Retificação do aço ABNT 4340 endurecido com geometria interrompida sob condição de refrigeração convencional e otimizada utilizando rebolo de óxido de alumínio com ligante resinoide e vitrificado
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Data
2017-07-28
Autores
Mello, Hamilton José de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A busca por melhorias no processo de usinagem é cada vez maior, principalmente no que diz respeito aos procedimentos finais de corte, como a retificação. Isso porque tais técnicas é que irão garantir, na maioria das vezes, os parâmetros tão desejados no produto final, como tolerâncias dimensionais e geométricas, além da rugosidade. Especificamente no campo da retificação, muito já se avançou com o desenvolvimento de métodos de dressagem de rebolos, de lubrirrefrigeração e outros mais. Todavia, todos estes progressos foram conseguidos apenas no que diz respeito ao corte contínuo. Nesse sentido, torna-se necessário o estudo de todos estes parâmetros no processo de retificação por corte interrompido (peça com ranhuras), pois pouco, ou mesmo nenhum conhecimento e/ou estudo foi desenvolvido com este enfoque, visto que não é encontrado material algum na literatura formal, salvo aqueles em que o rebolo é o detentor das ranhuras. Na retificação, o calor gerado na zona de corte é extremamente elevado e o uso de fluidos de corte se faz indispensável para que seja possível refrigerar tanto a peça quanto o rebolo. O uso adequado dos fluidos implica em melhorias na operação de corte, propiciando uma maior produtividade, e, por isso, o mais comum é a utilização de fluido em abundância, tendo em vista que os agentes de arrefecimento e lubrificação são capazes de proporcionar uma retificação muito satisfatória, sem que haja quaisquer danos térmicos. Portanto, a presente tese teve o propósito de estudar o processo de retificação cilíndrica externa de mergulho do aço ABNT 4340, temperado e revenido com dureza média de 54 HRC com corte descontínuo (no qual o corpo de prova é que possui os entalhes) sob aplicação de refrigeração abundante e de alta pressão. Os rebolos que foram utilizados são do tipo convencional de óxido de alumínio, com ligante vitrificado e outro com ligante resinoide. A análise dos resultados foi feita através da avaliação das variáveis de saída do processo de retificação, tais como: comportamento de força tangencial de corte, rugosidade, desvios de circularidade, emissão acústica, desgaste diametral do rebolo, microscopia óptica e microdureza.
The search for improvement in the process of machining is always increasing, especially in regards to the final cutting procedures, like grinding. That is because such techniques will guarantee, most of the time, the much desired parameters of the final product, such as dimensional and geometric tolerances, besides surface roughness. Specifically in the field of grinding, there has been much advancement with the development of grinding wheel dressing methods, lubrication and cooling and more. However, all this progress was obtained only when it comes to continuous cutting. In that sense, it becomes necessary to study all these parameters in the process of interrupted cutting in grinding (workpiece with grooves), since little to no knowledge and/or study was developed with that focus, seeing that no material is found in the formal literature, except for that in which the grinding wheel is the element with grooves. In grinding, the heat generated in the cutting zone is extremely high and the use of cutting fluids becomes indispensable to allow the cooling of both workpiece and grinding wheel. The adequate use of cutting fluids brings improvements in the cutting operation, providing higher productivity, and, because of that, the most usual technique is to use abundant cutting fluids, seeing that the cooling and lubrication agents are capable of providing a much more satisfactory grinding, without the occurrence of thermal damage. Therefore, the present thesis held the purpose of studying the process of external cylindrical grinding of the ABNT 4340 steel, quenched and tempered with an average hardness of 54 HRc in discontinuous grinding (in which the workpiece is the element with grooves) under application of abundant and high pressure cooling. The grinding wheels used were conventional aluminum oxide wheels, one with vitrified bond and the other with resin bond. The analysis of the results was made through the evaluation of the output variables of the grinding process, such as: behaviour of tangential cutting force, surface roughness, circularity deviations, acoustic emission, diametrical wear of grinding wheel, optic microscopy and microhardness of the workpiece.
The search for improvement in the process of machining is always increasing, especially in regards to the final cutting procedures, like grinding. That is because such techniques will guarantee, most of the time, the much desired parameters of the final product, such as dimensional and geometric tolerances, besides surface roughness. Specifically in the field of grinding, there has been much advancement with the development of grinding wheel dressing methods, lubrication and cooling and more. However, all this progress was obtained only when it comes to continuous cutting. In that sense, it becomes necessary to study all these parameters in the process of interrupted cutting in grinding (workpiece with grooves), since little to no knowledge and/or study was developed with that focus, seeing that no material is found in the formal literature, except for that in which the grinding wheel is the element with grooves. In grinding, the heat generated in the cutting zone is extremely high and the use of cutting fluids becomes indispensable to allow the cooling of both workpiece and grinding wheel. The adequate use of cutting fluids brings improvements in the cutting operation, providing higher productivity, and, because of that, the most usual technique is to use abundant cutting fluids, seeing that the cooling and lubrication agents are capable of providing a much more satisfactory grinding, without the occurrence of thermal damage. Therefore, the present thesis held the purpose of studying the process of external cylindrical grinding of the ABNT 4340 steel, quenched and tempered with an average hardness of 54 HRc in discontinuous grinding (in which the workpiece is the element with grooves) under application of abundant and high pressure cooling. The grinding wheels used were conventional aluminum oxide wheels, one with vitrified bond and the other with resin bond. The analysis of the results was made through the evaluation of the output variables of the grinding process, such as: behaviour of tangential cutting force, surface roughness, circularity deviations, acoustic emission, diametrical wear of grinding wheel, optic microscopy and microhardness of the workpiece.
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Palavras-chave
Retificação cilíndrica, Corte interrompido, Aço ABNT 4340, Fluido de corte, Refrigeração, Cylindrical grinding, Interrupted cutting, ABNT 4340 steel, Cutting fluid, Cooling