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Research Papers

A Rate-Sensitive Plasticity-Based Model for Machining of Face-Centered Cubic Single-Crystals—Part I: Model Development

[+] Author and Article Information
Nithyanand Kota

Department of Mechanical Engineering,  Carnegie Mellon University, Pittsburgh, PA 15213

Anthony D. Rollett

Department of Materials Science and Engineering,  Carnegie Mellon University, Pittsburgh, PA 15213

O. Burak Ozdoganlar1

Department of Mechanical Engineering, Department of Materials Science and Engineering,  Carnegie Mellon University, Pittsburgh, PA 15213 e-mail: ozdoganlar@cmu.edu

Critical resolved shear stress is the amount of stress required on a slip plane to cause slip on that particular plane.

1

Corresponding author.

J. Manuf. Sci. Eng 133(3), 031017 (Jul 01, 2011) (8 pages) doi:10.1115/1.4004134 History: Received March 17, 2010; Revised March 29, 2011; Published July 01, 2011; Online July 01, 2011

With the increased application of micromachining, including micromilling and microdrilling, the need to develop accurate models for machining at the microscale has been recognized. In particular, the crystallographic effects that are generally neglected in the macroscale cutting models must be incorporated into the micromachining models. Diamond turning and mechanical nanomanufacturing techniques also require an understanding of crystallographic effects during material removal. This work presents a rate-sensitive plasticity-based machining (RSPM) model that is used to determine the specific energies (and thus forces) for orthogonal cutting of face-centered cubic (fcc) single-crystals. The RSPM model uses kinematics and geometry of orthogonal cutting for an ideally sharp cutting edge. The total power is expressed in terms of the plastic power, which is spent for shearing the material within a finite shear zone, and the friction power, which is spent for overcoming the friction at the rake face. In calculating the shearing power, rate-sensitive plastic behavior of fcc metals is considered. In addition, realistic effects of lattice rotation and strain hardening are included in the model. Subsequently, the total power is minimized within the space of geometrically allowable shear angles to determine the shear angle solution, and associated cutting and thrust specific energies, as a function of cutting plane orientation, cutting direction (with respect to the crystal orientation), rake angle, and the coefficient of friction. The calibration procedure for and the experimental validation of the model are provided in Part II.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) The geometry of orthogonal cutting process, indicating the workpiece zone axis [abc], cutting direction [hkl], and cutting plane normal [uvw] and (b) components of the machining force, Merchant’s force-circle diagram, and the shear zone

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Figure 2

(a) Deformation in the primary deformation zone and (b) an incremental deformation Δγ that occurs as a result of incremental plastic work ΔWpk

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Figure 3

Illustration of the lattice rotation; the final deformation is a result of slip on (a) only one system (along 1l ) and (b) two slip systems (simultaneously along 1l and 2l ), and a rotation. The same deformation is obtained with different lattice orientations.

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Figure 4

Typical behavior of reference stress

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Figure 5

Typical behavior of total power with shear angle candidates

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