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Research Papers

Effect of Process Parameters on Burrs Produced in Micromilling of a Thin Nitinol Foil

[+] Author and Article Information
George K. Mathai

e-mail: georgekm@gatech.edu

Shreyes N. Melkote

e-mail: shreyes.melkote@me.gatech.edu

David W. Rosen

e-mail: david.rosen@me.gatech.edu
The George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received October 21, 2012; final manuscript received March 18, 2013; published online May 2, 2013. Assoc. Editor: Stefan Dimov.

J. Micro Nano-Manuf 1(2), 021005 (May 02, 2013) (10 pages) Paper No: JMNM-12-1070; doi: 10.1115/1.4024099 History: Received October 21, 2012; Revised March 18, 2013

This paper examines the formation of burrs in micromilling of a thin nickel–titanium alloy (nitinol) foil used in implantable biomedical device applications. The paper analyzes the effects of key micromilling process parameters such as spindle speed, feed, tool wear, backing material, and adhesive used to attach the foil to the backing material on the burr height. It is found that burr height is larger on the downmilling side for grooves cut with a worn tool at high feeds, low spindle speeds with a softer backing material, and a weaker adhesive bond. Some important interaction effects of these factors are also studied. The study also shows that the mechanics of burr formation in such thin materials depends on whether the mode of cutting is dominated by tearing or chip formation, which is a function of the feed rate. A kinematic model to predict burr widths is developed and verified through experiments.

Copyright © 2013 by ASME
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Figures

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Fig. 2

Experimental setup

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Fig. 3

Tool wear: (a) new tool, (b) used tool, (c) used tool (portion that contacts foil), (d) worn tool, and (e) detail view of worn tool

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Fig. 4

Measurement of peel strength: (a) test setup, (b) comparison of peel strength, pc = PMMA backing material with cyanoacrylate adhesive, pe = PMMA backing material with epoxy adhesive, ac = aluminum backing material with cyanoacrylate adhesive, ae = aluminum backing material with epoxy adhesive

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Fig. 5

High speed video stills of burr formation: (a) stage 1: foil pushed up, (b) stage 2: foil tearing, (c) stage 3: foil tearing closer to upmilling side, (d) burr fracture (before), (e) burr fracture (after), (f) foil machining by chip formation, and (g) burr formation with slow feed viewed from upmilling side

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Fig. 6

Chip formation: (a) PMMA chip, foil interaction, (b) large, continuous PMMA chip, (c) large continuous aluminum chip, and (d) epoxy chip and machined foil

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Fig. 7

Burr shapes: (a) rollover type, (b) feathery type, (c) wall type, (d) small, evenly spaced rollover type, 10 μm/tooth, and (e) small, evenly spaced rollover type, 1 μm/tooth

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Fig. 8

Schematic of burr formation: (a) rollover type, (b) wall type, (c) wall type with low feed

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Fig. 9

Histogram of burr height for grooves milled with PMMA backing, cyanoacrylate adhesive and a new tool (N = spindle speed: − = 30,000 rpm, + = 60,000 rpm, fz = feed: − = 1 μm/tooth, + = 10 μm/tooth, m = milling side: − = downmilling, + = upmilling)

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Fig. 10

Boxplot of burr height for grooves milled with PMMA backing, cyanoacrylate adhesive and a new tool

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Fig. 11

Mean effects plot (A = adhesive: − = cyanoacrylate, + = epoxy, M: backing material: − = PMMA, + = aluminum, W = tool wear: − = new tool, + = worn tool, N = spindle speed: − = 30,000 rpm, + = 60,000 rpm, fz = feed: − = 1 μm/tooth, + = 10 μm/tooth, m = milling side: − = downmilling, + = upmilling)

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Fig. 12

Interaction effects plot (A = adhesive: − = cyanoacrylate, + = epoxy, M: backing material: − = PMMA, += aluminum, W= tool wear: − = new tool, + = worn tool, N = spindle speed: − = 30,000 rpm, + = 60,000 rpm, fz = feed: − = 1 μm/tooth, + = 10 μm/tooth, m= milling side: − =downmilling, + = upmilling)

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Fig. 13

Effect of feed on burr height: (a) upmilling side, (b) downmilling side, (c) 1 μm/tooth, (d) 2.5 μm/tooth, (e) 5 μm/tooth, (f) 7.5 μm/tooth, (g) 10 μm/tooth, (h) 25 μm/tooth, (i) 50 μm/tooth, and (j) 100 μm/tooth. Images oriented with upmilling side towards the top.

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Fig. 14

Burr formation model: (a) schematic of tooth engaging with foil, (b) enlarged view of tooth before penetration into foil, (c) kinematics of foil at tooth tip, (d) force balance in foil, (e) undeformed length and strained length at failure when εt  < εf, and (f) foil failure at initial penetration when εt  > εf

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Fig. 15

Predicted versus experimental burr width

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