Additive Manufacturing of Metal-Polymer Hybrid Parts: Relevant Aspects and Potential Techniques – A Review

The combination of lightweight metals and polymers on hybrid structures is an important strategy deployed by the aircraft industry to further decrease the total weight of airplanes. One of the current fields of interest concerning such a combination of materials is their joining, which nowadays is performed normally by either mechanical fastening or adhesive bonding. Although effective, both techniques introduce further processing steps that could be trimmed out by directly assembling the polymeric part over/around the metallic one by additive manufacturing (AM). Moreover, the geometry flexibility introduced by AM processes allows the user to design topologically-optimized structures, which yield even further weight reductions and are not easily attained by more traditional processing routes. Therefore, AM can improve the buy-to-fly ratio –the weight ratio between the required amount of raw material and the final component weight – potentially reducing manufacturing costs. Coupling different AM processes, however, introduces issues that must be overcome in order to achieve a satisfactory mechanical integrity. Those issues are either mostly material-dependent (e.g. galvanic corrosion) or process-dependent (e.g. lack of appropriate roughness on the metallic substrate capable of promoting mechanical interlocking with the printed polymeric material); other possible issues may also have both material and process components, such as lack of polymer adsorption to the metallic substrate and process temperature-related microstructural changes. This work is therefore aimed at reviewing the most common AM processes for metals and polymers, with special focus on associating their main features with challenges pertaining to coupling those different material classes.