The Influence of Lead on Metal-Cutting Forces and Temperatures

The effects of additions of lead and sulphur to steel upon tool-face friction F, cutting energy per unit volume u, and tool-face temperature $θ¯t$ were investigated. By means of high-speed flash pictures of chips in the process of being formed, it was found that lead was effective in decreasing chip thickness at all speeds, but particularly at high speeds. Sulphur, on the other hand, was found most effective in this regard at tool temperatures (speeds) below about 900 F. It was found that certain cutting fluids (principally cutting oils) interfered with the action of lead and sulphur, and fluids that are normally effective on ordinary steels may give poorer results than air upon steels containing lead or sulphur. In all cases leaded steels were found to give lower values of F, u, and $θ¯t$ than comparable nonleaded steels and the improvement due to lead was far greater than could be achieved from cutting fluids at speeds of 150 fpm and above. The paper ends with a note of warning that the results on F, u, and $θ¯t$ cannot be used to predict tool life directly and an example is presented which illustrates this point.