ABSTRACT Flow drilling process produces bushes for removable joints that can be threaded by forming tapping process, reducing stages in production of components of automobile industry and in construction sheds. High strength and low alloy steels (HSLA) are employed on several applications in the processing industry. Benefits provided by these materials make them an efficient solution, since their high cold resistance allows reducing weight on structures, as well as maintaining the required mechanical properties. The present study evaluated the conventional and friction drilling processes in HSLA steel sheets with a thickness of 4.25 mm. Specimens were subjected to cyclic loadings, with no rework after holemaking, so the resultant characteristics of each process were maintained. Fractured surfaces were analyzed with a scanning electron microscope (SEM) to identify the fracture mechanism in different drilling processes. Fractographies obtained on both processes indicated that the failure mechanism occurred due to ductile fracture resulting from the nucleation, growth and coalescence of micro cavities.

RESUMO O processo de furação por escoamento produz buchas para uniões removíveis que podem ser roscadas pelo processo de rosqueamento por conformação, reduzindo etapas da produção de componentes da indústria automobilística e em galpões da construção civil. Aços de alta resistência e baixa liga (ARBL) são empregados em variadas aplicações na indústria de transformação. Os benefícios proporcionados por tais materiais tornam-se uma solução eficiente, pois sua alta resistência a frio possibilita a redução de peso em estruturas, além de manter as propriedades mecânicas requeridas. O presente estudo avaliou os processos de furação convencional e por escoamento em chapas de ARBL com 4,25 mm de espessura. Modelos de corpos de prova foram submetidos a carregamentos cíclicos, sem sofrer retrabalho após o furo, mantendo as características resultantes de cada processo. As superfícies fraturadas foram analisadas com microscópio eletrônico de varredura (MEV) para identificar o mecanismo de fratura nos diferentes processos de furação. As fractografias obtidas em ambos os processos indicaram que o mecanismo de falha ocorreu por fratura dúctil resultante da nucleação, crescimento e coalescência de microcavidades.

ABSTRACT Flow drilling process produces bushes for removable joints that can be threaded by forming tapping process, reducing stages in production of components of automobile industry and in construction sheds. High strength and low alloy steels (HSLA) are employed on several applications in the processing industry. Benefits provided by these materials make them an efficient solution, since their high cold resistance allows reducing weight on structures, as well as maintaining the required mechanical properties. The present study evaluated the conventional and friction drilling processes in HSLA steel sheets with a thickness of 4.25 mm. Specimens were subjected to cyclic loadings, with no rework after holemaking, so the resultant characteristics of each process were maintained. Fractured surfaces were analyzed with a scanning electron microscope (SEM) to identify the fracture mechanism in different drilling processes. Fractographies obtained on both processes indicated that the failure mechanism occurred due to ductile fracture resulting from the nucleation, growth and coalescence of micro cavities.