The Metal Cutting Process as a Means of Studying the Properties of Extreme Pressure Lubricants

Abstract

AbstractThe cutting of metals by a single point tool involves two main problems of interest to physicists and engineers, namely, the plastic deformation and failure of metals and the friction and wear of sliding surfaces. The material in front of a cutting tool is removed by a process of shear, and fundamental studies of the strength of materials in the fields of solid state physics, engineering plasticity, and physical metallurgy are pertinent to this phase of the cutting process. The material that is detached from the workpiece moves in sliding contact up the face of the cutting tool. The surface of the sliding metal chip is subjected to very high stress, for the entire cutting force is transmitted from the tool to the work material across this surface. The basic principles established by workers in the fields of friction, wear, and lubrication are directly applicable to this second phase of the cutting process. In the present paper, the interrelationship between the shearing and sliding phases of cutting is considered, but only the sliding and frictional aspects of the process are discussed in detail.The cutting process offers a convenient means for studying the frictional properties of metals in sliding contact. By measuring the horizontal and vertical components of force on the tool and the ratio of the length of chip to length of cut, the coefficient of friction between the tool and the chip may be determined. A simple two component force dynamometer is described which enables the coefficient of friction to be determined. Friction data obtained from this dynamometer for specimens of commercially pure aluminum sliding across a hard steel surface in the presence of carefully purified short chain length saturated and unsaturated chlorinated hydrocarbons are presented and discussed. The chemical reactivity of several of the aluminum‐fluid combinations is presented as determined by noting the time required for a chemical reaction to set in when aluminum is kept in contact with the fluid at an elevated temperature. General agreement is seen to exist between the relative reactivity of a fluid toward aluminum and its frictional performance when used in the cutting of aluminum. It is found that cutting fluids in the gaseous state may be equally as effective as those applied in the liquid state. These observations tend to substantiate the view that fluids are effective lubricants in the extreme region of boundary lubrication, embracing metal cutting by virtue of their ability to react chemically with the chip metal to form a low shear strength solid lubricant. Other frictional data for aluminum cut in conjunction with representative members of a number of homologous series are presented and discussed.The paper is concluded by a brief discussion of the inherent advantages of the two dimensional cutting process as a means for studying the frictional characteristics of sliding metal surfaces.