The effect of cutting fluids on the machining of hardened AISI 4340 steel

The knowledge over the performance of cutting fluids when applied to different work materials and operations is of crucial importance in order to improve the efficiency of most conventional machining processes. This efficiency can be measured, among other parameters, through cutting tool life and workpiece surface finish. However, the costs associated with the purchase, handling and disposal of cutting fluids are leading to the development of tool materials and coatings which do not require their application. In this work, the performance of three types of cutting fluids (two emulsions and one synthetic fluid) were compared to dry cutting when continuous turning hardened AISI 4340 steel (49 HRC) using mixed alumina inserts. The following parameters were evaluated: tool life, surface finish, tool wear mechanisms and chips form. The results indicated that, in general, the emulsion-based fluid (without mineral oil) and dry cutting gave the best results followed by synthetic fluid and emulsion containing mineral oil, both presenting similar results.