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Research Papers

Chatter Stability of General Turning Operations With Process Damping

[+] Author and Article Information
M. Eynian

Manufacturing Automation Laboratory, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, BC, V6T 1Z4, Canadaeynian@interchange.ubc.ca

Y. Altintas

Manufacturing Automation Laboratory, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, BC, V6T 1Z4, Canadaaltintas@interchange.ubc.ca

J. Manuf. Sci. Eng 131(4), 041005 (Jul 08, 2009) (10 pages) doi:10.1115/1.3159047 History: Received July 29, 2008; Revised April 27, 2009; Published July 08, 2009

The accurate prediction of chatter stability in general turning operations requires the inclusion of tool geometry and cutting conditions. This paper presents regenerative chip and regenerative chip area/cutting edge contact length based dynamic cutting force models, which consider cutting conditions and turning tool geometry. The cutting process is modeled as it takes place along the equivalent chord length between the two end points of the cutting edge. The regenerative chip model is simple, and the stability can be solved directly. However, the three-dimensional model considers the effect of tool vibrations at the present and previous spindle revolutions on the chip area, chord length, and force directions and is solved using Nyquist stability criterion. The penetration of worn tool flank into the finish surface is considered as a source of process damping. The effects of the nose radius, approach angle of the tool, and feedrate are investigated. The proposed stability model is compared favorably against the experimental results.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Turning tool with nose radius, (a) three-dimensional turning process with structural flexibility in three directions, (b) a three-dimensional view of cutting with a tool having a nose radius, and (c) top view of a cutting tool with nose radius and chip geometry

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Figure 5

Comparison of three stability prediction methods: (a) stability chart for a tool with rε=0.8 mm and κr=60 deg, c=0.1 mm/rev; (b) effect of approach angle; (c) effect of nose radius; and (d) effect of feed. See Fig. 4 for cutting force coefficients.

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Figure 6

(a) Effect of nose radius and (b) effect of feed on stability limit. Tool: Sandvik CNMA1204 KR 3205 series coated inserts on DLCNL holder with −6 deg rake, −6 deg inclination, and κr=95 deg approach angles, respectively.

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Figure 8

Displacement of the cutting edge in the depth of cut direction depth of cut larger (a) a>rε(1−cos κr) and (b) a≤rε(1−cos κr)

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Figure 2

Chip geometry produced by a tool having a nose radius and approach angle, (a) a>rε(1−cos κr) and (b) a≤rε(1−cos κr)

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Figure 3

Model of process damping forces caused by tool wear

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Figure 4

Comparison of the experimental and predicted cutting forces with the nonlinear model (Eq. 11). Material: AISI 1045 steel with 211 HB hardness. Tool: Kennametal insert (TNMA332KC850) and holder (CTGPL-123B NG7), nose radius rε=0.8 mm with 90 deg approach and 0 deg inclination and rake angles. Cutting force coefficients: Kn0=39 N,  Kr0=−146 N,  Kt0=−3 N; Knl=75,000 N/m,KrL=90,000 N/m,  KtL=73,000 N/m; and KnA=1065 MPa,  KrA=647 MPa,  KtA=2516 MPa, cutting speed Vc=219 m/min. Feed rates: (a) 004 mm/rev, (b) 0.08 mm/rev, (c) 0.12 mm/rev, and (d) 0.20 mm/rev.

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Figure 7

Comparison of predicted and experimentally observed chatter stability results for turning with sample vibration measurements at stable (a=2.5 mm,  n=200 rpm) and unstable (a=2.5 mm,  n=400 rpm) cutting conditions. Feedrate c=0.1 mm/rev and nose radius rε=0.8 mm. See Tables  23 for the modal parameters and cutting coefficients, respectively.

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