Vibration analysis of cutting force in titanium alloy milling

Machining processes such as milling, which are characterized by interrupted cutting, are often susceptible to problems involving vibration of the machine-tool-workpiece fixation device system because of the proximity between their natural frequency harmonics and the frequency of tool entry on the workpiece. This phenomenon is particularly important in the milling of titanium alloys, because these materials show a low Young modulus, and hence, an extended elastic behavior, which means tremendous variations in chip thickness and fluctuating cutting forces. Moreover, very low heat conductivity causes the formation of serrated chips, which further increase the fluctuation in cutting forces. The purpose of this work is to study the influence of the tool entering angle on the stability of the process and on tool life based on a time and frequency domain analysis of the cutting forces. The results show that lower entering angles may provide stabler cutting, as indicated by the regular tool wear instead of the microchipping resulting from the use of a higher value of this angle. Although cutting forces are larger at lower entering angles, the tool life is much longer, since most of this load is associated with low frequencies, at which the tool behaves like a rigid body.