Machinability of Leaded Brass

The function of lead included in free cutting brass has not been realized closely, although it is widely known that the existence of lead improves the machinability considerablly. The object of the experiment is to clarify the mechanisms how the lead within brass contributes to the machinability, to compare the behavior with that of a cutting fluid supplied from outside and to find out the optimum amount of lead for the best machinability in terms of cutting force and chip formation.The experiment has revealed that the lead not only acts as a lubricant at the tool-chip interface, but it causes the localization of stress or strain ahead of the tool, which results in the reduction of the tool-chip contact area. Besides, an apparent difference of the lubricating manner from that of cutting fluids supplied from outside is that the lead lowers the frictional stress on the rake face uniformly all over the tool-chip interface while the cutting fluids cannot enter the region near the cutting edge, nor can they reduce the frictional stress of the region.