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TECHNICAL PAPERS

Material Strengthening Mechanisms and Their Contribution to Size Effect in Micro-Cutting

[+] Author and Article Information
Kai Liu, Shreyes N. Melkote

The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0406

J. Manuf. Sci. Eng 128(3), 730-738 (Nov 30, 2005) (9 pages) doi:10.1115/1.2193548 History: Received June 09, 2005; Revised November 30, 2005

The specific cutting energy in machining is known to increase nonlinearly with decrease in uncut chip thickness. It has been reported in the literature that this phenomenon is dependent on several factors such as material strengthening, ploughing due to finite edge radius, and material separation effects. This paper examines the material strengthening effect where the material strength increases nonlinearly as the uncut chip thickness is reduced to a few microns. This increase in strength has been attributed in the past to various factors such as strain rate, strain gradient, and temperature effects. Given that the increase in material strength can occur due to many factors, it is important to understand the contributions of each factor to the increase in specific cutting energy and the conditions under which they are dominant. This paper analyzes two material strengthening factors, (i) the contribution of the decrease in the secondary deformation zone cutting temperature and (ii) strain gradient strengthening, and their relative contributions to the increase in specific cutting energy as the uncut chip thickness is reduced. Finite element (FE)-based orthogonal cutting simulations are performed with Aluminum 5083-H116, a work material with a small strain rate hardening exponent, thus minimizing strain rate effects. Suitable cutting conditions are identified under which the temperature and strain gradient effects are dominant. Orthogonal cutting experiments are used to validate the model in terms of cutting forces. The simulation results are then analyzed to identify the contributions of the material strengthening factors to the size effect in specific cutting energy.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Illustration of material separation using the pure deformation method

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Figure 2

Finite element model configuration

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Figure 3

The diffuse approximation method

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Figure 4

Overall simulation approach

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Figure 5

SEM image of SCD tool

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Figure 6

Schematic of orthogonal micro-cutting experiment

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Figure 7

Schematic of orthogonal micro-cutting process carried out on the two-axis precision motion stages

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Figure 8

Flow stress data for Al5083-H116 (41)

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Figure 9

Comparison of experimental and simulated cutting forces at 200m∕min

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Figure 10

Comparison of experimental and simulated cutting forces at 10m∕min

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Figure 11

Strain gradient contour (uncut chip thickness 1μm, 10m∕min cutting speed)

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Figure 12

Variation of specific cutting energy with uncut chip thickness at 10m∕min

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Figure 13

Variation of specific cutting energy with uncut chip thickness at 200m∕min

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Figure 14

Variation of maximum temperature in the primary and secondary shear zones at 200m∕min cutting speed (PSZ: primary shear zone, SSZ: secondary shear zone)

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Figure 15

Variation of specific cutting energy with uncut chip thickness at 240m∕min

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Figure 16

Variation of maximum temperature in the primary and secondary shear zones at 240m∕min cutting speed

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