Abstract
The formation of serrated chips is an important feature during machining of difficult-to-cut materials, such as titanium alloy, nickel based alloy, and some steels. In this study, Ti6Al4V alloys with equiaxial and acicular martensitic microstructures were adopted to analyze the effects of material structures on the formation of serrated chips in straight line micro orthogonal machining. The martensitic alloy was obtained using highly efficient electropulsing treatment (EPT) followed by water quenching. The results showed that serrated chips could be formed on both Ti6Al4V alloys, however the chip features varied with material microstructures. The number of chip segments per unit length of the alloy with martensite was more than that of the equiaxial alloy due to poor ductility. Besides, the average cutting and thrust forces were about 8.41 and 4.53 N, respectively, for the equiaxed Ti6Al4V alloys, which were consistently lower than those with a martensitic structure. The high cutting force of martensitic alloy is because of the large yield stress required to overcome plastic deformation, and this force is also significantly affected by the orientations of the martensite. Power spectral density (PSD) analyses indicated that the characteristic frequency of cutting force variation of the equiaxed alloy ranged from 100 to 200 Hz, while it ranged from 200 to 400 Hz for workpieces with martensites, which was supposedly due to the formation of serrated chips during the machining process.
Highlights
To date, Ti6Al4V alloy is increasingly applied within the aerospace field due to its low weight, superior strength, and corrosion resistance [1,2]
The serrated chip formation of Ti6Al4V alloys was experimentally investigated in this study, which provides useful instructions for analyzing chip features with respect to equiaxed and martensitic microstructures during the micro machining of Ti6Al4V alloys
Conclusions could be drawn as follows: (1) The needlelike martensitic microstructure of the Ti6Al4V alloy with widths ranging from 100 to 500 nm could be obtained by electropulsing treatment for 2 min followed by water quenching
Summary
Ti6Al4V alloy is increasingly applied within the aerospace field due to its low weight, superior strength, and corrosion resistance [1,2]. The generation of serrated chips is totally different from the formation of continuous chips that are usually obtained in cutting most easy-to-machine materials, such as copper, aluminum, and most of their alloys [8,9,10]. Heat is not prone to being dispersed during the machining hard-to-cut alloys because of their poor thermal conductivity or fracture properties, resulting in serrated chip formation according to the thermal softening effect or periodical crack generation [11,12,13]. Komanduri and Von Turkovich [14] proposed that the generation of an adiabatic shear band gives rise to the formation of serrated chips in the high-speed machining of titanium alloys. This research aims to investigate the effects of equiaxial and martensitic microstructures on the serrated chip formation of Ti6Al4V alloys via micro orthogonal machining
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