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Research Papers

Metal Embedded Optical Fiber Sensors: Laser-Based Layered Manufacturing Procedures

[+] Author and Article Information
Hamidreza Alemohammad

Ehsan Toyserkani

 Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada

J. Manuf. Sci. Eng 133(3), 031015 (Jun 16, 2011) (12 pages) doi:10.1115/1.4004203 History: Received August 23, 2010; Revised May 01, 2011; Published June 16, 2011; Online June 16, 2011

This paper describes laser-based layered manufacturing processes for embedding optical fiber Bragg gratings (FBGs) in metal structures to develop cutting tools with embedded sensors. FBG is a type of optical fiber that is used for the measurement of parameters manifesting as the changes of strain or temperature. The unique features of FBGs have encouraged their widespread use in structural measurements, failure diagnostics, thermal measurements, pressure monitoring, etc. Considering the unique features of FBGs, embedding of the sensors in metal parts for in-situ load monitoring is a cutting-edge research topic with a variety of applications in machining tools, aerospace, and automotive industries. The metal embedding process is a challenging task, as the thermal decay of UV-written gratings can start at a temperature of ∼200 °C and accelerates at higher temperatures. The embedding process described in this paper consists of low temperature laser microdeposition of on-fiber silver thin films followed by nickel electroplating in a steel part. A microscale laser-based direct write (DW) method, called laser-assisted maskless microdeposition (LAMM), is employed to deposit silver thin films on optical fibers. To attain thin films with optimum quality, a characterization scheme is designed to study the geometrical, mechanical, and microstructural properties of the thin films in terms of the LAMM process parameters. To realize the application of embedded FBG sensors in machining tools, the electroplating process is followed by the deposition of a layer of tungsten carbide-cobalt (WC-Co) by using laser solid freeform fabrication (LSFF). An optomechanical model is also developed to predict the optical response of the embedded FBGs. The performance of the embedded sensor is evaluated in a thermal cycle. The results show that the sensor attains its linear behavior after embedding. Microscopic analysis of the tool with the embedded sensor clearly exhibits the integrity of the deposited layers without cracks, porosity, and delamination.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) FBG with modulations of the index of refraction, (b) FBG reflection spectrum, and (c) Bragg wavelength shift resulted from changes in temperature and/or strain

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Figure 2

Strain components e1,e2,ande3 applied on optical fiber

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Figure 3

Meshed model for thermal–structural finite element analysis in COMSOL multiphysics

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Figure 4

Schematic diagram of the fabrication processes for embedding FBG sensor

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Figure 5

Laser sintering mechanism of nanoparticles (a) before sintering, (b) liquid evaporation, (c) start of agglomeration, and (d) end of agglomeration

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Figure 6

Path followed by the deposition head of LAMM relative to the optical fiber for the deposition of on-fiber silver thin films

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Figure 7

(a) Schematic diagram of the LAMM deposition tip and the optical fiber and (b) for each set of depositions the fiber is rotated by 90°

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Figure 8

Schematic cross section of the sample with embedded FBG

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Figure 9

In-lens images of the microstructure of the silver thin film sintered at 1.35 W taken at magnifications of (a) 20 k× and (b) 35 k×

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Figure 10

In-lens images of the microstructure of the silver thin film sintered at 3.28 W at magnifications of (a) 20 k× and (b) 35 k×

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Figure 11

XRD spectra of the silver thin films sintered at different laser powers

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Figure 12

XRD peaks for (200) planes at different laser powers

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Figure 13

Nanoindentation profiles at six locations on a silver thin film

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Figure 14

Load displacement curves obtained from the nanoindentation test at five locations of the silver thin films sintered at (a) 1.35 W, (b) 2.41 W, and (c) 3.28 W

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Figure 15

Hardness of silver thin films as a function of incident laser power obtained from nanoindentation tests

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Figure 16

Modulus of elasticity of silver thin films as a function of incident laser power obtained from nanoindentation tests

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Figure 17

Prototyped sample with metal-embedded FBG using LAMM and electroplating

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Figure 18

Cross section of the sample with embedded FBG manufactured by LAMM and nickel electroplating

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Figure 19

Reflection spectra of the FBG before and after embedding at room temperature

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Figure 20

Reflection spectra of the embedded FBG at different temperatures ranging from 32.2 to 121.7 °C

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Figure 21

Bragg wavelength as a function of temperature obtained from experiments for embedded FBG showing a sensitivity of 25.8 pm/°C

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Figure 22

Bragg wavelength changes of the embedded FBG as a function of temperature obtained from optomechanical modeling showing a sensitivity of 24 pm/°C

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Figure 23

FE analysis results for von Mises stress at 121.7 °C

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