I came across a large quantity of pure lead bricks that are painted and a bit dirty so I melted some down to clean the metal up.  Discovered the 99cent Walmart muffin tins had some sort of coating on them that would bubble under the lead and make the lead look like doodoo.  So I made an aluminum mold.  It's tube cut in half and welded to angle, everything is 1/4 inch thick.  I have a squatewave 200  wasn't sure if I would be able to weld it but it did fine after I preheated with a propane torch until the condensation evaporated.  

The mold is heavy enough that the aluminum solidifies instantly and I can dump it out immediately.   I'm going to add a handle of some sort.  The half-round blocks are about 3.5lb.  

I'm surprised I was able to weld such heavy material.

I know you likely used what materials you had, and that's good!

That being said, replace the piece of tube with c-channel and the bricks are a nice stackable shape. That's what I use for molds. 3" c-channel about 6 inches long yields 5 lb lead bricks.

I tried to make a rectangular mold by cutting 4 corners from a sheet and folding the sides up, but without a brake the 1/8 sheet didn’t bend nicely.  I’m going to Try that again in the machine shop at work with a brake - the bricks will stack nice and be the perfect size to fit into my lead pot.

If you've got 1/8 sheet just cut 5 peices and weld. You can build in some trapezoid taper so things pop right out.

I use a bread loaf pan for big bricks, had the same coating issue until I threw it into the woodstove and burnt it clean.

The best advice I’ve received as far as aluminum welding is hot and fast.  Max out your machine and dial back on the pedal if necessary.