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Research Papers

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

[+] Author and Article Information
Md. Anayet U. Patwari

Department of Mechanical and Chemical Engineering, Islamic University of Technology, Gazipur Dhaka 1704, Bangladesh

A. K. M. Nurul Amin1

Department of Manufacturing and Materials Engineering, International Islamic University of Malaysia, 53100 Kuala Lumpur, Malaysiaakamin@iiu.edu.my

Waleed F. Faris

Department of Mechanical Engineering, Faculty of Engineering, International Islamic University of Malaysia, 53100 Kuala Lumpur, Malaysia

1

Corresponding author.

J. Manuf. Sci. Eng 133(1), 011013 (Feb 16, 2011) (12 pages) doi:10.1115/1.4003478 History: Received May 22, 2010; Revised January 07, 2011; Published February 16, 2011; Online February 16, 2011

This paper includes the findings of an experimental study on instabilities of the chip formation process during end milling of Ti6Al4V alloy and the influence 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 Ti6Al4V 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 certain number of primary serrated teeth also happen to appear at the free or constrained edge of the chip, especially when the system 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 and finite element modal analyses, and vibration responses during actual cutting have also been recorded using an online vibration monitoring system. The vibration signals in frequency domain (fast Fourier transform) have been analyzed to identify the chatter frequencies and the peak amplitude values. Chatter was found to occur at two dominant 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 frequency 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 spindle in this particular case.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Experimental setup for end milling

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Figure 2

Insert shape and geometry

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Figure 3

Experimental modal analysis power spectrum responses (FFT) for (a) Collet and (b) spindle casing of vertical machining center

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Figure 4

Operational Modal analysis of inner spindle: (a) under no load and (b) load conditions

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Figure 5

Selected eigenmodes of the different machine components of vertical machining center

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Figure 6

SEM top view of the chip with the serrated elements (cutting speed of 40 m/min, depth of cut 2.2 mm, and feed 0.16 mm/tooth) during machining of Ti6Al4V

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Figure 7

Chip formed by cutting the carbon steel AISI 1045 at 2 mm depth of cut, 200 m/min with overhang of 60 mm with (a) 50× and (b) 150× magnifications (26)

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Figure 8

Chip morphology: (a) SEM view and (b) lengthwise sectional view (under optical microscope) and the frequencies of formation of the primary serrated teeth at different cutting speeds with feed and depth of cut maintained constant at 0.16 mm/tooth and 2.2 mm, respectively

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Figure 9

FFT power spectra of vibrations during machining for end milling at different cutting speeds with feed 0.16 mm/tooth and depth of cut 2.2 mm

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Figure 10

Mechanism of chip serration in end milling

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Figure 11

Effect of cutting speed on acceleration amplitude at different mode shapes

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Figure 12

Variation of acceleration amplitude against ratio of w and wn for the two mode shapes (natural frequencies) of the spindle

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Figure 13

SEM views of chip for different depths of cut (2.0 mm and 2.2 mm) at cutting speed of 30 m/min and feed value of 0.16 mm/tooth with full immersion

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Figure 14

FFT power spectra during machining for end milling at two different cutting speeds for two different depths of cut (2.0 mm and 2.2 mm)

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Figure 15

Effect of depth of cut and spindle’s natural frequency on chip serration and chatter frequency

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Figure 16

Effect of depth of cut on acceleration amplitude

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Figure 17

Chip morphology—SEM view at different feeds

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Figure 18

FFT power spectrum during machining for end milling at two different cutting speeds with three different feed values

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Figure 19

Effect of feed on chip serration frequency and chatter formation

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Figure 20

Effect of feed on acceleration amplitude

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