Effect of Low-Frequency Modulation on Lubrication of Chip-Tool Interface in Machining

[+] Author and Article Information
Wilfredo Moscoso, Efe Olgun, W. Dale Compton, Srinivasan Chandrasekar

Center for Materials Processing and Tribology Purdue University, IE, GRIS 315 North Grant Street, West Lafayette, IN-47907-2023 Tel. (765) 494-5409

J. Tribol 127(1), 238-244 (Feb 07, 2005) (7 pages) doi:10.1115/1.1829720 History: Received March 02, 2004; Revised September 30, 2004; Online February 07, 2005
Copyright © 2005 by ASME
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Typical photomicrograph of the tool rake face after cutting dry. Two distinct regions can be seen in the area of contact between tool and chip—an intimate contact region adjoining the cutting edge that is devoid of visible metal deposits and a region of metal deposits farther away from the cutting edge wherein intermittent, Coulombic sliding contact is known to prevail. Tool: plain HSS and workpiece: aluminum.
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Schematic of the experimental setup used for 2D orthogonal machining with superimposed low-frequency modulation. The direction of the modulation is parallel to the direction of the cutting velocity (Vc). Since the tool has a 0 deg rake angle, the normal (Fn) and tangential (Ft) forces acting on the tool are also, respectively, the cutting and thrust forces.
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Sample dynamometer and capacitance probe outputs showing force components and displacement of the tool with respect to the workpiece during cutting, (a) modulation amplitude=52 μm and (b) modulation amplitude=26 μm. In Fig. 3(a), the modulation amplitude is high enough to cause physical separation of the chip-tool contact in each cycle of modulation. This results in cutting and no-cutting intervals within each modulation cycle. This condition of modulation is referred to as high-amplitude modulation. Although there are also intervals of cutting and no-cutting in Fig. 3(b), the amplitude is not high enough to cause physical separation of the tool from the chip—a case of low-amplitude modulation. Workpiece: aluminum, modulation frequency=75 Hz, cutting velocity=10 mm/s, depth of cut (undeformed chip thickness)=0.20 mm, fluid: Coolube 2210. r=tool displacement, Fn=normal force, Ft=friction force, t=time. The modulation amplitudes were derived from the tool displacement traces.
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Variation of forces and friction coefficient with modulation amplitude when cutting with a fluid. Normal and friction forces are given per unit width of workpiece. Modulation frequency=75 Hz, cutting velocity=10 mm/s, depth of cut (undeformed chip thickness)=0.10 mm, tool: plain HSS, workpiece: aluminum and fluid: Coolube 2210.
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Photomicrographs of partially formed chips when cutting with fluid (Coolube 2210), (a) no-modulation cutting, workpiece: aluminum, (b) no-modulation cutting, workpiece: copper, (c) high-amplitude modulation cutting of aluminum, frequency=75 Hz,amplitude=52 μm and (d) high-amplitude modulation cutting of copper, frequency=75 Hz,amplitude=52 μm. The flow lines in Figs. 5(a) and 5(b) are highly curved in the vicinity of the rake face, indicating significant secondary shear. In contrast, the flow lines near the rake face in Figs. 5(c) and 5(d) in high-amplitude modulation cutting are practically straight, indicating reduced secondary shear. Cutting velocity=10 mm/s. The tool moves from right to left.
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Sequence of images of the tool rake face in one complete cycle of high-amplitude modulation cutting with fluid (Coolube 2210). The images were taken when cutting lead with an optically transparent sapphire tool at a frame rate of 125 Hz (time between frames=0.008 s). Chip-tool contact is broken in frame 1. Fluid then penetrates and remains at the interface during the cutting interval (white bubbles in frames 8 to 10), except in the black band immediately adjacent to the cutting edge. Depth of cut (undeformed chip thickness)=0.20 mm, cutting velocity=5 mm/s, modulation frequency=12.5 Hz, modulation amplitude=400 μm, tool rake angle=5 deg.




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