Investigation of the bonding behavior between thermosets and thermoplastic elastomers in multi-material additive manufacturing

Multi-material additive manufacturing (AM) pushes the boundaries of modern processing by creating parts with synergetic material-related effects and superior properties. A promising technology is represented by the socalled fusion jetting (FJ) process which simultaneously combines thermosets and thermoplastics into multimaterial AM parts. However, the bonding behavior between thermoset-reinforced and non-reinforced regions proved to be a challenge within FJ processing which is investigated in the context of this study. Based on shear testing, significant impact factors and improving process strategies regarding interlaminar bonding are highlighted. A viable shear specimen design is derived for material combinations with strong dissimilarity of the individual material elasticities. For this investigation, acrylate-based photopolymers are combined with thermoplastic polyurethanes (TPU). Based on the shear testing results, a minimized layer height of 100 mu m is identified to achieve maximum mechanical bonding. Further, increased laser powers between 15 and 17 W positively impact the bonding strength between photopolymer-reinforced and non-reinforced regions due to the increase of the volumetric energy density and promotion of interlocking effects with embedded TPU particles. Additionally, an increase in bonding strength is achieved through specific tailoring of the laser power within selected layers. The results showed that decreased laser powers promote interlocking effects by infiltration of the photopolymer in already melted subjacent regions. All in all, this investigation not only contributes to the advancement of FJ processing but successfully sketches a transferable strategy for the characterization and improvement of interlaminar bonding in various AM technologies targeting hard/soft structures.