16. Molding and Casting¶
- Review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them
- Design a mold around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts
For this week, I wanted to create a grip for my wand using a hard cast.
First, I created a rippled sketch for the grip and revolve the sketch to create the rounded shape.
Then, I placed a 3 cm wide chord on the side of the body and extruded away the rest of the body to create a piece of the grip that could attach to the recentagular sides of my wand body.
Next, I created a shell to house the mold and I used the move tool to move the positive shape to bottom of the shell.
Finally, I joined the bodies together.
I had used the CAM component of Fusion 360 before so I had a slight idea of the CAM workflow. I began by creating a setup and positioning the origin of the setup to the bottom right-hand corner of the model.
However, I didn’t have any clue about the bits that I could use due to the coronavirus quarantine policies, so I used the bits that William Knight used during this week.
To remove the majority of the stock material, I used “Adaptive Clearing” and unselected the “Stock to leave” option since the previous simulations revealed that the option left unwanted stock material. The simulation revealed a blocky but defined positive shape in the center.
Next, I addressed the issue of finer details. I used “Parallel” to smooth the ridges in between the recesses.
Then I used “Contour” to smooth the recesses by seting the maximum stepdown to .1 mm.
The simulation of the entire setup yielded a positive shape with much finer details.
I had to mill on foam because there was no wax pieces large enough to accomodate my design. However, when I milled out the design on a piece of foam, the bit went too far into the foam. After several attempts and consulting other alumni, I found out that I needed to use the z-plate on top of the stock and that my stock origin should be on the upper corner of the stock.
With the foam milled out, it was time to create a mold. Since the grip was to be made out of a hard cast, I needed a soft mold and used Ecoflex.
To use any molding and casting materials, the part A substance must be mixed with the part B substance in a predefined ratio and poured during the potable period. Ecoflex has a 1:1 ratio by volume, so we poured part A and part B into seperate measuring cups with equal volume. Then, we poured them together and mixed the mixture for about a minute.
Next, we poured the mixture into the foam cast and waited for 90 minutes.
With the soft mold done, I could move on to casting the hard grip. Task 8 is a hard casting material that was readily available at the lab, so it was an obvious choice. The mixing ratio was 1:1 by volume so we repeated the same mixing process for Ecoflex.
Task 8 sets at a much slower rate than Ecoflex, but we could check on the progress by using a temperature gun because the process is highly exothermic.
Finally, the cast cooled down and hardned, yielding a replica of the grip.
Here is the result:
This week, I learned how molding and casting can be used to create replicas of a shape with differing material properties. This experience will help me create parts of my wand that require physical properties that casting material can only provide.