Aluminum: It's in everything from airplanes
to beer cans, but how do we manipulate this metal into something useful? One method
is lost wax casting. Typically, wax is sculpted into the shape of the object
you would like to create. It is then submerged in investment plaster, the wax is burned out,
and molten aluminum is poured in. Seems straightforward enough,are you ready to
watch me fail... repeatedly? Because this... is Ten Tries!
In my first attempt, I printed PLA parts on my 3d printer,
and hot glued them to a printed sprue. The sprue design came from the YouTuber
Veg Oil Guy, so be sure to check out his channel. Link is in the description.
I used an empty soup can as a makeshift flask. I'm not cheap, I'm recycling... wink.
Here, I'm securing the casting tree to the can with 17 gauge steel wire and hot glue.
I mixed a ratio of five parts plaster to three parts water by weight for three minutes
...and I didn't quite make enough.
Beautiful! I let the plaster cure for 12 hours before I started the burnout process.
Heat the flask at 100C for three hours, ramp up to 550C over two hours,
maintain the temperature at 550C for three hours, put the aluminum filled crucible into
the furnace and ramp up to 740C which will be my pour temperature. Maintain the temperature at 740C
for one and a half hours then I pour as you can see here. Look at that glow!
Beautiful! You can't see the aluminum glow because the lighting was too bright in this shot.
All that's left to do is clean out the plaster.
Look at that!
It's pretty good for first try.
I had thought the casting plaster would allow more air to escape, but I was wrong.
It is important to use a peach can to ensure the plaster flavor comes out right….
That’s a joke. Seriously, don’t eat plaster!
Some lost wax casting flasks have holes so let’s try that.
I mixed, poured, and cured the casting plaster the same as before.
The burnout process was the same as well.
Uh... let's move on...
So those perforated flasks are supposed to be used in a vacuum machine.
I don’t have the money for that, and I should really have had better results
with all the ventilation anyway. Maybe the temperature of the plaster is too low?
Let’s make sure it is hot enough for this next run. I made the sprue a little larger so the
aluminum won’t cool down as quickly while flows through the mold. I kept the plaster
in the furnace for 2 hours at 760 degrees Celsius. That’s half an hour longer and 20 degrees hotter.
That is a little better. Some of the teeth on these gears look like teeth, but none of these
gears are remotely accurate enough to work. Temperature clearly wasn’t the problem, which
means the aluminum is not hardening prematurely.. It actually looks like air might be getting
trapped…So I did some research on the casting plaster I bought. I made a pretty dumb mistake.
It is casting plaster, but is not the right kind for investment casting. Apparently, the Hydrocal
White plaster is for casting paintable plaques, trinkets, and figurines. I found the product that
I should have used. USG Hydroperm. Looking at the MSDS sheet for Hydrocal White, it looks like
it is just ordinary plaster. If we compare that to Hydroperm, it is ordinary plaster with talc
added. Since I’m cheap and like a challenge, I’m going to replicate it. I probably could
have made an entire video of this process, but it was pretty boring. So let's skip to the results!
My idea is that a more porous structure will allow air to escape as the aluminum fills the mold.
I don't own a scanning electron microscope or even a powerful regular microscope, so I use
density as an estimation of porosity. My formula is plaster based, and includes three additives:
talc, which allows heat to transfer more easily to reduce cracking, dish soap,
which creates tiny bubbles that cause the mixture to turn into a foam before setting, and graphite,
which burns away in the burnout cycle if there's oxygen present. This is my indicator for airflow.
Armed with a new investment formula, I threw a few random printed parts on a sprue.
And the result was better! It seems the porosity of the plaster really helped.
I know it isn't the quality that I want but look at those holes on the top
look at them it seems the porosity of the plaster really helped out a lot!
I realized that assembling casting trees is time consuming and all just to have a bunch
of cast aluminum “art” around. Also, using soup cans for just a one-time use is tedious,
so I bought a few stainless steel pint cups that happen to be about the right size for this. They
shouldn’t rust as much, and if I’m lucky, I’ll be able to pop out the plaster after it cures.
Not bad. If you look closely at some of these rounded masses of aluminum,
it looks like some of the aluminum drained out when I drenched the plaster in water.
The aluminum looks far too smooth to have been formed against plaster.
Water, on the other hand, would cool the aluminum into smooth, rounded shapes.
As proof of this, I put together this very scientific test.
It also appears that the printer lines are still incorporated into these recessed areas.
Both of these defects must be caused by drenching the aluminum-filled mold in water before the
aluminum fully solidifies. If we look back at previous tries, we can see the same defects.
So, let’s fix that. Previously, I would allow the mold to cool for about 5 minutes before
drenching. For this try, I will allow the mold to cool much longer. One hour should do it.
By the time I drenched the plaster the outer temperature of the flask
had cooled to about room temperature. This tells me that the aluminum inside
should be fully solidified. The drench doesn't make that satisfying sizzle anymore,
but two of these parts actually look somewhat usable! Most of the fine details are intact.
There are a couple small imperfections but they would likely work. I can still do better