381 research outputs found

    Six-Sigma Quality Management of Additive Manufacturing

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    Quality is a key determinant in deploying new processes, products, or services and influences the adoption of emerging manufacturing technologies. The advent of additive manufacturing (AM) as a manufacturing process has the potential to revolutionize a host of enterprise-related functions from production to the supply chain. The unprecedented level of design flexibility and expanded functionality offered by AM, coupled with greatly reduced lead times, can potentially pave the way for mass customization. However, widespread application of AM is currently hampered by technical challenges in process repeatability and quality management. The breakthrough effect of six sigma (6S) has been demonstrated in traditional manufacturing industries (e.g., semiconductor and automotive industries) in the context of quality planning, control, and improvement through the intensive use of data, statistics, and optimization. 6S entails a data-driven DMAIC methodology of five steps—define, measure, analyze, improve, and control. Notwithstanding the sustained successes of the 6S knowledge body in a variety of established industries ranging from manufacturing, healthcare, logistics, and beyond, there is a dearth of concentrated application of 6S quality management approaches in the context of AM. In this article, we propose to design, develop, and implement the new DMAIC methodology for the 6S quality management of AM. First, we define the specific quality challenges arising from AM layerwise fabrication and mass customization (even one-of-a-kind production). Second, we present a review of AM metrology and sensing techniques, from materials through design, process, and environment, to post-build inspection. Third, we contextualize a framework for realizing the full potential of data from AM systems and emphasize the need for analytical methods and tools. We propose and delineate the utility of new data-driven analytical methods, including deep learning, machine learning, and network science, to characterize and model the interrelationships between engineering design, machine setting, process variability, and final build quality. Fourth, we present the methodologies of ontology analytics, design of experiments (DOE), and simulation analysis for AM system improvements. In closing, new process control approaches are discussed to optimize the action plans, once an anomaly is detected, with specific consideration of lead time and energy consumption. We posit that this work will catalyze more in-depth investigations and multidisciplinary research efforts to accelerate the application of 6S quality management in AM

    Metal Additive Manufacturing – State of the Art 2020

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    Additive Manufacturing (AM), more popularly known as 3D printing, is transforming the industry. AM of metal components with virtually no geometric limitations has enabled new product design options and opportunities, increased product performance, shorter cycle time in part production, total cost reduction, shortened lead time, improved material efficiency, more sustainable products and processes, full circularity in the economy, and new revenue streams. This Special Issue of Metals gives an up-to-date account of the state of the art in AM

    Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation and Experimentation

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    Among the many additive manufacturing (AM) processes for metallic materials, selective laser melting (SLM) is arguably the most versatile in terms of its potential to realize complex geometries along with tailored microstructure. However, the complexity of the SLM process, and the need for predictive relation of powder and process parameters to the part properties, demands further development of computational and experimental methods. This review addresses the fundamental physical phenomena of SLM, with a special emphasis on the associated thermal behavior. Simulation and experimental methods are discussed according to three primary categories. First, macroscopic approaches aim to answer questions at the component level and consider for example the determination of residual stresses or dimensional distortion effects prevalent in SLM. Second, mesoscopic approaches focus on the detection of defects such as excessive surface roughness, residual porosity or inclusions that occur at the mesoscopic length scale of individual powder particles. Third, microscopic approaches investigate the metallurgical microstructure evolution resulting from the high temperature gradients and extreme heating and cooling rates induced by the SLM process. Consideration of physical phenomena on all of these three length scales is mandatory to establish the understanding needed to realize high part quality in many applications, and to fully exploit the potential of SLM and related metal AM processes

    Additive Manufacturing (AM) of Metallic Alloys

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    The introduction of metal AM processes in such industrial sectors as the aerospace, automotive, defense, jewelry, medical and tool-making fields, has led to a significant reduction in waste material and in the lead times of the components, innovative designs with higher strength, lower weight, and fewer potential failure points from joining features. This Special Issue on “Additive Manufacturing (AM) of Metallic Alloys” contains a mixture of review articles and original contributions on some problems that limit the wider uptake and exploitation of metals in AM

    Feasibility studies on Laser Powder Bed Fusion of powders mixtures based on Aluminium alloys or High Entropy Alloys

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    Powder bed fusion additive layer manufacturing of titanium alloys

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    Powder bed fusion (PBF) techniques for additive layer manufacturing (ALM) are reviewed with a focus on titanium alloys production. Selective laser melting and electron beam melting are discussed in terms of feedstock production and processing-microstructure relationships. To control the PBF processes, an outline is presented on the computational modelling approaches for simulating process parameters and defects such as residual stresses and porosity at different length scales. It is concluded that by improving powder production techniques, designing new alloys and further developing ALM hardware, PBF techniques can reach commercial maturity. This review was submitted as part of the 2019 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged

    Laser powder bed fusion of INCONEL® 718: optimization of process parameters and residual stress analysis before and after heat treatment

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    Metals Additive Manufacturing (AM) is a “flourishing” technology, developing fast and successfully. Laser Powder Bed Fusion (LPBF) is among the most used metals AM processes in industry. Inconel® 718 (IN718) is a nickel-based superalloy that maintains its exceptional properties at high and low temperatures, thereby, it is a material commonly used to fabricate high performance components. The purpose of this work is to study the residual stress (RS) evolution of IN718 parts fabricated by LPBF, before and after heat treatment. Firstly, specimens with different combinations of parameters were fabricated to select the optimal LPBF process parameters. With the results from that part of the work, the influence of the individual process parameters on the porosity was studied. Then, new specimens were fabricated with the selected parameters and the RS analyzed by the hole-drilling strain-gage method, in as-built, solution annealed (SA) and SA plus double-aged (DA) conditions. It was concluded that increasing the scanning speed contributes to the reduction of the porosity. Also, for lower scanning speeds, 400 mm/s and lower, a hatching distance of 0.13 mm was defined as optimal. For higher scanning speeds, 600 and 800 mm/s, no relevant influence of the hatching distance, from 0.05 to 0.11 mm, on the porosity was observed. Laser power and layer thickness were not studied. Larger pores were found in specimens with higher porosity. Also, the specimens with higher porosity presented irregular pores and with lower porosity presented spherical-like pores. Regarding the RS evolution, as-built top surface presented uniform RS distribution of approximately 400 MPa. Lateral surface presented anisotropic distribution, with RS magnitudes of 600 to 800 MPa in build direction and 200 to 300 MPa horizontally. After the SA heat treatment, the RS decrease greatly to values between 50 – 200 MPa. Series of carbides were found at the grain boundaries, which were attributed as the cause for oscillations in the RS profile. SA plus DA condition presented RS between 10 to 50 MPa. Heat-treated specimens revealed compressive RS at immediately near the surface.A fabricação aditiva (FA) de metais é uma tecnologia “florescente”, em rápido desenvolvimento e com sucesso. Fusão a laser em leito de pó (LPBF) está entre os processos de FA de metais mais usados na indústria. Inconel® 718 é uma superliga à base de Nickel, que mantém as suas propriedades excecionais a altas e baixas temperaturas, desse modo, é comummente usada para produzir componentes de alto desempenho. O objetivo deste trabalho é estudar a evolução das tensões residuais (TR) de partes produzidas por LPBF, antes e pós tratamento térmico. Primeiramente, produziram-se amostras com diferentes combinações de parâmetros do processo LPBF para selecionar os melhores parâmetros. Com os resultados obtidos dessa parte do trabalho, foi estudada a influência na porosidade dos diferentes parâmetros. Então, produziram-se novas amostras com os parâmetros selecionados e foram analisadas as TR pelo método do furo cego incremental, nas condições: “as-built”, recozido (SA) e SA mais envelhecimento duplo (DA). Concluiu-se que o aumento da velocidade de varredura contribuí para a redução da porosidade. Também, para velocidades mais baixas, 400 mm/s e abaixo, a distância entre passagens de 0.13 mm foi definida como ótima. Para velocidades mais altas, 600 mm/s e 800 mm/s, a influência da distância entre passagens, de 0.05 a 0.11 mm, na porosidade é desprezível. A potência do laser e a espessura das camadas não foram estudados. Poros maiores foram observados nas amostras com maior porosidade. Também, as amostras com maior porosidade exibiram poros irregulares, e com menor porosidade poros esféricos. Em relação à evolução das TR, a face superior “as-built” apresentou uma distribuição das TR uniforme de aproximadamente 400 MPa. A face lateral apresentou distribuição anisotrópica, com TR entre 600 e 800 MPa na direção de deposição, e entre 200 e 300 MPa horizontalmente. Nas amostras SA, as TR reduziram substancialmente para valores entre 50 e 200 MPa. Foram detetados conjuntos de carbonetos, aos quais se atribuiu a ocorrência de oscilações no perfil das TR. A condição SA mais DA apresentou TR entre 10 e 50 MPa. As amostras tratadas termicamente revelaram TR à compressão bem próximo da superfície

    Re-inforcing nano-particle integration into metal AM and produced part characterisation

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    Metal matrix composites (MMCs) are an important class of materials replacing monolithic alloys in applications where high specific strength and temperature and wear resistance are critical. However, the ductility of the matrix is very often negatively affected by the presence of the harder reinforcing phase and the existing production routes can be of high cost or difficult to implement either due to complex part design or the requirement for specialised equipment. Recently, the additive manufacturing technique known as laser-powder bed fusion (L-PBF) has proved a promising method for manufacturing MMCs as it promises to suppress several of the existing challenges concerning MMC production. The focus of this thesis is on the fabrication and characterisation of stainless steel 316L nanometre-scale silicon carbide and tungsten carbide reinforced MMCs, in an attempt to bring understanding and solutions to current issues concerning MMCs production and their integrity. Firstly, two aspects of L-PBF currently lacking in knowledge and that have implications on MMCs integrity were studied: assessment of part-properties dependency of on the printing location across the build platform in L-PBF, and identification of influencing factors and assessment of the optimal powder spreading conditions within the L-PBF system. Secondly a feedstock powder for L-PBF of MMCs, driven by the requirements of a homogeneous mixture and improve powder rheology, was developed and tested using the simple and cost effective route of powder metallurgy. Thirdly, the developed powder and the optimised parameters in the L-PBF of MMCs were examined. Lastly, a commercial L-PBF system was implemented to work with a colloid form of feedstock material, as well as powdered form, during the manufacturing of MMCs. Several relevant material characterisation techniques were utilised to assess the feedstock materials and the prepared samples so that meaningful scientific information could be obtained and detailed explanations of these results presented

    Evaluation of the thermal treatment effect on the entrapment of the powder in internal channels of PBF-LB parts

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    Additive manufacturing (AM) can be seen as a disruptive process that builds complex components layer upon layer. Two of its distinct technologies are Selective Laser Melting (SLM) and Electron Beam Melting (EBM), which are powder bed fusion processes that create metallic parts with the aid of a beam source. Two of the most studied and manufactured superalloys in metal AM are the Inconel 718 (IN718) and the Ti-6Al-4V. The former is commonly employed in the marine, nuclear power plants, gas turbines, and aerospace field due to its capacity of retaining good mechanical properties at high temperatures, while the latter is often used in the aerospace field due to its low density and high melting point, and in the biomedical area owing to its high corrosion resistance and excellent biocompatibility when in contact with tissues or bones of the human body. Nevertheless, the aforementioned alloys frequently require a post-processing heat treatment in order to enhance certain mechanical properties, modify the microstructure and reduce the residual stresses (RS), which are induced by thermal principles, as the gradient temperature is high because of the heating and thermal expansion upon the deposition of a new layer, and its subsequent cooling. Therefore, production errors in the components might occur due to geometrical distortion. Thus, it is mandatory to understand the expected orientation and magnitude of the RS in order to do accurate predictions of the final part properties. The initial goal of this dissertation was to evaluate the thermal treatment effect on the entrapment of IN718 powder in internal channels of laser beam powder beam fusion manufactured components. However, due to the current pandemic, Polito’s laboratories could only be used by researchers and PhD students. Having that constraint, I was advised, by Professor Francisco Silva, to write two review papers that would replace the experimental work of this thesis, being the first about residual stresses and heat treatments of Selective Laser Melted IN718 parts and the second about residual stresses and heat treatments of Electron Beam Melted and Selective Laser Melted Ti-6Al-4V components. From the first scientific paper one can conclude that the expected microstructure in the as-built state of the IN718 components is characterized by fine columnar grains and a saturated γ matrix with the presence of the Laves phase and carbides. This heterogeneous microstructure promotes unfavourable anisotropic mechanical properties, meaning that, for high and cyclic loads applications, heat treatments must be conducted. In addition, it was also shown that RS can be lowered by applying heat treatments and favourable printing parameters, i.e. high scanning speed and low laser power. Finally, from the second review paper, it can be concluded that that the expected asbuilt microstructure of the Ti–6Al–4V alloy is different in both manufacturing processes, mainly due to the distinct cooling rates. However, heat treatments can modify the microstructure, reduce RS, and increase the ductility, fatigue life, and hardness of the components. Furthermore, distinct post-treatments can induce compressive RS on the part’s surface, consequently enhancing the fatigue life.A manufatura aditiva pode ser vista como um processo disruptivo que cria componentes complexos camada após camada. Duas das suas tecnologias distintas são o derretimento seletivo em laser e a fusão por feixe de eletrões, que são processos de fusão em cama de pó que criam peças metálicas com o auxílio de feixe laser e eletrões, respetivamente. Algumas das superligas mais estudadas e fabricadas na manufatura aditiva de metais são o Inconel 718 e o Ti-6Al-4V. O primeiro é normalmente utilizado na marinha, centrais nucleares, turbinas a gás e no campo aeroespacial devido à sua capacidade de reter boas propriedades mecânicas a altas temperaturas, enquanto o último é frequentemente usado no campo aeroespacial devido à sua baixa densidade e alto ponto de fusão, e na área biomédica pela sua alta resistência à corrosão e excelente biocompatibilidade quando em contato com tecidos ou ossos do corpo humano. No entanto, as peças feitas das ligas anteriormente citadas frequentemente requerem um tratamento térmico após fabricadas a fim de potencializar certas propriedades mecânicas, modificar a microestrutura e reduzir as tensões residuais, que são induzidas por princípios térmicos, uma vez que o gradiente de temperatura é alto devido ao aquecimento e expansão térmica mediante a deposição de uma nova camada e o seu posterior arrefecimento. Portanto, podem surgir componentes com erros dimensionais derivados da distorção geométrica. Assim, é obrigatório entender a orientação esperada e a magnitude das tensões residuais de modo a fazer previsões precisas das propriedades da peça final. O objetivo inicial desta dissertação era avaliar o efeito do tratamento térmico no aprisionamento do pó IN718 em canais internos de componentes fabricados por derretimento seletivo em laser. No entanto, devido à atual pandemia, os laboratórios de Polito só podiam ser usados por investigadores e alunos de doutoramento. Tendo essa restrição, fui aconselhado, pelo Professor Francisco Silva, a escrever dois artigos de revisão bibliográfica que iriam substituir o trabalho experimental desta tese, sendo o primeiro sobre tensões residuais e tratamentos térmicos de peças de IN718 produzidas por derretimento seletivo em laser, e o segundo sobre tensões residuais e tratamentos térmicos de componentes de Ti-6Al-4V fabricados por fusão de feixe de eletrões e derretimento seletivo em laser. Do primeiro artigo científico pode-se concluir que a microestrutura esperada no estado as-built dos componentes do IN718 é caracterizada por grãos colunares finos e uma matriz γ saturada com a presença da fase Laves e carbonetos. Essa microestrutura heterogénea promove propriedades mecânicas anisotrópicas desfavoráveis, fazendo com que, para aplicações com cargas elevadas e cíclicas, sejam realizados tratamentos térmicos. Além disso, também foi mostrado que as tensões residuais podem ser reduzidas pela aplicação de tratamentos térmicos e parâmetros de impressão favoráveis, ou seja, alta velocidade de scan e baixa potência do laser. Finalmente, a partir do segundo artigo de revisão, pode concluir-se que a microestrutura as-built esperada da liga Ti–6Al–4V é diferente em ambas as tecnologias de fabrico, principalmente devido às distintas taxas de arrefecimento das mesmas. No entanto, os tratamentos térmicos podem modificar a microestrutura, reduzir as tensões residuais, aumentar a ductilidade bem como a vida à fadiga e dureza dos componentes. Além disso, pós-processamentos distintos podem induzir tensões residuais compressivas na superfície das peças e, consequentemente, aumentar a vida à fadiga das mesmas
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