Simulation of robot paths and heat effects in welding

The objective of this thesis is to develop a simulation tool and a method by which robot trajectories, temperature histories, residual stresses and distortion can be analysed and optimized off-line. This was performed by integrating robot simulation software with finite element analysis software. A special interface was created which facilitated information exchange between the two software programs. To validate the method comparisons were made between simulation results and measurements during real welding.

The method was used to program welding trajectories, both for planar plates and for parts with complex shapes. The welding trajectories were downloaded to the finite element analysis software where temperature and residual stress prediction were performed. Good agreement was found between the programmed robot trajectory, and the actual trajectory, necessitating only minor adjustments. Temperature measurements were performed using both thermocouples and infrared imaging. Good agreement was also found between the results using these two methods, as well as between predicted and measured temperatures.

Predicted residual stress distributions were compared with neutron diffraction measurements and fair agreement was found. A specified software architecture was developed which allowed full time synchronization between different simulation systems. Finally, weld velocity optimization was performed through a developed algorithm making it possible to minimize distortion.

The research conducted in the present work indicates that the models and computer programs that were developed could be combined to create powerful tools for the evaluation and optimisation of welding processes.