein Maschinen- und Steuerungskonzept entwickelt worden, dass auch die Herstellung von nichtrotationssymmetrischen Bauteilen erlaubt. Neben experimentellen Untersuchungen zur Verfahrensentwicklung wurde ebenfalls eine numerische Verfahrensoptimierung des neu entwickelten Prozesses „Unrunddrücken“ durchgeführt, um unrunde Bauteile falten- und rissfrei sowie mit geringer Blechdickenreduktion herstellen zu können. In ersten experimentellen Untersuchungen wurden die technologischen Haupteinflussgrößen auf die Versagensformen Falten- und Rissbildung sowie die Blechausdünung ermittelt. Aufbauend auf diesen Ergebnissen ist ein kalibriertes Simulationsmodell erarbeitet worden, mit dem es möglich ist, das Prozessverständnis zu erhöhen und somit die Versagensfälle ganzheitlich über den Prozess zu betrachten. Die daraus gewonnenen Erkenntnisse wurden genutzt, um Optimierungsmaßnahmen für das Unrunddrücken abzuleiten. Es konnte experimentell nachgewiesen werden, dass sowohl die Falten- und Rissbildung als auch die Blechdickenreduktion durch die Optimierungsmaßnahmen deutlich reduziert werden können. Das in der vorliegenden Arbeit entwickelte Verfahren des Unrunddrückens stellt einen effizienten, kostengünstigen und vor allem flexiblen Fertigungsprozess für die Herstellung von nichtrotationssymmetrischen Bauteilen mit nahezu konstantem Blechdickenverlauf dar.

1. Scope of the Study<BR> ---------------------<BR> In the modern engineering world, technological advancements drive the product design process. Increasingly powerful CAD programs make more complex product designs possible, which in turn boost the demand for more complex prototypes. At the same time, fast-moving competitive markets require frequent design changes, shorter lead times, and tighter budgets. In short, prototyping must be faster, better, and less expensive.<BR> <BR> Within this context, rapid prototyping in sheet metal is highly desirable because the manufacturing of functional prototypes speeds up the time to market. While the market is well developed when it comes to rapid prototyping for plastic parts, the options for prototyping geometrically complicated sheet metal components are more limited and extremely expensive, because all the methods available require expensive tooling, machinery or manual labor.<BR> <BR> Unlike many other sheet metal forming processes, incremental forming does not require any dedicated dies or punches to form a complex shape. Instead, the process uses a standard smooth-end tool, the diameter of which is far smaller than the part being made, mounted on a three-axis CNC milling machine.<BR> <BR> The sheet metal blank is clamped around its edges using a blank-holder. During the forming process, the tool moves along a succession of contours, which follow the final geometry of the part, and deforms the sheet into its desired shape incrementally.<BR> <BR> 2. Context of the Research<BR> --------------------------<BR> The work presented in this thesis was started in October 2003 in the framework of the SeMPeR project (Sheet Metal oriented Prototyping and Rapid manufacturing). This was a four-year-long project, whose purpose was to develop a research platform that would support an in-depth analysis of the incremental forming and laser forming processes. This platform supported experimental, numerical, and analytical research activities, the interaction between which was expected to lead to the design of new and improved process variants and the identification of effective process planning and control strategies.<BR> <BR> Four research partners from three different universities were involved in the project, covering the various academic disciplines required. As project leader, the PMA Department of the Catholic University of Leuven (KUL) provided extensive background knowledge in numerically controlled sheet metal forming processes, as well as long-term experience of experimental hardware development and process planning. This department was in charge of the experimental study of the processes. The MTM Department from the same university studied the processes in detail using accurate finite element models. The MEMC Department of the Free University of Brussels (VUB) provided expertise in in-process strain and displacement measurement, and material characterization by means of inverse method techniques. Finally, the ArGEnCo Department of the University of Liège (ULg), to which the present author is affiliated, undertook the task of developing a finite element code adapted to the incremental forming process.<BR> <BR> Because of its promising outcome, the project held wide industrial interest: several companies assisted in ensuring the ultimate industrial relevance of the research and provided logistical support in terms of hardware, materials, and specific data.<BR> <BR> 3. Objective of the Thesis<BR> --------------------------<BR> Although the SeMPeR project aimed at studying two rapid prototyping processes, the present work focused only on one of those: incremental forming. The goal of the team at the University of Liège was to adapt a department-made finite element code, Lagamine, to the incremental forming process. In particular, the computation time had to be reduced as much as possible while maintaining a sufficient level of accuracy.<BR> <BR> 4. Outline of the Thesis<BR> ------------------------<BR> The body of the text is divided into three parts.<BR> <BR> The first part contains two chapters. The first of these provides a literature review in the field of incremental forming. More specifically, it introduces the process, presents an overview of its practical implementation and experimental setup requirements, and shows its benefits and limitations. Then, the chapter focuses on the latest developments in terms of finite element modeling and analytical computations.<BR> <BR> The second chapter presents the numerical tools used throughout this research. This consists mainly of the finite element code, the elements, and the constitutive laws. Then, this chapter gives an overview of the experimental setup and measuring devices used during the experimental tests performed in Leuven. The second part focuses on dynamic explicit simulations of incremental forming and contains four chapters. The first justifies the use of a dynamic explicit strategy. The second presents the new features added to the finite element code in order to be able to model incremental forming with such a strategy. The third explains the computation of the mass matrix of the shell element used throughout this part of the thesis and justifies this computation. Finally, the fourth chapter analyzes the overall performance of the dynamic explicit simulations both in terms of accuracy and computation time.<BR> <BR> The third part of this thesis contains an in-depth analysis of the incremental forming process using more classic implicit finite element simulations. This analysis is performed in two steps. In a first chapter, the influence of using a partial mesh for the simulations is evaluated in terms of accuracy and computation time. Then, in a second and final chapter, a detailed analysis of the deformation mechanism occurring during this forming process is carried out.<BR> <BR> Finally, this thesis ends with the major conclusions drawn from the research and perspectives on possible means of further improving the simulation tool.<BR> <BR> 5. Original Contributions<BR> -------------------------<BR> Through this research, several major contributions were achieved.<BR> <BR> First, a comprehensive literature review of the incremental forming process was carried out. In particular, the review focused on original articles concerning the limitations of the process and possible ways of bypassing them; on the most recent explanations for the increased formability observed during the process; and on the state of the art in finite element simulations of incremental forming. Understanding the concepts and difficulties inherent in these publications was made possible particularly by the SeMPeR project thanks to the discussions held and the monthly follow-ups on research performed by its members.<BR> <BR> Secondly, Lagamine's shell element was corrected and its mass matrix modified to enable its use with an explicit strategy. Following this, a new approach for modeling the contact between an element and the forming tool during simulations in a dynamic explicit strategy was developed and thoroughly tested. A detailed comparison of the influence of various finite element parameters on the simulations' results was performed, in particular regarding the choice between using the implicit and explicit strategies and the use of mass scaling to reduce the computation time.<BR> <BR> In addition, many simulations were validated thanks to experimental results.<BR> <BR> Moreover, the computation time required for simulations of the forming of parts with rotational symmetry was radically reduced by using a partial model with a new type of boundary conditions.<BR> <BR> Finally, the material behavior occurring during incremental forming was analyzed.

Drückwalzen als inkrementelles Umformverfahren ist aufgrund seiner Verfahrenscharakteristik mit sehr hohen Rechenzeiten bei der Finite-Elemente-Methode (FEM) verbunden. Die Modelle ModIni und FloSim sind zwei analytisch-elementare Ansätze, um dieser Prämisse entgegenzuwirken. Das für ModIni entwickelte Geometriemodell wird in der vorliegenden Arbeit weiterentwickelt, so dass eine werkstoffunabhängige Berechnung der Staugeometrie ermöglicht wird und ein deutlich größeres Anwendungsspektrum der Methode bereitsteht. Die Simulationsmethode FloSim basiert auf dem oberen Schrankenverfahren und ermöglicht somit eine Berechnung von Zylinderdrückwalzprozessen innerhalb weniger Minuten. Für die Optimierung der Methode FloSim wurden in der vorliegenden Arbeit die analytischen Grundlagen für die Berechnung der Bauteillänge sowie der Umformzonentemperatur während des Prozesses erarbeitet. Weiterhin wurde auf Basis von numerisch realisierten Parameteranalysen ein Ansatz für die analytische Berechnung des Vergleichsumformgrades von Drückwalzprozessen entwickelt. Diese drei Ansätze, zu Bauteillänge, Temperatur und Umformgrad wurden in die Simulationssoftware FloSim integriert und führen zu einer deutlichen Genauigkeitssteigerung der Methode. / Flow Forming as incremental forming process is connected with extreme long computation times for Finite-Element-Analyses. ModIni and FloSim are two analytical/elementary models to antagonize this situation. The geometry model, which was developed for ModIni, is improved within the presented work. The improvement enables the material independent computation of the pile-up geometry and permits a wider application scope of ModIni. The simulation method FloSim is based on the upper bound method, which enables the computation of cylindrical Flow Forming processes within minutes. For the optimization of the method FloSim, the basics for the analytical computation of the workpiece length during the process and the computation of the forming zone temperature were developed within this work. Fur-thermore, an analytical approach for the computation of the equivalent plastic strain of cylindrical Flow Forming processes was developed based on numerical parameter analyses. This tree approaches for computing the workpiece length, the temperature and the equivalent plastic strain were integrated in FloSim and lead to an increased accuracy.