Development of robotic welding stations for pressure vessels: interactive digital manufacturing approaches

This paper examines the issues pertaining to the design and development of robotic welding stations for large intricate products, by example of a fabric dying machine, combining large sheet metal parts into a shell and smaller parts in the form of pipes, ducts and flanges. The main relevant issues concern: (a) layout of the workstation considering the size and shape constraints of parts and the working volume of the robot, (b) design of the work-holding jigs and fixtures including checks for strength and allowable deformation, (c) definition of the poses of the robot along the welding path to comply with good welding practice and avoid collisions within joint position and speed capabilities and (d) automatic off-line programming of the robot. These issues are solved by exploiting constraint-based digital models of parts and, kinematic simulation and finite element analysis in interactive mode, which is demonstrably most efficient in the presence of variable welding seam cross-section, complex seam 3D-geometry and constrained workspace. Furthermore, the challenge of substantial absolute deviation between actual and nominal shape of large sheet metal parts is dealt with by applying photogrammetry in order to superimpose the actual welding seam shape on the digital model. Appropriate data interfaces between digital models are used in order to automate the work flow up to the automatic generation of robot programs from the computed coordinates of the robot joints.