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TECHNICAL PAPERS

Microstructure-Level Model for the Prediction of Tool Failure in WC-Co Cutting Tool Materials

[+] Author and Article Information
Sunghyuk Park, Shiv G. Kapoor, Richard E. DeVor

Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

J. Manuf. Sci. Eng 128(3), 739-748 (Jan 20, 2006) (10 pages) doi:10.1115/1.2194233 History: Received August 11, 2005; Revised January 20, 2006

A model to predict tool failure due to chipping in machining via the microstructure-level finite element cutting process simulation is presented and applied to a wide variety of WC-Co tool materials. The methodology includes the creation of arbitrary microstructures comprised of WC and Co phases to simulate various grades of WC-Co alloys. Equivalent stress, strain, and strain energy are then obtained via orthogonal microstructure-level finite element machining simulations. A model was developed to predict the occurrence of tool failure based on the mixed mode fracture criterion. Turning experiments were conducted to validate the model and the results showed that the model predictions agree well with the observations from the experiments. The model was then employed to study the effects of microstructural parameters and feedrate on chipping and failure.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Microstructure examples of WC/Co materials (a) WC 1μm4wt.% Co; (b) WC 3μm16wt.% Co

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Figure 2

Measurement of microstructural parameters; major and minor axes (A and B) of the WC grain, center points (×), and orientation angle (θ)

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Figure 3

Statistical observation results of 1μm WC grain size micrographs

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Figure 4

Schematic illustration of simulating distorted quadrangles for WC grains; A for major axis, B for minor axis, and θ for a random orientation angle

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Figure 5

Randomly distributed WC grains: dark phases are WC grains and voids are Co phases

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Figure 6

Schematic illustration of WC skeleton simulation using Boolean operations: (1) Overlapped area, (2) ADD areas, and (3) DIVIDE area by the line

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Figure 7

Typical simulated microstructures: dark regions for WC grains and light regions for Co phases (a) WC 1μm15wt.% Co; (b) WC 1μm10wt.% Co; (c) WC 3μm6wt.% Co

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Figure 8

Stress-strain curves of pure Co specimen at a wide range of temperature

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Figure 9

Stress-strain curves of pure WC specimen at a wide range of temperature

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Figure 10

Initial geometry of homogeneous tool and workpiece materials

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Figure 11

Strain energy for brittle fracture; arrows identify elements with high degree of the stored strain energy per unit area

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Figure 12

Plastic strain for ductile fracture; arrows identify elements with high plastic strain and stress triaxiality

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Figure 13

The length of a surface crack and its orientation angle in the original stress state α′; α′for the orientation angle and l for the surface crack length, solid lines for elements fractured in a brittle manner and polygons for elements fractured in a ductile manner

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Figure 14

Fracture locus drawn by using Eq. 2: dashed lines indicate cracks with various length and orientation angle for F=1 under σc=1821MPa and τ=750MPa

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Figure 15

SEM images of chipped surfaces (a) S114; (b) K322; (c) K3070

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Figure 16

Example of three surface cracks from WC 1μm Co 10wt.% (a) and fracture locus (b)

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Figure 17

Relationship between WC grain size and F at two different Co amounts

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Figure 18

Relationship between feed rate and F for WC 1μm6wt.% Co and WC 3μm6wt.% Co

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Figure 19

Relationship between microstructural parameters and F at a 200μm feed rate

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