Molding and Casting¶
Goals¶
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.
Prior Knowledge¶
None, besides printing the molds.
Projected Timeline¶
Molding and casting in the span of two days. Since this overlapped with finishing machine week, I needed to work efficiently.
Actual Timeline¶
- Monday
- Print mold
- Tuesday
- Cast
Group Assignment¶
I was in a group with Angel Fang, Noah Smith, and Kathryn Wu. We compared the datasheets of our materials.
You can see our documentation on our group site.
Individual Assignment¶
Datasheet¶
I used Part A and B silicone for this mold. I checked the information in the data sheet to ensure that I was properly pouring and maintaining the mold while it cured.
I looked at the shelf life, pot life, and cure time of a cast. Shelf life is the duration that the product works once opened, before expiring. Pot life is how much time one has to modify the cast when being used. Cure time describes the amount of time before the cast fully sets. One uses a cast before its shelf life ends, works with the material during its pot life, and waits until the cure time ends to remove the cast.
- Shelf life: 6 months to 2 years
- Pot life: 2-5 minutes
- Cure time: 10-15 minutes
Designing the Mold¶
I decided on creating a star. Although somewhat basic-looking, I’ve never tried making a star in Fusion 360, and I knew using the points on the side would be physically challenging to work with.
After creating a star, I sketched a surrounding square. I extruded both 1/10 of an inche and extruded the surrounding material half an inch. Albeit small, this would be fairly easy to handle, with less room for error.
Printing the Mold¶
This was a straightforward process with no main issues. I simply exported and printed the design.
Casting¶
I poured the Part A and Part B liquid rubber into the 3D printing. 24 hours later, I observed that the cast cured and turned into a somewhat flexible shape.
I dealt with the issue of having to use the point of a scissors to pry it out, however, it became much easier once I extricated the first side from the mold. Since I used a rigid mold, the cast needed to be fairly soft.
Post-Processing¶
As the layer lines of the 3D print were still showing, I needed to post-process the mold using XLA and re-cast with the smoother surface.
Re-Molding Plan¶
I decided that, since I understood the procedure here and knew my issue was just the resin I used, I would switch over to my final project. I talked to Mrs. Morrow, and she confirmed that I can 3D print and post-process the molds for the lake and bunkers. Note that the reason why I did not just 3D print containers and leave it at that is to keep the container invisible and malleable to emulate water or sand.
Design¶
I took measurements for each hole using a ruler. Since the molds use tension, I would round up and add half an inch to each measurement. The lake is much too large for one print, so I will be attaching them with a joint. The measurements are below - rounded up, but without the half inch added.
Bunkers: - 5.54.25 - 3.252.5 - 4*5
Lake: - 20*9.5
I 3D printed the 4*5 bunker to avoid decimals in measurement.
An XLA coat let me postprocess the material, as I was used to doing. After the tedium of this process, I decided to move away from this technique and towards smoother filament, at least for larger objects.
The resin coat never cured. I used the correct Part A and Part B, however, this was already a gamble. In part, because the 1A:1B ratio was an approximation, although they appeared to be mixed in equal amounts. Mainly, though, cavities have a wall between the empty space and the container. I just poured it over and expected it to work like the XLA.
Not only did this fail from a scientific standpoint, it did so mathematically! Adding a half inch to each measurement does not preserve the ellipse proportions, and while the fit could still work with a flexible material, I could not settle for a distorted container. I can keep the original measurments instead. The offset ledge at the top was one of my better ideas - since I extruded it .1 inches downwards, the AstroTurf could easily cover the layer. With a half inch ledge all around, I would not need to rely on tension for a proper fit, and the weight of the layer would prevent the layer from caving. If not, any resin-friendly adhesive would do so adequately.
To summarize: - Preserve original measurements - Keep top ledge - Measure precisely - Create closed space for material to cure
The first three were quick fixes. The fourth, less so. Consider the star I made for the original molding and casting assignmeent. What if I decided to reverse it and cast a cavity, as opposed to the star itself? I just create negative space around it and take it out. While difficult at times, I can do so because the space does not connect at the bottom. I can simply remove the sides.
If I were to do the same with a cup, I cannot physically take it out once it cures. If I do not connect the cup from the bottom, it’s not a cup, it’s a funnel. I need to create a proper cup.
Except I don’t need to connect it from the bottom, do I? It took a minute, but I realized I can just rotate the object. To better visualize the design, I designed the same bunker, applying the other fixes as well.
I will, of course, be trimming the mold after to fit the dimensions. Since I created a shell, the ellipse measuements are in fact smaller than the original, although the ledge and extra resin will negate the discrepancy.
I printed with Very Fine filament. The print took over 15 hours.
Datasheet¶
I used Ecoflex 00-30, which took 4 hours to fully cure into a somewhat flexible cast.
Cast¶
At first, the material seemed overly flexible and unable to hold sand. Luckily, it hardened to an ideal texture.
The instructions on the back described both types of the product, I followed those for rubber.
Of course, it turned out that I put the ledge on the bottom and not the top, rendering it pointless for holding sand. Still, the mold worked smoothly.
The final result is below.
Reflection¶
While molding and casting is a generally tedious process, it produces a quick and smooth result. I also found no major issues in either molding or casting. Since I intend to mold containers for the lakes and projects in my final project once I establish the proper dimensions, this introduced me to the specific process. I learned that I would need to 3D print a box around the container, with the container itself being empty. I will need to experiment and research a bit more to find logistics and previously used methods.
Group Work¶
I learned a bit about the various datasheets and usage of multiple molding and casting materials.
Positives¶
I have never tried curing the resin from a 3D design, and the products are quite versatile. The main perk of this week was having another tool to work with.
Negatives¶
The logistics, datasheets, and wait time in order to find the products. Preventing layer lines requires often difficult measures.
Takeaways¶
Interestingly, I learned more about mathematical applications than I did about resin. If measured, poured, and cured properly, the instructions produce a straightforward result. The challenge lies in setting up and refining the product into a usable vessel.
Lessons¶
- A soft cast belongs in a hard mold and vice versa.
- There are multiple ways to make a mold, mainly printing and milling.
- I never personally had trouble understanding this, but pour the resin into a tray or other established space for molding. Do not do so in a random storage basket. You know who you are.