Influence of cutting fluids on the performance of the micro milling process of tool steel

Direct milling of micro structured parts becomes more important due to its inherent advantages, such as the possibility to machine three- dimensional geometrical structures over a wide range of materials in low production volumes. Despite micro milling being an issue for increased research in the past years, processes still lack of reliability and stability. Moreover, factors exerting a critical influence on conventional machining processes, such as cutting fluids, have not been regarded in detail in micro milling operations. Thus, the main purpose of this work is to investigate the mode of action of different cutting fluids and to deduct its influences on main process response variables. A profile is developed which reflects those properties of cutting fluids required to cope best with the specifications, requirements and demands of the micro milling process. It could be clearly shown that oil based coolants are superior to water based systems in micro milling. It can be concluded that the lubrication effect of the fluid has a higher importance and that strong cooling properties even lead to an increased wear rate of the tool. Flushing away chips of the cutting zone is a major function of the cutting fluid and can be achieved by minimum quantity lubrication. An optimum viscosity is low enough to enable the entrance into the cutting zone and ease the chip transport but high enough to remain in the cutting zone in order to reach sufficient lubrication properties. Cutting fluids with moderate specific heat, heat of vaporization, thermal conductivity and thermal capacity should be used to restrict its cooling action. Constrained space in micro milling applications demands the use of tailor-made solutions of cutting fluid methods of application. Complex loading exerted normal to the cutting tool during a micro milling process may make the delivery of a cutting fluid necessary, particularly at the interface between the tool clearance face and the newly cut machined surface.