In-process monitoring of joining operations for piezoceramic elements

The direct integration of piezo elements into micro structured aluminum sheets is a new approach for adaptronics and lightweight constructions. With the integration of the active piezoceramic elements the aluminum sheets gain sensor and actuator functionalities. The mechanical interconnections and the preload of the piezoceramic elements is an important issue for the sensor and actuator capability of the later smart material. State of the art are post-process inspection methods to characterize the mechanical interconnection of the joining partners and the performance of the transducer after the joining operation. Scope of the paper is the development of a novel in-process monitoring method that utilizes the piezoceramic transducer as inherent sensor for failure mode detection and preload evaluation during the joining by forming operation. Within this study, results of forming experiments with array batches of interconnected piezoceramic elements are presented. The piezoceramic batches are electrically contacted inside the joining tool and are utilized as material inherent sensor during joining by forming experiments. Test samples are characterized by impedance spectroscopy during the joining operation. Furthermore, cracks or defects are detected by optical microscopy inspection. Based on the experimental results, a novel in-process-monitoring method utilizing the piezoceramic joining partners as inherent sensor is outlined.