How about Zombiebots?
The idea was taken from this Cortex Command mod http://forums.datarealms.com/viewtopic.php?f=61&t=17686
Basically, they tear apart anything made of metal to make new Zombots. They have drones that salvage, grunts that fight and lots of others. They salvage bits of spacecraft and use them as boarding/landing pods. They never mount weapons on their spaceships because they don't want to vaporize precious metal. Their spaceships only contain the bare minimums, because most of the metal has been used on new zombots. While they do have ranged weapons, they prefer claws to tear of armour and use it to repair themselves. Individually they are pretty stupid, but they are linked up
sublight communications, forming a hive mind. (Maybe they can join together to form a giant walking battletank?)
EDIT: Expansion time! While all the zombiebots are equipped with basic tools to repair themselves, they have a special Furnacebot (pic yet to be drawn) that collects materials from the battlefield and forges them into new bots. There is also a jetbot, which is used for aerial and astral combat. Armed with thermal cutting tools, they hijack planes and space fighters, kill the crew, and pilot them back to a base or spaceship for salvaging.
If the situation demands it (i.e. They found a city-world or something) they will build large engines of war, piloted normally by a crew of grunts and forges.
Beware, that piece of space junk is actually killer, self-repairing, self-replicating robots with giant claws!