In-Process Monitoring of Joining Operations for Piezoceramic Elements

Abstract

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 are an important issue for the sensor and actuator capability of the later smart material. Post-process inspection methods to characterize the mechanical interconnection of the joining partners and the performance of the transducer after the joining operation are state of the art. 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 utilized as material inherent sensor during joining by forming experiments. Test samples are characterized by impedance spectroscopy during the joining operation. Based on the experimental results, a novel in-process-monitoring method utilizing the piezoceramic joining partners as inherent sensor is outlined. It is shown, that with this method a sufficient preload can be adjust on the basis of the intensity of the resonance peak without an overload. Furthermore, error effects to the transducer can be detected at an early stage.

Sensor-integrated structures in mechanical engineering: challenges and opportunities for mechanical joining processes

“…After the pressing force is removed, spring back of the elastic deformation of the structure occurs, and a certain amount of force-fit joint remains to preload the piezoelectric elements [25]. To ensure the setting of sufficient preload and to detect faulty joining, an approach for in-process monitoring of the preload based on the intensity of the resonance peak without overload is presented by Müller et al [26].…”

In-process calibration of smart structures produced by incremental forming

“…Since joining by forming allows for target-oriented prestress conditions, the transducer to be integrated can also be used to monitor and even control the joining process. Müller et al developed an in-process monitoring method for the preload evaluation and for fault detection during the integration of piezo modules into micro-structured aluminum sheets [14]. In order to obtain defined preload and therefore reproducible sensory properties of the sensory structures produced by incremental forming processes, Krech et al use the signal of the force transducer that is to be integrated to control its preload during the integration process [15].…”