Fundamental studies for development of real-time model-based feedback control with model adaptation for small scale resistance spot welding.

摘要

Small scale resistance spot welding (SSRSW) is extensively used in electronic and biomedical devices manufacturing. The process has its own features that are quite different from normal scale RSW process. These features bring difficulties in the reliable monitoring and control of the process. A real-time model-based feedback control with model adaptation has been proposed for the quality assurance of the process. Several aspects of the model were studies.; Monitoring is the first step for a successful control. An optical sensor was used for workpiece thickness and electrode displacement measurement. A load cell was placed at the bottom of lower electrode seat to record the clamping and change of clamping force in welding. The welding current and voltage were also measured. From these signatures it is an easy task to monitor the occurrence of expulsion in the process. The weld nugget size can also be related to electrode displacement. Specifically, through observing the electrode separation using a high-speed video camera, it is confirmed that the nugget size is more closely related to high-speed part of the electrode displacement curve. The way the optical sensor was implemented introduced measurement noise. However, the true displacement can be recovered by identification of the sensor holder system model followed by feeding of measured displacement to this model. This way a reliable displacement measurement was obtained that is suitable for the utilization of a real-time control.; The interaction between the primary process and the welding machine affects welding quality. Future real-time control must consider this interaction, because this interaction also influences the measured value of the process variables. A more flexible machine will allow the electrodes to separate more under the pushing force of heated materials than a more rigid welding machine. Due to the interaction between different part of welding machine and the primary process, some measurable process variables might not be independent to each other.; Analytical heat transfer model for the process was constructed using a one- and two-dimensional formulation. Temperature field and history were obtained.; Finally, future scope is projected in the development of the proposed control for SSRSW process.