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Research Papers

Experimental and Numerical Investigations on Microcoining of Stainless Steel 304

[+] Author and Article Information
Gap-Yong Kim1

Department of Mechanical Engineering, Iowa State University, Ames, IA 50011gykim@iastate.edu

Muammer Koç

Department of Mechanical Engineering, Virginia Commonwealth University, Richmond, VA 23284

Jun Ni

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109

1

Corresponding author.

J. Manuf. Sci. Eng 130(4), 041017 (Jul 22, 2008) (6 pages) doi:10.1115/1.2953235 History: Received May 12, 2007; Revised May 19, 2008; Published July 22, 2008

Increasing demands for miniature metallic parts have driven the application of microforming in various industries. Only a limited amount of research is, however, available on the forming of miniature features in high strength materials. This study investigated the forming of microfeatures in Type 304 stainless steel by using the coining process. Experimental work was performed to study the effects of workpiece thickness, preform shape, grain size, and feature size on the formation of features ranging from 320μmto800μm. It was found that certain preform shapes enhance feature formation by allowing a favorable flow of the bulk material. In addition, a flow stress model for Type 304 stainless steel that took into consideration the effects of the grain and feature sizes was developed to accurately model and better understand the coining process. Weakening of the material, as the grain size increased at the miniature scale, was explained by the Hall–Petch relationship and the feature size effect.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

Heat treatment of stainless steel and obtained grain structure

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Figure 4

Parameters α and β for specimens with rectangular cross sections, and their dependence on the grain number (n)(13)

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Figure 8

Variation of the protrusion heights for as-received sample at 650kN

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Figure 9

The effects of workpiece thickness and preform shapes on the feature formation (650kN)

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Figure 10

Effect of grain size on feature formation for stainless steel (650kN)

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Figure 11

Grain deformation of stainless steel specimen (Row 2)

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Figure 12

Force-displacement curve and channel formation at various strokes

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Figure 13

Comparison of the feature height predicted by simulation and measured from experiment for stainless steel at 650kN

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Figure 7

A typical force-displacement curve measured and a stainless steel specimen formed at 650kN

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Figure 6

The simulation model and the flow stress curves applied to each row

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Figure 5

The true stress-true strain curves of Type 304 stainless steel at various grain sizes (23)

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Figure 2

Fabricated die and microchannel dimensions

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Figure 1

Experimental setup and fabricated punch∕die set: (a) compression testing system and (b) die∕punch set

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