Joining by forming of piezoceramic macro-fiber arrays within micro-structured surfaces of aluminum sheets

Abstract

Functional integration of smart materials in sheet metal enables lightweight composite parts which are enhanced by new functionalities. Locally integrated piezoceramic/metal composites consist of a prefabricated array of ten parallel piezoceramic macro-fibers with dimensions of 0.277 mm by 0.232 mm by 10 mm which are joined in micro-formed cavities within the surface of an aluminum sheet metal. By the use of joining by forming, the interference–fit, preload and form–fit of macro-fiber arrays are achieved in a single process step. The paper describes investigations of the joining by forming process in formal planned experiments using the design of experiments method. The influence of the dimensions and preparation of the joining partners, the maximum forming force and the velocity of the forming stamp are varied. The interference–fit and preload depend on the maximum forming force. In contrast, the quality of the form–fit is primarily related to the geometric dimensions and the forming force. Fiber fractures and incipient cracks are the major failure mechanisms during joining by forming of the macro-fibers. The number of cracks is significantly reduced by the use of lower die velocities, lower maximum joining forces and the introduction of additional geometric elements in the microstructure of the metal surface. Concluding, constraints with regard to the design of parts and the process are derived from the experiments.