Welding a tin can is not possible, but brazing it together will work. A tin can is either made from aluminum or steel with a tin coating (plating) on the outside. The metal is very thin and does not withstand the heat from welding. Brace tin cans together using a soldering iron and solder. This process is easily done at home. Clean the cans thoroughly before starting the soldering process. Clamp the cans into the desired position and solder the seam.
Things You'll Need
Plug in the soldering iron and let heat.
Clamp the tin cans together in the desired positions.
Touch the tip of the soldering iron 1/4-inch from the top seam. Let the soldering tip sit in the area for 10 seconds, and touch the end of the soft solder to the seam. The solder will melt when the tin is at a sufficient temperature. Repeat the process until the solder melts.
Move the tip down 1/2 inch and touch the tip to the metal seam. Touch the tip of the solder to the seam. Heat until the solder melts. Continue down the seam until the entire seam is sealed with solder.