Research Papers

High-Speed Fabrication of Microchannels Using Line-Based Laser Induced Plasma Micromachining

[+] Author and Article Information
Ishan Saxena

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: ishan@u.northwestern.edu

Rajiv Malhotra

Department of Mechanical,
Industrial and Manufacturing Engineering,
Oregon State University,
Corvallis, OR 97331
e-mail: Rajiv.Malhotra@oregonstate.edu

Kornel Ehmann

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: k-ehmann@northwestern.edu

Jian Cao

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: jcao@northwestern.edu

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received October 2, 2014; final manuscript received February 25, 2015; published online March 18, 2015. Assoc. Editor: Nicholas Fang.

J. Micro Nano-Manuf 3(2), 021006 (Jun 01, 2015) (8 pages) Paper No: JMNM-14-1066; doi: 10.1115/1.4029935 History: Received October 02, 2014; Revised February 25, 2015; Online March 18, 2015

Microtexturing of surfaces has various applications that often involve texturing over large (macroscale) areas with high precision and resolution. This demands scalability and speed of texturing while retaining feature sizes of the order of a few microns. Microchannels are a versatile microfeature, which are often used in microfluidic devices and can be arrayed or joined to form patterns and free-form geometries. We present a technique to fabricate microchannels on surfaces with high-speed and by using a multimaterial process, namely, laser induced plasma micromachining (LIPMM). The process has the potential to machine metals, ceramics, polymers, and other transparent, brittle, and hard-to-machine materials. The presented technique uses an optical system to modify the laser spot into the shape of a line, to fabricate microchannels directly without scanning as in the case of a regular circular spot. The process schematics are shown, and micromachining experiments on polished aluminum are discussed. Moreover, it is shown that the depth and width of the channels may be varied by changing process parameters like the pulse energy, pulse frequency, and number of exposures.

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Fig. 1

(a) Focal spot created with a converging lens and (b) focal line created with a focusing lens and cylindrical lens

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Fig. 2

CCD images of focal spots created with: (a) converging lens and (b) focusing lens and cylindrical lens

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Fig. 3

Schematic representation of beam focal spot modification through the use of a cylindrical lens

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Fig. 4

(a) Length and (b) depth of the focal line, as a function of separation between the cylindrical lens and the focusing triplet

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Fig. 5

Intensity distribution at cross sections along the axis of propagation at different distances from the cylindrical lens: (a) 9.5 mm, (b) 10.6 mm, (c) 11.5 mm, (d) 12.5 mm, (e) 13.5 mm, (f) 15.5 mm, (g) 16.5 mm, and (h) 17.5 mm. Note: focal spots approximately at (b) and (g).

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Fig. 6

Laser system, as shown with the beam delivery system and the 5-axis motion stage

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Fig. 7

Qualitative comparison between: (a) incident intensity variation and (b) resulting depth profile of channel along its length

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Fig. 8

(a) Perspective view, (b) depth contour plot, and (c) depth profile for microchannels machined by L-LIPMM

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Fig. 9

Schematic of focal line variation process

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Fig. 10

Channel (a) depth and (b) width for different number of exposures

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Fig. 11

Microchannel after 12 exposures at 2 μm increments, deepest profile shown

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Fig. 12

Effect of changing pulse frequency on: (a) depth and (b) width of microchannels

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Fig. 13

Channel profile at maximum depth (100 kHz repetition rate)

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Fig. 14

Channel depth profiles with tapered and near-vertical walls (V and U shapes) for: (a) 20 kHz and (b) 100 kHz repetition rates

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Fig. 15

Effect of power variation on channel depth, at different pulse repetition rates

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Fig. 16

Effect of changing power on the length of microchannels, the power increases from top to bottom

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Fig. 17

Microchannel array on aluminum, 100 μm lateral spacing



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