Investigation of Deformation Size Effects During Microextrusion

[+] Author and Article Information
Sunal Ahmet Parasiz, Brad Kinsey

Mechanical Engineering, University of New Hampshire, Kingsbury Hall, 33 College Rd., Durham, NH 03824

Neil Krishnan, Jian Cao

Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208

Ming Li

 Alcoa Technical Center, Alcoa Center, PA 15069

J. Manuf. Sci. Eng 129(4), 690-697 (Dec 14, 2006) (8 pages) doi:10.1115/1.2738107 History: Received December 21, 2005; Revised December 14, 2006

Microextrusion has recently emerged as a feasible manufacturing process to fabricate metallic micropins having characteristic dimensions on the order of less <1mm. At this length scale, the deformation of the workpiece is dominated by the so-called size effects, e.g., material property and frictional behavior variations at small length scales. In extrusion experiments performed to produce submillimeter-sized pins having a base diameter of 0.76mm and an extruded diameter of 0.57mm, the extruded pins exhibited a curving tendency when a workpiece with a relatively coarse grain size of 211μm was used. This phenomenon was not observed when workpieces with a finer grain size of 32μm were used. In this paper, results from microhardness tests and microstructure analyses for both grain sizes are presented to investigate this phenomenon and to characterize the deformation during microextrusion. The results obtained from this analysis show that as the grain size approaches the specimen feature size, the deformation characteristics of the extruded pins are dominated by the size and location of specific grains, leading to a nonuniform distribution of plastic strain and measured hardness and, thus, the curving tendency. Microhardness tests of the initial billet material and tensile test specimens are also presented as supplementary analyses.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 2

Extrusion die fabricated using micro-EDM

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Figure 1

Microextrusion setup: (a) segmented dies, (b) forming assembly, (c) loading stage, and (d) force-displacement response

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Figure 6

Average hardness values in the undeformed billet material

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Figure 7

Hardness values in the reduction area for a 32μm grain size pin

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Figure 8

Average hardness values in the deformed pins at an axial location of 1500μm

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Figure 9

(a)32μm grain size, straight pin and (b) the corresponding hardness values along the reduced length

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Figure 10

(a)211μm grain size, curved pin and (b) the corresponding hardness values along the reduced length

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Figure 11

Hardness distribution along the gage length of the tensile specimens

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Figure 12

Tensile test curves of 32μm and 211μm grain size specimens

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Figure 13

Half cross section of tensile specimen pieces (a)211μm grain size (b)32μm grain size

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Figure 14

Microstructure of 32μm grain size pins at (a) reduction and (b) straight portion of the pin after reduction

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Figure 15

Microstructure of 211μm grain size pins at (a) reduction and (b) straight portion of the pin after reduction

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Figure 16

Microstructure of 211μm grain size pins at curvature location showing (a) typical extrusion deformation before curvature and (b) large grains in the center of the pin at the curvature location

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Figure 3

Microstructure of brass samples after heat treatment: (a)550°C for 1hr (32μm grain size), (b)700°C for 1hr (211μm grain size)

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Figure 4

Samples of pins extruded using the 0.76:0.57mm die and work pieces having a grain size of 32μm or 211μm

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Figure 5

Axial and radial location definition on the extruded pin



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