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Parametric Study of Microchannel Fabricated

by Laser Beam Machining

As part of

(Flow Boiling Heat Transfer in Microchannels)

Submitted By

Harshit Kumar Gupta

Roll No: 2010078

Supervisor

Prof.TanujaSheorey

MECHANICAL ENGINEERING DESCIPLINE

INDIAN INSTITUTE OF INFORMATION TECHNOLOGY,

DESIGN AND MANUFACTURING JABALPUR

(July 22- August 6 ,2013 )

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1. IntroductionOver the past few years, laser technology has emerged as a powerful tool in area of

micromachining [1]. A key advantage of laser micromachining over other conventional

patterning or etching techniques is the ability to remove materials ranging from ceramics and

metals to semiconductors and polymers without the need to change tooling or chemicalprocessing. Other notable qualities include lesser thermal distortion i.e. smaller heat affected

zone (HAZ), better cutting edge, better surface morphology, etc. Amongst available lasers,

pulsed laser is being used more extensively for micromachining because it enables large

degree of flexibility in terms of process parameters. Laser pulse may be varied by variation in

traverse velocity, laser power, pulse frequency, spot size, to name a few. To obtained

microchannel of requisite depth, width, surface roughness above parameters need to be

chosen judiciously [2, 3]. In the present work effect of process parameters on fabricated

microchannel has been shown.

2. Present InvestigationIn this phase, primary focus was on fabrication of microchannel of designed dimensions with

EPILOG laser cutting machine and characterization of its process parameters to obtain desired

microchannel. To get proper understanding of process parameters, experiment were

performed based upon design of experiments (DOE) made in last stage, which is shown

below in table 1.

2.1 Design of Experiments (DOE)

Material: Plexiglas

Desired dimensions of cut: 2cm x 50 x75

Profile Required

S.No Velocity

Settings

(%)

Power

Settings

(%)

Frequency

Settings

(Hz)

Spot

settings

(inches)

Aim of study

1 20% 10 % 2500 0.002" Effect of power

2 20% 30% 2500 0.002 Effect of power

3 20 15 2500 0.002 Effect of power

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Table 1: Design of expeiments

The microchannels fabricated were then analysed regarding their shape, accuracy of the

dimensions with the use of SEM at PDPM IIITDM Jabalpur. Results for which are shown in

next section alongwith the discussion on emerging effects.

3. Results and Disscussions

S.No SEM Image Remarks

In this a reference was created for

benchmarking further results.

Material is being removed form of

spherical cavity thats why channel

formed is having spherical cross

section, making it more useful.

Fig 1. SEM image of microchannel with 20% Velocity/20% Power/

2500 Hz Freq/ 0.002 spot size settings

4 15 20 2500 0.002 Effect of velocity

5 25 20 2500 0.002 Effect of velocity

6 20 20 3500 0.002 Effect of pulse frequency

7 20 20 1500 0.002 Effect of pulse frequency

8 20 20 2500 0.003 Effect of spot size on width of cut (kerf

width)and depth

9 20 20 20 0.002 Effect of traversing twice the same

section on surface morphology

10 15 25 2500 0.002 Combined effect

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1a. Channel is having reasonable surfacefinish but it is having material

deposition at the centre of

microchannel due to melting and

resolidification. Material removal in

LBM is by two mechanisms namely

melting and/or vapourization. Due to

improper cooling, molten metal getsolidified before getting vapourized,

leading to material deposition hence

degrading surface finish. Also kerf

width obtained is within desired

accuracy.

Fig 1a. SEM image of microchannel with 20% Velocity/20% Power/

2500 Hz Freq/ 0.002 spot

2. With increase in power input ,depth of increases from 163 m to

360 m because larger power

leads more concentrated energyhence more penetration. But cross

section of channel is not purely

circular .There is increase in melting

of neighborhood region as well due

to increase in power which can be

seen in



3. In this effect of reduction of powerwas analysed. With reduction in

power input, smaller depth along

with smaller HAZ region has been

obtained.

Fig 3. SEM image of microchannel with 20% Velocity/15 % Power/


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4. In this effect of reduction in traversevelocity was analysed. Comparing

with fig 1 with reduction in traverse

velocity, laser will be concentrating

at a point for larger time, hence leads

to more penetration. Smaller HAZ is

obtained in comparison with fig 2

due to lesser intensity.



5. In this effect of increase in traverse

velocity was analysed. Due toincrease in velocity, material is

reaching to molten state but not

vaporizing as the exposure time to

the laser light at each position

becomes shorter. There is not

enough time for temperature rise

and/or photon-matter interaction,

leading to degradation of surface

finish [4].



6. In this effect of increase in pulsefrequency was analysed. By

increasing the pulse frequency of the

laser during cutting, a smoother cut

was created. Partly this is due to the

increased pulse frequency taking

smaller bites out of the material likea fine tooth saw blade. The more

frequent laser pulses also create

more localized heat which melts the

area smooth. There is almost no

change in depth [4].



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7.

Fig7. SEM image of microchannel with 20% Velocity/20% Power/

1500 Hz Freq/ 0.002 spot8 In this effect of increase in spot size

was analyzed. With increase in spotsize, intensity decreases leading to

decrease in depth and smaller HAZ.

Also change in kerf width need to be

analyzed by taking top view SEM

image of channel.



9a. In this effect of traversing the sameprofile twice was analysed.When

laser was allowed to traverse same

path twice, deposited material was

drained off during second stroke,

leading to no central deposition and

hence smoother channel (Fig9b).However increase in depth was

found because same amount of

power was given twice.

In comparision with fig 1 HAZ

obtained is very small.

Fig 9a. SEM image of microchannel with Traversing Twice 20%

Velocity/20% Power/ 2500 Hz Freq/ 0.002 spot

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9b.

Fig 9b. SEM image of microchannel with Traversing Twice 20%

Velocity/20% Power/ 3500 Hz Freq/ 0.002 spot

10. In this combined effect of velocity

and power is analysed. With increasein velocity and reduction in power

depth reduces by larger factor as

both the factors are leading to

decrease in intensity at a point.



4. Conclusiona) For any given traverse velocity, spot size and frequency, increasing power

increases depth but also increases unwanted HAZ.

b) Variation in traverse velocity van control depth without affecting much HAZ. Sotraverse velocity can control depth better than power.

c) Microchannel with best surface finish can be obtained by increasing pulsefrequency and by cutting channel with two strokes repeating one over other and

power and velocity settings to cut almost up to half depth

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d) Increase in power, decrease in velocity, and decrease in spot size leads to increasein depth while opposite change leads to reduction in depth while depth is almost

independent of pulse frequency.

e) Kerf width increases with increase in spot size while it is almost independent ofother parameters.

4.2 Futuristic Direction

In the next phase the task is to fabricate requisite microchannel by fixing process parameters

along with two reservoirs to make it flow .

4.3 References

[1] N Prabhat, D Gupta, Fabrication and Analysis of microchannels Department of

Mechanical Engineering, Indian Institute of Technology Bombay.

[2] Dr. V.K Jain Laser Beam Machining, Advanced Machining Processes, Allied

Publishers Mumbai, 2002

[3] B. Pratap, C.B. Arnold and A. Piqu, Depth And Surface Roughness Control On Laser

Micromachined Polyimide For Direct-Write Deposition, SPIE MF 2003, Jan 20-24, 2003,

San Jose CA, Proceedings Vol. 4979, 217-226(2003)

[4] Xianghua Wang, Giuseppe Yickhong Mak and Hoi Wai Choi,Laser Micromachining and

Micro-Patterning with a Nanosecond UV Laser, Micromachining Techniques for Fabrication

of Micro and Nano Structures.

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