12. Molding and Casting

This week I learned how to make molds and used different machines in the lab to create them.

2-Step Mold CAD and CAM

I used Fusion to design my mold, as well as create the toolpath for it to be milled.

To start, I wanted to make a 2-step mold. This would allow me to cast soft material (since the mold would be hard).

Designing the Mold

I wanted to make a basic design of the mask worn by the Knight in the video game Hollow Knight.

To start the design, I obtained an image from the internet, traced it in a sketch, and extruded that sketch to create the mask. I also added some fillets to make the design smoother. Next, I created a rectangular prism for the actual mold, and I cut out the intersection between it and the mask (using the Combine tool in Fusion).

Printing the Mold (Prusa Mini)

At this point, I exported the design as an STL file and converted it to gcode for the Prusa Mini printer through PrusaSlicer. I sent the gcode to the printer, and there were no problems along the way.

Creating Toolpath

I also wanted to attempt to use my lab’s milling machines to create a mold.

I used the Manufacture workspace in Fusion to create the CAM toolpath. First, I defined a new setup and set the machine to a generic Autodesk 3-axis. I configured settings for the positions of the axes and origin.For the stock, since I wanted it to be approximately the same size as my designed mold, I used a relative size box with no offset from the mold box.

Once the setup was configured, I made two toolpaths: one for a roughing pass and one for a finishing pass.

For the roughing pass, I used a 3D adaptive clearing since my design has some rounded parts. I set the tool to a 1/8” flat end mill (since it can easily remove a lot of material), and I set the maximum stepdown to 1 mm. I initially had an error that set that the toolpath was empty, but I fixed this when I realized that the stock went along the inside of the molding shape.

Next, I used a 3D contour path for the side finishing path and a 3D flat path for the bottom finishing path. I used a 1/16” flat end mill tool, and I set the maximum roughing stepdown to 0.75 mm. These toolpaths did not take long to generate at all, and they had a very short run time (roughly 10 minutes combined).

Exporting Toolpaths and Milling

I used the NC Program tool in Fusion to export the toolpaths. I ensured that I set the machine to the Bantam Tools machine (since that was the one our lab had), named the files, and exported them as .gcode files.

I planned on using my lab’s milling machines to mill the design out of wax.

I imported the toolpaths into the Bantam Tools software, and I milled them similarly to circuit boards from previous weeks. The only slight difference was that since the wax isn’t conductive, I needed to measure the height manually with calipers.

The milling process went smoothly.

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3-Step Mold CAD and CAM

My instructor, Mr. Dubick, also wanted us to make a 3-step mold for this week. This would allow us to make a hard final cast (since the mold and cast should be opposites).

Designing the Mold

I first made a rectangular prism for the bottom of the mold. Next, I added the mask design to the top of it. Finally, I added sides to the mold that went higher than the mask in order to create a bottom part for the mold that would be casted from this mold.

I planned to use my lab’s resin printer to print this as part of this week’s group project.

Printing the Mold

Hasn’t been done yet.

Casting a Soft Mold

I used the mold printed by the Prusa Mini 3D printer for casting due to time constraints. When deciding which material I wanted to use for casting, I chose Smooth-On’s Mold Star 15 Slow.

To figure out the approximate volume of my mold for apportioning how much silicone I would need to fill it, I used the Fusion model. I right clicked on the mask model and checked its properties, and it stated that the volume of the mask was 0.77 in^3. I converted this to mL to get roughly 12.6 mL.

Collin Kanofsky was also working on casting at the same time as me, so we collaborated throughout this process.

I obtained the containers with Part A and Part B of Mold Star, and we mixed them well. For Mold Star, parts a and B have a 1:1 ratio, so to get how much of each part I needed, I just divided 12.6 by 2, getting approximately 6.3 mL of each part.

After also accounting for Collin’s necessary volume, we poured our combined amounts of Part A and B into two separate cups. Once our measurements for each part were correct, we poured the two parts together and stirred for some time.

I poured the silicone mixture into my mold, and I made it so that it slightly overflowed (so the bottom of my cast could be even).

I then waited for the silicone to harden.

Once hardened, I was able to take out the mold using a scraper tool. Since there was some overflow in the mold, there was some excess silicone that I needed to cut off.

Here is the cast after cutting excess off:

We also had some excess silicone, so for fun, Collin and I made a smiley face.

Group Portion

This week, I worked with Richard Shan. Our documentation can be found [here].

We have not started this yet due to absences.

Credits

All credits are mentioned where they are used respectively.