Building Industry
If you need more industry at a particular world, you can build more, but this is fairly expensive. It costs 5 metal to build each new unit of industry (unless you are an Emperor, in which case it only costs 4 metal).
Note that this means you must already have at least 5 industry (or 4 industry, if you're an Emperor) at a world before you can build more industry. If you don't have this much industry to start with, the only way to make more industry at a world is by scrapping I-Ships.