In the present state of the art, the function integration into lightweight metal structures is generally based upon adhesive bonding of sensors or actuators to the surface. A new technology enables a direct structural integration of lead-zirconatetitanate (PZT) fibers into local microstructures of metal sheets and subsequent joining by forming. This provides a complete functional integration of the piezoelectric ceramic in the metal for sensors and actuators purposes. In a further process step, the composite is shaped by deep drawing with a cup with double curvature radii of 100 mm into a complex 3D surface. During the shaping process it is expected that the PZT- fibers get damaged with the result of degradation of the piezoelectric function. This paper describes the application of various surface processing methods to improve the shaping behavior of the piezoceramic fibers.
The production of interconnected parallel fibers is based on piezoceramic plates. The plates are treated by different surface processing. One experimental series is lapped and another series is extra polished by chemical mechanical polishing (CMP). The resulting plates were examined with regard to the fracture strength and the degradation of the piezoelectric properties during manufacturing and operation. It has been shown that the lapped and polished plates have a clearly better persistence with regard to the shaping processes compared to the unprocessed plates. The best results in this process were achieved by the polished plates, which is also transferable to the fibers. Furthermore, the piezoelectric characteristics were better preserved by the lapped and polished plates and fibers.
Current technologies for smart sheet metal part production base upon adhesive bonding of piezo-patches to the surface. A novel concept and process chain is the assembly of piezoceramic micro parts into local microstructures of metal sheets and subsequent joining by forming. This results in a full functional integration of the piezoceramic in the metal for sensor and actuator purposes. Mechanical coupling is non-positive without elastic interlayers and the electrical coupling is characterized by the metal being the ground electrode of the sensor. The paper describes the design, methods and tolerance management to overcome the challenges for reliable parallel microassembly and joining of prefabricated batches of 10 piezoceramic fibers with dimensions of 0.267 × 0.250 × 10 mm3 and nominal assembly clearances of ±0.018 mm. The prefabrication of the batches is achieved by stacking and dicing of piezoceramic plates. Both the principles of precision machining and elastic averaging are applied for reliable production and joining of the batches. In experiments, equally spaced piezoceramic fibers within the batches were achieved. Prototypes were assembled and joined by forming achieving functional piezo-metal composites. With the given tolerances of the parts and the microstructure a statistical tolerance analysis has been performed in order to determine the maximum allowable position uncertainty of the microassembly system. An assembly yield of > 95% is expected for future scaled up high volume assembly of piezo-metal composites.