Machinability of Lead-Free Brass Alloys with Cryogenic Minimum Quantity Lubrication

Due to the harmfulness of lead to humans and the environment and due to legal requirements, the brass processing industry is increasingly switching to lead-free materials. As lead improves the machining performance by reducing the cutting temperature as well as inducing chip breakage, manufacturing faces additional challenges. Higher temperatures cause a shorter tool life which in turn increases production cost and has a negative impact on the energy efficiency of the process. This investigation discusses and compares the cooling strategies of flood cooling and cryogenic cooling, with and without minimum quantity lubrication (cMQL), in terms of process temperature and cutting forces, to address this issue. The cutting temperature is measured directly at the cutting edge by means of a three-dimensional coating structure of the cutting insert which enables a thermocouple-like function. In an additional set of experiments, liquid carbon dioxide (LCO 2 ) is applied in high-frequency pulses to facilitate chip breakage by short impulses onto the chip creation zone while also cooling the tool. The results highlight that the lowest cutting temperature is achieved by cMQL. However, this improved alternative cooling strategy also leads to the creation of longer chips. While the chip length is effectively influenced by the high frequency LCO 2 pulses, this strategy must be optimized to achieve a satisfying minimal chip length.