Evaluation of the Restricted Air Entry on the Discharge Rate from Silos

Storage and distribution of solid materials, as well as control under powder discharge, has been fundamental to ore transportation and lately, Additive Manufacturing (AM). AM demands fine powders materials to be fed with high accuracy, by hoppers. It is not only the reliability of flow that becomes important but also to have a trace of repeatability of material discharges and flow characteristics. In this perspective, two types of hopper feeders have been utilized the most: screw feeder and scraper feeder. In the present work, the characteristics of a steady granular flow through an orifice in scraper feeders with a flat and conical bottom have been experimentally investigated under the influence of top ventilation. The discharge rate of granular particles of magnesium, alumina, glass beads and crushed glass have been studied as a function of the outlet diameter and the ventilation configuration. Tests were performed three times under the same configuration, which consisted for both apparatuses, a measurement of discharge time and the mass through outlet orifices of 15, 30 and 50 mm, with different vent area percentage. The results have shown that the discharge rate increases with the increasing outlet diameter and top ventilation in the majority of the materials studied. In both hopper geometries, a rise in mass flow rate was generally observed when ventilation was added to the system, even though the difference when doubled the vent area was not significant

Um método inovativo de monitoramento utilizando um software capaz de gerar mapa 3D com dados do processo de Deposição por Energia Direcionada a laser (L-DED)

In metal additive manufacturing, the complex thermal activity of newly deposited layers and its influence in previously deposited material affects the part\'s shape and quality. With this regard, the aim of this research is to develop a methodology for monitoring laser power, feed speed and melt pool to evaluate effective material joining and maintenance of good deposited layers on the build of metal parts. This novel methodology combines the data acquisition from a L-DED hybrid machine with a cladding head with 2 mm laser spot size in focus. To aid the monitoring method, some software were developed (DTConnect, MPImageGrabber, MPImageProcessor, DTMap2D and DTMap3D) and tested in four geometries: zigzag line and thin wall (2D); a pyramid, and a pyramid mould (3D). The 3D geometries were printed at four different laser configurations (500 W, 550 – 450 W, 700 W and 800 – 700 W), at the constant feed speed of 600 mm/min, and mass flow rate of 8.3 g/min, under the scanning strategies of contour and zigzag. These parameters were defined to promote one set that presents major defects and other with uniform microstructure. The pyramid built with 550 – 450 W in zigzag strategy has presented the higher percentage of porosity, estimated in 2.76%, whilst the set of 500 W produced the lowest (1.36%). Overall, the 3D builds printed with 500 W have presented defects such as lack of fusion, poor dilution, and porosity. The percentage of porosity has decreased considerably (> 5 times) with the increase of laser power to 700 W and 800 – 700 W, which significantly enhanced the quality and homogeneity in both geometries, highly mitigating the defects aforementioned. Each one of the software designed plays an important role from data acquiring and processing, to its graphic representation. Regarding all conditions tested, both DTMap2D and DTMap3D were able to display the process variables of interest in an interactive color map, therefore making human spatially identification of minor changes in the dataset easier. This makes the DTMap3D a potential tool to speed up the identification of critical regions for post-build inspection. This study contributes towards further knowledge in metal additive manufacturing by bringing to the field a monitoring methodology with new monitoring tools, which easy the correlation between printing parameters and the as-built metal workpiece quality.Na manufatura aditiva de metais, a atividade térmica nas camadas recém-depositadas durante a impressão, e sua influência no material previamente depositado, afetam a geometria e qualidade da peça. Assim, o objetivo desta pesquisa é desenvolver uma metodologia para monitorar a potência do laser, a velocidade de avanço e a poça de fusão para avaliar a deposição de camadas com boa qualidade na impressão de peças metálicas. Esta nova metodologia combina a aquisição de dados de uma máquina híbrida de L-DED com um cabeçote de deposição e diâmetro do feixe de laser de 2 mm no ponto focal. Para o monitoramento, alguns softwares foram desenvolvidos (DTConnect, MPIG, MPIP, DTMap2D e DTMap3D) e testados em quatro geometrias: linha em ziguezague e parede fina (2D); uma pirâmide e um molde de pirâmide (3D). As geometrias 3D foram impressas em quatro configurações de laser (500 W, 550 – 450 W, 700 W e 800 – 700 W), velocidade de avanço constante em 600 mm/min e taxa de alimentação de pó de 8, 3 g/min, nas estratégias de deposição contorno e ziguezague. Esses parâmetros foram definidos visando promover um conjunto que apresenta defeitos e outro com microestrutura uniforme. A pirâmide construída com 550 – 450 W em estratégia de ziguezague apresentou o maior percentual de porosidade, estimado em 2, 76%, enquanto o conjunto impresso com 500 W produziu o menor (1,36%). No geral, as geometrias 3D impressas com 500 W apresentaram defeitos como falta de fusão, má diluição no substrato e porosidade. A percentagem de porosidade diminuiu consideravelmente (> 5 vezes) com o aumento da potência do laser para 700 W e 800 – 700 W, o que melhorou a qualidade e homogeneidade em ambas as geometrias, mitigando os defeitos mencionados. Cada um dos softwares desenvolvidos desempenhou um papel importante desde a aquisição e processamento dos dados, até a sua representação gráfica. Considerando todas as condições testadas, ambos DTMap2D e DTMap3D foram capazes de exibir as variáveis do processo de DED em um mapa de cores interativo, facilitando a identificação espacial de pequenas alterações nos conjuntos de dados. Essas características tornam o DTMap3D uma ferramenta com potencial para identificar regiões críticas da peça. Este estudo contribui para a manufatura aditiva de metais ao propor uma metodologia de monitoramento com novas ferramentas, que facilitam a correlação entre os parâmetros de deposição e a qualidade da peça de metal construída

Monitoring of tool condition in micro-milling via cutting power and acoustic emission signals

Considerando as dimensões reduzidas das ferramentas de microfresamento, a seleção não otimizada dos parâmetros de corte tende a maximizar o desgaste e a quebra da ferramenta durante operações de microusinagem. Isto posto, o desenvolvimento de um sistema de monitoramento para explorar as condições da microfresa durante a usinagem é fundamental. Portanto, o objetivo desta pesquisa é monitorar via sinais de potência e emissão acústica (EA) o desgaste da ferramenta e a estabilidade de corte em operações de microfresamento do aço COS AR60 e COS AR60 de grãos ultrafinos (GUF). Os testes de microfresamento foram realizados com ferramentas de diâmetro de 1 mm e duas arestas, com substrato de metal duro e revestimento (Ti, Al, Cr) N, em um centro de usinagem CNC Romi D800 High Performance adaptado com um cabeçote de alta rotação. O microfresamento ocorreu nos dois materiais sem aplicação de fluido de corte e com velocidade de corte de 62,5 m/min e 125 m/min, mantendo constante a velocidade de avanço de 240 mm/min (fz = 6 μm/aresta e 3 μm/aresta), profundidade de usinagem de 100 m e comprimento de usinagem de 104 mm em corte em cheio. O sinal de potência e EA foram adquiridos à taxa de 5 kHz e 1,25 MHz, respectivamente. Os dados foram adquiridos em LabVIEW® e processados em LabVIEW® e MATLAB®. Os resultados de caracterização dos desgastes apontaram um desgaste de flanco mais expressivo e a formação de Aresta Postiça de Corte (APC) no GUF para vc = 125 m/min, e a presença de desgaste de cratera em todas as condições de corte. O aumento da potência de corte média representou a predominância do desgaste de flanco, e desgaste de cratera em sua redução. De forma semelhante, a ANOVA dos valores de EA RMS indicaram com significância (95% de confiança) uma correlação diretamente proporcional entre EA RMS e evolução do desgaste de flanco na microfresa. Quanto à estabilidade de corte, ambos os sinais apresentaram um aumento expressivo de amplitude quando o corte foi instável. Com isso, os métodos de monitoramento utilizados foram capazes de indicar a evolução do desgaste da microfresa e a ocorrência de chatter em operações de microfresamento.Regarding the reduced dimensions of micro-milling tools, a non-optimised selection of cutting parameters tends to maximise tool wear and breakage during cutting operations. Hereupon the development of a monitoring system for exploring microtool conditions during machining is imperative. Therefore, the aim of this research is to monitor tool wear and cutting stability via cutting power and acoustic emission (AE) signals in micro-milling operations of steel COS AR60 and ultra fine-grained steel COS AR 60 (GUF). Cutting tests were performed by carbide endmill tools with (Ti, Al, Cr) N coating, two flutes and 1 mm diameter in a CNC machining centre Romi D800 High Performance adapted with a high spindle speed head. Micro-milling operations were carried out in both materials without cutting fluid application at 62.5 m/min and 125 m/min, and constant parameters of feed, set at 240 mm/min (fz = 6 μm/tooth and 3 μm/tooth), depth of cut of 100 m and cutting length of 104 mm performed in sloth cutting strategy. Cutting power and AE signals were acquired at the rate of 5 kHz and 1.25 MHz, respectively. The data were acquired in LabVIEW® and processed in both LabVIEW® and MATLAB®. The results on wear characterisation revealed a major flank wear and the formation of Built Up-Edge (BUE) in GUF at vc = 125 m/min, along with the occurrence of crater wear in all cutting conditions set. An increase in the average cutting power levels is linked to the predominancy of flank wear, while crater wear to its decrease. Likewise, the Analysis of Variance (ANOVA) of EA RMS values indicated with significancy (95% confidence) a direct proportion between AE RMS and flank wear in the microtool. In terms of cutting stability both EA and cutting power signals have shown an expressive rise when performing instable cutting. Thus, the methods of monitoring were feasible for recognising tool wear evolution and chatter in micro-milling operations

A teoria de metodologia ativa na prática: uma vivência entre pós-graduandos e graduandos numa atividade extraclasse

As metodologias ativas de ensino apresentam técnicas de ensino-aprendizagem baseadas na construção ativa de conhecimento, com foco no estudante. A formação de pós-graduandos e novos docentes capazes de utilizar tais metodologias se faz necessária no cenário atual do ensino superior. O conceito de Metodologia Ativa foi apresentado aos estudantes de Pós-Graduação na disciplina de Preparação Pedagógica oferecida no Programa de Pós-Graduação em Engenharia Mecânica da Escola de Engenharia de São Carlos (PPGEM-EESC USP). Para colocar em prática as metodologias apresentadas, sugeriu-se a participação dos pós-graduandos como mediadores de conhecimento em uma atividade extraclasse da disciplina de Desenho Técnico Mecânico I (DTM I), oferecida aos estudantes do curso de graduação em Engenharia Mecânica da EESC-USP. A atividade foi desenvolvida durante quatro semanas consecutivas, contando com a participação voluntária de quatro pósgraduandos e catorze estudantes de graduação. O desempenho dos estudantes de graduação participantes das atividades melhorou em relação à prova anterior e também foi superior ao desempenho médio de todos os alunos da turma. Do ponto de vista dos pós-graduandos, a atividade permitiu uma experiência de planejar e executar um plano de aula que fizesse uso de metodologias ativas em sala. Os resultados acadêmicos dos alunos de graduação e o relato dos pós-graduandos mostram como tais atividades são uma forma de melhoria do ensino e aprendizagem, com destaque para o benefício proporcionado pela integração entre alunos de graduação e de pós-graduação no contexto da formação de novos docentes.Active learning methods are techniques based on the active construction of knowledge, focusing on the student. The education of graduate students to be teachers that will able to use such methods is necessary in the current scenario of higher education. The concept of active learning was presented to the graduate students in the Pedagogical Preparation course, offered by the Graduate Program in Mechanical Engineering of the São Carlos School of Engineering (PPGEM-EESC-USP). To put the presented methodologies into practice, the graduate students were invited to act as knowledge mediators in an extra-class activity for the Mechanical Engineering Drawing I course (DTM I), offered to undergraduate students in Mechanical Engineering at EESC- USP. The activity was developed for 4 consecutive weeks, with the voluntary participation of 4 postgraduate students and 14 undergraduate students. The performance of undergraduate students participating in the activities improved when compared to the previous test and was also superior to the average performance of all students in the class. From the perspective of graduate students, the activity provided an experience of planning and executing a lesson plan based on active learning methods. The academic results of undergraduate students and the report of graduate students show how such activities are a way of improving teaching and learning, highlighting the benefit provided by the integration between undergraduate and postgraduate students in the context of training future higher education teachers

Abrasive and non‑conventional post‑processing techniques to improve surface finish of additively manufactured metals : a review

Metal additive manufacturing (MAM) has attracted global industry and academia due to its flexibility and ability to achieve complex geometry. The inherent rough surfaces are of concerns and need to be addressed to meet the strict requirement of critical engineering components. This paper reviews the working principles for common MAM processes and summarizes current post-processing techniques for surface finish improvement. Relevant finishing techniques using abrasives and non-conventional techniques, such as grinding, polishing, laser, peening, buffing, and electrochemical polishing are reviewed, and typical results are documented for different AM processes. Limitation of each process and enhancing techniques using magnetism, ultrasonic, and pulsed current for selected processes are presented. Post processing not only reduces surface roughness, but also contributes to dimensional and form tolerances, and prolongs long-term fatigue and creep life of AM metals. Although post-processing techniques can effectively remove surface defects to achieve submicron surface finish, controlling of surface defects that extend deeply below a surface is still a challenge. Future hybrid system that combines AM and a non-traditional post-process would meet the requirement for MAM