Cutting through 1" A356 Aluminum foam

I have an idea for a project that requires cutting a rectangle out of A356 Aluminum foam. Its not really foam, more like aluminum casting with a bunch of air pockets in it that are pretty large. I have read most of the information on milling aluminum and it all seems to be focused on 6061 but nothing talks about A356. I also have found very little information about its hardness, McMaster-Carr does not have a rating for it. Probably due to it having a foam like structure. Any suggestions on how to proceed? I don’t mind experimenting but welding bit after bit gets old and the aluminum foam is not cheap. Thanks.

Todd

You might try matweb.com. I’ve worked with aluminum for years, but have zero experience with A356 so I can’t comment on that specifically, but matweb is my go to. You can sign up for a free membership and use their database, compare materials, etc…

Dan

First off, you should be able to salvage the endmills — soaking them in lye (available as drain cleaner — just get a brand which doesn’t already have aluminum in it) or muriatic acid should dissolve the aluminum w/o damaging carbide or HSS — YMMV on coatings, check the chemistry (submerge fully, use outdoors and downwind of anything metallic), rinse in baking soda solution afterwards to neutralize the acid.

A356 is listed as containing: 7% Si, 0.3% Mg with 0.2 Fe (max) and 0.10 Zn (max) — 5000 series w/ magnesium is listed as “machinability poor” on the wiki: https://www.shapeoko.com/wiki/index.php/Materials#Aluminium and we don’t have anything on 4000 series w/ silicon

This site: http://www.espimetals.com/index.php/technical-data/24-aluminum-machining suggests

The use of tools tipped with TiN or TiCN by PVD deposition only is highly advisable for machining alloys that contain no more than 7% silicon. (Angle of 15 o for diamond coated carbide (CVD Diamond) tools and polycrystalline diamond (PCD) tools.) Provided tooling is designed for aluminum alloys, tool life is much longer than for machining steels, all other factors being equal.

Worryingly a search on machining aluminum foam mostly reveals efforts to avoid needing to do so (additive manufacturing, using lasers).

Hopefully the above will help! Please let us know how it works out and we’ll add it to the wiki.

I’ll let you know what I find out when the Al. foam arrives and I get to milling it. This should be interesting if nothing else.

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Are you using the proper coated end mills? NOTHING sticks to them if you are doing it correctly.

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I am in the design process for a few items in the same material-though only half as thick… already have it, hunting down the same parameters-and getting the machine completely ready to go!
Seems like you can cut it with a spoon- but I do want a bit more precision!

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anyone want to explain why they’re machining aluminum foam?

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That’s pretty simple…

  1. The lack of the ability to precisely form this material in an additive method…
  2. The lack of the ability to precisely form it by another another more convenient subtractive method.

Essentially the same reasons anyone machines anything…To precisely change its shape or finish…

I want to make:

  1. A set of backlit vents than look organic in material, and man made in shape
  2. The best backlit heatsink I could come up with that does not look like a heatsink.

CNC machining will give me the precise fit I want that carving it with a spoon might not…I didn’t want to grind it…ever seen an aluminum dust fire?

I tried mixing aluminum powder with pourable/castable resins and bubbling air through them…fun, but no joy!

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Pulling out my industrial design hat here… Not that you asked for my input, but thought it might be helpful ask what the intent was before advising on processing, because how to do something with a given material will turn out to not matter if it isn’t the right match for the job.

If you’re trying to make a heatsink, you probably want to consider an alternative material as A356 is less thermally conductive because of the pockets than bulk aluminum would be. See Matweb notes:

http://www.matweb.com/search/datasheet.aspx?matguid=488c7071140a48ffb11a5cdb75cdaba9&ckck=1

Most resins are also not going to be as thermally conductive as you’d like, short of 2-part epoxy resins specifically designed for that like:

http://www.arcticsilver.com/arctic_silver_thermal_adhesive.htm

And these are still not nearly as conductive as the metals they’re usually used to bond, and anything you mix into such a system is likely to decrease thermal or mechanical performance, or both. They’re already pretty tightly tuned as it is.

Speaking of thermal conductivity, it’d be worthwhile to look at the range of values present in many common materials:

If you’re looking for what to make a vent out of, then it’s less about conduction and more about airflow, and you can use whatever material makes sense for that (A356 foam, whatever) and it’s more about your design—as long as it doesn’t impede flow and prevent your fans—or convection currents, in the case of passive cooling—from doing their job. Having handled aluminum foams before, the thought I can’t get around is how do you plan to deal with the dust that will accumulate in it? At least for the stuff I’ve seen and handled, it’s got all kinds of sharp little inclusions that’ll be a pain to vacuum out.

If you’re looking for what to do for a unique heat-sink or radiator, you’re likely going to want to stick to materials appropriate to the job and then consider treatments to apply to them to improve appearance that don’t interfere with the function. You could use bulk aluminum and do interesting engraved surface finishes on a heat-sink, and if you’re looking for an organic material appearance, you could do all kinds of texturing that wouldn’t impede heat conduction or radiation. If you use copper, then you can patina it without impacting it too much either.

I presume this is for a PC or equipment enclosure of some kind, so I presume you’re looking for backlight through a radiator’s vanes rather than just a bulk-material heat-sink, so I would suggest you could cut your radiator vanes into interesting biology-inspired shapes similar to what Nervous systems does: http://n-e-r-v-o-u-s.com/index.php

As for what materials could make a literal heat-sink, then you’re interested in the specific heat of a material by volume or by mass: https://en.wikipedia.org/wiki/Heat_capacity where you’ll see why water-based cooling makes sense for this kind of thing, as it can carry away a lot of heat per unit of volume pumped through an exchanger sitting over a chip.

If you’re looking for organic design, perhaps a water-cooled system would open up options as you could put any kind of outer sleeving on your tubing and machine or surface-treat the exchange blocks to your liking.

Hopefully that’s some helpful feedback, curious to see what you come up with!

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I REALLY appreciate the information and time you put into that! Your information might well change the project-but it absolutley will be used in the next project! Thank You.

My ideas were…

The vent was the first idea-it was the one I tried the metallic resin on-(then found the aluminum foam)only a vent, not a heatsink…just to let pre-filtered ambient air flow through something cool(neat not cold) looking! This one may well stay the same… Anodized dark in its recesses, but bright on the machined edge-featuring a backlit logo!

On the heat sink, My idea was to fit the foam into the fins of any existing heatsink such that the fins were not visible-more of a metallic foam grill that looked like a speaker grille, but felt completely different and much more interesting! I considered it a bonus that the foam could not actually insulate the heat-and was considering using heat sink compound to augment that possibility! The heat sink was to match the vent, allowing me to use the same design elements both inside and outside the project.

I like to give the interior and exterior of a larger project direct and related continuity when is it possible…even if the shared element is not as functional in one environment as the other.

I do have the foam where it can be touched on purpose, but not where it can be accidentally encountered-I want it to be an interesting interaction, not a potentially painful one…
Thank You again for the additional information!
William Stokes

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Glad to help—looking forward to the pics of what you build! :slight_smile:

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