Madeinusa

Urethane Prototypes
&
Silicone Prototypes

Urethane Prototypes

Urethane prototypes are cast utilizing RTV urethanes – which come in a wide range of properties such as:  Shore A, Shore D, Flame Resistant, UL Rated, Optically clear as well as food grade.

Cast urethane prototypes (RTV molding) are often used when color, surface quality, and toughness are required creating plastic prototypes with material properties similar to engineered production plastics. These prototypes are cast from two part liquid polyurethanes into silicone rubber molds.

Silicone insulator for the Lighting Industry

Silicone Prototypes

Silicone prototypes are made by casting RTV silicones into SLA or CNC Machined molds.  Material properties range from Shore 10A to Shore 60A. 

Silicone materials can provide high transparency, dielectric properties and high chemical resistance.  Color matching available.  Example applications include:

Gasket & Seals
Flexible Membranes
Insulators
Electrical connectors
Functional prototypes

Casting of lipstick
Production level part for the Cosmetics Industry

Production Level Parts

Urethane casting provides end-use parts with production level quality & material properties.

Urethane cast parts are made without expensive and time-consuming hard tooling.  The urethane casting processes uses a 3D printed master pattern with the required finish to create a silicone mold (soft tool) which delivers high quality, short-run parts.

Urethane casting is an cost effective way to bridge the gap between prototype and production.

Application Examples:

Functional Prototypes
Visual Models
Product Testing
Color Testing
Engineering Design Verification
Small Batch Manufacturing
Market Testing
Pre-Production Parts
Urethane cast part for the fashion industry
Micro casting mold

Summary of Casting Process

Utilizing a 3D CAD file (provided to us or generated by us) and one of our rapid prototyping technologies, we create a master pattern. 

The master pattern is then finished based on the project requirements.

We use this master pattern to create a silicone mold with gating and venting. 

The silicone mold is filled with liquid polyurethane and placed under heat and pressure. 

The cured part is then extracted and gates and any flash is removed.  The part is then inspected for feature integrity and aesthetics.

Silicone mold with urethane cast parts.

Casting Process Technical Details

  1. Mold Life:  Molds are generally good for about 20 to 25 castings depending on material selected and part features such as under cuts, surface texture, thin features, inserts, etc.  Also keep in mind that some urethane materials (i.e. clear) are chemically more aggressive and can reduce the life of a silicone mold.
     
  2. Accuracy:  Standard tolerances are ±0.015″ or ±0.003 inch per inch, whichever is greater.  Tighter tolerances may be offered on a case-by-case basis.

  3. Inspection:  Overall visual inspection of feature integrity and aesthetics is performed on every part.

Cast Prototype Specification Guidelines

Outlined below are the options which need to be specified when ordering a urethane cast prototype. This includes materials, finish, and options.

Standard Material Selection:*

*Custom material requests welcomed.
Specification Writers: These values are a guide and not intended for use in preparing specifications.

Base Color:  Off-White

Shore A Hardness:  20A            ASTM-2240
Tensile Strength: 200 psi           ASTM D-412
100% Modulus:  27 psi             ASTM D-412
Elongation at Break:  1,000%    ASTM D-412
Die C Tear Strength: 60 pli        ASTM D-624

Base Color:  Off-White

Shore A Hardness:  30A             ASTM-2240
Tensile Strength:  450 psi           ASTM D-412
100% Modulus: 67 psi               ASTM D-412
Elongation at Break:  1,000%     ASTM D-412
Die C Tear Strength:  82 pli        ASTM D-624

Base Color:  Off-White

Shore A Hardness: 40A              ASTM-2240
Tensile Strength: 490 psi            ASTM D-412
100% Modulus:  73 psi              ASTM D-412
Elongation at Break: 1,000%      ASTM D-412
Die C Tear Strength: 85 pli         ASTM D-624

Base Color:  Off-White

Shore A Hardness:  50A            ASTM-2240
Tensile Strength: 580 psi           ASTM D-412
100% Modulus: 152 psi            ASTM D-412
Elongation at Break:  435%      ASTM D-412
Die C Tear Strength: 120 pli      ASTM D-624

Base Color:  Off-White

Shore A Hardness: 60A            ASTM-2240
Tensile Strength: 782 psi          ASTM D-412
100% Modulus:  256 psi          ASTM D-412
Elongation at Break:  581%     ASTM D-412
Die C Tear Strength:  132 pli    ASTM D-624 

Base Color:  Clear Amber

Shore A Hardness:  70A ± 5                ASTM D2240-04e1
Tensile Strength: 2,200 psi                ASTM D412-98a(2002)e1
Tensile Modulus:  800 psi                 ASTM D412-98a(2002)e1
Elongation:  860%                            ASTM D412-98a(2002)e1
Tear Strength:  300 pli                      ASTM D624-00e1
Dielectric Constant, 1 MHz: 5.84      ASTM-D150-87
Dissipation Factor, 1 MHz:  0.068     ASTM D-150-87

Base Color:  Clear Amber

Shore A Hardness:  80A ± 5                ASTM D2240-04e1
Tensile Strength :  2,800 psi              ASTM D412-98a(2002)e1
Tensile Modulus:  1,300 psi               ASTM D412-98a(2002)e1
Elongation:  720%                             ASTM D412-98a(2002)e1
Tear Strength:  350 pli                       ASTM D624-00e1
Dielectric Constant, 1 MHz:  5.55      ASTM-D150-87
Dissipation Factor, 1 MHz:  0.0614    ASTM D150-87

Base Color:  Clear

Shore A Hardness: 30A            ASTM D-2240
Tensile Strength: 725 psi          ASTM D-412
Elongation at Break:  675%     ASTM D-412
Die C Tear Strength:  54 pli      ASTM D-624 

Electrical Properties:
Volume Resistance :  >7.646E+13 ohm        ASTM D-150-98
Volume Resistivity:  >6.014E+15 Ohm cm    ASTM D-150-98
Dielectric Constant k’@100 Hz:  6.62           ASTM D-150-98
Dissipation Factor @100 Hz:  0.103              ASTM D-150-98
Dielectric Strength (V/mil):  474                    ASTM D-147-97a

Index of Refraction:  1.48822 at 20ºC,  1.48649 at 25ºC

Base Color:  Clear

Shore A Hardness: 50A            ASTM D-2240
Tensile Strength: 250 psi          ASTM D-412
Elongation at Break:  500%     ASTM D-412
Die C Tear Strength:  25 pli      ASTM D-624 

Electrical Properties:
Volume Resistance :  >7.646E+13 ohm        ASTM D-150-98
Volume Resistivity:  >6.014E+15 Ohm cm    ASTM D-150-98
Dielectric Constant k’@100 Hz:  6.62            ASTM D-150-98
Dissipation Factor @100 Hz:  0.103              ASTM D-150-98
Dielectric Strength (V/mil):  474                    ASTM D-147-97a

Index of Refraction:  1.48822 at 20ºC,  1.48649 at 25ºC

Base Color:  Clear

Shore A Hardness: 95A            ASTM D-2240
Tensile Strength: 2,500 psi       ASTM D-412
Elongation at Break:  175%     ASTM D-412
Die C Tear Strength:  200 pli    ASTM D-624 

Electrical Properties:
Volume Resistance :  >7.646E+13 ohm        ASTM D-150-98
Volume Resistivity:  >6.014E+15 Ohm cm    ASTM D-150-98
Dielectric Constant k’@100 Hz:  6.62            ASTM D-150-98
Dissipation Factor @100 Hz:  0.103              ASTM D-150-98
Dielectric Strength (V/mil):  474                    ASTM D-147-97a

Index of Refraction:  1.49317 at 20ºC,  1.49151 at 25ºC

Base Color:  Clear Amber

Shore D Hardness:  D60 ± 5             ASTM D2240-04e1
Tensile Strength :  5,000 psi              ASTM D638-03
Tensile Modulus:  2.19 x 10⁴ psi        ASTM D638-03
Elongation:  525%                             ASTM D638-03
Tear Strength:  585 psi                       ASTM D624-00e1
Flexural Strength: 1,930 psi               ASTM-D790-00
Flexural Modulus:  4.78 x 10⁴ psi       ASTM D790-00

Base Color:  White

Shore D Hardness:  D65
Heat Deflection Temp:  149º F
Tensile Strength :  2.936 psi
Elastic Modulus:  72,627 psi
Flexural Modulus: 93,112 psi
Flexural Strength, 5% strain:  3,915 psi
Elongation:  13.9%

Base Color:  White

Shore D Hardness:  D70
Heat Deflection Temp:  164ºF
Tensile Strength :  4,387 psi
Elastic Modulus:  134,685 psi
Flexural Modulus: 157,356 psi
Flexural Strength, 5% strain:  6,125 psi
Elongation:  5.1%

Base Color:  White

Shore D Hardness:  75D                       ASTM D-2240
Ultimate Tensile:  5,500 psi                   ASTM D-638
Tensile Modulus:  270,000 psi               ASTM D-638
Elongation @ Break:  7.5%                    ASTM D-638
Flexural Strength:  7,100 psi                  ASTM D-790
Flexural Modulus:  250,000 psi              ASTM D-790
Compressive Strength:  7,100 psi          ASTM D-695
Compressive Modulus:  78,500 psi        ASTM D-695
Heat Deflection Temp:  144º F / 62º C   ASTM D-648

Base Color:  Off-White

Shore D Hardness:  80D                       ASTM D-2240
Ultimate Tensile:  5,840 psi                   ASTM D-638
Tensile Modulus:  246,000 psi               ASTM D-638
Elongation @ Break:  4%                      ASTM D-638
Flexural Strength:  8,280 psi                  ASTM D-790
Flexural Modulus:  271,000 psi              ASTM D-790
Compressive Strength:  8,760 psi          ASTM D-695
Compressive Modulus:  77,400 psi        ASTM D-695
Heat Deflection Temp:  194º F / 90º C   ASTM D-648

Color:  Water Clear

Shore D Hardness:  80D
Elongation:  7%
Heat Deflection Temp:  138ºF
Tensile Strength:  6,083 psi
Elastic Modulus:  133,956 psi
Flexural Modulus:  250,992 psi
Flexural Strength, 5% Strain:  8,478 psi

Base Color:  Off-White

Shore D Hardness:  73D                       ASTM D-2240
Ultimate Tensile:  3,390 psi                   ASTM D-638
Tensile Modulus:  150,700 psi               ASTM D-638
Elongation @ Break:  15.1%                    ASTM D-638
Flexural Strength:  5,450 psi                  ASTM D-790
Flexural Modulus:  148,900 psi              ASTM D-790
Compressive Strength:  5,140 psi          ASTM D-695
Compressive Modulus:  57,600 psi        ASTM D-695
Heat Deflection Temp:  131º F / 55º C   ASTM D-648

Base Color:  Off-White/Tan

Shore D Hardness:  65D
Elongation:  9%
Heat Deflection Temp.:  165ºF
Tensile Strength:  3,170 psi
Elastic Modulus:  85,928 psi
Flexural Modulus:  117,878 psi
Flexural Strength:  4,284 psi

Base Color:  Translucent

Shore A Hardness:  10A                     ASTM D-2240
Tensile Strength:  475 psi                   ASTM D-412
100% Modulus:  22 psi                      ASTM D-412
Elongation at Break:  1,000%             ASTM D-412
Die B Tear Strength:  102 pli               ASTM D-624
Dielectric Strength:  >350 volts/mil    ASTM D-149
Service Temperature Range:   -65ºF to +450ºF  (-53ºC to +232ºC)

Base Color:  Translucent

Shore A Hardness:  15A                     ASTM D-2240
Tensile Strength:  537 psi                   ASTM D-412
100% Modulus:  40 psi                       ASTM D-412
Elongation at Break:  771   %             ASTM D-412
Die B Tear Strength:  112 pli               ASTM D-624
Dielectric Strength:  >350 volts/mil    ASTM D-149
Service Temperature Range:   -65ºF to +450ºF  (-53ºC to +232ºC)

Base Color:  Translucent

Shore A Hardness:  20A                     ASTM D-2240
Tensile Strength:  550 psi                   ASTM D-412
100% Modulus:  49 psi                      ASTM D-412
Elongation at Break:  620%                ASTM D-412
Die B Tear Strength:  120 pli               ASTM D-624
Dielectric Strength:  >350 volts/mil    ASTM D-149
Service Temperature Range:   -65ºF to +450ºF  (-53ºC to +232ºC)

Base Color:  Translucent

Shore A Hardness:  30A                     ASTM D-2240
Tensile Strength:  500 psi                   ASTM D-412
100% Modulus:  86 psi                       ASTM D-412
Elongation at Break:  364%                ASTM D-412
Die B Tear Strength:  108 pli               ASTM D-624
Dielectric Strength:  >350 volts/mil    ASTM D-149
Service Temperature Range:   -65ºF to +450ºF  (-53ºC to +232ºC)

Transparent encapsulant with good flame resistance.
Suitable for LED lighting encapsulation, power supplies, connectors, sensors, industrial controls, transformers, amplifiers, and relays.

Shore A Hardness:  43A
Thermal conductivity:  0.15 btu/hr ft ºF  (0.27 W/m ºK)
Dielectric Strength:  500 volts/mil ( 19 kV/mm)
Volume Resistivity:  2.9E+14 ohm*cm
Dissipation Factor at 100 Hz:  0.00257
Dissipation Factor at 100 kHz:  0.00133
Dielectric Constant at 100 Hz:  2.72
Dielectric Constant at 100 kHz:  2.68
Linear CTE (by DMA):  340 ppm/ºC
Tensile Strength:  980 PSI  (6.7 MPa, 69 Kg/cm²)
Refractive Index @ 589 nm:  1.4118
Refractive Index @ 632.8 nm:  1.4225
Refractive Index @ 1321 nm:  1.4028
Refractive Index @ 1554 nm:  1.3997
UL RTI Rating:  150ºC

Basic Finish

If SLA, layer lines ARE NOT removed.
If Machined, as machined.

Standard Finish

If SLA, layer lines ARE removed - leaving a matte finish.
If machined, tool markings ARE removed - leaving a matte finish.
Layer lines may be present on internal or difficult to reach features.

Custom Finish Examples

Gloss finish
Textured Finish
EMI/RFI shielding
color matching
decorating
metal inserts.

Custom finish requests welcomed

Master Pattern Finishing Options

Elastomeric Prototypes

Design for Urethane Casting

You can design for the casting process, however, it is more advantageous to design for the manufacturing process you will ultimately be using.  Then make any small changes needed for the casting process, if any.

So if you are making a plastic container which will be manufactured utilizing injection molding, please use injection molding design considerations.

If you are unsure of the ultimate manufacturing process to be used, it is safe to use injection molding standards but keep in mind the tolerances shown in our Casting Design Considerations.

Urethane Casting Design Considerations

You can design for the casting process, however, it is more advantageous to design for the manufacturing process you will ultimately be using.  Then make any small changes needed for the casting process, if any. So if you are making a plastic container which will be manufactured utilizing injection molding, please use injection molding design considerations. If you are unsure of the ultimate manufacturing process to be used, it is safe to use injection molding standards but keep in mind the tolerances shown below.

Bosses are used to facilitate the registration of mating parts, for attaching fasteners such as screws, or for accepting inserts.

Wall thickness of bosses should be less than 60% of the nominal wall to minimize sinking.  The base radius should be a minimum of 0.25 x thickness.  Bosses can be strengthened by incorporating gussets at the base or by using connecting ribs attaching to nearby walls.

Draft and undercuts are not a concern when designing for the urethane casting process itself. However, if you are building prototypes that are intended to move on to another production methods such as injection molding where hard tooling is required, you should create your design as intended for production tooling. The urethane casting process is still ideal for prototypes and short run of parts that will move on to other production technologies.

Both raised and recessed letters and logos can be molded into cast urethane parts.  The key factors are:  height or depth of the feature, width of the feature, radii on the feature and space between features.

The recommended minimum space between features is 0.050″.  Width to height ratios should be at least 2.  The radii should be at least equal to half the height.  Larger radii are better.

A fillet radius of 0.125″ is recommended on inside corners to increase strength. The inner corners of bosses can use 0.060″ radii to help reduce wall thickness. Use these radii whenever you make transitions between surfaces. Radii are important because rigid urethanes are notch sensitive materials.

Ribs are used in a design to increase the bending stiffness of a part without adding thickness. Ribs increase the moment of inertia, which increases bending stiffness. Rib thickness should be less than wall thickness to minimize shrink and sink marks.

The recommended rib thickness should not exceed 60 percent of the nominal thickness. Plus, the rib should be attached with corner radii as generous as possible. Because the thickness of the material will be greater at rib intersections, coring or another means of reducing material should be employed to avoid excessive sinking from occurring on the opposite side.

The height of a rib should be limited to less than three times its thickness. It is better to use multiple ribs to increase bending stiffness than use one very tall rib. A rib is oriented to provide maximum bending stiffness to the part. By paying attention to part geometry, designers must be conscious of the orientation of the rib to the bending load or there will be no increase in stiffness.

Snap fits can be used in all urethane casting processes following design practices used for thermoplastic resins.

In most molding processes, troublesome shrinkage problems can be caused by intersection of walls that are not uniform in wall thickness. Examples might include ribs, bosses, or any other projection of the nominal wall. Since thicker walls solidify slower, the area they are attached to at the nominal wall will shrink as the projection shrinks. This can result in a sunken area in the nominal wall. Such shrinking can be minimized if a rib thickness is maintained between 50 – 60% of the walls they are attached to.

Minimum wall thickness for cast urethane parts is 0.020 in. While a good design practice is to maintain a uniform wall thickness, you can vary your wall thickness in the urethane casting process without impacting the resulting parts. This is the perfect process when you require non-typical wall thicknesses.

Urethane & Silicone Prototype Quote Request

You will receive an e-mail confirming receipt of your request.

Files up to 20MB may be sent via e-mail to:  Sales@Versadyne.net