Rust in the Factory-I

Inside a pitched battle rages. Monsters vs machine. Who will win?

An old factory in the quarter. The brick walls are coated in fine layers of rust and the sounds of battle can be heard from inside.
Inside the Factory a group of machines seem to be in a pitched battle with several monsters. The monsters, while slow, have the upper hand and are slowly eating their way through the metal group.
NEEDS MAP

Depending on the size of the party this should be a Hard battle fighting Rust Monsters. Xp Threshold by Character Level

Rust Monster

Modrons
The Rust monsters are only interested in eating metal. They will ignore anyone who does not have metal equipped and attack the closest creature that does.
The Modrons will assist the PC's if the PC's are not hostile towards them. There should be a Medium Xp amount of Modrons, including at least one Pentadrone.