Size effects play a significant role in metal processing when the specimen dimensions are reduced. In this study, influence of size effects were investigated on two problem specific processes. First, numerical simulations of a small-scale forward extrusion with varying grain size were performed for both 2D and 3D cases. Here, grains were assigned to non-homogeneous properties in a random fashion. The computational geometry was obtained from Voronoi tessellation in MATLAB, and python-scripting in ABAQUS. Then the effects of size and property non-homogeneity were investigated. Second, a numerical model was simulated to predict final form shapes, punch load requirement, and thickness distribution of hemispherical bowl-shaped forming. The die, punch and cover plate were fabricated using stereolithographic apparatus (SLA). Numerically obtained punch load requirement, thickness distribution, von-Mises contours, and equivalent plastic strain contours were compared for different thickness specimens. Finally, the models were validated by experimental results.

O presente trabalho estuda a conformação da liga de magnésio AZ61 pelos processos de extrusão direta e forjamento, ambos a quente. No processo de extrusão, são submetidos à conformação corpos-de-prova da liga de magnésio AZ61 nos estados fundido e recristalizado. As geometrias de ferramenta são variadas e a influência destas variações sobre a força de processamento e propriedades mecânicas e microestrutura do material são analisada. Demonstra-se que a liga no estado inicialmente recristalizado tem propriedades mecânicas finais superiores à liga inicialmente fundida, embora demande de maior força de processamento. Demonstra-se também que a geometria de ferramenta tem influência sobre as respostas mecânicas obtidas das peças após extrusão. Referente ao processo de forjamento, a liga de magnésio AZ61 é processada apenas no estado recristalizado, variando-se a temperatura e o número de tapas de forjamento. Foi avaliada a influência destas variações de processo nas propriedades mecânicas finais da peça. Ao fim, percebe-se que ao se forjar as peças com múltiplas etapas de forjamento e temperaturas decrescentes, impede-se a recristalização do material, alcançando alto encruamento dos grãos, o que gera, na peça final, propriedades mecânicas superiores ao processo convencional. / This thesis studies the deformation of a magnesium alloy AZ61 by forward extrusion and forging processes, at elevated temperatures. In the extrusion process, the samples were deformed in as cast and recrystallized conditions. The tools geometries were variated and the influences on processing force, mechanical properties and material microstructure were analyzed. Was found that the recrystallized samples have better mechanical properties than as cast samples, after extruded, although it requires more processing force. Also was found that the tool geometry influences on mechanical properties and microstructure of extruded magnesium alloy. Relatively to the forging process, magnesium alloy AZ61 was processed only in the recrystallized state, varying the process temperature and the number of forging steps. Aimed to evaluate the process variations influences on the mechanical properties and microstructure of the final parts. At the end, was observed that when forging parts with multi-step forging and decreasing temperatures, to prevent recrystallization of the material, achieving high strain hardening of the grains, which results in final part with superior mechanical properties to the conventional process.

O presente trabalho estuda a conformação da liga de magnésio AZ61 pelos processos de extrusão direta e forjamento, ambos a quente. No processo de extrusão, são submetidos à conformação corpos-de-prova da liga de magnésio AZ61 nos estados fundido e recristalizado. As geometrias de ferramenta são variadas e a influência destas variações sobre a força de processamento e propriedades mecânicas e microestrutura do material são analisada. Demonstra-se que a liga no estado inicialmente recristalizado tem propriedades mecânicas finais superiores à liga inicialmente fundida, embora demande de maior força de processamento. Demonstra-se também que a geometria de ferramenta tem influência sobre as respostas mecânicas obtidas das peças após extrusão. Referente ao processo de forjamento, a liga de magnésio AZ61 é processada apenas no estado recristalizado, variando-se a temperatura e o número de tapas de forjamento. Foi avaliada a influência destas variações de processo nas propriedades mecânicas finais da peça. Ao fim, percebe-se que ao se forjar as peças com múltiplas etapas de forjamento e temperaturas decrescentes, impede-se a recristalização do material, alcançando alto encruamento dos grãos, o que gera, na peça final, propriedades mecânicas superiores ao processo convencional. / This thesis studies the deformation of a magnesium alloy AZ61 by forward extrusion and forging processes, at elevated temperatures. In the extrusion process, the samples were deformed in as cast and recrystallized conditions. The tools geometries were variated and the influences on processing force, mechanical properties and material microstructure were analyzed. Was found that the recrystallized samples have better mechanical properties than as cast samples, after extruded, although it requires more processing force. Also was found that the tool geometry influences on mechanical properties and microstructure of extruded magnesium alloy. Relatively to the forging process, magnesium alloy AZ61 was processed only in the recrystallized state, varying the process temperature and the number of forging steps. Aimed to evaluate the process variations influences on the mechanical properties and microstructure of the final parts. At the end, was observed that when forging parts with multi-step forging and decreasing temperatures, to prevent recrystallization of the material, achieving high strain hardening of the grains, which results in final part with superior mechanical properties to the conventional process.

O presente trabalho estuda a conformação da liga de magnésio AZ61 pelos processos de extrusão direta e forjamento, ambos a quente. No processo de extrusão, são submetidos à conformação corpos-de-prova da liga de magnésio AZ61 nos estados fundido e recristalizado. As geometrias de ferramenta são variadas e a influência destas variações sobre a força de processamento e propriedades mecânicas e microestrutura do material são analisada. Demonstra-se que a liga no estado inicialmente recristalizado tem propriedades mecânicas finais superiores à liga inicialmente fundida, embora demande de maior força de processamento. Demonstra-se também que a geometria de ferramenta tem influência sobre as respostas mecânicas obtidas das peças após extrusão. Referente ao processo de forjamento, a liga de magnésio AZ61 é processada apenas no estado recristalizado, variando-se a temperatura e o número de tapas de forjamento. Foi avaliada a influência destas variações de processo nas propriedades mecânicas finais da peça. Ao fim, percebe-se que ao se forjar as peças com múltiplas etapas de forjamento e temperaturas decrescentes, impede-se a recristalização do material, alcançando alto encruamento dos grãos, o que gera, na peça final, propriedades mecânicas superiores ao processo convencional. / This thesis studies the deformation of a magnesium alloy AZ61 by forward extrusion and forging processes, at elevated temperatures. In the extrusion process, the samples were deformed in as cast and recrystallized conditions. The tools geometries were variated and the influences on processing force, mechanical properties and material microstructure were analyzed. Was found that the recrystallized samples have better mechanical properties than as cast samples, after extruded, although it requires more processing force. Also was found that the tool geometry influences on mechanical properties and microstructure of extruded magnesium alloy. Relatively to the forging process, magnesium alloy AZ61 was processed only in the recrystallized state, varying the process temperature and the number of forging steps. Aimed to evaluate the process variations influences on the mechanical properties and microstructure of the final parts. At the end, was observed that when forging parts with multi-step forging and decreasing temperatures, to prevent recrystallization of the material, achieving high strain hardening of the grains, which results in final part with superior mechanical properties to the conventional process.

One of the decisive factors of effective using of forward extrusion technology is lifetime of forming tools. Die is very loaded forming tool which loading and therewith related lifetime can be significantly affected by its construction. Construction also affected quality of extruded material. Finete element method allows to simulate this process and assess force which is needed to extrusion and state of stress in die and extruded material. Numerical simulation was realized in program ANSYS 11.0. Influence of reduction, angle of reduction, lenght of extruded material, rounding transition of die parts, extruded material and friction coefficient on die loading and emergence of cracks in extruded material was set in this diploma thesis. Results can be used to die construction optimalization.

This Master’s thesis deals with the influence of process parameters in forward extrusion on the initiation of chevron cracks in material by numerical simulation. Solution was executed by ANSYS 11 and the influence of fiction, angle of reduction, reduction and numbers of extrusion operations was solved for the 12 050.3 steel by the chosen conditions.

The purpose of this thesis is to deal with the initiation of chevron cracks in forward extrusion. Using numerical simulation, the ability of selected fracture models which prognosticates the initiation of chevron cracks is observed. The influence of process parameters is studied (friction, reductions in cross section and angles of reduction) on the initiation and diffusion of damage. Solutions was executed by Abaqus for material 12 050.

The presented work is concerning with ductile fracture problematic under monotonic loading which is result of gradual material degradation at large plastic deformation. At present, a large number of models, which calibration is not trivial, are used for its prediction. Ductile fracture mechanisms and cut-off region are described in the literature search part. Next, there is given a summary of criteria which are based on different approaches to ductile fracture. There were proposed and used KHPS and KHPS2 criteria within this PhD thesis. Procedure of assessment of the stress-strain curve and ductile fracture criteria calibration are described in last part of the literature search. A summary of tests, which were done in order to calibrate chosen criteria, is given in experimental part. Various stress states within broad range of stress triaxiality and Lode parameter were reached using these tests. Special type of specimen, by which very low stress triaxiality value is reached, was designed within this work. All specimens were made from the steel 12 050. Wrought rods of one melt with circular cross-section of 27 mm in diameter were used as semi-product. Calibration of chosen ductile fracture criteria was performed using foregoing tests. These criteria were implemented by author into explicit finite element software ABAQUS/Explicit using user subroutine VUMAT. Chosen criteria were used for simulation of multistep extrusion at which formation of internal central cracks occurs. These criteria were also used for simulation of cutting of circular cross-section rods. Results from simulation were compared to experiments which were done by industrial partner J-VST.

The master’s thesis submits a technological project of production of splined sleeve used in automotive as a component of propeller shaft. The part is made of steel ČSN 11 523 by bulk forming technology in an annual production series of 20 000 pieces. Production process was designed in four operations, after the second operation there was recrystallization annealing included for regeneration of plasticity before following extrusion. There were made technological calculations for these production operations. Operations were projected to be done by common one-operation press machines available in local manufacturing facility. For all the operations were designed functional tools and tools setups. In conclusion, there was performed technical-economic evaluation. As emerged from this evaluation the final amount of total production costs for one piece is 131,- Kč. When 9 393 pieces are produced, the production series reaches to the break-even point and then the profit starts to be generated.

The project presents a proposal for the technology of production of the pressure filter casing used in hydraulic systems, which is made of non-alloy carbon steel 12 020. With the help of a literature study of cold extrusion and calculations, the production of the component was designed, which will take place in two operations. Before each operation, the surface treatment is performed by phosphating and soaping and inter-operational annealing must take place. Tool sets were designed for both operations and a press was selected from the company's machine park with a nominal force of 25,000 kN. Finally, a technical and economic evaluation was proved, which shows that the price of production of one piece is CZK 187. The turning point was set at 3 497 pieces per year.