DESIGN OF A PENETRATING DEPOSITION NOZZLE FOR Z-PINNING ADDITIVE MANUFACTURING

Fused Filament Fabrication is an Additive Manufacturing method where a thermoplastic filament is deposited layer by layer to create a three-dimensional part. The printed structures often demonstrate a high degree of mechanical anisotropy, leading to a drop in material strength when comparing structures along the disposition path (X and Y-Axis) to the build direction (Z-Axis). To reduce the mechanical isotropy, a z-pinning process was developed which deposited continuous pins in the build direction. This process demonstrated significant gains in inter-layer strength and toughness, especially for fiber-reinforced materials. However, the deposition of pins also created flaws in the structures that increased in severity and frequency as the pins grew in length and diameter. To mitigate these flaws, a penetrating nozzle has been proposed, in which a fine-tipped extrusion nozzle extends into the pin cavity and simultaneously extrudes z-pins as it retracts. By extending the extruder nozzle to a length that would permit it to penetrate the pin cavity heat loss through the nozzle, and therefor filament cooling, is going to become a major issue. To investigate the thermal properties of the penetrating nozzle, multiple finite element models were analyzed. The finite element analysis was conducted with a stock nozzle and 50.8 mm material nozzles extensions with two common extruder materials. The finite element analysis demonstrated that a 304 stainless-steel nozzle could be extended to a maximum length of 0.917 mm, which would allow the nozzle to penetrate 3 layers during the pinning process. Creating a brass penetrating nozzle would in turn, allow the penetrating nozzle to be extended to 2.205 mm, letting the nozzle to penetrate 8 layers into the pin cavity.