So, you might have seen our last attempt at making a heat sink where we took a
reciprocating saw to a block of aluminum with what could best be described as
limited success. But, of course, persistence is the name
of the game here at LMG. So, we went through the YouTube comments which were
full of suggestions about casting our
own heat sink from molten aluminum and
decided to set about doing it. But is
that really the kind of thing that you can do with $100 worth of supplies and
an empty warehouse? Well, there's only one way to know for
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So, casting then. I guess we'll need a
couch to No, we're talking about the
kind of casting where a molten material is poured into a mold so that it
solidifies in the desired shape. There are a couple of important elements that
you need. A foam or plastic replica of
the intended finished design and a material that you can mold around it
that can hold its shape. The primary
design considerations for our heat sink
were how easy it would be to cast and
how much heat it could dissipate. We kept it as simple as possible in Solid
Works with the two pieces coming off the heat sink being to allow for the metal
to be poured into one end and the gases to vent out of the other. And the mold
had to be orientated in such a way that the bottom would be the most likely
surface to have a smooth, flat finish.
Although the fins ended up thicker than we'd have liked, when it comes to heat
sinks, size matters, and we calculated a
theoretical heat dissipation of over 200
watts. So then we went ahead and printed
our design using PLA plastic at 103%
size to account for the shrinkage of the aluminum during cooling. We chose PLA
because it's made from corn, so when it burns, it shouldn't poison us.
To improve our odds of success, we needed castingrade aluminum. But buying
that stuff new is pretty expensive.
Fortunately, there's a large source of casting grade aluminum, the scrapyard.
So, we headed there and picked out our victim, extracting the engine out of
this 2002 Toyota Yurus. Back in the
shop, we took apart the engine, cleaned off the dirt, and chopped it into pieces
small enough to melt. We used foam then
to extend our pouring and venting holes.
Then we mixed up clay, sand, and water
until it reached a consistency where it was pliable but able to hold its shape.
This mixture called green sand was packed around the 3D print and then
baked for a couple of minutes to partially melt the plastic and to harden
the clay. This whole process is called
lost PLA casting. We then placed the
aluminum scraps that we had into a graphite crucible, which is basically a
a large cup that can withstand really high temperatures, and set about melting
the metal in a crude furnace that we made out of fire bricks. One of the best
and worst things about aluminum is that when it's exposed to air, it almost
immediately forms an aluminum oxide layer on the surface. This is good for
preventing further corrosion, but it
makes it very annoying for melting. So,
it's important when casting then to remove the aluminum oxide layer that
floats to the top called dross so that it doesn't contaminate the finished
cast. With the dross removed, we were ready for our first pouring attempt.
Though it should be noted we weren't sure how much of the PLA had actually
melted on this one. Turns out
not much. Clearly the aluminum barely
made it into the mold and wasn't able to
melt much of the plastic in the process. So to troubleshoot, then we made a
different riser design out of foam so that the aluminum would be able to enter
across the entire top of the mold. Green
sand melt, purify, and pour again. And
we ended up once more with a face only a
mother could love. So, we moved on then from lost PLA
casting to lost foam casting, which is an extremely popular and much easier way
of creating molds. Due to the low melting point of foam, when the aluminum
is poured in, it immediately melts it away and fills the space. In theory, our
foam mold wasn't perfect by any means, but we were cautiously optimistic that
it would work. So fire melt and pour
again and we get to see what kind of a
result we were going to get.
Unfortunately, this wasn't a massive success either.
Although the foam did melt away and we
were able to create a good base layer
and even where the mounting plate would be was fairly well done, we simply
didn't have enough static pressure to force the molten metal up into the fin
shapes. We could solve this by creating
a much taller riser. But by this point,
the time crunch had become real, and our engineering department realized that he
needed to produce something usable or I
might melt him down. So, he made a clay
and fire brick sandwich and assembled a mold using a method that bears more
using a method that bears more resemblance to grade one art class than
to precision crafting.
To ensure on this the final attempt that
the metal would thoroughly melt, the furnace was remade and heated until the
entire crucible was red hot. Upon
pouring the aluminum into the mold, it started bubbling from the steam escaping
from the clay, making the metal of the finished product more porous, a problem
we hadn't had before when we were using green sand. So then with a bit of
massaging from the reciprocating saw to make it fit on a motherboard,
it was finally ready to mount.
The processor chosen was an Intel Q6600,
mainly because the old ASUS motherboard it was on was the only one where the
heat sink didn't interfere with the VRM.
And to help fill in the air pockets on the bottom of the heat sink, we added a
more than generous dollop of thermal paste. Topping off the creation with a
handful of zip ties.
And this was actually the first time I
laid eyes on what three of my staff had
been doing all week.
I don't know how anything could have been worse than what I was expecting,
but this may have achieved it.
I mean, the name of the series is
sketchy heat sinks, and um
I guess mission accomplished there. With
all of that said, testing an IDA 64
turned out better than expected. And sketchy heat sink number two was able to
keep the CPU reasonably cool for a fairly long time. Although this is
likely more to do with its large thermal mass than its ability to dissipate heat.
Ambitious but rubbish. 10 out of 10 IGN.
So yeah, in the end this turned out to be the no man's sky of heat sinks. Sure,
we had high goals set and we believed with the resources we had, we could pull
it off. But it took three times longer than originally planned and the end
result performs poorly, looks bad, and has almost none of the features that we
said it would have in the beginning.
So then, all that's left to say is thanks in advance to the metalworking
experts who by now have filled the comments with advice. We will bear it in
mind for the next installment then of sketchy heat sinks.
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