Concebido há milhares de anos, o forjamento passa por melhorias contínuas, mantendo-se como um processo de fabricação moderno, capaz de agregar características importantes a produtos forjados que são utilizados em inúmeras aplicações. Na indústria automobilística, responsável pelo consumo de cerca de 60% de todos os produtos forjados, o forjamento mostrou-se como um processo de conformação plástica eficaz no atendimento das especificações de resistência mecânica e nos quesitos de produtividade. Esta demanda por produtos forjados estimulou a busca por processos mais robustos, nos quais as ferramentas de forjamento possuem papel fundamental para possibilitar a produção de lotes maiores sem paradas de máquina devido a falhas. Cerca de 70% das falhas estão relacionadas ao desgaste das ferramentas. Este trabalho buscou identificar no ambiente industrial, os modos de desgaste responsáveis pela degradação da superfície de contato de um punção, fabricado em aço H-10. Um conjunto de punções foi utilizado no forjamento a quente em prensa mecânica excêntrica horizontal e automática de múltiplos estágios, que utiliza água na refrigeração das ferramentas, durante a fabricação de porcas de roda, em aço SAE 1045. Os resultados obtidos basearam-se: (i) nas análises da superfície e da seção transversal de seis punções em microscópio eletrônico de varredura, (ii) na análise da nanodureza e (iii) na variação dimensional e da massa dos punções. Os resultados apontaram para o desgaste da superfície dos punções logo nas primeiras peças forjadas devido à transferência de óxidos do blank para a superfície da ferramenta. Nesta camada transferida para a superfície dos punções, foram encontrados danos causados pelo desgaste abrasivo e pela fadiga térmica. / Since the initial development, thousands of years ago, forging has faced continuous improvements, remaining as a modern manufacturing process, capable of adding important characteristics to forged products that are used in numerous applications. In the automotive industry, responsible for the consumption of approximately 60% of all forged products, the forging has proved to be an effective metal forming process in terms of mechanical strength specifications and productivity requirements. This demand for forged parts has stimulated the search for more robust processes in which the forging tool has a fundamental role to enable the production of larger batches without downtime due to failures. Approximately 70% of these failures are related to tool wear. This work aimed identifying, in an industrial environmental, the wear modes responsible for the degradation of the contact surface of a punch, made of H-10 steel. A series of punches was used for hot forging in a horizontal and automatic multi-stage eccentric mechanical press which uses water for tool cooling, during the manufacture of wheel nuts, made of SAE 1045 steel. Results were based: (i) on the analysis of the surface and cross section of six punches in a scanning electronic microscope, (ii) on nanohardness analyses and (iii) as well as on mass and dimensional variations. Results pointed to the punch wear in the first forged pieces, due to oxides transferring from blank to the punch surface. On this transferred layer to punch surface, have also found damage caused by abrasive wear and thermal fatigue.

Este trabalho tem como objetivo o estudo dos coeficientes de atrito obtidos através do ensaio do anel, que é um dos métodos clássicos para verificação e a caracterização do atrito, comparado com a extrusão por duplo copo, DCE (Double Cup Extrusion). Foram feitos ensaios utilizando como material para confecção dos corpos de prova o alumínio AA6351 e variando três situações de lubrificação: teflon, grafite e ensaios sem lubrificação. Para o DCE foi desenvolvido o projeto e fabricação do ferramental, permitindo variar punções de duas dimensões diferentes. Os resultados obtidos nos experimentos com cada uma das técnicas foram comparados e apresentados, traçando-se um paralelo do atrito verificado, bem como o comportamento do material em relação às ferramentas utilizadas nos experimentos e as variações de lubrificação. / This work aims to study the friction coefficients obtained by the ring test, which is one of the classic methods for verification and characterization of friction, compared with DCE (Double Cup Extrusion). The tests were made using as material for preparation of specimens, the aluminum AA6351 and varying three situations lubrication, Teflon, graphite and tests without lubrication. For DCE was developed the design and manufacture of tooling, allowing vary punctures in two differ dimensions. The results obtained in the experiments with each of the techniques have been compared and shown by drawing a parallel scanned the friction and the material behavior in relation to the tools used in the experiments and lubrication changes.

L’Inconel 718 est un superalliage base nickel, élaboré dans les années 60, utilisé dans la fabrication de pièces pour les parties chaudes des moteurs d’avion. Il acquiert ses propriétés mécaniques et sa microstructure finale au cours du procédé de mise en forme appelé forgeage à chaud. La maîtrise de ce procédé nécessite de comprendre l’interaction entre les phénomènes d’écrouissage et de recristallisation dynamique tout en intégrant l’influence de diverses conditions thermomécaniques. Cette étude s’est focalisée, expérimentalement, sur les phénomènes liés au forgeage à chaud en mise en forme unipasses et multipasses super-δ-solvus (1050 °C). Afin de les caractériser, des essais de compression ont été réalisés à l’échelle de pions. Des trempes à l’hélium, après déformation, ont permis de figer les microstructures dans le but de comprendre leur évolution en fonction des paramètres thermomécaniques (ε, et T). Des observations ont ensuite été réalisées expérimentalement : microscopie optique et à balayage, EBSD et diffraction des neutrons. Une attention particulière a été portée sur l’évolution de la phase δ, influençant indirectement les propriétés mécaniques de l’alliage, au cours de traitements thermiques puis thermomécaniques. La quantification ainsi que la détermination des cinétiques d’évolution statiques et dynamiques de cette phase a permis de mieux comprendre son influence au cours du forgeage sub-δ-solvus (980 °C). Un chaînage séquentiel a été développé entre deux modèles, l’un de plasticité cristalline implémenté dans un code éléments finis (CPFEM) et l’autre de recristallisation, implémenté dans un code automates cellulaires. Ce chaînage séquentiel permet de décrire les évolutions de champs mécaniques et de microstructures au cours du forgeage à chaud et a été validé par une comparaison avec les résultats expérimentaux. MOTS CLÉS : forgeage à chaud, Inconel 718, recristallisation dynamique, mise en forme multipasses, phase δ, plasticité cristalline (CPFEM), automates cellulaires, chaînage séquentiel, agrégats polycristallins 3D. / Developed in the 60’s, the nickel-base superalloy, Inconel 718, is widely used for hot parts of aircraft engines. The hot forging process confers to the alloy its final microstructure and its mechanical properties. The control of the process requires a deep knowledge of the interactions between the hardening phenomena and the dynamic recrystallization for the various thermomechanical conditions which are used. The present study mainly focuses on the experimental characterization of the phenomena linked to hot forging in the super-δ-solvus domain (1050 °C), as well for a single pass process as for a multipass one. Hot compression tests are used to simulate forging. After deformation, samples are helium quenched in order to freeze the microstructure that allows understanding its evolution as a function of the thermomechanical parameters (ε, and T). Microstructure analyses have then been performed using optical and scanning microscopy, EBSD, and neutron diffraction. A specific attention is paid on the study of the -phase evolution as it has a direct influence on the mechanical properties of the alloy. Its evolution is followed along thermal and thermomechanical treatments. The measure of the static and dynamic precipitation kinetics has led to a better understanding of the -phase role during hot forging at temperatures below solvus (980 °C). A sequential coupling is developed, based on two models; the first one is a crystal plasticity model implemented in a finite element code (CPFEM), the second one being a modeling of recrystallization using a cellular automata approach. The coupling allows the evolutions of the mechanical fields and the microstructure to be simulated during hot forging. The numerical results fit correctly most of the experimental data, mechanical and structural.

A Resistência Térmica de Contato entre a ferramenta de forjamento e a peça é um parâmetro importante para a otimização, por simulação computacional, do comportamento do material forjado. Os procedimentos atuais destinados à determinação da Resistência Térmica de Contato apresentam discrepância significativa nos resultados. A falta de valores confiáveis deste parâmetro afeta a precisão da simulação. Visando a importância das ferramentas computacionais para a otimização do processo de forjamento, no presente trabalho foi desenvolvida uma nova técnica para determinar a Resistência Térmica de Contato. A técnica inovadora inclui o método de medição de temperaturas interfaciais desconhecido anteriormente, a montagem para realizá-lo e o sistema de medição de temperaturas volumétricas. Esta técnica é destinada ao uso sob condições de altas e moderadas temperatura e pressão muito grande, o que é característico da zona de contato material forjado–ferramenta. A inovação foi testada com sucesso para alguns materiais típicos (aço, liga de alumínio e liga de titânio) utilizados no forjamento a quente ou a morno. Os valores da Resistência Térmica de Contato, obtidos nos testes, são recomendados para uso em programas de simulação computacional. / The Thermal Contact Resistance between a die and a blank is an important parameter in the computer simulation used for the optimization of the blank plastic deformation. The known procedures intended for the determination of the Thermal Contact Resistance show significant discrepancy in results. The lack of reliable values of this parameter affects the precision of the simulation. Taking in account the importance of computer tools for the optimization of the forging process, a new technique for the determination of the Thermal Contact Resistance has been developed in the present study. The developed technique includes a method for the measurement of the interface temperatures, which was unknown before, and the equipment for the realization of this method as well as the system for the measurement of the volumetric temperatures. This technique is intended for use under moderate and high temperature / high pressure conditions at the die–workpiece interface. The innovation has been tested successfully on some typical materials (steel, aluminium alloy e titanium alloy) used in warm and hot forging. Values of the Thermal Contact Resistance obtained by these tests are recommended for use in computer simulations.

Esse trabalho propõe a investigação da geometria dos contornos internos de eixos vazados para aerogeradores quando aplicados mandris com diferentes diâmetros ao longo de seu comprimento no forjamento incremental em matriz aberta. Tem-se por finalidade a fabricação de um mandril que proporcione à peça forjada formato mais perto do formato final proposto. Foram estudados através do uso de simulações numéricas computacionais com o software Simufact.forming 12 e ensaios com o material modelo plasticina possíveis geometrias de mandris, variando a angulação na região de troca de diâmetros ao longo do comprimento entre 0˚, 30˚ e 60˚, e analisados o comportamento do escoamento do material na região. Com o processo simulatório concluído, foi produzido o mandril que apresentou melhor desempenho e foram realizados testes práticos. No total, duas peças foram forjadas e analisados seus resultados. A geometria proposta da peça foi alcançada, confirmando a escolha da cinemática do processo. A temperatura do mandril foi aferida e comparada com a temperatura durante a simulação, onde no último passe, a medida foi 720°C e a simulada em torno de 620°C. As forças de forjamento apresentaram diferença entre a simulação e forjado na média de 7,6%. / This work proposes the investigation of the internal contour of hollow shafts for wind turbines when applied mandrels with different diameters along its length in incremental open-die forging. It is intended to manufacture a mandrel to provide a forged part closer to the final proposed geometry. Studies were conducted using the numerical computer simulations software Simufact.forming 12 and models of plasticine aiming possible mandrel geometries, varying the angle of the different-diameters region along the length between 0˚, 30˚ and 60˚ and analyzed the behavior of the material flow in the region. As the simulation process was concluded, the mandrel with the best performance was produced and practical tests were performed. In total, two workpieces were forged and analyzed its results. The proposed geometry was achieved, confirming the choice of process kinematics. The temperature of the mandrel was measured and compared with the temperature during the simulation at the last pass, the measurement resulted in 720°C and the simulated around 620°C. The forging forces showed differences between simulation and forging of an average of 7.6%.

A falha devido à ocorrência de fadiga térmica de materiais utilizados como ferramentas para trabalho a quente é identificada durante serviço e ocorre devido ao acúmulo de dano localizado. O aço AISI H13 é comumente utilizado em ferramentas para a conformação a quente devido à sua boa tenacidade à fratura e resistência ao desgaste, e considerável resistência à perda de dureza a quente. Este trabalho teve como motivação estudar a relação entre a microestrutura do aço H13 e os carregamentos térmicos e mecânicos, que possam levar à falha de ferramentas para forjamento a quente. Para este estudo, fez-se uso de meios computacionais (simulação numérica) aliados aos conhecimentos de caracterização microestrutural e do comportamento mecânico dos materiais. Nesta abordagem, elabora-se uma malha na microestrutura do referido aço no software OOF2®, do NIST, e as análises são feitas a partir da aplicação do método dos elementos finitos com o emprego do software Abaqus®. Com isso, torna-se possível examinar o efeito de aspectos microestruturais, como a influência dos precipitados, na ocorrência de tensões e de deformações na microestrutura de forma a obter um mapeamento de regiões críticas ao dano e à falha na ferramenta de forjar a quente. Os estudos são baseados e comparados com trabalhos já publicados, e simulam carregamentos e variações de temperatura no material em questão de modo a verificar as condições que favorecem a nucleação de trincas por fadiga térmica. Como principais conclusões e contribuições obtidas da análise realizada, podem ser destacadas: (i-) as regiões críticas que vêm a propiciar a nucleação de trincas térmicas são os precipitados e as interfaces; (ii-) no campo de tensões, a propriedade das fases que exerce a maior influência é o módulo de elasticidade; (iii-) os diferentes coeficientes de expansão térmica das fases geram deformações térmicas mais elevadas e tensões compressivas nas interfaces; (iv-) as deformações térmicas nos precipitados são superiores às da matriz devido à influência no campo de tensões; (v-) em termos de tensões térmicas, o momento do ciclo térmico mais crítico para a matriz é o resfriamento; e (vi-) ao passo que, nos precipitados, a etapa mais crítica é o aquecimento. / Failure due to thermal fatigue can occur in hot working tool materials and its onset takes place in the regions where the highest stress and strain are reached. AISI H13 steel is often used as a hot working tool since it has good toughness and wear resistance, and also a sensible resistance to loss of hot hardness. This study was carried out by means of finite element method (FEM) combined with microstructural characterization and mechanical behavior of materials analysis. According to this approach, H13 steel microstructure, in which carbides could be observed, was meshed by means of OOF2® (NIST). Moreover, the ABAQUS® commercial FEM software was used to simulate thermal and mechanical loading applied in the tool throughout mechanical processing. The conducted analysis allowed to observe the effect of precipitates on stress-strain distribution at different temperatures and loads. Hence, critical regions, in which damage could be favored as well failure onset in the microstructure of the hot forging tool, are displayed. The investigation was based on and compared to literature results and it showed that it can be possible to design the microstructure of hot forging materials, in which an improvement in the thermal fatigue resistance could be improved. The main remarks and conclusions of this work are as follows: (i-) precipitates and interfaces are preferential regions to nucleation and growth of cracks, and they seem to work as stress concentrators; (ii-) modulus of elasticity of phases has the strongest influence in the stress fields of the microstructure; (iii-) the mismatch between thermal expansion coefficients of the phases leads to compressive stresses on interfaces and also the highest thermal strain; (iv-) thermal strains are higher on the precipitates than on the steel matrix; (v-) elastic-plastic properties of steel matrix influenced on thermal cycles. In addition, cooling is the most critical condition of thermal stresses by analyzing each thermal cycle in this phase; and (vi-) whereas the precipitates have elastic behavior, and the most critical step is the heating, in which the maximum temperature of the cycle is reached.

This doctoral thesis presents a modeling method fordemonstrating the behavior of inclusions and their surroundingmatrix during plastic deformation of steels. Inclusions are inescapable components of all steels. Moreknowledge about their behavior in processes such as rolling andforging is necessary for carrying out the forming processes ina more proper way so that the properties of the final productare improved. This work is focussed on deformation ofinclusions together with void formation at the inclusion-matrixinterface. The topic of the work is analyzed by differentFE-codes. The relative plasticity index is considered as an importantmeasure for describing the deformability of inclusions. Theindex could be analyzed quantitatively, enabling a deeperunderstanding of the deformation mechanisms. The workingtemperature is found to be an important process parameter. Thisis very clear when the deformation of silicate inclusions in alow-carbon steel is studied during hot rolling. Here a narrowtransition temperature region exists, meaning that theinclusion behaves as non-plastic at lower temperatures and asplastic at higher. The results are in agreement withexperiments published by other authors. Regarding void formation, the simulations have been carriedout by utilizing an interfacial debonding criterion. Thedifference in yield stress between the matrix and the inclusionis one common reason for void initiation and propagation.During large compressive deformation the evolution of voidsgoes through a sequence of shapes, from convex with two cuspsto concave with three cusps together with self-welding lines.It is concluded that the formation of voids is alwaysassociated with a large relative sliding between the inclusionand the matrix. In order to study the local behavior of the material closeto inclusions during hot rolling a mesomechanical approach isused. Uncoupled macro- and micro- models have been developed.By means of the macro-model, the stress-strain historythroughout each sub-volume of the steel is evaluated. Thestress components or velocity fields are recorded with respectto time as history data. No consideration is taken to theexistence of inclusions. The micro-model, which includes bothinclusion and steel matrix, utilizes the stress components orthe velocity fields from the macro-model as boundaryconditions. <b>Keywords</b>: Inclusion; Steel; Plastic deformation; Void;Rolling; Forging; Finite Element; Mesomechanical approach.

Shear blades are mostly made of cold-work tool steels and manufactured by rolling process. Rolling process is performed not only for forming the tool but also for improving the mechanical properties. In this study, an alternative method, involving sand casting, hot forging and heat treatment processes to manufacture the shear blades, has been proposed. In the proposed method, plastic deformation will be carried out by means of forging instead of rolling. The material has been selected as X48CrMoV8-1. For both of casting and forging processes, simulations have been conducted by using Computer Aided Engineering Software. According to the results of casting process simulation, the billets have been poured. These billets have been soft annealed first and then taken as the initial raw material for the forging process. After the forging process, quenching and tempering processes have been applied. The specimens have been taken as cast, as forged and as tempered and the microstructural analysis and mechanical tests have been performed on these. The same tests and analysis have been repeated for a commercially available shear blade sample which is manufactured by rolling. All these investigations have shown that the properties of the forged shear blade are very similar to the rolled shear blade. Therefore, the new proposed method has been verified to be used as an alternative manufacturing method for the cold-work tool steel shear blades.

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.

Manufacturing of dies has been presenting greater requirements of geometrical accuracy, dimensional precision and surface quality as well as decrease in costs and manufacturing times. Although proper cutting parameter values are utilized to obtain high geometrical accuracy and surface quality, there may exist geometrical discrepancy between the designed and the manufactured surface profile of the die cavities. In milling process / cutting speed, step over and feed are the main cutting parameters and these parameters affect geometrical accuracy and surface quality of the forging die cavities. In this study, effects of the cutting parameters on geometrical error have been examined on a representative die cavity profile. To remove undesired volume in the die cavities, available cutting strategies are investigated. Feed rate optimization is performed to maintain the constant metal removal rate along the trajectory of the milling cutter during rough cutting process. In the finish cutting process of the die cavities, Design of Experiment Method has been employed to find out the effects of the cutting parameters on the geometrical accuracy of the manufactured cavity profile. Prediction formula is derived to estimate the geometrical error value in terms of the values of the cutting parameters. Validity of the prediction formula has been tested by conducting verification experiments for the representative die geometry and die cavity geometry of a forging part used in industry. Good agreement between the predicted error values and the measured error values has been observed.