Evaluation of grinding process using simultaneously MQL technique and cleaning jet on grinding wheel surface

In the last years, many researchers have proposed improvements to the minimum quantity lubrication (MQL) technique, in order to increase its efficiency and make it a viable alternative to the conventional application of cutting fluids for a cleaner machining. Besides the lubri-cooling effect inherent to the MQL technique, the cleaning of grinding wheel is pursued, since its surface undergoes the clogging phenomenon resulting in decreasing of the process performance. The main objective of this study is to assess the influence of the auxiliary wheel cleaning jet (WCJ) in an attempt to reduce the wheel clogging phenomenon and increase lubri-cooling and machining efficiencies in the cylindrical external grinding of AISI 4340 steel under the application of the MQL technique using aluminum oxide grinding wheel. The MQL combined with cleaning jet was compared to both flood application (conventional) and MQL without WCJ (traditional). MQL grinding employed oil flow rates of 30, 60 and 120 mL/h in order to evaluate the effects of amount of grinding fluid in the assessment. The conventional and MQL + WCJ methods produced lower surface roughness and roundness deviation compared to the other methods used due to the fact that they kept the wheel sharpness longer. Moreover, conventional and MQL + WCJ methods increased G ratio and reduced tangential grinding forces and specific energy in comparison to traditional MQL. The MQL + WCJ method enabled the removal of part of chips adhered on the grinding wheel active surface (GWAS) when compared to the traditional MQL, reducing the wheel clogging, which is one of the reasons for loss of wheel sharpness. Tubular chip form occurred not only in MQL + WCJ grinding but also in traditional MQL grinding, although it is not mentioned in literature.