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Special Section: Micromanufacturing

An Acoustic Emission-Based Method for Determining Contact Between a Tool and Workpiece at the Microscale

[+] Author and Article Information
Keith A. Bourne

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801kbourne2@uiuc.edu

Martin B. Jun

Department of Mechanical Engineering, University of Victoria, Victoria, BC, Canadambgjun@uvic.ca

Shiv G. Kapoor

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801sgkapoor@uiuc.edu

Richard E. DeVor

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801redevor@uiuc.edu

J. Manuf. Sci. Eng 130(3), 031101 (May 05, 2008) (8 pages) doi:10.1115/1.2917285 History: Received July 27, 2006; Revised January 17, 2008; Published May 05, 2008

Abstract

An acoustic emission-based touch-off detection system has been developed to determine contact between a rotating microtool and a workpiece surface with micron-level accuracy. The system has been implemented on an existing three-axis microscale machine tool. The system has been tested with microendmills as small as $50μm$ in diameter and microdrills as small as $254μm$ in diameter. The accuracy of the system has been found to depend on tool geometry and workpiece surface characteristics and is generally on the order of $1μm$. An analytical model has been constructed to predict touch-off detection error. The calibrated model has been shown to predict surface overshoot and undershoot trends quite well. Simulations have shown that touch-off error is dominated by part surface roughness.

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Figures

Figure 1

AE Bursts from microendmill-workpiece contact

Figure 2

Touch-off between an inclined workpiece and a (a) microendmill and a (b) microdrill

Figure 3

Tool-workpiece contact points using multipoint touch-off algorithm

Figure 4

UIUC three-axis mMT and machine coordinate system

Figure 5

(Left) Nano30 AE sensor (right) sensor-workpiece mount

Figure 6

Micromilling machine z-stage overshoot

Figure 7

Effect of detection threshold and wear on touch-off overshoot∕undershoot with a 50.8μm diameter endmill

Figure 8

4μm deep feature cut into aluminum with a 50.8μm diameter endmill

Figure 9

Tool marks due to touch-off: (a) endmill diameter=254μm, Ra=0.05μm; (b) endmill diameter=254μm, Ra=0.2μm; (c) endmill diameter=254μm, Ra=0.38μm; (d) drill diameter=508μm, Ra=0.38μm

Figure 10

Microendmill touch-off model

Figure 11

Model calibration for aluminum

Figure 12

AE burst magnitude trend from touch-off against a surface with 0.42μmRa

Figure 13

Effect of detection threshold, varying surface roughness, and tool diameter on predicted undershoot

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