fabrication of microchannel

7/27/2019 Fabrication of Microchannel

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Fabrication of Microchannels

As part of

(Flow Boiling Heat Transfer in Microchannels)

Submitted By

Harshit Kumar Gupta

Roll No: 2010078

Supervisor

Prof. Tanuja Sheorey

MECHANICAL ENGINEERING DESCIPLINE

INDIAN INSTITUTE OF INFORMATION TECHNOLOGY,

DESIGN AND MANUFACTURING JABALPUR

(July 5- July 22 ,2013 )


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1. IntroductionThe importance of study of flow through microchannels and various fabrication techniques

involved in their manufacturing lies in its applications in MEMS devices, biochemistry,

biomedical, lab-on-a chip devices, electrophoresis, etc. Conventionally, any channel or tube

having hydraulic diameter less than 1 mm is called a microchannel. Thus, its fabrication is

done using nonconventional micro manufacturing machines, which itself is animportant field

for research. There are various fabrication techniques available for manufacturing micro

devices, namely laser cutting, photolithiography, chemical vapour deposition, physical vapour

deposition, electric discharge machining[1,2,3]. Flow and heat transfer characteristics of

macroscopic devices are studied quite extensively and now known, but when it comes tomicrochannel flow, flow becomes significantly different. Hence there is a needto further

investigate the flow physics in this domain via experiments and computational methods,

making fabrication of microchannel very important work.

2. Present Investigation

In this phase, primary focus was on fabrication of microchannel with inhouse available

facilities. At the same time, other known techniques were studied.In the presented work laser

beam machining has been used to cut microchannels of designed dimensions.

2.1Laser Beam Machining (LBM)

Laser Beam machiningis an unconventional

machining process in which a beam of

highly coherent light calledLaser is directed

towards the work piece for machining. Since

the rays of a laser beam are monochromatic

and parallel, it can be focused to a very small

diameter(figure 1), known as laser spot, and

can produce energy as high as 100 MWon a

square millimeter of area[4]. It can be used

to perform precision micro-machiningon all

microelectronic substrates such as ceramic, silicon, diamond and graphite.


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2.2Epilog Legend 36 EXT Laser Machine (Figure 2)

2.2.1 Specifications:

Maximum Engraving Area: 36 x 24

Maximum Material Thickness 12-14

Laser source: air-cooled CO2 laser

tubes

Material Engraving Techniques: Raster

and vector

Laser Source specifications:

Spot Diameter : 25 -75 m

2.2.2 Operation of Laser Machine

Epilog laser can mark(engrave) and cut a variety of non-metallic materials. The CO2 laser

beam itself is invisible. The laser beam is having spot size range of 25 to 75 m[5]. At the

spot,the energy density is concentratedand the beam traces the pattern to be cut.The pattern is

provided in a simplified 2-D drawing. It allowsvery precise material removal that is

characteristic of laser engraving.

Procedure:

a) Give input file in .cdr format(preferably made in coral draw)b) Input machine specifications for vector cutting:

Velocity: 0-100%

Power: 0-100%

Frequency: 0-5000 Hz

c) Apply these specifications and then start machining the job

Here frequency, power and traverse speed decide depth of cut, while other geometric

specifications are provided in input drawing file. Depth increases with increase in power,

while decreases with increase in traverse speed. First few experiments are conducted to

understand cutting behavior of laser beam for a particular material under variableparameters. The same is given in detail with analysis in the following sections.


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2.2.3 Material and dimension of test piece

Job was designed with2cm x 1.5 cm dimensions and Plexiglas (acrylic) material (figure 3),

taking into consideration sample requirements of SEM so that it can be analysed in SEM

without any additional processing requirements.

Fig 3: Uncut job peice Fig 4: Fabricated microchannel

2.2.4 Cut material

A CAD drawing was prepared with the requisite dimension of microchannel profile to be

cut(figure 4).

2.3 Analysis of Channel geometry

The microchannel fabricated on Epilog Laser Cutting Machine was then analysed using

Scanning Electron Microscope (SEM) at PDPM IIITDM Jabalpur having accelerating

voltage 200 V -30 KV, probe current upto 2 , image processing up to 4096 x 3536 pixels,

vaccum pressure ranging from 6e-4 Pa to 2600 Pascal (figure 5).The Scanning Electron

Microscope (SEM) is a microscope that uses electrons instead of light to form an image.

There are many advantages of using the SEM instead of a light microscope

The SEM produces images of high resolution, which means that closely spacedfeatures can be examined at a high magnification.

Preparation of the samples is relatively easy since most SEMs only require the sampleto be conductive (if not conductive, for few materials like Plexiglas it can be given

conductive path by use of carbon tape (figure 4)).


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Fig 5 FEI Quanta 2000 Scanning Electron Microscope

2.3.1 Working of SEM

The SEM uses electrons instead of light to form an image. A beam of electrons is produced atthe top of the microscope by heating of a metallic filament. The electron beam follows a

vertical path through the column of the microscope. It makes its way through electromagnetic

lenses which focus and direct the beam down towards the sample. Once it hits the sample,

other electrons (backscattered or secondary) are ejected from the sample. Detectors collect the

secondary or backscattered electrons, and convert them to a signal that is sent to a viewing

screen similar to the one in an ordinary television, producing an image. Here we magnify the

image by providing more and more voltage.

3. Results and Discussion

Several experiments were performed to get the basic understanding of LBM using Epilog

laser cutting machine at PDPM IIITDM Jabalpur Design Lab and then those fabricated micro

channels were analysed in SEM lab at PDPM IIITDM Jabalpur. Following results were

obtained from SEM images obtained.


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Fig 6 SEM image with 20% power/ 20% velocity / 2500Hz

pulsating frequency / spot size 25m

Fig 7 SEM image with 20% power/ 20% velocity /

2500Hz pulsating frequency / spot size 50m

Fig 8 SEM image with 20% power/ 20% velocity / 2500Hz pulsating frequency / spot size 50m

SEM images ((figures6 and 7)) show that with the Laser spot sizes of 25 and 50 microns, the

width of channels cut by Laser are 136 and 208 microns respectively. To obtain depth of cut

of the channel, the cut is made upto the end of test piece. Figure 8 shows end section of the

cut channel with depth of cut of 163 micron for Laser spot size of 50 micron. All the three

cuts are done by a single traverse of Laser. It has been found that LBM is giving resonable

surface fininsh. LBM strikes on material, heat it and material is removed due to melting. A

pool of molten metal can be seen clearly at the centre of the channel after solidification,

because material is removed from circular spot having power intensity concentrated at its

center.


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4. ConclusionBased on SEM images and analysis of characteristics of cut channel, study can be concluded

in the following points.

a) Epilog laser can be used for cutting microchannels efficiently and with reasonableaccuracy.

b) Surface morphology of the obtained channel is also in accordance with designrequirements. It is having reasonable surface finish within the channel.

c) Material is being removed form of spherical cavity thats why channel formed is having spherical cross section, making it more useful.

d) Effect of variation in traverse speed and power on depth of channel is not clear, sosome more experiments need to be performed for which design of experiments has

been made as explained in the next section.

4.1 Design of experiment (DOE)

DOEis the design of any information-gathering exercises where variation is present, whether

under the full control of the experimenter or not. It is done to find out effect of process

parameters. In our case to find out effect of power and traverse velocity on depth following

DOE has been made.

Material: Plexiglas

Desired dimensions of cut: 2cm x 50 x75

S.No Profile Required Parameters Aim

1. Power : 20%

Velocity: 20%

Frequency: 2500Hz

Focus diameter: 50m

To check working of laser on

plexiglass and observing accuracy of

operation


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2. Power : 20%

Velocity: 20%

Frequency: 2500Hz

Focus diameter: 50m

To check repeatability of operation

3. Power : 20%

Velocity: 20%

Frequency: 2500Hz

Focus diameter: 25m

To find effect of focus

diameter(decrease in focus diameter)

on roughness patterns

4. Power : 20%

Velocity: 20%

Frequency: 2500Hz

Focus diameter: 75m

To find effect of focus diameter

(increase in focus diameter) on

roughness patterns

5. Power : 20%

Velocity: 20%

Frequency: 2500Hz

Focus diameter: 50m

To calibrate process parameter

power for depth and observe change

in roughness pattern

6. Power : 40%

Velocity: 20%

Frequency: 2500Hz

Focus diameter: 50m


power(increase in power) for depth

and observe change in roughness

pattern

7. Power : 20%

Velocity: 15%

Frequency: 2500Hz

Focus diameter: 50m


traverse velocity (decrease in

traverse velocity) for depth and

observe change in roughness pattern

8. Power : 20%

Velocity: 25%

Frequency: 2500Hz

Focus diameter: 50m


traverse velocity (increase in

traverse velocity) for depth and

observe change in roughness pattern


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4.2 Futuristic Direction

In the next phase the task is to perform experiments designed in section 4.1 to get proper

understanding of Epilog Laser Cutting Machine and its process parameters. After that

requisite size channel with two reservoirs at the end would be fabricated to capture

characteristics.

4.3 References

[1] M.K. Boyajian, Z. Zhang Microchannel fabrication and bio related application

unpublished 2010

[2] Sean Ashman, Satish G. Kandlikar A review of manufacturing processes for

microchannel heat exchanger fabrication4th internatioanal conference on nanochannels,

microchannels, minichannels Ireland 2006

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

Mechanical Engineering, Indian Institute of Technology Bombay.

[4] Dr. VK Jain Laser Beam Machining ,Advanced Machining Processes, Allied

Publishers Mumbai, 2002

fabrication of microchannel

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