Jose Alegria - Fab Academy

Molding and Casting

Assignment

wHAT iS THE ASSIGNMENT ABOUT?

- Design a 3D mold around the stock and tooling that you will be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts.

GROUP ASSIGNMENT:

Review the safety data sheets for each of your molding and casting materials.

Make and compare test casts with each of them.

What did I learn:

- There are a lot of different molding and casting processes that can be used. Each of them has a very different know how and has its pros and cons.

1^st Step. Setting up the parameters

As part of the group assignment, we tried to work with different materials to expand the possibilities of molding in our lab. I took the rubber mold compound. This requires the fabrication of a positive mold for which I decided to use 3D Printing. I printed our university informal logo, a letter A, there was no problem in the material needed to make the mold because this process does not involve temperature nor mechanical forces. Then, I have to make a negative mold using the rubber compound, for this I will be using a compound sold by <<Smooth On>> and denominated PMC-770. Once this is done, we can cast anything with our mold. For this assignment, I tried casting with plaster.

So, this is the list of materials I will be using:

- Positive: ABS 3D Printing (Datasheet)

- Negative: Smooth On PMC-770 Rubber Mold Compound (Datasheet)

- Casting: Plaster

2^nd Step. Making the positive mold

For this I used a design that was made by my coworkers using the Anahuac University Logo. This was made with ABS in our Sindoh 3D Wox Printer. The procedure is explained in the 06 - 3D Printing and Scanning Assignment.

3^rd step. MAking the negative mold

This is the main step of the assignment. Once I 3D printed the positive mold, I started the process to create the negative mold by thermoforming. This is the procedure followed:

- Prepare the positive mold and container with a release agent, this could be of any supplier as long as it does not damage the materials. The product I applied was the Universal Mold Release from the same brand.

o Apply a continuos coating to model and mold surface and surrounding forms.

o Brush the release agent to minimize air entrapment.

o Apply another coating and let stand for at least 5 minutes.

- Pour both compounds in a 1:1 weight ratio in a different container

- Mix it thoroughly for at least 3 minutes.

- Pour the resulting mix in a single spot at the lowest point of the container, let the rubber seek its level up and over the model. The liquid rubber should level off at least 1 cm over the model surface.

- Allow the mold to cure at room temperature for at least 16 h.

- Release the mold and apply again the release agent before using it to cast a model.

4^th step. Casting

Having already a negative mold, I continued to the casting step of the assignment with a polymeric resin. The process consists in mixing the resin with an activating compound to start a chemical reaction. This process can be seen in the following video.

The resin-activator ratio should be between 100:1 and 100:2.

Second casting

I made a second iteration of this assignment by changing the materials used and the way I made the mold. This time I used a wax mold instead of 3D printing the negative. To do this I used a Fablab logo to get the tilted surface I needed for the assignment. Then, I will be using this wax mold to cast a soft rubber piece.

1^st Step. Setting up the parameters

For this part, I was going to make a mold milled into wax, then I will cast a soft rubber piece out of it.

So, this is the list of materials I will be using:

- Negative: Wax

- Casting: Rubber compound (Poliformas Molduflex)

2^nd Step. Making the NEgative mold

For this, I used the design of the Fablab logo to make a wax mold, to do this I exported the file as a .stl in order to be able to create the gcode file that will be used by the Modela MX-40 to mill the mold.

To do the conversion from stl to the gcode I used the mods app, then opened the server program called mill 2.5D stl and finally followed the steps from a tutorial made for the Fabacademy by the Kannai Fablab.

3^rd step. Casting the piece

This is the main step of the molding and casting assignment. This is the procedure followed:

- Prepare the negative mold and container with a release agent. The product I applied was the Universal Mold Release from the first part of the assignment.

o Apply a continuous coating to model and mold surface and surrounding forms.

o Brush the release agent to minimize air entrapment.

o Apply another coating and let stand for at least 5 minutes.

- Before mixing the rubber compound you need to measure the quantities needed, for this I filled the container with water and measured the height needed to cast the piece I needed.

- Once I know the quantity I had to set the catalyzer apart in a ratio of 2%-3%, which means around 100 droplets per each 100 g of rubber compound to be used.

- Pour both compounds in a 1:1 weight ratio in a different container

- Mix it thoroughly for at least 5 minutes.

- Pour the resulting mix in a single spot at the lowest point of the container, let the rubber seek its level up and over the model. The liquid rubber should level off at least 1 cm over the model surface.

- Allow the piece to cure at room temperature for at least 6 h.

- Release the piece.

- Cut away the discardable material.

Conclussions

This assignment showed us that there are many ways to make a mold and cast anything into it. I incorporated the digital process at 3D printing the original model at first, and by milling the mold with the Modela at the second iteration. Nevertheless, the mold fabrication and the piece casting is still manual.

Original Files

1. A logo STL File

2. Fablab Logo Fusion

3. Fablab Logo STL

4. Fablab Logo IGES

Nueval Checklist

- Linked to the group assignment page and reflected on your individual page what you have learned.

- Reviewed the safety data sheets for each of your molding and casting materials, then made and compared test casts with each of them.

- Documented how you designed your 3D mold and created your rough and finish toolpaths for machining, including machine settings.

- Shown how you made your mold and cast the parts.

- Described problems and how you fixed them.

- Included your design files and hero shot of the mold and the final object.

2022