Conformal (or freeform) and steep concave optics are important classes of optics that are difficult to finish using conventional techniques due to mechanical interferences and steep local slopes. One suitable way to polish these classes of optics is by using a jet of abrasive/fluid mixture. The energy required for polishing may be supplied by the radial spread of a liquid jet, which impinges a surface to be polished. Such fluid flow may generate sufficient surface shear stress to provide material removal in the regime of chemical mechanical polishing. Once translated into a polishing technique, this unique tool may resolve a challenging problem of finishing steep concave surfaces and cavities. A fundamental property of a fluid jet is that it begins to lose its coherence as the jet exits a nozzle. This is due to a combination of abruptly imposed longitudinal and lateral pressure gradients, surface tension forces, and aerodynamic disturbance. This results in instability of the flow over the impact zone and consequently polishing spot instability. To be utilized in deterministic high precision finishing of remote objects, a stable, relatively high-speed, low viscosity fluid jet, which remains collimated and coherent before it impinges the surface to be polished, is required. A method of jet stabilization has been proposed, developed, and demonstrated whereby the round jet of magnetorheological fluid is magnetized by an axial magnetic field when it flows out of the nozzle. It has been experimentally shown that a magnetically stabilized round jet of magnetorheological (MR) polishing fluid generates a reproducible material removal function (polishing spot) at a distance of several tens of centimeters from the nozzle. The interferometrically derived distribution of material removal for an axisymmetric MR Jet™ , which impinges normal to a plane glass surface, coincides well with the radial distribution of rate of work calculated using computational fluid dynamics (CFD) modeling. Polishing results support the assertion that the MR Jet finishing process may produce high precision surfaces on glass and single crystals. The technology is most attractive for the finishing of complex shapes like freeform optics, steep concaves, and cavities.

1.
Cook
,
L. M.
, 1990, “
Chemical Processes in Glass Polishing
,”
J. Non-Cryst. Solids
0022-3093,
120
, pp.
152
171
.
2.
Agarwal
,
A.
,
Tomozawa
,
M.
, and
Lanford
,
W. A.
, 1994, “
Effect of Stress on Water Diffusion in Silica Glass at Various Temperatures
,”
J. Non-Cryst. Solids
0022-3093,
167
, pp.
139
148
.
3.
Evans
,
C. J.
,
Paul
,
E.
,
Dornfield
,
D.
,
Lucca
,
D. A.
,
Byrne
,
G.
,
Tricard
,
M.
,
Klocke
,
F.
,
Dambon
,
O.
, and
Mullany
,
B. A.
, 2003, “
Material Removal Mechanisms in Lapping and Polishing
,”
CIRP Ann.
0007-8506,
52
(
2
), pp.
611
633
.
4.
Golini
,
D.
,
Jacobs
,
S.
,
Kordonski
,
W.
, and
Dumas
,
P.
, 1997, “
Precision Optics Fabrication Using Magnetorheological Finishing
,”
Advanced Materials for Optics and Precision Structures
,
SPIE Proc.
,
CR67-16
, pp.
251
273
.
5.
Golini
,
D.
,
Jacobs
,
S.
,
Kordonski
,
W.
, and
Dumas
,
P.
, “
Precision Optics Finishing Using Magnetorheological Finishing
,”
Optical Manufacturing and Testing Conference II
,
SPIE Proc.
,
SPIE Annual Meeting
,
San Diego, CA
.
6.
Gormley
,
J.
,
Manfra
,
M.
, and
Calawa
,
A.
, 1991, “
Hydroplane Polishing of Semiconductor Crystals
,”
Rev. Sci. Instrum.
0034-6748,
52
(
8
), pp.
1256
1259
.
7.
Mori
,
Y.
,
Yamauchi
,
K.
, and
Endo
,
K.
, 1988, “
Mechanism of Atomic Removal in Elastic Emission Machining
,”
Stud. Cerc. Mat.
0039-4068,
10
(
1
), pp.
24
28
.
8.
Momber
,
A.
, and
Kovacevic
,
R.
, 1998,
Principles of Abrasive Water Jet Machining
,
Springer
, New York, Chap. 9.6.
9.
Booij
,
S.
,
Hedser van Brug
,
B. J.
, and
Fahnle
,
O.
, 2002, “
Nanometer Deep Shaping With Fluid Jet Polishing
,”
Opt. Eng.
0091-3286,
41
(
8
), pp.
1926
1931
.
10.
Kordonski
,
W.
,
Shorey
,
A.
, and
Sekeres
,
A.
, 2004, “
New Magnetically Assisted: Material Removal With Magnetorheological Fluid Jet
,”
Proc. SPIE
0277-786X,
5180
,
107
114
.
11.
Kordonski
,
W.
,
Golini
,
D.
,
Hogan
,
S.
, and
Sekeres
,
A.
, 1999, “
System for Abrasive Jet Shaping and Polishing of Surface Using Magnetorheological Fluid
,” U.S. Patent No. 5,971,835.
12.
Kordonski
,
W.
, 1984, “
Apparatus and Method for Abrasive Jet Finishing of Deeply Concave Surfaces Using Magnetorheological Fluid
,” U.S. Patent No. 6,561,874.
13.
Preston
,
F. W.
, 1927, “
The Theory and Design of Plate Glass Polishing Machines
,”
J. Soc. Glass Technol.
0368-4105,
11
, pp.
214
256
.
14.
Blevins
,
R. D.
, 1984,
Applied Fluid Dynamics Handbook
,
Van Nostrand Reinhold Co., Inc.
, New York.
15.
Fluent, Flow Modeling Software, Version 6, Fluent Inc., Lebanon, NH.