Jackson M.J. Micro and Nanomanufacturing

Подождите немного. Документ загружается.

Manufacturing High Aspect Ratio Microstructures 141

23.

Olsson A, Larsson O, Horn J, Lundbladh L, Ohman O and Stemme

G, 1997, Valve-less diffuser micropumps fabricated using thermoplastic

replication, Proc. IEEE Tenth Annu. Int. Workshop on Micro-Electro Me-

chanical Systems, MEMS'97 (Nagoya, Japan, 26-30 Jan. 1997), pp 305-

10.

24.

Schomburg W K, Ahrens R, Bacher W, Martin J and Saile V,

1999,

AMANDA-Surface micromachining, molding, and diaphragm trans-

fer, Sensors Actuators A, 76, 343-8.

25.

Dopper J, Clemens M, Ehrfeld W, Kamper K-P and Lehr H, 1996,

Development of low-cost injection molded micropumps, Actuator'96:

Proc.

Fifth Int.

Conf.

on New Actuators, pp 37-40.

26.

Fahrenberg J, Bier W, Maas D, Menz W, Ruprecht R and Schom-

burg W K, 1995, Micro valve system fabricated by thermoplastic molding,

J. Micromech. Microeng., 5,

169-71.

27.

Goll C, Bacher W, Bustgens B, Maas D, Menz W and Schomburg

W K, 1996, Microvalves with bistable buckled polymer diaphragms, J.

Micromech. Microeng., 6, 77-9.

28.

Goll C, Bacher W, Bustgens B, Maas D, Ruprecht R and Schom-

burg W K, 1997, Electrostatically actuated polymer micro valve equipped

with a movable membrane electrode, J. Micromech. Microeng., 7, 224-6.

29.

Gerlach A, Knebel G, Guber A, Heckele M, Herrmann D, Muslija

A and Schaller T, 2002, Microfabrication of single-use plastic microfluidic

devices for high-throughput screening and DNA analysis, Microsyst.

TechnoL, 7, 265-8.

30.

Rummler Z, Berndt M, Hartl H-G, Hempel M, Peters R and

Schomburg W K, 2000, Micro-degasser made of inert polymers for HPLC

devices, ASME Winter Annual Meeting (Orlando, FL, 5-10 Nov. 2000).

31.

Lee G-B, Chen S-H, Huang G-R, Lin Y-H, Sung W-C and Lin Y-

H, 2001, Microfabricated plastic chips by hot embossing methods and their

applications for DNA separation and detection. Sensors Actuators B, 75,

142-8.

32.

Blankenstein G, 2000, Microfluidic devices for biomedical appli-

cations, MST News (Sept. 2000), 14-15, published by: VDIAHOE-

Technologiezentrumlnformationstechnik.

33.

Grass B, Neyer A, Johnck M, Siepe D, Eisenbeiss F, Weber G and

Hergenroder R, 2001, A new PMMA-microchip device for isotachophore-

sis with integrated conductivity detector. Sensors Actuators B, 72, 249-58.

34.

Weston DF, Smekal T, Rhine D B and Blackwell J, 2001, Fabrica-

tion of microfluidic devices in silicon and plastic using plasma etching, J.

Vac.

Sci. Technol. B, 19,

2846-51.

35.

Kashanim D, Williams V, Shvets I V, Volkov Y and Kelleher D,

2000,

Microfluidic biochips for cell guidance and separation, Proc. First

142 Micro-and Nanomanufacturing

Annu. Int. lEEE-EMBS Special Topic Conference on Microtechnologies

in Medicine and Biology (Lyon, France, 12-14 Oct. 2000), pp 279-82,

(Catalogue no. 00EX451).

36.

Martin J, Bacher W, Hagena O F and Schomburg W K, 1998,

Strain gauge pressure and volume-flow transducers made by thermoplastic

molding and membrane transfer, Proc. Int. Workshop on Micro-Electro

Mechanical Systems, MEMS'98 (Heidelberg, Germany, 25-29 Jan. 1998),

pp 361-6.

37.

Dittman D, Ahrens R, Rummler Z, Schlote-Holubek K and

Schomburg W K, 2001, Low-cost flow transducer fabricated with the

AMANDA process, 11th Int. Conf On SoUd-State Sensors and Actuators,

Transducers'Ol (Munich, Germany, 10-14 June 2001), paper 4B2.10P.

38.

Chou SY, Krauss PR and Renstrom PJ, 1995, Imprint of sub-25

nm vias and trenches in polymers, Appl. Phys. Lett., 67, 3114-6.

39.

Roos N, Luxbacher T, Glinsner T, Pfeiffer K, Schulz H and Scheer

H-C, 2001, Nanoimprint lithography with a commercial 4 inch bond sys-

tem for hot embossing, Conf Emerging Lithographic Technologies V,

(Santa Clara, CA, 27 Feb.-l Mar. 2001), Proc. SPIE

4343,

427-35.

40.

Lebib A, Chen Y, Cambril E, Youinou P, Studer V, Natali M, Pe-

pin A, Janssen H M and Sijbesma R P, 2002, Room-temperature and low-

pressure nanoimprint lithography, Microelectron. Eng., 61-62, 371-7.

41.

Malaquin L, Carcenac F, Vieu C and Mauzac M, 2002, Using

polydimenthylsiloxane as a thermocurable resist for a soft imprint lithog-

raphy process, Microelectron. Eng., 61-62, 379-84.

42.

Roos N, Schulz H, Bendfeldt L, Fink M, Pfeiffer K and Scheer H-

C, 2002, First and second generation purely thermoset stamps for hot em-

bossing, Microelectron. Eng., 61-62, 399-405.

43.

Schift H, Heydermann LJ, Padeste C and Gobrecht J, 2002,

Chemical nano-patteming using hot embossing lithography, Microelec-

tron. Eng., 61-62,423-8.

44.

Both A, Bacher W, Heckele M, Miiller KD, Ruprecht R and

Strohrmann M, 1995, Molding process with high alignment precision for

the LIGA technology, Proc. Micro-Electro Mechanical Systems (Amster-

dam, The Netherlands, 29 Jan-2 Feb.), pp 186-90, (IEEE Catalogue Num-

ber 95 CH35754).

45.

Ehrhardt E, GehauBer T, Giousouf

Kuck H, Mohr R and Wark-

entin D, 2002, Innovative concept for the fabrication of micromechanical

sensor and actuator device using selectively metallized polymers. Sensors

Actuators A, 97-98, 473-7.

46.

Worgull M and Heckele M,

2003,

New aspects of simulation in

hot-embossing, Proc. DTIP (Cannes Madelieu, 5-7 May 2003).

4. Meso-Micromachining

4.1 Introduction

When metal is removed by machining there is a substantial in-

crease in the specific energy required with decrease in chip size. It is

generally believed this is due to the fact that all metals contain de-

fects (grain boundaries, missing and impurity atoms, etc.), and when

the size of the material removed decreases the probability of encoun-

tering a stress-reducing defect decreases. Since the shear stress and

strain in metal cutting is unusually high discontinuous microcracks

usually form on the metal cutting shear plane. If the material being

cut is very brittle, or the compressive stress on the shear plane is

relatively low, microcracks will grow into gross cracks giving rise to

discontinuous chip formation. When discontinuous microcracks

form on the shear plane they will weld and reform as strain pro-

ceeds,

thus joining the transport of dislocations in accounting for the

total slip of the shear plane. In the presence of a contaminant, such

as CCI4 vapor at a low cutting speed, the re-welding of microcracks

will decrease, resulting in a decrease in the cutting force required for

chip formation. A number of special experiments that support the

transport of microcraks across the shear plane, and the important

role compressive stress plays on the shear plane are presented. Rela-

tively recently an alternative explanation for the size effect in cutting

is based on the premise that shear stress increases with increase in

strain rate. When an attempt is made to apply this to metal cutting, it

is assumed in the analysis that the von Mises criterion pertains to the

shear plane. This is inconsistent with the experimental findings by

Merchant that are discussed in great detail in this chapter. Until this

difficulty is taken care of together with the premised experimental

verification of

the

strain rate approach, it should be assumed that the

144 Micro- and Nanomanufacturing

strain rate effect may be responsible for some portion of the size ef-

fect in metal cutting.

4.2 Size Effects in IVIachining Processes

It has been known for a very long time that a size effect exists in

metal cutting, where the specific energy increases with decrease in

deformation size. Backer et al. [1] performed a special series of ex-

periments in which the shear energy per unit volume deformed (us)

was determined as a function of specimen size for a ductile metal

(SAE 1112 steel). The deformation processes involved were as fol-

lows,

listed from top to bottom with increasing size of specimen de-

formed:

surface grinding

micromilling

turning

tensile test

The surface grinding experiments were performed under rela-

tively mild conditions involving plunge type experiments in which

8-inch

(20.3 cm) diameter wheel was directed radially downward

against a square specimen of length and width 0.5 in (1.27 cm), as

shown in Fig. 4.1. The width of the wheel was sufficient to grind the

entire surface of the work at different downfeed rates (t). The verti-

cal and horizontal forces were measured by a dynamometer support-

ing the workpiece. This enabled the specific energy (us) and the

shear stress on the shear plane

(T)

to be obtained for different values

of undeformed chip thickness (t) as shown in Fig. 4.2. The points

corresponding to a constant specific energy below a value of down

feed of about 28 jiiinch (0.7 |Lim) are on a horizontal line due to a

constant theoretical strength of the material being reached when the

value of

goes below approximately 28 |Liinch (0.7 |Lim). The reason-

ing in support of this conclusion is presented in Backer et al [1].

Meso-micromachining 145

Fig. 4.1. Plunge grinding cut with wheel engaging complete area of work with

downfeed t and wheel speed V [\]

In the micromilling experiments a carefully balanced 6-inch (152

cm) carbide tipped milling cutter was used with all but one of the

teeth relieved so that it operated as a fly milling cutter. Horizontal

and vertical forces were measured for a number of depths of cut {i)

when machining the same sized surface as in grinding.

146 Micro

1 'T

i Z,

X 4

- and Nanomanufacturin

.T-^^^

- Z,^

-22

-20

"18

-16

- 14

- 12

-10

- 8

-6

- 4

" 2

- 0

0 5 10 15 20 25 30 35" 40 50

t,^in

Fig. 4.2. Specific energy-depth of cut curve for grinding experiments [1]

The shear stress on the shear plane

(T)

was estimated by a rather

detailed method presented in Backer et al [1]. Turning experiments

were performed on a 2.25-inch (5.72 cm) diameter SAE 1112 steel

bar pre-machined in the form of a thin-walled tube having a wall

thickness of 0.2 inch (5 mm). A zero degree rake angle carbide tool

was operated in a steady-state two-dimensional orthogonal cutting

mode as it machined the end of the tube. Values of shear stress on

the shear plane (T) versus undeformed chip thickness were deter-

mined for experiments at a constant cutting speed and different val-

ues of axial infeed rate and for variable cutting speeds and a constant

axial infeed rate. The grinding, micromilling, and turning results are

shown in Fig. 4.3.

Meso-micromachining 147

10~

10"

—^

^^^^^4-rf-

ii 1

1 j j 1

rinding

1 rli

Microj

^•^i^

z±it

'Mil "~~

r'nt

•••

wi-

m==

rtiM

nilling

^^±:^

t i

III

J !,.-,„

"**==iir"

•.yjg_qfc..|,^

?S^

Turnin

\\\\

gffiiH

!fH7.tiiH5|

! •

! !

ilHl

10-'

10"*

10"^

specimen

size,

t, in

10-

Fig. 4.3. Variation of shear stress on shear plane when cutting SAE 1112 steel

[1]

A true stress-strain tensile test was performed on a 0.505-inch

(1.28 cm) diameter by 2-inch (5.08 cm) gage length specimen of the

same SAE 1112 steel. The mean shear stress at fracture was 22,000

psi (151.7 MPa). This value is not shown in Fig. 4.3 since it falls too

far to the right.

In 1993 Dr. Nono Taniguchi was the American Society of Preci-

sion Engineers' distinguished lecturer in Seattle, WA. For his lec-

ture,

discussing the art of nanotechnology [2], Dr. Tanigiuchi dis-

cussed the size effect in cutting and forming and presented his

version of Fig. 4.3 in Fig. 4.4, which is more complete since it in-

cludes the tensile test.

Shaw [3] discusses the origin of the size effect in metal cutting,

which is believed to be primarily due to short-range inhomogeneities

present in all commercial engineering metals.

148 Micro- and Nanomanufacturing

l3000 I .-»-—^"T^^^-^^'^t'^^^ shearing strength

10000 f-

5000

1000

b/i 500 r

100

500

Chip thickness,

j.ini

(Corresponding to processiug unit)

Fig. 4.4. Relationship between chip thickness and resisting shear stress for Fig

4.3 as modified by Taniguchi [2]

When the back of a metal cutting chip is examined at very high

magnification by means of an electron microscope individual slip

lines are evident as shown in Fig. 4.5. In deformation studies, Hei-

denreich and Shockley [4] found that slip does not occur on all

atomic planes but only on certain discrete planes. In experiments on

deformed aluminum single crystals the minimum spacing of adja-

cent slip planes was found to be approximately 50 atomic spaces

while the mean slip distance along the active slip planes was found

to be about 500 atomic spaces as shown in Fig. 4.6. These experi-

ments further support the observation that metals are not homogene-

ous and suggest that the planes along which slip occurs are associ-

ated with inhomogeneities in the metal.

Strain is not uniformly distributed in many cases. For example,

the size effect in a tensile test is usually observed only for specimens

less than 0.1 inch (2.5 mm) in diameter. On the other hand, a size ef-

fect in a torsion test occurs for considerably larger samples due to

the greater stress gradient present in a torsion test than in a tensile

test. This effect and several other related ones are discussed in detail

in Shaw [3].

Meso-micromachining 149

Fig. 4.5. Back free surface of chip showing regions of discontinuous strain or

microfracture

0.8

(0.02

pLtn)

(0.2

iim)

Fig. 4.6. Spacing of adjacent sHp planes for pure aluminum single crystal [4]

150 Micro-and Nanomanufacturing

4.2.1 Shear angle prediction

There have been many notable attempts to derive an equation for the

shear angle

(([))

shown in Fig. 4.7 for steady-state orthogonal cutting.

Ernst and Merchant [5] presented the first quantitative analysis.

Figure 4.8 shows forces acting on a chip at the tool point

where:

R =

the resultant force on the tool face, R' = the resultant force in the

shear

plane,

Nc and Fc are the components of

normal to and paral-

lel to the tool face,

A^^and

F^are the components of

7?'

normal to and

parallel to the cutting direction,

and

are the components of R

normal to and parallel to the cutting direction, and

tan"^

Fc/Nc

(is

called the friction angle).

0 te

Fig. 4.7. Nomenclature for two-dimensional Steady-State orthogonal cutting

process