https://repositorio.ufu.br/handle/123456789/5146 2026-09-21T14:44:08Z https://repositorio.ufu.br/handle/123456789/50294 Title: Avaliação da diluição de aço inoxidável ER308LSi depositado em aço carbono SAE1020 via manufatura aditiva por deposição a arco Abstract: Wire arc additive manufacturing (WAAM) has become a viable alternative to produce medium and large-scale metallic components, offering high deposition rates and reduced material waste. When applied to dissimilar material pairs, however, the mixing between filler metal and substrate during weld pool formation changes the first layers’ chemical composition, affecting the microstructure and mechanical properties. This work aims to study the chromium and nickel dilution along the build direction in an ER308LSi austenitic stainless steel preform deposited on carbon steel substrate by WAAM. The preform cross-section was analyzed by macrography, optical microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy microanalysis and Vickers microhardness testing. The penetration of the first bead into the substrate was 2.8 mm. The compositional profile revealed an abrupt transition at the interface, followed by a plateau of constant composition extending over 3.0 mm, with average contents of 13.22 % chromium and 5.99 % nickel, and by progressive enrichment up to 17.86 % chromium and 7.83 % nickel at the top of the preform. Dilution estimated by mass balance ranged from 32 to 46 % in the first bead, decreasing to between 9 and 30 % at the top. The microhardness profile followed the compositional profile, with a marked increase in the diluted region, attributed to the loss of austenite stability caused by the reduction in nickel content and the consequent formation of martensite, an interpretation supported by the Schaeffler diagram. It was further observed that the microstructural boundary, defined by the hardness drop, lies approximately 0.9 mm above the compositional boundary, a lag consistent with the fact that austenite stability is governed by nickel content. 2026-08-07T00:00:00Z https://repositorio.ufu.br/handle/123456789/50253 Title: Contribuição para monitoramento de roçamento em máquinas rotativas utilizando a técnica de emissão acústica Abstract: Early detection of faults in rotating machinery is critical for maintaining operational reliability and efficiency across various industrial sectors. The Acoustic Emission technique has emerged as a promising method for structural health monitoring, particularly in identifying incipient defects such as light rubbing. Light rubbing faults, defined by contact between rotating and stationary surfaces, can accelerate mechanical degradation and result in catastrophic failures if not promptly detected. This thesis examines the use of the Acoustic Emission technique for detecting and characterizing rubbing faults in rotating machinery, with a focus on low-cost piezoelectric sensors, including lead zirconate titanate transducers and buzzers, integrated with machine learning algorithms for signal processing and classification. Experimental data were collected using a dedicated test rig under multiple operating conditions. Analyses employed both conventional signal processing methods, such as the Fast Fourier Transform and envelope analysis based on the Hilbert Transform, as well as machine learning-based techniques. The findings indicate that Acoustic Emission enables reliable identification of light rubbing faults even in noisy environments where traditional vibration analysis methods are limited. These results underscore the potential of Acoustic Emission as an effective and complementary approach for continuous condition monitoring of rotating machinery. 2025-02-28T00:00:00Z https://repositorio.ufu.br/handle/123456789/50201 Title: Desenvolvimento e avaliação de um sistema para sincronização da alimentação de arame pulsada com a corrente de soldagem no processo TIG Abstract: Pulsed (dynamic) wire feeding can modify the weld pool, metal transfer and heat input in arc welding processes. However, although some commercial solutions already exploit such technologies, they rely on proprietary feeders and/or torches. Furthermore, studies evaluating wire pulsation synchronized with the welding current remain scarce, which also motivated the development of this thesis. Thus, the objective of this work was to develop and evaluate a device compatible with conventional feeders and torches and with independent adjustment of frequency and amplitude for wire feed pulsation in the TIG process and to investigate the effects of synchronization between wire feed pulsation and current on the resulting deposits. The work methodology was organized into sequential stages. First, a pulsation device was built and characterized based on the cyclic deflection of part of the wire conduit. Next, a working envelope for the TIG process with pulsed wire feeding was established. Synchronization between wire pulsation and current was then implemented based on the electrode-to-wire voltage. The effects of wire pulsation parameters and current mode on bead geometry were subsequently evaluated. Finally, geometric, metallurgical, chemical, and thermal characteristics of the deposits produced. Characterization of the pulsation device demonstrated pulsation amplitudes of 2 to 15 mm at frequencies of up to 25 Hz, with tolerance for different wire materials and diameters. The pulsed feeding modified the bead geometry, being wire pulsation frequency the parameter with the greatest influence and wire stubbing (contact of the wire tip with the base metal at the bottom of the weld pool) the operational limiting factor at low current and high wire feed speed under constant current. The synchronization system achieved latency below 10 ms and enabled stable operation at boundaries previously unviable under constant current with pulsed feeding, thereby expanding the process working envelope. Under pulsed current synchronized with pulsed wire feeding, increasing frequency from 2 to 15 Hz reduced bead width approximately by 20%, penetration by 17%, and dilution by 20%. In the evaluation with the ER2594 wire, synchronization enabled an approximately 30% increase in wire feed speed compared with the limit achieved with constant current and pulsed feeding under an equivalent welding energy. Furthermore, synchronization yielded deposits with larger width and reinforcement, lower penetration and lower dilution, better preservation of Cr and Ni, with no relevant differences in hardness and ferrite/austenite balance. Thus, it is concluded that the developed device, combined with the synchronization strategy, can increase deposition capacity and improve deposit characteristics, opening up prospects for applications such as cladding and additive manufacturing, for instance. 2026-08-03T00:00:00Z https://repositorio.ufu.br/handle/123456789/50165 Title: Torneamento de Ti6Al4V com ferramentas texturizadas por laser de femtossegundos Abstract: The machining of the Ti-6Al-4V titanium alloy presents significant challenges due to its high specific strength, low thermal conductivity, high chemical reactivity, strong tendency toward adhesion, and accelerated cutting-tool wear. In this context, surface texturing of cutting tools has been investigated as a promising strategy for modifying the tribological conditions at the tool–chip and tool–workpiece interfaces and improving machining performance, particularly by extending tool life. Therefore, this study aimed to investigate the influence of microtextures produced on the rake face of cemented carbide tools during the turning of Ti-6Al-4V, evaluating their effects on machining forces, workpiece surface roughness, and tool life. The study was conducted in three experimental stages. In the first stage, different microtexture geometries were evaluated through an experimental design to identify the geometric parameters with the greatest influence on the machining process. At this stage, some configurations significantly improved the surface finish, reducing the average surface roughness (Ra) by up to 41.94% compared with the untextured tool, in addition to reducing machining forces by up to 8.64%. In the second stage, the geometric parameters of the selected textures were refined to optimize the microgroove geometry. The results indicated that certain configurations provided additional reductions in cutting forces, reaching a decrease of 8.02% compared with the conventional tool, as well as a 6.80% reduction in surface roughness. In the third and final stage, the optimized texture geometry was compared with an untextured tool and with textured-tool variants containing MoS₂ solid lubricant under finishing and roughing conditions. The results showed that, under finishing conditions, textured tools without lubricant reduced machining forces by 4.3%, whereas, under roughing conditions, the combination of texture and MoS₂ resulted in reductions of up to 57.9% in machining forces. Regarding surface roughness, improvements of up to 8% were observed during finishing, depending on the machining condition. Tool-life analysis indicated that textured tools without solid lubricant exhibited the best overall performance, achieving greater volumes of removed material before reaching the end-of-tool-life criterion, with average increases of 58% under finishing conditions and 24% under roughing conditions. 2026-08-11T00:00:00Z