Fab Academy 2019 - Lucas Lim
10. Molding and Casting

Assignment :

Week 10 learning journey :

I am new to the molding and casting, beside the making of ice cubes with my fridge at home. This week topic look fun and exciting.

This week assignment :
A simple explanation of this week assignment is to mill a piece of material to create a mold for rasin casting.

We are actually 'looping' back and axpanding on the topic of 3D model design and 'large format CNC machining'. However this time we have to create a 3D toolpath for 3-axis machining.

3D Printer vs molding and casting :
Prof. Neil had mentioned one interesting contrast between molding and casting vs 3D printing. Actually we could also use a 3D printer to print out the mold, however a typical 3D-printed mold is not going to have a smooth 'surface finish' as it might contain tiny jagged edges along its surface. To have a better and smoother surface finish, we would need to machine the mold. Example LEGO® brick is created using molding and casting and not 3D print.

3D Toolpath :
This week we had to mill my mold creation block using 3-axis machining. Therefore our design has to reflect some 'contoured' surface or sculptured surfaces whereby the cnc machine will move in all three axes (x,y and z) at the same time..

Problem I faced this week :
The CNC machine in the Fab lab is having issue with the tool changer and I had to book the CNC machine at another location, but their CCN machine is only available for me to use on Wednesday (next lesson date) and subsequent Friday. So for this week assignment, I encoutered a bit of delay.

Molding and Casting

Molding is a process of creating a 'hollow' container with a desired shape of the 3D model/object. This hollow container is call a 'mold' (or 'mould') and will be use to shape the casting materials and thereby we are able to create duplicate copies of the model/object from the mold.

Mold can be a
- Simple one part mold – for models with a flat back and no undercuts
- Flexible block mold – for 3D models with undercuts
- Two part mold – for models with challenging shapes and undercuts

Casting is the process of pouring the liquid casting material (example metal, water, plastic, etc) into the mold while the material is still in its molten form and then allowed to solidify. The solidified part is also known as a 'casting', which is ejected or broken out of the mold to complete the process.

Curing is a chemical process to make the casting material toughen (or harden) by cross-linking of polymer chains, to give the final casting piece more strength.

Example liquid epoxy resin are typically mixed/cured by the use of catalyst, often called 'hardener'. There will be a chemical reaction which generate heat causing the resin to harden.

Colorant like color dye or pigment is added to the casting resin to give the final product a color. Usually one to three drops.

Reference :
- Instructables: Mold making & casting basics
- Wikipedia: Molding
- Wikipedia: Casting
- Wikipedia: Curing (chemistry)
- Castin'Craft Ideal Book by Casey Carlton
- What is the difference between a 2.5 and 3 axis machine?

Getting to work :

(1) "Designing the mold around the tool!"
From past exprience, the first step is to always to check the CNC router to be use, like availability and what it can do, etc.

Next is to check the end mill or cutting tool available for use, in order to determine the 'cut diameter' and the 'flute' length/length of cut, and the 'shank diameter'. As the cutting tool will affect your 3D model design, like how deep you can cut.

(2) Molding and Casting Supplies
I went to 'ArtFriend', a local art and craft store, and purchased the molding and casting material as well as some accessories like funnel, measuring cup, etc.

Equipment : CNC Router and End Mills

I am using a small cnc router in the FabSTUDIO, with a 2mm / 3mm diameter end mill. The 2mm diameter end mill has a 'flute' or cut depth of around 9.8mm.


Molding and Casting Material

For molding, I am using EasyMold™ Silicone Rubber (Liquid) and for casting material I am using 'FastCast™ Urethane Casting Resin'. Both are manaufacture by ETI (Environmental Technology Inc.).

Molding material : EasyMold™ Silicone Rubber (Liquid)
EasyMold Silicone Rubber is a easy to use, odor free, non-toxic, two component silicone rubber. ~ www.eti-usa.com
Working Time : 45 minutes to 1 hour of working time at 70° F / 21° C.
Mix Ratio : 1 : 1
Curing Time : 24 hours

Casting material : FastCast™ Urethane Casting Resin
"FastCast™ is a two-component clear urethane casting resin, which turns white once set. Easy to use, 1:1 ratio and is odorless. Ideal for casting, quick prototyping, miniatures, models, taxidermy and more. FastCast™ sets to a hard cast in approximately 10 minutes at 70°F. Once cured, FastCast can be drilled, sanded, shaped and painted."" ~ www.eti-usa.com
Working Time : maximum 2 minutes of working time at 70° F / 21°. Mix for 2 minutes and pour immediately into mold
Mix Ratio : 1 : 1
Curing Time : 10 to 15 minutes (cooler room temperature or high humidity might take longer)

Safety Data Sheet (SDS)

A safety data sheet (SDS), or previously called material safety data sheet (MSDS), or might be also known as product safety data sheet (PSDS) is a document which is usually prepared by the manufacturer to help you learn more about the substance/chemical/product pertaining to the safe use of the substance/chemical/product or occupational safety and health aspect.

The SDS describes the chemical and physical properties, like stability and reactivity, flammable properties (flash point, etc), handling and storage, physical hazards and health effect, first aid measures and other useful information.

The company, ETI, has provided section on 'SDS' for all the their product range, including the EasyMold and FastCast.

Safety Data sheet for :
- EasyMold™ Silicone Rubber Part A
- EasyMold™ Silicone Rubber Part B
- FastCast™ Urethane Casting Resin Part A
- FastCast™ Urethane Casting Resin Part B

I looked through the datasheets. First thing is to make sure the product code (or product name) in the SDS header matches the product that I be using.

SDS of EasyMold™ Silicone Rubber :
Hazards :
Next is to look throught the datasheet to look for any information regarding the physical hazards of the product. There is no acute or chronic health effects, however product might cause slight eye irritation if some of the product comes in contact with the eye. Skin contact: No acute toxic skin effects are expected. Inhalation: Inhalation is not expected due to low vapor pressure.

First Aid measure :
After contact with the skin: Wipe off excess material with cloth or paper. Use a waterless hand cleaner to remove as much of the remaining material as possible. Wash with soap and water.
After contact with the eyes: If contact with eyes, immediately hold eyelids apart and flush with plenty of water for at least 15 min. After swallowing: No special treatment is required.

Handling and Storage :
To me, this section is the second most important piece of information to look out for. How the product can be store in the Fab Lab and how to handle it. Example you might not want to trigger any unwanted chemical reaction.
- Open and hanld container with care
- Ensure adequate ventilation
- Do not store with basic substances (e.g. alkalis, ammonia, amines), oxidizing agents, strong acids
- Protect against moisture
Personal Protection :
Hand protection: Recommendation: Any liquid-tight rubber or vinyl gloves.
Eye protection: Recommendation: Safety glasses with side shields.

SDS of FastCast™ Urethane Casting Resin :
The Casting Resin is a much more harzardous than the molding material and need to be taken more seriously.

Hazards :
Harmful if inhaled.
Causes skin irritation.
Causes serious eye irritation.
May cause allergy or asthma symptoms or breathing difficulties if inhaled.
May cause an allergic skin reaction.
May cause respiratory irritation.
May cause damage to organs (Respiratory System) through prolonged or repeated exposure.
Handling and Storage :
Do not breathe mist or vapor.
Avoid contact with eyes, skin, and clothing.
Avoid prolonged exposure.
Use only outdoors or in a well-ventilated area.
Wear appropriate personal protective equipment.
Wash thoroughly after handling.
Observe good industrial hygiene practices.
Personal Protection :
Wear safety glasses or goggles
Wear chemical resistance gloves

Safe handling and personal protection

The SDS provide information about the hazards and following is a summarised list of Do's and Don'ts of casting that I extracted from the ebook on titled 'Castin'Craft Ideal Book by Casey Carlton' on ETI website.

Model creation : An Avengers Medallion (2.5 axis machining)

The 'Avengers: End Game' movie is showing next month, so I thought it will be cool to make An Avengers Medallion. I drawn out the logo as not to infrige on an copyright issue. My logo is not an 100% exact copy as I simply just drawn it out as quickly as I can for this week assignment.

Model creation : A star pendant (two-part mold)

My experiment on a two-part mold to make a star pendant.


Before you dive right in to make the mold or cast the pieces, it is a good idea to make test cast to do a compatibility test on the surface of the foam block (for mold creation) and the mold material (EasyMold™ Silicone Rubber (Liquid).

Apply a small amount of EasyMold Silicone Rubber and allow the silicone rubber to cure for 24 hours, then check to see if the silicone rubber has cured properly and that it has not affected the surface on the original piece.

2) I am using 'left-over' pieces of 2-inch thick foam block from a student's past project. I used a 'hot wire cutter' in my Project Lab (carpentry workshop) to cut them up into smaller pieces.

Casting the parts

I refer to the video demostration by ETI on using FastCast™. FastCast™ is a two-component clear urethane casting resin, which turns white once set. Easy to use, 1:1 ratio and is odorless. Ideal for casting, quick prototyping, miniatures, models, taxidermy and more. FastCast™ sets to a hard cast in approximately 10 minutes at 70°F. Once cured, FastCast can be drilled, sanded, shaped and painted.

Source : https://www.eti-usa.com/how-to-use-fastcast-urethane-casting-resin-video

Reference :
- Castin'Craft Ideal Book by Casey Carlton

Reflection :

Molding and casting is fun!

However it is not as simple and straight forward when first thought. You need to do a bit of reading, like the hazards, know the Dos and Don'ts, the process of molding and casting, and might required to do a few tries/experimentations to get it right.

Files :

My design in Fusion 360 :
My file

References :

Instructables: Mold making & casting basics
Smooth-On: Basics of Mold Making
Fusion 360: Star Pendant
Product Design Online : Tutorials on Fusion 360
Fusion 360: Mold Making Tips
Autodesk Fusion 360 - Mold Creation
Fusion 360 Creating a pewter mold
Fusion 360 Simplified - Lesson 1 of 3
CAM for CNC Router: Fusion 360 Beginner Tutorial
Making TOOLPATHS and exporting G-CODES | Fusion 360 | Quick Tip
Casey Carlton, 1982, Castin'Craft Ideal Book by Casey Carlton, Field Landings, CA