Molding and Casting
Group Assignment:
Review the safety data sheets for each of your molding and casting materials
Make and compare test casts with each of them
Compare printing vs milling molds
Individual Assignment:
Design a mold around the process you'll be using, produce it with a smooth surface finish that does not show the production process, and use it to cast parts.
Have you answered these questions?
Linked to the group assignment page and reflected on your individual page what you have learned ✅
Documented how you designed and created your 3D mold, including machine settings ✅
Ensured your mold has smooth surface finish, that does not show the production process (by postprocessing if necessary) ✅
Shown how you safely 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 ✅
Group assignment
Review the safety data sheets for each of your molding and casting materials
Make and compare test casts with each of them
Compare printing vs milling molds
Reflections
This week, I deepened my understanding of using F-20 Plus silicone and Silikast-Pro polyester resin for molding and casting. I was impressed by the versatility of RTV silicone, especially its tear resistance and ability to capture fine details. The resin, on the other hand, offered excellent rigidity and mechanical strength, although its short working time required me to be more efficient during the casting process.
One of the main challenges was the precise handling of components. Mixing the silicone with the catalyst required exact measurements to ensure proper curing. Additionally, pouring the resin had to be done quickly and accurately to avoid air bubbles and ensure a smooth surface finish in the final pieces.
Individual assignment
Design a mold around the process you'll be using, produce it with a smooth surface finish that does not show the production process, and use it to cast parts.
1. Concept / Mold Design (CAD)
I’ve been thinking about the idea of creating a 3D heart using 3D printing. I decided to make it using two types of molds: one will be the 3D print itself, and the other will be a traditional mold for casting. The plan is to use both and compare the results and processes.
The design I created is quite simple—I chose this approach to test how the pieces come out without complicating things with more detailed shapes, especially since more complex designs take longer to print, and right now, time is not on my side.
I’m using Rhinoceros software, which allows me to work with curved forms, just like I imagined. I didn’t find it necessary to add a draft angle because the shape is simple and should be easy to remove from the mold. What I am considering is the pouring channel, which will also serve as an air vent for casting the material—I'll document this part later. Since the model doesn’t have many details, I expect it will be easy to demold.
This is the first design I created, and I will 3D print it. This mold will be entirely made using 3D printing.
I export this Rhinoceros file in STL format, then configure it and save it as G-code.
And this is the design for the other mold: I will first 3D print the positive, and then I’ll make the negative using silicone.
I export this Rhinoceros file in STL format, then configure it and save it as G-code.
2. G-code
The molds that will be 3D printed and is saved in STL format is uploaded and opened in the Ultimaker Cura software. This software will help me check if the file has any errors, but most importantly, it will show me the estimated printing time.
In Ultimaker Cura, the configuration I will use to achieve high quality is as follows:
Layer resolution: 0.12 mm
Fill percentage: 30%
Extruder temperature: 205°C
Build plate temperature: 60°C
This file consists of two pieces. According to the estimates, one will take 4 hours and 56 minutes, while the other mold will take 5 hours to print.
These files have an approximate 3D printing time of 4 hours and 54 minutes for one of the molds, and 4 hours and 57 minutes for the other.
I open these files in Ultimaker Cura, and then save them as G-code, which is the format read by the 3D printer. The printer I’m using is an Ender 3 V2.
3. 3D Printing the Mold
To start the 3D printing process, I save the files on a USB drive, select the material—which in this case is blue PLA—check that all settings are correct, and then begin printing the four pieces.
Part of the 3D printing process
With the prints ready, I now move on to the next step, which is preparing the mold.
4. Mold Preparation
For the mold made with 3D printing, the next step was to prepare it, since one of the requirements of this assignment was to achieve the cleanest possible finish, avoiding visible 3D print lines.
To achieve this, I carefully sanded the pieces. In the case of the mold that would be used as-is, directly from the 3D print, I applied a resin coating to give it a smoother, more professional finish.
I looked into it using ChatGPT and found that I could apply resin, which has a drying time of 24 hours. So in this case, I decided to apply resin as the final layer.
For the other mold, the one that serves as the positive, due to time constraints and drying process, I only sanded it. This mold is specifically intended for pouring the silicone to create the negative.
5. Materials
The materials I will use for the process are:
- Two 3D printed molds:
- One is the final mold (used as-is).
- The other is the positive mold for casting the silicone negative.
- RTV Silicone
- General-purpose polyester resin
- Resin catalyst
- Silicone catalyst
- Paraffin wax
6. Molding Process
"The method I used to estimate the volume of material needed for the silicone mold was the following: I poured rice into the positive mold and then transferred it to a measuring cup. This allowed me to approximate how much material I would need. In this case, I used about 100 ml and added 2% catalyst.
To create the mold, I attempted to calculate the volume in Rhinoceros through the 'Analyze' menu, but I couldn't get the volume to display. Since the dimensions were fairly similar, I followed Cristian's guide from the academy. As a result, I used 100 ml of silicone and 3 ml of catalyst. This turned out to be the perfect amount to make the mold.
Did I have any issues completing this assignment?
Yes, I did encounter some problems. The silicone I was given was expired, so the mold never cured properly. I had to purchase a new product and start the process over. One of the issues this caused was that, when I removed the mold, it was sticky and rubbery. I had to carefully wash it to remove imperfections and make sure it was completely dry and free of any greasy residue before I could remake the mold.
This is the result.With the new product, and using the correct proportions —100 ml of silicone with 2 ml of catalyst—, the process worked as expected. I kept checking the mixture, and after about 2 hours I noticed a slightly gelatinous texture. I was a bit worried it might not fully harden, but by the next morning it was completely solid. By 9 a.m., the negative mold was ready.
This is the result. I'm really happy with the result!
7. Casting Process
7.1. Wax
To perform the casting of the 3D printed mold, I did a volume analysis to estimate how much material I would need. To do this, in Rhinoceros, there is an option in the top menu called "Analyze." Then, I selected "Mass Properties" and clicked on "Volume." There, I obtained the following volume: Volume = 83227.3912 (+/- 0.00053) cubic millimeters. This is the total volume for the two pieces.
For the casting, I also used a simple homemade method to estimate the volume I would need. In the case of paraffin, it was easier because I just had to cut the approximate amount of material, without needing to mix anything.
To melt the paraffin, I place the material in a heat-resistant container and melt it. Then, I pour the melted paraffin into the mold that was 3D printed.
Part of the 3D printing process
Here I show the demolding process.
I am happy with the result. In the photo, you can see that the texture of the 3D print is not noticeable, as it went through a previous process of sanding and resin application to mask the texture. The only difficulty I had was during the demolding process, but it turned out well in the end. I believe that with more practice, the demolding process will improve.
7.2. Resin
I also used rice to calculate the volume needed for the resin. In this case, the amount was less than 100 ml since I was using the same mold I had previously used with the paraffin. Since the resin required accurate proportions to harden properly, I prepared 100 ml of the mixture and added 2% catalyst.
Resin on its own is somewhat more toxic, so I wear safety equipment, which is very important, such as goggles, latex gloves, and a mask. This is necessary for health precautions, as the smell of the resin is strong.
To measure 100 ml, I used a standard measuring cup, which is 240 ml. According to what ChatGPT told me, the corresponding amount would be approximately 1/4 of a cup, as:
100 / 240 ≈ 0.42 cup
This is a little more than 1/4 of a cup. To be more precise, 100 ml is approximately 1/4 of a cup + 2 additional tablespoons (approximately). Therefore, 1/4 of a cup is close to 100 ml, but if I need more precision, I can add a little more liquid to reach exactly 100 ml.
This information was helpful to determine the proportion of resin I was going to use, along with the mixture of the catalyst. The catalyst I used was 20 drops, and then I mixed the resin with the catalyst for about 1 minute. After making sure the mixture was well integrated, I poured it into the mold that had been 3D printed.
"The resin was much easier to demold from the 3D-printed mold, which is quite rigid on its own. The result turned out great. I really enjoyed the process, especially the texture of the 3D print, which wasn’t too noticeable thanks to the prior sanding. I did this casting at 2 a.m., and it had already hardened within just 4 hours.
7.3. Jello
I also used the same method of calculating the volume with rice for the silicone mold. In this case, it was much easier to estimate.
For the casting, I used a negative mold made of silicone. I secured it with rubber bands to prevent any leaks.
As I started working on this, I realized that the mold design should include some kind of protective feature to stop the liquid from leaking.
Indeed, some of the liquid did leak out. It wasn’t much, but I think it’s definitely something that should be taken into account in the design. To be honest, I hadn’t thought of it, but it’s a valuable lesson for the future.
Despite the small issues I had while doing this project, the result turned out really beautiful—and it looked delicious! But… there's something I need to make very clear.
For this experiment, I chose to use gelatin, but the silicone mold I used isn’t food-safe, as it was made with a chemical catalyst that’s not safe for edible use. There are special food-grade silicones, but unfortunately, I couldn’t find any when I went shopping. That’s definitely something to keep in mind.
So I was left wishing I could eat it 😢
Reflections
This week’s assignment focused on molding and casting, and I learned how to create molds using 3D printing. I took advantage of this technique to create a positive mold and then used it to apply a traditional method by casting a negative mold in silicone. My goal was to compare both methods and evaluate which one suited my design needs better. In the end, both methods worked well for what I was aiming to achieve.
Using 3D printing had its pros and cons. One big advantage was that I could take the printer home and continue working on the assignment. However, time was a challenge—I had to constantly monitor the machine, level it properly, test the nozzle and bed temperatures, and reprint some parts until everything was set correctly. Each part took around 5 hours, and since I printed four pieces, I invested around 20 hours just in printing, not including the time spent on failures and adjustments. Despite that, it was very rewarding to see the molds come to life and work as expected.
In terms of results, the 3D printed mold had some complications during demolding, especially with wax, which tended to stick. On the other hand, resin demolding was smoother and quicker. At the end, I did a small test using gelatin, and although the result was interesting, there were some leaks. That made me realize that when working with very liquid materials, the mold design needs to be more precise and better sealed. It’s definitely something I’ll keep in mind for future projects.
Another valuable takeaway was learning about the different types of silicone and their textures. I would have liked to try making a food-safe silicone mold, but now I know what kind of material I need and how to calculate the right amount based on the volume of my design.