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Advisor(s)
Abstract(s)
As ligas de titânio possuem uma combinação excelente de propriedades mecânicas como
elevada resistência à corrosão, baixa densidade, elevada resistência específica e baixo módulo
de elasticidade, o que as torna muito atrativas para a indústria aeroespacial. No entanto, este
tipo de ligas são muito difíceis de maquinar devido à sua baixa condutividade térmica, alta
reatividade química, alta dureza, o que implica que as ferramentas necessitem de possuir
características específicas para conseguirem maquinar e ter um tempo de vida útil que seja
rentável para o processo. Estas ligas são, portanto, ligas designadas como materiais difíceis de
maquinar. Os materiais base convencionais para fabrico de ferramentas de corte, como o aço
rápido, não têm a capacidade de manter a dureza e outras propriedades mecânicas quando
submetidos a elevadas velocidades de corte. No entanto, verificou-se que o uso de
revestimentos duros sobre a superfície das ferramentas de corte permitem melhorar o seu
desempenho, aumentar a rentabilidade do processo e a qualidade da superfície das peças
maquinadas. Assim, o objetivo desta dissertação consiste em avaliar o comportamento ao
desgaste de fresas revestidas pela empresa Inovatools, durante a maquinagem de ligas de
titânio. O tempo de vida das ferramentas foi avaliado, variando a velocidade de corte, variando
comprimento de corte e avanço por dente. Após a realização dos ensaios de maquinagem, foi
analisada a rugosidade da superfície da peça maquinada, avaliado o desgaste da ferramenta,
caracterizados os mecanismos de desgaste e determinado o tempo de vida da ferramenta. Foi
constatado que o avanço por dente tem uma forte influência no desgaste das fresas e na
rugosidade superficial da peça maquinada. Quanto maior é este parâmetro pior é a qualidade
da superfície e maior o desgaste da ferramenta. Também se verificou que com o aumento do
comprimento de corte a qualidade superficial diminui e o desgaste aumenta gradualmente,
independentemente do valor de velocidade de corte. Relativamente aos mecanismos de
desgaste identificados, predominantemente, o desgaste é abrasivo. Observou-se também
desgaste adesivo, principalmente para maiores valores de avanço por dente, em que as fresas
apresentaram muitas aparas, contribuindo para a aderência ao substrato. Quanto à vida útil da
ferramenta, foi observado que quanto maior a velocidade de corte, maior o desgaste,
principalmente para maiores valores de comprimento de corte e, consequentemente, menor a
vida útil da ferramenta. Assim, o parâmetro que teve maior influência na vida útil da
ferramenta, para além do comprimento de corte, foi a velocidade de corte.
Titanium alloys have an excellent combination of mechanical properties such as high corrosion resistance, low density, high specific strength and low modulus of elasticity, which makes them very attractive for the aerospace industry. However, these types of alloys are very difficult to machine due to their low thermal conductivity, high chemical reactivity and high hardness, which means that the tools need to have specific characteristics in order to be able to machine and have a useful life that is profitable for the process. These alloys are therefore designated as difficult-to-machine materials. Conventional base materials for manufacturing cutting tools, such as high-speed steel, do not have the ability to maintain hardness and other mechanical properties when subjected to high cutting speeds. However, it has been found that the use of hard coatings on the surface of cutting tools allows for improved performance, increased process profitability and the surface quality of machined parts. Thus, the objective of this dissertation is to evaluate the wear behavior of milling cutters coated by the company Inovatools, during the machining of titanium alloys. The tool life was evaluated, varying the cutting speed, cutting length and feed per tooth. After performing the machining tests, the surface roughness of the machined parts were analyzed, tool wear was evaluated, the wear mechanisms were characterized and the tool lifetime was accessed. It was found that the feed per tooth has a strong impact on the wear of the milling cutters and on the surface roughness of the machined parts. The higher this parameter is, the worse the surface quality and the greater the tool wear are. It was also found that with the increase in the cutting length, the surface quality decreases; and the wear gradually increases, regardless of the cutting speed used. Regarding the wear mechanisms, the predominant wear abrasive wear. Adhesive wear was also observed, especially when the feed rate per tooth was higher, in which the cutters presented many chips, contributing to their adhesion to the substrate. Regarding tool life, it was found that the higher the cutting speed, the greater the wear, especially for higher cutting length values and, consequently, the shorter the tool lifetime. Thus, the parameter that had the greatest influence on tool life, besides cutting length, was cutting speed.
Titanium alloys have an excellent combination of mechanical properties such as high corrosion resistance, low density, high specific strength and low modulus of elasticity, which makes them very attractive for the aerospace industry. However, these types of alloys are very difficult to machine due to their low thermal conductivity, high chemical reactivity and high hardness, which means that the tools need to have specific characteristics in order to be able to machine and have a useful life that is profitable for the process. These alloys are therefore designated as difficult-to-machine materials. Conventional base materials for manufacturing cutting tools, such as high-speed steel, do not have the ability to maintain hardness and other mechanical properties when subjected to high cutting speeds. However, it has been found that the use of hard coatings on the surface of cutting tools allows for improved performance, increased process profitability and the surface quality of machined parts. Thus, the objective of this dissertation is to evaluate the wear behavior of milling cutters coated by the company Inovatools, during the machining of titanium alloys. The tool life was evaluated, varying the cutting speed, cutting length and feed per tooth. After performing the machining tests, the surface roughness of the machined parts were analyzed, tool wear was evaluated, the wear mechanisms were characterized and the tool lifetime was accessed. It was found that the feed per tooth has a strong impact on the wear of the milling cutters and on the surface roughness of the machined parts. The higher this parameter is, the worse the surface quality and the greater the tool wear are. It was also found that with the increase in the cutting length, the surface quality decreases; and the wear gradually increases, regardless of the cutting speed used. Regarding the wear mechanisms, the predominant wear abrasive wear. Adhesive wear was also observed, especially when the feed rate per tooth was higher, in which the cutters presented many chips, contributing to their adhesion to the substrate. Regarding tool life, it was found that the higher the cutting speed, the greater the wear, especially for higher cutting length values and, consequently, the shorter the tool lifetime. Thus, the parameter that had the greatest influence on tool life, besides cutting length, was cutting speed.
Description
Keywords
Milling Titanium alloys Cutting tools Aerospace engineering applications Fresagem Ligas de titânio Ferramentas de corte Aplicações de engenharia aeroespacial