Estudo do desempenho de ferramentas de aço-rápido na usinagem criogênica do aço ABNT 1020

Abstract

This work presents a study about the performance of HSS cutting tools when turning an ABNT 1020 steel under cryogenic condition using liquid nitrogen (LN2) applied onto the cutting region. In this case, the main purpose was to keep the cutting tool temperature below the softening temperature of the HSS (normally above 650oC) improving the performance of these cutting tools at cutting speeds upper than that normally used in dry or wet conventional machining. A series of rapid facing trials was carried out at dry (SECO) and applying LN2 at three different points on the cutting region [on the rake face (SS), on the flank face (SF) and on the rake and flank faces simultaneously (SS/SF)]. It could be verified that the use of LN2 the cutting was able to machine cutting speeds higher than at dry condition. When the LN2 was applied onto the rake and flank face simultaneously, the cutting speed showed an increase of 35% (on average) compared to the dry condition; when the LN2 was applied only onto the flank face, the improvement was of 24,12% and of 20,94% for the LN2 applied only onto the rake face. These results showed that the use of LN2 tended to improve the performance of the trialled HSS cutting tools and this improvement was more effective when the LN2 was applied onto the rake and flank faces simultaneously. For the variable called “failure point” (point where the cutting tool collapsed) a statistical analysis showed no difference among the conditions (SECO-SF), (SECO-SS), (SS-SF) and (SF-SS/SF). However, it could be observed statistical differences between the conditions (SECO-SS/SF) and the conditions (SS-SS/SF) when they are compared two by two. Compared to the dry condition, the results of average roughness (Ra) showed a tendency to drop when LN2 was applied. Additional longitudinal turning trials were carried out to verify the performance of the HSS cutting tools assisted by LN2 at this condition. It was observed an improvement upper to 100%.