There are two popular types of industrial welding robots capable of robotic welding.  They are articulating robots and rectilinear robots.  Robotics control the movement of a rotating robotic arm in space.  Rectilinear robots move in line with any of three axes (X, Y, Z).  In addition to linear movement of the robot along axes there is a wrist attached to the robotic welding arm to allow rotational movement.  This creates a square cube working environment that the robotic arm can weld in.

Articulating robots use robotic arms and rotating joints to accomplish welding metal work.  These robots move like a human arm with a rotating wrist joint on the robotic welding arm.  This creates an more random shaped area for the robot welding arm to work within.