Orthogonal cutting of titanium alloys

Abstract

A method, based on experimental information, of relating the energy required for the orthogonal cutting of titanium alloys with the chip geometry and the mechanical properties of the material, is discussed. The solution is obtained from the extension of the apparent strain analysis of orthogonal cutting of ductile materials to the case of less ductile materials which exhibit segmental chip formation. The apparent equivalent strain is defined as the strain which bounds an area under the equivalent stress-strain diagram equal to the total specific energy of the process, and includes the real strain experienced
by the material and a frictional component. The mean equivalent strain undergone by the material during deformation is found from this apparent equivalent strain, and the work done per unit volume of material removed in overcoming the total resistance to the movement of the chip at the tool face, thus itis unnecessary to define a model of chip formation. The mean equivalent strain is shown to be a smaller proportion of the apparent equivalent strain for titanium alloys than for ductile materials when cut under similar conditions. This agrees with observations of chip fcrmation which indicate fracture of the titanium alloy chips after limited plastic deformation. The mean equivalent strain in conditions of segmental chip formation is thus considered to represent the sum of plastic deformation and fracture energies. A practical method of determining the cutting ratio of segmental chips, as a ratio of areas before and after chip deformation, is described. Relationships are derived from the experimental information which enable the specific cutting energy and tool forces, during orthogonal cutting of titanium alloys, to be estimated from a simply determined cutting characteristic and the equivalent stressstrain diagram for the material. Good correlation is shown between the predicted trends and the measured values of cutting energy and forces. Also from the experimental work it is shown that the minimum values of specific cutting energy for titanium alloys occur
when the rake angle and undeformed chip thickness are largb.