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Research Papers

Microscale Drilling of Bulk Metallic Glass

[+] Author and Article Information
James Zhu, Hyun Jin Kim

Graduate Research Assistant

Shiv G. Kapoor

e-mail: sgkapoor@illinois.edu
Grayce Wicall Gauthier Chair in
Mechanical Science and Engineering,
Department of Mechanical
Science and Engineering,
University of Illinois: Urbana-Champaign,
Urbana, IL 61801

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF Micro- AND Nano-Manufacturing. Manuscript received June 14, 2013; final manuscript received September 19, 2013; published online November 13, 2013. Assoc. Editor: Stefan Dimov.

J. Micro Nano-Manuf 1(4), 041004 (Nov 13, 2013) (9 pages) Paper No: JMNM-13-1050; doi: 10.1115/1.4025538 History: Received June 14, 2013; Revised September 19, 2013

The microscale drilling performance of a Zr-based bulk metallic glass (BMG) is investigated in this paper. Crystallization, drill temperature, axial force, spindle load (SL), acoustic emissions (AE), chip morphology, hole diameter, and entry burr height are measured and analyzed with varying cutting speed and chip load. The progression of tool wear is assessed using stereo-microscopy techniques. At small chip loads, minimum chip thickness (MCT) is observed to shift cutting mechanics from a shear-dominated to a ploughing-dominated regime. Consequently, evidence of drill instability and larger burr height are observed. As drilling temperatures rise above the glass transition temperature, the BMG thermally softens due to the transition to a super-cooled liquid state and begins to exhibit viscous characteristics. In the tool wear study using tungsten carbide microdrills, rake wear is found to dominate compared to flank wear. This is attributed to a combination of a high rate of diffusion wear on the rake face as well as lower abrasion on the flank due to the decreased hardness from thermal softening-induced viscous flow of BMG.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Microdrilling configuration

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Fig. 2

KT-0200-S drill bit schematic (mm) [6]

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Fig. 3

Central composite design cutting conditions

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Fig. 4

IR camera intensity map during drilling

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Fig. 5

Laser scan profile: (a) raw and (b) filtered

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Fig. 6

Entry burr height calculation

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Fig. 7

Stereoscopic 3D surface model

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Fig. 8

Definition of flank wear and rake wear

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Fig. 9

Response surface contour plots: (a) drill temperature (°C), (b) axial force (N), (c) spindle load (V), (d) acoustic emission (V), (e) average entry burr height (μm), and (f) hole diameter (μm)

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Fig. 10

Time-domain spindle load measurements: constant cutting speed (28.73 m/min), varying chip load

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Fig. 11

XRD 2-theta scan: (a) as-received and (b) after drilling

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Fig. 12

Chip morphology with varying cutting conditions: cutting speed/chip load (a) 17.56/5.75, (b) 28.73/6.68, (c) 39.90/5.75, (d) 12.77/3.5, (e) 28.73/3.5, (f) 44.69/3.5, (g) 17.56/1.25, (h) 28.73/0.318, and (i) 39.90/1.25

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Fig. 13

Desirability contour plot

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Fig. 14

3D stereoscopic tool wear images: (a) 0 holes, (b) 10 holes, (c) 20 holes, (d) 40 holes, (e) 60 holes, and (f) 100 holes

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Fig. 15

Tool wear versus number of holes drilled: (a) flank wear and (b) rake wear

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