Press forming machine for optical devices

Details Press forming machine for optical devices Press forming machine for optical devices

2001-02-15

2002-04-16

Fiorilla, Christopher A. (Department: 1731)

Glass manufacturing

Press molding machine

With means for heating or cooling apparatus

C065S268000, C065S286000, C425S174400

Reexamination Certificate

active

06370918

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-036708, filed Feb. 15, 2000; and No. 2000-046232, filed Feb. 23, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a press forming machine for optical devices which manufactures a glass optical device such as a lens, prism, and optical communication component by press forming.
FIG. 5
is a schematic view showing the structure of a conventional press forming machine for optical devices disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-186230.
A fixed shaft
2
extends downward from the upper portion of a frame
1
, and an upper die unit
4
is attached to the lower end face of the shaft
2
with a heat insulating block
3
made of a ceramic material. The upper die unit
4
is comprised of a die plate made of metal
5
, an upper die
6
made of ceramic (or sintered hard alloy), and a fixed die
7
. The fixed die
7
fixes the upper die
6
to the die plate
5
and forms part of a die.
A driving unit
8
(a screw jack in this example) is provided to the lower portion of the frame
1
. The driving unit
8
has a servo motor
8
a
as a driving source and converts rotation of the servo motor
8
a
into a thrust of linear motion. A moving shaft
9
is attached to the distal end of the driving shaft of the driving unit
8
with a load cell
8
b.
The moving shaft
9
extends upward to oppose the fixed shaft
2
. The speed, position, and axial load of the moving shaft
9
are controlled by a program input to a controller
28
, so the moving shaft
9
can move in the vertical direction.
A lower die unit
11
is attached to the upper end face of the moving shaft
9
with a ceramic heat insulating block
10
. The lower die unit
11
is comprised of a die plate
12
made of metal, a lower die
13
made of ceramic (or sintered hard alloy), and a moving die
14
. The moving die
14
fixes the lower die
13
to the die plate
12
and forms part of a die.
The fixed shaft
2
extends through an opening formed at the central portion of an upper plate
15
. The upper plate
15
is driven in the vertical direction by a driving unit (not shown). An O-ring is fitted in the opening of the upper plate
15
, and the upper plate
15
can slide in the vertical direction with a portion between it and the outer surface of the fixed shaft
2
being kept airtight.
The moving shaft
9
extends through an opening formed at the central portion of a lower plate
1
a.
The lower plate
1
a
is fixed to the frame
1
. An O-ring is fitted in the opening of the lower plate
1
a,
and the moving shaft
9
can slide in the vertical direction with a portion between it and the inner surface of the lower plate
1
a
being kept airtight.
The upper and lower die units
4
and
11
which form a pair, the heat insulating blocks
3
and
10
, the lower end of the fixed shaft
2
, and the upper end of the moving shaft
9
are surrounded by a cylindrical member made of silica glass (transparent quartz tube
16
). The upper end face of the transparent quartz tube
16
abuts against the lower surface of the upper plate
15
, and an O-ring is mounted in that portion of the upper plate
15
which comes into contact with the transparent quartz tube
16
to maintain airtightness. Similarly, the lower end face of the transparent quartz tube
16
abuts against the upper surface of the lower plate
1
a,
and an O-ring is mounted in that portion of the lower plate
1
a
which comes into contact with the transparent quartz tube
16
to maintain airtightness. Hence, a forming chamber
17
which is airtight against the outside is formed inside the transparent quartz tube
16
.
An outer tube
18
is arranged to surround the transparent quartz tube
16
. The upper end of the outer tube
18
is connected to the outer surface of the upper plate
15
, and the lower end of the outer tube
18
is in contact with the upper surface of the lower plate
1
a.
A lamp unit
19
is mounted at the middle stage of the outer tube
18
. The upper and lower die units
4
and
11
located inside the transparent quartz tube
16
are heated by radiation from the lamp unit
19
. The lamp unit
19
is comprised of infrared lamps
20
, a reflecting mirror
21
arranged behind the infrared lamps
20
, a water-cooled pipe
22
for cooling the reflecting mirror
21
. Both the infrared lamps
20
and reflecting mirror
21
are formed by stacking in a plurality of stages ring-like components each constituted by mating two semicircular arcuate elements, to form a cylindrical shape as a whole.
The fixed shaft
2
, moving shaft
9
, and upper plate
15
respectively have gas supply paths
23
,
24
, and
25
. The lower plate
1
a
has an exhaust port
26
. An inert gas is supplied into the forming chamber
17
at a predetermined flow rate through the gas supply paths
23
,
24
, and
25
, and is discharged through the exhaust port
26
, to maintain the interior of the forming chamber
17
in an inert gas atmosphere and to cool the upper and lower die units
4
and
11
.
A thermocouple
27
is attached to the rear surface of the die plate
12
. The thermocouple
27
detects the temperature of the lower die unit
11
.
When manufacturing an optical device of ordinary optical glass (with a glass transition point of 800° C. or less), press forming is performed at a temperature of about 800° C. by using the machine as shown in FIG.
5
.
For example, a stepper lens used in a semiconductor manufacturing process requires a high ultraviolet transmittance, and accordingly silica glass is used to form it. In a V-groove board used for an optical communication V-groove connector, silica glass is used so that the thermal expansion coefficient of the optical communication V-groove connector coincides with that of a silica glass optical fiber and optical waveguide. This silica glass optical device is conventionally manufactured by grinding and polishing processes. Therefore, to manufacture such an optical device requires a long period of time and high cost.
If such a silica glass optical component is to be manufactured by press forming in order to reduce the manufacturing cost, as the silica glass has a high glass transition point and a high forming temperature of about 1,300° C. to 1,600° C., the following various problems arise in the performance of the machine at elevated temperature.
(a) Since the temperature of the transparent quartz tube
16
increases, the transparent quartz tube
16
may deform, the seal packings in contact with the two ends of the transparent quartz tube
16
may be damaged, and a reaction product may attach to the inner and outer surfaces of the transparent quartz tube
16
.
(b) Since the temperature of the quartz bulbs surrounding the filaments of the infrared lamps
20
increases, the quartz bulbs deform.
(c) Since the temperature of the reflecting mirror
21
arranged behind the infrared lamps
20
increases, the reflecting coating film (e.g., gilt finish film) applied to the reflecting surface peeks off.
(d) Since the temperature of the terminal portions of the infrared lamps
20
increases to 300° C. or more, the molybdenum foils and pins of the sealing portions of the terminals of the infrared lamps
20
are oxidized. This shortens the service life of the infrared lamps
20
.
Furthermore, to increase the forming temperature to 1,000° C. or more is not easy with the conventional forming machine due to the following reason.
In the conventional press forming machine for optical devices, as shown in
FIG. 5
, the lamp unit
19
is arranged outside the transparent quartz tube
16
to surround the pair of upper and lower die units
4
and
11
. The pair of upper and lower die units
4
and
11
and a preform
30
are heated by infrared rays radiated from the lamp unit
19
. Since most of the infrared rays are transmitted through the preform
30
made of silica glass, the preform
30
is mainly heated by the heat conduct

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