16. Molding and casting¶

Assignments for week 15 :¶

This week we have a group assignment and an individual assignment .
The group assignment for this week is to review the safety data sheets for each of my molding and casting materials, then make and compare test casts with each of them .
The individual assignment for this week is to design a mold around the stock and tooling that i will be using, mill it rough cut + at least three-axis finish cut and use it to cast parts .

The goal for this week is to learn about molding and casting and the Techniques that are used in order to make one part or two part molds, also to learn everything about the materials that we are going to use this week such as safety rules and how to use those materials in the best way possible .

Files to download¶

I have included all the files that you can download down below and here you can find them directly :

Group assignment :¶

For the group assignment this week i have to review the safety data sheets for each of my molding and casting materials, then make and compare test casts with each of them .
In order to start let me show you the materials we have in the lab and compare between them, then the safety rules for each one of them so lets start !!

Silicones we have in the Lab :¶

Here im going to show the Silicones we have in the lab and explain each one in a detailed way :

1. OOMOO™ 30 ¶

Brief details about OOMOO™ 30 :¶

No Vacuuming No Scale Easy To Use, OOMOO™ 30 is an easy to use tin cure silicone rubber compound that features a convenient one-to-one by volume mix ratio (no scale necessary).
It has low viscosity for easy mixing and pouring, vacuum degassing is not necessary.
This product cures at room temperature with negligible shrinkage, OOMOO™ 30 has a 30-minute pot life, with a six-hour cure time.
For The Novice Mold Maker OOMOO™ silicones do not have great tear strength, They are good for making simple one- or twopiece block molds.
If you require a high-tear strength silicone, Mold Max™ silicones are recommended.
OOMOO™ 30 is suitable for a variety of art-related and industrial applications including making one and two-piece block molds for sculpture and prototype reproduction, casting plaster, resins and wax. OOMOO™ silicones are also suitable for electrical potting and encapsulation applications.

Features of OOMOO™ 30 :¶

Convenient one-to-one by volume mix ratio (no scale necessary) .
Low viscosity for easy mixing and pouring vacuum degassing is not necessary .

Safety for OOMOO™ 30 :¶

Use in a properly ventilated area (“room size” ventilation).
Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk.
Wear vinyl gloves only, Latex gloves will inhibit the cure of the rubber.

How to store OOMOO™ 30:¶

Store and use material at room temperature (73°F/23°C).
Storing material at warmer temperatures will also reduce the usable shelf life of unused material, These products have a limited shelf life and should be used as soon as possible.
Premix Parts A and B thoroughly before using.

Cure Inhibition :¶

Silicone rubber may be inhibited by certain contaminants in or on the pattern to be molded, resulting in tackiness at the pattern interface or a total lack of cure throughout the mold.
If compatibility between the rubber and the surface is a concern, a small-scale test is recommended.
Apply a small amount of rubber onto a non-critical area of the pattern, Inhibition has occurred if the rubber is gummy or uncured after the recommended cure time has passed.
Materials found to cause cure inhibition include sulfurbased modeling clays and latex rubber.
in order to prevent inhibition apply a sealing agent, apply a “barrier coat” of clear acrylic lacquer sprayed onto the clay surface.

Applying A Release Agent :¶

Although not usually necessary, a release agent will make demolding easier when pouring into or over most surfaces.
Ease Release™ 200 is a proven release agent for making molds with silicone rubber and for releasing new silicone from cured silicone.

Measuring & Mixing :¶

Before you begin, pre-mix Parts A and B thoroughly.
After dispensing equal amounts of Parts A and B into mixing container, mix thoroughly for 3 minutes making sure that you scrape the sides and bottom of the mixing container several times.
Mixture should have a uniform color with no color streaks.
If you observe color streaks, continue mixing until they are eliminated.

Pouring :¶

For best results, pour your mixture in a single spot at the lowest point of the containment field.
Let the rubber seek its level up and over the model.
A uniform flow will help minimize entrapped air, The liquid rubber should level off at least 1/2” (1.3 cm) over the highest point of the model surface.

Curing :¶

Allow to cure for 6 hours at room temperature (73°F/23°C) before demolding.
Post curing the mold an additional 4 hours at 150°F (65°C) will eliminate any residual moisture and alcohol which is a by product of the condensation process and may inhibit some resins.
Allow mold to cool to room temperature before using. Do not cure rubber where temperature is less than 65°F/18°C.

Using The Mold :¶

No release agent is necessary when casting wax or gypsum.
Applying a release agent (Ease Release™ 200) prior to casting polyurethane, polyester and epoxy resins is recommended to prevent sticking and mold degradation.

Mold Performance & Storage :¶

The physical life of the mold depends on how you use it (materials cast, frequency, etc.).
Casting abrasive materials such as concrete will quickly erode mold detail, while casting non-abrasive materials (wax) will not affect mold detail.
Before storing, the mold should be cleaned with a soap solution and wiped fully dry. Two part (or more) molds should be assembled. Molds should be stored on a level surface in a cool, dry environment.

2. OOMOO™ 25 ¶

Brief details about OOMOO™ 25 :¶

No Vacuuming No Scale Easy To Use, OOMOO™ 25 is an easy to use tin cure silicone rubber compound that features a convenient one-to-one by volume mix ratio (no scale necessary).
It has a low viscosity for easy mixing and pouring, vacuum degassing is not necessary.
This product cures at room temperature with negligible shrinkage, OOMOO™ 25 has a 15-minute pot life and 75-minute cure time.
For The Novice Mold Maker - OOMOO™ silicones do not have great tear strength, They are good for making simple one or two-piece block molds.
As OOMOO™ 30 If you require a high tear strength silicone, Mold Max™ silicones are recommended.
OOMOO™ 25 is suitable for a variety of art-related and industrial applications including making one and two-piece block molds for sculpture and prototype reproduction, casting plaster, resins and wax. OOMOO™ silicones are also suitable for electrical potting and encapsulation applications.

Features of OOMOO™ 25 :¶

The features of OOMOO™ 25 are the same as OOMOO™ 30 .

Safety for OOMOO™ 25 :¶

The safety rules are also like the OOMOO™ 30 rules but im going to mention them anyway :
Use in a properly ventilated area (“room size” ventilation).
Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk.
Wear vinyl gloves only. Latex gloves will inhibit the cure of the rubber.

How to store OOMOO™ 25 :¶

Store and use material at room temperature (73°F/23°C).
Storing material at warmer temperatures will also reduce the usable shelf life of unused material, These products have a limited shelf life and should be used as soon as possible.
Premix Parts A and B thoroughly before using.

Cure Inhibition :¶

Silicone rubber may be inhibited by certain contaminants in or on the pattern to be molded, resulting in tackiness at the pattern interface or a total lack of cure throughout the mold.
If compatibility between the rubber and the surface is a concern, a small-scale test is recommended.
Apply a small amount of rubber onto a non-critical area of the pattern, Inhibition has occurred if the rubber is gummy or uncured after the recommended cure time has passed.
Materials found to cause cure inhibition include sulfur-based modeling clays and latex rubber.
To prevent inhibition apply a sealing agent apply a “barrier coat” of clear acrylic lacquer sprayed onto the clay surface.

Measuring & Mixing :¶

Before you begin, pre-mix Parts A and B thoroughly.
After dispensing equal amounts of Parts A and B into mixing container, mix thoroughly for 3 minutes making sure that you scrape the sides and bottom of the mixing container several times.
Mixture should have a uniform color with no color streaks.
If you observe color streaks, continue mixing until they are eliminated.

Pouring :¶

For best results, pour your mixture in a single spot at the lowest point of the containment field.
Let the rubber seek its level up and over the model.
A uniform flow will help minimize entrapped air, The liquid rubber should level off at least 1/2” (1.3 cm) over the highest point of the model surface.

Curing :¶

Allow to cure for 75 minutes at room temperature (73°F/23°C) before demolding.
Post curing the mold an additional 4 hours at 150°F (65°C) will eliminate any residual moisture and alcohol which is a by product of the condensation process and may inhibit some resins.
Allow mold to cool to room temperature before using. Do not cure rubber where temperature is less than 65°F/18°C.

Using The Mold :¶

No release agent is necessary when casting wax or gypsum.
Applying a release agent (Ease Release™ 200) prior to casting polyurethane, polyester and epoxy resins is recommended to prevent sticking and mold degradation.

Mold Performance & Storage :¶

The physical life of the mold depends on how you use it (materials cast, frequency, etc.).
Casting abrasive materials such as concrete will quickly erode mold detail, while casting non-abrasive materials (wax) will not affect mold detail.
Before storing, the mold should be cleaned with a soap solution and wiped fully dry. Two part (or more) molds should be assembled. Molds should be stored on a level surface in a cool, dry environment.

3. Mold Max™ 60 ¶

Brief details about Mold Max™ 60 :¶

Mold Max™ 60 is a Shore 60A tin catalyzed silicone mold rubber formulated for applications requiring high heat resistance (up to 560°F/294°C).
It features a low mixed viscosity and cured rubber exhibits very low linear shrinkage.
Parts A & B are mixed 100A & 3B by weight.
Pot life is 40 minutes and cure time is 24 hours.
Applications include making foundry patterns, flat pattern reproductions and casting low-melt metal alloys such as tin and pewter.

Features of Mold Max™ 60:¶

Developed for high-heat resistance applications and will withstand up to 560°F / 294°C.
Features a low mixed viscosity and cured rubber exhibits very low linear shrinkage .

Safety for Mold Max™ 60 :¶

Please Note: THI-VEX™ Silicone Thickener is NOT recommended for use with Mold Max™ 60.
Important: you must weigh Part A & B components using a gram scale to be successful with Mold Max™ 60.
Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk.

How to store Mold Max™ 60 :¶

Materials should be stored and used in at room temperature (73°F/23°C).
These products have a limited shelf life and should be used as soon as possible.

Cure inhibition :¶

Rubber may be inhibited by sulfur base clays resulting in tackiness at the pattern interface or a total lack of cure throughout the mold.
If compatibility between the rubber and the surface is a concern, a small-scale test is recommended.
Apply a small amount of rubber onto a non-critical area of the pattern.
Inhibition has occurred if the rubber is gummy or uncured after the recommended cure time has passed.

Measuring & Mixing :¶

Before you begin, pre-mix Part A (base) thoroughly to re-disperse fillers that may have settled.
Using a gram scale, dispense required amounts of parts A and B into a mixing container and mix for 3 minutes.
Scrape the sides and bottom of the container several times.
After mixing parts A and B, vacuum degassing is recommended to eliminate any entrapped air.
Vacuum material for 2-3 minutes (29 inches of mercury), making sure that you leave enough room in container for product expansion.

Pouring / Curing / Post Curing for Mold Max™ 60 :¶

For best results, pour your mixture in a single spot at the lowest point of the containment field.
Let the rubber seek its level up and over the model.
A uniform flow will help minimize entrapped air, The liquid rubber should level off at least 1/2” (1.3 cm) over the highest point of the model surface.
Allow the mold to cure overnight (at least 24 hours) at room temperature (73°F/23°C) before demolding.
Post curing the mold an additional 4 - 5 hours at 125°F (51°C) will eliminate any residual moisture and alcohol that is a by-product of the condensation reaction.
This water and alcohol can inhibit the cure of some casting resins.
Allow mold to cool to room temperature before using.
Do not cure rubber where temperature is less than 65°F /18°C.

Using The Mold :¶

New silicone rubber molds exhibit natural release characteristics.
Depending on what is being cast into the mold, mold lubricity may be depleted over time and parts will begin to stick.
No release agent is necessary when casting wax or gypsum.

Mold Performance & Storage :¶

The physical life of the mold depends on how you use it (materials cast, frequency, etc.).
Casting abrasive materials such as concrete can quickly erode mold detail, while casting non-abrasive materials (wax) will not affect mold detail.
Before storing, the mold should be cleaned with a soap solution and wiped fully dry.
Two part (or more) molds should be assembled, Molds should be stored on a level surface in a cool, dry environment.

4. SORTA-Clear™ 18 ¶

Brief details about SORTA-Clear™ 18 :¶

SORTA-Clear™ Series rubbers are premium water white translucent silicone rubbers (platinum catalyst) which cure at room temperature with negligible shrinkage.
This product requires a gram scale for measuring parts A + B.
SORTA-Clear™ 18 comes in Shore 18A hardness and features high tensile and tear strength.
SORTA-Clear™ silicones are ideal for making prototype, jewelry or other molds of any configuration where model visibility is important (i.e. extracting a model from the mold via cutting).
Materials such as urethane, epoxy or polyester resins can then be cast into SORTA-Clear™ silicone without application of a release agent.
Other materials such as wax and low melt metal alloys can also be cast into SORTA-Clear™.
SORTA Clear™ 18 silicone rubber is FOOD SAFE and can be used for culinary applications including casting chocolate which i will do and other confections.
SORTA-Clear™ 18 is also SKIN SAFE and certified by an independent laboratory.

Safety for SORTA-Clear™ 18 :¶

Use in a properly ventilated area “room size” ventilation.
Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk.
Wear vinyl gloves only. Latex gloves will inhibit the cure of the rubber.

How to store SORTA-Clear™ 18 :¶

Store and use material at room temperature (73°F/23°C).
Warmer temperatures will drastically reduce working time and cure time.
Storing material at warmer temperatures will also reduce the usable shelf life of unused material.
These products have a limited shelf life and should be used as soon as possible.

Cure Inhibition :¶

Addition-cure silicone rubber may be inhibited by certain contaminants in or on the pattern to be molded resulting in tackiness at the pattern interface or a total lack of cure throughout the mold.
Latex, tin-cure silicone, sulfur clays, certain wood surfaces, newly cast polyester, epoxy or urethane rubber may cause inhibition.
If compatibility between the rubber and the surface is a concern, a small-scale test is recommended.
Apply a small amount of rubber onto a non-critical area of the pattern, Inhibition has occurred if the rubber is gummy or uncured after the recommended cure time has passed.
in order to prevent inhibition, one or more coatings of a clear acrylic lacquer applied to the model surface is usually effective.
Allow any sealer to thoroughly dry before applying rubber.
Note: Even with a sealer, platinum silicones will not work with modeling clays containing heavy amounts of sulfur. Do a small scale test for compatibility before using on your project.

Applying A Release Agent :¶

Although not usually necessary, a release agent will make demolding easier when pouring into or over most surfaces, Ease Release™ 200 is a proven release agent for making molds with silicone rubber.
IMPORTANT: To ensure thorough coverage, lightly brush the release agent with a soft brush over all surfaces of the model.
Follow with a light mist coating and let the release agent dry for 30 minutes .

Measuring and mixing :¶

Before you begin, pre-mix Part B thoroughly.
After dispensing the required amounts of Parts A and B into mixing container, mix thoroughly for 3 minutes making sure that you scrape the sides and bottom of the mixing container several times.
After mixing parts A and B, vacuum degassing is recommended to eliminate any entrapped air.
Vacuum material for 2-3 minutes (29 inches of mercury), making sure that you leave enough room in container for product volume expansion.

Pouring :¶

For best results, pour your mixture in a single spot at the lowest point of the containment field.
Let the rubber seek its level up and over the model.
A uniform flow will help minimize entrapped air.
The liquid rubber should level off at least 1/2” (1.3 cm) over the highest point of the model surface.

Curing :¶

Allow the material to cure fully at room temperature (73°F / 23°C) before demolding.
SORTA-Clear™ 18 cures in 24 hours.
Do not cure rubber where temperature is less than 65°F / 18°C.
Time to demold can be reduced with mild heat.
important : Rubber will darken considerably when exposed to heat.
Note : Allow mold to cool to room temperature before handling.
Smooth-On’s Plat Cat™ platinum silicone accelerator can also be used to accelerate Sorta-Clear rubber.

Post Curing :¶

Post curing the mold will aid in quickly attaining maximum physical and performance properties.
After curing at room temperature, expose the rubber to 176° F / 80° C for 2 hours and 212° F / 100° C for 1 hour.
Allow mold to cool to room temperature before using.

Using The Mold :¶

New silicone rubber molds exhibit natural release characteristics.
Depending on what is being cast into the mold, mold lubricity may be depleted over time and parts will begin to stick.
No release agent is necessary when casting wax or gypsum.
Applying a release agent such as Ease Release™ 200 (available from Smooth-On) prior to casting polyurethane, polyester and epoxy resins is recommended to maximize mold life.

Mold Performance & Storage :¶

The physical life of the mold depends on how you use it (materials cast, frequency, etc.).
Casting abrasive materials such as concrete can quickly erode mold detail, while casting non-abrasive materials (wax) will not affect mold detail.
Before storing, the mold should be cleaned with a soap solution and wiped fully dry. Two part (or more) molds should be assembled. Molds should be stored on a level surface in a cool, dry environment.

Material Test Casts :¶

In the lab We made some tests casts using OOMOO™ 30 and SORTA-Clear™ 18, you can see here what we have done :

Table to compare between those Silicones :¶

This is a table for the silicones we have in the lab :

Product Name	OOMOO™ 30	OOMOO™ 25	Mold Max™ 60	SORTA-Clear™ 18
Product Type	Silicone Rubber - Tin Cure	Silicone Rubber - Tin Cure	Silicone Rubber - Tin Cure	Silicone Rubber - Platinum Cure
Mixed Viscosity	4,250 cps	4,250 cps	20,000 cps	21,000 cps
Mix Ratio By Volume	1A:1B	1A:1B	—	—
Mix Ratio By Weight	100A:130B	100A:130B	100A:3B	100A:10B
Pot Life	30 minutes	15 minutes	40 minutes	60 minutes
Cure Time	6 hours	75 minutes	24 hours	24 hours
Shore A Hardness	30	25	60	18
Specific Gravity	1.34 g/cc	1.34 g/cc	1.45 g/cc	1.08 g/cc
Specific Volume	20.6 cu. in./lb.	20.6 cu. in./lb.	19.1 cu. in./lb.	25.6 cu. in./lb.
Color	Lavender	Light Blue	Red	Water Clear translucent
Die B Tear Strength	40 pli	40 pli	63 pli	80 pli
Tensile Strength	240 psi	240 psi	398 psi	425 psi
Elongation and Break	250 %	250 %	132 %	545 %
100% Modulus	100 psi	100 psi	331 psi	35 psi
Shrinkage	0.0025 in. / in.	0.0025 in. / in.	0.0015 in. / in.	<.001 in. / in.
Useful Temperature (min)	-65 °F	-65 °F	-65 °F	-65 °F
Useful Temperature (max)	400 °F	400 °F	560 °F	450 °F

This table helped me to understand more about the materials we have in the lab, so the materials are liquid silicone rubber .

individual assignment :¶

For the individual assignment this week i have to design a mold around the stock and tooling that i will be using, mill it rough cut + at least three-axis finish cut and use it to cast parts .

And i decided to make a chocolate mold bar and to design this bar i am going to use Fusion 360 and the dimensions of the wax are “15 * 15 * 4”, so let’s start !!

Designing using Fusion 360 :¶

Design N.1 :¶

You can go back to Week 3 if you want to know everything about this software .
First i have to know the dimensions of the wax that im going to use and its “15 * 15 * 4”, and as i said im going to design a chocolate mold bar so the idea is to put my name’s initial letters on a small cat shapes, BUT !! it turned out that using this mold will cost lots of material which is not a good thing also the cat legs were so small that if i wanted to remove the mold they will break so i have changed my mind and designed a new mold bar .
Also i wanted to cut this design on The SRM-20 roland PCB machine and i have figured out that it will take at least 6 hours to finish the job which made me change my mind and used the CNC shopbot .
Here is a picture of the design :

And here is a video :

Here is the design file :

Here is the design file

Design N.2 :¶

As i said before the fisrt design was not a great idea and it will cost a lot of material so i had another idea which is to use a smaller wax with the dimensions of “17 , 7.5 , 4” and to use my final project case as a shape for chocolates, it will be more Useful and in this way i will use less material, i had my friend faisal who helped me in the design so big thanks to him, the design was made in Blender and it was the first time i use another software than my fav one which is Fusion 360.
Here you can see how the shape of the chocolate will be :

Here is a look for the mold design :

And here is the design files :

Cat mold design

I will use VCarve-pro for this job and if you want to know about VCarve check my Documentation on Week8 to know everything about this software and how you can use it.

Setting up VCarve-pro :¶

I have used VCarve to create the toolpaths as follows :
For the rough toolpath, I have used 2 flute end mill (1/4) bit.
For the finishing toolpath I used 2 flute ball nose (1/8) bit.
First i opened VCarve and created a new file and you can go to job setup in order to insert the machinable wax block size as you can see in the picture X-axis “178.0mm”, Y-axis “76.0mm”, next you have to click File then import your 3D stl file.

Second i have decided to use rough toolpath, i have used end mill (1/4)” bit :

Next i have decided to use finishing toolpath, i have used the ball nose(1/8) :
then i checked the estimated time for the “roughing” and “finishing” as you can see :

Finally you can see how the roughing and finishing supposed to be :

Here i have put the wax on the shopbot like this and added a silicone on the edges in order to hold the wax in a better way :

Now i have set and checked the Z AXIS :

Here i have set the machine to the zero position :

Cutting the wax¶

Here is the wax being cut :

Here is the final result :

Cleaning and setting up the wax :¶

Now the wax is ready to be used so its time to clean it and get it ready for the SORTA-Clear™ 18 .
Here you can see i have used oil after cleaning the wax :