The welding arms are designed to activate whenever an object comes within a certain radius. Usually these things are placed along assembly lines. They don't have any incredible intelligence but are dangerous just the same.

Suggested Method of Attack - The welding arms can take quite a bit of damage and do quite a bit as well. Shields aren't going to help you out so just be sure to stay out of their range. TDs or Mortars are the fastest way to take them out, but a series of blaster shots will do in a pinch.