Molding and Casting
Assignments
group assignment:
-review the safety data sheets for each of your molding and casting materials,
-then make and compare test casts with each of them
-extra credit: try other molding and casting processes
individual assignment:
-design a mold around the stock and tooling that you'll be using,
-mill it (rough cut + three-axis finish cut),
-and use it to cast parts
extra credit: use more then two mold parts
Research
throughout the week
Group Work
Group Site link
This week for group work I helped to test silicone along with testing other materials with my group.
From this I learned that if I want a soft mold silicone is usually good because it cures fast and is easy to use.
Molding and Casting
Fusion 360
To start everything off I had to make a mold to cast for this week. I was thinking about what I could make that would be relevant to the soda machine and decided to make an ice mold for it. I wanted to make a diamond ice mold to make diamond ice with. To start everything off I had to make a model of what I wanted to mill. So I made a 2 part mold that would be cast to make many molds, so I could have multiple ice molds. Because of this I started by making a 2 part mold that could be connected to make a mold and left it empty, so I could put an object in.
So Next I then designed the diamond and split it apart putting both sides into the boxes for it to be molded.
Lastly for fusion I had to make a cut path for my model. So I started by selecting a 1/8" wax ball bit and using the adaptive 3d path option. In that I selected a .125" max step down rate so that the bit would not be damaged but would not take forever. I then changed the bit feed rate to 760mm/min this way it could cut my wax stock I was using. Lastly I added a ramp path to smooth all the ramps after I milled it. I then his process and it generated the toolpath.
After finished the tool path in fusion all that was left was to export it to the bantam milling software.
Bantam software
After importing my code for my gem file I had to set the size of my wax stock I was using and make sure it was all aligned. I then taped down my wax stock onto the milling machine.
One mistake I made that I only realized while cutting was that I had accidentally added an x and y offset to the stock, so it was not placed right on zero in the file but it was on zero on the machine. Luckily I had left some room for error and while it was a close call it still all was within the wax.
milling
All that was left was to make sure the right bit was in and then to press go. Once I pressed mill it started cutting the wax perfectly just like in the file. This was also when I realized their had been an offset but nothing bad happened because of it. Here is a video and picture of the milling process and the final result.
Molding
Once I was done milling the mold I needed to get all the materials to mold the mold of my diamond. So I started by getting part A and B of Mold Star 16' Fast Platinum Silicon Rubber to make my mold of the diamond.
Following the steps to use it listed on its data sheet and on the bottle itself I started by pouring and equal of amount of each part A and B into separate cups. With it being measured to 125ml each I then poured them into one cup stirred for 45 seconds to get out all the air bubbles. After that I quickly poured all the silicone into the mold before it started to harden. I poured it at and angle so that more air could escape.
After I poured it I waited for 30 minutes for it to cure like it said to on the bottle. I then ran a knife along the edge of the mold and pulled it out. Here Is an image of the first mold.
Here is how they both fit together.
It was now that I realized I had forgotten to add a hole for resin to go in, so before I cast another one I just cut a hole in it to see if it would still work.
After cutting it out I got all the materials out to pour the Smooth-Cast 65D White Semi-Rigid Urithane Plastic into the mold. After getting equal amount parts of part A and B into separate cups as seen here.
I then quickly poured both together and stirred because it only has a 5-minute pot life, which means I have 5 mins to get everything in place before it starts to harden. After waiting 10 minutes I then started to de-mold the diamond and here was the result.
Because of the lack of a big hole it did not work. I decided to try the whole thing one more time before remolding my silicone mold. Here was the result of my second try.
Because it did not work I decided to actually remold my silicone mold but glue down a straw in the middle so that I would have a proper hole for the resin to go into.
After I put the straw in I just remolded the silicon using the same steps I did the first time but with a straw in the middle for a hole.
After getting a good hole for resin to use I then molded the resin another time in the silicone mold with this time resin cleanly going into the mold, and it actually filled the whole mold before hardening.
After Getting the Resin out of the mold, here is the final result.
Revisions
After my local advisor told me that using the 1/8" ball bit twice was not a roughing and finishing path and that I needed to start with a flat end mill then go to a ball end mill for the finishing path. Because of this I decided to quickly make a model in fusion to do both paths correctly to show that I learned this. Here is the original model.
I then started by doing a pocket rough tool path with a 1/8" flat end mill at 760mm/min cutting feed rate. Here is an image of the rough cut.
Then I added a parralel finishing tool path with a 1/8" ball bit with the same cutting feed rate. Here is an image of that tool path.
The next step was to export it and send it to bantam milling machine and set all the stock sizes correctly. Then I just had to put in the 1/8" flat end mill bit and I was then ready to start the cut.
After 10 minutes it was done with the roughing pass as seen in this picture here.
I then had to replace the bit with a 1/8" ball bit to do the parralell finishing path. This path moves like how a you might mov your lawn in lines going over everything to smooth it down. You can see this motion happening in this video here.
With this motion and a ball bit we can a much better finish with a smooth curve / step down as seen in the final picture of my second mill.
Summary
This week I learned way more about how to actually mill something in 3D instead of the normal 2D PCB boards I mill. I also learned how to use multiple cut paths to have a better final result. Lastly I learned how to mold with materials like silicone and resin. With what I learned this week I should actually be able to make some really nice button caps for my final project that will feel nice and rubbery instead of like a plastic 3D print. I will do this by 3D printing some button caps and then casting them in silicone to make a mold from them, and then I will have a mold where I can make multiple button caps.