Manufacture of three-dimensional valveless micropump

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Journal of Materials Processing Technology 192–193 (2007) 229–236

Manufacture of three-dimensional valveless micropump

Yih-Lin Cheng ∗, Jiang-Hong LinDepartment of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei, Taiwan

bstract

Up to the present, the manufacture of the micropump generally used MEMS processes to obtain micro scale channels. However, the geometryf the channels is usually 2.5D and the cost is relatively high due to the characteristics of the most micro fabrication techniques. In this research,e focused on manufacture of three-dimensional valveless micropumps in inexpensive approach. The design of the micropump consists of threeorizontal inlet channels and one vertical outlet channel. The 3D geometry of the channels with minimum width of 80 �m gives great challengesn fabrication and is difficult to be achieved by traditional micro fabrication techniques. Shape deposition manufacturing (SDM) process, aayered manufacturing technique involving repeated material deposition and removal, was used to manufacture the chamber and channels of the

icropump. CAD/CAM software was applied to slice the 3D model and plan the manufacturing sequences. The piezoelectric buzzer was attached
o the fabricated valveless micropump chamber to test the performance. Three different channel width designs were manufactured successfullynd tested at various piezo-triggered frequencies. This research provides a solution to manufacture the three-dimensional micropump geometrynexpensively. SDM process was proved to be a suitable approach to generate pre-assembled valveless micropump structure with micro channels,nd is applicable to other similar applications. 2007 Elsevier B.V. All rights reserved.
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eywords: Micropump; Valveless; Microchannel; Layered manufacturing; Sha

. Introduction

Micropumps have been developed for more than two decades.heir characteristic of handling small and precise volumes of liq-id and/or gas makes them able to serve chemical, medical, andiomedical applications with great scientific and commercialotential. Fuel delivery in a fuel cell system [1], drug deliv-ry [2], and integration with miniaturized chemical analyzerss a “Micro total analysis system (�TAS)”[3] are some of thexamples. The design of micropumps can be divided into valve-ased and velveless. In valve-based pumps, mechanical checkalves in terms of membranes or flaps are used. Wear, fatigue,nd valve blocking are issues concerned in this type and limit itspplications. Valveless micropumps, first introduced by Stemmend Stemme [4], use diffuser/nozzle elements to perform ascheck valve. The construction of valveless micropumps is

elatively simple compared to check valves and can avoid theroblems mentioned above. Most common actuation methods
n micropumps include electromagnetic [5], electrostatic [6],hape memory alloy [7], thermopneumatic [8], and piezoelec-ric [4,9–12]. Piezoelectric actuation can provide relatively a
∗ Corresponding author. Tel.: +886 2 2737 6450; fax: +886 2 2737 6460.E-mail address: [email protected] (Y.-L. Cheng).

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924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2007.04.055

position manufacturing (SDM); Piezoelectric

igh actuation force and a fast mechanical response, therefore,s widely used in micropump development.

Micro-electro-mechanical system (MEMS) technologies arehe major manufacturing approach to build micropumps in recentesearches. Silicon micromachining and polymer-based micro-achining techniques are the main categories. Silicon moving

arts can avoid wear and fatigue problems in the long-runests, but the material choice is limited and fabrication costs relatively high. In polymer microfabrication, such as thick-esist lithography, soft lithography, micro stereolithography, andicro injection molding, the advantage is the possibility of

sing different polymeric materials to meet biocompatibility andhemical resistance for its potential applications. However, theimited material lifetime can be an issue and the goal of trueow-cost micropump is still not achieved yet. Besides, most ofhe MEMS techniques can only build 2.5-dimensional geome-ry rather than a true three-dimensional one. The microchanneleometry was hence limited in the most designs. Therefore, theres a need to develop some manufacturing alternatives which areapable of building true 3D geometry at lower cost.

In this research, we focused on manufacture of three-
imensional valveless micropumps in inexpensive approach.
special micropump design with vertical and horizontal dif-users/nozzles is proposed initially as a micro-submarine’sropulsion system, but is not limited to this specific application.

mailto:[email protected]

dx.doi.org/10.1016/j.jmatprotec.2007.04.055

230 Y.-L. Cheng, J.-H. Lin / Journal of Materials Processing Technology 192–193 (2007) 229–236

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ig. 1. Schematic drawings of a valveless micropump placed at the end of aicro-submarine with three inlets and one outlet.

manufacturing alternative, shape deposition manufactur-ng (SDM) process, which can build true 3D geometry, waspplied to fabricate pre-assembled chamber with inlet and out-et channels. Moreover, three valveless micropump designs withifferent channel width were fabricated and tested.

. Design of the valveless micropump

The micropump developed in this research is a piezoelectric-ctuated valveless pump. This pump consists of a chamber, threeorizontal inlet channels, and one vertical outlet channel. Thisas originally designed for propelling a micro-submarine with

he configuration of inlets from the side perpendicular to oneutlet in the back as shown in Fig. 1.

.1. Diffuser design

In the traditional valveless micropump, the working theoryan be illustrated in Fig. 2. The dimension difference at the bothnds of the diffuser causes the pressure difference and drives the

Fig. 2. The working theory of a traditional valveless micropump [13].

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Fig. 3. Conical and flat-w

Fig. 4. The stability map of a diffuser [15].

uid. In the supply mode, the actuator increases the chamberolume, resulting in a lower pressure inside the chamber. In thisituation, the inlet flow is greater than the outlet flow; therefore,he fluid is supplied into the chamber. Reversely, in the pump

ode, the decrease in the chamber volume increases the chamberressure and, as a result, the outlet flow is greater than the inletow.

The diffuser/nozzle design determines the performance of theicropump. Diffusers can be categorized as conical and flat-alled with circular and rectangular cross-section, respectively

Fig. 3). According to the literature [15], the length of the flat-alled diffuser will be 10–80% shorter than that of the conicalne under the same flow performance. Therefore, flat-wallediffuser design was chosen in this research. The major dimen-ions of a diffuser with the same channel height b include throatidth W1, exit width W2, length L, and total included diffuser

ngle 2θ.According to the stability map of a diffuser (Fig. 4), the dif-

user operates in four different regions depending on the diffuser
eometry. In the bistable steady stall (between b–b and c–c lines)nd jet flow (above c–c line) regions, the flow performance isoor to extremely poor. Under the line a–a, the no stall region,he flow is steady viscous without separation at the diffuser walls
alled diffusers [14].

Y.-L. Cheng, J.-H. Lin / Journal of Materials Processing Technology 192–193 (2007) 229–236 231

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fThe length L is calculated based on L/W1 = 16. The exit channelwidth (W2), which is not listed in the table, can be determinedby W1, 2θ, and L.

Fig. 5. The performance map for a flat-walled diffuser [15].

nd a moderate performance is achieved. In the transitory steadytall region between a–a and b–b lines, the flow is unsteady. Min-mum pressure loss and maximum pressure-recovery coefficient

p occur in this region, and hence the diffuser geometry will beesigned accordingly. The typical performance map for a flat-alled diffuser is shown in Fig. 5. The AR is defined as the area

atio between exit and throat. From the map, the maximum Cpccurs when L/W1 is between 16 and 18, 2θ is around 10◦, andR falls between 3.5 and 4. Therefore, the diffuser geometryas designed to be L/W1 = 16, AR = 3.5, and 2θ = 10◦.

.2. Piezoelectric actuator

A commercial available piezoelectric buzzer was used as thectuator. The buzzer, illustrated in Fig. 6, consists of a brassayer for resonance and a piezoelectric ceramic layer with aliver coating for external-drive connection. In order to keep the
verall size of the micropump small, the smallest diameter fromhe products of KEPO Electronic Co., Ltd. was selected. Theimensions are listed in Table 1.
able 1imensions of selected piezoelectric buzzer

Diameter (mm) Thickness (mm)

rass layer 9 0.2eramic layer 6 0.2

Fig. 6. Piezoelectric buzzer.

.3. Micropump design

The exploded view of the final micropump design and itsomponent list are shown in Fig. 7. The chamber is 8 mm iniameter due to the dimension of the selected piezoelectricuzzer, and 110 �m in height. Three inlet channels are locatedt the side of the chamber and a outlet channel is placed at theottom with the channel height b three times of that for inlethannels to balance the flow amount. The general view and theross-section view of the micropump’s chamber and channelsre shown in Fig. 8.

In this research, three types of micropump design were manu-actured and tested. The dimensions are summarized in Table 2.

Fig. 7. Exploded view of micropump and component list.


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Fig. 8. Micropump’s chamber and channels.

. Manufacture of chamber and channels

.1. Challenges in manufacturing

In the previous researches, the micropumps were usuallyesigned to place the inlet and outlet diffuser/nozzle channelsn the same plane. That is, the geometry is 2.5D without criticalhape change in the third axis. Micro fabrication techniques areapable of fabricating these features and are often utilized inhese applications even though the cost may be relatively highn the prototyping stage. However, for the specific design in thisesearch, inlet and outlet channels are placed in 3D space. Mostf the micromachining methods are 2.5D and will introduceteps between layers, which means they are incapable of pro-ucing smooth 3D surfaces for diffuser channels. Besides the 3Deometry, the minimum channel width of 80 �m and the high-spect ratio of the vertical channel also give great challenges inanufacturing.

.2. Material and process selection

In material selection, polymers are the top choice due tots ease of shaping and machining. Three possible processesan be used to shape complex parts—parts can be machined

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able 2imensions of inlet and outlet channels

ype W1 (�m) 2θ L (�m)

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1280I 100 1600II 120 1920

Fig. 9. SDM process [17].

rom available bulk material, can be injection molded, or cane cast. In our micropump design, the machining approach willeed additional assemblies of the chamber and channels. Align-ent is an issue and special fixture is required. The high cost of

ie makes injection molding not economically favored in low-olume production. Casting is a feasible approach if suitableolding techniques are applied. Room-temperature-cured poly-ers are preferred because they reduce the need of furnace and

pecial temperature control systems. Molds can be permanentr fugitive. Fugitive molds are more flexible and mold releasean be done by chemical or thermal means. As a result, shapeeposition manufacturing process [16], developed by Carnegieellon University and Stanford University, provides a solution

or room-temperature polymer casting.SDM is a layer manufacturing technique with a sequence of

dditive and subtractive processing steps for fabricating complexD parts (Fig. 9). In each layer, part material or support mate-ial are deposited and machined to net shapes. After the parts completely built, the support material is removed chemicallyr thermally, depending on the material characteristics. Variousaterials, such as metals and polymers, can be fabricated byDM.

Since the original polymer part materials used by Stanfordniversity’s Rapid Prototyping Laboratory [17] are not com-ercially available anymore, we searched for new part material

hat is room-temperature-cured with similar properties to AdtechE-501/530 epoxy. As a result, Ciba FC 52Isocynate/52Polyolas chosen. It takes 60–90 min to cure, and the density is.6–1.7 g/cm3. Other properties are listed in Table 3. The sup-ort material used in this research is the same as that used attanford, a combination of 25% File-a-wax and 75% Protowax.he support material is removed by BIOACT 280 at 70 ◦C withltrasonic vibration.

.3. Manufacturing approaches and results

The manufacturing of the chamber with inlet and outlet chan-els were divided into three sections—bottom, middle, and top.he bottom section contains a vertical outlet channel with high-

Inlet channel height, b (�m) Outlet channel height, b (�m)

80 240


Table 3Material properties of Ciba FC 52 Isocynate/52 Polyol

Mixing ratio 1:1

Ultimate tensile strength 35 MPaDensity 1.6–1.7 g/cm3

Hardness 75–80DDeflection temperature 85–90 ◦CGel time 5–6 minDemolding time 60–90 minMixing ratio 1:1

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Fig. 10. High-aspect ratio outlet channel feature.

spect ratio (Fig. 10), which is the most difficult to manufacturemong three sections. The middle section (Fig. 11) includes inlethannels, while the top section (Fig. 12) includes the main cham-er body and the fixture feature for integration with the actuator.hree sections are built sequentially. The support material, wax,as removed at the end to obtain a chamber with inlet and outlet

hannels without assembly.In the bottom section, the vertical outlet channel is filled

y support material, wax. Since the channel dimension is verymall, it is hard to find a suitable cutting tool to machine theavity out of the part material and then pour in support material.herefore, the SDM process planning implemented this section

nto two stages. In the first stage, a wax substrate rather than aolymer substrate was used. The wax substrate was machinedp to channel’s partial surfaces, and the part material was cast to

Fig. 11. Middle section.

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Fig. 12. Top section.

ll up the machined area. The second stage machined the otherortion up to channel’s remaining surfaces, and cast in the cav-ty with the part material. In this approach, the channel area washe only wax region left as we wanted. Since the region to be

achined is larger than the available tool size, general endmillsan be used directly and no special small cutting tool is required.he next issue is to determine the portion for the first stage. Due

o the small wax region left during and after machining in theecond stage, it is very likely to break off during machining.herefore, more bonding surfaces to the first-stage part materialan provide stronger bonding and are preferred. As a result, twoonsecutive surfaces were selected as the machining boundaryurfaces for the first stage (Fig. 13a), and the other two surfacesere for the second stage (Fig. 13b). The arrow direction shows

he portion to be machined away in each stage.In the middle section, support material was deposited on the

ottom section and machined to define the geometry of inlethannels. Since these channels are placed horizontally, therere no high-aspect ratio and bonding issues, and one round ofupport material deposition and machining is sufficient. The topection was done by casting the part material and machining to
he required shape. The complete fabrication flow is summarizedn Fig. 14. For each section, the total machining time and materialeposition time are listed in Table 4.
Fig. 13. The machining boundary surfaces for the two stages.


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Fig. 15. Fabricated micropump chamber with inlets and a outlet.

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ig. 14. Fabrication flow of chamber and inlet/outlet channels for micropump.

The finished chamber with three inlets and one outlet beforessembled with the piezoelectric actuator is shown in Fig. 15.n order to shown the inlet channels more clearly, we put hairsabout 60–80 �m) through channels as shown in Fig. 16. The

able 4abrication time required for each section

ottom section Minutes % of total

Total part material curing time 300 48.1Total machining time 74 11.9Subtotal 374 60

iddle sectionSupport material deposition time 15 2.4Total machining time 40 6.4Subtotal 55 8.8

op sectionTotal part material curing time 150 24.0Total machining time 45 7.2Subtotal 195 31.2

otal 624 100

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Fig. 16. Hairs through inlet channels.

abricated outlet dimensions were measured under an opticalicroscope. The designed and measured dimensions at throat

nd exit are compared in Table 5. The area error is about 5%.

. Micropump tests

A piezoelectric buzzer was attached to the finished cham-er sealing with silicone for water-proof purpose (Fig. 17). Ahort aluminum pipe was glued to the end of outlet for testingurpose. The performance of the assembled micropump was
ested by their back pressure and flow rate. The micropump waslaced in a cup filled with water, and an outside Teflon tube with.86 mm inner diameter was connected to the aluminum pipe.or measuring back pressure, the Teflon tube was placed ver-
able 5utlet dimensions measurement

hroat W1 × b (�m) Area (�m2) Error

esign 80 × 240 19200 5.4%abricated 79 × 230 18170

xit W2 × b (�m) Area (�m2) Error

esign 305 × 240 73200 5.6%abricated 294 × 235 69090


Fig. 17. Front (left) and back (right) views of assembled micropump.

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Table 6Micropump testing results

Types (W1) Frequency (kHz) 1 3 5 7 10

I (80 �m)Back pressure (Pa) 3.9 8.8 12.8 15.7 16.7Flow rate (�l/min) 0.29 0.41 0.75 0.93 1.10

II (100 �m)Back pressure (Pa) 2.0 3.9 6.9 8.8 10.8Flow rate (�l/min) 0.08 0.24 0.37 0.42 0.66

III (120 �m)Back pressure (Pa) 2.0 3.9 5.9 6.9 7.9Flow rate (�l/min) 0.06 0.20 0.29 0.35 0.41

Fig. 20. Back pressure comparison.

Fig. 18. The schematic of back pressure measurement.

ically (Fig. 18). The water level differences between cup andube, h, is measured to calculate back pressure. In flow rate mea-urement, the tube is placed horizontally at the same height ofater surface in the cup (Fig. 19). The flow rate can be calculatedy measuring the distance that flow travels within a time period.he testing results of three types of micropump fabricated in

his research are summarized in Table 6. Figs. 20 and 21 com-are back pressure and flow rate of the three designs at variousrequencies.

From the above results, we can summarize as follows:

1) In our measured frequency range, when the frequencyincreases, both back pressure and flow rate increase.

Fig. 19. The schematic of flow rate measurement. Fig. 21. Flow rate comparison.

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36 Y.-L. Cheng, J.-H. Lin / Journal of Materials

2) Type I (W1 = 80 �m) has higher back pressure and flow ratethan Type II (W1 = 100 �m) and III (W1 = 120 �m).

3) Type II and III perform similar at lower frequencies (1 Kand 3 kHz).

4) Type I has the best back pressure and flow rate at 10 kHzamong all data.

. Conclusions

In this research, a new valveless micropump design was pro-osed with three inlets perpendicular to one outlet. With this 3Deature, common microfabrication techniques which can onlyenerate 2.5D geometry are not applicable. As a result, a lay-red manufacturing technique, SDM process, was utilized toabricate 3D microchannels successfully and was proven to be auitable approach to generate pre-assembled valveless microp-mp structure. After attached to a piezoelectric buzzer, threeypes of working micropumps designed with different channelidths were tested at various frequencies.

cknowledgements

This work is funded by National Science Council, ROC,nder the project number 93-2212-E-011-033.

eferences

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[9] H. van Lintel, F. van den Pol, S. Bouwstra, A piezoelectric micropumpbased on micro machining in silicon, Sens. Actuators 15 (1988) 153–167.

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14] A. Olsson, Valve-less diffuser micropumps, PhD thesis, Stockholm, 1998.15] F. White, Fluid Mechanics, McGraw-Hill, New York, 1986.16] R. Merz, F.B. Prinz, K. Ramaswami, M. Terk, L. Weiss, Shape deposi-

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Manufacture of three-dimensional valveless micropump