Some critical issues in cryo-grinding by a vitrified bonded alumina wheel using liquid nitrogen jet

Beneficial effects of liquid nitrogen (LN2) as a metal working fluid (MWF) in high speed machining applications are well recognized. However, adequate attention is not given on possible deleterious effects because of its extremely low boiling point. In the present work, an in-depth investigation has been carried out to explore pros and cons of LN2 application when a vitrified bonded Al2O3 wheel was used for grinding hardened AISI 52100 steel. It was observed that LN2 application in place of soluble oil could substantially enhance G-ratio. Although, this observation is in agreement with the reported literatures, the other findings contradicted the notion that cryogenic application is favorable for grinding. Unlike under soluble oil environment, the vitrified bonded wheel failed to produce a good finish when LN2 was used. There were evidentially more number of microscopic zones having smeared, re-deposited chips and micro-folded ridges on ground surface. Interestingly, larger wear flat areas on wheel topography were observed under LN2 environment. When critically investigated, it was found that its extremely low temperature unfavorably strengthened bond, which led to undesirable retention of progressively wearing grits. Such an unfavorable alteration in wheel topography led to higher power consumption in the process. Additionally, ground specimen suffered from higher dimensional inaccuracy. Microscopic morphology of chips indicated prevalence of low temperature in the vicinity of grinding zone under this environment but interestingly the ground specimen experienced unfavorably more tensile residual stress with LN2 than with soluble oil.