Week 12 - Casting and Molding
Group Project
Molding Materials in Group Project Page
CADed Mold
I decided to create a mold for a wheel that I could use on the frisbee shooter if my first wheel failed. Below is my CAD.
Creating A Resin Mold
Resin Printing
After creating the CAD model, I used OnForm, a resin printing software to export g-code to the printer.
I then cleaned the bed of the resin printer and printed my first print
However, around half way through the print, some of the solid resin parts got into the liquid resin and it caused the print to fail.
After cleaning up the mess, I went back to the OnForm and figured out that a "cup" error caused the print to fail. After some research, I learned that the only way to fix this issue is either add a hole which wouldn't work for a mold, or to flip the mold upside down and use supports which was what I did. Below is the final print
Resin Wash
Now that the print was done, I put it in the resin wash which basically swirls alcohol around the print cleaning off any excess resin not intended to be on the print.
One issue that arose was that when I took out the print 20 min. later, the inside of the mold was filled with alcohol and it spilled everywhere when I set the plate down. I cleaned up my mess and went to the curing machine
Resin Cure
I first took the print off the plate with gloves and then placed it on the table in the curing machine. Lastly I set the time to cure at 60 min and started it. Below is the curing happening mid print
Problems with removing supports
The first problem that arose when I tried to remove supports was that the supports were too strongly attached and too many in number. To solve taking off the main supports, I used a hand saw.
Then I had to remove the supports inside. Once again they were too hard to remove so I used pliers and yanked out parts of the supports. This ended up working really well and lastly used a dremel with a metal flat sanding end to smooth the floor of the print that was rough from supports.
Creating a Wax Mold
Before I could mill my design out of machine wax, I first had to melt the wax into a big enough shape for my design.
Melting Machine Wax
We found this tutorial by machineWax.com that taught us what supplies we needed and how to remelt wax. I then drove to Harris Teater to acquire materials such as baking pans, molds for the wax and more.
Then, I got the short wax pieces from my fellow fab students who I subjected to cutting the wax. The picture below is 2/3 of a total wax piece that I cut up
I then headed to the kitchen in our school and put wax pieces into the non-stick trays I got.
Next, I turned the oven on to 280 degrees Fahrenheit but later increased it to 295. The wax took around 45 min. to melt. The picture is of the wax half way melted.
Finally, when the wax was fully melted, I poured the wax into the mold containers I bought and filled with tinfoil. My teacher helped me pour as seen below.
I waited 30 min. to let them cool a bit and moved them into the lab to cool for another 2 days.
Machining the wax into a mold
I took the cooled wax and cut it in half so it would fit on the milling machines bed
CAM - Creating the toolpath
I won't go into a ton of detail because I did that in CNC week but I will cover some key points.
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I created 2 main toolpaths using Fusion Manufacturing. The first one was a roughing pass using the adaptive clearing toolpath and a 1/8 in. endmill that I will talk about later. The second toolpath was a finishing toolpath that cleaned up the outside and also some minor toolpaths for the inside of the mold.
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I used a 1/8 in. 2.25 in. endmill bit to cut out both the roughing and finishing passes. My reasoning for using such a long bit is because my mold design in 2 in. tall which means I can only use a long straight bit. 1/8 was the smallest long bit we had and it just barely could fit my design. Because of this, I ended up having to use the 1/8 bit to do both the roughing and finishing cuts.
Small Timelapse of the Cut :
I used this sandpaper on the end of a stick to smooth the bottom of the mold because I didn't have a bit capable of doing a finishing path.
Casting into the molds
For my cast's material, I chose Platinum Cure Silicon Rubber. I chose this material because of it's firm yet flexible form that would allow expansion during the spindle spinning but wouldn't expand to the point of exploding.
This material has a Part A to Part B ratio of 1 : 1. Then, I used onshape to find the cubic inches of volume my final result would be. Finally, I timesd by 3 for my 3 molds, converted to milliliters due to my container, and divided by 2 to get how much of each part I would need.
Creating a 2 Part Mold
For the first mold, I 3D printed a inverse mold and casted silicon in it. After the silicon mold was made, I found a solid plaster like material. When I first opened Part A and Part B of type 8 Moldstar, Part B had a solid precipitate at the bottom and I was unable to stir it in no matter how hard I tried. When I went to a teacher for help, doctor taylor had me look for an expiration date and it had expired in 2022.
After some more searching, I found a more recent type 8, shook them till my arms hurt(They were smaller than the big one), and then poured them into a 1:1 ratio as the instructions said.
Then I poured the 2 into 1 and poured the mixed mixture into my silicon mold.
After about 2 mins. and an extremely potent exothermic reaction, the cast had hardened and around 10 min later, I took it out of the mold.
Finally, I wanted a flat top and bottom because the type 8 expanded during the reaction. To achieve this, I used a sanding machine while I wore a gas mask to not inhale any particles. Below is the final result.
Final 3D Printed Cast
Final Resin Cast
Final Milled Cast
Final Type 8 Solid Cast
Strength Test Type 8 Solid Cast
Conclusion : Very Strong, took little to no damage
Reflection
This week was probably one of the most impactful weeks for me. In my final project, I have been doing a ton of molding and casting and it's super cool to do. I learned how different molds create different types of casts and how each have their distinct advantages and disadvantages. For example, 3D printing is super easy but it leaves lines on the top of your prints and can't make circular objects actually circular. I also learned how to create 2 part molds that allow for a hard material cast. Overall, this week was super fun and I know I will be casting a lot in the future.