In cold forming operations, tool geometry has a direct influence on the product quality, forming force, load acting on dies and tool life. Finite element method provides a means to analyse these parameters to predict forming defects and die failures. In this study, shrink fitting the components of a bolt forming die is modelled and the finite element results are compared with the analytical solutions and experiments. In order to perform die stress analyses, deformable die models are implemented in the forging simulations. Furthermore, effect of using rigid and deformable dies on the stress distributions in the tools, forming force and product dimensions are examined. Some applications of tool geometry improvements and optimization of prestressing are presented in the case studies. In the second part of the study, the appropriate friction model for the cold forming operation of bolts is investigated. For this purpose, ring compression and forward rod extrusion tests are conducted. Dimensional variations and deformation forces are compared with the finite element simulations performed for different friction models and constants. The results of shrink fit analyses of die prestressing are in good agreement with the elasticity formulations and real applications. In the studied bolt production cases, after improving the die stress distributions by using FE simulations, longer tool lives are achieved. Finally, for more accurate results, Coulomb friction model is determined as an appropiate model for bolt forming analyses.

Forging operations are widely used for manufacturing processes. Forging process is done hot, warm or cold. All three temperature ranges have advantages and disadvantages. The aim of this study is to combine the advantages of hot and cold forging in a flange forming process with cylindirical workpieces in a single step. The process idea is the partial heating of the workpiece at locations where large deformations occur and to keep the parts of the workpiece cold at regions where high precision forming is required. Firstly, the process idea has been investigated virtually by the finite element method supplying the theoretical verification of the feasibility of the novel process. By this analysis also the process limits have been estimated. All analysis are based on an elastoplastic large strain material law with thermomechanical coupling. The experimental part of the study served to realize the new process idea and to verify the process window. In the experimental study two different materials, three different part geometries and different initial conditions such as temperature field, lubrication etc. have been investigated. The specifimens are heated by induction.

Friction is one of the important parameters in metal forming processes since it affects metal flow in the die, forming load, strain distribution, tool and die life, surface quality of the product etc. The range of coefficient of friction in different metal forming applications is not well known and the factors affecting variation are ambiguous. Commercially available FEA packages input the coefficient of friction as constant among the whole process which is not a realistic approach. In this study, utility of user-subroutines is integrated into MSC SuperForm v.2004 and MSC Marc v.2003 FEA packages, to apply a variable coefficient of friction depending on the contact interface conditions. Instead of using comparatively simple friction models such as Coulomb, Shear (constant) models, friction models proposed by Wanheim-Bay and Levanov were used to simulate some cold forging operations. The FEA results are compared with the experimental results available in literature for cylinder upsetting. Results show that, large variation on the coefficient of friction is possible depending on the friction model used, the part geometry and the ratio of contact normal pressure to equivalent yield stress. For the ratio of contact normal pressure to equivalent yield stress values above 4, coefficient of friction values are approximately same for both friction models.

As metals have high formability at elevated temperatures, hot forming is preferred and widely used in manufacturing of complicated geometries. The term hot forming is usually used if the whole workpiece is processed at elevated temperatures. However, for certain products high formability is required only locally. Forming by local heating is proposed to provide ease of manufacturing of local forms on the workpiece. Also, tools can be simplified by this method. In this study, local laser heating procedures are applied to obtain local forms on cylindrical bulk metal products in a single step. Locally heated workpieces are formed between two flat dies. Both solid and hollow products have been investigated experimentally and by finite element modeling. The experimental studies and finite element analyses are done simultaneously in order to obtain optimum local deformation characteristics. Three different materials together with different initial geometries and various local laser-heating procedures are applied to search for the process window. The limits of applicability are determined and examples of application are supplied.

A conformação mecânica está presente em diversos processos industriais e classificam-se em diversas categorias com base em critérios como: o tipo de esforço que provoca a deformação do material, a variação relativa da espessura da peça, o regime de operação de conformação, a temperatura de trabalho, o propósito da deformação. Basicamente, os processos de conformação mecânica podem ser classificados em: conformação de chapas, extrusão, trefilação, laminação e forjamento. O desempenho dos componentes mecânicos pode ser avaliado por uma série de ferramentas matemáticas, porém o conjunto de soluções analíticas nem sempre atendem a solução do problema, o que leva ao uso de métodos numéricos com soluções aproximadas. Com a evolução tecnológica muito tem se utilizado das simulações computacionais visando obter resultados mais rápidos, confiáveis e econômicos. Muitos métodos tem sido implementados para a realização de simulações e em destaque tem-se a modelagem por elementos finitos. O método dos elementos finitos considera a região de solução do problema formada por pequenos elementos conectados entre si, onde a região em estudo é analiticamente modelada ou aproximada por um conjunto de elementos discretos pré-definidos. A metodologia utilizada, consiste nas definições do produto a ser estampado, processo de conformação, e os projetos das ferramentas que serão utilizadas na fabricação do produto, após estas definições, serão modelados no software Inventor os componentes que atuam diretamente na conformação, em seguida serão inseridos no software DEFORM as ferramentas modeladas, e as informações técnicas referentes ao processo e todas as condições que podem influenciar no trabalho de conformação. Após a realização da simulação, é feita a análise das informações obtidas para que seja avaliada a viabilidade do processo, se o processo se mostrar capaz de atingir as especificações desejadas é dado prosseguimento na fabricação do produto, caso contrário serão feitas revisões e correções para que sejam alcançados as especificações, sem que seja necessário a construção de ferramentas. / The mechanical conformation is present in many industrial processes and are classified into several categories based on criteria such as: the type of stress that causes the deformation of the material, the relative variation of the thickness of the workpiece, the scheme forming operation, the temperature work, the purpose of deformation. Basically, the mechanical forming processes can be classified as: sheet metal forming, extrusion, wire drawing, rolling and forging. The performance of mechanical parts can be assessed by a number of mathematical tools, but the joint analytical solutions do not always meet the problem solution, which leads to the use of numerical methods to approximate solutions. With the technological evolution has long been used computational simulations to obtain results faster, reliable and economic. Many methods have been implemented to carry out simulations and has been highlighted by finite element modeling. The finite element method considers the region of solving the problem consists of small elements connected to each other, where the region under study is analytically approximated or modeled by a set of predefined discrete elements. The methodology used is the product settings to be printed, forming processes, and the tools projects that will be used in the manufacture of the product, after these settings, will be modeled in Inventor software components that act directly on the conformation then be entered into the software DEFORM patterned tools, and technical information related to the process, and all the conditions that may influence on the conformation work. Upon completion of the simulation is made analysis of information to be made to evaluate the process of viability, if the process proves capable of achieving the desired specifications are given further in the manufacture of the product, otherwise revisions and corrections will be made that the specifications are achieved without the build tools required.

Une nouvelle approche appelée “Approche Pseudo Inverse” (API) est développée pour la modélisation du procédé de forgeage à froid des pièces axisymétriques. L'API est basée sur la connaissance de la forme de la pièce finale. Certaines configurations intermédiaires « réalistes » ont été introduites dans l'API pour considérer le chemin de déformations. Elles sont créées géométriquement sans traitement de contact et ensuite corrigées par la méthode de surface libre afin de respecter l'équilibre, les conditions aux limites et la condition d'incompressibilité. Un nouvel algorithme direct de plasticité est développé, conduisant à une méthode d'intégration plastique très rapide, précise et robuste même dans le cas de très grands incréments de déformations. Un modèle d'endommagement en déformation, est couplé à la plasticité et implémenté dans l'API. Les validations numériques montrent que l'API donne des résultats très proches des résultats de l'approche incrémentale mais en utilisant beaucoup moins de temps de calcul.L'API est adoptée comme solveur du forgeage pour la conception et l'optimisation des préformes du forgeage multi-passes. La rapidité et la robustesse de l'API rendent la procédure d'optimisation très performante. Une nouvelle technique est développée pour générer automatiquement le contour initial d'un outil de préforme pour la procédure d'optimisation. Les variables de conception sont les positions verticales des points de contrôle des courbes B-spline définissant les formes des outils de préforme. Notre optimisation multi-objectif consiste à minimiser la variation de la déformation plastique équivalente dans la pièce finale et la force du poinçon au cours du forgeage. Un algorithme génétique et un algorithme de recuit simulé sont utilisés pour trouver les points d'optimum de Pareto. Pour réduire le nombre de simulations de forgeage, un méta-modèle de substitution basé sur la méthode de krigeage est adopté pour établir une surface de réponse approximative. Les résultats obtenus par l'API en utilisant les outils de préforme optimaux issues de l'optimisation sont comparés à ceux obtenus par les approches incrémentales classiques pour montrer l'efficacité et les limites de l'API. La procédure d'optimisation combinée avec l'API peut être un outil numérique rapide et performant pour la conception et l'optimisation des outillages de préforme. / A new method called “Pseudo Inverse Approach” (PIA) is developed for the axi-symmetrical cold forging modelling. The PIA is based on the knowledge of the final part shape. Some « realistic » intermediate configurations are introduced in the PIA to consider the deformation path. They are created geometrically without contact treatment, and then corrected by using a free surface method in order to satisfy the equilibrium, the boundary conditions and the metal incompressibility. A new direct algorithm of plasticity is proposed, leading to a very fast, accurate and robust plastic integration method even in the case of very large strain increments. An isotropic damage model in deformation is coupled with the plasticity and implemented in the PIA. Numerical tests have shown that the Pseudo Inverse Approach gives very close results to those obtained by the incremental approach, but using much less calculation time.The PIA is adopted as forging solver for the design and optimization of preform tools in the multi-stage forging process. The rapidity and robustness of the PIA make the optimization procedure very powerful. A new method is developed to automatically generate the initial preform tool shape for the optimization procedure. The design variables are the vertical positions of the control points of B-spline curves describing the preform tool shape. Our multi-objective optimization is to minimize the equivalent plastic strain in the final part and the punch force during the forging process. The Genetic algorithm and Simulated Annealing algorithm are used to find optimal Pareto points. To reduce the number of forging simulations, a surrogate meta-model based on the kriging method is adopted to build an approximate response surface. The results obtained by the PIA using the optimal preform tools issued from the optimization procedure are compared to those obtained by using the classical incremental approaches to show the effectiveness and limitations of the PIA. The optimization procedure combined with the PIA can be a rapid and powerful tool for the design and optimization of the preform tools.