Influence of Chip Serration Frequency on Chatter Formation During End Milling of Ti6Al4V

Abstract

This paper iticludes the findings of an experitnental study on instabilities of the chip formation process during end milling ofTi6Al4V alloy and the infiuence of these instabilities on chatter formation. It has been identified that the chip formation process has a discrete nature, associated with the periodic shearing process during machining. The chip formed during machining of titanium alloy TÍ6A14V is found to be mainly with primary serrated teeth appearing in the main body of the chip. Secondary .serrated teeth resulting from the coagulation of a certctin number of primary serrated teeth also happen to appear at the free or constrained edge of the chip, especially when the .nstetn enters into chatter. In order to identify the interaction of these chip instabilities with the prominent natural vibration of the machine tools system components, the different mode frequencies of the vibrating components of the system have been identified using experimental atid finite eletnent modal atialyses, and vibration responses during actual cutting have also been recorded using an online vibration tnonitoring system. The vibration signals in frequency domain (fast Fourier transform) have been atiahzed to identify the chatter frequencies and the peak amplitude values. Chatter was found to occur at two domitiant mode frequencies of the spindle. These mode frequencies at which chatter occurred have been compared with the chip serration frequencies in a wide cutting speed range for different conditions of cutting. It has been concluded from these findings that chatter occurs during end milling due to the resonance of the machine tools system component when the frequeticy of primary .serrated teeth formation is approximately equal to the "prominent natural frequency" modes of the system components, which are the two mode frequencies of the VMC machine spitidle in this particular case.

Metallurgical Analysis of Chip Forming Process when Machining High Strength Bainitic Steels

“…High frequency signal analysis showed that the amplitudes of the serration signal varied widely, i.e., from 5 N to several hundred newtons. These large amplitudes may be the result of resonance phenomena [19]. Anayet Ullah Patwari et al observed that with the increase of the cutting speed, the natural frequency of the spindle is excited, and the amplitude is going to increase up to the resonance cutting speed before decreasing again.…”

“…Papers usually present the contribution of the workmaterial composition and mechanical properties on machining. Other studies focus on vibrations: the usually undesirable vibrations largely influence chip formation and surface integrity, which has led to three main types of studies, i.e., on the role of the workpiece and cutting conditions in the occurrence of such phenomena (ex: flexible workpiece used by Urbikain et al [18]), on the influence of chip serration on the occurrence of chatter vibrations [19] and finally, studies that used this vibration to improve chip serration and breakability by inducing forced and controlled vibrations on the cutting tool [20] (vibration-assisted machining).…”

Efficient tool path generation for five-axis machining of a difficult machined centrifugal impeller

“…9,10 However, titanium alloys are difficult to be machined because of its material characteristics such as high chemical activation, low elastic modulus, and poor thermal conductivity. Patwari et al 11 studied the influence of chip serration frequency on chatter formation during end milling of Ti-6Al-4V; it included the findings of an experimental study on instabilities of the chip formation process and the influence of these instabilities on chatter formation during end milling of Ti-6Al-4V alloy. Huang et al 12 proposed a milling force vibration analysis in high-speed-milling titanium alloy.…”

The investigation of the chip behaviour during the end milling cutting process

“…By interpolation of the previous two chip classifications, four major chip types are obtained: stable (complete), unstable, critical and severe chips. More recent Patwari et al [17] developed a mathematical model to predict the instability process of the chip formation by using the concept of chip serration frequencies.…”