2 research outputs found

    Friction in deep drawing

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    Optimization of industrial processes for forging of carbon and stainless steels

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    The possibility to produce stainless steel components at limited cost and characterized by elevated mechanical properties, has gained more importance in the last years. Nowadays, the cold and warm forging processes of carbon steels are widely used to form industrial parts due to their economic advantages, but there is still lack of extensive research on industrial process design and evaluation of the microstructural properties of cold-warm forged stainless steel parts. In the last few decades, the environment concerning the recent forging industry has been rapidly changed. Now, near-net-shape or net-shape manufacturing processes are becoming a useful practice in metal forming, resulting in saving material and energy. Many parts produced with machining can be manufactured at lower cost by cold and warm forging. Traditionally, forging design is carried out using mainly empirical guidelines, experience, and trial-and-error, which results in a long process development time and high production costs. In order to avoid this, in recent years, computer-aided simulation approaches have proved to be powerful tools to predict and analyze material deformation during a metal forming operation. There are now many commercial finite-element (FE) packages to simulate forging and bulk metalworking processes. To date, most have focussed on predicting the shape of the final product after simple or complex single- or multi-stage forming operations. On the other hand, other aspects are being included in these numerical models, such as an improved understanding of the constitutive material behaviour, friction and lubrication conditions, and the properties of the final product, in order to predict more complicated phenomena such as tool life prediction, ductile fracture and microstructure evaluation. The focus of this PhD thesis is the development of an innovative approach based on the design of integrated experimental procedures and modelling tools, in order to accurately re-design a range of industrial single-stage cold-warm forming processes to form stainless steel components and investigate the microstructural evolution of forged parts obtained at different forging temperatures. In addition, the design of a multi-stage cold forging process of a low-carbon steel and the prediction of surface defects that occur in each stage of the forming-sequence have been carried out. To this aim, a series of tensile tests were conducted to evaluate the influence of temperature and strain rate on the materials elasto-plastic properties. Futhermore, an innovative experimental setup was used to reproduce the realistic friction conditions at the tool-workpiece interface, in order to accurately predict metal flow during forging cycles. Experimental data were subsequently validated and implemented in a commercial 3D-FE software and accurately calibrated to perform fully coupled numerical simulations for the reference processes. Finally, the forged parts obtained were characterized by macro- and microstructural inspections in order to evaluate the presence of underfilling problems and surface defects, which were consistent with the numerical FE results coming from both simulated processes (i.e. single- and multi-stage forging), and to analyze the microstructural evolution of α- and γ-phase during single-stage tests both at room temperature and from 400 to 700 °C. The materials investigated in this work are low-carbon AISI 1005 ferritic-pearlitic steel (Wr. N. 1.0303), AISI 304L austenitic (Wr. N. 1.4307) and commercially named Duplex 2205 ferritic-austenitic stainless steel (Wr. N. 1.4462). The developed experimental tests are suitable to proper evaluation of steels behaviour in terms of mechanical properties, and to precisely calibrate coupled numerical models when they are applied to conventional and re-design forging processes. The techniques used in this work include: tensile tests, T-shape compression tests, visual inspections (i.e. supported by vernier calliper and micrometer measurements), hardness and micro-hardness tests, LOM (Light Optical Microscopy), FEG-ESEM (Field-Emission Gun Environmental Scanning Electron Microscope), EDS (Energy Dispersive X-ray Spectroscopy), EBSD (Electron Back Scattering Diffraction) and numerical models carried out with FORGE2011®-3D
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