Prototyping Injection Molded Optical Parts
Application Bulletin
Optimizing Molding Processes
Injection molded silicone resins are being commercialized for
optical parts in a variety of applications. These silicones are well
suited to precision molding, as micrometer-sized features can
be replicated on the lens surface for benefits in directing light
output. Silicones have been fabricated using a variety of
techniques, including injection molding, casting/cavity molding
and others. However, the optimal molding equipment and
processing conditions are very different from traditional
thermoplastics or liquid silicone rubbers. In order to assist
customers in evaluating these materials without the high cost
of capital expenditures, Dow Corning has installed equipment
to prototype and help optimize molding processes for
manufacturing of silicone lenses or optical parts.
The unit is a V-style plunger design capable of metered shots
up to approximately 12 grams. Larger shots can be made with
modified intrusion software to partially fill the mold using the fill
screw and doing final pressure and fill with the plunger. The unit
has controls for two sets of heaters, maximum capacity of 2 kW
for the unit. Typically ½" cartridge heaters are used, while the
thermocouple for control can either be remote via bayonet mount
or included in the heaters. Note that this equipment utilizes
type K thermocouples.
In order to make prototyping more cost effective, we also have
a Progressive Components RTI® 08/09 Rapid Tooling Insert
Frame. Drawings of the U-frame are shown in sketch A below.
This unit will accept 5" x 8" Solid Units (RTS-0809), 5" x 8"
Laminated Units (RTL-0809) or 7.85" x 9" T-Style Units
(RTT-0809). Please contact us for details prior to cutting steel
on these inserts.
The primary equipment in Dow Corning’s Auburn facility is a
Sodick Plustech 40-ton horizontal injection molding machine,
which can accept molds up to 310 mm (12.2") between the
tie bars for installation with a 100 mm (3.9") mounting ring.
A
0
4.000
9.000
8.000
9.000
8.000
2.625
4.000
0
1.126ø
7.850
5.500
5.000
4.120
5.000
3.975
5.500
7.850
4.000
3.500 (3)
.000
2.125 (4)
3.375
3.000
4.000
2.728
2.498
2.000 (8)
0
1.219 (4)
B
.000
To further reduce prototyping costs, we also have a rapid tooling
insert with pre-machined pockets for core and cavity inserts
available. This is the RTI® Complete as shown in sketch D.
This unit incorporates a 3" x 5" insert, which can be cut and
placed into the tool. While limiting the design flexibility and
size slightly, this can be an inexpensive way to obtain a small
number of sample parts.
For all of these mold options, we do not have machining
capability in-house, but do have access to local tool and
die shops that can prepare such molds at a reasonable cost.
Machining costs are typically borne by the customer.
4.000
3.500 (3)
Tubular Dowels (2)
.000
3.375
In general, we recommend keeping the sprue length as short as
possible for both waste and removal considerations. The sprue
should have a larger draft angle than that typically used for
liquid silicone rubber or plastic and should be draw polished
to allow for pulling of the sprue. Cavities are typically highly
polished for optical parts, but the runners should also be
polished to prevent the material from sticking. Ejector pins,
if used, should be a tapered design with a small amount of
preloading to seat them in order to prevent flash down the pin
and into the movable portion of the mold. Gates are designed
to prevent turbulence; impingement as in plastic molds is
not recommended. Fill should be from the bottom of the
cavity with venting at the top to allow bubbles to escape. The
materials are very flowable at mold temperatures. Drawings of
the prototyping inserts are shown in sketches B and C at right.
4.000
3.500 (4)
RP & SHCS
2.498
2.728
3.375
3.563 (4)
RP & SHCS
1.750 (4)
2.728 0
2.498
2.000 (4)
C
.000
2.498
2.728
4.00
0
D
Clearance pocket in ear plate
2.00
.250 R (Typ)
2.500 (4)
Clearance
pocket
4.500 (4)
C'bore for
1/4-20 SHCS
(4 in Ear Plate
4 in Ejector Plate)
3/8-16
x 1-1/4"
.500ø
.760ø
.40
3.375
8.000
.000
2.125 (4)
3.500 (3)
1/4-20 x 3/8"
.246ø
Vents (4)
.25 (4)
0
.230
.252
.625ø
.750
A ±.001
A2
.751ø
2.000 (4)
3/8-16
4.996
.000
B2
.188
.203
.40
5.456
.50ø x 2.5"
.93ø
.863ø
.375ø
.750
2.625
.500
.500
.338
.50 x 45°
.37 x 15°
Tubular Dowels (2)
.218
3.87
.251
.81ø
4.00
.500ø
8.000
Spirolox
RRN-75
3.375
.760ø
.000
1/4-20 x 5/8"
.64ø
7.87
3.500 (3)
±.001
.125
Vents (4)
.751ø
B
.405
.230
.531
.350
0
.246
A ±.001
.751ø
2.000
Spirolox
RRN-86
.288
4.996
.000
5.456
B ±.001
.531
.246
.863ø
.500
2.625
.500
3.87
7.87
4.00
1.125 (TYP)
.750
5.0000
+.0000
- .0005
Insert Pocket
.625 (4)
0
A
±.001
B
±.001
A2
.500 (4)
3.0000
B2
+.0000
- .0005
Insert Pocket
.500 (4)
.875 (4)
5.000
+.010
- .000
Pin Plate Insert Pocket
RSP75L2.6 (2)
Support Pillars (Included)
.750
2.625
3.000
+.010
- .000
Pin Plate Insert Pocket
Drawings used with the permission of Rapid Tooling, Inc.
Additional input on Rapid Tooling Inserts (RTIs) from Progressive Components
can be obtained at www.procomps.com, or by calling 1-800-269-6653.
Your Global Connection
If a customer would like a demonstration of molding
capability or to see a material in use, we do have some
standard molds that can be demonstrated or used to prepare
parts. These are a standard “dog-bone” tensile bar (as
shown below), a ~35mm aspherical lens and a few different
sized rods. Parts from these molds are often available on a
limited basis.
.2500
R.5600
.1250
.7500
R.0600
1.3000
R1.0000
4.5000
Please contact your local Dow Corning sales representative
with questions or to schedule a visit or prototype run.
Learn More
Dow Corning has sales offices and manufacturing sites, as well
as science and technology laboratories, around the globe. For
more information please email electronics@dowcorning.com
or visit dowcorning.com/contactus.
AMERICAS:
Dow Corning Corporation
Corporate Center
PO Box 994
Midland, MI 48686-0994
United States
Tel: +1 989 496 4400
Fax: +1 989 496 6731
EUROPE:
Dow Corning Europe SA
Parc Industriel – Zone C
Rue Jules Bordet
7180 Seneffe
Belgium
Tel: +32 64 888 000
Fax: +32 64 888 401
ASIA:
Dow Corning Toray Co., Ltd.
Otemachi First Square Building
East Tower 23F,
5-1, Otemachi 1-chome,
Chiyoda-ku, Tokyo
Japan 100-004
Tel: +81 3 3287 1011
Fax: +81 3 3287 1201
Dow Corning Taiwan, Inc.
10F, No. 246, Sec. 1, Nei Hu Road
Taipei-Nei Hu 11493
Taiwan
Tel: +86 21 3899 5500
Fax: +86 21 5079 6567
Dow Corning (China) Holding Co., Ltd.
1077 Zhangheng Road
Zhangjiang Hi-Tech Park,
Shanghai
P.R.C.
201203
Tel: +86 21 3899 5500
Fax: +86 21 5079 6567
Images: AV20230, AV20234, AV20233
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The information contained herein is offered in good faith and is believed to be accurate. However, because
conditions and methods of use of our products are beyond our control, this information should not be used in
substitution for customer’s tests to ensure that our products are safe, effective and fully satisfactory for the
intended end use. Suggestions of use shall not be taken as inducements to infringe any patent.
Test and Instruction Disclaimer: To the full extent permitted by law, Dow Corning disclaims any and all
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RTI is a registered trademark of Rapid Tooling, Inc.
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AMPM149-13
Form No. 11-1715A-01