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Since Dr. Carl Salomon proposed the well-known hypothesis on cutting temperatures in 1931, the debate on the hypothesis has never stopped. It shows that evolutions of temperatures with the increase of cutting speed measured at different points are different. From the tool wear and surface integrity point of view, this paper focuses on the evolutions of chip temperature (Chip temp.), tool-chip contact temperature (T-C temp.), and tool-workpiece contact temperature (T-W temp.) with the increase of cutting speed from low (100 m/min) to very high (7000 m/min). First, the cutting heat generation and the temperature increment in machining are theoretically analyzed. Then the influences of chip shape and mechanical property variations with the increase of cutting speed on the temperatures are analyzed. Finally, the cutting temperatures are semiquantitatively derived from chip colors and other heat characteristics in the chip and cutting tool obtained in cutting experiments: evolutions of Chip temp., T-C temp., and T-W temp. with the increase of cutting speed are presented based on the experiment results. The influence of chip shape and temperature variation on tool wear are also discussed. [ABSTRACT FROM AUTHOR]

Saw tooth chip is a typical characteristic encountered in high-speed machining. It consists of nearly undeformed segments and highly sheared concentrated shear bands. However, no consensus on the formation of the concentrated shear band has been reached though several saw tooth chip formation models have been built. In this paper, the concentrated shear band formation procedure is analyzed based on a new proposed saw tooth chip formation model. Cutting experiments have been conducted to validate the proposed mode. It shows that the plastic side flow and elastic compression of the uncut chip are crucial for the concentrated shear band formation. The localized shear at the inner end (tool tip side) of the primary shear plane firstly takes place under the indentation of cutting tool. Then, the second localized shear is produced at the outer end (free surface side) of the primary shear plane due to stress concentration there, after which the whole concentrated shear band forms. The stress transition at the outer end of the primary shear plane makes the second localized shear easier evolve into cracks. Influences of material brittleness and cutting speed on initiation and propagation of the concentrated shear band are also analyzed. [ABSTRACT FROM AUTHOR]

The contact stress and heating effect between the cutting tool and workpiece in metal machining is symmetrical. However, the symmetry may be destroyed by changes in the workpiece material mechanical properties, such as ductility. The goal of this study is to reveal the wear characteristics of the cutting tool in machining a ductile metal with the cutting speed at which the metal is embrittled by the high-strain-rate-embrittle effect (HSREE). Orthogonal high-speed turning experiments were carried out. Pure iron type DT8 was cut at different cutting speeds, ranging from 1000 m/min to 9000 m/min. The shape and morphology of the chips obtained in the experiment were observed and analyzed by optical microscope and scanning electron microscope (SEM). Tool wear characteristics at different cutting speeds were observed. It shows that the pure iron becomes completely brittle when the cutting speed is higher than 8000 m/min. On the rake face, the coating of the cutting tool bursts apart and peels off. A matrix crack originates in the cutting edge or rake face and extends to the flank face of the cutting tool. The effects of HSREE on the tool wear is discussed. The findings of this study are helpful for choosing a suitable tool for brittle cutting of the ductile metal pure iron with very high cutting speed and solving the problems in machining due to its high ductility and high stickiness. [ABSTRACT FROM AUTHOR]