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[smeeprocket]

wait you have a 3d printer and you are not spending all your time playing with that?

[GiglameshDespair]

...Are you sure 3d printed plastic wouldn't melt? Aluminium melts ~675 degrees C.

From a quick google, the melting point of 3d printer plastics is below 300'C easy. So it probably shouldn't part of the mold if it's anywhere near the actual molten metal.

Simply make a mold with wood and sand. There's plenty of instrucables etc available.

[Bohandas]

They could make a cast of the printout and use that as the mold

[smeeprocket]

I'm still perplexed as to why he isn't spending his time downloading stuff for that printer and making action figures and race cars and guns

[GiglameshDespair]

Clearly he needs to 3d print the sword and save time._{Effectiveness not guaranteed.}

[tonnot98]

I don't own one, a teacher at my school does and lets students use it if they have a good/fun reason to.

[wierd]

There is a reason why aluminium does not exist in appreciable quantities as a free metal in nature. (it DOES exist, but is quite rare.)

In order to smelt aluminium, you will *NEED* an inert gas smelting chamber. An additive powder+laser sintering printer will likewise require a hermetically sealed build chamber containing inert gas. (I suppose a DIY solution can be done using a Co2 laser module attached to a gantry, installed inside a suitably large glass aquarium filled with sulfur hexafluoride, or otherwise rigged to be air-tight, and filled with argon, or some similarly inert gas.  Sulfur hexafluoride has the unique property of being very much heavier than normal air, so you could fill the build chamber aquarium up by just pouring the gas inside and then turning on the printer.

This is because aluminium reacts strongly with oxygen in the air at temperatures that permit melting. Much of your aluminium cans will get turned into scummy aluminium oxide if you do not use inert gas. Some formulations of aluminium alloys can attain "Mild-steel" levels of strength and hardness, but are mostly exotic formulations with transition metals you are unlikely to get your hands on. (Like vanadium, and metallic chromium) There are a few older "aircraft aluminium" alloys, like 2025 (Aluminium and copper) and 7075 (aluminium and zinc), that could possibly be created with a home smelter. Be aware that the "Mild steel like qualities" of these formulation ONLY happens after work and heat hardening of these alloys!  At Cond-0, these are very soft.

Lead is not advisable. It makes poor quality anythings, except bullets.

[Arx]

The typical thing with casting aluminium is a sand mould. You can use ordinary beach sand, I believe, although you have to mix in oil if you want to make very fine details. I doubt you'll need anything more complex for a sword, but you could also look into the lost wax method.

Before selling any sharp weapon, consider who you're selling it to, why they want it, and whether you want to help someone hurt others. It might not be the person you sell it to, but it can happen. Plus, there's almost no reason a blunt sword is less awesome than a sharp sword, other than that it's easier to kill with. This is actually part of why I stopped trying to get into metalwork, actually.

If you want to forge iron instead, I think it's actually similar temperatures, just different techniques and structures. Be wary of scrapyard steel, as it's a nightmare to figure out the quality. A piece of railway track makes a good anvil, or a tree stump even, and hammers aren't bank-breakers by any means. Sword-smithing is ninety percent grinding and polishing, so bear that in mind.

Hope this helps, and sorry for moralising at you.

[wierd]

Since he intends to do smelting, I would suggest that he consider aluminium bronze, and make decorative pieces.

http://en.wikipedia.org/wiki/Aluminium_bronze

It has a very nice looking color, is reasonably hard, and mills/machines/casts well. It is possible he could obtain scrap copper to go along with his scrap aluminium.

Spoiler: For reference, this is what aluminium bronze looks like (click to show/hide)

I somehow doubt that people are going to brandish a reproduction gladius the same way they would brandish a shiny silver looking weapon.

[chaoticag]

Please please please don't work with aluminum unless you plan on hammering it into shape cold. I understand that it's an easier to access metal compared to iron or steel, but at this point, we're not just comparing the forging costs, but the healthcare costs. Plus, even if you can do it safely, it's going to tech you bad habits. Iron and aluminium have vastly different properties from the sounds of things.

If you really want to try casting something, you'd be better off with tin and copper into bronze, or just smelting copper. I think anyway.

[NAV]

I built an awesome aluminum mace once. Aluminum will never make as good a weapon as iron, but it can certainly make an effective mace, if you make it twice the usual size then add flanges or knobs.

[tonnot98]

Isn't copper pretty expensive, though? I've heard that in burglaries, some people steal copper piping because of the value of copper.

[wierd]

So is aluminium.  Aluminium recycling accounts for a good portion of the aluminium used in modern manufacture, since it is very (very) energy intensive to refine aluminium from ore. (many thousands of degrees to melt the chryolite, many hundreds of amperes of electricty delivered at several thousand volts through the dissolved solution, then you have the costs of disposal of the industrial effluent of spent electrolyte, etc.)

Copper is better known, and has a less common ore than aluminium, and is used all over as a conductor where aluminium is less so (it work hardens faster than copper, and thus is prone to breaking when drawn into wire), which is why more people hunt for it for black market recycling. (I call it black market, because stealing it from houses and hotels is illegal, and dealing in stolen goods is a black market) 

Industrially, the recycling of spent aluminium chips in metal fabrication is a very significant recovery stream. Good quality, unalloyed aluminium is quite valuable per pound.

[Itnetlolor]

I have an idea: Combine the efforts.

Make an aluminum shell, and a somewhat thick one, if possible. Fill it with lead, and make yourself a mace or hammer with combined efforts. The durability from the aluminum shell, and the density of the lead. Like a large caliber round with a handle.

In theory, it might be handy; but I'm not as well-versed in this as everyone else; but it's a thought.

EDIT:
Wait a tic, memory just kicked in. That combo would make for a really bad result. Lead would soften the aluminum shell, rendering it as durable as wet paper. It would work better as a trap to use on some unsuspecting fool that is more clueless than I just was a moment ago.

EDIT EDIT:
Or was that mercury and aluminum?

EDIT EDIT EDIT:
Did a search, it was mercury and gallium that resulted in really weak aluminum. Example

[DJ]

If the goal is to forge a sword, why bother casting? You need to hammer it anyway to give it structural integrity. And getting metal hot enough to work is easier than getting it hot enough to cast. Finding steel that gets malleable with charcoal fire should be doable. If rebar is like this (no clue if it is), a thick piece of it would be perfect for hammering out a sword.