AFK Smithing Methods in OSRS

By far the most AFK smithing method is creating cannonballs, letting you AFK for 2 and a half minutes at a time.

The XP is minimal though, so it should only really be done as a money maker.

Smelting iron or gold bars at a furnace is another decent AFK method, letting you AFK for a minute and 10 seconds per invent.

You can also smith items that only require 1 bar at a time, like darts, bolts or knives, and these are usually profitable and let you AFK for over a minute as well.