Three-dimension dithering and its effect on the interfacial strength of multi-material and emulated multi-material additive manufacturing processes

Multi-Material Additive Manufacturing (MMAM) offers the potential for superior functional parts by varying properties throughout a structure. Previous work has shown that the interface region of such MMAM parts has great importance on their overall strength. Most of these studies have focused on rigid–compliant interfaces within parts manufactured via material jetting (MJT). This work focuses, initially, on the creation of different interfacial geometries within functionally graded tensile bars by extending two dimensional dithering algorithms from the realm of image processing into the third dimension. It tests these dithered patterns, along with Schwarz P and Gyroid structures, across rigid–complaint MJT interfaces before further exploring the previously unaddressed question of how these different geometries affect interfacial strength across rigid–rigid interfaces for both UV cured materials, via MJT, and thermoplastic materials, via a new prototype electophotographic toner-based AM system. Within the MJT parts, the samples often failed inside the large regions of the more compliant material rather than at the interface itself. In addition, the interfacial length is shown to have more effect on the mechanical properties compared to interface pattern. However, the thermoplastic samples consistently failed within the interface region. The toughness of these thermoplastic parts increased with an increase in the connected surface area in the tensile direction between the largest regions of each of the two materials, with three dimensional random dithering over a 20 mm gradient length exhibiting the toughest interface overall (40.8% increase in the work at break when compared to a control sample with no special interfacial geometry). This work, therefore, provides a new emphasis to explore, within the context of the design of thermoplastic multi-material interfaces, geometries that increase this connected surface area.