The Role of Oxygen in Orthogonal Machining of Metals

This chapter presents an experimental investigation of the metal cutting tribology with the purpose of re-examining the role of oxygen in the process mechanics and obtaining a better understanding of the friction coefficient in terms of the major process parameters. Specially designed apparatus and tribological tools have been used to cut pure metals and metallic engineering materials under oxygen-rich surrounding medium. Friction coefficient has been evaluated, and the chip–tool interface has been observed in situ using optical microscopy. It has been shown that pressure-welded junctions occur near the point at which chip detaches from cutting tool, and it has been established that there is an intimate relation between the oxide films formation and the oxygen concentration in the surrounding medium. The chip curl, sticking and sliding zones were seen to change with oxygen concentration. It can be asserted that friction plays an important role in the free plastic flow of metal cutting due to the high friction coefficient values ranging from 0.3 to 1, or even higher. However, the main research contribution of this study is the remark of the friction coefficient as a function of the process parameters, rather than a constant numeric value representing complex phenomena at the contact interface between the chip and the cutting tool.