Development of a condition monitoring and diagnostic system for robotic resistance spot welding.

摘要

Robotic spot welding is becoming increasingly important for the automotive industry due to the fact that there are between 3,000 and 5,000 spot welds in a typical car. Consequently, the integrity of spot welds plays a critical role in the reliability of cars. The problem with this kind of manufacturing process is that electrode Tip Wear and the contact area becomes larger as the number of welds increase, for any given tip, resulting in lower current density and increased risk of cold welds. The goals of this project are: (1) to ensure good quality weld (zero default); (2) to minimize power usage; (3) to maximize tip life. These goals are expected to be achieved by completing the following three objectives in this research.; The first objective is to develop an analysis and diagnostic tool for weld quality. Currently, a data acquisition system containing 37 welding parameters has been employed to precisely evaluate the weld quality at our industrial partner, Van-Rob. The welding indicators directly related to the weld quality are obtained after performing parameter trend analysis and correlation analysis. The second objective is to optimize the step setting by simulation to guarantee that enough heat will be generated. This optimum step setting is expected to compensate and match the actual wear and contact area change without too much current (resulting in weld explosion) or too little current (resulting in under-size or cold welds). It can also decrease power usage and increase the tip life. The third objective is to design a preventative maintenance policy based on minimum cost for tip replacement in such a high productivity line. The simulation results of tip opportunistic replacement policy show great potential of cost savings.