Tecnologia delle strutture cellulari

Porosity in dense engineering materials is often undesirable for load-bearing applications. However, porosity is highly beneficial for weight and cost reduction, damping, thermal insulation and specific strength. Moreover, porous materials are extensively used in several industrial applications: automotive, aeronautics, and naval. In the last years, the attention has been focused on new materials because of the combination of high performances and low weight. Cellular materials were initially produced by means of organic compounds: recently, technologies for the processing of metallic cellular materials have been introduced as well. In the present work, a new foaming process is described for thermosetting resins. Uncured resin tablets are fabricated by pressing commercial powders in a steel mould at room temperature, and used as foam precursors. The tablets foam when heated in a muffle at high temperature. No blowing agent is added as the foaming mechanism depends on the uncured resin boiling point. The foaming temperature is set to be high enough to rapidly produce the resin boiling but not excessive to avoid the thermal degradation. During boiling, the resin polymerizes and the bubbles froze in the final structure. By means of this technology, composite and nano-composite foams may be produced as well. In fact, before compaction, the resin powder may be easily mixed with several fillers such as ceramic or metallic micro and nano-particles. As regards the aluminium foams, a new foaming technology was also proposed to produce open-cell aluminium foams by “replication”. Particularly, the process consisted of four main steps: the preparation of a pre-form of sodium chloride (NaCl); the infiltration of the pre-form with molten aluminium; the metal solidification; the water dissolution of the salt. Coarse NaCl grains were used to produce the pre-forms and the mechanical properties of the solidified foams were evaluated. In conclusion, a different method to shape commercial metallic foam panels was proposed by using a diode laser. Open- and closed-cell panels were laser bent and the effect of the main process parameters (laser power and scan velocity) on the bending efficiency was investigated. As a result, a very good formability was observed for the laser processed panels.