Browsing by Author "Silva, Francisco José Gomes da"
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- A comparative study of heat-treatment effects on high-strength ductile cast irons weldmentsPublication . Silva, Francisco José Gomes da; Sousa, V. F. C.; Pereira, A. B.; Fecheira, J. S.Ductile cast irons have known significant developments, closely following the evolution in mechanical strength recorded in other metal alloys. In fact, the chemical composition and treatments that ductile cast irons can currently be subjected to, give them mechanical strength far superior to the ductile cast irons that existed three decades ago, with rupture stresses in the order of 500 MPa and even higher. These properties combined with the fact that it is easy to manufacture parts with an almost final shape, makes these alloys highly sought after in some types of industry, such as the automotive industry. Due to the high content of carbon and other alloy elements with identical effects, welding is not a process that is seen as viable for the manufacture of parts in this type of alloys. However, the same is no longer the case in terms of repair, where welding can play a key role. Through a comparative study, this work intends to show that there is no single way to improve the mechanical properties in the welding of this type of alloys, and that each alloy should be properly studied in order to obtain the best results. In this case, the heat treatments applied to ductile cast iron with an ultimate tensile strength of 450 MPa and 700 MPa from the same manufacturer are compared, making it clear that to achieve the best results in terms of mechanical resistance, it is necessary to follow different routes, that is, choose to preheating or post-heating treatments, depending on the microstructure of the alloy used. Thus, the results obtained intend to show the mechanisms in which treatment is actually acting on the alloy, promoting greater efficiency of the joint and having been achieved interesting results at this level.
- Cutting Forces Assessment in CNC Machining Processes: A Critical ReviewPublication . Sousa, Vitor F. C.; Silva, Francisco José Gomes da; Fecheira, José S.; Lopes, Hernâni M. L; Martinho, Rui Pedro; Casais, Rafaela B.; Ferreira, Luís PintoMachining processes remain an unavoidable technique in the production of high-precision parts. Tool behavior is of the utmost importance in machining productivity and costs. Tool performance can be assessed by the roughness left on the machined surfaces, as well as of the forces developed during the process. There are various techniques to determine these cutting forces, such as cutting force prediction or measurement, using dynamometers and other sensor systems. This technique has often been used by numerous researchers in this area. This paper aims to give a review of the different techniques and devices for measuring the forces developed for machining processes, allowing a quick perception of the advantages and limitations of each technique, through the literature research carried out, using recently published works
- Estudo da otimização do cabo metálico na produção de Bowden CablesPublication . Silva, Francisco José Gomes da; Koch, Luís Pedro MoreiraHoje em dia, mais do que nunca, num mercado cada vez mais global e competitivo, as organizações necessitam de estar constantemente à procura da inovação, do aumento da qualidade dos seus produtos, assim como da produtividade global dos seus processos. A pandemia de COVID-19 veio aumentar esta obrigatoriedade pela melhoria contínua. O setor automóvel é caracterizado como sendo uma das áreas de negócio mais competitivas e que se encontra em constante evolução. Assim sendo, procurar o desenvolvimento de produtos da mais alta qualidade e maximizar os lucros é essencial para uma organização sobreviver e prosperar no mercado, o que pode ser alcançado através da eliminação dos desperdícios existente ao longo do fluxo produtivo. Para se obter as melhorias pretendidas, a metodologia usada foi o Six Sigma, onde se utilizou o ciclo DMAIC, assim como certas ferramentas Lean. Na revisão bibliográfica, fez-se inicialmente uma introdução ao setor automóvel, destacando a sua importância a nível global, bem como as principais dificuldades que este setor está a enfrentar; fez-se uma revisão da metodologia Six Sigma, destacando o ciclo DMAIC e, por fim, foi abordada a filosofia Lean Manufacturing. O presente trabalho foi desenvolvido na empresa Fico Cables, especializada na produção de componentes para automóveis e teve como principal objetivo a redução ou eliminação da ponta de cabo na operação de aparar nas linhas de produção, uma vez que a empresa apresentava anualmente milhares de metros de cabo desperdiçado. Após chegar à conclusão sobre quais os fatores que permitiriam a eliminação e diminuição do aparado de cabo das linhas de montagem, foram definidas e implementadas ações de melhoria. Com as ações implementadas, obteve-se um ganho anual de cerca de 89 289 € e, até aproximadamente 2026, será obtido um ganho de 288 343 €, tendo sido eliminado o aparado em cinco linhas de montagem, diminuindo se igualmente o aparado em oito linhas de montagem.
- Handbook of Welding: Processes, Control and SimulationPublication . Pereira, António Manuel de Bastos; Silva, Francisco José Gomes daFrom conventional welding techniques to electron or laser beam, this book provides a comprehensive overview about processes, metallurgy, quality assessment, testing, and numerical simulation in welded structures.
- Mechanical strength of thermoplastics and composite thermoplastics welded by laser – a reviewPublication . Pereira, A. B.; Fernandes, F. A. O.; Silva, Francisco José Gomes daThermoplastic welding is currently well implemented in the market, with several competitive and suitable processes, ranging from simple hot plate to ultrasonic welding. By its side, laser welding of plastics is still in a relatively early stage of research. This process is one of the most recent in the welding of thermoplastics and of great interest in the market. The welding technique is based on heating the thermoplastics by transmitting heat in the form of radiation. This is due to the ability of certain plastics to absorb the beam. Usually, one of the parts to be welded must be transparent and the other opaque to radiation. These two parts are kept under pressure as the laser beams are transmitted through the transparent part. The laser beam is concentrated in the joint area of the opaque part, heating and melting it. There are relatively few scientific studies on the joining of thermoplastics by laser and, in the case of thermoplastic matrix composites, there are even fewer. The main conclusion is that the mechanical strength of a laser welded joint is in the range of 30-50 MPa, a value that is frankly weak when compared to the value that the base material can handle and which is usually more than double for thermoplastics and 10 times for composites. Although the fusion process is contactless, one of the great limitations of laser welding of plastics is the need to exert pressure on the joint, which conditions and complicates the execution of a weld. However, despite everything, it is certain that laser welding presents mechanical strength values superior to those of a bonded connection and the processing time is much shorter, therefore, it is clear the interest on the process.
- Recent Advances in WeldingPublication . Silva, Francisco José Gomes da; Pereira, António Manuel de BastosWelding is a conventional joining process that has followed the recent developments in other manufacturing processes, continuing to be an extremely used and investigated process. Several technologies developed in other areas of knowledge have converged in the area of welding, allowing significant improvements in the quality of the products obtained and in the increased productivity of the processes. Although some techniques have been implemented and studied for several decades, the interest of researchers in welding has not diminished, as it can be seen through new processes that have emerged, such as Friction Stir Welding, in addition to many other notable developments in welding processes which apparently seemed to have reached their final stage of maturity. This work brings together a set of very interesting works, being a living proof that welding continues to be heavily investigated and that the developments around this manufacturing process are constantly emerging. Because the materials continue to evolve and the technology around welding also continues to develop at a very good pace, studies on the weldability of new materials and the application of new techniques and technologies to already well known welding processes does not stops happening. The editors are proud to have collected this set of works that can help scholars and researchers to broaden their knowledge in the field of welding, thus contributing to the creation of a knowledge base that allows researchers to start new investigations and achievements in the coming decades.
- Recent developments on friction stir welding of aluminium alloys: a comprehensive reviewPublication . Silva, Francisco José Gomes da; Pereira, A. B.; Fecheira, J. S.; Sousa, V. F. C.Friction stir welding is a relatively new joining technology, that has been succefuly applied in the connection of large and complex structures, with considerable progress being made throughout time. The development of this new solid-state welding technique has opened up new possibilities for joining similar and dissimilar materials, allowing the obtention of extremely interesting mechanical properties. This welding technique becomes even more interesting when applied to materials that are traditionally considered difficult to weld by conventional fusion methods. As it is well known, despite the fact that aluminum alloys have a low melting point, these are difficult to weld due, mainly, to their high thermal conductivity, requiring relatively high amounts of energy, wich can interfere with the low melting temperature of the alloys. Thus, numerous studies have been carried out around the Friction Stir Welding (FSW) process in various different alloys, however, given the intensive use of aluminum alloys in the most diverse sectors, these have deserved special attention by the researchers. In this chapter, the welding of different aluminum alloys with different process parameters and their influence on mechanical property of the joints are analyzed. This review intends to describe, in a structured way, the most recent developments around FSW of aluminium alloys, with special attention given to the microstructure and mechanical properties of the joints obtained by this process, as well as the parameters able to achieve the best joint properties.