Empty aluminium beer and soda cans can be melted down into ingots. These compact ingots, also called pigs, can be recycled or remelted later for more advanced metalworking projects. The heat source used will be an ordinary propane torch. A steel cup or open-topped heavy steel canister wider than a crushed soda can will serve as a crucible.
Crush the cans as small as you can. You want your raw materials to be as compact as possible so you don't just burn the aluminium. Condensing them allows them to melt more easily. A can crusher works great for this, or you can simply place them on the ground standing up and carefully stomp straight down on them.
Press your steel cup bottom-down into the sand-filled bowl. This serves two purposes. The sand stabilises the crucible so it won't tip over easily, and it also insulates whatever work surface you're using. Your work should be on the ground and definitely outside. Besides being extremely flammable, melting aluminium can give off unpleasant fumes as its impurities burn.
Put one or two crushed cans in the crucible and play the torch over them until they melt. Aluminium melts at 1,200F/660C, and the torch produces a flame more than twice that temperature. As the initial cans melt, add more cans. The later ones will melt even more quickly because molten aluminium transmits the torch's heat much better than air.
The residue from the cans' coating and paint will float on the surface of the molten metal. This is called dross, and you can skim this off with a steel ladle, letting it cool somewhere safely before throwing it out.
At this point, the crucible needs to be picked up to pour it out. Do not touch it with unprotected hands. Use the pliers to pick it up by clamping securely onto either the handle, if present, or onto the lip of the crucible's sides.
Quickly but carefully pour the molten aluminium in roughly equal amounts into the wells of the muffin tin. After cooling, the completed ingots should slide right out of the wells.
Be extremely careful: Molten aluminium is very dangerous. Never allow your hands or any unskilled people near the molten metal, and always be aware of the environment you're working in.